ca01 only detailed ToC 1..24

Science of Synthesis 

Houben–Weyl Methods of Molecular Transformations 

Category 1: 

Organometallics 

1 Compounds with Transition Metal-Carbon ð-Bonds and Compounds 

of Groups 10–8 (Ni, Pd, Pt, Co, Rh, Ir, Fe, Ru, Os) 

M. Lautens 

2 Compounds of Groups 7–3 (Mn…,Cr…,V…, Ti…,Sc…, La…,Ac…) 

T. Imamoto 

3 Compounds of Groups 12 and 11 (Zn, Cd, Hg, Cu, Ag, Au) 

I. O Neil 

4 Compounds of Group 15 (As, Sb, Bi) and Silicon Compounds 

I. Fleming 

5 Compounds of Group 14 (Ge, Sn, Pb) 

M. G. Moloney 

6 Boron Compounds 

D. Kaufmann and D. S. Matteson 

7 Compounds of Groups 13 and 2 (Al, Ga, In, Tl, Be … Ba) 

H. Yamamoto 

8 Compounds of Group 1 (Li … Cs) 

V. Snieckus and M. Majewski 

b 

2003 

Georg Thieme Verlag 

Stuttgart · New York



Editorial Board D. Bellus P. J. Reider 

E. N. Jacobsen E. Schaumann 

S. V. Ley I. Shinkai 

R. Noyori E. J. Thomas 

M. Regitz B. M. Trost 

Managing Director G. F. Herrmann 

Managing Editor M. F. Shortt de Hernandez



www.science-of-synthesis.com 

2003 Georg Thieme Verlag 

Rüdigerstrasse 14 

D-70469 Stuttgart 

Copyright and all related rights reserved, especially the right of copying and 

distribution, multiplication and reproduction, as well as of translation. No 

part of this publication may be reproduced by any process, whether by photostat 

or microfilm or any other procedure, without previous written consent by 

the publisher. This also includes the use of electronic media of data processing 

on reproduction of any kind. 

If you have any queries or comments about the content 

of Science of Synthesis, please contact: 

Dr. M. Fiona Shortt de Hernandez 

Managing Editor 

Science of Synthesis/Houben–Weyl 

Thieme Chemistry 

Georg Thieme Verlag 



Phone: +49 711 8931-783 

Fax: +49 711 8931-777 

E-mail: fiona.shortt@thieme.de 

www.science-of-synthesis.com

Table of Contents 

Preface ................................................................ 9 

Tables of Contents 

Volume 1 Compounds with Transition Metal–Carbon ð-Bonds 

and Compounds of Groups 10–8 (Ni, Pd, Pt, Co, Rh, Ir, Fe, Ru, Os) ........... 11 

Volume 2 Compounds of Groups 7–3 (Mn…, Cr…, V…, Ti…, Sc…, La…, Ac…) .......... 13 

Volume 4 Compounds of Group 15 (As, Sb, Bi) and Silicon Compounds ................ 15 

Volume 5 Compounds of Group 14 (Ge, Sn, Pb) ..................................... 18 

Sample Contributions 

Volume 1 Product Class 1: Organometallic Complexes of Nickel 

J. Montgomery .......................................................... 25 

Volume 2 Product Class 6: Organometallic Complexes of Chromium, 

Molybdenum, and Tungsten without Carbonyl Ligands 

R. Poli and K. M. Smith .................................................... 83 

Volume 4 Product Subclass 4.4.27: Æ-Haloalkylsilanes 

N. J. Lawrence .......................................................... 141 

Volume 5 Product Subclass 22: Aryl- and Heteroarylgermanes 

A. C. Spivey and C. M. Diaper .............................................. 163 

Abbreviations .......................................................... 177 

7

8 Science of Synthesis Category 1: Organometallics

Preface 

As our understanding of the natural world increases, we begin to understand complex 

phenomena at molecular levels. This level of understanding allows for the design of molecular 

entities for functions ranging from material science to biology. Such design requires 

synthesis and, as the structures increase in complexity as a necessity for specificity, 

puts increasing demands on the level of sophistication of the synthetic methods. Such 

needs stimulate the improvement of existing methods and, more importantly, the development 

of new methods. As scientists confront the synthetic problems posed by the molecular 

targets, they require access to a source of reliable synthetic information. Thus, the 

need for a new, comprehensive, and critical treatment of synthetic chemistry has become 

apparent. To meet this challenge, an entirely new edition of the esteemed reference work 

Houben–Weyl Methods of Organic Chemistry will be published starting in the year 2000. 

To reflect the new broader need and focus, this new edition has a new title, Science of 

Synthesis, Houben–Weyl Methods of Molecular Transformations. Science of Synthesis 

will benefit from more than 90 years of experience and will continue the tradition of excellence 

in publishing synthetic chemistry reference works. Science of Synthesis will be a 

balanced and critical reference work produced by the collaborative efforts of chemists, 

from both industry and academia, selected by the editorial board. All published results 

from journals, books, and patent literature from the early 1800s until the year of publication 

will be considered by our authors, who are among the leading experts in their field. 

The 48 volumes of Science of Synthesis will provide chemists with the most reliable methods 

to solve their synthesis problems. Science of Synthesis will be updated periodically 

and will become a prime source of information for chemists in the 21st century. 

Science of Synthesis will be organized in a logical hierarchical system based on the 

target molecule to be synthesized. The critical coverage of methods will be supported by 

information intended to help the user choose the most suitable method for their application, 

thus providing a strong foundation from which to develop a successful synthetic 

route. Within each category of product, illuminating background information such as 

history, nomenclature, structure, stability, reactivity, properties, safety, and environmental 

aspects will be discussed along with a detailed selection of reliable methods. Each 

method and variation will be accompanied by reaction schemes, tables of examples, experimental 

procedures, and a background discussion of the scope and limitations of the 

reaction described. 

The policy of the editorial board is to make Science of Synthesis the ultimate tool for 

the synthetic chemist in the 21st century. 

We would like to thank all of our authors for submitting contributions of such outstanding 

quality, and, also for the dedication and commitment they have shown throughout 

the entire editorial process. 

The Editorial Board October 2000 

D. Bellus (Basel, Switzerland) E. Schaumann (Clausthal-Zellerfeld, Germany) 

S. V. Ley (Cambridge, UK) I. Shinkai (Tsukuba, Japan) 

R. Noyori (Nagoya, Japan) E. J. Thomas (Manchester, UK) 

M. Regitz (Kaiserslautern, Germany) B. M. Trost (Stanford, USA) 

P. J. Reider (New Jersey, USA) 

9

Volume 1: 

Compounds withTransition Metal–Carbon ð-Bonds 

and Compounds of Groups 10–8 (Ni, Pd, Pt, Co, Rh, 

Ir, Fe, Ru, Os) 

Introduction 

M. Lautens 

1.1 Product Class 1: Organometallic Complexes of Nickel 

J. Montgomery 

1.2 Product Class 2: Organometallic Complexes of Palladium 

1.2.1 Product Subclass 1: Palladium–Diene Complexes 

J. M. Takacs, X. Jiang, and S. Vayalakkada 

1.2.2 Product Subclass 2: Palladium–Allyl Complexes 

R. W. Friesen 

1.2.3 Product Subclass 3: Palladium–Alkyne Complexes 

J. M. Takacs, S. Vayalakkada, and X. Jiang 

1.2.4 Product Subclass 4: Palladium–Alkene Complexes 

J. M. Takacs and S. Vayalakkada 

1.3 Product Class 3: Organometallic Complexes of Platinum 

A. Ogawa and T. Hirao 

1.4 Product Class 4: Organometallic Complexes of Cobalt 

M. Malacria, C. Aubert, and J.-L. Renaud 

1.5 Product Class 5: Organometallic Complexes of Rhodium 

I. Ojima, A. T. Vu, and D. Bonafoux 

1.6 Product Class 6: Organometallic Complexes of Iridium 

J. M. O Connor 

1.7 Product Class 7: Organometallic Complexes of Iron 

1.7.1 Product Subclass 1: Iron–Arene Complexes 

G. R. Stephenson 

1.7.2 Product Subclass 2: Iron–Dienyl Complexes 


1.7.3 Product Subclass 3: Iron–Diene Complexes 


11

12 Science of Synthesis Category 1: Organometallics 

1.7.4 Product Subclass 4: Iron–Allyl Complexes 


1.7.5 Product Subclass 5: Iron–Alkene Complexes 


1.7.6 Product Subclass 6: Iron–Carbene Complexes 


1.7.7 Product Subclass 7: Iron–Alkyl Complexes 


1.7.8 Product Subclass 8: Ferrocenes 

M. Perseghini and A. Togni 

1.8 Product Class 8: Organometallic Complexes of Ruthenium 

N. Chatani 

1.9 Product Class 9: Organometallic Complexes of Osmium 

J. Gonzalez and W. D. Harman

Table of Contents Volume 2 13 

Volume 2: 

Compounds of Groups 7–3 

(Mn…, Cr…, V…,Ti…, Sc…, La…, Ac…) 

Introduction 

T. Imamoto 

2.1 Product Class 1: Organometallic Complexes of Manganese 

K. Oshima 

2.2 Product Class 2: Organometallic Complexes of Technetium 

I. D. Gridnev and T. Imamoto 

2.3 Product Class 3: Organometallic Complexes of Rhenium 

F. E. Kühn, C. C. Rom¼o, and W. A. Herrmann 

2.4 Product Class 4: Arene Organometallic Complexes of Chromium, 

Molybdenum, and Tungsten 

E. P. Kündig and S. H. Pache 

2.5 Product Class 5: Organometallic ð-Complexes of Chromium, 

Molybdenum, and Tungsten Excluding Arenes 

K. H. Theopold, A. Mommertz, and B. A. Salisbury 

2.6 Product Class 6: Organometallic Complexes of Chromium, 


R. Poli and K. M. Smith 

2.7 Product Class 7: Carbonyl Complexes of Chromium, Molybdenum, 

and Tungsten with ó-Bonded Ligands 

T. Ito and M. Minato 

2.8 Product Class 8: Organometallic Complexes of Vanadium 

T. Imamoto and I. D. Gridnev 

2.9 Product Class 9: Organometallic Complexes of Niobium and Tantalum 

K. Mashima and A. Nakamura 

2.10 Product Class 10: Organometallic Complexes of Titanium 

K. Mikami, Y. Matsumoto, and T. Shiono 

2.11 Product Class 11: Organometallic Complexes of Zirconium and Hafnium 

E.-i. Negishi and T. Takahashi


2.12 Product Class 12: Organometallic Complexes of Scandium, Yttrium 

and the Lanthanides 

Z. Hou and Y. Wakatsuki 

2.13 Product Class 13: Organometallic Complexes of the Actinides 

A. Dormond and D. Barbier-Baudry

Table of Contents 15 

Volume 4: 

Compounds of Group 15 (As, Sb, Bi) 

and Silicon Compounds 

Introduction 

Ian Fleming 

4.1 Product Class 1: Arsenic Compounds 

M. D. Smith 

4.2 Product Class 2: Antimony Compounds 

J. W. Burton 

4.3 Product Class 3: BismuthCompounds 

H. Suzuki and T. Ikegami 

4.4 Product Class 4: Silicon Compounds 

4.4.1 Product Subclass 1: Disilenes 

K. M. Baines and M. S. Samuel 

4.4.2 Product Subclass 2: Silenes 

K. M. Baines and M. S. Samuel 

4.4.3 Product Subclass 3: Silylenes 

P. P. Gaspar and D. Zhou 

4.4.4 Product Subclass 4: Silyl Hydrides 

J. Pietruszka 

4.4.5 Product Subclass 5: Disilanes 

J. R. Hwu and K. S. Ethiraj 

4.4.6 Product Subclass 6: Silyltin Reagents 

I. Hemeon and R. D. Singer 

4.4.7 Product Subclass 7: Silylboron Reagents 


4.4.8 Product Subclass 8: Silylaluminum Reagents 


4.4.9 Product Subclass 9: Silylzinc Reagents 


4.4.10 Product Subclass 10: Silylcopper Reagents 

R. D. Singer


4.4.11 Product Subclass 11: Silyllithium Reagents 

R. D. Singer 

4.4.12 Product Subclass 12: Haloorganosilanes 

M. Nilsson † 

4.4.13 Product Subclass 13: Silyl Diethers 

T. Skrydstrup 

4.4.14 Product Subclass 14: Silyl Esters 

M. Jaspars 

4.4.15 Product Subclass 15: Silyl Imidic Esters (Silylimino Ethers) 

E. Lukevics and O. Pudova 

4.4.16 Product Subclass 16: Silyl Enol Ethers 

S. Kobayashi, K. Manabe, H. Ishitani, and J.-I. Matsuo 

4.4.17 Product Subclass 17: Silyl Ethers 

J. D. White and R. G. Carter 

4.4.18 Product Subclass 18: Silyl Peroxides 

K. Tamao, J.-I. Yoshida and K. Itami 

4.4.19 Product Subclass 19: Silyl Sulfides and Selenides 

A. Ricci and M. Comes-Franchini 

4.4.20 Product Subclass 20: Silyl Azides 

C. Moberg and H. Adolfsson 

4.4.21 Product Subclass 21: Silylamines 

K. Tamao and A. Kawachi 

4.4.22 Product Subclass 22: Silyl Phosphines 

J. Pietruszka 

4.4.23 Product Subclass 23: Silylmethyl Anions 

D. Wang and T. H. Chan 

4.4.24 Product Subclass 24: Silyl Cyanides 

M. North 

4.4.25 Product Subclass 25: Acylsilanes 

P. C. B. Page and M. J. McKenzie 

4.4.26 Product Subclass 26: 1-Diazo-1-silylalkanes 

T. Aoyama and T. Shioiri


4.4.27 Product Subclass 27: Æ-Haloalkylsilanes 

N. J. Lawrence 

4.4.28 Product Subclass 28: Æ-Silyl Alcohols, Ethers, and Amines 

J. M. Aizpurua and C. Palomo 

4.4.29 Product Subclass 29: Æ,â-Epoxysilanes 

G. H. Whitham 

4.4.30 Product Subclass 30: Alkynyl[Ethynyl]silanes 

T. Hiyama and A. Mori 

4.4.31 Product Subclass 31: Silylketenes 

J.-M. Pons and P. J. Kocienski 

4.4.32 Product Subclass 32: Allenylsilanes 

J. Pornet 

4.4.33 Product Subclass 33: Arylsilanes 

B. A. Keay 

4.4.34 Product Subclass 34: Vinylsilanes 

K. Oshima 

4.4.35 Product Subclass 35: Æ-Silyl Carbonyl Compounds 

Y. Landais 

4.4.36 Product Subclass 36: â-Silyl Alkyl Halides 

W. E. Billups and R. K. Saini 

4.4.37 Product Subclass 37: â-Silyl Alcohols and the Peterson Reaction 

D. J. Ager 

4.4.38 Product Subclass 38: Propargylsilanes 

J. Pornet 

4.4.39 Product Subclass 39: Benzylsilanes 

B. Bennetau 

4.4.40 Product Subclass 40: Allylsilanes 

T. K. Sarkar 

4.4.41 Product Subclass 41: â-Silyl Carbonyl Compounds 

Ian Fleming 

4.4.42 Product Subclass 42: ª-Silyl Alkyl Halides, Alcohols, and Esters Thereof 

J. P. Michael and C. B. de Koning


Volume 5: 

Compounds of Group 14 (Ge, Sn, Pb) 

Introduction 

E. J. Thomas and M. G. Moloney 

5.1 Product Class 1: Germanium Compounds 

E. J. Thomas 

5.1.1 Product Subclass 1: Germanium Hydrides 

K. Oshima 

5.1.2 Product Subclass 2: Digermenes and Digermanes 

N. Takeda, N. Tokitoh, and R. Okazaki 

5.1.3 Product Subclass 3: Metalated Germanium Compounds 


5.1.4 Product Subclass 4: Germanium Oxides, Sulfides, Selenides, 

and Tellurides (Double Bonded) 


5.1.5 Product Subclass 5: Iminogermanes 


5.1.6 Product Subclass 6: Germenes 


5.1.7 Product Subclass 7: Germylenes 


5.1.8 Product Subclass 8: Organogermanium Halides 

P. Thornton 

5.1.9 Product Subclass 9: Germanium Oxides 

P. Thornton 

5.1.10 Product Subclass 10: Germanium Carboxylates, Phosphates, 

and Related Compounds 

P. Thornton 

5.1.11 Product Subclass 11: Germanium Sulfides, Sulfoxides, 


P. Thornton


5.1.12 Product Subclass 12: Germanium Selenides, Tellurides, 


P. Thornton 

5.1.13 Product Subclass 13: Germylamines 

P. Thornton 

5.1.14 Product Subclass 14: Germanium Phosphines, Arsines, and Stibines 

P. Thornton 

5.1.15 Product Subclass 15: Germanium Cyanides 

A. C. Spivey and C. M. Diaper 

5.1.16 Product Subclass 16: Acylgermanes 


5.1.17 Product Subclass 17: Imidoylgermanes (Æ-Iminoalkylgermanes) 

and Æ-Diazoalkylgermanes 


5.1.18 Product Subclass 18: Æ-Halo- and Æ-Alkoxyvinylgermanes 


5.1.19 Product Subclass 19: Æ-Halo-, Æ-Hydroxy-, Æ-Alkoxy-, 

and Æ-Aminoalkylgermanes 


5.1.20 Product Subclass 20: Alkynylgermanes 


5.1.21 Product Subclass 21: Germylketenes and Germylketenimines 


5.1.22 Product Subclass 22: Aryl- and Heteroarylgermanes 


5.1.23 Product Subclass 23: Vinylgermanes 


5.1.24 Product Subclass 24: Propargyl- and Allenylgermanes 


5.1.25 Product Subclass 25: Benzylgermanes 

A. C. Spivey and C. M. Diaper


5.1.26 Product Subclass 26: Allylgermanes 


5.1.27 Product Subclass 27: Alkylgermanes 


5.2 Product Class 2: Tin Compounds 

E. J. Thomas 

5.2.1 Product Subclass 1: Tin Hydrides 

A. J. Clark 

5.2.2 Product Subclass 2: Distannenes and Distannanes 

J. Podlech 

5.2.3 Product Subclass 3: Metalated Tin Compounds 

J. Podlech 

5.2.4 Product Subclass 4: Tin Oxides, Sulfides, Selenides, and Tellurides 

(Double Bonded) 


5.2.5 Product Subclass 5: Iminostannanes 


5.2.6 Product Subclass 6: Stannenes 


5.2.7 Product Subclass 7: Stannylenes 


5.2.8 Product Subclass 8: Tin Halides and Organotin Halides 

M. E. Wood 

5.2.9 Product Subclass 9: Tin Oxides 

B. Jousseaume 

5.2.10 Product Subclass 10: Tin Carboxylates and Phosphates 

B. Jousseaume 

5.2.11 Product Subclass 11: Tin Enol Ethers 

B. Jousseaume 

5.2.12 Product Subclass 12: Tin Sulfides, Thioalkoxides, 


B. Jousseaume


5.2.13 Product Subclass 13: Tin Selenides and Tellurides 

B. Jousseaume 

5.2.14 Product Subclass 14: Organostannylamines and Related Compounds 

B. Jousseaume 

5.2.15 Product Subclass 15: Organostannylphosphines 

B. Jousseaume 

5.2.16 Product Subclass 16: Tin Cyanides and Fulminates 

P. B. Wyatt 

5.2.17 Product Subclass 17: Acylstannanes (Including S, Se, and Te Analogues) 

P. B. Wyatt 

5.2.18 Product Subclass 18: Imidoylstannanes, Diazoalkylstannanes, 

Tin Isocyanates, and Tin Isothiocyanates 

P. B. Wyatt 

5.2.19 Product Subclass 19: 1-Halo-, 1-Alkoxy-, and 1-Aminovinylstannanes 

I. Coldham and G. P. Vennall 

5.2.20 Product Subclass 20: 1-Halo-, 1-Hydroxy-, 1-Alkoxy-, and 

1-Aminoalkylstannanes 

I. Coldham and G. P. Vennall 

5.2.21 Product Subclass 21: Alkynylstannanes 

G. T. Crisp 

5.2.22 Product Subclass 22: Ketenylstannanes and Derivatives 

G. T. Crisp 

5.2.23 Product Subclass 23: Allenylstannanes 

G. T. Crisp 

5.2.24 Product Subclass 24: Arylstannanes 

G. T. Crisp 

5.2.25 Product Subclass 25: Alk-1-enylstannanes 

G. T. Crisp 

5.2.26 Product Subclass 26: Propargylstannanes 

D. Young 

5.2.27 Product Subclass 27: Benzylstannanes 

R. L. Marshall


5.2.28 Product Subclass 28: Allylstannanes 

R. L. Marshall 

5.2.29 Product Subclass 29: Alkylstannanes 

D. Young 

5.3 Product Class 3: Lead Compounds 

M. G. Moloney 

5.3.1 Product Subclass 1: Lead Hydrides 

M. G. Moloney 

5.3.2 Product Subclass 2: Diplumbenes and Diplumbanes 


5.3.3 Product Subclass 3: Metalated Lead Compounds 


5.3.4 Product Subclass 4: Organoplumbyl Oxides, Sulfides, Selenides, 

and Tellurides (Double Bonded) 


5.3.5 Product Subclass 5: Plumbylenes 


5.3.6 Product Subclass 6: Halo(organo)plumbanes 

P. J. Guiry and P. J. McCormack 

5.3.7 Product Subclass 7: Organoplumboxanes and Related Compounds 


5.3.8 Product Subclass 8: Acyloxy(organo)plumbanes 


5.3.9 Product Subclass 9: Plumbyl Enol Ethers 


5.3.10 Product Subclass 10: Organoplumbane Sulfur Compounds 


5.3.11 Product Subclass 11: Organoplumbyl Selenides, Tellurides, 



5.3.12 Product Subclass 12: Organoplumbanamines and Related Compounds 

P. J. Guiry and P. J. McCormack


5.3.13 Product Subclass 13: Organoplumbyl Phosphines and Phosphine Oxides 


5.3.14 Product Subclass 14: 

Triorganolead Cyanides and Triorganolead Cyanates 

P. A. C. Eagle 

5.3.15 Product Subclass 15: Acylplumbanes 


5.3.16 Product Subclass 16: Lead Isocyanates, Isothiocyanates, Diazoplumbanes, 

and Iminoplumbanes 


5.3.17 Product Subclass 17: 1- or 2-Alkoxy- and 1- or 2-(Alkylsulfanyl) and 

1- or 2-Aminoalkenyl(triorgano)plumbanes 


5.3.18 Product Subclass 18: 1-Halo-, 1-Alkoxy-, 1-Hydroxy-, and 

1-Aminoalkylplumbanes 


5.3.19 Product Subclass 19: Alkynylplumbanes 


5.3.20 Product Subclass 20: Allenylplumbanes 


5.3.21 Product Subclass 21: Arylplumbanes 


5.3.22 Product Subclass 22: Vinylplumbanes 


5.3.23 Product Subclass 23: Benzylplumbanes 


5.3.24 Product Subclass 24: Allylplumbanes 


5.3.25 Product Subclass 25: Alkylplumbanes 

P. A. C. Eagle



Sample Contribution 

Category Organometallics 

Volume 1 Compounds with Transition Metal-Carbon 

ð-Bonds and Compounds of Groups 10 –8 

(Ni, Pd, Pt, Co, Rh, Ir, Fe, Ru, Os) 

Product Class 1.1 Organometallic Complexes of Nickel 

Written by J. Montgomery 

25




Printed in Germany 

Typesetting: Ziegler + Müller, Kirchentellinsfurt 

Printing: Konrad Triltsch, Ochsenfurt-Hohestadt 

Binding: Koch, Tübingen 

Die Deutsche Bibliothek – CIP-Einheitsaufnahme 

Science of Synthesis : Houben–Weyl methods 

of molecular transformations / 

ed. board: D. Bellus … Managing ed. G. F. Herrmann. – 

Stuttgart ; New York : Thieme 

Früher u.d. T.: Methoden der organischen Chemie 

Category 1. Organometallics 

Vol. 1: Compounds with transition metal-carbon 

ð-bonds and compounds of groups 10-8(Ni, Pd, Pt, Co, 

Rh, Ir, Fe, Ru, Os) / vol. ed. M. Lautens. Responsible 

member of the ed. Board B. M. Trost. 

Authors N. Chatani .... – 2001 

Library of Congress Cataloging in Publication Data 

Science of synthesis : Houben–Weyl methods of 

molecular transformations. 

p. cm. 

Includes bibliographical references and index. 

Contents: category 1. Organometallics. v. 1. Compounds 

with transition metal-carbon [pi]-bonds and 

compounds of groups 10-8(Ni, Pd, Pt, Co, Rh, Ir, Fe, 

Ru, Os) / volume editor, M. Lautens 

ISBN 3-13-112131-9 – ISBN 0-86577-940-6 (v. 1) 

1. Organic compounds–Synthesis. I. Title: Houben– 

Weyl methods of molecular transformations. 

QD262 .S35 2000 

547'.2–dc21 

00-061560 

British Library Cataloguing in Publication Data 


of molecular transformation 

Category 1: Organometallics: 

Vol. 1: Compounds with transition metal-carbon 

pi-bonds and compounds of groups 10-8(Ni, Pd, Pt, Co, 

Rh, Ir, Fe, Ru, Os) . – (Houben–Weyl methods 

of organic chemistry) 

1. Organicmetallic compounds – Synthesis 

I. Lautens, M., II. Chatani, N. 

547 .05 

ISBN 3-13-112131-9 

(Georg Thieme Verlag, Stuttgart) 

ISBN 0-86577-940-6 

(Thieme New York) 

Date of publication: August 29, 2001 

27 

Copyright and all related rights reserved, especially 

the right of copying and distribution, multiplication 

and reproduction, as well as of translation. No part of 

this publication may be reproduced by any process, 

whether by photostat or microfilm or any other procedure, 

without previous written consent by the publisher. 

This also includes the use of electronic media 

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This reference work mentions numerous commercial 

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not imply that any such selection of exclusion has 

been based on quality criteria or quality considerations. 

Warning! Read carefully the following: Although 

this reference work has been written by experts, the 

user must be advised that the handling of chemicals, 

microorganisms, and chemical apparatus carries potentially 

life-threatening risks. For example, serious 

dangers could occur through quantities being incorrectly 

given. The authors took the utmost care that 

the quantities and experimental details described 

herein reflected the current state of the art of science 

when the work was published. However, the authors, 

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correctness of the content. Further, scientific knowledge 

is constantly changing. As new information becomes 

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the authors, publishers, and editors took great care in 

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errors exist, including errors in the formulas given 

herein. Therefore, it is imperative that and the responsibility 

of every user to carefully check 

whether quantities, experimental details, or other 

information given herein are correct based on 

the user s own understanding as a scientist. Scaleup 

of experimental procedures published in Science 

of Synthesis carries additional risks. In cases of doubt, 

the user is strongly advised to seek the opinion of an 

expert in the field, the publishers, the editors, or the 

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28 

Biographical Sketch 

John Montgomery was born in 1965 in Concord, N.C. He received his 

A.B degree from the University of North Carolina at Chapel Hill in 

1987, and he carried out undergraduate research under the direction 

of Professors Joe Templeton and Maurice Brookhart. He received his 

Ph.D. at Colorado State University in 1991 under the direction of Professor 

Lou Hegedus. He was an American Cancer Society Postdoctoral 

Fellow at the University of California at Irvine from 1991 –1993 with 

Professor Larry Overman. In 1993, he began his independent career at 

Wayne State University where he is now Professor of Chemistry. His 

work at Wayne State has focused on applications of organonickel chemistry in reaction 

discovery, synthetic methodology development, and total synthesis, and on the development 

of new methods for the synthesis of amino acids utilizing nitroacetates as glycine 

templates. He has received a number of awards including an Arthur C. Cope Scholar 

Award, a Camille Dreyfus Teacher Scholar Award, and an NSF Career Award.

1.1 Product Class 1: Organometallic Complexes of Nickel 

J. Montgomery 

1.1 Product Class 1: Organometallic Complexes of Nickel ..................... 31 

1.1.1 Product Subclass 1: Nickel Complexes of 1,3-Dienes ...................... 32 

Synthesis of Product Subclass 1 ............................................ 32 

1.1.1.1 Method 1: Ligand Exchange with Bis(ç 4 -cycloocta-1,5-diene)nickel(0) ... 32 

Applications of Product Subclass 1 in Organic Synthesis ..................... 33 

1.1.1.2 Method 2: Diene–Diene Cycloadditions ................................ 33 

1.1.1.3 Method 3: Diene–Alkyne Cycloadditions ............................... 34 

1.1.1.4 Method 4: Diene–Aldehyde Reductive Cyclizations ..................... 35 

1.1.1.4.1 Variation 1: Triethylsilane-Mediated Reactions ........................... 35 

1.1.1.4.2 Variation 2: Triethylborane-Mediated Reactions ......................... 36 

1.1.1.5 Method 5: 1,4-Dialkylation of Dienes .................................. 36 

1.1.1.6 Method 6: Hydrocyanation of Dienes .................................. 37 

1.1.2 Product Subclass 2: Nickel–Allyl Complexes ............................... 37 


1.1.2.1 Method 1: Oxidative Addition of Nickel(0) with Allylic Electrophiles ...... 37 

1.1.2.2 Method 2: Addition of Allylmagnesium Halides to Nickel(II) Salts ........ 38 

1.1.2.3 Method 3: Oxidative Addition of Nickel(0) with Enones in 

the Presence of Lewis Acids ................................. 39 

1.1.2.4 Method 4: Oxidative Cyclization of Nickel(0) Complexes of 

Conjugated Dienes ......................................... 40 


1.1.2.5 Method 5: Coupling of Allyl Halide Derived Nickel–Allyl Complexes 

with Alkyl Halides and Other Electrophiles ................... 41 

1.1.2.6 Method 6: Coupling of Enal-Derived Nickel–Allyl Complexes 

with Alkyl Halides and Other Electrophiles ................... 42 

1.1.2.7 Method 7: Coupling of Nickel–Allyl Complexes with 

Main Group Organometallics ............................... 44 

1.1.2.7.1 Variation 1: Allylic Ether Derived ð-Allyl Complexes ...................... 44 

1.1.2.7.2 Variation 2: Enal-Derived ð-Allyl Complexes ............................. 46 

1.1.2.7.3 Variation 3: Allylic Alcohol Derived ð-Allyl Complexes .................... 46 

1.1.2.8 Method 8: Addition of Stabilized Nucleophiles to Nickel–Allyl Complexes 47 

1.1.2.9 Method 9: Alkyne Insertions with Nickel–Allyl Complexes ............... 47 

1.1.2.10 Method 10: Alkene Insertions with Nickel–Allyl Complexes ............... 49 

1.1.3 Product Subclass 3: Nickel–Alkyne Complexes ............................ 49 


1.1.3.1 Method 1: Ligand Exchange with Nickel–Alkene Complexes ............. 50 


1.1.3.2 Method 2: Coupling of Alkynes with Carbon Dioxide .................... 51 

1.1.3.3 Method 3: Coupling of Alkynes with Isocyanides ....................... 52 

29

30 

1.1.3.4 Method 4: Coupling of Alkynes with Aldehydes ......................... 52 

1.1.3.5 Method 5: Coupling of Two Alkynes ................................... 55 

1.1.3.6 Method 6: Coupling of Alkynes with Alkenes ........................... 56 

1.1.3.7 Method 7: [2 +2+2] Cycloadditions .................................... 58 

1.1.3.8 Method 8: Alkyne Carbonylation ...................................... 60 

1.1.3.9 Method 9: Alkyne Hydrocyanation ..................................... 60 

1.1.3.10 Method 10: Alkyne Hydrosilylation ...................................... 60 

1.1.3.11 Method 11: Alkyne Carbozincation ..................................... 61 

1.1.4 Product Subclass 4: Nickel–Alkene Complexes ............................ 62 


1.1.4.1 Method 1: Ligand Exchange with Nickel(0) Complexes .................. 62 

Applications of Product Subclass 4 in Organic Synthesis 63 

1.1.4.2 Method 2: Conjugate Addition to Electrophilic Double Bonds ........... 63 

1.1.4.2.1 Variation 1: Organoaluminums ......................................... 63 

1.1.4.2.2 Variation 2: Organozincs ............................................... 64 

1.1.4.2.3 Variation 3: Organozirconiums ......................................... 66 

1.1.4.2.4 Variation 4: Direct Conjugate Addition of Alkyl Halides ................... 67 

1.1.4.3 Method 3: Coupling of Two Alkenes ................................... 68 

1.1.4.4 Method 4: Alkene Carbonylation ...................................... 71 

1.1.4.5 Method 5: Alkene Hydrocyanation ..................................... 72 

1.1.4.6 Method 6: Alkene Hydrosilylation ..................................... 73 

1.1.4.7 Method 7: Alkene Hydroalumination .................................. 73 

1.1.4.8 Method 8: Alkene Hydrozincation ..................................... 75 

1.1.4.9 Method 9: Alkene Carbozincation ..................................... 76 

1.1.4.10 Method 10: Homo-Diels–Alder Cycloadditions ........................... 77 

1.1.4.11 Method 11: Alkene Polymerization ...................................... 77

1.1 Product Class 1: 

Organometallic Complexes of Nickel 

J. Montgomery 

General Introduction 

This contribution provides an overview of contemporary synthetic methods of broad applicability 

that involve the preparation and use of nickel ð-complexes as starting materials 

or reactive intermediates. Numerous excellent reviews on the chemistry of nickel 

have appeared that are complementary to this contribution in subject and scope. An outstanding 

review by Chetcuti describes the known ð-complexes of nickel, [1] and several 

other structural classes of nickel complexes have been reviewed; [2–4] ó-bonded organonickel 

compounds are reviewed in Houben–Weyl, Vol. 13/9b, pp 632–700. The historical development 

and early applications of nickel chemistry have been reviewed by Wilke [5] and 

Jolly, [6] industrial applications have been reviewed by Keim, [7] and several other reviews 

on specific groups of synthetic transformations have appeared. [8–12,187] The organometallic 

chemistry of nickel has a rich history dating back more than 100 years. [5] Despite its long 

history, fundamentally new reactions are still being developed at a rapid pace. Furthermore, 

existing reactions are being applied in new and creative ways to solve long-standing 

challenges in organic synthesis. More and more of the synthetic organic community is 

beginning to realize that nickel catalysis provides preparatively convenient reactions of 

broad scope in a variety of contexts. In many cases, the reactivity exhibited by nickel may 

not be achieved by any other transition element. At this time, organonickel chemistry 

seems to be well poised to provide an increasing number of new reactions and interesting 

mechanistic questions, as well as to gain an increasingly important role in the organic 

chemist s repertoire of mainstream synthetic transformations. 

The most commonly employed catalysts in nickel-catalyzed reactions are bis(acetylacetonato)nickel(II) 

(1), which is commercially available, bis(ç 4 -cycloocta-1,5-diene)nickel(0) 

(2) which is also commercially available or may be easily prepared (Scheme 1), [13] 

and dichlorobis(triphenylphosphine)nickel(II) (3) which can also be easily prepared 

(Scheme 2). [14] 

SAFETY: Tetracarbonylnickel(0) should be handled with extreme caution due to its 

volatility and high toxicity. All nickel compounds should be handled with care since 

many are cancer suspect agents. [188] 

Scheme 1 Synthesis of Bis(ç 4 -cycloocta-1,5-diene)nickel(0) [13] 

Ni(acac)2 

1 

1. cod, THF, −78 oC 2. DIBAL-H, THF, −78 oC 72% 

Ni(cod)2 

2 

Scheme 2 Synthesis of Dichlorobis(triphenylphosphine)nickel(II) [14] 

NiCl 2•6H 2O 

Ph 3P, AcOH, rt, 24 h 

84% 

NiCl2(PPh3) 2 

3 

31 

for references see p 79

32 Science of Synthesis 1.1 Organometallic Complexes of Nickel 

Bis(ç 4 -cycloocta-1,5-diene)nickel(0) (2): [13] 

A 250-mL Schlenk flask equipped with a stirring bar and a pressure-equalizing addition 

funnel was charged with technical grade [Ni(acac) 2](1; 4.67 g, 0.0182 mol, 1.00 equiv) and 

briefly dried under vacuum with a heat gun. After cooling and establishing a positive N 2 

atmosphere, the solid was suspended in THF (25 mL) and treated with cycloocta-1,5-diene 

(7.93 g, 0.0723 mol, 4.00 equiv). The suspension was cooled to –78 8C with a dry ice/acetone 

bath to give a green slurry. A 1.0 M soln of DIBAL-H in THF (45.4 mL, 0.0454 mol, 

2.50 equiv) was transferred to the addition funnel under N 2 via a cannula. The DIBAL-H 

soln was added over 1 h to give a dark, reddish-brown soln which was allowed to warm 

to 0 8C over a 1 h period. The soln was treated with Et 2O (65 mL) to give a light yellow precipitate. 

The suspension was cooled to –788C and allowed to stand for 12 h to complete 

precipitation. The solid product was isolated by filtration at –788C via a filter paper tipped 

cannula, washed with cold Et 2O (15 mL portions) until the brown residues were removed, 

and dried in vacuo. [Ni(cod) 2](2) was obtained as a pale yellow powder and was suitable for 

immediate use; yield: 3.2 g (72%). 

The material may be recrystallized by the following procedure. In a glovebox, crude 

[Ni(cod) 2] (3.2 g) was dissolved in a minimum volume of toluene (25 mL • g –1 )at258C and 

rapidly filtered through Celite to remove metallic nickel. The deep yellow soln was allowed 

to stand at –788C for 12 h to give bright yellow-orange needles. Removal of the supernatant 

at –788C through a filter paper tipped cannula, followed by a pentane wash 

(2 ” 15 mL), gave pure material; yield: 1.28g (40%). 

Dichlorobis(triphenylphosphine)nickel(II) (3): [14] 

A soln of NiCl 2 •6H 2O (2.38g, 0.01 mol) in H 2O (2 mL) was diluted with glacial AcOH 

(50 mL), and Ph 3P (5.25 g, 0.02 mol) in glacial AcOH (25 mL) was added. The olive-green microcrystalline 

precipitate, when kept in contact with its mother liquor for 24 h, gave dark 

blue crystals which were filtered off, washed with glacial AcOH, and dried in a vacuum 

desiccator (H 2SO 4, KOH); yield: 3.81 g (84%). 


Nickel Complexes of 1,3-Dienes 

Nickel complexes with 1,3-dienes are important intermediates in a variety of catalytic 

processes. In contrast to many classes of metal–diene complexes, such as those of iron 

and palladium in which metal complexation activates the ð-system towards nucleophilic 

attack, (ç 4 -diene)nickel complexes are most useful in cycloaddition processes and in couplings 

to polar ð-systems such as carbonyls. Few examples of diene–nickel complexes are 

structurally well characterized, but they are commonly invoked in the mechanisms of 

many synthetic procedures. 

Synthesis of Product Subclass 1 

1.1.1.1 Method 1: 

Ligand Exchange with Bis(ç 4 -cycloocta-1,5-diene)nickel(0) 

The high reactivity of nickel–diene complexes, which renders them very useful in catalytic 

applications, makes their isolation quite difficult in most cases. The few cases in which 

nickel–1,3-diene complexes (e.g., 4) have been isolated generally involve displacement of 

a ligand with a low binding constant such as cyclooctadiene. This should, in theory, be 

possible using nickel(II) salts reduced in situ, although bis(ç 4 -cycloocta-1,5-diene)nickel(0) 

or (ç 6 -cyclododeca-1,5,9-triene)nickel(0) (Scheme 3; cdt = cyclododeca-1,5,9-triene) are typically 

employed. [15]

1.1.1 Nickel Complexes of 1,3-Dienes 33 

Scheme 3 Preparation of a (ç 4 -Buta-1,3-diene)nickel(0) Complex [15] 

Ni(cdt) 

+ 

P P 

Pri Pri Pri Pri + 

Et 2O 

−78 o C 

85% 

Pri P 

P 

Ni Pri Pri Pri Pri [ì-(1,2,3,9-ç:6,7,8,10-ç)-3,6-Dimethyleneocta-1,7-diene]bis[ethane-1,2-diylbis(diisopropylphosphine-k 

2 P)]nickel (4): [15] 

3,6-Dimethyleneocta-1,7-diene (0.56 mL, 3.30 mmol) and iPr 2P(CH 2) 2P-iPr 2 (1.03 mL, 

3.30 mmol) were added to a suspension of Ni(cdt) (0.83 g, 3.31 mmol) in Et 2O (200 mL) 

cooled to –788C. The mixture was allowed to warm to rt over 5 h. A yellow solid precipitated 

which then redissolved to give a red soln. The mixture was stirred for 2 d, filtered 

through a pad of Avicel, and evaporated to dryness. The residue was dissolved in toluene 

(50 mL) at 508C and filtered. Cooling the filtrate to –788C gave compound 4 as red needles 

which were washed with precooled pentane (10 mL) at –788C and dried under high vacuum; 

yield: 1.09 g (85%). 

Applications of Product Subclass 1 in Organic Synthesis 

1.1.1.2 Method 2: 

Diene–Diene Cycloadditions 

The most widely used application of nickel–diene complexes is the dimerization of 1,3dienes. 

Pioneering studies by Wilke demonstrated many different modes of coupling, including 

dimerization, trimerization, and oligomerization of 1,3-dienes. [5,7] An overview of 

the product classes that may be obtained from 1,3-dienes is provided in Scheme 4 (see also 

Houben–Weyl, Vol. E 18, pp 93 and 932–937). The initially formed nickel complexes 5 and 

6 have not been isolated. However, the complexes may be stabilized by the addition of 

phosphines, and ð-allyl complexes 7–9 have been prepared and characterized. 

Scheme 4 Products of Nickel-Catalyzed Butadiene Dimerization and Trimerization [5,7] 

L nNi 

[Ni(0)] L nNi L nNi 

5 

Ni 

9 

7 

L nNi 

L nNi 

8 

6 

Pr i 

4 

Ni 

P 

P 

Pr i 

Pr i 



Despite the detail in which this process has been studied, its synthetic utility is limited 

owing to the low regio- and/or stereoselectivity in reactions of unsymmetrical dienes. 

This limitation was overcome in studies by Wender, on the intramolecular variant. [16–21] 

An impressive variety of structurally complex eight-membered rings can be synthesized 

by the nickel-catalyzed [4+4]-cycloaddition reaction (Scheme 5). This method provides 

one of the most direct and efficient procedures for synthesizing eight-membered rings. 

Scheme 5 A Synthetic Application of a Nickel-Catalyzed [4+4] Cycloaddition [19] 

OTBDMS 

10 

20% Ni(cod)2 2 

60% P(OC6H4-2-Ph)3 toluene, 85 oC, 3 h 

74% 

OTBDMS 

(7R ∗ ,10R ∗ )-11 

+ 

7:1 

OTBDMS 

(7R ∗ ,10S ∗ )-11 

(7R*,10R*)-10-(tert-Butyldimethylsiloxy)-7-methylbicyclo[5.3.1]undeca-1,5-diene 

[(7R*,10R*)-11] and (7R*,10S*)-10-(tert-Butyldimethylsiloxy)-7-methylbicyclo[5.3.1]undeca- 

1,5-diene [(7R*,10S*)-11]: [19] 

To a 200-mL Schlenk flask were added bis(diene) 10 (151 mg, 0.517 mmol), toluene 

(100 mL), heptadecane (50 ìL, GC internal standard), and tris(biphenyl-2-yl) phosphite 

(167 mg, 0.310 mmol) in toluene (10 mL) under argon. The flask was then heated to 85 8C 

and 0.09 M [Ni(cod) 2](2) in toluene (1.15 mL) was added by syringe from a stock soln, and 

the flask was sealed. Monitoring of the heptadecane/product ratio by GC indicated the 

completion of the reaction (3 h). The reaction was allowed to cool and then quenched by 

exposure to air for 1 h. Filtration of the toluene soln through a plug of silica gel and elution 

with Et 2O removed the nickel salts. Concentration in vacuo followed by flash chromatography 

(silica gel, 20 mm ” 15 cm, hexane) provided (7R*,10R*)-11 and (7R*,10S*)-11 

as clear oils; yields: 97.7 mg (65%) and 14.0 mg (9%), respectively. 

1.1.1.3 Method 3: 

Diene–Alkyne Cycloadditions 

The nickel-catalyzed [4+2] reaction is also a highly useful synthetic procedure. [22–26] At 

first glance, it may seem less useful because a strictly thermal counterpart does exist, unlike 

the nickel-catalyzed [4+4] cycloaddition. However, compared with the thermal process, 

nickel-catalyzed [4+2] cycloadditions proceed at low temperatures and are not subject 

to the often restrictive electronic requirements of the thermal Diels–Alder reaction 

(Scheme 6). Despite the involvement of a stepwise pathway, the reaction has been shown 

to be stereospecific. 

Scheme 6 A Synthetic Application of a Nickel-Catalyzed [4+2] Cycloaddition [26] 

MeO 

TMSO 

OMOM 

10% Ni(cod) 2 2 

20% P[OCH(CF3) 2] 3 

cyclohexane, rt, 1 h 

90% 

MeO 

OMOM 

12 13 

H 

OTMS

1.1.1 Nickel Complexes of 1,3-Dienes 35 

(1R*,5S*,7aR*)-4-[2-(Methoxymethoxy)ethyl]-5-(4-methoxyphenyl)-7amethyl-1-(trimethylsiloxy)-2,3,5,7a-tetrahydro-1H-indene 

(13): [26] 

To an acid-washed, base-washed, 200-mL Schlenk flask was added dienyne 12 (665 mg, 

1.595 mmol, 1.0 equiv). Under a positive N 2 flow, freshly distilled cyclohexane (160 mL) 

and tris[2,2,2-trifluoro-1-(trifluoromethyl)ethyl] phosphite (170 mg, 0.319 mmol, 

0.2 equiv) were added, followed by 0.075 M [Ni(cod) 2](2) in THF (2.13 ìL, 0.160 mmol, 

0.1 equiv) and the reaction was stirred at rt for 1 h. The clear soln slowly changed to a golden 

yellow soln which was then warmed to 808C and stirred for 17.5 h. The reaction was 

quenched by opening to air and stirring for 30 min. Purification by flash filtration 

through a 2.5-cm plug of silica gel (Et 2O/hexanes 1:4) followed by flash chromatography 

(silica gel, Et 2O/hexanes 1:7) gave the cyclohexa-1,4-diene 13; yield: 600 mg (90%). 

1.1.1.4 Method 4: 

Diene–Aldehyde Reductive Cyclizations 

Additions of dienes to aldehydes have emerged as a synthetically useful reaction class. 

The reaction is formally a reductive coupling and may produce either ª,ä-unsaturated or 

ä,å-unsaturated alcohols as products (Scheme 7). [27–31] Two mechanisms have been proposed, 

and it is likely that the reaction is initiated either by formation of an oxametallacycle 

or by hydrometalation of the diene. 

Scheme 7 Diene–Aldehyde Reductive Coupling [27–31] 

O 

R 1 H 

R2 + 

Ni catalyst 

reducing agent 

1.1.1.4.1 Variation1: 

Triethylsilane-Mediated Reactions 

OH 

R 1 R 2 

or 

OH 

R 1 R 2 

Studies by Mori demonstrate that triethylsilane and dienals undergo reductive cyclization 

in the presence of bis(ç 4 -cycloocta-1,5-diene)nickel(0) (2) and triphenylphosphine (1:2) to 

produce the silyl ether of cycloalkanols; [27–30] in this instance, ª,ä-unsaturated products 

are obtained. However, if the reaction is carried out in the presence of cyclohexa-1,3-diene, 

an analogous reaction proceeds to give ä,å-unsaturated products. This effect is reported 

to be derived from selective diene hydrometalation followed by addition of the organonickel 

intermediate to the tethered aldehyde. The reaction proceeds with five-, six-, 

and seven-membered ring formation and with heterocyclic substrates. Several synthetic 

applications of this cyclization methodology are reported (Scheme 8). Intermolecular 

processes with simple dienes and aldehydes to afford ª,ä-unsaturated silyl ethers are 

also possible. 

Scheme 8 Reductive Coupling with Triethylsilane [27–30] 

O 

H 

N 

CHO 

20 mol% Ni(cod)2 2 

40 mol% Ph3P Et3SiH (5 equiv), THF 

O 

H 

N 

40% 

OTES 

+ 

O 

H 

N 

38% 

OTES 




Triethylborane-Mediated Reactions 

The intermolecular process between simple dienes and aldehydes is reported by Tamaru. 

[31] Triethylborane is employed as the reducing agent, and yields are good for a variety 

of substituted electron-rich and electron-poor dienes. Interestingly, reactions employing 

triethylborane and bis(acetylacetonato)nickel(II) (1) produce 4,5-unsaturated alcohols 

(Scheme 9), whereas reactions employing bis(ç 4 -cycloocta-1,5-diene)nickel(0) (2), triphenylphosphine, 

and triethylsilane produce 3,4-unsaturated silyl ethers. The mechanistic basis 

for this reversal of regioselectivity has not been established. 

Scheme 9 Reductive Coupling with Triethylborane [31] 

O 

BEt3 (2.4 equiv) 

OH 

CO2Me + 

H Ph 

10 mol% Ni(acac) 2 1 

91% 

Ph 

CO2Me 14 15 

Methyl (2R*,4E)-2-[(R*)-Hydroxy(phenyl)methyl]hex-4-enoate (15): [31] 

Into a N 2-purged flask containing [Ni(acac) 2](1; 12.8mg, 0.05 mmol) were introduced successively 

freshly dried (Na benzophenone ketyl) THF (3 mL), methyl (2E,4E)-hexa-2,4-dienoate 

(14; 2.52 g, 20 mmol), PhCHO (530 mg, 5 mmol), and 1 M BEt 3 in hexane (12.0 mL) 

via a syringe. The homogeneous mixture was stirred at rt for 66 h until the PhCHO disappeared 

completely. After dilution with EtOAc (50 mL), the mixture was washed successively 

with 2 M HCl, sat. NaHCO 3, and sat. NaCl, and then dried (MgSO 4), and concentrated in 

vacuo. The residual oil was subjected to column chromatography (silica gel, hexanes/ 

EtOAc 16:1) to give an analytically pure sample of 15; yield: 1.07 g (91%). 

1.1.1.5 Method 5: 

1,4-Dialkylationof Dienes 

Studies by Chang demonstrate that two molecules of an iodoalkene (e.g., 17) readily add 

across a 1,3-diene (e.g., 16) to give predominantly symmetrical 1,4-addition products such 

as (18) (Scheme 10). [32] Nickel(0) is consumed in the reaction; however, the use of zinc 

powder as a reductant allows the nickel to be used in catalytic amounts. Generally, a cis 

orientation of the internal double bond is obtained. With cyclic dienes, a cis orientation of 

the two alkenyl substituents is obtained. 

Scheme 10 1,4-Dialkylation of a Conjugated Diene [32] 

16 

+ 

O 

NiBr2, Zn 

Ph3P, MeCN 

O O 

82% 

I 

17 18 

2,3-Dimethyl-1,4-bis(3-oxocyclohex-1-enyl)but-2-ene (18): [32] 

To a 50-mL side-arm flask were added NiBr 2 (0.0204 g, 0.100 mmol), Ph 3P (0.0262 g, 

0.100 mmol), and Zn powder (0.082 g, 1.25 mmol). The system was purged with N 2 three 

times. MeCN (0.50 mL), 3-iodocyclohex-2-en-1-one (17; 0.222 g, 1.00 mmol), and 2,3-dimethylbuta-1,3-diene 

(16; 0.246 g, 3.00 mmol) were added by syringe, and the soln was 

stirred at 808C for 2 h. During the reaction the soln gradually turned from yellow to red. 

At the end of the reaction the system was filtered through Celite. The filtrate was concen-

1.1.2 Nickel–Allyl Complexes 37 

trated on a rotary evaporator and was separated by column chromatography (silica gel, 

EtOAc/hexane) to afford 18 as an oil; yield: 0.112 g (82%). 

1.1.1.6 Method 6: 

Hydrocyanation of Dienes 

The hydrocyanation of butadienes is the basis of DuPont s process for the production of 

adiponitrile [hexanedinitrile (19), Scheme 11]. [33,34] The first step of the process involves 

hydrocyanation of buta-1,3-diene to produce an isomeric mixture of pentenenitriles. In a 

second step, nickel-catalyzed double-bond isomerization occurs to produce pent-4-enenitrile 

followed by alkene hydrocyanation to produce adiponitrile (19). The details of the alkene 

hydrocyanation reaction are discussed in further detail in Section 1.1.4.5. 

Scheme 11 Hydrocyanation of Buta-1,3-diene [33,34] 

HCN, Ni(0) 


Nickel–Allyl Complexes 

CN 

+ 

CN 

Ni(0) 

CN 

HCN, Ni(0) CN 

NC 

Nickel complexes with ç 3 -allyl ligands are important intermediates in a variety of catalytic 

processes. The most straightforward methods of preparation involving the addition of 

allyl electrophiles to nucleophilic nickel complexes and the addition of allyl nucleophiles 

to electrophilic nickel complexes unambiguously lead to ð-allyl complexes. Aside from 

these general classes of reactions, many other important catalytic processes potentially 

involve ð-allyl intermediates although their intermediacy has not, in most cases, been established. 

A very large variety of synthetic procedures involving nickel–ð-allyl complexes 

have been developed including the addition of hard and soft nucleophiles, addition of 

S N2-active and S N2-inactive electrophiles, and migratory insertions of alkenes and alkynes. 


1.1.2.1 Method 1: 

Oxidative Additionof Nickel(0) with Allylic Electrophiles 

A variety of nickel(0) complexes, when treated with allylic electrophiles, afford ð-allyl 

complexes (see also Houben–Weyl, Vol. E 18, pp 64 and 76). [6,8] In early studies, tetracarbonylnickel(0) 

was widely employed. However, owing to its extreme toxicity, it is now rarely 

used. Direct treatment of bis(ç 4 -cycloocta-1,5-diene)nickel(0) (2) with allyl halides such as 

20 is now the method of choice for the stoichiometric preparation of nickel–ð-allyl complexes. 

In the absence of strong donor ligands such as phosphines, halo-bridged dimers 

(e.g., 21) are typically obtained (Scheme 12). [35] In the presence of phosphines, monomeric 

species such as 22 may be obtained. [35] Other less-electrophilic allylic substrates such as 

allylic ethers and allylic alcohols also serve as precursors to nickel–ð-allyl complexes in 

catalytic procedures. However, these precursors are less widely used than allyl halides in 

the stoichiometric preparation of the ð-allyl complexes. 

19 



Scheme 12 Preparation of a Nickel–ç 3 -Allyl Complex from Nickel(0) and 

Allyl Electrophiles [35] 

Ni(cod) 2 + 

2 

OMe 

20 

Br 

Br 

MeO Ni Ni OMe 

Br 

21 

benzene 

4−25 oC 55% 

Br 

MeO Ni Ni OMe 

Br 

21 

+ Ph3P Et2O 

97% 

MeO 

Br 

Ni 

PPh3 

22 

Di-ì-bromobis[(ç 3 -2-methoxyallyl)nickel] (21): [35] 

[Ni(cod) 2](2; 2.63 g, 9.60 mmol) was suspended in argon-sat. benzene (40 mL) in a 100-mL 

two-necked flask fitted with a stopcock and a dropping funnel and was cooled to 4 8C. 3- 

Bromo-2-methoxypropene (20; 1.45 g, 9.6 mmol) in benzene (5 mL) was added dropwise to 

the stirred slurry. A deep red color developed immediately, and some metallic nickel precipitated. 

The mixture was allowed to warm to 25 8C and was stirred at this temperature 

for 0.5 h. It was then filtered under argon and concentrated to ~ 20 mL under aspirator 

vacuum, and petroleum ether (75 mL) was added. The resulting red slurry was cooled to 

–20 8C to complete crystallization, and the supernatant was removed with a syringe. Compound 

21 was obtained as a brick-red solid; yield: 1.00 g (55%). 

Bromo(ç 3 -2-methoxyallyl)(triphenylphosphine)nickel (22): [35] 

Ph 3P (0.29 g, 1.10 mmol) in Et 2O (5 mL) was added to complex 21 (0.23 g, 0.55 mmol) in 

Et 2O (10 mL) under argon at 25 8C. An orange precipitate formed immediately. After stirring 

at 258C for 0.5 h the slurry was allowed to settle, and the supernatant was removed 

with a syringe. Washing with Et 2O (10 mL) and drying under vacuum afforded compound 

22; yield: 0.50 g (97%). 

1.1.2.2 Method 2: 

Additionof Allylmagnesium Halides to Nickel(II) Salts 

Electrophilic nickel(II) salts, when treated with allyl organometallics, afford nickel(II)–ðallyl 

complexes. [8,36] Rather than producing dimeric halo-bridged complexes as observed 

by the oxidative addition route (Section 1.1.2.1), monomeric bis(allyl) complexes are instead 

obtained (Scheme 13). Although both the method described in Section 1.1.2.1 and 

this method afford structurally different ð-allyl complexes, disproportionation may, in 

some instances, allow the interconversion of a bis(allyl) complex 23 and the corresponding 

halo-bridged dimer 24 if a dihalonickel species is present. 

Scheme 13 Preparation of a ç 3 -Allylnickel Complex from Nickel(II) and 

Allyl Nucleophiles [8,36] 

MgBr 

Ni 

23 

+ 

NiBr2 

+ 

NiBr 2 

Et2O, −10 o C 

Ni 

23 

Br 

Ni Ni 

Br 

24 

+ 

MgBr2


Bis(ç 3 -2-methylallyl)nickel (23): [8] 

Following the general procedure of Wilke, [37,190] anhyd NiBr 2 (18.7 g, 0.086 mmol) was suspended 

in anhyd Et 2O (100 mL) in a 1-L three-necked flask fitted with a 500-mL dropping 

funnel, a mechanical stirrer, and a Claisen head containing a low-temperature thermometer 

and a three-way stopcock. The system was alternately evacuated to aspirator vacuum 

and filled with inert gas (N 2 or argon) several times, and cooled to –108C. 2-Methylallylmagnesium 

bromide (27.1 g, 0.17 mol) in Et 2O (300 mL) was added dropwise to the vigorously 

stirred soln over 2 h. The mixture was stirred for an additional 0.4 h at –108C, 

warmed to 258C, and filtered under inert gas. (The simplest technique is to use a reaction 

flask with a fritted disk and two-way stopcock attached to the bottom; the soln can be 

forced through the frit with positive pressure into a second flask which is also under inert 

gas.) The residue was washed with Et 2O (50 mL), filtered, and the combined Et 2O filtrates 

were concentrated under aspirator vacuum at –308C. Pentane (125 mL) was added, the resulting 

slurry was filtered under inert gas (most of the pentane was removed from the filtrate 

at aspirator vacuum), and the remaining brown soln was cooled to –788C. Impure 

brown crystals (mp 358C) of 23 were isolated by decanting the supernatant liquid under 

inert gas. (It is convenient to store the complex at this stage at –208C and then sublime the 

requisite quantity into the vessel for further reaction.) Sublimation at 258C/0.1 Torr with 

a –788C receiver afforded yellow crystals. No precise yield has been reported for this 

method. 

1.1.2.3 Method 3: 

Oxidative Addition of Nickel(0) with Enones in the Presence of Lewis Acids 

An advance by Mackenzie has made nickel–ð-allyl complexes accessible from enals and 

enones. [38,39] In a reaction that is mechanistically analogous to Method 1 in Section 

1.1.2.1, enals, when treated with bis(ç 4 -cycloocta-1,5-diene)nickel(0) (2) in the presence 

of chlorosilanes, afford chloro-bridged dimeric ç 3 -allylnickel complexes such as 25 

(Scheme 14). Enones are less reactive in the process and require pyridine to facilitate the 

oxidative addition. Rather than using bis(ç 4 -cycloocta-1,5-diene)nickel(0) (2), a more convenient 

and less expensive alternative involves the in situ reduction of dichlorotetrakis(pyridine)nickel(II) 

(26) with sodium metal in the presence of cyclooctadiene to give 

enone-derived ç 3 -allylnickel complexes (e.g., 27). 

Scheme 14 Preparation of Enone-Derived ç 3 -Allylnickel Complexes [38,39] 

H 

O 

NiCl2 6H2O 

+ 

Ni(cod) 2 

2 

py 

+ 

TMSCl 

NiCl2(py)4 

26 

86% 

TMSO 

1. 2Na, excess cod 

2. cyclopent-2-enone 

TBDMSCl 

Cl 

Ni Ni 

Cl 

25 

OTMS 

NiCl(py) 2 

27 

OTBDMS 

Di-ì-chlorobis{[ç 3 -1-(trimethylsiloxy)allyl]nickel(II)} (25): [38] 

In a drybox, a 50-mL Schlenk tube was charged with [Ni(cod) 2](2; 500 mg, 1.82 mmol, 

1.00 equiv). On a Schlenk line, a soln of propenal (244 ìL, 3.64 mmol, 2.00 equiv) in benzene 

(8mL) in a 25-mL Schlenk vessel was treated with (MeO)(TMSO)C=CMe 2 (185 ìL, 

0.909 mmol, 0.500 equiv; added as a proton-scavenging reagent), stirred for 5 min, and 



then transferred by cannula onto the [Ni(cod) 2]. The resulting purple-red slurry was stirred 

for 10 min and then treated with TMSCl (462 ìL, 3.64 mmol, 2.00 equiv) to afford a deep 

red soln. After 45 min, the volatiles were removed at 0.1 Torr to obtain an orange-red powder. 

This was extracted with pentane (20 mL) through a filter paper tipped cannula. The 

clear red filtrate was concentrated under vacuum to ca. 5 mL and then cooled to –208C for 

24 h to induce crystallization. The precipitate was isolated by removal of the supernatant 

through a filter paper tipped cannula while maintaining the mixture at –208C, and 

washed with pentane (2 ” 3 mL) to afford 25 as a burgundy-red crystalline solid; yield: 

0.35 g (86%). 

[(1,2,3-ç)-1-(tert-Butyldimethylsiloxy)cyclopentenyl]chlorobis(pyridine)nickel(II) (27): [38] 

A 100-mL Schlenk tube equipped with a magnetic stirring bar and rubber septum was 

charged with [NiCl 2(py) 4](26; 10.0 g, 22.4 mmol, 1.00 equiv) and evacuated and refilled 

with N 2 twice to establish an inert atmosphere. THF (40 mL) was added, followed by cycloocta-1,5-diene 

(8.20 mL, 67.2 mmol, 3.00 equiv), and the resulting mixture was cooled to 

0 8C. A second 100-mL Schlenk tube containing Na metal strips (1.03 g, 44.8mmol, 

2.00 equiv; each ca. 2 cm ” 0.4 cm ” 0.1 cm) was connected to this flask with a flexible 

adapter (available from Aldrich) under a rapid flow of N 2 (an inert atmosphere having previously 

been established in the second Schlenk tube and adapter by capping the free end 

of the adapter and evacuating and refilling with N 2). The Na strips were then transferred 

to the stirred 0–5 8C mixture in four portions over 1.5 h to give, after an additional 40 min at 

0–5 8C, a very dark brown (but not black) supernatant, a small amount of precipitated yellow 

[Ni(cod) 2], and no apparent blue [NiCl 2(py) 4]. This was treated with a soln of cyclopent-2enone 

(1.88mL, 22.4 mmol, 1.00 equiv) and TBDMSCl (3.38g, 22.4 mmol, 1.00 equiv) in THF 

(15 mL) and stirred at 258C for 30 min to afford an orange mixture. The soln of 27 thus obtained 

was directly used in coupling reactions; no purification or yield was reported. 

1.1.2.4 Method 4: 

Oxidative Cyclization of Nickel(0) Complexes of Conjugated Dienes 

ð-Allyl complexes are commonly invoked as intermediates in the reactions of (ç 4 -diene)nickel 

complexes. If a nickel(0) complex possesses both a conjugated diene ligand and another 

ð-bound ligand, an oxidative cyclization may occur to form a ð-allyl ligand within a 

nickel(II) metallacycle. Much of the [4+4]- and [4 +2]-cycloaddition chemistry described 

for ç 4 -diene complexes probably involves the intermediacy of nickel metallacycles that 

possess a ç 3 -allyl ligand. Oxidative cyclizations of this type are also useful in the stoichiometric 

preparation of nickel–ð-allyl complexes. The spectator ligand properties play a significant 

role in determining the position of the equilibrium for oxidative cyclization–reductive 

cleavage processes (Scheme 15). [40] 

Scheme 15 Ligand Dependence in the Formation of ð-Allyl Complexes by 

Oxidative Cyclization [40] 

CO2Me + Ni(cod)2 + Ph3P 

MeO2C 

Ph3P Ni 

2 

MeO2C CO 2Me 

+ Ni(cod) 2 + bipy 

2 

MeO2C 

MeO 2C 

Ni(bipy)



1.1.2.5 Method 5: 

Coupling of Allyl Halide Derived Nickel–Allyl Complexes 

with Alkyl Halides and Other Electrophiles 

Dimeric chloro-bridged nickel–ð-allyl complexes (e.g, 28) undergo a facile coupling reaction 

with a variety of electrophiles. Highly polar solvents are required, and light is often 

used to initiate the process. Interestingly, sp 2 -hybridized halides are more reactive than 

sp 3 -hybridized halides. Coupling generally occurs at the less-substituted terminus of the 

ð-allyl complex. Whereas couplings with aryl, alkenyl, and alkyl halides are often quite 

efficient, leading to products such as 29 (Scheme 16), couplings between nickel–ð-allyl 

complexes and allylic electrophiles are of limited utility since allylic scrambling leading 

to homocoupling often occurs (Scheme 17). [8] 

Scheme 16 Couplings of Nickel–ð-Allyl Complexes with Alkyl, Alkenyl, and Aryl Halides [8] 

Br 

Ni Ni 

Br 

28 

+ 

2 R 1 X 

DMF 

Scheme 17 Potential Scrambling with Allylic Electrophiles [8] 

R2 R2 R 

Br 

Ni Ni 

Br 

1 

R 1 

R 1 

+ 

R 2 

R 3 

R 2 

In addition to the widely used couplings of alkyl, alkenyl, and aryl halides with ð-allyl 

complexes, couplings of nickel–ð-allyl complexes with aldehydes and ketones are also efficient. 

[35,41] Couplings involving the 3-bromo-2-methoxypropene derived complex 30 are 

particularly useful as a method for introducing the acetonyl functional group into organic 

substrates to give ketones such as 31 (Scheme 18). 

Scheme 18 The Use of a 3-Bromo-2-methoxypropene Derived Complex for 

the Introduction of the Acetonyl Functionality by Coupling with Iodobenzene [35,41] 

Br 

MeO Ni Ni OMe 

Br 

+ 

PhI 

Br 

R 1 

+ 

DMF 

DMF 

30 31 

A detailed mechanistic study of the coupling of ð-allyl complexes and organic halides has 

been carried out. [42] A mechanism involving the establishment of a pre-equilibrium between 

bis(allyl)nickel complexes and monoallyl halo-bridged dimers is proposed. A single-electron-transfer 

mechanism then initiates cross coupling via nickel(I) intermediates. 

R 1 

R 2 

29 

O 

R 1 

R 3 

Ph 

+ 

R 3 

R 3 



4-(2-Methylallyl)cyclohexanol (29,R 1 = 4-hydroxycyclohexyl); Typical Procedure: [8] 

Di-ì-bromobis[(ç 3 -2-methylallyl)nickel] (28; 0.55 g, 1.42 mmol) was weighed under N 2 or 

argon into a flask equipped with a three-way stopcock and rubber septum. DMF (4.0 mL, 

distilled at 508C/30 Torr from CaH 2 and rendered air-free by alternately evacuating and 

filling with inert gas several times) was added via a syringe. Then a soln of trans-4-iodocyclohexanol 

(0.643 g, 2.84 mmol, prepared by reaction of 1,4-epoxycyclohexane with HI, 

mp 60–61 8C) in DMF (2.0 mL, air-free as above) was added rapidly by syringe. After addition, 

the soln was allowed to warm to 23 8C during 1 h and stirred at this temperature for 

22 h under a positive pressure of an inert gas. The mixture, now green, was poured into 

Et 2O and the Et 2O soln was washed with H 2O (4 ”), dried (MgSO 4), and concentrated at aspirator 

vacuum to afford 29 (R 1 = 4-hydroxycyclohexyl); yield: 388 mg (89%). 

Other alkyl halides used, together with products and yields, were iodobenzene fi (2methylallyl)benzene 

(98%), iodocyclohexane fi (2-methylallyl)cyclohexane (91%), bromoethene 

fi 2-methylpenta-1,4-diene (70%). 

1-Substituted Acetones; General Procedure: [35] 

Reactions were carried out in a 100-mL one-necked flask with a side arm capped with a 

septum, and containing a magnetic stirring bar and fitted with a stopcock. The reaction 

flask was flushed with argon and placed in a N 2-filled glove bag along with a flask containing 

complex 30. The desired amount of 30 (1–2 mmol) was transferred into the reaction 

flask through the side arm (in the glove bag), the side arm was recapped with the septum, 

and the reaction flask was removed from the glove bag. The complex was dissolved in argon-sat. 

DMF (30 mL solvent/mmol complex), giving a deep red soln. Liquid reactants (1.8– 

3.6 mmol) were directly added to the reaction flask, while solid reactants were dissolved 

in a minimum amount of DMF and added as solns. With organic halides as reactants, the 

soln turned emerald-green upon completion, whereas with ketones and aldehydes it 

turned brown-orange. Upon completion, the mixture was poured into a separatory funnel 

containing 3% aq HCl (50 mL) and Et 2O (50 mL), and was thoroughly shaken. The aqueous 

phase was washed with Et 2O (3 ” 20 mL), and the combined Et 2O extracts were washed 

with 3% aq HCl (3 ” 50 mL) to ensure complete hydrolysis of the enol ether and complete 

removal of DMF. The organic phase was dried (MgSO 4) and the solvent was removed under 

vacuum. The crude product, usually more than 90% pure, was purified by preparative layer 

chromatography (silica gel) or distillation. 

1.1.2.6 Method 6: 

Coupling of Enal-Derived Nickel–Allyl Complexes 

with Alkyl Halides and Other Electrophiles 

Most features of the couplings described for allyl halide-derived nickel–ð-allyl complexes 

also hold true for the closely related enone- and enal-derived complexes. Once the enoneor 

enal-derived complex is generated (e.g., 27, 32), couplings with alkyl halides generally 

are accomplished in dimethylformamide upon photolysis of the mixture with a sunlamp, 

to give products such as 33 and 34 (Scheme 19). [38] Strong donor ligands are not required 

for coupling reactions of enals, whereas couplings involving enones require the presence 

of pyridine. 

Scheme 19 Enone or Enal Couplings with Alkyl Halides [38] 

TBDMSO 

Br 

Ni Ni 

Br 

32 

OTBDMS 

+ 

I 

DMF 

photolysis 

68% 

33 

OTBDMS


NiCl(py)2 

27 

OTBDMS 

+ 

Br 

DMF 

photolysis 

72% 

34 

OTBDMS 

(E)-1-(tert-Butyldimethylsiloxy)-4-methylpent-1-ene (33): [38] 

A 100-mL Schlenk tube, equipped with a magnetic stirring bar, was sequentially charged 

with TBDMSCl (3.56 g, 23.6 mmol, 1.30 equiv), MeCN (30 mL), (MeO)(TMSO)C=CMe 2 

(3.69 mL, 18.2 mmol, 1.00 equiv; added as a proton-scavenging reagent), and propenal 

(2.43 mL, 36.4 mmol, 2.00 equiv). The mixture was stirred for 5 min, during which time 

N 2 was bubbled through the soln. The soln was then transferred via a cannula into a 100mL 

Schlenk tube containing [Ni(cod) 2](2; 5.00 g, 18.2 mmol, 1.00 equiv) and a spinning 

stirrer bar, followed by an MeCN wash (5 mL) to complete the transfer. The resulting 

deep burgundy-red soln was stirred for 1 h and then concentrated under reduced pressure 

(0.01 Torr) for 14 h to afford a dark red solid contaminated with cycloocta-1,5-diene. The 

solid was dissolved in MeCN (30 mL) and sequentially treated with (MeO)(TMSO)C=CMe 2 

(0.10 mL, 0.49 mmol, 0.03 equiv), DMF (14 mL, 182 mmol, 10.0 equiv), and 2-iodopropane 

(14.1 mL, 181 mmol, 10.0 equiv). The resulting burgundy-red soln was stirred for 5 min 

and then irradiated with sunlight or a 275-W GE Model RSW sunlamp until the burgundy-red 

color of the allylnickel complex had been completely discharged (ca. 12 h), during 

which time a brown-green crystalline precipitate was deposited and the supernatant became 

light blue-green or nearly colorless (depending on the completeness of the precipitation). 

The supernatant was transferred via a cannula into a round-bottomed flask containing 

pentane, and the cloudy mixture was stirred for 30 min to complete precipitation 

of the nickel dihalide coproduct. The supernatant was then transferred through a filter 

paper tipped cannula onto a stirred aq KH 2PO 4/NaOH buffer (150 mL, pH 7) (an emulsion 

tended to form at this stage if most of the nickel dihalide had not been removed through 

the prescribed procedure). The pentane layer was separated, washed with H 2O(3”20mL), 

dried (MgSO 4), and concentrated under reduced pressure (15 Torr) to afford the crude 

product [(E/Z) 10:1] as a clear, yellow oil, contaminated by cycloocta-1,5-diene and 2-iodopropane. 

Column chromatography (silica gel, 343 g, hexane/EtOAc 98:2) afforded pure 33; 

yield: 2.64 g (68%); bp 768C/15 Torr; (E/Z) > 40:1. 

1-(tert-Butyldimethylsiloxy)-3-vinylcyclopentene (34): [38] 

A 100-mL Schlenk tube equipped with a magnetic stirring bar and rubber septum was 

charged with [NiCl 2(py) 4] (10.0 g, 22.4 mmol, 1.00 equiv) and evacuated and refilled with 

N 2 twice to establish an inert atmosphere. THF (40 mL) was added, followed by cycloocta- 

1,5-diene (8.20 mL, 67.2 mmol, 3.00 equiv), and the resulting mixture cooled to 0 8C. A second 

100-mL Schlenk tube containing Na metal strips (1.03 g, 44.8mmol, 2.00 equiv; each 

ca. 2 cm ” 0.4 cm ” 0.1 cm) was connected to this flask with a flexible adapter (available 

from Aldrich) under a rapid flow of N 2 (an inert atmosphere having previously been established 

in the second Schlenk tube and adapter by capping the free end of the adapter and 

evacuating and refilling with N 2). The Na strips were then transferred to the stirred 0–58C 

mixture in four portions over 1.5 h to give, after an additional 40 min at 0–58C, a very 

dark brown (but not black) supernatant, a small amount of precipitated yellow [Ni(cod) 2], 

and no apparent blue [NiCl 2(py) 4]. The mixture was treated with a soln of cyclopent-2enone 

(1.88mL, 22.4 mmol, 1.00 equiv) and TBDMSCl (3.38g, 22.4 mmol, 1.00 equiv) in 

THF (15 mL) and stirred at 258C for 30 min to afford an orange mixture. A soln of bromoethene 

(4.74 mL, 67.2 mmol, 3.00 equiv) in THF (5 mL) was added via a cannula, and the 

mixture was irradiated at 10 8C with a 275-W GE Model RSW sunlamp for 12.5 h to afford 

an olive-green precipitate and a light brown supernatant. The mixture was poured into a 

2-L separatory funnel containing pentane (400 mL) and aq KH 2PO 4/NaOH buffer (400 mL, 



pH 7), and shaken to give an emulsion that was filtered with suction through Celite to 

achieve separation. The organic phase was washed with H 2O (3 ” 300 mL), dried (MgSO 4), 

filtered, and concentrated under reduced pressure (15 Torr) to afford a mixture of 34 and 

cycloocta-1,5-diene. Distillation through a 20-cm Vigreux column under reduced pressure 

afforded 34 as a clear, colorless oil; yield: 3.62 g (72%); bp 80–82 8C/3 Torr. 

1.1.2.7 Method 7: 

Coupling of Nickel–Allyl Complexes with Main Group Organometallics 

Nickel–ð-allyl complexes generated by a variety of methods undergo efficient coupling 

with nonstabilized main group organometallic reagents. Magnesium reagents have been 

most extensively investigated as the main group organometallic, [43] although organostannanes 

[39] and organoborates [44] have also been reported to participate in catalytic allylations. 

In some instances, efficient allylic reductions may be observed if the main group 

organometallic possesses a â-hydrogen. The mechanism typically proceeds by oxidative 

addition to afford the nickel–ð-allyl complex, transmetalation of the main group organometallic 

to produce an alkyl/allylnickel species, and reductive elimination to afford the 

coupled product (Scheme 20). The reductive elimination step has been studied in detail 

by Kurosawa who demonstrated that the rate of reductive elimination from an 18-electron 

(ç 3 -allyl)nickel complex is significantly greater than reductive elimination from either 

the ç 3 or ç 1 16-electron complexes. [45,46] Although nickel(0) and nickel(II) complexes 

are commonly invoked in this reaction class, the involvement of paramagnetic nickel 

species is well documented in related reaction classes and cannot be ruled out here. 

Scheme 20 Nickel-Catalyzed Allylation of Allylic Ethers and Enals [39,43,44] 

allylic ether or enal 

M = main group metal 

+ 

NiLn 1.1.2.7.1 Variation1: 

Allylic Ether Derived ð-Allyl Complexes 

In contrast to the very widely used palladium-catalyzed allylations involving allylic acetates, 

the corresponding nickel-catalyzed reactions commonly employ allylic ethers. The 

nickel-catalyzed allylation of main group organometallics normally favors the more-substituted 

regioisomer, and the reaction proceeds with overall inversion of configuration of 

the allylic ether (e.g., 35 fi 36; Scheme 21). [43] Hoveyda has demonstrated that substratedirected 

alkylations are possible by employing allylic ethers such as 37 with a tethered 

phosphine moiety. [47,48] Phosphine-containing substrates direct alkylation to the distal position 

of the allyl unit, giving products such as 38. Reductions employing ethylmagnesium 

bromide, however, are directed to the proximal position of the allyl unit (Scheme 

21). [49] Several asymmetric variants of allylations of Grignard reagents are utilized in relatively 

simple systems (Scheme 22). Interestingly, whereas the Hoveyda studies on directed 

reductions lead cleanly to hydrogen-atom incorporation in the presence of ethylmagnesium 

bromide and dichlorobis(triphenylphosphine)nickel(II) (3), [49] the asymmetric variants 

with chiral chelating phosphines give high yields of ethyl-group incorporation 

with ethylmagnesium bromide. [50,51] Related additions to unsaturated acetals are discussed 

in Section 1.1.4.9. 

R 1 M 

R 1 

NiL n 

R 1


Scheme 21 Regio- and Stereochemistry of Nickel-Catalyzed Allylations [43,47,48] 

( ) 5 

35 

OTES 

or 

OTES 

Ar 1 MgBr, NiCl2(dppf) 

OTES Ar 1 

MeO PPh 2 

37 

PhMgBr, NiCl 2(dppf) Ph 

major isomer 

MeMgBr, NiCl2(PPh3)2 3 

73% 

EtMgBr, NiCl2(PPh 3) 2 3 

82% 

Scheme 22 Asymmetric Alkylation of Allylic Ethers [51] 

Ph 

OMe 

Ph 

EtMgBr, Ni(cod) 2 2 

(S,S-Chiraphos) Ph 

91% 

( ) 5 

36 major isomer 

38 99:1 regioselectivity 

( ) 5 

99:1 regioselectivity 

3-Phenylbut-1-ene (36): [43] 

NiCl 2(dppf) (13.7 mg, 0.04 mmol) was added to a 25-mL two-necked flask equipped with a 

stirring bar, a septum, and a three-way stopcock. The vessel was then cooled to –788C, 

evacuated, and filled with argon. (E)-1-(Triethylsiloxy)but-2-ene (35; 373 mg, 2.0 mmol) 

and 1.2 M PhMgBr in Et 2O (3.3 mL, 4.0 mmol) were then added. The resulting mixture 

was stirred at rt for 4 h, and hydrolyzed with 10% HCl (5 mL) at 0 8C. An appropriate internal 

standard (normally an alkane) was added to the organic layer. GC analysis of the organic 

layer indicated the formation of 0.22 mmol (11%) of (E)-1-phenylbut-2-ene, 

0.02 mmol (1%) of (Z)-1-phenylbut-2-ene, and 1.76 mmol (88%) of 3-phenylbut-1-ene (36). 

The organic layer and Et 2O extracts from the aqueous layer were combined, washed 

with sat. NaHCO 3 soln and then H 2O, and dried (Na 2SO 4). After evaporation of the solvent, 

bulb-to-bulb distillation (95–110 8C bath temp/20 Torr) of the residue gave 224 mg (85%) of 

a mixture of coupling products, which were separated by preparative GC (Silicone DC550 

30% on Celite); no isolated yields were reported. 

(E)-1-(Diphenylphosphino)-5-methylundec-3-ene (38); Typical Procedure: [47] 

In a glovebox, NiCl 2(PPh 3) 2 (3; 8.8 mg, 13 ìmol) was transferred to a 10-mL flame-dried 

round-bottomed flask. The flask was then sealed with a rubber septum, removed from 

the glovebox, and kept under argon. (E)-1-(Diphenylphosphino)-3-methoxyundec-4-ene 

(37; 1.0 g, 0.27 mmol) was dissolved in anhyd THF (1.7 mL), and the resulting soln was 

then added by cannula to the original flask containing the catalyst. The soln was cooled 

to 08C, MeMgBr (1.0 mL, 1.3 mmol) was added in a dropwise fashion, and the mixture was 

stirred at 22 8C for 18h under argon. The mixture was cooled to 08C and quenched by the 

addition of H 2O (1.0 mL). After addition of more H 2O (15 mL), the mixture was washed 

R 

Et 

73% ee 

Ph 

PPh 2 

PPh 2 



with CH 2Cl 2 (3 ” 35 mL). The combined organic layers were dried (MgSO 4). Removal of the 

drying agent through filtration, followed by solvent evaporation in vacuo, afforded a yellow 

oil. Chromatography (silica gel, hexanes/EtOAc 15:1) afforded 38 as a colorless oil; 

yield: 69 mg (73%). 


Enal-Derived ð-Allyl Complexes 

Enal-derived nickel–ð-allyl complexes are efficient partners in cross-coupling reactions 

with alkenyl- and arylstannanes leading to products such as 39 (Scheme 23). [39] As described 

for the allylic ether derived complexes, the mechanism of the coupling process 

involves transmetalation followed by reductive elimination. The reaction is catalytic in 

nickel, unlike couplings of enals with alkyl halides which require stoichiometric quantities 

of nickel. Many other variants of nickel-catalyzed conjugate additions may involve ðallyl 

complexes, but these are treated separately in a section on alkenes (Section 1.1.4.2) 

because the mechanism is poorly defined in most nickel-catalyzed conjugate additions. 

Scheme 23 Addition of Organotins to Enal-Derived ð-Allyl Complexes [39] 

H 

O 

Bu3SnCH CH2 TBDMSCl, Ni(cod)2 2 

TBDMSO 

Cl 

Ni Ni 

Cl 

75% 

OTBDMS 

39 

OTBDMS 

(E)-1-(tert-Butyldimethylsiloxy)penta-1,4-diene (39): [39] 

A 25-mL Schlenk tube equipped with a stirring bar was sequentially charged with propenal 

(74.0 ìL, 1.11 mmol), (MeO)(TMSO)C=CMe 2 (30.0 mg, 0.148mmol), TBDMSCl (168mg, 

1.12 mmol), and CH 2Cl 2 (1.5 mL). The soln was stirred for 5 min, treated with [Ni(cod) 2](2; 

27 mg, 0.098mmol), stirred for an additional 5 min, and then treated with tributyl(vinyl)stannane 

(293 ìL, 1.00 mmol) to give a clear red soln. This was stirred at 258C for 

48h, near the end of which time the mixture turned black and deposited a metallic nickel 

precipitate. The mixture was diluted with pentane (25 mL) and washed with aq 0.1 M 

KH 2PO 4/NaOH buffer (2 ” 25 mL, pH 7). The organic layer was separated and the product 

was dried (MgSO 4), filtered, and concentrated under reduced pressure (15 Torr) to afford 

an oil [(E/Z) 19:1] which was chromatographed (silica gel, 35 g, hexane/EtOAc 98:2) to give 

39 as a clear, colorless oil; yield: 149 mg (75%); (E/Z) > 50:1 by 1 H NMR analysis. 


Allylic Alcohol Derived ð-Allyl Complexes 

Allylic alcohols readily undergo nickel-catalyzed allylation with Grignard reagents 

(Scheme 24). [52–55] Both isomers of 40 produce similar product ratios, and the reaction presumably 

proceeds via nickel–ð-allyl intermediates. Only simple Grignard reagents that 

lack â-hydrogens such as methylmagnesium bromide and phenylmagnesium bromide 

are reported, but considerable variation of the allylic alcohol is tolerated.


Scheme 24 Addition of Grignard Reagents to Allylic Alcohols [52–55] 

MeMgBr, NiCl2(PPh3) 2 3 

Bu + 

50% 

OH 

t But But 40 

41 4:1 

42 

4-tert-Butyl-1-methyl-1-vinylcyclohexane (41): [52] 

A 0.74 M soln of MeMgBr in Et 2O (35 mL) was distilled under N 2 nearly to dryness, and dry 

benzene (20 mL), NiCl 2(PPh 3) 2 (3; 417 mg), and a soln of a 5:3 mixture of cis- and trans-isomers 

of 40 (1.00 g, 5.5 mmol) in dry benzene (15 mL) were added successively. The mixture 

was heated at reflux under N 2 for 24 h, and sat. NH 4Cl soln (25 mL) was added. The 

organic layer was washed with H 2O, dried (Na 2SO 4), and evaporated. Distillation of the residue 

afforded a 77:20 mixture of 41 and 42; yield: 500 mg (50%); bp 93–988C/16 Torr, accompanied 

by a 3% yield of the diastereomer of 41. 

1.1.2.8 Method 8: 

Additionof Stabilized Nucleophiles to Nickel–Allyl Complexes 

The allylic alkylation with weak nucleophiles employing nickel catalysts is generally not 

as efficient as the corresponding palladium-catalyzed methods. However, allylic acetates, 

allyl phenyl ethers, and allylic carbonates undergo efficient couplings with amines, phenols, 

and malonates in the presence of nickel(0) catalysts (Scheme 25). [56,57] 

Scheme 25 Addition of Weak Nucleophiles to Allylic 

Acetates, Carbonates, and Ethers [56,57] 

OR 1 

+ 

NuH 

R1 = Ac, Ph, CO2Me Nu = NEt2, OPh, CH(CO2R2 ) 2 

Ni(dppe)2 Nu 

1.1.2.9 Method 9: 

Alkyne Insertions with Nickel–Allyl Complexes 

Migratory insertion of an alkyne into a nickel–ð-allyl complex has not been rigorously established. 

However, this mechanistic scenario has been postulated in several synthetically 

useful processes. Ikeda has demonstrated that treatment of a mixture of allyl chlorides, 

terminal alkynes, and alkynyltin reagents with catalytic amounts of nickel(0) without 

phosphine leads to the production of conjugated enynes (e.g., 43; Scheme 26). [58–60] 

Whereas couplings with allyl chlorides proceed in high yield, the analogous procedure 

with allyl acetates and allyl carbonates is less efficient. Interestingly, reactions carried 

out in the presence of triphenylphosphine afford the product derived from direct coupling 

of the allyl chloride and alkynyltin. [60] Both inter- and intramolecular variants are 

quite general. 



Scheme 26 Nickel-Catalyzed Coupling of an Allylic Acetate, an Alkyne, and an Organotin 

[58–60] 

R 1 

Cl 

+ 

R 2 

H + R SnBu3 3 

Ni(acac) 2 1 

DIBAL-H 

67−83% 

Carbonylative cyclizations have also been developed that likely involve the insertion of 

alkynes into nickel–ð-allyl complexes. [61,62] Chiusoli, who was the pioneer in this area, 

demonstrated that either cyclic or acyclic products may be isolated depending on the concentration 

of methanol (Scheme 27). Allyl halides are the more commonly used allyl complex 

precursor, and enals are also utilized; an example of the latter is the formation of 44 

and 45. [63] 

Scheme 27 Carbonylative Cyclizations of Nickel–ð-Allyl Complexes [61–63] 

OC CO 

OC Ni 

Cl 

CO + H H 

CO, MeOH 

O Ni 

Cl 

OTMS 

Cl 

Ni Ni 

Cl 

TMSO R1 R1 + 

R 3 

R 2 

O 

OMe 

if high conc. of MeOH 

R 3 

CO, MeOH 

R 2 R 1 

O 

44 

OMe 

or 

+ 

R 3 

R 3 

R 2 

43 

O 

H 

R 1 

OMe 

O 

if low conc. of MeOH 

R 2 R 1 

(Z)-3-Butyl-1-phenylhepta-3,6-dien-1-yne (43,R 1 =H;R 2 = Bu; R 3 = Ph); Typical Procedure: [58] 

To a soln of [Ni(acac) 2](1; 26 mg, 0.1 mmol) in THF (5 mL) was added 1.0 M DIBAL-H in toluene 

(0.1 mL, 0.1 mmol) at 0 8C under N 2, and the mixture was stirred for 5 min. To this 

black soln were then added tributyl(phenylethynyl)stannane (380 mg, 0.97 mmol), hex-1yne 

(99 mg, 1.21 mmol), 3-chloroprop-1-ene (73 mg, 0.95 mmol), at 08C, and then the mixture 

was stirred at reflux for 1 h. To this soln was added aq NH 4F (30 mL), and stirring was 

continued for 30 min to remove the Bu 3SnCl. After filtration through Celite, the aqueous 

layer was extracted with Et 2O (40 mL ” 3). The combined organic layers were washed with 

brine, dried (MgSO 4) for 30 min, filtered, and concentrated in vacuo [40 8C (bath)/25 Torr]. 

The residue was purified by column chromatography, R f = 0.64 (silica gel, hexane) to give 

43 as a pale yellow oil; yield: 149 mg (70%). An analytical sample of the product was obtained 

by bulb-to-bulb distillation [140 8C (oven)/4 Torr). The isomeric purity of the obtained 

product was determined by 1 H NMR and GC. 

O 

45 

OMe 

OMe

1.1.3 Nickel–Alkyne Complexes 49 

Carbonylative Cyclizations to Cyclopentenes 44 and 45; General Procedure: [63] 

To a 100-mL Schlenk flask filled with argon was added [Ni(cod) 2](2; 1.24 g, 4.51 mmol) and 

anhyd toluene (20 mL). The temperature was maintained at –40 8C and propenal (0.50 g, 

9.02 mmol) was added dropwise. Soon, a red insoluble complex of Ni(CH 2=CHCHO) 2 was 

formed. The temperature was allowed to warm to –20 8C, when TMSCl (0.49 g, 4.51 mmol) 

was added dropwise. The original red solid gradually dissolved. At –108C the oxidative addition 

was complete and a deep red homogeneous soln resulted. The temperature was 

lowered again to –788C. At this point, the alkyne (4.51 mmol) was added and the argon 

was replaced by CO by means of a vacuum line. The temperature was again allowed to 

rise and an excess of MeOH was added at –158C for activated alkynes and at rt for unactivated 

alkynes. The reaction was allowed to proceed for 4 h, and the solvent was completely 

evaporated in vacuo. The residue was treated with H 2O and extracted several times with 

Et 2O. The combined organic phases were dried (Na 2SO 4) and evaporated to dryness. The 

crude oil was chromatographed (hexane/EtOAc) on silica gel that had been treated with 

a soln of Et 3N, and the solvent was removed to obtain the adducts 44 and 45. 

1.1.2.10 Method 10: 

Alkene Insertions with Nickel–Allyl Complexes 

The cyclization of allylic acetates tethered with alkenes has been extensively investigated 

by Oppolzer, employing a number of transition metals including nickel. The process has 

been termed a “metallo-ene” reaction; however, the mechanism likely involves a sequence 

of oxidative addition to generate a ð-allyl complex, alkene insertion, and â-hydride 

elimination. [64] The process is quite general in scope and provides a very useful 

method for the preparation of 1,4-dienes such as 46 (Scheme 28). 

Scheme 28 Intramolecular Nickel-Catalyzed Alkene–Allylic Acetate Couplings [64] 

AcO 

Ts 

N 


Nickel–Alkyne Complexes 

Ni(cod)2 2, dppb 

Ts 

N 

+ 

Ni 

Ln + 

H Ni 

Ln 

Nickel complexes of alkynes are involved in many important catalytic transformations. A 

fundamental transformation of nickel(0)–alkyne complexes that forms the basis of a 

number of useful stoichiometric and catalytic reactions is the oxidative cyclization of 

one alkyne and a second unsaturated unit to form a five-membered metallacyclopentene 

47 (Scheme 29). If the second unsaturated unit is also an alkyne, linear oligomerizations 

or cyclooligomerizations result. The catalytic tetramerization of acetylene to octatetraene 

was discovered more than 50 years ago by Reppe, [65] and an excellent review on the 

historical development of this area has appeared. [5] The complexities of the mechanistic 

Ts 

N 

88% 

LnNi + 

Ts 

N 

46 

Ts 

N 



steps of alkyne cyclooligomerizations have been further documented by Eisch. [66] Alternatively, 

many selective transformations have been reported in which one alkyne and a different 

unsaturated unit couple in an oxidative cyclization. Oxidative cyclizations of this 

class form the basis of many useful procedures. [187] An outstanding review on the formation 

of oxa- and azametallacycles has appeared. [9] 

Scheme 29 Oxidative Cyclization of an Alkyne 

and a Second Unsaturated Unit [9,187] 

R 1 

L L 

Ni 

Y 

X 

R1 Ni 

R 

Y 

X 

1 

R1 L L 

47 


1.1.3.1 Method 1: 

Ligand Exchange with Nickel–Alkene Complexes 

Nickel–alkyne complexes are typically unstable owing to their propensity to catalyze alkyne 

polymerization to yield polyacetylenes. The most common preparative method involves 

the displacement of alkenes under conditions in which the stoichiometry is carefully 

controlled. Numerous bis(ligand)nickel(0)–mono(alkyne) complexes (e.g., 48) have 

been reported and fully characterized by Pörschke (Scheme 30). [67] Further treatment of 

the monoalkyne complex with alkyne leads to formation of the bis(alkyne) complex. (ç 6 - 

Cyclododeca-1,5,9-triene)nickel(0) [Ni(cdt)] [68] is a common starting nickel(0) complex for 

the preparation of alkyne complexes. Bis(alkyne)nickel(0) complexes 50 have also been 

prepared by Rosenthal and Pörschke from nickel(0) complexes of hepta-1,6-diene (e.g., 

49) by ligand displacement (Scheme 31). [69] 

Scheme 30 Preparation of Nickel(0)–Alkyne Complexes [67] 

Ni(cdt) + H 2C 

CH2 + Cy 3P Cy 3P Ni 

Scheme 31 Preparation of Nickel(0)–Bis(alkyne) Complexes [69] 

N Ni 

49 

+ 

Ph 

TMS 

80% 

H H 

82% 

TMS 

N Ni 

TMS 

50 

Ph 

Ph 

Cy 3P Ni 

(Acetylene)(ethene)(tricyclohexylphosphine)nickel(0) (48): [67] 

Acetylene (50 mL, 6 mmol) was added at –508C without stirring to an Et 2O soln (40 mL) of 

[Ni(C 2H 4) 2(PCy 3)] (5.0 mmol) [prepared from Ni(cdt) (1.165 g, 5.0 mmol Ni), ethene, and 

Cy 3P (1.40 g, 5.0 mmol)]. The color of the yellow soln changed to light red, and at –788C 

over the course of 2 d small yellow crystals formed. The mother liquor was decanted, 

and the crystals were washed with cold Et 2O (2 ”) and dried in vacuo at –308C to afford 

48; yield: 1.62 g (82%). 

48


(2,6-Dimethylpyridine)bis[phenyl(trimethylsilyl)acetylene]nickel(0) (50): [69] 

PhC”CTMS (810 mg, 4.66 mmol) was added at 208C to the light yellow soln of 49 (610 mg, 

2.33 mmol) in pentane (10 mL). Upon heating the mixture for a short period to 458C the 

color turned intense red. Cooling to –788C afforded red cubes which were separated from 

the mother liquor using a capillary frit, washed with cold pentane (2 ”), and dried in vacuo 

at 208C to afford 50; yield: 960 mg (80%). 


1.1.3.2 Method 2: 

Coupling of Alkynes with Carbon Dioxide 

Nickel(0) complexes of alkynes in the presence of carbon dioxide undergo oxidative cyclization 

to produce oxametallacycles 51 (Scheme 32). [70,71] Direct cleavage of the oxametallacycle 

in the presence of strong acids affords unsaturated carboxylic acids 52 (Scheme 

33). [72] The coupling of diynes with carbon dioxide leads to an efficient synthesis of bicyclic 

Æ-pyrones such as 53 by a formal [2+2+2] cycloaddition (Scheme 33). [73,74] 

Scheme 32 Coupling of Alkynes and Carbon Dioxide: Metallacycle Formation [70,71] 

Me2 

N 

NiLn N 

Me2 

+ 

CO 2 

+ 

Et 

Et 

Et 

Me2 N 

Ni 

N O 

Me2 

51 

Scheme 33 Coupling of Alkynes and Carbon Dioxide: Synthetic Utility [72–74] 

R 1 

R 1 

Et 

Et 

+ CO 2 

+ CO 2 

1. Ni(cod) 2 2, bipy 

2. H2SO4 Ni(cod)2 2, Cy3P 

64% 

R 1 

H 

R 1 

CO2H 52 

1,4-Diethyl-5,6,7,8-tetrahydro-3H-benzopyran-3-one (53): [74] 

In a 50-mL stainless steel autoclave were placed, under N 2, a soln of [Ni(cod) 2](2; 0.024 g, 

0.090 mmol) in THF (1.8mL), a soln of Cy 3P (0.05 g, 0.18mmol) in toluene (0.17 mL), and 

THF (8.2 mL). The mixture was stirred for several min, dodeca-3,9-diyne (0.19 mL, 

0.90 mmol) was added, followed by CO 2 gas to a compression of 3.7 ” 10 4 Torr at rt. The 

mixture was magnetically stirred for 20 h at rt. The unreacted CO 2 gas was purged and 

the mixture was transferred to a flask using Et 2O (20 mL). The soln was concentrated to 

give a residue that was purified by preparative layer chromatography (hexane/Et 2O 2:1) 

to give 53; yield: 0.12 g (64%). 

Et 

Et 

53 

O 

O 

Et 

O 



1.1.3.3 Method 3: 

Coupling of Alkynes with Isocyanides 

Little is known about the mechanistic details of isocyanide–alkyne couplings. However, a 

useful stoichiometric cyclization of enynes and diynes with isocyanides was developed by 

Tamao and Ito, [75] and Buchwald later developed a catalytic variant (Scheme 34). [76] The resulting 

cyclopentenimines may be hydrolyzed to cyclopentenones. A variety of carbocyclic 

and heterocyclic templates are tolerated in the sequence. 

Scheme 34 Cyclizations of Enynes and Isocyanides [75,76] 

O 

Ph 

+ 

NC 

Ni(cod) 2 2, bipy 

Cyclization of Enynes To Form Bicyclic Cyclopentenones; General Procedure: [76] 

In an inert-atmosphere glovebox, [Ni(cod) 2](2; 14 mg, 0.05 mmol), bis(diphenylmethylene)ethylenediamine 

(24 mg, 0.06 mmol), the enyne (1.0 mmol), and TIPSCN (201 mg, 

1.1 mmol) were dissolved in DMF (46 mL) in a 100-mL sealable Schlenk flask. The Schlenk 

flask was sealed, removed from the glovebox, and heated at 110–135 8C until the enyne 

was consumed (as determined by GC, 8–36 h). The flask was cooled to 0 8C, treated with 

sat. aq oxalic acid (10 mL), and stirred at rt for 12–24 h. Et 2O (80 mL) and sat. aq NaHCO 3 

(40 mL) were added to the soln and the layers were separated. The aqueous layer was extracted 

with Et 2O (3 ” 50 mL) and the combined Et 2O extracts were washed with H 2O 

(3 ” 40 mL) and brine (40 mL). The Et 2O soln was dried (MgSO 4) and concentrated in vacuo 

to give an oily residue which was purified by flash chromatography (silica gel, Et 2O/hexane 

1:1–2) to give the desired cyclopentenone, typically as a colorless to pale yellow oil. 

1.1.3.4 Method 4: 

Coupling of Alkynes with Aldehydes 

Couplings of alkynes and aldehydes have been investigated in a number of contexts. Although 

no metallacycles derived from oxidative couplings of one alkyne and one aldehyde 

have been isolated, the reaction probably proceeds in a fashion similar to the coupling 

of alkynes and carbon dioxide (Section 1.1.3.2). Tsuda and Saegusa have reported 

the formal hydroacylation of alkynes by a process that involves the coupling of an alkyne 

and an aldehyde (Scheme 35). [77] Two possible mechanisms are proposed for the formation 

of the enone 54, and one involving the formation of an oxametallacycle is depicted. 

The corresponding coupling of diynes and aldehydes is also reported by the same investigators 

to afford the dihydropyran 55. [78] 

80% 

O 

Ph 

N


Scheme 35 Nickel-Catalyzed Aldehyde–Alkyne Couplings [77,78] 

X 

O 

H 

+ 

Pr 

Pr 

Ni(cod) 2 2 

L L 

Ni 

Pr 

O 

L L 

H 

Ni Pr 

R 

Ni(cod) 2 2, Cy3P + 

1 O 

R2 X 

R1 R 

H O 

2 

O 

Pr 

Pr 

R 1 

R 1 

55 

60% 

O 

H Pr 

Montgomery has developed a procedure for the three-component coupling of aldehydes, 

alkynes, and organozincs to produce allylic alcohols (Scheme 36). [79] Two-component couplings 

involving ynals are also reported. If no phosphine is employed, the organozinc ligand 

is incorporated into the allylic alcohol product 56. However, if bis(ç 4 -cycloocta-1,5diene)nickel(0) 

(2) and tributylphosphine are employed and if the organozinc possesses a 

â-hydrogen, a hydrogen atom is instead introduced from the organozinc to generate product 

57. Triethylsilane may also be employed as the reducing agent, and this variant has 

been utilized in the total synthesis of allopumiliotoxin 267A (58; Scheme 37). [80] The ynal 

cyclization method is quite general with functionalized substrates. 

Scheme 36 Three-Component Aldehyde, Alkyne, Organozinc Couplings [79] 

O 

R 1 H 

+ 

R 2 

L L 

Ni 

R 

O 

3 

R2 R1 H 

R 3 

ZnR 4 2 

L nNi(0) 

R 4 ZnO 

R 1 

R 

LnNi 

4 

R 1 

H 

L L 

O Ni 

H 

OH R 4 

R2 56 

R2 H R1 

L = THF 

R 3 

R 2 

R 3 

R 3 

large substituent 

small substituent 

(or tether chain) 

L = Bu3P 

R 4 ZnO 

H 

LnNi 

R 1 H 

54 

R 3 

R 2 

Pr 

OH H 

R3 R2 R1 H 

57 

(intramolecular variant only) 



Scheme 37 Ynal Cyclizations in Pumiliotoxin Synthesis [80] 

N 

H 

H 

O 

OBn 

Et 3SiH 

Ni(cod) 2 2 

Bu3P N 

H 

OTES 

OBn 

N 

H 

OH 

OH 

58 allopumiliotoxin 267A 

Hodgson has developed a variant on the Nozaki–Kishi coupling [81] in which a haloalkene, 

an alkyne, and an aldehyde undergo coupling to produce allylic alcohols with a tetrasubstituted 

alkene (Scheme 38). [82] Only the fully intramolecular procedure is reported. 

Scheme 38 Aryl Iodide–Aldehyde–Alkyne Coupling [82] 

I 

O 

H 

CrCl 2, NiCl 2 

DMF, 25 o C 

2-Methyl-4-propyloct-4-en-3-one (54): [77] 

In a 50-mL stainless steel autoclave were placed under N 2, THF (8.50 mL), a soln of 

[Ni(cod) 2] (2; 14 mg, 0.050 mmol) in THF (1.20 mL), and trioctylphosphine (0.046 mL, 

0.10 mmol). The mixture was stirred for several min, then oct-4-yne (0.147 mL, 

1.00 mmol) and isobutyraldehyde (0.136 mL, 1.50 mmol) were added. The mixture was 

magnetically stirred for 20 h at 808C. The soln was concentrated to give a residue which 

was purified by preparative layer chromatography (hexane/Et 2O 15:1) to give a 7:1 mixture 

of 54 and a 2:1 adduct; yield: 0.124 g (60%). 

Alkylative Cyclization of Ynals; General Procedure: [79] 

A 0.5–0.6 M soln of ZnCl 2 (2.5–3.0 equiv) in THF was stirred at 0 8C, and the organolithium 

or Grignard reagent (3.7–4.5 equiv) was added by syringe followed by stirring for 10– 

15 min at 08C. A 0.02–0.04 M soln of [Ni(cod) 2](2; 0.05–0.20 equiv) in THF was added and 

the resulting mixture was immediately transferred by cannula to a 0.1–0.2 M soln of the 

ynal (1.0 equiv). After consumption of starting material as measured by TLC analysis (typically 

0.25–0.5 h at 08C), the mixture was subjected to an extractive workup with NH 4Cl/ 

NH 4OH buffer (pH 8) and Et 2O followed by flash chromatography (silica gel). 

Reductive Cyclization of Ynals; General Procedure: [79] 

A 0.04–0.05 M soln of Bu 3P {4 equiv relative to [Ni(cod) 2]} in THF was added to [Ni(cod) 2](2; 

0.05–0.20 equiv) at 25 8C followed by stirring for 3–5 min. The nickel soln was transferred 

to a 0.5–0.6 M soln of commercial Et 2Zn (2.5–3.5 equiv) in THF at 0 8C, and the resulting 

mixture was immediately transferred by cannula to a 0.10 M soln of the ynal (1.0 equiv) 

in THF at 08C. After consumption of starting material as measured by TLC analysis (typically 

0.25–2.0 h at 0 8C), the mixture was subjected to an extractive workup with NH 4Cl/ 

NH 4OH buffer (pH 8) and Et 2O followed by flash chromatography (silica gel). 

Three-Component Couplings; General Procedure: [79] 

A 1.0 M soln of ZnCl 2 (2.5–3.0 equiv) in THF was stirred at 0 8C, and the organolithium or 

Grignard reagent (4.5–5.4 equiv) was added by syringe followed by stirring for 10–15 min 

HO


at 0 8C. A 0.05 M soln of [Ni(cod) 2](2; 0.20 equiv) in THF and a soln containing the aldehyde 

(3.0 equiv) and alkyne (1.0 equiv, 0.3–0.4 M relative to the alkyne) in THF were added sequentially 

to the organozinc reagent. After consumption of starting material as measured 

by TLC analysis (typically 0.25–0.5 h at 0 8C), the mixture was subjected to an extractive 

workup with NH 4Cl/NH 4OH buffer (pH 8) and Et 2O followed by flash chromatography (silica 

gel). With the alkyne as the limiting reagent, the product derived from direct addition 

of the organozinc to the aldehyde was observed as a significant byproduct. In cases in 

which separation of this byproduct was problematic, slightly lower yields were obtained 

by employing the aldehyde as the limiting reagent; however, the purification was simpler. 

1.1.3.5 Method 5: 

Coupling of Two Alkynes 

The couplings of diynes with a third unsaturated component are described in several subsections 

throughout Section 1.1.3. However, several other processes merit discussion 

here that do not fall into the other categories described. The hydrosilylation of diynes provides 

an excellent route to cyclic dienylsilanes. A mechanism was proposed that involves 

Si-H oxidative addition, alkyne silylmetalation, alkyne insertion, and C-H bond reductive 

elimination to give 59 (Scheme 39). [83] A related process ensues when diynes are treated 

with hydrodisilanes, and bicyclic silacyclopentadienes 60 are produced (Scheme 40). [83] 

The intermolecular version of this process was first reported by Lappert. [84] 

Scheme 39 Diyne Hydrosilylation [83] 

R 1 

R1 SiX3 

Ni 

H 

+ HSiX 3 

Ni(acac) 2 1, DIBAL-H 

L nNi 

R 1 

H 

SiX3 H 

Scheme 40 Diyne Hydrosilylation with Hydrodisilanes [83] 

R 1 

R 2 

+ HSiR 3 2SiX 3 

Ni(acac) 2 1, DIBAL-H, R 1 3P 

H 

R 

59 

1 

SiX3 

H 

R 1 

R 

60 

2 

SiR 3 2 

H 

SiX3 

Ni 

R1 Ln 

H 

Cheng has demonstrated that spirocyclic cyclopentadienes such as 61 may be produced 

upon treatment of an iodoalkene with an alkyne (Scheme 41). [85] A mechanism involving 

oxidative addition of nickel(0) to the iodoalkene followed by two sequential alkyne insertions 

has been proposed. 



Scheme 41 Iodoalkene–Alkyne Couplings [85] 

O 

I 

+ 

Et Et 

NiBr 2, Zn 

85% 

6,7,8,9-Tetraethylspiro[4.4]nona-6,8-dien-2-one (61): [85] 

To a mixture of NiBr 2 (0.080 g, 0.36 mmol), Zn powder (0.14 g, 2.2 mmol), and 3-iodocyclopent-2-enone 

(0.40 g, 1.8mmol) in MeCN (1.0 mL) was added hex-3-yne (0.30 g, 3.6 mmol). 

The system was then heated under N 2 at 608C with stirring for 20 h. During the course of 

catalysis, the color of the soln changed from light green to a persistent dark red in the 

first few hours. The MeCN soln was cooled, the soln was concentrated, and the resulting 

compounds were separated by column chromatography (silica gel, hexane/EtOAc 10:1) to 

give the desired product 61; yield: 0.40 g (85%). 

1.1.3.6 Method 6: 

Coupling of Alkynes with Alkenes 

The couplings of enynes with a third unsaturated component are described in Sections 

1.1.3.3 and 1.1.3.7. However, several other processes merit discussion here that do not 

fall into the other categories described. For example, Ikeda and Montgomery have extensively 

investigated intermolecular couplings of enones and alkynes with organometallic 

reagents such as organozincs [86,87] and organotins. [88,89] Intermolecular couplings efficiently 

produce ª,ä-unsaturated ketones with highly selective tri- or tetrasubstituted alkene 

formation (Scheme 42). The scope of the process is quite broad, and the mechanism is 

likely to involve the formation of metallacycles as key intermediates. 

Scheme 42 Enone–Alkyne Couplings with Organozincs or Organoaluminums [86–89] 

O 

O 

L L 

Ni 

M = AlR 3 2 or ZnR 2 

H 

+ 

R 1 

R1 H + MR2 MR 2 

MO 

Et 

O 

Et 

61 

Et 

Et 

Ni(acac) 2 1 or Ni(cod) 2 2, Ph 3P 

LnNi 

R1 R2 Montgomery has investigated the intramolecular variant of this process. [90–93] The addition 

of triphenylphosphine promotes a â-hydride elimination process that leads to hydrogen-atom 

introduction instead of alkyl-group introduction. In both cases, the exocyclic 

double bond is created with complete selectivity (Scheme 43). A formal synthesis of (+)- 

Æ-allokainic acid (62) was completed employing this methodology as the key step 

(Scheme 44). [94] 

H 

MO 

O 

R 2 

R 2 

H 

R 1 

R 1


Scheme 43 Alkynyl Enone Cyclization with Alkylation or Reduction [90–93] 

R 1 

O 

R 2 

+ R 3 2Zn 

Ni(cod) 2 2 

Ni(cod)2 2, Ph3P 

R 3 = Et 

Scheme 44 Alkyne-Unsaturated Acyloxazolidinone Cyclizations in (+)-Æ-Allokainic Acid 

Synthesis [94] 

O 

O N 

O 

N 

O 

O 

OTBDMS 

Me 3Al, Ni(cod) 2 2 

O 

O 

N 

O 

O 

R 1 

O 

R 1 

O 

N 

HO 

O 

O 

R 3 

H 

R 2 

R 2 

OTBDMS 

HO 

N 

O 

H 

62 (+)-α-allokainic acid 

Trost has developed a cycloisomerization of enynes involving a nickel–chromium catalyst 

system (Scheme 45). [95] High yields among a broad range of substrates are noted. 

Scheme 45 Nickel-Catalyzed Enyne Cycloisomerization [95] 

OH 

NiCl2(PPh3)2 3, CrCl2 

Alkylative Cyclization of Alkynyl Enones; General Procedure: [91] 

A 0.3–0.5 M soln of ZnCl 2 (2.5–3.0 equiv) in THF was stirred at 0 8C, and the organolithium 

or Grignard reagent (3.7–4.5 equiv) was added by syringe followed by stirring for 0.25–1 h 

at 0 8C. A 0.02–0.04 M soln of [Ni(cod) 2](2; 0.04–0.06 equiv) in THF was added and the resulting 

mixture was immediately transferred by cannula to a 0.1–0.2 M soln of the unsaturated 

substrate (1.0 equiv). After consumption of starting material as judged by TLC analysis 

(typically 0.25–2.0 h at 0 8C), the mixture was subjected to an extractive workup with 

NaHCO 3/EtOAc or NH 4Cl/NH 4OH buffer (pH 8) and Et 2O followed by flash chromatography 

(silica gel). Although the above procedure was typically used, commercially available diorganozinc 

reagents performed comparably. 

OH 

H 



Reductive Cyclization of Alkynyl Enones; General Procedure: [91] 

A 0.03–0.06 M soln of Ph 3P (0.2–0.3 equiv) in THF was added to [Ni(cod) 2] (2; 0.04– 

0.06 equiv) at 258C and stirred for 3–5 min. This soln was then transferred to a 0.5–0.6 M 

soln of Et 2Zn in THF at 08C, and the resulting mixture was immediately transferred by 

cannula to a 0.10–0.50 M soln of the unsaturated substrate (1.0 equiv) in THF at 0 8C. After 

consumption of starting material as judged by TLC analysis (typically 0.25–2.0 h at 0 8C), 

the mixture was subjected to an extractive workup of NaHCO 3/EtOAc or NH 4Cl/NH 4OH 

(pH 8) buffer and Et 2O followed by flash chromatography (silica gel). 

1.1.3.7 Method 7: 

[2+2+2] Cycloadditions 

Dating from the original discovery from Reppe [65] on the cyclooligomerization of acetylene, 

nickel-catalyzed multicomponent cycloadditions have attracted considerable attention 

(see also Houben–Weyl, Vol. E 18, pp 987, 993). [96] Metallacycles have been proposed as 

important intermediates in most classes of cyclotrimerizations. The mechanism is likely 

to involve initial oxidative cyclization to a five-membered metallacycle, followed by insertion 

of a third unsaturated component, and finally reductive elimination to afford sixmembered 

ring products (Scheme 46). 

Scheme 46 General Mechanism of Nickel-Catalyzed [2+2+2] Cycloadditions [96] 

R 1 

R 1 

L n 

Ni 

R 1 

R 1 

R 1 

R 1 

Ni 

R 1 

1 R R1 

R 1 

R 1 

R 1 

L n 

Ni 

R 1 R 1 

A common limitation of most classes of cyclotrimerizations is the difficulty associated 

with controlling the chemoselectivity of the process. In most instances involving intermolecular 

couplings, multiple incorporation of the same alkyne unit is unavoidable. 

However, with systems in which two alkynes, or one alkene and one alkyne are tethered, 

synthetically useful processes become possible. The first example of a selective addition 

of two equivalents of an alkyne and one alkene was reported by Chalk. [97] Tsuda has applied 

this process to applications in polymer chemistry, [98] and Ikeda has developed a similar 

method employing cyclic enones (Scheme 47). [99] 

Scheme 47 Fully Intermolecular [2 + 2+2] Cycloadditions [99] 

O 

+ 

H 

R 1 

Me3Al, Ni(acac) 2 1 

Ph3P, PhOH 

O 

R 1 

R 1 

major isomer 

(after oxidation) 

Bhatarah and Smith have reported that nickel(0)-promoted cyclizations of diynes and simple 

alkynes afford good yields of substituted benzenes. [100] Mori has developed the corresponding 

cyclotrimerization to 63 in an asymmetric fashion by using bis(ç 4 -cycloocta-1,5diene)nickel(0) 

(2) and a chiral phosphine (Scheme 48). [101] Ikeda has developed a cyclotrimerization 

to 64 that introduces two sp 3 -hybridized centers by cycloaddition of a diyne 

with an enone (Scheme 48). [102] Montgomery reported that four contiguous stereocenters 

may be introduced to give 65 by the 1:1 cycloaddition of alkynyl enones and simple 

R 1 

R 1 

R 1 

R 1 

R 1 

R 1 

R 1 

R 1


enones (Scheme 48). [103] This latter process was found to be highly stereoselective but nonstereospecific. 

Scheme 48 Partially Intramolecular [2+2+2] Cycloadditions [101–103] 

R 2 

TMS 

O 

NR 1 

R 2 

OTBDMS 

Ph Ph 

+ H H 

+ 

+ 

O 

O 

Ni(cod)2 2 

chiral phosphine 

NiCl 2, Zn, ZnCl 2 

80% 

Ni(cod) 2 2, Ph 3P 

75% 

R 2 

NR1 ∗ 

R 2 

63 12−73% ee 

O 

O 

Ph 

TMS 

H 

64 

65 

OTBDMS 

A fully intramolecular version involving an enediyne substrate is reported to undergo reasonably 

efficient cyclization to afford the tricyclic cyclohexadiene 66 (Scheme 49). [93] Only 

one example of the process is reported. 

Scheme 49 Fully Intramolecular [2 + 2+2] Cycloadditions [93] 

Ph 

O 

Ni(cod) 2 2 

t-BuLi, ZnCl2 52% 

Cotrimerization and Aromatization of Enones and Alkynes; General Procedure: [99] 

To a soln of [Ni(acac) 2](1; 13 mg, 0.05 mmol) and Ph 3P (26 mg, 0.1 mmol) in THF (5 mL) was 

added 1.0 M Me 3Al in hexane (0.4 mL) at 0 8C under N 2. After stirring for 5 min, PhOH 

(92 mg, 1.0 mmol) was added to this soln, and the mixture was stirred for 5 min. To this 

dark red soln were added the alkyne (2.05 mmol) and the enone (1.0 mmol) at 0 8C, and 

the mixture was then stirred at rt for 2 h. DBU (350 mg, 2.3 mmol) was added to the mixture, 

and the soln was opened to the air and stirred at rt overnight. Aq 0.2 M HCl (30 mL) 

was added, and stirring was continued for 10 min. The aqueous layer was extracted with 

Et 2O (3 ” 40 mL) and the combined organic layers were washed with aq NaHCO 3 (50 mL) 

and then with brine (50 mL), dried (MgSO 4) for 30 min, filtered, and concentrated in vacuo. 

The residue was purified by column chromatography (silica gel) to yield aromatic 

compounds. 

O 

Ph 

H 

66 

O 

Ph 



Nickel-Catalyzed [2 +2+2] Cycloadditions; General Procedure: [103] 

A 0.02–0.04 M soln of Ph 3P (0.4–1.0 equiv) in THF was added to [Ni(cod) 2](2; 0.20–0.25 equiv) 

at 0 8C and stirred for 2 min. The nickel soln was transferred by cannula to a 0.4–0.5 M soln 

of the simple enone (5.0 equiv) and the alkynyl enone substrate (1.0 equiv) in THF at 0 8C. 

The reaction was stirred at 0 8C for 5 min and then at 258C until the starting material was 

consumed (generally 1.5–3.0 h). The mixture was subjected to an extractive workup with 

NH 4Cl/NH 4OH (pH 8) buffer and Et 2O followed by flash chromatography (silica gel). 

1.1.3.8 Method 8: 

Alkyne Carbonylation 

The carbonylation of alkynes in the presence of methanol or water and carbon monoxide 

produces Æ,â-unsaturated carboxylic acids or esters (Scheme 50). [7,104] This reaction is rarely 

used in large-molecule synthetic applications; however, it has been very important in 

the industrial preparation of acrylic acid from acetylene. 

Scheme 50 Preparation of Acrylic Acid From Acetylene [104] 

H H + H 2O + CO 

1.1.3.9 Method 9: 

Alkyne Hydrocyanation 

The hydrocyanation of alkynes provides a direct method for preparing Æ,â-unsaturated 

nitriles such as 67. The reactions proceed at 1208C in an autoclave with hydrogen cyanide 

and catalytic tetrakis(triphenyl phosphite)nickel(0) (Scheme 51). [105] Lower temperatures 

may be employed if the alkyne and hydrogen cyanide are added very slowly. The hydrocyanation 

of dienes and alkenes (Sections 1.1.1.6 and 1.1.4.5) are much more widely used 

procedures than the hydrocyanation of alkynes. 

Scheme 51 Hydrocyanation of Alkynes [105] 

Ph Ph + HCN 

(E)-2,3-Diphenylprop-2-enenitrile (67): [105] 

Ni 

Ni[P(OPh) 3] 4 

93% 

Ph 

H 

H 

H 

H 

Ph 

CN 

67 

CAUTION: Hydrogen cyanide is highly toxic! Appropriate safety precautions and procedures 

should be adopted during all stages of the handling and disposal of this reagent. 

Into a 75-mL stainless steel autoclave were placed Ni[P(OPh) 3] 4 (0.24 g, 0.2 mmol), P(OPh) 3 

(0.8g, 2.5 mmol), PhC”CPh (7 g, 39 mmol), HCN (1.25 mL, 32 mmol), and benzene (25 mL). 

The vessel was heated at 1208C for 18h. After cooling, the benzene was removed by distillation. 

Column chromatography (basic alumina, activity II, Et 2O/petroleum ether 1:9) 

followed by distillation gave the unsaturated nitrile 67; yield: 6.12 g (93%). 

1.1.3.10 Method 10: 

Alkyne Hydrosilylation 

Two distinct product classes, silylethenes and 1,2-disilylethenes, may be obtained from 

the hydrosilylation of alkynes. The addition of trichlorosilane to alkynes in the presence 

CO2H


of (2,2¢-bipyridyl)diethylnickel(II) leads to the production of a mixture of both of these 

product classes (Scheme 52). The mechanism for the formation of the unusual disilyl substituted 

ethenes may involve a novel nickel disilyl species. [106] Hydrosilylations of bis(alkynes) 

are described in the section on the couplings of two alkynes (Section 1.1.3.5). 

Scheme 52 Hydrosilylation of Alkynes 

R 1 R 1 + HSiCl 3 

1.1.3.11 Method 11: 

Alkyne Carbozincation 

NiEt 2(bipy) 

R1 Cl3Si R1 SiCl3 R1 H 

R1 SiCl3 + 

major minor 

Knochel has demonstrated that phenylacetylenes undergo a highly stereoselective syncarbozincation 

reaction by treatment with dialkylzincs or diphenylzinc in the presence 

of catalytic bis(acetylacetonato)nickel(II) (1). [107,108] With alkynes that possess one aromatic 

and one aliphatic substituent, the regioselectivity is very high, favoring the addition of 

the organozinc substituent to the carbon that bears the aliphatic alkyne substituent, 

whereas the regiochemical outcome reverses with aryl(silyl)alkynes (Scheme 53). The intermediate 

alkenylzinc reagents may be quenched with a proton, iodine, or a variety of 

other electrophiles in copper-catalyzed alkylations (Scheme 54). The combination of the 

above methods provides a very versatile entry to tetrasubstituted alkenes. 

Scheme 53 Nickel-Catalyzed Alkyne Carbozincation [107,108] 

Ar 1 R 1 + R 2 2Zn 

Ni(acac) 2 1 

Ar1 H 

R1 R2 Ar1 R2 R1 H 

R1 = aliphatic R1 or 

= TMS 

Scheme 54 Sequential Alkyne Carbozincation and Electrophilic Trapping [107,108] 

Ph Ph + R 1 2Zn 

R 1 

Ph 

Ni(acac) 2 1 

I 

Ph 

I 2 

R 1 

Ph 

ZnR 1 

Ph 

1. CuCN 2LiCl 

Br 

2. 

CO2Et 

1. CuCN 2LiCl 

2. R2COCl R 1 

Ph 

O 

Ph 

R 2 

R 1 

Ph 

CO2Et 

Ph 

68 71% 

Ethyl (Z)-2-Methylene-4,5-diphenylhept-4-enoate (68,R 1 = Et); Typical Procedure: [108] 

[Ni(acac) 2](1; 320 mg, 1.25 mmol, 25%) and PhC”CPh (0.89 g, 5 mmol, 1 equiv) were dissolved 

in THF (3.8mL) and NMP (1.3 mL) at –408C under argon. Et 2Zn (1.0 mL, 10 mmol, 

2 equiv) was carefully added via syringe at –78 8C. The mixture was allowed to warm to 

–35 8C and was stirred for 2.5 h. Meanwhile, a mixture of CuCN (1.79 g, 20 mmol, 4 equiv) 

and LiCl (1.69 g, 40 mmol, 8equiv) was dried in vacuo at 1308C for 2 h and then dissolved in 

THF (10 mL). The soln was cooled to –608C and added by syringe to the mixture at –788C. 

The resulting dark soln was warmed to 0 8C for a few min and then cooled again to –788C. 

Ethyl (2-bromomethyl)acrylate (4.82 g, 25 mmol, 5 equiv) was added and the mixture was 



allowed to warm to 258C and worked up. The crude product was purified by flash chromatography 

(silica gel, hexane/Et 2O 20:1), affording the ester 68 as a white powder; yield: 

1.13 g (71%); (Z/E) > 99:1. 


Nickel–Alkene Complexes 

Nickel complexes of alkenes are involved in many catalytic transformations. Many of the 

reaction classes of alkenes involve migratory insertion of an alkylnickel or a hydridonickel 

species. Alternatively, some transformations are initiated by the oxidative cyclization 

of nickel–alkene complexes with a second unsaturated component to produce five-membered 

metallacycles. Several examples of nickel–bis(alkene) complexes and nickel 

metallacyclopentanes are known, and the interconversion of these two structural classes 

has been studied (Scheme 55). [109,110] 

Scheme 55 Ligand Dependence of Nickel Metallacycle Decomposition [109,110] 

LNi L 2Ni L 3Ni 

L = trialkyl- or triarylphosphine 


1.1.4.1 Method 1: 

Ligand Exchange with Nickel(0) Complexes 

2 H 2C CH 2 

Many crystal structures of nickel–alkene complexes have been reported. As demonstrated 

in Scheme 55, bis(alkene) complexes may exist in equilibrium with the corresponding 

metallacyclopentane complex. However, several alkene complexes which have the potential 

to undergo oxidative cyclization to a metallacycle have been fully characterized. The 

substitution chemistry of bis(ç 4 -cycloocta-1,5-diene)nickel(0) (2) is representative of most 

nickel(0)–alkene complexes, which are readily substituted by a variety of ligands. 

Bis(ç 2 -ethene)(tricyclohexylphosphine)nickel(0) has been prepared and fully characterized, 

[111,189] and a variety of complexes of electron-deficient alkenes such as 69 have been 

prepared which tend to be more stable than the complexes of ethene (Scheme 56). [112–114] 

The alkene complexes may be prepared directly from bis(ç 4 -cycloocta-1,5-diene)nickel(0) 

(2) [113] or from nickel(II) chloride [112] that is reduced by zinc metal. 

Scheme 56 Preparation of Bis(methyl acrylate)(pyridine)nickel(0) [112] 

NiCl 2 6H 2O + Zn + 

N 

+ 

CO2Me THF, 60 oC 70% 

N Ni 

CO2Me 

CO2Me 69

1.1.4 Nickel–Alkene Complexes 63 

Bis(methyl acrylate)(pyridine)nickel(0) (69): [112] 

To NiCl 2 •6H 2O (4.7 g, 20 mmol), methyl acrylate (5.0 mL, 55 mmol), and pyridine (5.0 mL, 

61 mmol) in THF (50 mL) was added Zn powder (5.0 g, 76 mmol). The suspension was heated 

to 608C, and the oil bath was removed. After 2 h the mixture was filtered, and the solid 

residue was washed with THF (3 ” 15 mL). After removal of the solvent in vacuo, extraction 

with Et 2O (50 mL) left behind the insoluble zinc salts. Filtration and evaporation of 

the extract in vacuo gave a red oil which was treated with hexane to dissolve the excess 

pyridine and methyl acrylate. The hexane layer was discarded, and the residual oil was 

dissolved in Et 2O (50 mL). Cooling to –188C afforded 69 as a pale orange powder; yield: 

4.3 g (70%); mp 808C (dec). 


1.1.4.2 Method 2: 

Conjugate Addition to Electrophilic Double Bonds 

Nickel-catalyzed conjugate additions are among the most widely used synthetic applications 

of nickel chemistry. Conjugate additions of a broad range of main-group and transition-metal 

organometallics have been reported to be accelerated by nickel catalysis. 

Bis(acetylacetonato)nickel(II) (1) is the most widely used catalyst due to its low cost and 

air stability, although bis(ç 4 -cycloocta-1,5-diene)nickel(0) (2) is an excellent catalyst for 

most conjugate additions. Bis(acetylacetonato)nickel(II) (1) may be reduced by the nucleophilic 

organometallic reagent (organozinc, organoaluminum, etc.), or more typically it 

may be reduced with diisobutylaluminum hydride prior to treatment with the nucleophilic 

organometallic reagent. The primary advantages of nickel-catalyzed conjugate additions 

relative to organocuprates are increased thermal stability of the reagents and increased 

efficiency with sterically hindered substrates. Several asymmetric variants have 

been reported, but no general solution to the problem of asymmetric catalysis has been 

reported. The four variations listed below have received the most attention, although additions 

of triorganoindiums, [115] alkenylboranes, [116] and organotitaniums [117] have been reported. 

Mackenzie has reported a related procedure with organotins that likely bears 

mechanistic similarity to the procedures described here. [39] However, since this reaction 

class was demonstrated to involve nickel–ð-allyl complexes, its description is included 

in Section 1.1.2.7.2. It is worth noting that the variations described below may possibly 

involve ð-allyl complexes as reactive intermediates in direct analogy to the model proposed 

by Mackenzie. A comprehensive review of nickel-catalyzed nucleophilic additions 

to activated alkenes has appeared. [186] 


Organoaluminums 

The bis(acetylacetonato)nickel(II)-catalyzed addition of trimethylaluminum was the firstreported 

variant of nickel-catalyzed conjugate additions, [118,119] and a later report demonstrated 

that the process is efficient with sterically demanding substrates such as 70 that 

possess â,â-disubstituted enones (Scheme 57). [120] Significantly, alkynylaluminum reagents 

efficiently transfer the alkynyl unit in a conjugate fashion to enones such as 71 

(Scheme 57). [121,122] This transformation is notoriously difficult with organocopper chemistry. 

Therefore, the nickel-catalyzed procedure is exceptionally useful. 



Scheme 57 Nickel-Catalyzed Conjugate Addition of Organoaluminums [120–122] 

O 

O 

70 

71 

O 

O 

+ 

+ 

Me 3Al 

Ni(acac)2 1 

87% 

Me2Al Bu t 

O 

O 

dr 1.5:1 

Ni(acac) 2 1, DIBAL-H 

Trimethylaluminum Conjugate Addition; General Procedure: [120] 

CAUTION: Neat Me 3Al is highly pyrophoric! Appropriate safety precautions and procedures 


To a stirred soln of [Ni(acac) 2](1; 128mg, 0.5 mmol), dry THF (15 mL) or EtOAc (15 mL), and 

the enone (10 mmol) was added Me 3Al (1 mL, 10.5 mmol) dropwise at 0 8C. After an appropriate 

time, the reaction was diluted with hexane (15 mL) and quenched by careful addition 

of sat. aq NH 4Cl (1.5 mL) and worked up. 


Organozincs 

The conjugate addition of organozinc reagents under the influence of nickel catalysis is 

by far the most widely used and most studied of the different variations. The original report 

from Luche describes the conjugate addition of organozincs generated from a broad 

range of alkyl, alkenyl, and aryl iodides, lithium metal, and anhydrous zinc(II) bromide to 

give species such as 72 (Scheme 58). [123–125] Alternatively, the organozinc may be used as 

the commercially available, salt-free organozinc, or as the in situ-generated diorganozinc 

from transmetalation of zinc(II) chloride with an organolithium or organomagnesium reagent. 

An interesting report from Houpis demonstrates that triorganozincates are more 

effective than diorganozincs with less electrophilic substrates such as vinyl sulfoxides 

and vinylpyridines (Scheme 58). [126,127] Organozinc conjugate additions have been widely 

used in a variety of complex synthetic applications (Scheme 59). [128–130] 

Scheme 58 Nickel-Catalyzed Conjugate Additions of Organozincs [123–127] 

R 1 

O 

R 2 

R 3 R 4 

MeO 

O 

+ 

R 5 I 

Li, ZnBr 2 

Ni(acac) 2 1, ))) 

N 

50−90% 

R 1 

67% 

O 

R 3 

PhMgCl/ZnCl2 (3:1) 

Ni(acac) 2 1 

93% 

72 

R 4 

R 2 

R 5 

MeO 

O 

O 

73 

Bu t 

Ph 

O 

N


Scheme 59 Applications of Nickel-Catalyzed Conjugate Additions in Total Synthesis [128–130] 

O 

O 

O 

O 

O 

O 

Me 2Zn, LiBr 

Ni(acac) 2 1, Et2O 

78% 

1. Me2Zn, Ni(acac)2 1 

2. TMSCl, Et 3N 

O 

O 

TMSO 

Advantages of organozinc conjugate additions compared with cuprate additions are the 

thermal stability of the organozincs and increased reactivity of the kinetic zinc enolate 

formed during the addition. The high reactivity of the kinetic zinc enolates allows conjugate 

addition–enolate alkylation sequences to be quite effective, although some applications 

require the use of sp 2 -hybridized organozincs, e.g. in the synthesis of (1R*,2R*,3R*)and 

(1S*,2R*,3R*)-75 from bis(enone) 74 (Scheme 60). [91,131] Many asymmetric variants 

have been reported with varying degrees of success. [132–138] 

Scheme 60 Tandem Conjugate Additions of Bis(enones) with Organozincs [91,131] 

O O 

74 

PhLi, ZnCl2 

Ni(cod)2 2 

Ph 

Ac 

Ac 

(1R ∗ ,2R ∗ ,3R ∗ )-75 58% 

+ 

Ph 

O 

O 

O 

Ac 

Ac 

(1S ∗ ,2R ∗ ,3R ∗ )-75 12% 

Nickel-Catalyzed Conjugate Addition of Organozincs by Ultrasonication; 

General Procedure: [125] 

Solvents used were pure Et 2O, pure THF, or a mixture of toluene/THF (5:1 or 10:1). The organic 

halide (10 mmol) and ZnBr 2 (1.13 g, 5.0 mmol) in the required solvent (23 mL) were 

placed in the reaction flask under argon. The Li wire (150 mg, 21 mmol) was placed in the 

holder under the ultrasonic probe. The flask was cooled in an ice bath, and stirring with a 

magnetic bar ensured a homogeneous temperature. The energy level of the sonication 

was adjusted to the minimum giving the cavitation noise, and a black color immediately 

developed. After 30 min, irradiation was discontinued, and the resulting black soln (colorless 

in reactions of MeI or MeBr) was transferred via a syringe into a round-bottomed flask 

with a magnetic bar, under argon. When necessary, the flask was cooled in an ice or dry 

ice/acetone bath. A soln of the substrate (2.5–4.8mmol) and [Ni(acac) 2](1; 20 mg) in the 

required solvent (2 mL) was then added dropwise over a few min. When necessary, this 

addition was made at a lower temperature and then allowed to warm slowly. After disappearance 

of the starting material (TLC), the mixture was poured into sat. aq NH 4Cl, and 

the product was worked up and isolated in the usual manner. Purification was effected 

by column chromatography (silica gel) and the material was identified by the usual physical 

methods. 

4-{2-[3-(Cyclopentyloxy)-4-methoxyphenyl]-2-phenylethyl}pyridine (73): [127] 

A soln of 0.5 M ZnCl 2 in THF (4 mL, 2 mmol) was cooled to 08C and treated with 2 M 

PhMgCl in THF (3 mL, 6 mmol) so that the internal temperature did not exceed 108C. 



The slurry was then warmed to rt and stirred for 30 min. Additional THF (1 mL) was added 

to facilitate stirring. The alkene (288 mg, 0.98 mmol) and [Ni(acac) 2](1; 18mg, 0.07 mmol) 

were added sequentially as solids, and the resulting dark soln was heated immediately to 

49–50 8C for 2–3 h. The reaction was monitored by HPLC and upon completion was 

quenched with aq 1 M NH 4Cl. The resulting mixture was partitioned with EtOAc and the 

organic layer was dried (Na 2SO 4) and concentrated under reduced pressure. The residue 

was chromatographed to afford 73; yield: 348mg (93%). 

1-[(1R*,2R*,3R*)-2-Acetyl-3-phenylcyclohexyl]acetone [(1R*,2R*,3R*)-75]: [131] 

A1.59Mt-BuLi soln in pentane (1.7 mL, 2.7 mmol) was added dropwise to a soln of PhI 

(0.273 g, 0.150 mL, 1.34 mmol) in THF (6 mL) at –788C. After stirring for 30 min at –788C 

the yellow mixture was allowed to warm to 08C, and 1.0 M ZnCl 2 in Et 2O (0.90 mL, 

0.90 mmol) was added dropwise by syringe. After 1 h, the resulting mixture and a soln of 

[Ni(cod) 2](2; 5 mg, 0.018mmol) in THF (2 mL) were simultaneously transferred by cannula 

to a soln of 74 (72 mg, 0.40 mmol) in THF (1 mL) at 08C. After stirring at 0 8C for 2 h the 

brown mixture was quenched with sat. NaHCO 3 (25 mL), extracted with EtOAc 

(3 ” 25 mL), dried (Na 2SO 4), filtered, and concentrated. Flash chromatography (silica gel, 

hexanes/EtOAc 5:1) afforded, in order of elution, (1S*,2R*,3R*)-75 as a pale yellow oil and 

(1R*,2R*,3R*)-75 as a white solid; both were homogeneous as judged by TLC analysis; 

yields: (1S*,2R*,3R*)-75, 12 mg (12%); (1R*,2R*,3R*)-75, 60 mg (58%). 


Organozirconiums 

The conjugate addition of organozirconium reagents in the presence of catalytic amounts 

of bis(acetylacetonato)nickel(II) (1) has received a modest level of attention (Scheme 

61). [139–142] The alkenylzirconium 76 may be generated in situ by treatment of alkynes 

with chloro(hydrido)zirconocene. It has perhaps received less attention than might be expected 

owing to the popularity of the copper-catalyzed conjugate addition of organozirconiums. 

[143] 

Scheme 61 Conjugate Addition of Alkenylzirconiums [140–143] 

ZrCp2Cl(H) 

H Cp2ClZr H 

H 

76 

O 

Ni(acac)2 1 

3-[(E)-3,3-Dimethylbut-1-enyl]cyclohexanone (77): [139] 

Complex 76 (1.924 g, 5.67 mmol) and cyclohex-2-enone (0.623 g, 6.48mmol) were dissolved 

in THF (30 mL) and cooled to 08C. [Ni(acac) 2](1; 0.151 g, 0.59 mmol) was added and 

the mixture was stirred at 0 8C for 6.5 h. The mixture was quenched with NH 4Cl and extracted 

with Et 2O. Compound 77 was isolated by distillation of the Et 2O solvent, followed 

by preparative liquid chromatography of the resulting oil. Distillation of solvent from the 

fraction containing the product gave 77; yield: 0.744 g (73%). 

73% 

O 

77



Direct Conjugate Addition of Alkyl Halides 

In contrast to each of the above variations, alkyl iodides may also be utilized directly in 

nickel-catalyzed conjugate additions. The mechanism of this class of reactions is not well 

defined; however, the related stoichiometric coupling of enals (e.g., 79) with alkyl halides 

(e.g., 78) has been demonstrated to proceed through nickel–ð-allyl intermediates. [38] The 

most widely used variant employs nickel(II) chloride hexahydrate in either catalytic or 

stoichiometric quantities with activated zinc as a stoichiometric reductant (Scheme 

62). [144–148] The organic halide may be either sp 2 or sp 3 hybridized, and alkene geometry 

in the final product (e.g., 80) is maintained with alkenyl iodides. 

Scheme 62 Conjugate Addition of Alkyl Iodides [145] 

TBDMSO 

O O 

S 

H 

H 

OTBDMS 

78 

H 

I 

+ 

NiCl2 6H2O 

Zn, py 

73% 

CO2Et 

79 

TBDMSO 

O O 

S 

H 

H 

OTBDMS 

80 

H 

CO 2Et 

The intramolecular conjugate addition of alkenyl iodides (e.g., 81) in the presence of a sixto 

sevenfold excess of bis(ç 4 -cycloocta-1,5-diene)nickel(0) (2) has been reported (Scheme 

63). [149,150] A large excess of nickel is required owing to its dual role of conjugate-addition 

catalyst and nitroaromatic reducing agent. This provides an effective route to (€)-19,20-didehydrotubifoline 

(80). Alkenyl iodides also add to nonactivated double bonds. [151,152] 

Scheme 63 Conjugate Addition of Alkenyl Iodides [149,150] 

O 

O2N N 

81 

I 

Ni(cod) 2 2 

Et3N, LiCN 

40% 

N 

N 

82 

H 



Ethyl (5R)-5-[(1R,3aS,4E,7aR)-4-{[(4S,6R)-4,6-Bis(tert-butyldimethylsiloxy)-2,2-dioxo- 

1,3,4,5,6,7-hexahydrobenzo[c]thiophen-1-yl]methylene}-7a-methyloctahydro-1Hinden-1-yl]hexanoate 

(80): [145] 

A mixture of pulverized NiCl 2 •6H 2O (2.38g, 10 mmol), Zn powder (3.27 g, 50 mmol), and 

ethyl acrylate (79; 4.88 mL, 45 mmol) in pyridine (20 mL) was stirred at 608C under argon 

for 30 min. The resulting dark red, heterogeneous mixture was cooled to 23 8C and treated 

with a soln of 78 (7.49 g, 10 mmol) in pyridine (20 mL), producing a slight exotherm (23– 

288C). After being stirred at rt for 2.5 h the mixture was worked up to give a pale yellow 

foam (7.22 g), which was purified by flash chromatography (silica gel, 95 g, EtOAc/hexane 

3:97; then EtOAc/hexane 5:95) to give, after evaporation of the solvents, 80; yield: 5.28g 

(73%). 

(€)-19,20-Didehydrotubifoline (82): [150] 

A soln of the vinyl iodide 81 (47 mg, 0.11 mmol), 0.5 M LiCN in DMF (2.15 mL, 1.1 mmol), 

and Et 3N (45 ìL, 0.32 mmol) in MeCN (5 mL) was added at rt to [Ni(cod) 2](2; 195 mg, 

0.71 mmol). The resulting mixture was stirred at rt for 2.5 h and filtered through Celite, 

washing carefully with Et 2O. The filtrate was sequentially washed with sat. aq Na 2CO 3 

and brine. The dried organic phase was concentrated and chromatographed (Florisil, 

CH 2Cl 2/MeOH 95:5) to give 82; yield: 11 mg (40%). 

1.1.4.3 Method 3: 

Coupling of Two Alkenes 

The oxidative coupling of two unsaturated components coordinated to nickel(0) is a common 

mechanistic theme throughout nickel chemistry (see also Houben–Weyl, Vol. E 18, 

p 865). In the case of nickel–bis(alkene) complexes, a saturated nickel metallacyclopentane 

is produced from such an oxidative cyclization. The interconversion of nickel(0)– 

bis(alkene) complexes and nickel(II) metallacycles has been documented and carefully 

studied (Scheme 55). However, most catalytic applications of this process have not been 

rigorously defined from a mechanistic perspective. One case, however, that has been rigorously 

studied is the formal [2+2+1] cycloaddition of an oxygen atom with two alkenes 

to produce tetrahydrofurans. [153] The reaction proceeds by oxidative cyclization of a nickel(0)–bis(alkene) 

complex to give a metallacycle 83, insertion of an oxygen atom from dinitrogen 

monoxide into a C-Ni bond of metallacycle 83 to produce 84, and then oxidatively 

induced reductive elimination with diiodine to produce the substituted tetrahydrofuran 

85 (Scheme 64). Each of the intermediates shown was isolated and characterized. 

Only strained alkenes were shown to participate in the process. 

Scheme 64 [2+2+1] Cycloaddition of an Oxygen Atom and Two Alkenes [153] 

Ni(cod)(bipy) 

(bipy)Ni 

83 

N2O 

44% 

O 

(bipy)Ni 

The involvement of metallacycles has been proposed for the [3+2] cycloaddition of methylenecyclopropanes 

with alkenes to produce methylenecyclopentanes. [154–156] Oxidative 

cyclization of a methylenecyclopropane and an electron-deficient alkene produces a spirocyclic 

metallacyclopentane 86. Cyclopropane ring opening followed by reductive elimination 

affords the observed methylenecyclopentane products 87 and 88 (Scheme 65). Another 

report describes the novel use of nanostructured nickel clusters as catalysts. [157] 

84 

I2 

47% 

O 

85


Scheme 65 [3+2] Cycloadditions Involving Methylenecyclopropanes [154–156] 

L nNi 

E 

R 1 

+ 

R 2 

R 2 

R 1 

E 

E = electron-withdrawing group 

Ni(cod)2 2 

L nNi 

E 

86 

R 1 

R 2 

R 1 

E R 2 

87 

+ 

R 1 

LnNi 

E R 2 

88 

R 1 

E R 2 

+ L nNi 

R 1 

E R 2 

The reductive coupling of bis(enones) is another reaction class that may involve alkenederived 

metallacyclopentanes. Treatment of a symmetrical bis(enone) 89 with bis(ç 4 -cycloocta-1,5-diene)nickel(0) 

(2) and butyllithium/zinc(II) chloride leads to coupling of the 

two enone â-carbons followed by an intramolecular aldol addition to afford bicyclo[3.3.0]octanols 

90 (Scheme 66). [91,131] Sterically hindered enones have also been shown to participate 

in this reaction class, as evidenced by the spirocyclization of a substituted cyclopentenone 

to produce an angular triquinane (Scheme 66). [158] 

Scheme 66 Reductive Cyclization–Aldol Addition of Bis(enones) [91,131,158] 

R 1 

O 

O 

89 

O 

O 

R 1 

N 

O 

O 

Ni(cod) 2 2 

BuLi, ZnCl2 BuZnO O 

R 1 

R 1 = Ph 60% 

O 

Ni(cod)2 2 

Et2Zn, ZnCl2 

O H 

58% H 

R 1 

R 1 

O 

HO 

R 1 

H H 

The dimerization of alkenes has been extensively studied by Wilke (Scheme 67). [5] In the 

tail-to-tail dimerization of methyl acrylate, cationic nickel hydride species have been proposed 

as the active catalysts. The mechanism of this process proceeds by alkene hydrometalation, 

insertion of a second equivalent of methyl acrylate, and then â-hydride elimination 

to release the product and generate the nickel hydride catalyst. 

90 



Scheme 67 Tail-to-Tail Dimerization of Methyl Acrylate [5] 

MeO2C 

MeO 2C 

MeO 2C 

Ni PMe + 3 

CO 2Me 

MeO2C 

MeO 2C 

MeO 2C 

MeO 2C 

Ni PMe + 3 

CO 2Me 

MeO 2C 

MeO2C 

H + PMe3 

Ni 

CO 2Me 

CO2Me 

RajanBabu has developed an asymmetric protocol for the heterodimerization of vinylarenes 

and ethene. [159] The use of Hayashi s novel, weakly chelating phosphine 91 is critical 

to the success of this asymmetric reaction (Scheme 68). 1,6-Dienes (e.g., 92) also undergo 

direct cycloisomerization in the presence of bis[allyl(bromo)nickel] to afford methylenecyclopentane 

products (e.g., 93; Scheme 69). The scope of the intramolecular process 

allows preparation of a variety of carbocyclic and heterocyclic ring systems. A reaction 

mechanism involving in situ generation of a nickel hydride catalyst, alkene hydrometalation, 

cyclization, and â-hydride elimination has been proposed. [160] 

Scheme 68 Asymmetric Hydrovinylation of Alkenes [159] 

H 

Ar 1 

L ∗ = 

R 1 = Me, Bn 

+ 

91 

OR 1 

PPh2 

[NiBr(H2C CHCH 2)] 2, NaBAr 4, L ∗ 

Scheme 69 Cycloisomerization of Dienes [160] 

R 1 

R 1 

92 

Ar 1 

O O 

[NiBr(H 2C CHCH 2)] 2, R 1 3P 

[NiHL n] + 

R 1 

R 1 

81% 

NiL n + 

R 1 

R 1 NiL n + 

− [NiHLn] + 

92% 

R 1 

R 1 

93


[5,5¢-Bi(bicyclo[2.2.1]hept-2-en)-6-yl-kC 6 -6¢-olato-kO](2,2¢-bipyridyl-k 2 N 1 ,N 1 ¢)nickel (84): [153] 

A sample of 83 (0.35 g, 0.94 mmol) and benzene (10 mL) were placed in a round-bottomed 

flask attached to a swivel-frit assembly. The soln was stirred under N 2O (1 atm) at 55 8C for 

3 d, after which the soln was filtered and the filtrate was taken to dryness under vacuum. 

The resulting solid was washed with petroleum ether (3 ” 5 mL), and the blue product was 

collected on a filter frit to give microcrystalline 84; yield: 0.16 g (44%). 

exo-trans-endo-3-Oxapentacyclo[9.2.1.1 5,8 .0 2,10 .0 4,9 ]pentadeca-6,12-diene (85): [153] 

A sample of 84 (0.12 g, 0.31 mmol) and benzene (10 mL) were placed in a round-bottomed 

flask, to which I 2 (0.08g, 0.31 mmol) was added under an argon counterflow. There was an 

immediate color change from blue to brown. The soln was stirred for 30 min at rt and filtered, 

and the filtrate was evaporated using a rotary evaporator. The residue was chromatographed 

(silica gel, hexane/EtOAc 100:3) to give 85 as a colorless oil; yield: 0.03 g 

(47%). 

(1R*,2S*,3R*,5R*)-2-Benzoyl-3-phenylbicyclo[3.3.0]octane-3-ol (90, R 1 = Ph); 

Typical Procedure: [131] 

A mixture of 2.44 M BuLi in hexane (0.43 mL, 1.05 mmol) and 1.0 M ZnCl 2 in Et 2O (0.70 mL, 

0.70 mmol) in THF (5 mL) was stirred for 1 h at 08C. A soln of [Ni(cod) 2] (2; 3mg, 

0.01 mmol) in THF (2 mL) was added by syringe, and the resulting soln was immediately 

transferred by cannula to a soln of 89 (91 mg, 0.30 mmol) in THF (3 mL) at 08C. After stirring 

for 1.5 h at 0 8C the deep red mixture was quenched with sat. NaHCO 3 (20 mL), extracted 

with EtOAc (3 ” 25 mL), dried (Na 2SO 4), filtered, and concentrated. The residue 

was chromatographed (silica gel, Et 2O/pentane 1:15) to afford 90 (R 1 = Ph) as a white crystalline 

solid; yield: 56 mg (60%). 

Dimethyl 3-Methyl-4-methylenecyclopentane-1,1-dicarboxylate (93,R 1 =CO 2Me); 


The catalyst precursor was prepared as follows. To a soln of [{Ni(allyl)Br} 2] (4.2 mg, 

0.012 mmol, 2.5 mol%, 0.05 equiv in Ni) in CH 2Cl 2 (1 mL) was added tris(4-methoxyphenyl)phosphine 

(8.5 mg, 0.024 mmol) in CH 2Cl 2 (1 mL). The mixture was stirred for 30 min, after 

which AgOTf (6 mg, 0.024 mmol) was added in one lot. After 30 min of stirring, a precipitate 

was formed (AgBr), which was subsequently removed by filtration through a pipet 

containing a plug of Celite. The catalyst was cooled to –348C and introduced into a 

soln of 92 (100 mg, 0.47 mmol) in CH 2Cl 2 (2 mL) at rt. The soln was stirred at rt for 2 h, after 

which the reaction was stopped and the mixture was concentrated. Analysis of the crude 

product showed it to be 92% of the expected product 93 and 8% starting material. The 

crude product was chromatographed on a column (silica gel, hexane/Et 2O 9:1) to afford 

pure 93 (R 1 =CO 2Me); yield: 92 mg (92%). 

1.1.4.4 Method 4: 

Alkene Carbonylation 

The carbonylation of alkenes proceeds readily upon treatment of an alkene with a nickel 

catalyst in the presence of carbon monoxide and an alcohol or water (Scheme 70). [7,11,104] 

Tetracarbonylnickel(0) is the most commonly used nickel catalyst, although it is highly 

toxic. [188] This process is very useful for the carbonylation of simple alkenes such as 

ethene, but it has seen little use with complex organic molecules. 

Scheme 70 Carbonylation of Alkenes [104] 

H 2C CH 2 + CO + H 2O 

Ni 

CO 2H 



1.1.4.5 Method 5: 

Alkene Hydrocyanation 

The hydrocyanation of alkenes is a well-studied and synthetically useful process. [33,161,162] 

A significant amount of the attention that this reaction has received is derived from its 

utility in the preparation of adiponitrile from butadiene (Section 1.1.1.6). A complete catalytic 

cycle for the hydrocyanation of alkenes is shown in Scheme 71. Steric effects in the 

Lewis acid promoter have been shown to affect critically the reaction selectivities. [163] 

Scheme 71 Mechanism of Alkene Hydrocyanation [33] 

EtCN 

L C2H4 L 

NC 

Ni Et 

L 

L 

Ni 

L 

L Ni Et L Ni H 

CN 

CN 

H2C CH2 HCN 

L2 Ni 

CN 

H 

The asymmetric hydrocyanation of alkenes has also received considerable attention. 

[164,165] In a representative example by RajanBabu, the glucose-derived phosphine ligand 

94 allows useful enantioselectivities to be obtained in the hydrocyanation of arylsubstituted 

alkenes (Scheme 72). 

Scheme 72 Asymmetric Hydrocyanation of Alkenes [164,165] 

1 Ar + HCN 

L = Ph O 

O 

O 

O 

O 

Ar2 Ar 

2P 

2 2P 

94 

OPh 

NiL 

Ar 1 

CN 

up to 90% ee 

Asymmetric Hydrocyanation; General Procedure: [164] 

CAUTION: Hydrogen cyanide is highly toxic! Appropriate safety precautions and procedures 


Catalyst scouting reactions were carried out by the dropwise addition of a toluene soln of 

HCN (typically 0.05–1.0 equiv of HCN per equiv of alkene) to a hexane soln of the alkene 

(0.1–0.2 M), [Ni(cod) 2](2; 0.01–0.5 equiv), and the chiral ligand (0.01–0.05 equiv). Ligands 

that were insoluble in hexane were stirred separately with [Ni(cod) 2] in benzene. The resulting 

catalyst solns were evaporated to dryness and then the residue dissolved or slurried 

with hexane and the substrate. Hydrocyanation reactions were usually stirred at rt 

(~ 258C) overnight. The product nitriles were isolated by flash chromatography (typically 

silica gel, hexane/Et 2O 90:10). 

L


1.1.4.6 Method 6: 

Alkene Hydrosilylation 

The hydrosilylation of alkenes is an effective method for converting terminal or cyclic alkenes 

into functionalized silanes (Scheme 73). [12,166] Silicon is directed to the more electron-rich 

alkene terminus. Trichlorosilane is generally the most effective silane, and a variety 

of nickel catalysts may be employed. Relatively high temperatures are required 

(1208C), and nickel catalysts substituted with electron-rich phosphines generally are the 

most efficient. 

Scheme 73 Hydrosilylation of Alkenes [166] 

R 1 

R 2 

+ 

HSiCl 3 

NiCl2(PR 3 3)2 

Alkene Hydrosilylation; General Procedure: [166] 

Alkene (1 equiv), hydrosilane (2 equiv), and nickel catalyst (10 –3 equiv) were placed in a 

glass ampule and degassed at –1968C, and the ampule was then sealed. After heating for 

a given period of time, the ampule was cooled to –788C before opening. Products were 

isolated by fractional distillation where possible, or by preparative GC after flash distillation. 

1.1.4.7 Method 7: 

Alkene Hydroalumination 

The nickel-catalyzed hydroalumination of alkenes has been extensively investigated in a 

variety of contexts. The interaction of aluminum hydrides with nickel(0) and the mechanism 

of alkene hydroalumination has been studied in detail by Wilke, [5] Eisch, [167] and 

Zweifel. [168] The most extensive synthetic applications from Lautens involve the hydroalumination 

of oxabicyclic alkenes followed by ring opening to produce substituted cyclohexenes 

and cycloheptenes (Scheme 74). [169–171] An asymmetric variant employing 

2,2¢-bis(diphenylphosphino)-1,1¢-binaphthyl (BINAP) is also quite general for various oxabicyclic 

starting materials. 

Cl 3Si 

Scheme 74 Nickel-Catalyzed Hydroalumination–Ring-Opening Sequence [169–171] 

O 

O 

O 

OMe 

OMe 

OBn 

OMe 

OMe 

DIBAL-H 

10 mol% Ni(cod) 2 2 

DIBAL-H 


DIBAL-H 


5 mol% (R)-BINAP 

95% 

O 

Bu 

H 

i 2Al 

O 

Bui H 

2Al 

R 1 

H 

R 2 

OMe 

OMe 

OMe 

OBn 

OH 

97% ee 

OMe 

iBu2AlCl 

HO 

OMe 

OH 

OBn 

OMe 



It is unclear whether the hydroalumination proceeds by hydronickelation or aluminonickelation, 

and the mechanistic details may vary according to substrate and catalyst 

structure. However, the pathways shown in Scheme 75 are likely mechanistic pathways 

based on the data obtained. 

Scheme 75 Mechanism of the Hydroalumination–Ring-Opening Sequence [169–171] 

O 

H Ni AlR2 2 

O 

H Ni AlR 2 2 

O 

R 2 2Al Ni H 

O 

H AlR 2 2 

O 

product 

A related procedure for the cleavage of allyl ethers has been developed by Ogasawara. 

Treatment of an allyl ether with diisobutylaluminum hydride and catalytic [1,3-bis(diphenylphosphino)propane]dichloronickel 

leads to facile cleavage of the allylic C-O 

bond (Scheme 76). [172,173] A mechanism similar to that proposed for the hydroalumination–ring 

opening of oxabicyclic alkenes is suggested. 

Scheme 76 Nickel-Catalyzed Allyl Ether Cleavage [172,173] 

R 1 O 

95 

DIBAL-H (1.5 equiv) 

1 mol% NiCl2(dppp) R 1 O 

AlBui 2 

H 

R 1 = 4-MeOC6H4 90% 

R 1 OH + 

Reductive Ring Opening; General Procedure: [171] 

The reaction scale was typically 0.3–0.5 mmol. [Ni(cod) 2](2; 0.1 equiv) in toluene (1.0 mL) 

was added to dppb (0.2 equiv), and the resulting light brown soln was stirred at rt for 1 h. 

Substrates bearing a free hydroxy moiety were premixed with 1.0 M DIBAL-H in hexanes 

(1.1 equiv) in toluene (1.0 mL) to form the aluminum alkoxide. Protected alcohols were 

dissolved in toluene (1.0 mL) and added directly to the flask containing [Ni(cod) 2] and 

dppb. DIBAL-H (1.1–1.9 equiv) was added via a syringe pump over the indicated time. The 

reaction was quenched by the addition of sat. aq NH 4Cl, and sufficient 10% HCl was added 

to make the aqueous layer transparent. The organic layer was separated, and the aqueous 

layer was extracted with Et 2O (3 ”). The combined organics were dried (MgSO 4). Removal 

of the solvent in vacuo yielded a product mixture that was purified by chromatography. If 

the reaction product was a diol, the reaction was quenched by 1.1 M potassium sodium 

tartrate soln (1.0 mL). The resulting suspension was stirred at rt for 4 h and filtered, and 

the white gel was washed with hot EtOAc several times. The combined filtrate was dried 

(Na 2SO 4) and removal of the solvent in vacuo yielded a product mixture that was purified 

by chromatography. 

96


4-Methoxyphenol (96,R 1 = 4-MeOC 6H 4); Typical Procedure: [172] 

A 1.5 M soln of DIBAL-H in toluene (600 ìL, 0.9 mmol) was added dropwise to a stirred soln 

of 95 (R 1 = 4-MeOC 6H 4; 100 mg, 0.6 mmol) and NiCl 2(dppp) (3 mg, 6 ìmol) in Et 2O(2mL) 

under argon at 0 8C. The mixture was stirred for 5 min at the same temperature and then 

for 2 h at rt. The mixture was diluted with Et 2O (3 mL), quenched by addition of H 2O 

(600 ìL) and, after stirring for 1 h, dried (MgSO 4), filtered through a Celite pad, and concentrated 

under reduced pressure to leave the crude product which was chromatographed 

(silica gel, 3 g, Et 2O/hexane 1:4) to give pure 96 (R 1 = 4-MeOC 6H 4); yield: 68mg 

(90%). 

1.1.4.8 Method 8: 

Alkene Hydrozincation 

The nickel-catalyzed hydrozincation of alkenes provides a novel method for the preparation 

of functionalized organozincs such as (97) (Scheme 77). [174,175] The resulting functionalized 

organozincs may be transformed into cuprate reagents and then alkylated with a 

variety of electrophiles. A hydronickelation step is likely involved in the reaction pathway. 

Scheme 77 Nickel-Catalyzed Hydrozincation of Alkenes [174,175] 

2 

R 1 

ZnEt 2 

+ ZnEt 2 

Ni(acac) 2 1 

R 1 

Dioctylzinc [97,R 1 =(CH 2) 5Me]: [175] 

2 

1−2 mol% Ni(acac)2 1 

1−4 mol% cod 

acac 

LnNi Et 

Zn 

R 1 = (CH 2) 5Me 38% 

ZnEt 2 

acac 

LnNi 

H 

acac 

LnNi Zn 

1 R + 

2 

97 

R 1 

R 1 

acac 

LnNi H 

2 H 2C CH 2 

H2C CH2 

CAUTION: Large quantities of gaseous ethene are produced in the reaction, especially for largescale 

reactions! 

A 50-mL two-necked flask equipped with an argon inlet, a magnetic stirring bar, and a septum 

cap was charged with [Ni(acac) 2](1; 26 mg, 0.10 mmol, 1 mol%) and cycloocta-1,5-diene 

(22 mg, 0.20 mmol, 2 mol%), followed by oct-1-ene (1.12 g, 10.0 mmol). The mixture 

was cooled to 0 8C, and ZnEt 2 (0.61 mL, 6.0 mmol, 0.6 equiv) was added dropwise. The cooling 

bath was removed, and the mixture was stirred in a preheated oil bath at 50–60 8C for 

3 h. The conversion was checked by iodolysis of an aliquot of the mixture (40–45%). The 

excess ZnEt 2 and unreacted alkene was distilled off in vacuo, yielding 97 [R 1 =(CH 2) 5Me]; 

yield: 0.65 g (38%). 

R 1 



1.1.4.9 Method 9: 

Alkene Carbozincation 

The nickel-catalyzed carbozincation has been developed into a broadly useful method for 

the cyclization of alkenes tethered to alkyl iodides (Scheme 78). [176–178] The functionalized 

organozincs (e.g., 99) prepared by the nickel-catalyzed cyclizations may be further utilized 

in a wide variety of copper-mediated alkylations of reactive electrophiles. The reaction 

mechanism may not involve the formation of nickel–alkene complexes; however, 

this reaction class is included owing to its synthetic relationship to many processes that 

do include nickel–alkene complexes. A free-radical cyclization appears to be most consistent 

with the data provided. 

Scheme 78 Nickel-Catalyzed Carbozincation [176–178] 

I 

O 

OR 1 R 2 

98 

+ ZnEt2 

Ni(acac)2 1 

R 1 O 

O 

99 

CH2ZnI 

A nickel-catalyzed carbozincation in which an allylzinc adds across the double bond of an 

unsaturated acetal has also been reported (Scheme 79). [179] This procedure effectively provides 

a reverse-polarity approach to the functionalization of unsaturated carbonyl derivatives. 

Non-allylic Grignard reagents, however, add to cyclic unsaturated acetals with the 

opposite regiochemistry. This latter procedure provides the basis for an enantioselective 

conjugate addition to cyclic enones (in 53% ee for the cyclopentenyl substrate and 85% ee 

for the cyclohexenyl homologue). [180] 

Scheme 79 Addition of Organozincs to Unsaturated Acetals [179,180] 

O 

O 

R 1 O OR 1 

R 2 = alkyl or aryl 

+ 

+ 

R 2 MgBr 

ZnBr 

Ph2 

P 

NiCl2 

P 

Ph2 

NiBr2(PBu3)2 

[(5-Butoxytetrahydrofuran-3-yl)methyl](iodo)zinc(II) (99, R 1 = Bu; R 2 =H); 


A 50-mL three-necked flask equipped with an argon inlet, a magnetic stirring bar, an internal 

thermometer, and a septum cap was charged with [Ni(acac) 2](1; 15 mg, 0.06 mmol, 

2 mol%), and a soln of the iodoalkane 98 (R 1 = Bu, R 2 = H; 0.85 g, 3.0 mmol, 1 equiv) in THF 

(5 mL) was added. The resulting green suspension was cooled to –788C, and ZnEt 2 (0.6 mL, 

6.0 mmol, 2 equiv) was added dropwise. The mixture was allowed to warm to 0 8C and 

stirred at this temperature for 2 h. The excess of Et 2Zn and the solvent were removed in 

vacuo (rt, 2 h) to leave the crude product; no yield was reported. 

OR 1 

R 2 

R 2 

ZnBr 

O 

O


1.1.4.10 Method 10: 

Homo-Diels–Alder Cycloadditions 

The nickel-catalyzed homo-Diels–Alder cycloaddition with norbornadienes and electrondeficient 

alkenes is an effective method for generating strained polycyclic compounds. [181] 

At the time of writing, this method is the only strategy for carrying out a nickel-catalyzed 

[2+2+2] cycloaddition with three alkene ð-systems such that six contiguous stereocenters 

may be generated. Both acyclic and cyclic enones participate in the process (Scheme 

80). 

Scheme 80 Nickel-Catalyzed Homo-Diels–Alder Reactions [181] 

+ 

O 

5−10 mol% Ni(cod) 2 2 

10−20 mol% Ph3P 56% H H 

Nickel-Catalyzed Diels–Alder Cycloaddition; General Procedure: [181] 

[Ni(cod) 2](2; 10–25 mol%) was added to a flame-dried flask equipped with a magnetic stirring 

bar and a rubber septum in the glovebox. Ph 3P (2 equiv, with respect to Ni) was introduced 

against a positive flow of N 2, and the diene (1 mmol) was added in 1,2-dichloroethane 

or toluene followed by the dienophile (2 mmol) as a neat liquid. The mixture was 

stirred at the desired temperature under N 2 for 16–48h. The workup was as follows: The 

catalyst was oxidized by stirring with the flask open to the air for 1–2 h. The reaction mixture 

was filtered through a plug of silica gel using CH 2Cl 2 (100 mL) as the eluant. Evaporation 

of the solvent gave a crude product, which was purified by Kugelrohr (bulb-to-bulb) 

distillation or flash chromatography on silica gel. 

1.1.4.11 Method 11: 

Alkene Polymerization 

While not emphasized in this review, the oligomerization and polymerization of ethene 

forms the basis of some of the most significant industrial processes involving nickel catalysis 

(see also Houben–Weyl, Vol. E 18, pp 847–863; E 20/II, pp 807–813). The Shell Higher 

Order Process (SHOP), nicely described in a review by Keim, involves the oligomerization 

of ethene to produce Æ-alkenes (Scheme 81). [7] Nickel polymerization catalysts were first 

reported in the 1950s; [7] however, cationic nickel diimine complexes have been identified 

by Brookhart as highly efficient ethene polymerization catalysts (Scheme 82). [182–185] The 

unique ligand class with highly hindered ortho-substituted aryl rings on the nitrogens of 

the diimine ligand results in rates of chain propagation which are much greater than 

chain transfer rates, thus allowing the formation of high-molecular-weight polymers. 

Scheme 81 Shell Higher Order Process [7] 

H2C CH2 LnNi H LnNi C2H5 O 

L = 

− 

O 

PPh2 

O 

L nNi CH 2CH 2R 1 

L nNi C 4H 9 

R 1 

L nNi H 



Scheme 82 Nickel-Catalyzed Ethene Polymerization [182–185] 

Ar 1 = 

R 1 

R 1 

Ar 1 

N 

Ni 

N 

Ar 1 

Br 

Br 

H2C CH2 

methylaluminoxane 

Ar 

N 

Ni 

N 

1 

Ar1 + 

Ar 

N 

Ni 

N 

1 

Ar1 + Me 

n 

polyethene

References 79 

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[10] Chiusoli, G. P., Acc. Chem. Res., (1973) 6, 422. 

[11] Kubiak, C. P., In Encyclopedia of Inorganic Chemistry, King, R. B., Ed.; Wiley: Chichester, (1994); 

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Volume 2 Compounds of Groups 7–3 

(Mn…,Cr…,V…, Ti…,Sc…,La…,Ac…) 

Product Class 2.6 Organometallic Complexes of 

Chromium, Molybdenum, and Tungsten 

without Carbonyl Ligands 

Written by R. Poli and K. M. Smith 

83





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Bibliothek 

Die Deutsche Bibliothek lists this publication in the 

Deutsche Nationalbibliografie; detailed bibliographic 

data is available on the internet at 




p. cm. 



of groups 7–3 (Mn … ,Cr … ,V … ,Ti … ,Sc … , 

La … ,Ac … ) / volume editor, T. Imamoto 

ISBN 3-13-112141-6 – ISBN 0-86577-941-4 (v. 2) 



QD262 .S35 2000 

547'.2–dc21 

00-061560 

(Houben–Weyl methods of organic chemistry) 





Vol. 2: Compounds of groups 7–3 (Mn … ,Cr … ,V … , 

Ti … ,Sc … ,La … ,Ac … ). – (Houben–Weyl methods 


1. Organometallic compounds – Synthesis 

I. Imamoto, T., II. Barbier-Baudry, D. 

547' .05 

ISBN 3-13-112141-6 


ISBN 0-86577-941-4 


Date of publication: October 9, 2002 

85 





















































86 

Biographical Sketches 

Rinaldo Poli obtained his Ph.D. in 1985 from the Scuola Normale Superiore 

in Pisa under the supervision of Fausto Calderazzo. He spent one 

year with Geoffrey Wilkinson (exchange student, 1983–1984) and two 

years with Al Cotton (research associate, 1985–1987). He started his 

career at the University of Maryland, College Park, where he rose the 

ranks to Full Professor, and moved to his current Professor position in 

1996. He has been Camille and Henry Dreyfus Distinguished New 

Faculty (1987), Presidential Young Investigator (1990), Alfred P. Sloan 

Research Fellow (1992), Alexander von Humboldt Forschungsstipendiat 

(1993), and a recipient of the Medaglia Nasini from the Italian Chemical Society (1992). 

Visiting Professor positions include the Technische Universität München (1993–1994), 

Tokyo Metropolitan University (1995), the Inorganic Chemistry Laboratory in Oxford 

(1998), and Los Alamos National Laboratory (2001 and 2002). 

Kevin Smith was born in 1969 in Toronto, Canada. He received a B. Sc. 

degree in chemistry from the University of Toronto in 1992 and a Ph.D. 

in inorganic chemistry from the University of British Columbia in 1998 

with Peter Legzdins. After postdoctoral research with Rinaldo Poli, he 

joined the faculty at the University of Prince Edward Island in 2000, 

where he is now Assistant Professor.

2.6 Product Class 6: Organometallic Complexes of Chromium, 



2.6 Product Class 6: Organometallic Complexes of Chromium, Molybdenum, 

and Tungsten without Carbonyl Ligands .................................. 90 

2.6.1 Product Subclass 1: Metal–Carbene Complexes ........................... 90 


2.6.1.1 Method 1: By Æ-Hydrogen Elimination from Alkyl Complexes ........... 91 

2.6.1.1.1 Variation 1: Alkylation of Chloride Precursors ............................ 91 

2.6.1.1.2 Variation 2: Ligand Addition ............................................ 92 

2.6.1.1.3 Variation 3: Replacement of an Oxo or Imido Ligand ..................... 93 

2.6.1.1.4 Variation 4: Deprotonation with an External Base ........................ 94 

2.6.1.2 Method 2: By Stoichiometric Alkene Metathesis ........................ 94 

2.6.1.3 Method 3: By Carbene Transfer ........................................ 95 

2.6.1.4 Method 4: From Carbyne Complexes .................................. 96 


2.6.1.5 Method 5: Alkene Metathesis ......................................... 97 

2.6.1.5.1 Variation 1: Ring-Opening Metathesis Polymerization (ROMP) ............ 98 

2.6.1.5.2 Variation 2: Alkyne Polymerization ...................................... 98 

2.6.1.5.3 Variation 3: Ring-Closing Metathesis .................................... 99 

2.6.1.5.4 Variation 4: Other Selective Metathesis Processes ...................... 101 

2.6.1.6 Method 6: Carbonylmethylenation ................................... 102 

2.6.2 Product Subclass 2: Metal–Carbyne Complexes .......................... 103 

Synthesis of Product Subclass 2 ........................................... 104 

2.6.2.1 Method 1: By Æ,Æ-Hydrogen Elimination from Alkyl Complexes ........ 104 

2.6.2.2 Method 2: By Addition of Alkynes to Compounds with 

Metal-Metal Triple Bonds ................................. 105 

2.6.2.3 Method 3: By Stoichiometric Alkyne Metathesis ....................... 106 

2.6.2.4 Method 4: By Oxidation of Fischer-Type Carbyne Complexes ........... 107 

2.6.2.5 Method 5: By Rearrangement of Vinyl Complexes ..................... 108 

2.6.2.6 Method 6: By Other Rearrangement Processes ........................ 109 

Applications of Product Subclass 2 in Organic Synthesis .................... 110 

2.6.2.7 Method 7: Alkyne Metathesis ........................................ 110 

2.6.3 Product Subclass 3: Metal–ó-Alkyl and –ó-Aryl Homoleptic Complexes .. 110 


2.6.3.1 Method 1: By Transmetalation ........................................ 111 

2.6.4 Product Subclass 4: Metal–ó-Alkyl and –ó-Aryl Non-homoleptic Complexes 112 



2.6.4.2 Method 2: By Oxidative Addition of Alkyl Halides ...................... 114 

2.6.4.2.1 Variation 1: One-Electron Oxidative Additions .......................... 114 

87

88 

2.6.4.2.2 Variation 2: Two-Electron Oxidative Additions .......................... 114 

2.6.4.3 Method 3: By Oxidative Addition of Alkanes and Arenes ............... 115 

2.6.4.4 Method 4: By Protonation of Carbene and Carbyne Ligands ............ 116 


2.6.4.5 Method 5: Addition of Organochromium(III) Compounds to 

Carbonyl Compounds ..................................... 117 

2.6.4.5.1 Variation 1: Reaction of Organochromium(III) Compounds Prepared 

from Organochromium(III) Chloride by Transmetalation ..... 117 

2.6.4.5.2 Variation 2: Reaction of Organochromium(III) Compounds Prepared 

from Chromium(II) Chloride by Oxidative Addition 

(The Nozaki–Hiyama–Kishi Procedure) ..................... 118 

2.6.4.5.3 Variation 3: Catalytic Nozaki–Hiyama–Kishi Reaction 

(The Fürstner Procedure) .................................. 119 

2.6.4.6 Method 6: Additive–Reductive Carbonyl Dimerization ................. 119 

2.6.5 Product Subclass 5: Metallacyclic Complexes ............................ 120 



2.6.5.2 Method 2: By Reductive Coupling of Alkenes .......................... 122 

2.6.5.3 Method 3: By Addition of Alkenes to Carbene Complexes .............. 123 

2.6.6 Product Subclass 6: Complexes with Triply Bonded 

Heteroelement Ligands .................................................. 123 

2.6.7 Product Subclass 7: Complexes with Doubly Bonded 



2.6.7.1 Method 1: From Complexes Containing Singly Bonded 

Heteroelement Ligands ................................... 125 

2.6.7.2 Method 2: From Other Complexes Containing Doubly Bonded 


2.6.7.3 Method 3: From Complexes Containing Triply Bonded 


2.6.7.4 Method 4: By Oxidative Processes .................................... 128 


2.6.7.5 Method 5: Catalytic Epoxidation of Alkenes ........................... 129 

2.6.8 Product Subclass 8: Complexes with Singly Bonded 



2.6.8.1 Method 1: By Oxidative Addition of Compounds with Single Bonds 

between Heteroelements ................................. 130 


2.6.8.3 Method 3: From ó-Alkyl Complexes ................................... 131 

2.6.8.4 Method 4: From Carbene or Carbyne Complexes ...................... 132

2.6.8.5 Method 5: From Complexes Containing Doubly Bonded 


2.6.9 Product Subclass 9: Miscellaneous Complexes ........................... 133 


2.6.9.1 Method 1: Allylidene Complexes from Cyclopropenes ................. 133 

89

90 

2.6 Product Class 6: 

Organometallic Complexes of Chromium, Molybdenum, 

and Tungsten without Carbonyl Ligands 



Almost all of the complexes described in this product class are air- and/or moisture-sensitive, 

both as solids and in solution. Prior to use all solvents should be dried and distilled 

under nitrogen or argon, and the compounds should be synthesized, handled, and stored 

under an inert atmosphere using Schlenk or glovebox techniques. The bonds between 

group 6 metals and carbon are often readily hydrolyzed, with the notable exception of 

several alkylchromium(III) species. In general, these compounds are less sensitive to oxygen 

when the metals are formally in the +6 oxidation state, and are thus incapable of being 

oxidized further, although the extreme atmospheric sensitivity of molybdenum(VI) 

ring-closing metathesis catalysts (Section 2.6.1.5.3) provides a striking exception to this 

trend. [1] 

Due in part to their hydrolytic instability, the toxicity of the organometallic complexes 

described in this product class have generally not been investigated. A prominent 

exception is dichlorobis(cyclopentadienyl)molybdenum(IV), which has been studied as an 

antitumor agent. [2,3] Purely inorganic compounds of chromium(VI) are well-established 

carcinogens, in contrast to the relatively low toxicity characteristic of chromium(III) species. 

While chromium(III) compounds are not readily transported through cell walls, the 

negative charge and tetrahedral structure of the chromate dianion makes it analogous to 

the phosphate and sulfate ions, and so chromium(VI) is brought into the cell via nonspecific 

anion transport channels. Chromium(VI) is then reduced to chromium(III) inside the 

cell, leading to the DNA lesions responsible for the carcinogenic activity. [4] In the absence 

of more detailed toxicity studies for organometallic group 6 complexes, care should be 

taken when handling all the compounds in this product class. 


Metal–Carbene Complexes 

While group 6 complexes containing carbonyl ligands (Fischer-type) are most common 

for chromium, those without carbonyl ligands (Schrock-type, also called alkylidene complexes) 

are more typical of molybdenum and tungsten. Although a few chromium examples 

are known, [5] our attention will be almost completely devoted to molybdenum and 

tungsten systems. These complexes are generally found in high oxidation states (‡4) and 

supported by electronegative, ð-donor ligands (alkoxo, amido, imido). These ligands have 

the possibility of stabilizing low-coordination environments by ð-donation in excess of 

the valence requirement (e.g., ó +2ð M”OorM”NR for oxo and imido derivatives), resulting 

in tetrahedral species. Often, however, these complexes allow expansion of the coordination 

sphere by formation of dimers (e.g., halide bridged) or by addition of a two-electron 

donor with formation of five-coordinate and occasionally six-coordinate species, the 

formation of which is more likely for tungsten than for molybdenum and when the metal 

bears electron-withdrawing ligands. [6] 

Group 6 metal–carbene complexes are most stable when devoid of â-hydrogen atoms 

on the carbene ligand, the latter leading to decomposition by 1,2-H migration and formation 

of alkene derivatives. [7] The carbene ligand usually bears hydrogen or alkyl substitu-

2.6.1 Metal–Carbene Complexes 91 

ents, and is normally considered as a dinegative (=CR 1 R 2 ) 2– ligand for the purpose of formal 

oxidation state assignment. Like all other Schrock-type carbene complexes, those of 

group 6 metals present marked nucleophilic reactivity and undergo Wittig chemistry 

with X=Y molecules, the thermodynamics favoring the M=X and R 2C=Y combination 

where X is harder than Y. [8] This reaction, however, does not represent particular advantages 

over classical Wittig reagents for organic synthesis, a major use being the metal removal 

at the end of organic transformations carried out on carbene complexes (e.g., alkene 

metathesis, see Section 2.6.1.5). 


2.6.1.1 Method 1: 

By Æ-Hydrogen Elimination from Alkyl Complexes 

High oxidation state dialkyl complexes may undergo transfer of an Æ-hydrogen atom 

from one alkyl ligand to the second one under suitable conditions, with formation of a 

carbene product and elimination of alkane. The reaction is favored by an increase of steric 

bulk in the metal coordination sphere. This has been achieved in a number of ways, as 

outlined in the following variations. 

2.6.1.1.1 Variation 1: 

Alkylation of Chloride Precursors 

The replacement of a halide with a bulky alkyl group is often sufficient to induce the alkane 

elimination process. Thus, while the complex tert-butylimidochlorotris(2,2-dimethylpropyl)molybdenum(VI) 

(1) does not spontaneously undergo the Æ-hydrogen elimination 

process, substitution of the chloride ligand with a fourth 2,2-dimethylpropyl ligand 

directly affords the carbene product 2 (Scheme 1). [9] For the analogous tungsten system, 

tetraalkylimido intermediates, e.g. phenylimidotetrakis[(trimethylsilyl)methyl]tungsten(VI), 

have been isolated, and their slow first-order elimination to the alkylidene product 

has been investigated. [10] Other alkane eliminations from stable dialkyl derivatives 

may be induced by simple irradiation, [11,12] e.g. the transformation of 3 into 4. [13] 

Scheme 1 Æ-Hydrogen Elimination Induced by Alkylation [9,13] 

Cl 

Mo 

CH2But NBut ButH2C ButH2C W 

3 

1 

t-BuCH2Li, benzene 

rt, 10 min 

75% 

toluene, hν (Xe, 340 nm) 

26 h 

64% 

= 4-t-Bu-calix[4]-(O)4 

H Pr 

W 

4 

Bu 

Mo 

tH2C But NBu 

H2C 

t 

CHBut {4-tert-Butylcalix[4]-(O) 4}butylidenetungsten(VI) (4): [13] 

A soln of W(cyclo-C 4H 8){4-t-Bu-calix[4]-(O) 4} (8.45 g, 8.77 mmol) in toluene (200 mL) was irradiated 

with a Xe lamp (540 W •m –2 at 340 nm) for 26 h. Volatiles were removed in vacuo, 

pentane (60 mL) was added to the residue, and pale brown 4 was collected and dried in 

vacuo; yield: 5.62 g (64%); 1 H NMR (benzene-d 6, ä): 10.0 [t, 3 J = 7.5 Hz, 1H, WC(Pr)H], 5.47 

[m, 2H, WC(H)CH 2CH 2CH 3], 1.69 [m, 2H, WC(H)CH 2CH 2CH 3], 1.15 [t, 3 J = 7.2 Hz, 3H, WC(H)- 

2 


92 Science of Synthesis 2.6 Complexes of Cr, Mo, and W without CO Ligands 

CH 2CH 2CH 3]; 13 C NMR (benzene-d 6, ä): 272 [d, WC(Pr)H, 1 J CW = 180 Hz, 1 J CH = 142 Hz], 41.6 

(WCCH 2CH 2CH 3), 29.5 (WCCH 2CH 2CH 3), 14.5 (WCCH 2CH 2CH 3). 

2.6.1.1.2 Variation 2: 

Ligand Addition 

When di- or polyalkyl complexes do not spontaneously give rise to Æ-hydrogen elimination, 

this process may often be accomplished by addition of two-electron ligands (e.g., 

phosphines). [14,15] Thus, the tris(2,2-dimethylpropyl)(2,2-dimethylpropylidyne)tungsten 

complex 5 transforms into the (2,2-dimethylpropyl)(2,2-dimethylpropylidene)(2,2-dimethylpropylidyne) 

product 6 upon addition of trimethylphosphine (Scheme 2). The conditions 

required to induce this process depend on the system, from –788C for dibromotetrakis[(trimethylsilyl)methyl]dimolybdenum(III)(Mo”Mo) 

[15] to room temperature for cyclopentadienylbis(2,2-dimethylpropyl)nitrosylmolybdenum(II). 

[16] 

In the synthesis of compound 7, substitution of two alkoxide ligands with the less 

sterically encumbering (and also poorer ð-donor) chlorides opens up the coordination 

sphere to the coordination of a bidentate 1,2-dimethoxyethane molecule, inducing carbene 

formation. The dialkoxo precursor, albeit five coordinate, does not spontaneously 

undergo the alkane elimination process. [17] The increase of the coordination sphere can 

also be achieved by replacement of a monodentate ligand (e.g., chloride) with a polyfunctional 

ligand, e.g. hydrotris(pyrazolyl)borate [18] or 2-[(dimethylamino)methyl]phenyl (see 

synthesis of 8) (Scheme 2). [19] This strategy has also been utilized in other cases via replacement 

of a bulky alkyl with chloride by protonation with LH + Cl – in the presence of excess 

ligand L. [10] 

Scheme 2 Æ-Hydrogen Elimination Induced by Ligand Addition [14,17,19] 

ButH2C W CBut But Bu 

H2C 

tH2C 5 

OBu 

W N 

t 

OBut ButH2C But Pr 

H2C i 

Pri CH2TMS 

NPh 

Cl W 

CH2TMS 

CH2TMS Me3P (neat) 

100 oC, 5 min 

quant 

PCl5, DME 

−35 oC 90% 

2-Me 2NCH 2C 6H 4Li 

Et 2O, −78 o C 

70% 

But Me3P t CBu 

H2C W 

CHBu 

Me3P 

t 

6 

Pr i 

Cl 

N 

W 

Cl 

CHBut O 

O 

Pri Me 

Me 

8 

7 

NMe2 

NPh 

W 

CHTMS 

CH2TMS Dichloro[(2,6-diisopropylphenyl)imido](1,2-dimethoxyethane-O,O¢)(2,2-dimethylpropylidene)tungsten(VI) 

(7); Typical Procedure: [17] 

Finely ground PCl 5 (2.25 g, 10.8 mmol) was added to a chilled (–358C) soln of [W(CH 2t- 

Bu) 2(Ot-Bu 2) 2(=NC 6H 3-2,6-iPr 2) (7.0 g, 10.8 mmol) in DME (120 mL). The mixture was 

warmed to rt and stirred for an additional 1 h after all the solids had disappeared. The 

mixture was then concentrated in vacuo until an orange powder formed. This material 

was washed with cold pentane to give the product as a yellow-orange powder. This synthesis 

can fail virtually completely if the DME is not scrupulously dried and the PCl 5 not


rigorously purified; yield: 5.75 g (90%); 1 H NMR (benzene-d 6, ä): 9.97 (s, J HW = 7.3 Hz, CHt- 

Bu); 13 C NMR (benzene-d 6, ä): 283.8 (d, W=C, 1 J CH = 114 Hz, 1 J CW = 163 Hz). 

2.6.1.1.3 Variation 3: 

Replacement of an Oxo or Imido Ligand 

Replacement of an oxo [20–22] or imido [23] ligand with two singly bonded heteroelement ligands 

has often proven to be an efficient method for inducing the Æ-elimination process 

from dialkyl compounds. Examples of syntheses of these types are shown in Scheme 3. 

The interaction between a dialkoxodialkyloxo complex of tungsten(VI) and a Lewis acid 

(AX n, viz. aluminum trichloride, tin(IV) chloride, magnesium bromide, etc.) proceeds via 

an isolable adduct containing the W=O-AX n moiety when conducted in hexane, which 

then yields the dialkoxodihalocarbene product. [24] Although this procedure is not general, 

subsequent ligand exchange or stoichiometric alkene metathesis (see Section 2.6.1.2) allows 

the preparation of a much broader series of derivatives. [21,22] Lewis base adducts such 

as compound 9 easily undergo exchange of the Lewis base, or can be converted into the 

base-free material. The reaction yielding 10 is the most convenient entry into the catalytically 

active dialkoxo(alkylidene)imido complexes of molybdenum and tungsten, since 

the trifluoromethanesulfonate ligands can be easily replaced with a variety of alkoxide 

groups, and the dialkyldiimido precursor complex is readily available in two high-yield 

steps from commercially available dichlorodioxotungsten(VI) or ammonium dimolybdate. 

[17,25] 

Scheme 3 Æ-Hydrogen Elimination Induced by Substitution of Oxo or Imido 

Ligands [8,17,23,29] 

ButN Mo 

But CH2Bu 

N 

t 

CH2But Pr i 

Pri N 

M 

Pr N 

i 

CH2R1 CH2R1 Pr i 

M = Mo, W 

R1 = t-Bu, CMe2Ph 

(CF3) 2CHOH (2 equiv) 

pentane, rt 

80% 

TfOH (3 equiv) 

DME, −30 oC 65−78% 

OCH(CF3) 2 

Mo NH2Bu OCH(CF3) 2 

t 

ButN ButHC 9 

M 

R1 Pr 

N 

OTf 

O 

HC O 

OTf 

i 

Pri Me 

Me 

[(2,6-Diisopropylphenyl)imido](1,2-dimethoxyethane-O,O¢)(2,2-dimethylpropylidene)bis(trifluoromethanesulfonato-O)molybdenum(VI) 

(10,M=Mo;R 1 = t-Bu); 


A prechilled soln of TfOH (3.15 mL, 35.5 mmol, 3 equiv) in DME (20 mL) was added in a 

dropwise manner to an orange soln of Mo(CH 2t-Bu) 2(=NC 6H 3-2,6-iPr 2) 2 (7.00 g, 11.8 mmol) 

in DME (200 mL) at –308C over a period of 10 min. [It is important in this step that the soln 

be homogeneous and cold. It is best to grind the crystals of the molybdenum starting complex 

to a fine powder to aid dissolution; the addition of some pentane (15–30 mL) may facilitate 

this step.] The soln was allowed to warm up to rt and stirred for 3 h. During this 

period the color changed from orange to dark yellow. The solvent was evaporated in vacuo 

to yield a yellow solid, which was then extracted with cold toluene (100–150 mL). The 

10 



extract was filtered through a bed of Celite and the toluene removed from the filtrate in 

vacuo to give the product as yellow flakes. The product should be checked by NMR for 

contamination by anilinium trifluoromethanesulfonate, which is slightly soluble in toluene; 

yield: 5.9 g (65%); 1 H NMR (benzene-d 6, ä): 14.29 (s, CHt-Bu); 13 C NMR (benzene-d 6, ä): 

331.9 (d, Mo=C, 1 J CH = 121 Hz). 

2.6.1.1.4 Variation 4: 

Deprotonation with an External Base 

Deprotonation of alkyl ligands at the Æ-position is another potentially general method for 

forming carbene complexes from alkyl compounds that are either electronically unsaturated 

or possess labile ligands. However, this method is little documented for group 6 

metals as well as for metals of other groups. The neutral dialkyl compound 11 reacts 

with a range of lithium reagents to yield the dimeric, anionic alkyl–alkylidene complex 

12, as shown in Scheme 4. [26] Methylidene product 13 is only stable at low temperature, 

decomposing upon warming in a nonselective manner to yield alkylidene-bridged dinuclear 

products. [27] 

Scheme 4 Deprotonation of Alkyl Complexes [26,27] 

Mo 

ON CH 2TMS 

CH 2TMS 

11 

[W(Me) 4Cp ∗ ] + PF 6 − + Et3N 

+ 

LiHMDS 

THF 

−100 oC to rt 

62% 

CH2Cl2 

< −40 o C 

TMS 

W(Me)3Cp ∗ ( 

13 

THF 

Li 

Mo NO ON Mo 

CH2TMS Li TMSH2C THF THF 

12 

TMS 

Bis{nitrosyl(ç 5 -pentamethylcyclopentadienyl)[(trimethylsilyl)methyl][(trimethylsilyl)methylidene]molybdenum(II)} 

(Dilithium)tris(tetrahydrofuran) (12): [26] 

[Mo(CH 2TMS) 2Cp*(NO)] (200 mg, 0.46 mmol) and LiHMDS (90 mg, 0.46 mmol) were intimately 

mixed and cooled to –1008C in a small flask. THF was slowly poured down the 

sides of the flask and allowed to freeze onto the solid mixture. Over the course of 4 h, a 

color change from purple to red occurred; the final mixture was taken to dryness in vacuo. 

The remaining red solid was extracted into pentane (2 mL), and the extracts were filtered 

through Celite. Slow evaporation of the pentane filtrate resulted in the deposition 

of pale red crystals, which were recrystallized (pentane) to obtain pale yellow crystals of 

12; yield: 143 mg (62%). 

2.6.1.2 Method 2: 

By Stoichiometric Alkene Metathesis 

The addition of an alkene to a carbene complex may lead to a metathesis reaction with 

exchange of the carbene ligand with one of the two halves of the alkene. The reaction proceeds 

via formation of an alkene–carbene complex, which rearranges via a metallacyclobutane 

intermediate. [28] This reaction is synthetically useful when a terminal alkene is 

used and vacuum evaporation of the more volatile alkene product (typically 3,3-dimethylbut-1-ene) 

is possible to displace the equilibrium. [22] An excess of the alkene reagent is also 

used to ensure a favorable equilibrium position (see Scheme 5). The properties of the an- 

CH 2)


cillary alkoxide ligands can influence whether this reaction results in metathesis or the 

formation of stable tungstacyclobutane derivatives (see Section 2.6.5). [17,29] 

Scheme 5 Stoichiometric Alkene Metathesis [8,17,22] 

M( CHBu t )(L) n + H 2C CR 1 R 2 M( CR 1 R 2 )(L) n + H 2C CHBu t 

M(L) n R1 R2 Conditions Yield (%) of 

[M(=CR1R2 )(L) n] 

Ref 

[WBr2(OCH2t-Bu) 2] (CH2) 4 CH2Cl2,rt,4h 87 [22] 

[Mo(=NC6H3-2,6-iPr2){OCMe(CF3) 2} 2] H TMS pentane, 

–308C, 2.5 h 

74 

[8] 

[W(OR3 ) 2(=NC6H3-2,6-iPr2)] a H Si(OMe) 3 pentane, rt, 

30 min to 2.5 h 

50–78 

[17] 

a R 3 = 2,6-iPr2C 6H 3,CMe 2(CF 3), CMe(CF 3) 2. 

Dibromo(cyclopentylidene)bis(2,2-dimethylpropan-1-olato)tungsten(VI); 


Methylenecyclopentane (0.36 mL, 3.42 mmol) was added to an orange soln of [WBr 2(=CHt- 

Bu)(OCH 2t-Bu) 2] (0.127 g, 0.215 mmol) in CH 2Cl 2 (10 mL). After 4 h, the volatiles of the red 

mixture were removed in vacuo, and the orange residue was washed twice with pentane 

to give the product as an orange powder; yield: 110 mg (87%); 13 C NMR (CD 2Cl 2, ä, gated 

decoupled): 47.1 (t, 1 J CH = 134 Hz, W=CCH 2), 28.2 (t, 1 J CH = 131 Hz, W=CCH 2CH 2); the W=C 

signal could not be observed. 

2.6.1.3 Method 3: 

By Carbene Transfer 

The carbene ligand may be either directly added to the metal center or exchanged for two 

X groups. The first strategy requires preparation of the metal in a reactive, reduced form. 

For the preparation of compound 14 (Scheme 6), this is achieved by sodium reduction of 

the dichloro precursor complex. [31] The phosphorane carbene transfer agent is readily accessible 

with a variety of carbene functionalities and the triphenylphosphine byproduct 

does not coordinate with the metal center, allowing its easy removal by scavenging with 

copper(I) chloride. For the tungsten(II) system 15 (L= tertiary phosphine), even ketones 

and imines are sufficiently good carbene transfer reagents, providing alkylideneoxo and 

alkylideneimido tungsten(VI) products 16, respectively, in remarkable four-electron oxidative 

addition reactions. [32] For ketones different than cyclopentanone, stable and unreactive 

bis(ç 2 -ketone) adducts are obtained by use of an excess of the ketone, but the 

use of one equivalent still leads to the alkylideneoxo product. 

The exchange strategy involves the use of reactive tantalum alkylidene complexes, 

resulting in the replacement of alkoxo ligands. This method, which is also accompanied 

by the scrambling of other ligands, applies equally well to the synthesis of the oxo and 

imido tungsten products 17, [33] but is limited by the availability of the tantalum alkylidene 

reagent and has not been reported for molybdenum. 



Scheme 6 Carbene Transfer [31–33] 

R 1 

R 1 

N 

R 1 = H, Me, iPr 

Cl 

L 

L W L 

Cl L 

15 

L = PMe 2Ph 

E = O, N-4-Tol 

R1 ,R2 = (CH2) 4, Me2 E 

W 

ButO OBut OBut ButO E = O, NPh 

Cl 

W 

Cl 

OCMe(CF3) 2 

OCMe(CF3) 2 

E 

R1 , benzene 

2 R 

45−88% 

Na/Hg, 

TaCl3( CHBut )(PMe3)2 

Et2O, rt, 12 h 

79−83% 

OMe 

benzene, THF, rt, 8 h 

71% 

E 

Cl W CR 

Cl 

1R2 L 

L 

16 

PPh3 

PMe3 Cl E 

W 

Cl CHBu 

PMe3 17 

t 

MeO 

(F3C) 2MeCO 

THF W 

OCMe(CF 

N 

3)2 

R 1 R 1 

(2,6-Dimethylphenylimido)bis(1,1,1,3,3,3-hexafluoro-2-methylpropan-2-olato)(2-methoxybenzylidene-kC)(tetrahydrofuran)tungsten(VI) 

(14,R 1 = Me); Typical Procedure: [31] 

The compounds [WCl 2{OCMe(CF 3) 2} 2(=NC 6H 3-2,6-Me 2)(THF)] (16.0 g, 19.8 mmol) and 

Ph 3P=CH(C 6H 4-2-OMe) (7.78 g, 20.3 mmol) were dissolved in a mixture of benzene and 

THF (160 mLand 2.5 mL, respectively) and the resulting soln was added to 1% Na/Hg 

(3.59 g of Na, 7.90 equiv). After being stirred for 8 h at rt, the mixture was allowed to settle, 

and the orange-brown supernatant was added via a cannula to CuCl (2.07 g, 20.9 mmol). 

The residual Na/Hg was washed with Et 2O (120 mL), and the combined benzene/Et 2O soln 

was stirred with CuCl for 12 h before removal of the solvent in vacuo. The brown solid 

was then extracted with Et 2O (260 mL). After addition of THF (2 mL) to the extract and filtering, 

the soln was slowly cooled to –508C to yield the product as an olive-yellow powder; 

yield: 12.0 g (71%); 1 H NMR (benzene-d 6, ä): 10.81 (s, W=CHAr). 

2.6.1.4 Method 4: 

FromCarbyne Complexes 

Addition of a proton to a carbyne ligand may transform it into a carbene. The proton can 

be provided by an external source or by transfer from another ligand. Examples of the 

first kind are provided by the addition of acids to complex 18 (see Scheme 7). [7] The use 

of pyridinium salts yields more stable pyridine adducts. This reaction can be reversed by 

the addition of a strong base (see Section 2.6.2). When an acid containing a noncoordinating 

anion is used, e.g. trifluoromethanesulfonic acid, cationic derivatives may be obtained. 

[34] Depending on the nature of the coligands, the proton may preferentially add 

to another position in the molecule (see Section 2.6.2). 

Internal proton transfer is observed for amido ligands. The reaction between the 1,2dimethoxyethane 

adduct of trichloro(carbyne)molybdenum or -tungsten complexes and 

(trimethylsilyl)arylamines produces the stable intermediates 20. The latter, however, re- 

14


arrange by a base-catalyzed proton transfer to the final carbene–imido products 21. [8,17,29] 

These proton-transfer processes occur much more slowly or not at all for the dialkoxo analogues, 

although the anticipated proton-transfer products are stable systems. A mechanism 

of reversible amine-assisted dehydrohalogenation has been proposed for this transformation. 

This synthetic route is inconvenient for the molybdenum system, mainly because 

of difficulties in the preparation of the precursors to the trichlorocarbyne complex 

of molybdenum. The tungsten analogue is more easily prepared (see Section 2.6.2). [29] 

However, even the tungsten product is more conveniently prepared by another procedure 

[Æ-H elimination from a bis(2,2-dimethylpropyl) precursor, Section 2.6.1.1]. [17] 

Scheme 7 Protonation of Carbyne Complexes [7,8,17] 

Bu t O 

CBu t 

W 

OBut OBut 18 

HX (2 equiv), toluene, rt 

51−85% 

X = Cl, Br, OAc, OBz, OPh, OC 6F 5, 4-ClC 6H 4O 

M( CBu t )Cl 3(DME) 

M = Mo, W; R 1 = Me, iPr 

R 1 

NH 

R1 Et2O, −40 o TMS 

C 

>95% 

X 

Bu 

W 

t Bu 

O 

tO X 

CHBut R 1 

19 

Cl 

N 

M 

CBu 

Cl 

t R1 Me 

O H 

O 

Me 

20 

Et3N 

>95% 

R 1 

Cl 

N 

M 

CHBu 

Cl 

t 

R1 Me 

O 

O 

Me 

Di-tert-butoxodichloro(2,2-dimethylpropylidene)(pyridine)tungsten(VI); 


The alkylidyne complex [W(”Ct-Bu)(Ot-Bu) 3] (1.00 g, 2.12 mmol) was added at rt as a solid 

to a CH 2Cl 2 soln (25 mL) of pyridine hydrochloride (4.2 mmol). After 10 min the solvent 

was removed in vacuo and the residue was recrystallized (pentane) to yield the product 

as orange crystals; yield: 0.92 g (79%); 1 H NMR (benzene-d 6, ä): 10.76 (s, CHt-Bu); 

13 C{ 1 H} NMR (benzene-d6, ä): 302.3 (CHt-Bu). 


2.6.1.5 Method 5: 

Alkene Metathesis 

High-valent molybdenum–carbene complexes bearing electronegative ancillary ligands 

are efficient catalysts for alkene metathesis reactions (Scheme 8). [20,35] This reaction proceeds 

via [2 +2] cycloaddition and formation of metallacyclobutane intermediates, some 

of which have been isolated under controlled conditions (see Section 2.6.5.3). [36] In order 

to make the reaction synthetically useful, it is necessary to have a driving force and high 

selectivities, and to suppress the self-metathesis if a cross-metathesis (e.g., R 1 „ R 2 ) is desired. 

The driving force may be provided by conjugation or by formation of polymeric materials. 

Selective processes often result from the removal of a volatile byproduct, such as 

ethene. 

21 



Scheme 8 Alkene Metathesis 

R 1 R 2 

+ 

R 1 

R 2 

+ H 2C CH 2 

2.6.1.5.1 Variation 1: 

Ring-Opening Metathesis Polymerization (ROMP) 

The living polymerization of strained cyclic alkenes such as norbornenes and substituted 

norbornadienes is catalyzed by molybdenum and tungsten carbene complexes (Scheme 

9). [35] The living nature of this process allows control of the chain length and the preparation 

of block copolymers, which may also have a high level of tacticity. [37] A Wittig-like 

capping reaction with aldehydes can be used to cleave the metal fragment off the living 

polymer. Essentially monodisperse products 22 with x up to 500 have been obtained from 

norbornene by using di-tert-butoxo[(2,6-diisopropylphenyl)imido](2,2-dimethylpropylidene)tungsten(VI) 

as a ROMP initiator. [38] The catalyst does not attack the less reactive 

double bonds in the polymeric product. The use of 7,8-bis(trifluoromethyl)tricyclo[4.2.2.0 

2,5 ]deca-3,7,9-triene as monomer gives oligomers from which polyenes with up 

to 15 conjugated double bonds have been obtained via a retro-Diels–Alder ejection of an 

arene upon thermolysis. [39] Other substrates suitable for the ROMP process are substituted 

cyclooctatetraenes, leading to functionalized and soluble polyacetylenes of low polydispersities. 

[40] 

Scheme 9 Ring-Opening Metathesis Polymerization of Norbornene [35] 

[W] CHBu t + x 

[W] = W(Ot-Bu) 2( NC6H3-2,6-iPr2) 

−80 o C 

[W] CHBut x 

PhCHO 

PhHC CHBut x 

22 

1,4-Dihydro-1,4-methanonaphthalene, Homopolymer (x = 100); Typical Procedure: [41] 

A soln of 1,4-dihydro-1,4-methanonaphthalene (291 mg, 2.05 mmol) in toluene (3.0 mL) 

was added dropwise to a rapidly stirred soln of [Mo(=CHt-Bu)(Ot-Bu) 2(=NC 6H 3-2,6-iPr 2)] 

(10 mg, 0.020 mmol) in toluene (3.0 mL) and the soln was stirred for 20 min. The polymerization 

was quenched by addition of pivalaldehyde (25 ìL). After 20 min, the soln was 

added to hexane (250 mL), and the precipitated polymer was isolated by centrifugation, 

washed with hexane, and placed under vacuum overnight; yield: 280 mg (94%). 

2.6.1.5.2 Variation 2: 

Alkyne Polymerization 

Terminal alkynes have yielded polyenes 23 with up to 150 conjugated double bonds under 

molybdenum–carbene catalysis (Scheme 10). [42] The nature (in particular the size) of 

the ancillary ligands is important in controlling the selective Æ-addition. Acetylene itself 

produces insoluble and air-sensitive polymers that are difficult to characterize. Cyclopolymerization 

of dipropargyl derivatives such as 24 have been shown to yield polyenes of 

low polydispersity containing only six-membered rings, following a selective â-addition


of the first triple bond. [43] The nature of the coordination sphere on the carbene initiator is 

of capital importance, as polymers containing both five- and six-membered rings that are 

a consequence of an initial Æ- orâ-addition, respectively, have been obtained with other 

initiators. [44] 

Scheme 10 Alkyne Polymerization [42,43] 

x R 1 

[Mo] CHCMe2Ph toluene, rt 

[Mo] 

[Mo] = 

OCMe(CF3)2 

N Mo 

OCMe(CF3) 2 

; R1 = 

TMS 

x 

EtO 2C 

[Mo] = 

24 

CO 2Et 

Bu t 

[Mo] CHt-Bu 

N Mo(O 2CCPh 3) 2 

R 1 

EtO2C 

EtO2C [Mo] 

CHCMe 2Ph 

x 

β-addition 

; x = up to 150 

CHBu t 

PhCHO 

PhCH 

EtO 2C 

[Mo] 

R 1 

x 

23 

CO2Et 

CHCMe 2Ph 

CHBut x 

2,2-Diprop-2-ynylmalonic Acid, Diethyl Ester, Homopolymer (x = 20); 


Polymerization stock solutions of diethyl 2,2-diprop-2-ynylmalonate (24; 0.406 M) and 

[Mo(=CHt-Bu)(O 2CCPh 3) 2(=NC 6H 42-t-Bu)] (0.00676 M) in toluene that had been distilled 

over sodium benzophenone ketyl, stored over molecular sieves (4 Š), and passed through 

alumina, were prepared. To the catalyst stock soln (3.007 mL), toluene (3 mL) was added 

and the monomer stock soln (1.0 mL) was squirted in. Within 30 s the mixture turned 

deep red. After 6 h, benzaldehyde (16 ìL) was added. After stirring for a further 3 h, the 

soln was concentrated in vacuo to about 1.5 mL. The polymer was precipitated in pentane 

(60 mL), collected on a frit, and dried in vacuo to yield a red, powdery material. All operations 

were carried out under a nitrogen atmosphere and the polymers were only briefly 

exposed to air for sample preparation for GC analysis; yield: 90 mg (91%); 13 C{ 1 H} NMR 

(CDCl 3, ä): 170.7 (CO 2Et), 54.5 (C quaternary). 

2.6.1.5.3 Variation 3: 

Ring-Closing Metathesis 

Ring-closing metathesis (Scheme 11) affords cyclic products 25 in competition with intermolecular 

metathesis processes to form polymeric materials. [45] The reaction is also complicated 

by the possibility of ROMP (Section 2.6.1.5.1). Which products are obtained is the 

result of an interplay of thermodynamic and kinetic parameters. Entropy (the generation 

of two molecules from one) and evaporative subtraction of the volatile acyclic alkene 

from solution provide the necessary driving force for the desired cyclization. The ringclosing 

metathesis procedure can be applied to the construction of macrocyclic natural 

products, although mixtures of E- and Z-isomers are often obtained in these cases (see 

also Section 2.6.2.7). [46] The most widely used group 6 catalyst for this process is 26, although 

ruthenium-based catalysts are generally preferred owing to their greater func- 



tional group tolerance and relatively low sensitivity to air, moisture, or solvent impurities. 

[47] The process has proven particularly useful for the formation of cyclic ethers, e.g. 

27. [48] A number of functional groups, including tertiary alcohols, do not interfere with 

the course of the reaction. Amine and amide functional groups can be tolerated if they 

cannot form unreactive chelated adducts for steric reasons. [49] A variant of this method 

follows the initial ring-closing metathesis step with a carbonyl alkenation process, e.g. 

the synthesis of 28, [50] which is, however, stoichiometric in metal because of the formation 

of a catalytically inactive metal–oxo byproduct. The success of this strategy rests on 

the fact that compound 26 metathesizes alkenes more rapidly than it alkenates ketones. 

Chiral analogues of 26 have been prepared using C 2 symmetric diol ligands, and these 

complexes, 29 [51] and 30, [52] have been used to perform the asymmetric ring-closing metathesis 

of dienes [52–54] and the synthesis of chiral furans via enantioselective desymmetrization 

reactions. [55] 

Scheme 11 Cycloalkenes by Ring-Closing Metathesis of Dienes [48,50] 

[M ] 

X X 

O 

F 3C 

F 3C 

O 

O 

Ph 

Ph 

25 

Pri N Pri O 

CF3 

Mo 

O CHCMe2Ph CF3 

29 

+ H2C CH 2 

Pr i 

N Pri (F3C) 2MeCO 

Mo 

(F3C) 2MeCO CHCMe2Ph 26 (cat.) 

benzene, 20 oC, 15 min 

Pr i 

92% 


Mo 

(F3C) 2MeCO CHCMe2Ph 

26 

benzene, 20 oC, 30 min 

84% 

Pri But O 

O 

Bu t 

O Ph 

27 

O 

28 

N Pri Mo 

CHCMe2Ph 1-[(2-Methyl-3-phenylallyl)oxy]methylcyclohex-1-ene (28); Typical Procedure: [50] 

1-[(2-Methyl-3-phenylallyl)oxy]oct-7-en-2-one (35 mg, 0.13 mmol) was added to a homogeneous 

yellow soln of catalyst 26 (100 mg, 0.13 mmol) in anhyd benzene (12 mL) under argon. 

The resulting mixture was stirred at 20 8C for 30 min, at which time TLC showed the 

reaction to be complete. The mixture was quenched by exposure to air, concentrated, and 

30 

Ph


purified by flash chromatography (0–7% EtOAc/hexane) to yield the substituted cyclohexene 

as a colorless oil; yield: 27 mg (84%); 1 H NMR (benzene-d 6, ä): 5.72 (br s, CHCH 2), 

2.05–1.45 (m, 8H, CH 2CH 2CH 2CH 2). 

2.6.1.5.4 Variation 4: 

Other Selective Metathesis Processes 

These processes are usually restrained to monosubstituted alkenes, yielding ethene as the 

byproduct. Fairly selective cross-coupling processes have been reported from a combination 

of an electron-poor alkene, especially one containing a ð-substituent (e.g., styrenes, 

acrylonitrile), [56,57] and a more nucleophilic one containing a small, electron-rich, nonconjugated 

substituent (see, for example, the synthesis of 31 in Scheme 12), [56] or with allylsilanes. 

[58] The electron-poor alkene self-metathesizes only slowly and, in addition, inhibits 

the self-metathesis of the nucleophilic alkene. Greater than 95% trans selectivity is observed 

in the reactions with styrene substrates, [56] while the cis-product is highly favored 

for cross-metatheses with acrylonitrile. [57] 

The formation of the homo dimer may also be significantly slowed down by steric 

bulk. For example, compounds 32 and 33 yield the cross-coupling product 34 without 

any self-metathesis of 32 and with only 26% yield of the 33 homo dimer. [59] The E/Z selectivities, 

however, are usually low for nonconjugated alkene products. 

Scheme 12 Cross-Coupling Alkene Metathesis [56,59] 

Ph 

O 

O 

+ 

CO 2Me 

( ) 5 

+ 

1.5 

32 33 

Pr i 


Mo 

(F3C)2MeCO CHCMe2Ph 26 (cat.) 

CH2Cl2, rt, 1 h 

CO2Me 

Ph 

( ) 

5 

+ 

( ) 5 

31 89%; E 100% 2% 

Pr i 

N Pri (F3C)2MeCO 

Mo 

(F3C) 2MeCO CHCMe2Ph 26 (cat.) 

83% 

O 

O 

CO 2Me 

( ) 5 

34 (E/Z) 2:1 

CO2Me 



(E)-1-Phenyloct-1-ene (31); Typical Procedure: [56] 

To a mixture containing styrene (208 mg, 2 mmol) and oct-1-ene (112 mg, 1 mmol) in 

CH 2Cl 2 (2 mL) was added [Mo(=CHCMe 2Ph){OCMe(CF 3) 2} 2(=NC 6H 32,6-iPr 2)] (7.7 mg, 

1 mol%). The resulting mixture was stirred at rt for 1 h, then passed through a pad of silica 

gel and rinsed with CH 2Cl 2. The solvent was removed under reduced pressure, and the 

crude residue was chromatographed on silica gel to give 31 as a colorless oil; yield: 

166 mg (89%). A similar reaction run with styrene (9.29 g, 89.2 mmol), oct-1-ene (5 g, 

44.6 mmol), and catalyst (342 mg, 1 mol%) in CH 2Cl 2 (60 mL) afforded 31; yield: 7.9 g 

(94%). 1 H NMR (CDCl 3, ä): 2.16 (q, J = 6.8 Hz, 2H, allylic CH 2), 6.20 (dt, J = 15.5 and 6.8 Hz, 

1H, PhCH=CH), 6.33 (d, J = 15.5 Hz, 1H, PhCH=CH). 

2.6.1.6 Method 6: 

Carbonylmethylenation 

The reaction of methyllithium or trimethylaluminum with molybdenum(V), molybdenum(VI), 

tungsten(V), and tungsten(VI) chlorides in tetrahydrofuran or diethyl ether at 

low temperatures produces complexes that liberate methane and convert into thermolabile 

ì-methylene complexes upon warming. The exact nature of these reagents has not 

been determined, but their subsequent addition to aldehydes and ketones results in their 

methylenation at the carbonyl function. The low basicity of these compounds proves advantageous 

in carbonylmethylenation of base-sensitive substrates, such as readily enolizable 

ketones as in the synthesis of 35 (Scheme 13). [60] By comparison, methylidenetriphenylphosphorane 

(Ph 3P=CH 2) provides only a 16% yield of 35. The base-sensitive ketone 

36 is cleaved via a retro-aldol process by methylidenetriphenylphosphorane as well 

as weakly basic chromium reagents. In contrast, molybdenum(V) and tungsten(V) reagents 

are capable of methylenating 36 with high regioselectivities. [61] The activity of 

these reagents is restricted only to a surprisingly small degree by alcohol and water, 

thus permitting carbonylmethylenation in aqueous or alcoholic media with useful applications 

to hydrophilic substances. 

The molybdenum reagents in particular display high aldehyde selectivities, paralleling 

those observed for alkylchromium(III) reagents in carbonylalkylation (Section 2.6.4.5). 

This is illustrated in Scheme 13 by the carbonylmethylenation of 37. [61,62] Basic groups 

such as hydroxy, alkoxy, dimethylamino, or alkylsulfanyl, in Æ- orâ-positions relative to 

a carbonyl group, exercise an accelerating effect. This neighboring effect permits the 

selective monomethylenation of diketones such as 36, the selectivity depending on the 

solvent in the order dichloromethane < tetrahydrofuran < 1,2-dimethoxyethane. 1,3-Diketones 

and 1,3,5-triketones can be selectively monomethylenated. In the case of triketones, 

a peripheral oxo group is methylenated. Ketones react faster than enones. The 

reagents obtained from trichlorooxomolybdenum(V), tetrachlorooxomolybdenum(VI), 

or decachlorodimolybdenum(V) in tetrahydrofuran do not alter a number of functional 

groups that are attacked by other methylenating agents. These include acyl chlorides, anhydrides, 

esters, amides, diaryl-substituted 1,2-diketones, nitro aromatics, alkenes, and 

dienes, as well as the individual compounds diphenylketene, benzonitrile, diphenylacetylene, 

chlorobenzene, benzyl chloride, and dichloromethane. [60] The corresponding tungsten 

compounds have not been well investigated. The reason for this lack of reactivity is 

in some cases due to the formation of stable reagent–substrate complexes, from which 

the substrate is released unchanged on addition of water. Functional groups that, on the 

other hand, interfere with the carbonylmethylenation reaction are azomethines, epoxides, 

and nitroso aromatics. A comparison of these molybdenum and tungsten reagents 

with other carbonylmethylenating agents in various applications is available. [60]

2.6.2 Metal–Carbyne Complexes 103 

Scheme 13 Carbonylmethylenation [60–62] 

Ph 

Ph 

O 

O 

O 

Ph 

37 

36 

WOCl 3/MeLi (1:2) (1.5 equiv) 

THF, −78 to 45 o C, 18 h 

95% 

Ph 

O 

1. A or B 

2. H + OH OH OH 

, H2O + 

O 

35 

Ph 

O 

A: WOCl3/MeLi (1:2) (1 equiv) 43% 

B: MoOCl3/MeLi (1:2) (1 equiv) 38% 

MoOCl3/MeLi (1:2) (2 equiv) 

THF, −78 to 20 oC, 18 h 

Carbonylmethylenation of 4-(4-Acetylphenyl)-4-hydroxypentan-2-one (36); 


To a red-brown suspension obtained by methylation of MoOCl 3(THF) 2 (1.57 g, 4.3 mmol) 

with MeLi (8.7 mmol) in THF (30 mL) at –708C was added dropwise a soln of 4-(4-acetylphenyl)-4-hydroxypentan-2-one 

(36; 0.48 g, 2.16 mmol) in THF (2 mL). The mixture was 

further stirred at –708C for 4 h, followed by warming to rt over 12 h. This was hydrolyzed 

with sat. aq NaHCO 3 (10 mL). After separation of the two phases and Et 2O extraction of the 

aqueous phase, the combined organic fractions were dried (Na 2SO 4), and the solvent was 

removed by rotary evaporation. Flash chromatography (3 cm ” 16 cm, silica gel, CH 2Cl 2/ 

acetone 40:1) afforded 2-(4-isopropenylphenyl)-4-methylpent-4-en-2-ol {fraction 1; yield: 

0.04 g (9%); IR í~ max: 3500 cm –1 (br, OH); 1 H NMR (CDCl 3, ä): 4.77 [m, 1H, CH 2C(CHH)CH 3], 

4.91 [m, 1H, CH 2C(CHH)CH 3], 5.09 [m, 1H, aryl-C(CHH)CH 3], 5.40 (m, 1H, aryl- 

C(CHH)CH 3]} as a colorless oil, 2-(4-acetylphenyl)-4-methylpent-4-en-ol [fraction 2; yield: 

0.18 g (38%); IR í~ max: 3420 cm –1 (br, OH); 1 H NMR (CDCl 3, ä): 4.75 (m, 1H, C=CHH), 4.91 

(m, 1H, C=CHH)] as a yellow oil, and unreacted 4-(4-acetylphenyl)-4-hydroxypentan-2one 

[fraction 3; yield: 0.08 g (17%)]. 


Metal–Carbyne Complexes 

As for the case of carbene complexes, carbonyl-free carbyne (Schrock-type alkylidyne) 

complexes are most common for high oxidation state (‡4) molybdenum and tungsten systems, 

[63] although chromium examples are known. [64] For the purpose of formal oxidation 

state assignment, the carbyne ligand is considered as (RC 3– ). The majority of d 0 complexes 

possess the formula M(”CR)X 3, but many adducts with neutral two-electron donor ligands 

L,M(”CR)X 3L n (n = 1 or 2), are also known. Derivatives with more electronegative X groups 

(e.g., fluorinated alkoxides) form base adducts more readily. The most common supporting 

ligands (X) are bulky alkyl ligands, alkoxides, and halides, but derivatives with 

amides, and alkyl- and arylthiolates are also known. Typical ligands (L) are amines, ethers, 

and phosphines. In lower formal oxidation states (+4 and +5), phosphines and halides or 

cyclopentadienyl coligands are usually found. The halide derivatives are the most versa- 

Ph 

O 

89% 

+ 

Ph 

5% 

9% 

2% 



tile for further transformations by ligand exchange. Exchange of the carbyne and an alkyl 

ligand by intramolecular scrambling of the Æ-H atoms is possible. [65,66] Since the carbyne 

function is polarized as M(ä + )”C(ä – ), these compounds are susceptible to electrophilic attack 

at the carbyne ligand (e.g., protonation) and nucleophilic attack at the metal center 

(e.g., ligand addition). The addition of acids (HX) converts carbyne complexes into carbene 

complexes (see Section 2.6.1.4), [7] although, in many cases, the reagents attack other ancillary 

ligands and the carbyne function remains intact. Examples are the reactions of trialkyl 

derivatives with hydrochloric acid, ammonium chloride, or carboxylic acids. [67–69] 


2.6.2.1 Method 1: 

By Æ,Æ-Hydrogen Elimination from Alkyl Complexes 

The increase of steric bulk in a high oxidation state complex containing alkyl ligands, or 

the in situ generation of encumbered complexes of this type by transmetalation reactions 

(see Section 2.6.1.1), induces Æ,Æ-hydrogen elimination processes with formation of carbyne 

products. The alkylation reaction works better from oxo or alkoxo derivatives than 

from the corresponding chlorides, because these are less susceptible to competing reductive 

processes. [70] This reaction appears to be the preferred entry into 2,2-dimethylpropylidyne 

derivatives of molybdenum(VI) and tungsten(VI) through formation of the tris(2,2dimethylpropyl) 

derivatives 38 and 39 (see Scheme 14). Other 2,2-dimethylpropylidyne 

derivatives are then readily obtained by treating 38 and 39 with sufficiently strong acids, 

e.g. hydrochloric or carboxylic acid, or by further ligand exchange from the trichloride 

derivatives. This process is presumed to take place stepwise, via intermediate carbene 

complexes (see Section 2.6.1.4), even when these are not observed. Some carbyne products 

have been obtained by alkane elimination from carbene complexes, [15] although 

this strategy does not appear to have general synthetic utility. 

A particular case of Æ,Æ-hydrogen elimination from an alkyl ligand leads to the formation 

of complex 40. [71] The two hydrogen atoms are eliminated as dihydrogen rather 

than being transferred to alkyl ligands. Thus, the reaction involves a formal metal oxidation 

and is so far limited to the system shown. The process is much faster for tungsten 

than for molybdenum, this being ascribed to a more favorable pre-equilibrium yielding 

the alkylidene–hydride intermediate. While the alkyl precursors can be isolated for molybdenum, 

they may only be obtained in situ for tungsten by transmetalation from the 

corresponding chloride. Other related rearrangements for cycloalkyl derivatives, leading 

to carbyne products in some cases, have also been observed for this system (see Section 

2.6.2.5). [72] The synthesis of 41 [73] may be mechanistically related to the synthesis of 40, 

the dihydrogen byproduct being transferred to the vinyl group. 

Scheme 14 Æ,Æ-Hydrogen Elimination Processes [67,68] 

MoO 2Cl 2 

WCl 3(OMe) 3 

t-BuCH2MgCl (6 equiv) 

Et2O, −78 oC 34% 

t-BuCH2MgCl (6 equiv) 

Et2O, −78 oC 50−70% 

CBu t 

Mo 

But CH2Bu 

H2C t 

CH2But 38 

Bu t H 2C 

CBu t 

W CH2But CH2But 39


N 

M 

N 

N 

Cl TMS 

TMS 

N 

TMS 

R 1 CH2Li 

Et 2O 

or THF 

M = Mo, W; R 1 = H, Me, Pr, Ph, TMS, t-Bu 

WBr 2(PMe 3) 4 

THF, 69 o TMS 

C 

90% 

TMS 

TMS N 

N 

CH2R 

N 

M 

1 

TMS 

N 

CEt 

PMe3 

Me3P W PMe3 Me3P Br 

41 

25−80 o C 

− H 2 

73−91% 

TMS 

TMS N 

N 

CR 1 TMS 

Tris(2,2-dimethylpropyl)(2,2-dimethylpropylidyne)tungsten(VI) (39): [68] 

A soln of WCl 3(OMe) 3 (19.1 g, 50 mmol) in a mixture of THF and Et 2O was added very slowly 

to 1 M t-BuCH 2MgCl (0.3 mol) in Et 2Oat–78 8C with vigorous stirring. The color of the 

soln gradually turned yellow-green. After the addition was complete, no significant 

amount of precipitate was apparent. The mixture was allowed to warm slowly from –78 

to 258C over a period of 10 h to give a red-brown soln and abundant precipitate. After filtration 

from Celite followed by washing of the filter cake with Et 2O, the solvent was removed 

in vacuo to give a thick red-brown oily liquid. Pentane (200 mL) was added to the 

residue, followed by another filtration and evaporation to dryness. The resulting oily red 

liquid was distilled at ca. 808C/0.001 Torr through a short-path distillation apparatus; 

yield 55–60%. An additional 5–10% yield can usually be recovered by extracting the tarlike 

residue with pentane, filtering off the insolubles, removing the pentane in vacuo, and 

again distilling the residue as before. 1 H NMR (benzene-d 6, ä): 1.66 (Ct-Bu); 13 C{ 1 H} NMR 

(benzene-d 6, ä): 316.2 (W”C). 

Ethylidyne(N¢-(trimethylsilyl)-N,N-bis{2-[(trimethylsilyl)amino-kN]ethyl}ethane-1,2-diamido-kN,kN¢)tungsten(VI) 

(40, M=W;R 1 = Me); Typical Procedure: [71] 

An Et 2O (25 mL) soln of [WCl{N(CH 2CH 2NTMS) 3}] (0.20 g, 0.345 mmol) was treated with 

EtLi (0.019 g, 0.52 mmol) at 258C. The mixture turned light yellow as gas evolved. The resulting 

mixture was stirred for another 3 h and then evaporated to dryness in vacuo. The 

yellow residue was extracted with pentane (60 mL), and the extract was filtered. The filtrate 

was concentrated to ca. 5 mLin vacuo and chilled at –408C for several h to yield the 

product as light yellow crystals; yield: 0.16 g (81%); 1 H NMR (benzene-d 6, ä): 3.73 

(W”CCH 3, 3 J WH = 7.9 Hz); 13 C{ 1 H} NMR (benzene-d 6, ä): 274.33 (W”C). 

2.6.2.2 Method 2: 

By Addition of Alkynes to Compounds with Metal-Metal Triple Bonds 

Symmetrical alkynes provide access to carbyne complexes 42 upon reaction with symmetrical 

triply bonded tungsten alkoxy, aryloxy, and mixed alkyl–alkoxy complexes 

(Scheme 15). [74,75] This reaction occurs readily when R 1 is a simple alkyl group but also 

for functionalized alkynes, more easily so in the presence of nitrogen donors (in which 

case the base adducts are obtained). [74] This reaction is very sensitive to steric factors. 

The formation of alkyne adducts, bis-alkyne adducts, and products of C-C couplings are 

possible alternatives. [75,76] Other group 6 triply bonded dimers such as hexakis(dimethylamido)- 

or hexaalkylditungsten(III) and molybdenum alkoxides do not cleave internal alkynes. 

M 

N 

40 

N 



Unsymmetrical alkynes can often be cleaved even if one of the substituents is bulky, 

giving a 1:1 mixture of the two carbyne products. However, use of an excess of the alkyne 

increases the yield of one carbyne product, e.g. 43, by the metathesis procedure described 

in Section 2.6.2.3, provided the lower-boiling alkyne is removed. Some of these reactions 

afford satisfactory results only in the presence of a stabilizing base, e.g. quinuclidine. [74] 

Terminal alkynes react with both tungsten and molybdenum alkoxides, but the CH product 

is not isolable unless a stabilizing base is present. [77] The triple bond of selected nitriles 

is also cleaved to afford a mixture of the carbyne and the sparingly soluble nitride products. 

[78,79] 

Scheme 15 Addition of an Alkyne to a Compound Containing 

a Metal-Metal Triple Bond [74,79] 

X 3W WX 3 + R 1 C CR 1 

pentane, Et2O DME or THF 


47−91% 

WX 3 = W(Ot-Bu) 3, W(CH 2t-Bu)(O-iPr) 2 

R 1 = Me, Et, Pr, CH 2NMe 2, CH 2NEt 2, MOM, CH 2OTMS 

(Bu t O) 3W W(OBu t ) 3 + R 1 C CR 2 

pentane, Et2O 

DME or THF 


R1 = t-Bu, TMS, Ph, 

R2 CH CH2, CH(OEt)2, CO2Me, CH2CO2Me, Ac, St-Bu 

= Me, Et 

2 W( CR1 )X3 42 

W( CR 

43 

1 )(OBut ) 3 W( CR2 )(OBut + 

) 3 

Tri-tert-butoxy(ethylidyne)tungsten(VI) (42,X=Ot-Bu; R 1 = Me); Typical Procedure: [74] 

But-2-yne (80.1 ìL, 1.02 mmol) was added to a soln of [W 2(Ot-Bu) 6] (0.75 g, 0.93 mmol) in 

pentane (30 mL) at –408C. The soln was maintained at –408C for 1 h and allowed to 

warm to rt. The orange color faded to light amber, and after 2 h at rt the volatile components 

were removed in vacuo, leaving a light brown solid. Larger scale preparations sometimes 

yielded a brown oil initially, but the oil always crystallized with time in vacuo or 

when seeded. Sublimation of the light brown residue at 258C/10 –6 Torr onto a –788C 

probe afforded the pure, white product; yield: 0.59 g (74%). This material is very oxygenand 

moisture-sensitive and darkens slightly when removed from the probe in a drybox. It 

was generally prepared in pentane or THF and utilized directly for further reactions, assuming 

a quantitative yield. 13 C{ 1 H} NMR (benzene-d 6, ä): 254.3 (W”CMe). 

2.6.2.3 Method 3: 

By Stoichiometric Alkyne Metathesis 

A variety of alkoxo–carbyne complexes may be obtained from a preexisting carbyne complex 

and an alkyne by a metathesis process (Scheme 16). This exchange takes place via a 

metallacyclobutadiene intermediate 44, which has been observed or isolated for the corresponding 

aryloxo and fluorinated alkoxo systems. Such intermediates have greater stability 

for the tungsten systems. [67] This procedure is synthetically useful for symmetrical, 

unsymmetrical, and terminal alkynes. Like the reactions examined in Section 2.6.2.2, 

these are also sensitive to steric factors. [67,74] Electronic factors are also important, however, 

fluoroalkoxo complexes reacting more readily than the corresponding alkoxo complexes 

without fluorine substituents. Terminal acetylenes also react with bulkier carbyne 

complexes, but the reaction is often complicated and other products (e.g., deprotonated 

metallacyclobutadiene derivatives) may be obtained, limiting the synthetic utility. [67]

Scheme 16 Stoichiometric Alkyne Metathesis [67,74] 

M( CR 2 )(OR 1 ) 3(L) + R 3 C CR 4 (excess) (R 1 O) 3(L)M 

44 

R 2 

R 3 

M( CR 3 )(OR 1 ) 3(L) 

R 4 

+ R 2 C CR 4 

M L R 1 R 2 R 3 R 4 Conditions Yield (%) of 

[M(”CR 3 ) 

(=OR 1 ) 3(L)] 

Mo DMECMe(CF 3) 2 t-Bu a a Et 2O, rt, 

15 min 

Mo – t-Bu t-Bu b H E t 2O, rt, 

30 min 

W quinoline t-Bu Me C”CEt Et pentane, rt, 

2d 

a R 3 =R 4 = Me, Et, Pr, Ph. 

b R 3 = Pr, iPr, Ph. 


80–90 

quant. 

Addition of one equivalent of an internal alkyne, trichloro(1,2-dimethoxyethane-O,O¢)- 

(2,2-dimethylpropylidyne)tungsten(VI) affords a stable tungstacyclobutadiene product, 

but reaction with additional alkyne yields ç 5 -cyclopentadienyl products of further alkyne 

insertion rather than products of alkyne metathesis. [69,80] 

Butylidynetris(1,1,1-trifluoro-2-methylpropan-2-olato)molybdenum(VI); 


Excess PrC”CPr (125 ìL, 0.85 mmol) was added to [Mo(”Ct-Bu){OCMe 2(CF 3)} 3] (0.09 g, 

0.16 mmol) dissolved in Et 2O (3 mL). After 30 min, the solvent was removed in vacuo, leaving 

white needles that were pure by NMR; 13 C{ 1 H} NMR (benzene-d 6, ä): 299.3 (Mo”CPr). 

2.6.2.4 Method 4: 

By Oxidation of Fischer-Type Carbyne Complexes 

The dibromine oxidation of (alkylidyne)bromotetracarbonyl complexes of molybdenum 

and tungsten in the presence of 1,2-dimethoxyethane (DME) provides a direct access to 

DME-stabilized (alkylidyne)tribromo complexes, while the corresponding chromium systems 

lead to complete degradation. [81] The advantage of this procedure is the direct access 

to complexes with a wide variety of carbyne substituents starting from the corresponding, 

easily accessible Fischer-type carbyne precursor. The phenyl derivative 45, in particular, 

is easily synthesized in a one-pot procedure from the precursor as shown in Scheme 

17. 

Scheme 17 Oxidation of Fischer-Type Carbyne Complexes [81,82] 

Me 4N[M(COPh)(CO) 5] 

oxalyl bromide 

CH2Cl2, −78 oC MBr( CPh)(CO) 4 

Br2, DME 

CH2Cl2 −78 oC M = Mo 80% 

M = W 88% 

64 

Ref 

[67] 

[67] 

[74] 

MBr3( CPh)(DME) 

45 



Benzylidynetribromo(1,2-dimethoxyethane-O,O¢)tungsten(VI) (45,M=W): [81,82] 

Me 4N[W(COPh)(CO) 5] (10.00 g, 19.87 mmol) was completely dissolved in CH 2Cl 2 (300 mL) 

then the soln was cooled to –788C. Oxalyl bromide (1.87 mL, 20.0 mmol) was dissolved in 

CH 2Cl 2 (40 mL) and cooled to –78 8C, then quickly added against a N 2 stream to the acyl 

soln. This soln was left to stir at –788C for 15 min, then warmed in an ice bath just until 

a bright yellow color developed. It was immediately recooled to –788C; then this soln was 

filtered through a dry-ice jacketed frit, having a 2-cm layer of dry cellulose on it, into a 

cooled (–78 8C) receiving flask (500-mLSchlenk). To the soln of [WBr(”CPh)(CO) 4] at 

–78 8C was added DME (10 mL). A freshly prepared 1.0 M soln of Br 2 in CH 2Cl 2 (20 mL) 

with an additional quantity of CH 2Cl 2 (20 mL) was cooled to –788C and added (poured) 

against a strong N 2 stream as quickly as possible. The color became red briefly then dark 

orange. The stirred soln was allowed to warm to rt under vacuum; much gas was evolved 

during the warming step. The solvent was removed in vacuo and the dark brown oily solid 

was washed with pentane (50 mL). The solid was then dissolved in CH 2Cl 2 (30 mL) and filtered. 

The volume was reduced to 15 mLand pentane (100 mL) was added gradually to precipitate 

the product as a green-brown solid. This precipitation process was repeated until 

the product in CH 2Cl 2 was emerald green. The final product was a dark green microcrystalline 

powder; yield: 10.49 g (88%); 13 C{ 1 H} NMR (benzene-d 6, ä): 331.7 (W”CPh). 

2.6.2.5 Method 5: 

By Rearrangement of Vinyl Complexes 

Vinyl complexes can, under favorable circumstances, rearrange by a [1,2]-H shift to carbyne 

complexes (Scheme 18). [83] The reaction appears to proceed via a ç 2 -vinyl complex 

46, which has been isolated in some cases, [84] and thus requires an open coordination 

site on the metal center. The vinyl precursors are often prepared in situ by hydride addition 

to alkyne complexes, e.g. for the synthesis of 47 and indenyl analogues, [84] by deprotonation 

of alkene complexes, [13] or by transmetalation, as for the synthesis of 48. [73] The 

vinyl complex intermediate may not be observed in some cases. ç 3 -Allyl complexes are 

possible byproducts of this reaction when the substituents R 2 and R 3 bear Æ-hydrogen atoms 

(e.g., 47), [85] in which case the rearrangement to the carbyne product is favored by the 

presence of free ligands and higher temperatures. 

Scheme 18 [1,2]-H Shift from Vinyl Complexes [73,84] 

[M] 

R 3 

R 1 

R 2 

Mo 

(MeO)3P 

(MeO)3P 

WCl 2(PMe 3) 4 

H 

Pr i 

+ 

[M] 

R 3 

R 2 

R1 46 

NaBH4 P(OMe) 3 (excess) 

THF, rt, 2 h 

58% 

(5 equiv) 

Si(OMe) 3 

THF, reflux, 8 h 

93% 

[1,2]-R 1 shift 

Mo 

(MeO) 3P 

(MeO)3P 

47 

CMe 

PMe3 Me3P W PMe3 Me3P Cl 

48 

[M] 

CH 2Pr i 

R1 R3 R2


ç 5 -Cyclopentadienyl(3,3-dimethylbutylidyne)bis(trimethyl phosphite-P)molybdenum(IV): 

[84] 

A soln of [MoCp{ó-(E)-CH=CHt-Bu}{P(OMe) 3} 3] (0.35 g, 0.5 mmol) in hexane (10 mL) contained 

in an evacuated sealed tube (50 mL) fitted with a Westoff stopcock was heated at 

808C for 12 h. The mixture became bright yellow. The volatile material was removed in 

vacuo and the residue was dissolved in Et 2O (5 mL) and chromatographed on an aluminapacked 

column. Elution with hexane gave a bright yellow band, which was collected and 

the volume of the solvent was reduced (to 5 mL); cooling (–788C, 3 d) afforded the product 

as bright yellow crystals; yield: 0.21 g (85%); 1 H NMR (benzene-d 6, ä): 5.2 (s, 5H, Cp), 2.2 (t, 

2H, CH 2t-Bu, 3 J HP = 4.0 Hz); 13 C{ 1 H} NMR (benzene-d 6, ä): 299.8 (t, Mo”C, 2 J CP = 27.0 Hz). 

2.6.2.6 Method 6: 

By Other Rearrangement Processes 

The stability of the metal–alkylidyne bond, especially for tungsten, induces other remarkable 

rearrangements from a variey of systems. The high-yield synthesis of compound 49 

upon photolysis of hexamethyltungsten(VI) in neat trimethylphosphine involves a methyl 

migration onto a proposed carbyne intermediate (Scheme 19). [86] 

Other rearrangement processes have been established for selected cycloalkyl complexes. 

[13,72] For molybdenum complexes, the cyclobutyl complex 50 converts into the butylidyne 

product 52 without observation of a metallacyclopentene intermediate 51. [72] For 

tungsten complexes, on the other hand, alkylation of the chloro precursor complex with 

cyclobutyllithium yields the stable complex 51 directly, which is further transformed to 

the carbyne product 52 upon warming (Scheme 19). [71] Cyclopropyl derivatives undergo 

elimination of ethene and formation of a methylidyne product, while the cyclopentyl derivatives 

do not undergo the ring-opening step. 

Scheme 19 Other Rearrangement Processes [71,72,86] 

WMe 6 

Me3P (neat), hν 

− 2CH4 TMS 

TMS 

TMS N 

N 

M 

N 

N 

50 

[W( CH)(Me) 3(PMe 3) n] 

TMS 

TMS 

TMS N 

N 

M 

N 

N 

51 

M = W quant 

− CH 4 

90% 

[W(Me) 2( CHMe)(PMe 3) n] 

W(Me)( CMe)(PMe3) 4 

49 

TMS 

TMS 

TMS N 

N 

M 

N 

N 

52 M = Mo 86% 

Butylidyne(N¢-(trimethylsilyl)-N,N-bis{2-[(trimethylsilyl)amino-kN]ethyl}ethane-1,2diamido-kN,kN¢)molybdenum(VI) 

(52, M = Mo); Typical Procedure: [72] 

Compound 50 (M = Mo; 124 mg, 0.243 mmol) was dissolved in toluene (5 mL), and the soln 

was heated in a sealed tube to 608C for 2 h. The toluene was removed in vacuo, and the 

residue was dissolved in a minimum amount of pentane. The pentane soln was cooled to 

–40 8C to give brown crystals of the product after 24 h; yield: 107 mg (86%); 13 C{ 1 H} NMR 

(benzene-d 6, ä): 298.3 (Mo”C). 




The reactivity of Schrock-type carbyne complexes has to date been little exploited in organic 

synthetic applications in comparison with that of the corresponding carbene complexes 

(Section 2.6.1.5). For the most part, the interest has been limited to stoichiometric 

transformations to other organometallic products. Some carbyne compounds ([M]”CR) 

undergo Wittig-like reactions with X”Y molecules, affording [M]”X and RC”Y products. 

[63] As seen in Section 2.6.2.3, the addition of an alkyne (R 2 C”CR 2 ) to a carbyne complex 

([M]”CR 1 ) may afford the metathetical products (R 2 C”CR 1 +[M]”CR 2 ). Some of these 

complexes catalyze the alkyne metathesis reaction. [87] 

2.6.2.7 Method 7: 

Alkyne Metathesis 

Medium-large cycloalkynes 53 have been synthesized from diyne precursors by a ringclosing 

metathesis process in which a tungsten carbyne complex acts as a catalyst 

(Scheme 20). [46] The cycloalkyne obtained by this methodology can be partially reduced 

to obtain the cycloalkene exclusively as the Z-isomer. The stereoselectivity of this route 

is particularly notable, since current molybdenum- and ruthenium-based ring-closing metathesis 

catalysts usually provide mixtures of E- and Z-configured cycloalkenes from diene 

precursors (see Section 2.6.1.5.3). The catalyst tolerates various functional groups: lactones, 

lactams, and silyl ethers have been obtained by this method. The catalyst is incompatible 

with terminal acetylenes; thus, it is necessary to use precursors with R 1 ,R 2 „ H. 

The use of a high boiling point solvent (e.g., 1,2,4-trichlorobenzene) allows the removal 

of the alkyl byproduct (R 1 C”CR 2 ) under reduced pressure, with a positive effect on the 

conversion. 

Scheme 20 Cycloalkynes by Ring-Closing Metathesis of Diynes [46] 

X 

R 1 

R 1 

W( Ct-Bu)(Ot-Bu) 3 

52−97% 

R 1 = Me, Et; X = (CH 2) 2OC(O)(CH 2) 4C(O)O(CH 2) 2 

1,6-Dioxacyclotetradec-9-yne-2,5-dione [53,X=(CH 2) 2OC(O)(CH 2) 4C(O)O(CH 2) 2]; 


A soln of the diyne [MeC”C(CH 2) 2O(O)C(CH 2) 2] 2 (121 mg, 0.43 mmol) and [W(”Ct-Bu)(Ot- 

Bu) 3] (12 mg, 6 mol%) in chlorobenzene (20 mL) was stirred under argon at 808C for 2 h. 

The solvent was removed in vacuo, and the residue purified by flash chromatography 

(Merck silica gel, hexane/EtOAc 4:1). This led to the recovery of some unchanged starting 

material (12 mg, 10%) and afforded the cycloalkyne product as colorless crystals; yield: 

70 mg (73%); mp 106–1078C; 13 CNMR(ä): 173.0 (alkyne). 


Metal–ó-Alkyl and –ó-Aryl Homoleptic Complexes 

Compounds of this class are rather limited, their syntheses are generally low yielding, 

and have no general applications in organic synthesis. As is usually the case for any metal, 

the more robust complexes are those without â-hydrogens and aryl complexes. Well-characterized 

members of this class have the stoichiometries MR 6,MR 4,[MR 6] 3– ,[MR 5] 2– , 

[MR 4] – ,MR 3, and [MR 4] 2– . The MR 6 complexes are known only for tungsten and have a 

X 

53 

+ 

R 1 

R 1

2.6.3 Metal–s-Alkyl and –s-Aryl Homoleptic Complexes 111 

strong tendency to decompose by Æ-hydrogen elimination. The tetrahedral MR 4 complexes 

can only be obtained with sterically demanding ligands and are unexpectedly unreactive. 

While M(III) complexes with three unpaired electrons are common for chromium, 

no unambiguous example has been reported for molybdenum or tungsten. Delicate 

equilibria may exist between different species as a function of the size of R, the nature of 

the counterion, or even the solvent. For example, orange-yellow hexaphenylchromate(III), 

blue-green pentaphenylchromate(III), and cherry-red tetraphenylchromate(III) have been 

isolated under different conditions. [88–90] Neutral trialkylchromium(III) compounds are 

known only with very bulky R groups, e.g. bis(trimethylsilyl)methyl [CH(TMS) 2]. [91] Unambiguous 

M(II) complexes exist only for chromium. These are either paramagnetic (S =2) 

and square planar tetraalkylchromate(2–) monomers or diamagnetic tetraanionic dimers. 

The choice of nuclearity is highly dependent on the counterion and the solvent; for example, 

the lithium salt of tetramethylchromate(II) adopts a monomeric or a dimeric structure 

depending on whether the lithium cations are surrounded by tetramethylethylenediamine 

or by diethyl ether molecules. [92] 

The relatively high polarity of the metal-alkyl bonds makes these derivatives rather 

sensitive toward proton sources including water, especially when the latter can be 

activated by coordination to the metal center. Thus, these compounds must generally be 

synthesized and handled under scrupulously dry conditions. 


2.6.3.1 Method 1: 

By Transmetalation 

The only synthetic method that allows access to homoleptic alkyl and aryl complexes of 

group 6 metals is the transmetalation reaction (Scheme 21). Competitive electron-transfer 

processes and equilibria of association/dissociation of the alkylating reagent are often 

the reasons for the moderate yields usually associated with these syntheses. There is no 

general rule as to the best reagents and conditions to use for a specific product. Lithium 

and magnesium reagents are typically used, although other alkylating sources have also 

been employed. This is exemplified by the synthesis of hexamethyltungsten(VI) (54) [93,94] 

and tetracyclohexylchromium(IV) (55). [95] As a general rule, lithium reagents are more reactive 

than Grignard reagents, but have a greater tendency to engage in single-electrontransfer 

(SET) side reactions. The choice of solvent may also be a determinant factor. 

Tetrahydrofuran, diethyl ether, and toluene are the most commonly used solvents, the 

latter disfavoring SET processes. The group 6 metal sources are typically the halides, but 

the alkoxides have also been used, the latter usually reducing the SET reactivity. Many 

neutral metal(IV) compounds are obtained from lower oxidation state precursors in 


Hexamethyltungsten(VI) (54): [94] 

CAUTION: Hexamethyltungsten(VI) is known to decompose explosively. Proper safety precautions 

should be taken during its synthesis, storage, and handling. 

A 50-mLglass container with two openings was attached to a vacuum line, and WF 6 (1.1 g, 

3.7 mmol) and pentane (10 mL) were condensed into it in vacuo and with cooling (liq N 2). 

A 1 M soln of ZnMe 2 in heptane (11.5 mL) was slowly added dropwise at –788C. The mixture 

was stirred at –358C for 2 d, filtered at –10 8C, and concentrated in vacuo at –708Cto 

afford an orange soln. The yield (53%) was determined by the quantitative reaction of 54 

with NO and weighing the resulting product [WMe 4{ON(Me)NO} 2]. 


Metal–ó-Alkyl and –ó-Aryl Non-homoleptic Complexes 

Non-homoleptic (heteroleptic) complexes containing alkyl and aryl ligands are much 

more common, exist in a wider variety of formal oxidation states and coordination environments, 

and are more versatile in organic synthesis than the homoleptic complexes. 

The use of ancillary ligands with strong ð-donating properties increases the relative stability 

of high oxidation state derivatives. Thus, M(V) and M(VI) (M = Cr, Mo) alkyl and aryl 

complexes exist when supported by oxo, imido, or nitrido ligands, [96–99] whereas no homoleptic 

counterparts are known. Non-homoleptic tungsten(VI) complexes are more common 

and stable than the homoleptic ones. 

Like the homoleptic complexes (Section 2.6.3), the non-homoleptic complexes tend 

to decompose more readily when they bear hydrogen atoms on the â-position, via the 

ubiquitous â-hydrogen elimination pathway. As this pathway necessitates an empty metal 

orbital cis relative to the alkyl group and a coplanar transition state, stable complexes 

with â-hydrogen-bearing alkyl ligands may only be obtained when one or more of the 

above requirements are not met. [100] In particular, these compounds may be isolated 

when each valence-shell metal orbital is occupied by at least one electron and when the 

ligands cis to the alkyl group do not easily dissociate. Complexes whose alkyl substituents 

bear hydrogen atoms on the Æ-position may also decompose, this process being especially 

favored for high-valent molybdenum and tungsten complexes, providing good synthetic 

methods for carbene and carbyne complexes (see Sections 2.6.1 and 2.6.2, respectively). 

Other methods of decomposition are associated with intramolecular C-H bond activation 

of ancillary ligands, which is promoted by the metal electron richness, e.g. see 

Scheme 22. [101] Finally, homolytic cleavage of the metal-alkyl bond may occur with production 

of radicals and reduced metal complexes. Aryl derivatives are more robust than 

the alkyl complexes toward this decomposition pathway. 

Scheme 22 Decomposition of Alkyl Complexes by Alkane Elimination [101] 

Mo 

Me3P Me 

Me 3P PMe 3 

benzene-d6, >40 

− CH4 oC Me3P 

Mo 

Me3P P 

Me2 

Like the homoleptic complexes, the transmetalation reaction represents the most convenient 

entry to alkyl and aryl non-homoleptic complexes of group 6 metals. The metal-alkyl 

and metal-aryl bonds may also be formed, however, by oxidative addition reactions.

2.6.4 Metal–s-Alkyl and –s-Aryl Non-homoleptic Complexes 113 


2.6.4.1 Method 1: 


The ancillary ligands often provide steric and electronic protection to the transition-metal 

center, resulting in a greater selectivity and higher yields for the transmetalation reactions 

relative to those leading to the homoleptic counterparts (see Scheme 23). A typical 

example is the synthesis of 56. [102] The empiricism in the choice of alkylating/arylating 

agent and conditions parallels that discussed for the homoleptic products in Section 

2.6.3. In addition to lithium and magnesium reagents, the occasional use of dialkylzinc 

is also reported. The synthesis of compound 57 proceeds in good yields from the tri-tertbutoxo 

precursor, whereas no product is recovered when starting from the corresponding 

trichloride. [103] While the bis(imido)chromium(VI) precursors 58 afford products 

59 [96,97,104] and mesitylmagnesium bromide reacts cleanly with dichlorodioxomolybdenum(VI) 

to afford the corresponding dimesityldioxo product, use of mesitylmagnesium 

bromide with dichlorodioxochromium(VI) leads to chromium(V) and chromium(III) products. 

[97] 

The reaction between phenylmagnesium bromide and chromium(III) chloride in diethyl 

ether leads to chromium(I)-ð-arene complexes as final products. [105,106] The initial 

reaction does, however, generate chromium(III)-ó-phenyl species, and the greater coordinating 

ability of tetrahydrofuran permits the isolation of triphenyltris(tetrahydrofuran)chromium(III). 

[107] In some cases, the reduction accompanying transmetalation may be 

synthetically useful, e.g. the synthesis of 60. [108] 

Scheme 23 Transmetalation [96,97,102,103,108] 

W(Cp ∗ ) 2Cl 2 

MeLi (2 equiv), toluene 

80 oC, 2 h 

65% 

WMe 2(Cp ∗ ) 2 

Mo( N)(OBu 

t-BuCH2MgBr (3 equiv) 

83% 

57 

t )3 Mo(CH2But ) 3( N) 

R2 CrX2( NR 

MgY (2 equiv) 

58 

59 

1 ) 2 CrR2 2( NR1 ) 2 

X = OTMS; R 1 = t-Bu; R 2 = Mes, 2,6-Me 2C 6H 3 

X = Cl; R 1 = t-Bu, 2,6-iPr 2C 6H 3; R 2 = Me, Bn 

MOCl 4 

M = Mo, W 

MeLi or MeMgCl 

22−28% 

56 

[Mg(THF) 4][MOMe4] 2 

60 

Dimethylbis(ç 5 -pentamethylcyclopentadienyl)tungsten(IV) (56); Typical Procedure: [102] 

[W(Cp*) 2Cl 2] (2.0 g, 3.8 mmol) and MeLi (0.40 g, 18.2 mmol) were treated with toluene 

(20 mL) and heated to 80 8C for 2 h, giving a red-orange soln. The mixture was filtered 

and the toluene was removed under reduced pressure. The residue was extracted into 

pentane and cooled to –788C, giving orange needles of [W(Me) 2(Cp*) 2]; yield: 1.2 g (65%); 

1 H NMR (benzene-d6, ä): 1.60 (s, 30H, C 5Me 5), –0.54 (s, 6H, WMe). 



2.6.4.2 Method 2: 

By Oxidative Addition of Alkyl Halides 

This method has mostly been used for the synthesis of chromium(III) compounds, with 

wide application in the Nozaki–Hiyama–Kishi reaction (Section 2.6.4.5). Other group 6 derivatives 

have been prepared as well. 

2.6.4.2.1 Variation 1: 

One-Electron Oxidative Additions 

Chromium(II) precursors react with alkyl halide reagents to afford a 1:1 mixture of chromium(III) 

halide and alkylchromium(III) products. The mechanism involves single-electron-transfer 

steps and radical intermediates (Scheme 24). Other radical sources may be 

used instead, including hydroperoxides or alkane/hydrogen peroxide mixtures under 

thermal, flash photolysis, or pulse radiolysis conditions. [109] This procedure has been 

used to produce the alkylpentaaquachromium(III) ion 61. [110] The latter is long-lived but 

cannot be isolated and must be generated in situ. Activated alkyl halides react thermally 

with the chromium(III) ion, while other alkyls require photolytic or radiolytic conditions. 

The addition of ligands such as ethylenediamine or saturated tetraaza macrocycles makes 

the process more favorable for both thermodynamic and kinetic reasons. 

Scheme 24 One-Electron Oxidative Addition of Alkyl Halides [110] 

[Cr(OH2)6] 2+ 

− [CrX(OH2)5] 2+ 

R1X R1• [Cr(OH2)6] 2+ 

[CrR 1 (OH 2) 5] 2+ 

Reduction of Chloroform with Chromium(II) Perchlorate: [111] 

H 2O (1 L) was freed of oxygen and then shaken with CHCl 3 (10 mL). A 0.2 M soln of chromium(II) 

perchlorate (500 mL) was added in an atmosphere of N 2 and the soln allowed to 

stand for 2 or 3 h at rt. The grayish-red soln gave no precipitate with AgNO 3 soln at rt. A 

portion (100 mL) of this soln was placed on a column (15 cm ” 2 cm) of Dowex 50-X4 (200– 

400 mesh) in the hydrogen form and the column was eluted with 1 M HClO 4 at the rate of 

1–2 drops •s –1 . A green fraction (100 mL) was soon eluted, followed by a colorless soln 

(150 mL), and then by a red fraction (110 mL). The green and red fractions were identified 

as containing [Cr(H 2O) 5Cl] 2+ and [Cr(H 2O) 5(CHCl 2)] 2+ , respectively, by UV–vis spectroscopy 

and quantitative analysis with AgClO 4 and KMnO 4. 

2.6.4.2.2 Variation 2: 

Two-Electron Oxidative Additions 

Electron-rich metal complexes containing at least one electron pair in a metal-based orbital 

may undergo a classical two-electron oxidative addition of alkyl halides, making a 

new metal-alkyl bond (Scheme 25). This synthetic strategy is thus generally limited to 

systems supported by electron-donating ancillary ligands. No synthetically useful examples 

of this type of reactivity have been described for noncarbonyl-containing group 6 organometallic 

species where the halide ion is incorporated in the coordination sphere of 

the metal. However, there are examples of two-electron oxidative addition reactions of alkyl 

halides where the halide remains as an outer sphere counterion, as in the preparation 

of 62. [102] 

61


Scheme 25 Two-Electron Oxidative Addition of an Alkyl Halide [102] 

W(Cp ∗ ) 2( 

O) 

MeI, toluene 

rt, 12 h 

77% 

[WMe(Cp ∗ ) 2( 

62 

O)] + I − 

Methyloxobis(ç 5 -pentamethylcyclopentadienyl)tungsten(VI) Iodide (62): [102] 

A soln of [W(Cp*) 2(=O)] (150 mg, 0.32 mmol) in toluene (3 mL) was treated with MeI 

(0.2 mL, 3.2 mmol) and the mixture was stirred. After ca. 5 min a yellow microcrystalline 

deposit started to form. The stirring was continued for 12 h. The mixture was filtered and 

the solid was washed with pentane (3 ” 2 mL) and dried in vacuo to give yellow crystals of 

62; yield: 150 mg (77%); IR (Nujol) í~ max: [W(=O)] 868 (s) cm –1 ; 1 H NMR (CDCl 3, ä): 2.13 (s, 

15H, C 5Me 5), 1.07 (s, 3H, WMe). 

2.6.4.3 Method 3: 

By Oxidative Addition of Alkanes and Arenes 

Alkanes and arenes may be able to add oxidatively to a suitable metal complex, forming 

an alkyl (or aryl) hydride product (Scheme 26). Arenes are more suitable than alkanes for 

this methodology, for both kinetic and thermodynamic reasons. The metal complex must 

be quite electron-rich to accomplish this process. Sufficiently reactive metal substrates 

are usually generated in situ from more stable precursors by either a thermal or a photochemical 

dissociation or reductive elimination process. For example, the tungstenocene 

leading to product 63 is generated by photolytic reductive elimination of dihydrogen 

from bis(ç 5 -cyclopentadienyl)dihydridotungsten(IV). [112] Tungstenocene may also be generated 

by thermal alkane elimination from a dicyclopentadienyl–alkyl–hydride system. 

[113] The product of the oxidative addition step may further evolve to afford more stable 

alkyl or aryl products, as is the case for the synthesis of compound 64. 

Scheme 26 Oxidative Addition of Alkanes and Arenes [112,114] 

W(Cp) 2H 2 

ON 

hν, benzene 

− H2 W 

CH2But CH2But Me4Si (neat) 

70 oC, 2.5 d 

W 

benzene 

>80% 

W 

ON CHBu t 

Me4Si 

90% 

H 

(Cp) 2W 

Ph 

63 

ON 

W 

CH2TMS CH2But (2,2-Dimethylpropyl)nitrosyl(ç 5 -pentamethylcyclopentadienyl)[(trimethylsilyl)methyl]tungsten(II) 


In a glovebox an ampule (Teflon stopcock) was charged with [W(CH 2t-Bu) 2Cp*(NO)] 

(0.048 g, 0.098 mmol) and Me 4Si (1 mL). The resulting wine-red mixture was stirred and 

heated at 708C for 2.5 d, during which time it changed to a darker red soln. The organic 

volatiles were removed under reduced pressure. The remaining dark wine-red solid was 

redissolved in pentane and filtered through Celite. The resulting soln was stored for several 

days to provide 64 as maroon crystals; yield: 0.045 g (90%); 1 H NMR (benzene-d 6, ä): 

1.54 (s, 15H, C 5Me 5), 1.35 (s, 9H, t-Bu), 0.38 (s, 9H, TMS). 

64 



2.6.4.4 Method 4: 

By Protonation of Carbene and Carbyne Ligands 

Under suitable conditions, carbene and carbyne ligands can take up protons to generate 

alkyl derivatives. The proton source must be of low acidity to avoid further protonolysis 

of the alkyl product. This methodology is of rather limited synthetic utility. Two examples 

are shown in Scheme 27. [115,116] The formation of 65 involves loss of the pyridine ligand 

and proton transfer from the silanol to the carbene ligand, while even more extensive 

changes accompany the protonation of the carbyne ligand to give alkyl complex 66. 

Intramolecular proton transfer from other ligands (e.g., other alkyl groups) is also possible. 

[65,66] 

Scheme 27 Protonation of Carbene and Carbyne Ligands [115,116] 

ON 

Mo 

CHBut py 

W( CR 1 )(OBu t ) 3 

R 1 = t-Bu, TMS 

Ph3SiOH, benzene 

rt, 90 min 

75% 

Et4NOH, THF 

62−82% 

ON 

Mo 

CH2But OSiPh3 65 

[Et 4N][W(CH 2R 1 )O 3] 

ç 5 -Cyclopentadienyl(2,2-dimethylpropyl)nitrosyl(triphenylsilanolato)molybdenum(II) 


In a glovebox, [Mo(=CHt-Bu)Cp(pyridine)(NO)] (102 mg, 0.30 mmol) and Ph 3SiOH (83 mg, 

1.0 equiv) were weighed into the reaction vessel. Benzene (20 mL) was vacuum-transferred 

onto the solids. The mixture was then warmed to rt and stirred for 1.5 h. Over the 

course of the reaction a color change from amber to dark red-brown occurred. The solvent 

was removed from the final mixture in vacuo, and the residue was extracted with Et 2O 

(2 ” 25 mL). The extracts were filtered through Celite and the filtrate was concentrated under 

reduced pressure to incipient precipitation. Well-defined red blocks formed overnight 

and were isolated by cannulation; yield: 121 mg (75%); IR (Nujol) í~ max: (NO) 1607 

(vs) cm –1 ; 1 H NMR (benzene-d 6, ä): 3.79 (d, 1H, CHH, J HH = 9.9 Hz), 0.99 (d, 1H, CHH, 

J HH = 9.9 Hz). 


Alkylchromium(III) compounds are involved in the large-scale commercial polymerization 

of ethene and propene. Well-defined complexes that mimic the activity and selectivities 

of the commercial catalyst have been obtained. [117] An application of group 6 alkyl 

and aryl complexes that has been successfully applied to organic synthesis is the addition 

reaction to carbonyl compounds (see Sections 2.6.4.5 and 2.6.4.6). Other chromium-based 

systems have been developed for single-electron-transfer chemistry, [118] oxidation of alkanes 

via hydrogen atom abstraction, [119] and asymmetric ring opening of meso-epoxides. 

[120] Although these latter systems are of interest for synthetic organic chemistry, 

they do not involve the formation of direct Cr-C bonds, and consequently these applications 

are not treated here. [121] 

66


2.6.4.5 Method 5: 

Addition of Organochromium(III) Compounds to Carbonyl Compounds 

Under certain circumstances, organochromium(III) compounds transfer their alkyl or 

aryl groups to aldehydes and, less frequently, to ketones. The particular selectivity and 

tolerance of this reaction make it particularly useful in organic synthesis. The use of these 

chromium reagents may be advantageous for use with acid-sensitive substrates, because 

of their reduced Lewis acidity relative to other transfer reagents [e.g., trichloromethyltitanium(IV) 

or alkyltriisopropoxotitanium(IV)]. 

2.6.4.5.1 Variation 1: 

Reaction of Organochromium(III) Compounds Prepared 

from Organochromium(III) Chloride by Transmetalation 

The organochromium(III) compound may be either isolated before the addition to the carbonyl 

compound or prepared in situ, as shown in Scheme 28. Triphenyltris(tetrahydrofuran)chromium(III) 

is able to react with ketones, viz. pentan-3-one (67) and cyclohexanone. 

[122] On the other hand, chlorodialkyl and dichloroalkyl derivatives are highly 

aldehyde selective, while alkylpentaaquachromium(III) is unreactive. The alkyldichlorochromium(III) 

reagent is particularly useful as it can be readily generated in situ by transmetalation 

from chromium(III) chloride and a Grignard reagent; see the formation of 

68. [123] These reagents are able to transfer the alkyl group to the organic substrate even 

in an alcoholic medium or in the presence of water. [124] Dichloro[(trimethylsilyl)methyl]chromium(III) 

allows an aldehyde-selective alkenation process after acid hydrolysis. [125] 

This procedure has been more recently supplanted by those described in the following 

variations. 

Scheme 28 Reaction of Organochromium(III) Complexes with Carbonyl Compounds [122,123] 

( )5 

O 

Cr(Ph)3(THF) 3 

THF, −30 to 20 o C 

Ph 

67 70% 

O 

H 

R 1 = Me, Pr, Bu, Bn 

1. CrR1Cl2(THF) 3, THF, −60 oC 2. H2O 65−85% 

OH 

+ 

OH 

H 

( ) 5 

R1 68 

Ph OH HO 

Reaction of Triphenyltris(tetrahydrofuran)chromium(III) with Pentan-3-one (67): [122] 

A briskly stirred suspension of [CrPh 3(THF) 3] [from CrCl 3(THF) 3 (16 g, 43 mmol) suspended 

in THF (500 mL) and PhMgBr (129 mmol)] in THF at –30 8C was treated dropwise with freshly 

distilled pentan-3-one (67; 20 mL, 190 mmol). The mixture was then allowed to warm 

up to rt. After 2 h at 208C the solvent was removed by distillation under reduced pressure 

and the product hydrolyzed with H 2O and filtered, both residue and filtrate being washed 

with Et 2O. The dried ethereal layer was evaporated and the residue (21.2 g) separated by 

distillation. The volatile component, bp 57–62 8C/0.01 Torr (14.9 g, 90 mmol, 70% relative 

to PhMgBr) was shown to be 3-phenylpentan-3-ol by a direct comparison of its IR spectrum 

with that of an authentic specimen. The semicrystalline residue (5.87 g) was chromatographed 

to give traces of oily products and 3-ethyl-4-methyl-5-phenylheptane-3,5diol; 

yield: 5.36 g (17% relative to PhMgBr); mp 90–92 8C (hexane). 

17% 

Et 



2.6.4.5.2 Variation 2: 

Reaction of Organochromium(III) Compounds Prepared 

from Chromium(II) Chloride by Oxidative Addition 

(The Nozaki–Hiyama–Kishi Procedure) 

This methodology was pioneered by Hiyama [126] and refined by Kishi [127] and Nozaki. [128] 

The organochromium reagent is readily formed from chromium(II) salts upon one-electron 

oxidative addition (Section 2.6.4.2.1) of a wide range of substrates including allyl, 

propargyl, alkenyl, and aryl halides, alkenyl trifluoromethanesulfonates, and allyl sulfonates 

and phosphates. The most convenient chromium(II) salt is the anhydrous chloride, 

which can either be purchased or prepared in situ from chromium(III) chloride and various 

reducing agents. The performance of the chromium(II) chloride reagent in forming 

the Cr-C bond is enhanced by the addition of a catalytic amount of nickel(II) chloride. 

[127,128] 

The alkylchromium(III) species are highly aldehyde selective, e.g. the formation of 69 

in Scheme 29. [126] The most important feature, however, is the unparalleled compatibility 

with a wide array of functional groups in both reaction partners. In addition, the method 

features useful stereoselectivities. Substituted allyl reagents lead to the homoallyl alcohols. 

If the allyl reagent is ª-monosubstituted, the anti-alcohol is favored independent of 

whether the starting halide is E or Z configured; see the synthesis of 70 where the antiproduct 

is obtained in 100% selectivity. [129] Alkenyl halides or trifluoromethanesulfonates 

react with complete retention of their double-bond geometry, e.g. the synthesis of 71. [128] 

These useful features have made chromium-induced inter- or intramolecular C-C bond 

formations a frequent key step in the total synthesis of molecules of utmost complexity, 

[130] including the total synthesis of brevetoxin B. [131] 

Scheme 29 The Nozaki–Hiyama–Kishi Reaction [126,128,129] 

OHC 

PhCHO + 

Ph 

OTf 

O 

Br 

+ PhCHO 

+ 

Br 

CrCl3/LiAlH4 THF, rt 

87% Ph 

CrCl2, NiCl2 (cat.) 

DMF, 25 oC 92% 

CrCl 2 (1.2 equiv), THF 

3,3,6-Trimethylhepta-1,5-dien-4-ol; Typical Procedure: [126] 

CrCl 3 (4.28 g, 27 mmol) was reduced with LiAlH 4 (513 mg, 13.5 mmol) in THF (20 mL). After 

stirring at rt for 10 min, 3-methylbut-2-enal (0.56 g, 6.1 mmol) and subsequently 1-bromo- 

3-methylbut-2-ene (2.01 g, 13.5 mmol) in THF (10 mL) were added dropwise over 20 min. 

Stirring for 3 h, followed by workup and distillation (97–100 8C/4 Torr, Kugelrohr), gave 

the product as an oil; yield: 0.90 g (88%). 

Ph 

OH 

70 

HO 

71 

66% 

Ph 

OH 

69 

O


2.6.4.5.3 Variation 3: 

Catalytic Nozaki–Hiyama–Kishi Reaction (The Fürstner Procedure) 

The examples outlined in Section 2.6.4.5.2 are stoichiometric in chromium(II) chloride 

and generally employ a large excess of this reagent. As shown in Scheme 30, reaction of 

the organic halide with two equivalents of chromium(II) halide yields the desired organochromium 

species 72 and one equivalent of chromium(III) halide. The nucleophile then 

adds to the aldehyde with formation of a chromium alkoxide species. The high stability of 

the oxygen-chromium(III) bond serves as the thermodynamic sink; the alcohol product 

is recovered by hydrolysis in the stoichiometric process. The use of halosilane, however, 

forces an exchange by virtue of the higher oxophilicity of silicon, producing an additional 

equivalent of chromium(III) halide. At this point the reaction can be made catalytic in 

chromium by simply using a reagent capable of reducing chromium(III) to chromium(II), 

e.g. metallic manganese. This modification does not compromise the scope, practicability, 

efficiency, and chemo- and diastereoselectivity of the C-C bond formation. [130,132,133] In 

addition, it reduces the consumption of the rather high-cost and toxic chromium reagent 

and paves the way for potential applications in enantioselective syntheses using chromium 

catalysts with chiral ancillary ligands. [134 ] 

Scheme 30 The Catalytic Nozaki–Hiyama–Kishi Reaction 

R 1 X 

2 CrX 2 

MnX 2 

CrX 3 

Mn 

CrX 3 

CrR1X2 72 

OTMS 

R 1 R 2 

OCrX 2 

R 1 R 2 

TMSX 

R 2 CHO 

2-Butyl-1-(4-methoxyphenyl)prop-2-en-1-ol: Typical Procedure: [130] 

A soln of 4-methoxybenzaldehyde (340 mg, 2.5 mmol), 2-[(trifluoromethyl)sulfonyloxy]hex-1-ene 

(1.06 g, 4.6 mmol), and TMSCl (0.75 mL, 6.0 mmol) in DMF (1.5 mL) and DME 

(5 mL) was dropped into a suspension of Mn powder (230 mg, 4.2 mmol), CrCl 2 (46 mg, 

0.38 mmol), and NiCl 2 (10 mg, 0.07 mmol) in DME (5 mL) at 508C. After being stirred for 

5 h at that temperature, the mixture was quenched with H 2O (15 mL) and extracted with 

EtOAc (3 ” 50 mL), and the combined organic layers were washed with brine. Aq TBAF 

(75% w/w) was added, and the soln was stirred at rt until TLC showed complete desilylation 

of the crude product. Standard workup followed by flash chromatography (hexane/ 

EtOAc 15:1) afforded the product as a colorless syrup; yield: 420 mg (76%). 

2.6.4.6 Method 6: 

Additive–Reductive Carbonyl Dimerization 

In this reaction an alkyl group R 3 is transferred from a suitable metal–alkyl complex to 

the electrophilic carbon of a carbonyl substrate 73 (Scheme 31), resulting in the deoxygenation 

and dimerization to product 74 in a single step. [135] The substrate 73 can be an 

aromatic aldehyde or ketone, a conjugated enone, or a benzoic acid derivative. The alkyl 

transfer reagents [R 3 M] are tungsten(V) compounds formulated as dialkyldipropoxo(ìpropoxo)tungsten(V) 

dimers 75. They are obtained in situ by alkylation of the correspond- 



ing dichloro dimers with lithium or Grignard reagents and they are not isolated in view of 

their extreme thermolability. A large variety of alkyl groups, (trimethylsilyl)methyl, and 

phenyl have been used as R 3 , including ones where the â-hydrogen elimination process is 

possible. [60] The procedure consists of the addition of the carbonyl substrate to 75 in tetrahydrofuran 

at –788C, followed by warming to reflux and room-temperature base hydrolysis. 

Various substituents (e.g., methoxy, dimethylamino, fluoro, chloro, and hydroxy) 

on phenyl groups are tolerated (e.g., see synthesis of 76), but the nitro and ethoxycarbonyl 

groups are not. [135] For R 3 = Me, the carbonyl group must be conjugated with an unsaturated 

group, otherwise the monomeric carbinol is obtained. With R 3 = Ph, however, 

even saturated ketones yield the additive–reductive carbonyl dimerization product. Rearrangement 

products can also be obtained, depending on the substituents linked to the 

carbonyl group; see, for example, the reaction of 2-furaldehyde (77). [60] 

Scheme 31 Additive–Reductive Carbonyl Dimerization [60,135] 

2 

Me 2N 

O 

R 1 R 2 

O 

77 

73 

CHO 

2 [R3 + M] 

O 

H 

R1 2(PrO) 2W W(OPr) 2R 

O 

1 Pr 

O 

2 

Pr 75 

R 1 = Me 82% 

Pr 

O 

Me2(PrO) 2W W(OPr) 2Me2 O 

Pr 

75 R 1 = Me 

R 1 

R 1 

R 

74 

2 

R3 R2 R3 O 

Me2N 

43% 

O 

+ 

76 

O O 

1,2-Bis[4-(dimethylamino)phenyl]-1,2-dimethylethane (76); Typical Procedure: [135] 

[W 2Cl 4(ì-OPr) 4(OPr) 4] (2.2 g, 2.50 mmol) was dissolved in THF (100 mL) at –788C, followed 

by treatment with 1.5 M MeLi in Et 2O (4 equiv), resulting in a color change to dark green. 

After 30 min, the Gilman test indicated the absence of MeLi. To this soln was added a THF 

soln (25 mL) of 4-(dimethylamino)benzaldehyde (2.50 mmol). After stirring for 15 min at 

–78 8C, the mixture was slowly warmed and refluxed for 3 h. The mixture was then hydrolyzed 

with 2 M NaOH (100 mL) at 20 8C. Et 2O (50 mL) and petroleum ether were added and 

the mixture was stirred until dissolution of the amorphous hydrolysis product occurred. 

The organic phase was removed and the aqueous phase was extracted with Et 2O 

(2 ” 100 mL). The combined organic phases were washed with H 2O and dried (Na 2SO 4). 

The solvents were removed by rotary evaporation, leaving a crude material which was 

identified (by GC in comparison with authentic samples) as a mixture of the title compound 

76; yield: 82% and 1-[4-(dimethylamino)phenyl]ethanol; yield: 4%. 


Metallacyclic Complexes 

In many respects, the synthetic methods and reactivity of metallacyclic complexes parallel 

those of analogous dialkyl complexes. Metallacyclobutanes and metallacyclopentanes, 

on the other hand, display unique features. They may easily transform into, or be pre- 

30% 

NMe2 

Et

2.6.5 Metallacyclic Complexes 121 

pared from, carbene–alkene and dialkene isomers, respectively (Scheme 32). The cyclic 

forms tend to be more stable for the heavier metal, with differences in stability of three 

orders of magnitude being reported for congeneric molybdenum and tungsten compounds. 

[8] 

Scheme 32 Transformations of Metallacyclobutanes and Metallacyclopentanes 

M 

M 

M 

M 

Metallacyclobutane complexes are involved as intermediates in alkene metathesis reactions 

catalyzed by alkylidene complexes and their use is equivalent to that of the carbene 

complexes in this particular organic application (see Section 2.6.1). Chromacyclopentane 

complexes are invoked as intermediates in the catalytic trimerization of ethene to hex-1ene. 

[136] This catalytic process takes place with good selectivity (74%), but has not yet found 

application for the oligomerization of other alkenes nor for cross-oligomerization 

processes. 


2.6.5.1 Method 1: 


This method is not as common as those described below for the preparation of group 6 

metallacyclic derivatives. Dilithium and di-Grignard reagents have been used, as exemplified 

by the syntheses of 78, 79, and 80 (see Scheme 33). [104,137] The synthesis of metallacycles 

with large ring sizes suffers from the competitive formation of oligomers and from âhydrogen 

elimination processes. 

Scheme 33 Metallacycles by Transmetalation [104,137] 

Bu 

Cr N 

tN But Br 

N Br 

N 

Me2 Cr 

Cl 

Cl 

Et 2O, −30 o C 

Li 

CH(TMS)Li(TMEDA) 

CH(TMS)Li(TMEDA) 

64% 

THF, −20 o C 

77% 

Li 

Bu 

Cr 

tN ButN N 

Me 2 

TMS 

TMS 

78 

Cr 

79 



N 

Me2 Cr 

Cl 

Cl 

ClMg 

THF, −30 o C 

49% 

Butane-1,4-diyl(ç 5 -pentamethylcyclopentadienyl)(trimethylphosphine)chromium(III); 


[CrCp*Cl 2(THF)] (100 mLof a 0.085 M THF soln, 8.5 mmol) was treated with Me 3P(1mL, 

9.88 mmol) and cooled to –508C. 1,4-Dilithiobutane (35 mLof a 0.277 M soln in Et 2O) was 

added slowly and the mixture was stirred at –358C. The mixture was evaporated to dryness 

and the residue was extracted with pentane (2 ” 150 mL) at –208C. The extract was 

filtered, cooled to –788C, and the resulting blood-red crystals isolated and dried under 

high vacuum; yield: 2.06 g (76%). 

2.6.5.2 Method 2: 

By Reductive Coupling of Alkenes 

This method is specific for metallacyclopentanes. The alkene-coupling process is favored 

by metal reduction. A typical synthetic strategy is the in situ reduction of a metal halide 

precursor in the presence of the alkene; see, for example, the synthesis of 79 in Scheme 

34. [137] An alkylidene precursor may also lead to a metallacycle with elimination of the carbene 

ligand as in the synthesis of 81, representing a deactivation pathway for alkene metathesis 

catalysts. [138] The two alkenes may be generated in situ in the coordination sphere 

by rearrangement processes, such as intramolecular hydrogen transfer from an alkyl–vinyl 

precursor. [139] 

MgCl 

N 

Me 2 

Scheme 34 Metallacyclopentanes by Reductive Coupling of Alkenes [137,138] 

N 

Me2 TMS 

N 

Cr 

Cl 

Cl 

Ph 

N 

W 

CH2But CH2But N 

TMS 

THF, −30 o Mg, H2C CH2 (excess) 

C 

90% 

H2C CH2 

(excess), 80 o C 

TMS 

N 

N 

Me 2 

Cr 

79 

Ph 

N 

W CH2 N 

TMS 

Cr 

80 

TMS 

N 

Ph 

N 

W 

N 

TMS 

81 

Butane-1,4-diyl(ç 5 -pentamethylcyclopentadienyl)(trimethylphosphine)chromium(III); 


The compound described in the experimental procedure in Section 2.6.5.1 can also be prepared 

in 68% yield by reacting [CrCp*Cl 2(THF)] with active Mg and Me 3PinanEt 2O soln 

saturated with ethene at –78 to –108C.

2.6.6 Complexes with Triply Bonded Heteroelement Ligands 123 

2.6.5.3 Method 3: 

By Addition of Alkenes to Carbene Complexes 

This method is specific for metallacyclobutane complexes. For stability reasons this method 

has been mostly applied to the preparation of high oxidation state tungstacyclobutane 

derivatives. Given the equilibrium shown in Scheme 32, the use of excess alkene may result 

in further exchange processes. The preparation of 82 in Scheme 35 is a two-step process 

involving the elimination of 3,3-dimethylbut-1-ene. [29] 

Scheme 35 Metallacyclobutanes by Alkene Addition to Carbene Complexes [29] 

Pr i 

Pri N 

W 

ButHC OCMe(CF OCMe(CF3) 2 

3) 2 

(excess) 

TMS 

pentane, rt, 2 h 

ca. quant 

Pr i 

Pr i 

N 

OCMe(CF3) 2 

W TMS 

TMS 

OCMe(CF3) 2 

82 

1,2-Bis(trimethylsilyl)propane-1,3-diyl(2,6-diisopropylphenylimido)bis(1,1,1,3,3,3-hexafluoro-2-methylpropan-2-olato)tungsten(VI) 


Trimethyl(vinyl)silane (124 ìL) was added to a soln of [W(=CHt-Bu)(=NC 6H 3-2,6-iPr 2){OC- 

Me(CF 3) 2} 2] (212 mg) in pentane (15 mL). The solvent was removed in vacuo after 2 h to 

give a light yellow product that was recrystallized from pentane to give light yellow crystals. 

The yield of the crude product was essentially quantitative. 


Complexes with Triply Bonded Heteroelement Ligands 

The only known examples are nitride complexes, whereas terminal phosphide and arsenide 

complexes are known only without metal-carbon bonds. The lone pair on the nitride 

ligand retains sufficient Lewis basicity for coordination. Consequently, electronically 

unsaturated derivatives yield polymeric or oligomeric structures where nitrido groups 

bridge two metal centers symmetrically or asymmetrically. [140,141] Mononuclear complexes 

with terminal nitrido ligands are only found when the Lewis acidity of the metal 

center is suppressed by ð-donation from other ligands, e.g. amido ligands as in bis(diisopropylamido)[(dimethylphenylsilyl)methyl]nitridochromium(VI). 

[142] In addition, oligonuclear 

structures where the nitrogen atom forms bonds of lower order with more metal atoms 

may be preferred to a triply bonded mononuclear structure. 

Almost all organometallic nitride complexes have been obtained by adding the organic 

group(s) to inorganic substrates that already contain the M”N function. An example 

is the synthesis of compound 57 shown in Scheme 23. [103] A large number of methods for 

assembling a metal-nitrogen triple bond in inorganic compounds are outlined in a review. 

[143] Some of these methods are also of potential applicability to organometallic substrates 

and are, therefore, briefly mentioned here (Scheme 36). 

The exchange of three halides with a nitride can be accomplished by use of the 

[Hg 2N] + ion, tris(trimethylsilyl)amine, or ammonia, with elimination of mercury(II) salts, 

trimethylsilyl halide, or hydrogen halide, respectively. In the latter case, excess ammonia 

is needed to neutralize the acid. The ammonolysis of trialkyl or alkyl–carbene complexes 

has been used successfully to prepare organometallic nitride complexes of group 4 and 5 

metals (see Sections 2.8–2.11) and could potentially be used for group 6 metals as well. 

Ammonolysis of a carbyne complex would appear to have the same potential. 

Nitride complexes are also obtained by exchange of a halide with groups capable of 

readily eliminating a stable byproduct while leaving a nitrogen atom bonded to the met- 



al, with concomitant metal oxidation. Azide is the ubiquitous ligand with these characteristics, 

leading to the expulsion of dinitrogen. It can be administered either as a hydrophilic 

alkali metal salt or as the lipophilic trimethylsilyl derivative. The reaction between 

trichloro(ç 5 -pentamethylcyclopentadienyl)molybdenum(IV) dimer and trimethylsilyl 

azide generates dichloro(ç 5 -pentamethylcyclopentadienyl)nitridomolybdenum(VI) 

which, however, further evolves to more complex products. [140] An alternative to the 

azide reagent is the deprotonated 9,10-dihydro-9,10-epiminoanthracene, [144] leading to 

the elimination of anthracene. 

Other nitride compounds have been obtained by oxidation of coordinated ammonia 

ligands. The deoxygenation of a nitrosyl ligand is of potentially wide applicability. The 

oxygen-abstracting agent is an oxophilic metal complex such as trimesityl(tetrahydrofuran)vanadium(III). 

[145] Nitride compounds are also the byproducts of the addition of nitriles 

to triply bonded molybdenum and tungsten compounds (see Section 2.6.2.2). The 

splitting of the dinitrogen triple bond by a metal complex is a more recent achievement 

[146] but is so far limited to a sterically protected triamidomolybdenum system. [147] 

Other methods include the use of nitrogen trichloride, trithiazyl chloride, or aryl azide 

reagents. [143,148] Splitting of nitrous oxide (N 2O) provides mixtures of nitrido and nitrosyl 

products. [148] 

Scheme 36 Methods for Assembling the M”N Function in Inorganic Compounds 

of Group 6 Metals 

X 

[M] X 

X 

[M] R1 R1 R1 CH2R 

[M] 

1 

CHR1 − 3X − 

[M] NO 

[N 3− ] 

− 3R1 NH3 

H 

NH3 

− 2R1 Me 

− [O] 

[M] N 

− 3e − 

− 3H + 

[M] NH 3 

[M] + 1/2 N N 

− N 2 

[M] N 3 

[M] 

− N 

N3 − 

N 

[M] X 

Phosphide and arsenide complexes have also been synthesized for the first time in nonorganometallic 

complexes. [149,150] Organometallic derivatives have yet to be reported. 


Complexes with Doubly Bonded Heteroelement Ligands 

The vast majority of examples in this subclass are oxo and imido derivatives. A fair number 

of sulfido derivatives are also known, whereas selenido and tellurido derivatives and 

compounds containing a double bond to phosphorus (phosphinidene complexes) are fewer. 

The relative small number of derivatives with phosphorus and the chalcogenides may 

be attributed to the weakness of the ð-interaction. The bonds between the aforementioned 

groups and a transition metal are considered double according to valency; however, 

these bonds are often relatively short and strong in electronically unsaturated systems, 

especially for oxo and imido ligands, because of the participation of an additional 

ligand lone pair to the bonding. 

In many cases a mononuclear structure with a terminal, doubly bonded heteroelement 

ligand may be unfavorable with respect to the alternative dinuclear structure where 

the ligand adopts a bridging, singly bonded conformation (Scheme 37). Facile interconversion 

of the two forms may occur, leading to analogous synthetic strategies and reactivity. 

−

2.6.7 Complexes with Doubly Bonded Heteroelement Ligands 125 

For this reason, bridged dinuclear compounds are also included in this section, although 

emphasis is placed on the terminally bonded derivatives. The mononuclear structure is 

favored by a sterically encumbering coordination sphere, whereas electronic configurations 

that allow the formation of metal-metal bonds lead preferentially to dinuclear 

structures. First-row heteroelement-containing ligands (oxo, imido) are found terminally 

bonded more frequently than their heavier congeners because of their superior ð-bonding 

ability. 

As seen for the triply bonded heteroelement derivatives, the most common synthetic 

method for the present subclass consists of the introduction of the organic fragment into 

an inorganic substrate that already contains the desired doubly bonded heteroelement ligand. 

This is especially true for the oxo compounds, as metal oxides or oxometalate precursors 

are readily available and inexpensive starting materials. The methods discussed 

in this section are those leading to the assembly of the metal-heteroatom double bond 

starting from substrates that already contain hydrocarbyl ligands. 

Scheme 37 Monomer–Dimer Dichotomy for Doubly Bonded Heteroelement Ligands 

2 [M] E [M] 

E 

E 

[M] 


2.6.7.1 Method 1: 

From Complexes Containing Singly Bonded Heteroelement Ligands 

Singly bonded heteroelement ligands that contain a hydrogen substituent may be deprotonated 

by either an internal or an external base and transformed into doubly bonded ligands. 

In many cases the singly bonded hydrogen-bearing ligand is formed in situ by 

ligand exchange from a halide or alkoxide precursor. This is the case for the reaction between 

dichlorobis(ç 5 -pentamethylcyclopentadienyl)tungsten(IV) and potassium hydroxide, 

leading to the oxo derivative 83 by spontaneous elimination of water; see Scheme 

38. [102] In this case the proton scavenger is a coordinated base (OH) and the conjugate 

acid is expelled. In high oxidation state systems, halides may be sufficiently good bases 

leading to the expulsion of the hydrogen halide, as in the hydrolysis of tetrabromo(ç 5 -cyclopentadienyl)molybdenum(V). 

[151] An intramolecular hydrogen transfer to a carbyne ligand 

furnishes the oxo–alkyl derivative 66 (Scheme 27). 

For the synthesis of 84, aminolysis of tungsten-methyl bonds yields an imido and an 

amido ligand in a first step. An external base, however, is necessary to produce the second 

imido ligand, as neither the residual methyl ligand nor excess aniline is sufficiently basic 

to carry out the last deprotonation. [152] Imido derivatives have also been obtained from trimethylsilylamido 

derivatives, the elimination of the trimethylsilyl group (a proton equivalent) 

being favored by the presence of chloro, alkoxo, or oxo ligands. An external base 

may also serve as a catalyst for the intramolecular proton transfer to another ligand, as 

shown in the triethylamine-catalyzed isomerization of the amido–carbyne complexes 20 

to the imido–carbene complexes 21 (Scheme 7). [8,17,29] 

A reverse strategy involves rearrangement from a precursor complex that contains 

the proton on the metal center and the base on the heteroatom ligand, as in the synthesis 

of the phosphinidene complex 85. [153] Ligand exchange from halide precursors with lithium 

disulfide has provided access to sulfido derivatives, occasionally involving metal oxidation, 

as in the formation of (ç 5 -pentamethylcyclopentadienyl)trisulfidotungstate(VI) 

86. [154] The same transformation can also be performed, although in lower yield, using hydrogen 

sulfide in the presence of triethylamine. [155] 



Scheme 38 Syntheses from Complexes Containing Singly Bonded 

Heteroelement Ligands [102,152–154] 

W(Cp ∗ ) 2Cl 2 

M(Cp) 2HLi 

WMe 4 

KOH (2 equiv) 

THF, H2O R 1 PCl 2 

+ 

PF 6 − 

M = Mo, W; R 1 = 2,4,6-t-Bu 3C 6H 2 

WCp ∗ Cl 4 

1. Li2S2, THF, rt, 1 h 

2. Ph4PBr, MeCN 

61% 

(Cp ∗ OH 

) 2W 

OH 

PhNH2 (2 equiv) 

CH2Cl2, rt, 2.5 h 

87% 

H 

(Cp) 2M 

PR1Cl − HCl 

[Ph4P][WCp ∗ S3] 86 

− H2O 36% 

W 

Me NPh 

NHPh 

Et3N, CH2Cl2 rt, 15 min 

94% 

W(Cp ∗ ) 2( O) 

83 

+ 

(Cp) 2M P 

R1 85 

PF 6 − 

Me 

W 

NPh 

NPh 

84 

tert-Butylammonium Trioxo(ç 5 -pentamethylcyclopentadienyl)tungstate(VI): [155] 

An excess of t-BuNH 2 (0.08 mL, 0.76 mmol) and H 2O (0.04 mL, 2.2 mmol) was added to a 

CH 2Cl 2 soln (25 mL) of [WCp*Cl(=O) 2] (140 mg, 0.36 mmol). The soln was stirred for 1 h, 

dried (MgSO 4), and filtered through a pad of Celite. The solvent volume was reduced to 

2–3 mLand hexane was added to induce precipitation of [WCp*(=O) 3][t-BuNH 3], which 

was isolated; yield: 137 mg (86%). 

2.6.7.2 Method 2: 

From Other Complexes Containing Doubly Bonded Heteroelement Ligands 

Compounds containing a metal-heteroatom double bond may be obtained from analogous 

derivatives by exchanging the heteroelement ligand. This strategy is especially useful 

for preparing imido and sulfido derivatives from more easily available oxo compounds. 

In most cases, this method is used for the preparation of inorganic materials 

that are subsequently converted into organometallic compounds via metathetical reactions 

(see Section 2.6.1.5). [25] The new function (X) can be administered as either the diprotic 

acid (H 2X) or the cumulene (O=C=X). 

The use of the acid presents potential problems in the presence of sensitive hydrocarbyl 

ligands. For particular systems, especially high oxidation state molybdenum and 

tungsten compounds, the metal-carbon bonds are sufficiently covalent and resist protonolysis. 

This is illustrated in the oxygen/sulfur exchange leading to products 87 in 

Scheme 39. [156] The relative strengths of the metal-heteroelement double bonds are 

against the exchange of oxygen by sulfur, whereas the weaker acidity of water vs hydrogen 

sulfide favors the exchange. Concerning the oxo/imido exchange, the acidity criteri-


on favors the conversion of imido ligands into oxo ligands, especially when the amine byproduct 

is further consumed by protonation in an acidic medium. [152] The synthetically 

more useful reverse exchange is favored by trapping water with the chlorotrimethylsilane/triethylamine 

combination, leading to hexamethyldisiloxane and triethylammonium 

chloride. [25] This reaction could in fact involve the in situ conversion of the primary 

amine into a bis(trimethylsilyl)amine which subsequently carries out the exchange process. 

The direct use of a trimethylsilyl-substituted amine has also led to satisfactory results. 

[157] 

The use of cumulenes has practical synthetic use only for the conversion of oxo into 

imido derivatives by the use of isocyanates. Formation of carbon dioxide provides the necessary 

driving force to the reaction. An example is the synthesis of compound 88, where 

the incompleteness of the second step limits the yield. [158] A problem of this synthesis is 

the potential cycloaddition of the imido product with excess isocyanate, leading to metalated 

ureas. 

Scheme 39 Syntheses from Other Complexes Containing Doubly Bonded 

Heteroelement Ligands [156,158] 

H2S, CS2 

M = W; R 87 

1 = Me 77% 

M = W; R1 = CH2TMS 40% 

M = Mo; R1 MCp 

− H2O 

= CH2TMS 77% 

∗ R1 ( O) 2 MCp ∗ R1 ( O)( S) 

W 

R 1 O 

O 

R2NCO, hexane 

140 oC, 1 week 

52% 

W 

R 1 NR 2 

O 

R2NCO, hexane 

125 oC, 20 d 

23% 

W 

R1 NR2 NR2 88 

Oxo(ç 5 -pentamethylcyclopentadienyl)sulfido[(trimethylsilyl)methyl]molybdenum(VI) 

(87, M = Mo; R 1 =CH 2TMS); Typical Procedure: [156] 

A soln of [Mo(CH 2TMS)Cp*(=O) 2] (25 mg, 0.071 mmol) in CS 2 (10 mL) saturated with H 2S 

was incubated at rt for 3 d, during which time the color of the soln changed from tinted 

yellow to red. The solvent was removed with a stream of N 2. The red residue was spotted 

on a 0.25-mm-thick silica gel TLC plate and then developed with Et 2O. The red band was 

collected to give [Mo(CH 2TMS)Cp*(=O)(=S)]; yield: 20.2 mg (77%). X-ray crystallographic 

quality, dark red crystals were grown from a saturated soln in hexane at –208C. 

2.6.7.3 Method 3: 

From Complexes Containing Triply Bonded Heteroelement Ligands 

This method is restricted to the transformation of terminal nitrides to imide compounds. 

A rare example of the application of this method to organometallic substrates is the protonation 

of tris(2,2-dimethylpropyl)nitridomolybdenum(VI) to afford the imido complexes 

89 (Scheme 40). [103,159] 



Scheme 40 Synthesis from a Complex Containing a 

Triply Bonded Heteroelement Ligand [159] 

Mo(CH2Bu t )3( N) 

X = F, Cl, Br, I, OPh, OSiPh 3 

HX, THF 

40−85% 

H 

N 

Bu t H2C Mo 

X 

89 

CH2Bu t 

CH 2Bu t 

Tris(2,2-dimethylpropyl)imido(triphenylsilanolato)molybdenum(VI) (89, X = OSiPh 3); 


[Mo(CH 2t-Bu) 3(”N)] (1.0 mmol) and triphenylsilanol (1.0 mmol) were placed in a Schlenk 

tube under argon and dissolved in THF (30 mL). The mixture was stirred at 60 8C for 48 h. 

Removal of the solvent under reduced pressure and extraction of the residue with hexane 

(5 mL) afforded [Mo(CH 2t-Bu) 3(=NH)(OSiPh 3)] as a white powder. Recrystallization from 

hexane at 08C gave white crystals; yield: 240 mg (40%); IR (Nujol) í~ max:(N-H) 3371 cm –1 . 

2.6.7.4 Method 4: 

By Oxidative Processes 

The most useful oxidizing agents for the preparation of organometallic oxo compounds 

have been nitrogen oxides such as trimethylamine oxide, nitrous oxide, and nitric oxide, 

allowing the preparation of compounds that cannot be accessed by other methods, although 

the oxidations are often accompanied by the formation of other products. [160] For 

selected systems, oxidation of a low-valent precursor with the heteroelement itself in its 

natural state (e.g., O 2,S 8) is sufficiently clean to be synthetically useful for the preparation 

of oxo and sulfido complexes. This is especially true for ç 5 -cyclopentadienyl and ç 5 -pentamethylcyclopentadienyl 

systems. The synthesis of 90 (Scheme 41), involving exhaustive 

decarbonylation, represents a typical example. [161] Photochemical activation of the carbonyl 

precursor is necessary in some cases. [162] Occasionally, elemental oxygen can be replaced 

by hydrogen peroxide, as, for example, in the synthesis of 91, but this requires the 

use of a strict stoichiometric ratio to avoid further conversion into peroxo analogues. [163] 

Hydrogen sulfide also leads to oxidation, with expulsion of dihydrogen, in the synthesis 

of compound 92. [164] The synthetic utility of the oxidation with a diazene to yield a bis(imido) 

product has only been illustrated for inorganic target systems. [165] 

Scheme 41 Oxidative Processes [161,163,164] 

{MCp(CO) 2} 2 

MCp(NO)R 1 2 

R 1 = Me, CH 2TMS; M = Mo, W 

Me 3P 

H 

Me 3P 

PMe3 PMe2 

Mo 

PMe 3 

air, CHCl3 or benzene, rt 

M = Mo 69% 

M = W 14% 

30% aq H2O2, rt, 1 h 

ca. 10−50% 

H2S, pentane, −78 o C 

− H 2 

60% 

(CpMO2)O 90 

MCpO 2R 1 

91 

Me3P 

S 

Mo 

PMe3 Me3P S 

PMe3 92


Chlorodioxo(ç 5 -pentamethylcyclopentadienyl)molybdenum(VI): [162] 

In a drybox, a 100-mLglass ampule (Teflon stopcock) was charged with a soln of 

[MoCp*Cl(CO) 3] (0.980 g, 2.79 mmol) in toluene (50 mL). O 2 was bubbled through the soln 

via a 24-gauge syringe needle at a rate of approximately 2 bubbles •s –1 while the soln was 

irradiated with a 450-W medium-pressure Hg immersion lamp at 58C. The reaction was 

monitored by IR spectroscopy and was stopped after 90 min when the absorbances due 

to the carbonyl ligands of the starting material at 1700–2000 cm –1 had disappeared. 

During the reaction the soln turned from a red-orange to an amber shade with some 

blue solids precipitated on the walls of the reaction vessel. The toluene was removed under 

vacuum, leaving a brown solid. The solid was taken up in toluene in the drybox and 

the resulting soln filtered through a medium-porosity sintered-glass frit to remove insoluble 

blue impurities. Recrystallization (toluene/hexane) afforded [MoCp*Cl(=O) 2] as a yellow 

solid; yield: 0.508 g (61%); IR (benzene-d 6) í~ max: (Mo=O) 920 (s), 890 (s) cm –1 ; 1 HNMR 

(benzene-d 6, ä): 1.63 (s, C 5Me 5). 

ç 5 -Cyclopentadienyldioxo[(trimethylsilyl)methyl]tungsten (91,R 1 =CH 2TMS; M = W); 


To a stirred, purple soln of [W(CH 2TMS) 2Cp(NO)] (1.20 g, 2.65 mmol) in Et 2O (50 mL) was 

added a 30% by weight aq soln of H 2O 2 (0.22 mL, 2.8 mmol of H 2O 2). The initial purple color 

of the mixture faded over the course of 1 h to pale yellow. An IR spectrum of the final yellow 

soln was devoid of absorptions due to the nitrosyl reactant. Volatiles were removed 

from the final mixture under reduced pressure to obtain a sticky yellow solid which was 

dried at 208C/0.005 Torr for 2 h. Recrystallization of the resulting pale yellow solid from 

Et 2O/hexanes (1:1) at –208C afforded [W(CH 2TMS)Cp(=O) 2] as a white microcrystalline solid; 

yield: 0.50 g (51%); IR (benzene-d 6) í~ max: (W=O) 948 (s), 907 (s) cm –1 ; 1 H NMR (benzened 

6, ä): 5.69 (s, 5H, Cp), 0.88 (s, 2H, CH 2), 0.28 (s, 9H, TMS). 


2.6.7.5 Method 5: 

Catalytic Epoxidation of Alkenes 

High oxidation state molybdenum oxo complexes are well-established catalysts for the 

epoxidation of alkenes by alkyl hydroperoxides, such as in the production of 2-methyloxirane 

(Halcon process). Chlorodioxo(ç 5 -pentamethylcyclopentadienyl)molybdenum(VI) 

provides an organometallic example of a catalytically active system. The epoxidation reaction 

is stereoselective, as shown by the selective formation of trans- and cis-1,2-diphenyloxirane 

from the respective E- and Z-alkenes, and can be applied to highly substituted 

alkenes; see Scheme 42. [162] Studies on this system have shown that the degradation of the 

catalyst involves oxidative poisoning to an unreactive peroxo complex. [162] 

Scheme 42 Catalytic Epoxidation of Alkenes [162] 

+ 

Bu t OOH 

MCpO2Cl (cat.) 

benzene, 25 

72% 

oC O O 

1,2-Epoxycyclooctane; Typical Procedure: [162] 

In a drybox, a soln of [MoCp*ClO 2] (0.101 g, 0.338 mmol) in benzene (5 mL) was placed into 

a 50-mLbomb. Cyclooctene (1.77 mL, 13.6 mmol) was added via a syringe. Outside the drybox, 

3 M t-BuOOH in 2,2,4-trimethylpentane (11.3 mL, 34 mmol) was added. The bomb 

was heated to 608C for 3 h. The soln was then diluted to a total volume of 150 mLwith 

benzene. The organic layer was washed with H 2O (6 ” 100 mL) to remove excess hydroper- 



oxide, and then washed with sat. NaCl soln (100 mL) and dried (MgSO 4). The benzene was 

removed under vacuum, and the crude product was purified by flash chromatography 

(silica gel, EtOAc/hexane 1:9), to give 1,2-epoxycyclooctane; yield: 1.37 g (80%); >95% 

pure by 1 H NMR spectroscopy. The epoxide was identified by comparison of its 1 HNMR 

spectrum and GC retention time with those of an authentic sample. 


Complexes with Singly Bonded Heteroelement Ligands 

The most important examples of this class are the halides, alkoxides, and amides, but derivatives 

with phosphorus, sulfur, selenium, and tellurium donors are also synthetically 

useful. Most hydrocarbyl functionalities are accessible from halide and alkoxide precursors. 


2.6.8.1 Method 1: 

By Oxidative Addition of Compounds with Single Bonds 

between Heteroelements 

The most practical synthetic route to halide derivatives is the oxidation of lower-valent 

carbonyl precursors either directly with the halogens or with other stoichiometric 

halogen sources such as phosphorus pentachloride or pentabromide, or iodobenzene dichloride. 

(ç 5 -Cyclopentadienyl)- and (ç 5 -pentamethylcyclopentadienyl)dicarbonylnitrosylchromium(I) 

are oxidized by iodine to the chromium(II) products 93, [166,167] while the analogous 

molybdenum and tungsten precursors react with a range of halogen sources to 

afford the dihalo derivatives such as 94 (Scheme 43). [168] The synthesis of tetrachloro(ç 5 - 

pentamethylcyclopentadienyl)molybdenum(V) (95) requires easily available starting materials, 

[27,169] while the alternative transmetalation from MCl 5 and cyclopentadienyl sources 

is precluded by competing reductive pathways. This oxidative procedure has also been 

used to access arylsulfido derivatives by use of disulfide reagents, as shown by the synthesis 

of 96. [170] 

Scheme 43 Oxidative Addition [166–170] 

Cr(η 5 -C 5R 1 5)(NO)(CO) 2 + I 2 

MCp ∗ (NO)(CO) 2 + PCl 5 

{MoCp ∗ (CO) 3} 2 + PhΙCl 2 

Me2Si 

N 

Me2Si PPh2 CrMe 

PPh2 + 1/2 PhSSPh 

MeCN, rt 

R1 = H 88% 

R1 = Me 62% 

MCp ∗ Et2O, −20 

Cl2(NO) oC M = Mo 90% 

M = W 83% 94 

CH2Cl2, rt 

82% 

toluene, 0 oC 66% 

{Cr(η5-C5R1 5)(µ-I)(NO)} 2 

93 

MoCp ∗ Cl4 95 

Me2Si PPh2 Me 

N Cr 

Me 

SPh 

2Si PPh2 96

2.6.8 Complexes with Singly Bonded Heteroelement Ligands 131 

1-[(Diphenylphosphino-kP)methyl]-N-{[(diphenylphosphino-kP)methyl]dimethylsilyl}- 

1,1-dimethylsilanamido-k,N](phenylsulfido)methylchromium(III) (96): [170] 

To a red-brown soln of [CrMe{N(SiMe 2CH 2PPh 2) 2}] (0.16 g, 0.27 mmol) in toluene (10 mL) 

cooled to 08C was added a soln of PhSSPh (0.03 g, 0.14 mmol) in toluene (5 mL). Immediately, 

the soln changed to a dark purple color. After the mixture was stirred for 1 h at 0 8C, 

the soln was warmed to rt and the solvent was removed almost to dryness. The residue 

was quickly dissolved in hexane (1 mL) and filtered through Celite, and the solvent was 

removed in vacuo. Recrystallization from hexanes/toluene (1 mL: 3 drops) in a –408C 

freezer yielded a thick oil, which upon agitation gave 96 as purple crystals; yield: 0.12 g 

(66%). 

2.6.8.2 Method 2: 


Compounds that already contain a single bond between the metal and a heteroatom ligand 

may exchange the latter upon treatment with a suitable salt of the desired new 

ligand. The ubiquitous substrates are the halides, especially the chlorides which are easily 

accessible by oxidative procedures (Section 2.6.8.1 above) or from inorganic halide precursors. 

One example is the synthesis of 20 in Scheme 7. Like the alkylating agents discussed 

previously (Sections 2.6.3.1 and 2.6.4.1), some salts are potential reducing agents, 

especially alkyl and aryl sulfides, phosphides, and amides. The reaction of precursor 97 

(Scheme 44) with a variety of lithium salts always affords the metathesis product in 

good yield when X 1 = alkoxo or amido. [171,172] When X 1 = chloro, 5% of reduction is afforded 

by the 4-tolylamide salt with the molybdenum system, while the diphenylphosphido reagent 

yields exclusively reduction products for both molybdenum and tungsten. [173] 

Scheme 44 Transmetalation [171–173] 

M 

Cl NO 

X1 97 

+ LiX 2 

25−82% 

M = Mo, W; X 1 = Cl, NHt-Bu, Ot-Bu; X 2 = NHt-Bu, Ot-Bu, PPh 2 

M 

X 2 NO 

X 1 

Bis(2,6-diisopropylphenolato)(2,6-diisopropylphenylimido)(2,2-dimethylpropylidene)tungsten; 


The lithium salt of 2,6-diisopropylphenoxide (1.60 g, 6.19 mmol) was added to [W(=CHt- 

Bu)Cl 2(=NC 6H 3-2,6-iPr 2)(DME)] (1.82 g, 3.09 mmol) in Et 2O (50 mL) at –40 8C. The soln was 

warmed to 258C and stirred for 45 min. The mixture was filtered, and the filtrates were 

concentrated to afford an orange solid. Recrystallization of this material from a minimum 

of pentane afforded the product as a bright yellow solid in two crops; yield: 1.74 g (72%). 

2.6.8.3 Method 3: 

From ó-Alkyl Complexes 

Protonolysis of the typically polar bond between a group 6 metal and a hydrocarbyl ligand 

is usually considered to be an unwanted decomposition reaction. When metal-heteroatom 

bonds are desired, however, selective alkane-elimination reactions can sometimes offer 

significant advantages, such as ready availability and stability of the protonated 

source of the desired ligand (such as carboxylic acids, alcohols, or amines) and the absence 

of inorganic salts as byproducts (the resulting alkane is normally easily removed 



in vacuo). The synthesis of 84 proceeds via the protonolysis of the tungsten-methyl bond 

with aniline to form an arylamide ligand (Scheme 38), [152] and Scheme 45 illustrates related 

examples involving benzoic acid and ammonium chloride (98 and 99, respectively). 

[174,175] Hydrocarbyl groups other than ó-alkyls may also be used as precursors for this 

reaction, as demonstrated by the reaction of chromocene with tert-butyl alcohol to give 

100. [176] 

Scheme 45 Syntheses from ó-Alkyl Complexes [174–176] 

W(Me)2(Cp) 2 

W(Me) 2(Cp) 2 

Cr(Cp) 2 + Bu t OH 

+ PhCO2H 

+ NH 4Cl 

petroleum ether 

60 oC 90% 

THF, 56 oC 61% 

toluene, 110 oC 84% 

WMe(Cp) 2Cl 

99 

{CrCp(OBut )} 2 

100 

WMe(Cp)2(O2CPh) 

(Benzoato-O)bis(ç 5 -cyclopentadienyl)methyltungsten(IV) (98); Typical Procedure: [174] 

The compound [W(Me) 2(Cp) 2] (0.52 g, 1.52 mmol) in petroleum ether (bp 100–1208C, 

25 mL) was treated with benzoic acid (0.19 g, 1.51 mmol) and the mixture was warmed to 

608C. Methane was evolved and the soln turned red. After 1 h the soln was filtered and 

slowly concentrated under reduced pressure. Red-brown crystals separated which were 

collected by filtration, washed with petroleum ether (2 ” 15 mL), and finally recrystallized 

(petroleum ether/Et 2O 2:1); yield: 0.61 g (90%). 

2.6.8.4 Method 4: 

FromCarbene or Carbyne Complexes 

Addition of the conjugate acid of the desired ligand to a metal–carbene or –carbyne compound 

results in protonation of the hydrocarbyl ligand (see also Sections 2.6.1.4 and 

2.6.4.4), transforming it into an alkyl or carbene ligand with formation of a new metalheteroatom 

bond. Examples are the preparations of compound 19 (Scheme 7) and compound 

65 (Scheme 27). The reaction of the carbene substrate 101 with tert-butyl alcohol 

produces product 102 (Scheme 46) which, upon heating, eliminates alkane and affords a 

new carbene compound in an overall process which resembles the protonolysis of an alkyl 

complex (Section 2.6.8.3). [19] The same reaction of 101 with triphenylsilanol at low 

temperatures leads to the protonolysis product directly. 

Scheme 46 Synthesis from a Carbene Complex [19] 

NMe2 

CH2TMS 

W 

CHTMS 

N 

Ph 

101 

+ ButOH pentane 

NMe2 

CH2TMS 

W CH2TMS 

98 

Bu N 

Ph 

tO 102

2.6.9 Miscellaneous Complexes 133 

ç 5 -Cyclopentadienyl(2,2-dimethylpropyl)nitrosyl(triphenylsilanolato)molybdenum(II) 


See Section 2.6.4.4. 

2.6.8.5 Method 5: 

From Complexes Containing Doubly Bonded Heteroelement Ligands 

Like the synthesis of alkyl compounds by selective protonation of carbene groups (Section 

2.6.8.4), ligands with metal-heteroatom single bonds may be obtained from oxo or 

imido complexes via a single-proton-transfer reaction, as illustrated for 103 in Scheme 

47. Alternatively, the metal-heteroatom bond may be protonated twice, with the external 

acid (HX) providing the M-X bond of the final product, as in the synthesis of 104. The 

replacement of an oxo or imido ligand with two singly bonded ligands may induce other 

modifications in the molecule, notably Æ-hydrogen elimination from an alkyl group, 

transforming it into a carbene ligand (see Section 2.6.1.1.3). 

Scheme 47 Syntheses from Complexes Containing Doubly Bonded 

Heteroelement Ligands [102,152] 

W(Cp ∗ ) 2( O) + HBF 4 OEt 2 

WMeCp ∗ ( 

NPh) 2 

+ 

TfOH 

Et2O 50% 

Et2O 80% 

[W(Cp ∗ ) 2(OH)] + BF 4 − 

103 

WMeCp ∗ (OTf) 2( 

104 

Hydroxobis(pentamethylcyclopentadienyl)tungsten(IV) Tetrafluoroborate (103): [102] 

A soln of [W(Cp*) 2(=O)] (120 mg, 0.26 mmol) in Et 2O (10 mL) was treated with HBF 4 • OEt 2 

(excess) at –78 8C. The mixture was warmed to rt and the product was deposited as a white 

solid which was isolated by filtration; yield: 75 mg (50%); IR (Nujol) í~ max: (WO-H) 3340 (s, 

br) cm –1 ; 1 H NMR (benzene-d 6, ä): 1.88 (s, C 5Me 5). 


Miscellaneous Complexes 


2.6.9.1 Method 1: 

Allylidene Complexes from Cyclopropenes 

Ring-opening reactions of 3,3-disubstituted cyclopropenes yield allylidene complexes, a 

synthetic route of particular utility for the generation of ruthenium-based alkene metathesis 

catalysts. [47] This methodology has been extended to tungsten allylidene compounds 

using tungsten(IV) oxo [177] or imido [178] precursors (Scheme 48). These reactions proceed 

via initial formation of the ç 2 -cyclopropene adduct 105, followed by ring opening. Metathesis 

of the chloride ligands with electron-withdrawing alkoxide groups furnishes alkene 

metathesis catalysts 106 (see Section 2.6.1.5). 

NPh) 



Scheme 48 Allylidene Complexes from Cyclopropenes [177,178] 

E 

X3P 

Cl W PX3 Cl 

PX3 E = O, NC6H3-2,6-iPr2 

Ph Ph 

benzene 

PX3 = PMePh2, PEt2Ph, P(OMe)3 

OR 1 = OCMe(CF3)2 

E 

X3P 

Cl W 

Cl PX3 Ph LiOR 1 (2 equiv) 

Ph 

R 1 O 

R 1 O 

105 106 

Dichloro(2,6-diisopropylphenylimido)(3,3-diphenylallylidene)bis(trimethyl phosphite- 

P)tungsten (105, E=NC 6H 3-2,6-iPr 2; X = OMe); Typical Procedure: [178] 

A soln of 3,3-diphenylcyclopropene (1.84 g, 9.55 mmol) in benzene (30 mL) was added via 

cannula to a soln of [WCl 2(=NC 6H 3-2,6-iPr 2){P(OMe) 3} 3] (7.12 g, 8.88 mmol) in benzene 

(60 mL), and the mixture was then stirred for 2 h at 808C. The solvent was removed in vacuo, 

and the resulting orange oil was left under dynamic vacuum for an additional 12 h. 

The product was then dissolved in THF (95 mL), and the resulting orange soln was filtered. 

After all but THF (10 mL) had been removed in vacuo, addition of pentane (150 mL) yielded 

an orange powder; yield: 5.50 g (72%); 1 H NMR (90 MHz, toluene-d 8, ä): 12.85 (dt, 1H, 

J HH = 12.75, J HP = 6.37, H Æ ), 10.23 (dt, 1H, J HH = 12.75, J HP = 2.45, H â ), 3.65 [t, 18H, P(OMe) 3]. 

E 

W 

PX 3 

Ph 

Ph

References 135 

References 

[1] Coles, M. P.; Gibson, V. C.; Clegg, W.; Elsegood, M. R. J.; Porrelli, P. A., J. Chem. Soc., 

Chem. Commun., (1996), 1963. 

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141 





Volume 4 Compounds of Group 15 (As, Sb, Bi) 

and Silicon Compounds 

Product Subclass 4.4.27 Æ-Haloalkylsilanes 

Written by N. J. Lawrence

142





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Stuttgart ; New York : Thieme 

Früher u.d. T.: Methoden der organischen Chemie 

Category 1. Organometallics 

Vol. 4: Compounds of group 15 (As, Sb, Bi) and silicon 

compounds / vol. ed. I. Fleming. Responsible member 

of the ed. Board S. V. Ley. 

Authors H. Adolfsson .... – 2002 




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/ volume editor, I. Fleming 

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Vol. 4: Compounds of group 15 (As, Sb, Bi) and silicon 

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547.2 

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144 

Biographical Sketch 

Nicholas Lawrence was born in 1963 in Chichester, West Sussex, UK. 

He graduated in Natural Sciences from Cambridge University in 1985. 

He remained at Cambridge to work with Professor Ian Fleming, FRS, 

gaining his Ph.D. in 1989, having investigated synthetic organosilicon 

chemistry and the synthesis of the pancreatic lipase inhibitor tetrahydrolipstatin 

(Orlistat). This was followed by postdoctoral research 

at Leicester University, UK, with Dr. Paul Jenkins, involving synthetic 

routes towards paclitaxel. He was appointed as a lecturer at UMIST in 

1991 and Senior Lecturer in organic chemistry in 1997. He was appointed 

to a University Senior Research Fellowship at Cardiff University in 2000. His research 

interests include the development of new synthetic methods and the synthesis, 

design, and isolation (from medicinal herbs) of potential anticancer drugs. His fascination 

for organosilicon chemistry continues in the study of synthetic applications of polysiloxanes.

4.4.27 Product Subclass 27: Æ-Haloalkylsilanes 


4.4.27 Product Subclass 27: Æ-Haloalkylsilanes ................................. 146 

145 

Synthesis of Product Subclass 27 .......................................... 147 

4.4.27.1 Method 1: Direct Halogenation of Alkylsilanes ........................ 147 

4.4.27.1.1 Variation 1: Chlorination of Alkylsilanes ................................ 148 

4.4.27.1.2 Variation 2: Bromination of Alkylsilanes ................................ 148 

4.4.27.2 Method 2: Substitution of Æ-Hydroxyalkylsilanes ...................... 149 

4.4.27.2.1 Variation 1: Substitution with Chloride Using Thionyl Chloride ........... 150 

4.4.27.2.2 Variation 2: Chlorination of Æ-Hydroxyalkylsilanes with 

Triphenylphosphine and Carbon Tetrachloride .............. 151 

4.4.27.2.3 Variation 3: Iodination of Æ-Hydroxyalkylsilanes with 

Methyl(triphenoxy)phosphonium Iodide .................... 151 

4.4.27.3 Method 3: Haloalkylation of Halosilanes .............................. 152 

4.4.27.4 Method 4: Reaction of Halosilanes with Diazomethane ................ 153 

4.4.27.5 Method 5: Nucleophilic Substitution of Halo(haloalkyl)silanes .......... 154 

4.4.27.6 Method 6: Alkylation of Æ-Haloalkylsilanes ............................ 155 

Applications of Product Subclass 27 in Organic Synthesis ................... 155

146 


Æ-Haloalkylsilanes 



Æ-Haloalkylsilanes are primarily used in organic synthesis to prepare Æ-metalated silanes, 

which react with a variety of electrophiles. The nucleophilic substitution of the halogen 

atom provides a second important mode of reaction. The general patterns of reactivity 

and synthetic importance of Æ-haloalkylsilanes are revealed in the reviews of the use of 

the structurally simple examples of the class, such as (chloromethyl)trimethylsilane, [1,2] 

(chloromethyl)(isopropoxy)dimethylsilane, [3] and (1-chloroethyl)trimethylsilane. [4] By far 

the most commonly encountered examples of the class are Æ-bromo- and Æ-chloroalkylsilanes. 

The use of iodides, such as (iodomethyl)trimethylsilane, [5] is less common and 

fluorides rare with one important exception, trimethyl(trifluoromethyl)silane (Ruppert s 

reagent). Some of the most important applications of Æ-haloalkylsilanes are discussed in 

Applications of Product Subclass 27. 

The general approaches to the synthesis of Æ-haloalkylsilanes are illustrated in 

Scheme 1. Arguably the most important route (via disconnections a) involves the combination 

of an alkylsilane and the halogen. Often this is achieved using a radical reaction 

(a 1 ). Several Æ-bromo- and chloroalkylsilanes are prepared in this manner. The incorporation 

of a good leaving group at the Æ-position of the alkylsilane allows nucleophilic substitution 

using a halide (a 3 ). Fluorides and iodides, in addition to chlorides and bromides, 

can be accessed using this method. The reaction of an electrophilic halogenating agent 

with an Æ-silyl anion is another method to form Æ-haloalkylsilanes (a 2 ). Alkylation of the 

anion derived from a chloromethyl- or bromomethylsilane is an effective way of 

achieving the synthesis of Æ-haloalkylsilanes via disconnection b. Some simple halosilanes 

also bearing Æ-haloalkyl groups are transformed via reaction with nucleophiles to 

other Æ-haloalkylsilanes (disconnection c). Silylation of a carbenoid-type haloalkyl anion 

also offers a versatile method (disconnection d). The following methods (1–6) illustrate 

these approaches in more detail.

4.4.27 Æ-Haloalkylsilanes 147 

Scheme 1 General Approaches to Æ-Haloalkylsilanes 

R 

2 R 

Si 

1 

R1 + 

a2 a3 b 

R3 Si 

X 

R2 R1 R1 (R3 Si X 

R 

) 

2 

R1 R1 − 

+ R3 Si 

R2 R1 R1 c d 

a 

− 

b 

X = F, Cl, Br, I 

− 

d 

c 

R 3 

R 3 

X 

Si 

(R2 ) − 

R1 R1 + 

X 

a 1 

R 

Si 

2 

R1 R1 • + X 

R 3 

R 

Si 

2 

R1 R1 + + X− 

R 3 

+ X+ 

SAFETY: The Æ-haloalkylsilyl group does not bestow any great toxicity upon a molecule, 

and as such Æ-haloalkylsilanes do not require any special handling techniques. However, 

since they can function as alkylating agents in a synthetic sense, the more-reactive compounds, 

such as Æ-iodoalkylsilanes, should be treated with care. Æ-Haloalkylsilanes are 

stable at room temperature and can be purified by standard techniques; Æ-iodoalkylsilanes 

should be protected from sunlight. 

Æ-Haloalkylsilanes have no special spectroscopic properties. However, representative 

NMR shifts [6–8] and coupling data for the series of (halomethyl)trimethylsilanes are 

summarized in Table 1. The analysis of Æ-fluoroalkylsilanes via 19 F NMR clearly presents 

an additional method of characterization. 

Table 1 NMR Spectroscopic Data of (Halomethyl)trimethylsilanes [6–8] 

1 H(ä) 13 C(ä) d 29 Si (ä) 

Me3SiCH2F 0.15, 4.4a 80.0b –1.8c Me3SiCH2Cl 0.11, 2.72 30.3 3.5 

Me3SiCH2Br 0.13, 2.42 17.4 2.3 

Me3SiCH2I 0.03, 1.93 –11.9 2.3 

a2 J(H -F) 47 Hz. 

b1 J(F -C) 124 Hz. 

c2 J(F -Si) 27 Hz. 

d Methylene signal. 


4.4.27.1 Method 1: 

Direct Halogenation of Alkylsilanes 

The direct halogenation of alkylsilanes, via the radical substitution of a hydrogen atom at 

the Æ-carbon, sometimes gives Æ-haloalkylsilanes in acceptable yields. This approach has 

been used mostly for the preparation of simple derivatives. [9–11] The reaction is considerably 

less selective for silanes of higher complexity, unless the radical generated at the Æ- 


148 Science of Synthesis 4.4 Silicon Compounds 

position is stabilized. It is therefore not surprising that the method has found use for the 

preparation of Æ-aryl-Æ-haloalkylsilanes. There are no examples of the synthesis of Æ-iodoalkylsilanes 

by direct combination of a silane with iodine. There is one example of the 

synthesis of Æ-fluoromethylsilanes from the reaction of tetramethylsilane and fluorine. [12] 

This is unlikely to be a useful method with any general applicability. However, the Grignard 

reagents derived from chloromethyl-substituted silanes react with the electrophilic 

fluorinating agent N-fluoropyridinium triflate to give fluoromethyl-substituted silanes. [13] 

4.4.27.1.1 Variation 1: 

Chlorination of Alkylsilanes 

There are many reports of the chlorination of simple alkylsilanes. For example, the transformation 

of tetramethylsilane (1) into (chloromethyl)trimethylsilane (2) is effected by 

the action of chlorine under photochemical conditions. [14] The yield of the reaction in carbon 

tetrachloride is not high, in common with other examples of this type of reaction. 

However, significantly higher yields are obtained when the photochemical reaction is performed 

in the gas phase. [15] The reaction has been used for the synthesis of (Æ-chloroethyl)triethylsilane 

from tetraethylsilane. [16] The radical chlorination of alkylsilanes is also 

effected by sulfuryl chloride in the presence of a peroxide initiator (usually dibenzoyl peroxide). 

The reaction is mostly limited to tetraalkylsilanes and triarylalkylsilanes or those 

only bearing a methyl group. [17] Disilanes also undergo the reaction (e.g., 3 fi 4) (Scheme 

2). The reaction of trihaloalkylsilanes [14] and dihaloalkylsilanes [18] is complicated by substitution 

at other positions in the alkyl chain. Indeed, trichloroalkylsilanes undergo substitution 

preferentially at the â-position. As expected for a radical reaction, an Æ-aryl group 

accelerates the reaction and allows selective Æ-chlorination of benzylic silanes. [14,19] 

Scheme 2 Chlorination of Alkylsilanes [11,14] 

Me4Si Cl2, hν 

74% 

Me3Si Cl 

1 2 

Cl 

Me2Si SiMe2 

SO2Cl2, (PhCO)2O2 

23% 

Cl Si 

Cl 

3 4 

Cl 

Me SiMe2 Cl 

1,2-Dichloro-1-(chloromethyl)-1,2,2-trimethyldisilane (4); Typical Procedure: [11] 

1,2-Dichloro-1,1,2,2-tetramethyldisilane (3; 40 g, 214 mmol) and benzoyl peroxide (0.1 g) 

were placed in a 100-mL three-necked flask equipped with a reflux condenser and pressure-equalizing 

dropping funnel. The mixture was heated to 80–85 8C and SO 2Cl 2 (43.5 g, 

320 mmol) added dropwise through the funnel over a period of 30 min. The mixture was 

heated for a further 3 h. Additional SO 2Cl 2 (20 g, 150 mmol) was added and the mixture 

was heated for another 5 h. After flash distillation, fractionation through a short column 

packed with glass helices gave, in addition to unchanged starting material 3 (yield: 14 g; 

bp 68–69 8C/50 Torr), the Æ-chlorodisilane 4; yield: 11 g (23%); bp 84–858C/20 Torr. 

4.4.27.1.2 Variation 2: 

Bromination of Alkylsilanes 

The bromination of alkylsilanes has not found widespread use as a general route to Æ-bromoalkylsilanes. 

A rare example is the efficient bromination of (isopropyl)trimethylsilane 

(5 fi 6). [20] The related bromination of (isopropyl)dimethylsilane clearly shows that a hy-


drosilyl group is oxidized to silyl bromide under the same conditions (7 fi 8) (Scheme 

3). [21] Difluorosilanes undergo the reaction without complication. [22] An Æ-methoxymethyl 

group is cleanly transformed into a Æ-bromo-Æ-methoxymethyl group. [23,24] The bromination 

of benzyltrialkylsilanes is synthetically useful. [25–28] Numerous reports detail the efficient 

reaction of bromine or N-bromosuccinimide and a benzylsilane (e.g., 9 fi 10) under 

irradiation or in the presence of an appropriate radical initiator. This is often 2,2¢-azobisisobutyronitrile 

or benzoyl peroxide. The reaction can sometimes be complicated by 

competing dibromination; [19] an excess of N-bromosuccinimide has been used deliberately 

in the preparation of the Æ,Æ-dibromosilane 11. [29,30] 

Scheme 3 Bromination of Alkylsilanes [19–21,28] 

R 

Me2Si 

1 

5 R 1 = Me 

7 R 1 = H 

Br2, 60 o C 

R 

Me2Si 1 

Br 

6 R 1 = Me 64% (from 5) 

8 R 1 = Br 55% (from 7) 

Me3Si Ph 

NBS, CCl4 

reflux, 10 h 

Me3Si Ph 

Br 

9 10 60% 

O 

12 

NPr i 2 

SiMe 3 

NBS, (PhCO 2)O 2, CCl 4 

reflux, 10 h 

79% 

+ 

Me 3Si Ph 

Br 

11 21% 

O 

NPri 2 

Br 

2-[Bromo(trimethylsilyl)methyl]-N,N-diisopropylbenzamide (13); Typical Procedure: [28] 

N,N-Diisopropyl-2-[(trimethylsilyl)methyl]benzamide (12; 1.14 g, 3.9 mmol) in CCl 4 

(200 mL) (CAUTION) was added to NBS (1.01 g, 5.0 mmol) and benzoyl peroxide (10 mg). 

The mixture was heated under reflux and irradiated by a UV sun lamp for 90 min. The 

mixture was cooled to rt and the succinimide removed by filtration through Celite. The 

filtrate was concentrated under reduced pressure to give a crude oil. The crude product 

was purified by chromatography (silica gel) to give the Æ-bromosilane 13 as a white solid 

after recrystallization (pentane); yield: 1.14 g (79%); mp 89–90 8C. 

4.4.27.2 Method 2: 

Substitution of Æ-Hydroxyalkylsilanes 

Æ-Haloalkylsilanes are most conveniently prepared by the nucleophilic substitution by 

halide of an Æ-nucleofuge, often derived from a hydroxy group. In very general terms, 

the method is applicable to the synthesis of Æ-fluoro- and Æ-iodoalkylsilanes, in addition 

to the more common Æ-chloro- and Æ-bromoalkylsilanes. The method is mostly limited by 

the availability of the silyl electrophile. Æ-Silyl alcohols (see Section 4.4.28) are often used 

as the source of this electrophile, which is formed in situ by a variety of methods (Sections 

4.4.27.2.1–4.4.27.2.3). However, other derivatives are sometimes used. For example, (fluoromethyl)trimethylsilane 

(15) has been prepared in 38% yield by the reaction of the 

tosylate 14 [derived from (hydroxymethyl)trimethylsilane] with dry potassium fluoride 

in diethylene glycol. [31] A small amount (ca. 10%) of the ethylsilane 16 (see Applications 

13 

SiMe 3 

Br 



of Product Subclass 27) is also produced (Scheme 4). The reaction of (trimethylsilyl)methyl 

trifluoromethanesulfonate with sodium iodide is a good method for the synthesis of 

(iodomethyl)trimethylsilane. [32] A siloxy group has been used as the leaving group in the 

synthesis of 9-chloro-3-methoxy-9-(trimethylsilyl)fluorene derivatives. [33] Æ-Alkoxymethylsilanes 

can be transformed into Æ-bromomethyl- and Æ-iodomethylsilanes by the action of 

triphenylphosphine/bromine and potassium iodide/phosphoric acid, respectively. [34] A 

more widely used, and related, reaction involves the ring opening of Æ,â-epoxysilanes 

(see Section 4.4.29) by halide. In this way, Æ-halo-â-hydroxyalkylsilanes are obtained 

with high regioselectivity by treatment of the epoxide with hydrochloric, [35] hydrobromic, 

[36] and hydriodic acids (e.g., 17 fi 18) [37] or tetrafluorosilane/water/diethylisopropylamine. 

[38] The silyl group accelerates the substitution at the Æ-position, even when it 

is more sterically hindered than the â-position. 

Scheme 4 Æ-Haloalkylsilanes by Nucleophilic Substitution of a Hydroxy-Derived 

Leaving Group and Ring Opening of an Æ,â-Epoxysilane by Halide Ion [31,37] 

Me3Si OTs 

14 

17 

SiMe3 

O 

KF, (HOCH 2CH 2) 2O 

aq HI 

70% 

18 

Me3Si F + Me3Si F 

15 38% 16 10% 

SiMe3 

4.4.27.2.1 Variation 1: 

Substitution with Chloride Using Thionyl Chloride 

Early examples of the substitution of Æ-hydroxysilanes with chloride employ thionyl chloride 

as the reagent. [39] The transformation is achieved simply by mixing the alcohol with 

thionyl chloride in diethyl ether (19 fi 20, Scheme 5). A benzylsilyl group is not cleaved 

by the hydrochloric acid produced under these conditions. The reaction has not seen 

many applications, probably because the yields are not generally high. This has prompted 

the development of other methods (Sections 4.4.27.2.2 and 4.4.27.2.3). 

Scheme 5 Æ-Chloroalkylsilanes from Æ-Hydroxyalkylsilanes and Thionyl Chloride [39] 

OH 

19 

SiMe3 

SOCl2, Et2O, 0 oC to rt 

78% 

(1-Chloropropyl)trimethylsilane (20); Typical Procedure: [39] 

(1-Hydroxypropyl)trimethylsilane (19; 0.75 g, 5.8 mmol) in dry Et 2O (5 mL) was added 

dropwise at 0 8C to a stirred soln of SOCl 2 (0.76 g, 6.4 mmol) in dry Et 2O (5 mL). The resulting 

soln was stirred at 08C for 20 min and at 258C for a further 20 min and then heated 

under reflux for 1 h. Evaporation produced the Æ-chloropropylsilane 20 as a crude light 

brown oil; yield: 0.68 g (78%). 

I 

OH 

Cl 

20 

SiMe3


4.4.27.2.2 Variation 2: 

Chlorination of Æ-Hydroxyalkylsilanes with 

Triphenylphosphine and Carbon Tetrachloride 

Significant improvements to the method were accomplished by Barrett and co-workers. 

They found that conversion of Æ-hydroxyalkylsilanes 21 {prepared by the addition of [(dimethyl)(phenyl)silyl]lithium 

to aldehydes} [40] into the Æ-chloroalkylsilanes 22 is effected 

by reaction with carbon tetrachloride and triphenylphosphine without complication 

(Scheme 6). The Grignard reagent derived from 22 proved to be excellent for the synthesis 

of Æ-ketosilanes, used in the synthesis of alkenes via the Peterson reaction (see Applications 

of Product Subclass 27). The reaction and subsequent purification of 22 is not complicated 

by competing Brook rearrangement. Æ-Bromoalkylsilanes can be prepared in a 

similar fashion from Æ-hydroxyalkylsilanes by treatment with carbon tetrabromide and 

triphenylphosphine, [41] phosphorus tribromide, [42] or dibromotriphenylphosphorane. [43] 

Scheme 6 Æ-Chloroalkylsilanes from Æ-Hydroxysilanes with 

Carbon Tetrachloride and Triphenylphosphine [40] 

OH 

R 1 SiMe 2Ph 

21 

CCl 4, Ph 3P 

Cl 

R 1 SiMe 2Ph 

22 R1 = (CH2)4Me 85% 

R1 = (CH2) 6Me 87% 

R1 = Cy 82% 

R1 = Ph 65% 

(1-Chlorohexyl)dimethylphenylsilane [22, R 1 =(CH 2) 4Me]; Typical Procedure: [40] 

A soln of the Æ-hydroxysilane 21 [R 1 =(CH 2) 4Me; 18.77 g, 80 mmol] and Ph 3P (27 g, 

100 mmol) in THF (300 mL) and CCl 4 (50 mL) (CAUTION) was heated under reflux for 6 h 

in a flask under an atmosphere of argon. After cooling the solvent was removed by vacuum 

distillation. The residue was extracted with hexanes (3 ” 300 mL). Evaporation and 

chromatography (silica gel, hexanes) of the residue gave the Æ-chlorosilane 22 as a colorless 

oil; yield: 17.2 g (85%). 

4.4.27.2.3 Variation 3: 

Iodination of Æ-Hydroxyalkylsilanes with 

Methyl(triphenoxy)phosphonium Iodide 

Barrett and co-workers also found that Æ-iodoalkylsilanes can be prepared by reaction 

with methyl(triphenoxy)phosphonium iodide (e.g., 23 fi 24, Scheme 7). [44] These compounds 

are of limited synthetic value in the Peterson reaction, since iodine/metal exchange 

is difficult. Nevertheless the method for their preparation is a rare and potentially 

important one. 

Scheme 7 Æ-Iodoalkylsilanes from Æ-Hydroxyalkylsilanes [44] 

( ) 4 

23 

OH 

SiMe3 

(PhO)3PMeI 

96% 

(1-Iodohexyl)trimethylsilane [24,R=(CH 2) 4Me]; Typical Procedure: [44] 

DMF (20 mL) was added to the crude alcohol 23 [R = (CH 2) 4Me; 5 mmol] under dry N 2.To 

this soln was added (PhO) 3PMeI (3.39 g, 7.5 mmol) and the mixture stirred for 12 h in the 

dark. MeOH (2 mL) and sat. aq Na 2S 2O 3 (1 mL) were added successively. The resulting mix- 

( ) 4 

24 

I 

SiMe 3 



ture was extracted with Et 2O (3 ” 30 mL). The combined Et 2O extracts were washed with 

sat. aq NH 4Cl and brine, dried (MgSO 4), and evaporated. The residue was purified by flash 

chromatography (silica gel, hexanes) followed by Kugelrohr distillation (1108C, 0.7 Torr) 

to give the stable Æ-iodoalkylsilane 24; yield 1.36 g (96%). 

4.4.27.3 Method 3: 

Haloalkylation of Halosilanes 

The haloalkylation of chlorosilanes by the reaction of a (Æ-haloalkyl)metal species is a useful 

and reasonably general method for the preparation of Æ-haloalkylsilanes (disconnection 

d, Scheme 1). Generally, the (chloroalkyl)lithium reagents are prepared in situ by the 

deprotonation of the corresponding alkyl halide. [45] For example, (chloromethyl)lithium 

is conveniently prepared in situ by the treatment of bromochloromethane with butyllithium 

at temperatures between –70 and –60 8C, in the presence of the chlorosilane 

(25 fi 26). [45] Under these conditions butyllithium does not react with the chlorosilane. 

The method is applicable to the synthesis of a wide variety of silanes including disilanes 

and allylsilanes. Bromomethyl and iodomethyl derivatives can be prepared with increasing 

difficulty by the use of dibromomethane and diiodomethane. 3-Haloprop-1-enes react 

in the same way with chlorotrimethylsilane and lithium dicyclohexylamide efficiently 

producing Æ-haloallylsilanes (allyl bromide fi 27, Scheme 8). [46] (Halomethyl)aryl compounds 

react in the same way when lithium diisopropylamide is used as the base. [47–49] 

Several heterocyclic derivatives have been prepared by this method. [Chloro(pyridin-3yl)methyl]lithium 

[prepared from lithium diisopropylamide and 3-(chloromethyl)pyridine] 

reacts well with chlorotrimethylsilane. [50] Similar processes can be used to silylate 

the lithio derivatives of 4-(chloromethyl)pyridine, [51] 4-(fluoromethyl)pyridine, [51] and 2- 

(chloromethyl)benzothiazole. [52] (Dihalomethyl)trialkylsilanes are prepared efficiently 

from dihalomethanes, lithium diisopropylamide, and chlorosilanes. [53] Deprotonation of 

trihalomethanes with butyllithium at low temperature, followed by reaction with chlorosilanes, 

generates trihalomethylsilanes. [54] Similar processes can be effected by formation 

of the Grignard reagent derived from polybromo- or polyiodomethane. [55] 1-Bromo-1-(trimethylsilyl)cyclopropanes 

[56] can be prepared by the treatment of 1,1-dibromocyclopropanes, 

magnesium, and chlorotrimethylsilane under ultrasonic irradiation. [57] 

Scheme 8 Reaction of Halosilanes with (Æ-Haloalkyl)lithium Reagents [45,46,60] 

Cl 

Me2Si 

Br 

Bu t 

O 

BrCH2Cl, BuLi 

THF, −60 oC 71% 

Me2Si 

25 26 

O 

28 

F 

1. Cy2NLi, TMSCl, −60 oC 2. H + /H2O 

55% 

71% 

Cl 

Me3Si 

Br 

27 

1. LDA (4 equiv), TMSCl (6 equiv), −78 oC 2. H + /H2O 

Bu 

O 

t O 

F 

SiMe3 29


In general, the approach works when electron-withdrawing groups are present at the Æposition. 

For example, Æ-haloesters are easily deprotonated with lithium diisopropylamide 

and silylated to give Æ-haloalkylsilanes. [58,59] The reactions are often complicated 

by competing O-silylation. An excess of both lithium diisopropylamide and chlorosilane 

ensures a good yield of tert-butyl Æ-fluoro-Æ-(trimethylsilyl)acetate (29) from tert-butyl Æfluoroacetate 

(28). [60] 

The treatment of silyl ethers of type 30 yields Æ-chloroalkylsilanes effectively by an 

in situ method of (Æ-haloalkyl)metal formation (Scheme 9). In this case the silyl group undergoes 

intramolecular transfer from the nearby silyl ether group. [61] Elimination of hydrochloric 

acid from the Æ-chloroalkylsilane 31 is a competing reaction producing 

alkenylsilanes as byproducts. 

Scheme 9 Intramolecular Reaction of a Silyl Ether with a (Haloalkyl)lithium Species [61] 

O 

SiMe 2Bu t 

Cl 

1. BuLi, t-BuOK, −70 oC, 10 min 

2. H2O 72% 

OH 

30 31 

SiMe 2Bu t 

Allyl(chloromethyl)dimethylsilane (26); Typical Procedure: [45] 

Allyl(chloro)dimethylsilane (25; 9.7 g, 70 mmol), BrCH 2Cl (9.3 g, 70 mmol) and dry THF 

(150 mL) were added to a 500-mL three-necked flask equipped with a magnetic stirrer 

bar, N 2 inlet tube, and thermometer. The mixture was cooled to –70 8C and 1.6 M BuLi in 

hexanes (45 mL, 70 mmol) added down the cold wall of the flask via a syringe over 40 min. 

During the addition the temperature of the mixture was maintained between –70 and 

–60 8C. The soln was then warmed to rt and H 2O (50 mL) was added. The mixture was extracted 

with hexanes (3 ” 100 mL). The combined extracts were dried (CaCl 2) and evaporated 

under reduced pressure. The residue was distilled to give the Æ-chloromethylsilane 26; 

yield: 7.6 g (71%); bp 778C/80 Torr. 

4.4.27.4 Method 4: 

Reaction of Halosilanes with Diazomethane 

Halosilanes react with diazoalkanes to form Æ-haloalkylsilanes (32 fi 33, Scheme 10). The 

reaction is facilitated by copper powder or copper(II) salts. [62–64] Fluorosilanes are the least 

reactive of the halides in this type of reaction and effectively do not react in this manner. 

The reaction is most efficient with di-, tri-, and tetrachlorosilanes. The reaction between 

tetrachlorosilane and diazomethane is violent at room temperature, but can be controlled 

at low temperature. In polyhalosilanes, the introduction of one halomethyl group 

generally retards the introduction of another. Nevertheless, the method is useful for the 

synthesis of dichloro[bis(chloromethyl)]silane from trichloro(chloromethyl)silane. [65] 

Bromosilanes are more reactive than chlorosilanes. The method is applicable to halodisilanes. 

[66] The reaction of iodotrimethylsilane or trimethylsilyl trifluoromethanesulfonate 

with diazomethane does not require catalysis, whereas that of bromotrimethylsilane proceeds 

conveniently in the presence of zinc dibromide. [67] 

Scheme 10 Reaction of Halosilanes with Diazomethane [64] 

CH2N2, Cu, Et2O, −60 

45% 

32 33 

o HSiCl3 C 

Cl 

H 

Cl 

Si Cl 

Cl 



Dichloro(chloromethyl)silane (33): [64] 

CAUTION: Diazomethane is highly toxic and irritating. It is also a detonator and appropriate 

safety precautions should be taken when using this reagent (e.g., special glassware, use of a blast 

shield, etc.). For further details on the safe handling of diazomethane see refs [68,69] . 

Trichlorosilane (32; 40 g, 0.296 mol) in anhyd Et 2O (100 mL) in a 1-L three-necked flask 

equipped with a mechanical stirrer, a Y-joint holding a thermometer and a drying tube 

filled with Drierite, and a dropping funnel was cooled to –608C and Cu powder (0.5 g) 

added. A cold soln of CH 2N 2 (0.194 mol) in Et 2O (350 mL) was added slowly through the 

dropping funnel, with vigorous stirring of the mixture. N 2 evolution began immediately. 

After the addition was complete the mixture was stirred for 2 h between –65 to –608C 

under dry N 2. The mixture was allowed to warm to rt and stirred for a further 2 h. The 

Et 2O was removed by distillation through an 18-inch column packed with glass helixes. 

Another preparation of the same scale was performed and the residues combined and 

fractionally distilled to give dichloro(chloromethyl)silane (33); yield: 40 g (45% based on 

32); bp 97.0–97.4 8C/773 Torr. 

4.4.27.5 Method 5: 

Nucleophilic Substitution of Halo(haloalkyl)silanes 

Substitution at silicon of silanes already bearing bromomethyl or chloromethyl groups is 

a common process for preparing Æ-halomethylsilanes. The principle reason for the popularity 

of the method is the availability of chloro(chloromethyl)dimethylsilane and (bromomethyl)(chloro)dimethylsilane. 

[70] Nevertheless the reaction does work well with other 

halo(Æ-haloalkyl)silanes. [14,71] Addition of Grignard [14,72] and organolithium reagents occurs 

without the complication of substitution of the halogen at the Æ-position (e.g., 

34 fi 35, Scheme 11). The method has been used to prepare Æ-halomethyl-substituted vinylsilanes 

from vinyl Grignard [73] and vinyllithum reagents. [74] Allyl, [75] alkynyl, [76] aryl, [77] 

and benzyl organometallic reagents also work well. Reaction of (bromomethyl)(chloro)dimethylsilane 

with alcohols and triethylamine [and sometimes 4-(dimethylamino)pyridine] 

is commonly used to prepare (bromomethyl)silyl ethers for radical cyclization. 

Scheme 11 Reaction of an Alkynyllithium Reagent with 

Chloro(chloromethyl)dimethylsilane [76] 

( ) 5 

1. BuLi 

2. ClMe2Si 

90% 

Cl 

( ) 5 SiMe2 Cl 

34 35 

(Chloromethyl)(dimethyl)oct-1-ynylsilane (35); Typical Procedure: [76] 

1.5 M BuLi in hexanes (37.3 mL, 55.9 mmol) was added at –788C to oct-1-yne (34; 6.15 g, 

55.9 mmol) in THF (60 mL). The mixture was allowed to warm to 08C and stirred for 1 h, 

and then at rt for a further 15 min. The mixture was cooled to –788C. Chloro(chloromethyl)dimethylsilane 

(8.0 g, 55.9 mmol) in THF (20 mL) was added dropwise to the mixture 

over 1 h. The resulting mixture was stirred overnight at –788C. The mixture was allowed 

to warm to rt and sat. aq NH 4Cl (50 mL) was added and the mixture extracted with EtOAc 

(2 ” 100 mL). The organic extracts were washed with brine, dried (Na 2SO 4), and evaporated 

under reduced pressure. The residue was distilled to give (chloromethyl)(dimethyl)oct-1ynylsilane 

(35) as an oil; yield: 10.9 g (90%); bp 54–57 8C/3 Torr.


4.4.27.6 Method 6: 

Alkylation of Æ-Haloalkylsilanes 

Æ-Haloalkylsilanes are deprotonated to provide an anion that reacts readily with haloalkanes 

(disconnection b, Scheme 1). The carbanion derived from (chloromethyl)trimethylsilane 

is stable at low temperature (decomposing slowly over 1 h at –408C) and reacts 

with a variety of electrophiles. Similar stability is evident for other members of the product 

class (36 fi 37, Scheme 12). Æ-Haloalkylsilanes are most commonly deprotonated 

with sec-butyllithium at –788C in the presence of N,N,N¢,N¢-tetramethylethylenediamine 

(TMEDA). [78–80] Under these conditions Æ-elimination is not a competing reaction. 

Scheme 12 Alkylation of (Chloromethyl)silanes [78] 

PhMe2Si 

Cl 

1. s-BuLi, TMEDA, −78 oC 2. MeI 

66% 

PhMe 2Si 

36 37 

(1-Chloroethyl)(dimethyl)phenylsilane (37); Typical Procedure: [78] 

1.4 M s-BuLi in cyclohexane/isopentane (92:8) (164 mL, 0.230 mol) was added dropwise 

over 1.5 h to (chloromethyl)(dimethyl)phenylsilane (36; 40.0 g, 0.217 mol) in THF 

(260 mL) at –788C. TMEDA (24.1 g, 0.21 mol) was added dropwise to the resulting mixture 

over 20 min, maintaining the temperature at –788C. The soln was stirred for 1 h at –788C 

and then allowed to warm to –558C. MeI (41.2 g, 0.29 mol) in THF (70 mL) was added dropwise 

over 1 h, and the mixture stirred for a further 40 min at –408C and then 16 h at rt. 

The mixture was added carefully to cold sat. aq NH 4Cl (700 mL) and extracted with Et 2O 

(3 ” 350 mL). The combined organic extracts were washed with H 2O, dried (Na 2SO 4), and 

evaporated under reduced pressure. The residue was distilled to give the silane 37 as an 

oil; yield: 28.3 g (66%); bp 768C/6 Torr. 


The Grignard reagents derived from Æ-haloalkylsilanes have found widespread use in organic 

synthesis. Perhaps the most common application of (chloromethyl)trimethylsilane 

[14] is as a methylenating agent in the Peterson reaction. [81] In this reaction addition 

of the Grignard reagent 38 to carbonyl compounds generates an alcohol 39, from which 

an alkene 40 is produced by base-catalyzed elimination (Scheme 13). The process offers a 

useful alternative to the Wittig reaction. The Grignard reagents derived from Æ-haloalkylsilanes 

are particularly useful for preparing â-ketosilanes, which are themselves useful in 

the stereoselective version of the Peterson alkenation reaction. [82] For example, the Grignard 

reagent derived from (Æ-chloroalkyl)(dimethyl)phenylsilane 22 reacts with acyl chlorides 

[with copper(I) catalysis] to give the ketone 41. Reaction of this ketone with an organometallic 

reagent (R 3 M) followed by potassium hydride or 4-toluenesulfonic acid 

yields either stereoisomer of the trisubstituted alkene (Scheme 13). A related process has 

shown that (iodomethyl)trimethylsilane generates alkenes directly from ketones by the 

use of samarium(II) trifluoromethanesulfonate. [83] (Æ-Silylalkyl)lithiums are produced 

from Æ-haloalkylsilanes via transmetalation by reaction with an alkyllithium [42] or by direct 

reaction with lithium metal. [19,84] 

Cl 



Scheme 13 Æ-Haloalkylsilanes in the Peterson Reaction [81,82] 

Me3Si 

R 1 

Cl 

MgCl 

1. R 1 COR 2 

2. H + /H2O 

R 

Me3Si 1 

HO R2 38 39 

SiMe2Ph 

1. Mg, Et 2O 

2. CuBr SMe 2 

3. R 2 COCl 

R 1 

22 41 

SiMe 2Ph 

O 

R 2 

KH 

1. R 3 M 

2. KH 

1. R 3 M 

2. TsOH 

The Grignard reagents of (chloroalkyl)(isopropoxy)dimethylsilane (42, R 1 = O-iPr) and 

(chloroalkyl)(dimethyl)phenylsilane (43, R 1 = Ph) provide excellent hydroxyalkyl anion 

equivalents, which react with electrophiles such as aldehydes, imines, [80] ketones and epoxides 

to give the adducts 44 and 45, respectively (Scheme 14). The hydroxyalkyl group 

46 is revealed using the standard silyl-to-hydroxy protocols. 

Scheme 14 Hydroxymethylation with Æ-Haloalkylsilanes [80] 

R 1 Me2Si Cl 

R 2 

42 R 1 = O-iPr; R 2 = alkyl 

43 R 1 = Ph; R 2 = alkyl 

1. Mg, THF 

2. E + 

R 1 Me2Si E 

R 2 

44 R 1 = O-iPr; R 2 = alkyl 

45 R 1 = Ph; R 2 = alkyl 

R 1 

for 44: H2O2, F − , base 

for 45: KBr, NaOAc 

AcOOH 

R 1 

R 1 

40 

R 2 

R 3 

R 2 

R 2 

R 3 

HO E 

Æ-Haloalkylsilanes readily undergo halogen substitution (e.g., 47 fi 48) by a wide range of 

nucleophiles such as iodide, [85] ammonia, azide, [86] amines, [87] diethyl phosphonacetate, [88] 

and phosphorus ylides [89] (Scheme 15). The use of iodide and fluoride as nucleophiles provides 

a useful method for the preparation of Æ-iodo- and Æ-fluoroalkylsilanes from Æ-bromo- 

and Æ-chloroalkylsilanes. Fluoromethyl-substituted silanes are prepared in moderate 

yield by the reaction of the corresponding chloromethyl compound with cesium fluoride 

in the presence of 18-crown-6. [90] A variation of the substitution reaction is the nucleophile-induced 

1,2-transfer of a group bound to the silicon atom (e.g., 49 fi 50), which 

can interfere sometimes with the direct displacement (e.g., 47 fi 48). 

Scheme 15 Halide Substitution in Æ-Haloalkylsilanes [85–90] 

R 1 3Si Cl 

R 2 

47 R 2 = alkyl 

R 1 3Si Cl 

R 2 

49 R 2 = alkyl 

Nu − 

Nu − 

R 1 3Si Nu 

48 

R 2 

NuR 1 2Si R 1 

50 

R 2 

R2 46


Æ-Haloalkylsilanes are deprotonated with lithium diisopropylamide or alkyllithium reagents 

[55,91] to generate an organolithium reagent which reacts readily with electrophiles 

such as aldehydes and ketones (Scheme 16). This reaction is incorporated into a useful 

protocol for the homologation of ketones and aldehydes, by acid-catalyzed transformation 

of the first formed Æ,â-epoxysilanes 51 (see Section 4.4.29). [79,92] The reaction does 

not work well with aldehydes or ketones that are either hindered or readily enolizable. 

Other electrophiles are compatible with the process. For example, the use of haloalkanes 

or deuterium oxide provides chain-extended Æ-haloalkylsilanes and Æ-halo-Æ-deuteroalkylsilanes, 

respectively. [93] 

Scheme 16 Alkylation of Æ-Haloalkylsilanes [79,92] 

Me 3Si 

Cl 

1. s-BuLi, TMEDA 

2. R 1 COR 2 

Me3Si 

51 

O 

R 2 

R 1 

aq H 2SO 4, MeOH 

R 1 R 2 

O H 

Silyl ethers incorporating an Æ-haloalkylsilyl moiety have been used to generate Æ-silyl 

radicals for radical cyclization (Scheme 17). Recent progress in the radical cyclization of 

(allyloxy)(bromomethyl)silanes, pioneered by Stork [94] and Nishiyama, [95] is summarized 

in an excellent review. [96] The initial product 53 of the reaction of silyl ether 52 is oxidatively 

cleaved to give a diol 54. Alternatively, treatment of 53 with potassium tert-butoxide 

in dimethyl sulfoxide gives the methyl-substituted alcohol 55. [97] Exceptional levels of 

stereocontrol are obtained in the acyclic series (e.g., 56 fi 57). [95] The reaction is usually 

performed with silyl ethers possessing a bromomethyl group as (bromomethyl)halo(dimethyl)silanes 

are commercially available. Nevertheless, Æ-alkyl-Æ-bromosilanes undergo 

the same type of reaction. [43] The use of intramolecular radical traps facilitates tandem 

radical cyclizations in a similar fashion. [98,99] (Chloromethyl)silanes and (bromomethyl)silanes 

are reduced under similar radical conditions to the corresponding trialkylmethylsilanes. 

[7,39,100] 

Scheme 17 Radical Cyclization of (Allyloxy)(bromomethyl)silanes [94–97] 

O 

Me2Si Br 

52 

OBu t 

O 

Me2Si Bu3SnH, AIBN 

benzene, reflux 

53 

OBu t 

DMF, KF, H 2O2 

t-BuOK, DMSO 

HO 

H 

HO 

54 88% 

HO 

H 

55 66% 

OBu t 

OBu t 



Me 2Si 

O 

Br 

Bu3SnH, AIBN 

Ph O 

benzene, reflux 

Me2Si DMF, KF 

H2O2 Ph HO Ph 

56 57 

Finally, no consideration of the chemistry of Æ-haloalkylsilanes would be complete without 

mention of Ruppert s reagent [101,102] (58). In the presence of a source of fluoride (usually 

tetrabutylammonium fluoride), the reagent will deliver a trifluoromethyl group to carbonyl 

groups of aldehydes and ketones, [103,104] esters, [105] and a variety of other functional 

groups (Scheme 18). The exceptional versatility of the reagent is revealed in an excellent 

review from Prakash and Yudin. [102] 

Scheme 18 Trifluoromethylation of Carbonyl Compounds with Ruppert s Reagent [101–104] 

R 1 

O 

R 2 

F3CSiMe3 58 

TBAF (cat.) 

HO CF 3 

R 1 

R 2 

HO


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163 





Volume 5 Compounds of Group 14 (Ge, Sn, Pb) 

Product Subclass 5.1.22 Aryl- and Heteroarylgermanes 

Written by A. C. Spivey and C. M. Diaper

164





Typesetting: epline, Kirchheim unter Teck 

Printing: Gulde, Tübingen 

Binding: Lachenmaier, Reutlingen 

Bibliographic Information published by Die Deutsche 

Bibliothek 

Die Deutsche Bibliothek lists this publication in the 

Deutsche Nationalbibliografie; detailed bibliographic 

data is available on the internet at 




p. cm. 



of group 14 (Ge, Sn, Pb)/ volume editor, M. 

Maloney 

ISBN 3-13-112181-5 – ISBN 0-86577-944-9 (v. 5) 



QD262 .S35 2000 

547'.2–dc21 

00-061560 






Vol. 5: Compounds of group 14 (Ge, Sn, Pb). – 



I. Maloney, M., II. Clark, A. 

547' .05 

ISBN 3-13-112181-5 


ISBN 0-86577-944-9 


Date of publication: December 23, 2002 

165 





















































166 

Biographical Sketches 

Alan Spivey received his BSc in chemistry in 1988 from the University 

of Nottingham, UK and his DPhil in 1991 from the University of Oxford 

under the guidance of Prof. Sir Jack Baldwin. After postdoctoral work 

at the UniversitØ de Gen›ve, Switzerland with the late Prof. Wolfgang 

Oppolzer, and at the University of Cambridge with Prof. Sir Alan Battersby, 

he moved to a lectureship at the University of Sheffield. In January 

2003 he moved to Imperial College London as a reader. Research 

in his group is focused on the development of new catalysts for asymmetric 

acylation, new linkers for solid phase organic synthesis, chemical 

aspects of signal transduction, and total synthesis of bioactive natural products. 

Chris Diaper received his BSc in chemistry in 1996 from the University 

of Bradford, UK and his PhD in 2000 from the University of Sheffield 

under the supervision of Dr Alan Spivey. After postdoctoral work at 

the University of Nottingham with Prof. Gerry Pattenden he moved to 

his current position as a postdoctoral fellow at the University of Alberta, 

Canada working with Prof. John Vederas. His research interests include 

the development of germanium based linkers for solid-phase 

synthesis, the total synthesis of marine natural products and mechanistic 

aspects of the diaminopimelate (DAP)biosynthetic pathway.

5.1.22 Product Subclass 22: Aryl- and Heteroarylgermanes 


5.1.22 Product Subclass 22: Aryl- and Heteroarylgermanes ..................... 168 

Synthesis of Product Subclass 22 .......................................... 170 

5.1.22.1 Method 1:From Halogermanes by Substitution with Arylmetals ............. 170 

5.1.22.1.1 Variation 1:Using Preformed Arylmetals ................................... 170 

5.1.22.1.2 Variation 2:Using Barbier-Type Reactions .................................. 171 

5.1.22.2 Method 2:From Aryl Halides by Palladium(0)-Mediated Coupling 

with Digermanes ......................................................... 171 

5.1.22.3 Method 3:From Aryl Halides by Insertion of Dichlorogermylene ............. 172 

5.1.22.4 Method 4:Heteroarylgermanes by Cycloaddition ........................... 173 

Applications of Product Subclass 22 in Organic Synthesis ................... 174 

5.1.22.5 Method 5:Arylgermanes as Linkers for Solid-Phase Synthesis ............... 174 

167

168 


Aryl- and Heteroarylgermanes 



Previously published information regarding aryl- and heteroarylgermanes can be found 

in Comprehensive Organic Functional Group Transformations, [1] The Chemistry of Organic Germanium, 

Tin and Lead Compounds, [2] Houben–Weyl, Vol. 13/6, and The Organic Compounds of 

Germanium. [3] 

Arylgermanes are thermally stable and amenable to purification by chromatographic 

techniques. In addition to spectroscopic studies, [4] reports dealing with the structural 

properties of germatriptycenes, [5] germametallocyclophanes, [6] tri-, [7] and tetrasubstituted 

arylgermanes have appeared, [8] focusing on the geometry and bonding of the sterically 

congested ligands around germanium. In addition, germanium congeners of triphenylmethyl 

radicals, [9] cations [10,11] (e.g., tropylium-type ions) [12] have been investigated. The 

photochemistry of arylgermanes has also been investigated. [13–15] 

A number of hypervalent derivatives of germanium have been synthesized. These include 

triarylgermanes with heteroatom functionality at the ortho position on the aromatic 

ring, [16–18] and germatranes. [19] Arylgermatranes such as 1 participate in Stille-type crosscoupling 

reactions giving, for example, biphenyl 2, presumably because hypervalent germanium 

is particularly susceptible to transmetalation with palladium(II)intermediates 

(Scheme 1). [20] In addition, aryl(trifuryl)germanes undergo fluoride-mediated Stille-type 

couplings, presumably via the hypervalent germanium species [ArGe(OH) 3F] – . [79] Chelation 

to germanium has also been used to stabilize thermodynamically highly reactive 

metallogermane, [21] germene, [22,23] germacumulene, [24] and germylene [25] derivatives. Sterically 

demanding aromatics are also commonly used to stabilize these reactive functionalities 

kinetically. 2,4-Di-tert-butyl-6-[(dimethylamino)methyl]phenyl (Mamx) groups combine 

both these features, facilitating isolation of germylene structures such as 3. [26] 

Scheme 1 Intramolecular Chelation Involving Arylgermanes [20,26] 

N 

Ge 

Ph 

1 

+ 4-TolBr 

Bu t 

Bu t 

Pd2(dba) 3, (2-Tol) 3P 

THF, 120 oC NMe 2 

GeR 1 

95% 

3 R 1 = Ot-Bu, O-iPr, OEt, OMe, C CPh, C CH, t-Bu, Bu, Me 

Although silane-based polymers are well-documented, [27] the corresponding germaniumbased 

materials have only recently been subjected to detailed investigation. This interest 

is a consequence of the physical properties of these materials common to the group 14 

based polymers, namely their electroluminescence and conductivity when doped, typi- 

Ph 

2 

4-Tol

5.1.22 Aryl- and Heteroarylgermanes 169 

cally with antimony(V)fluoride. [28] As with related polymers, these materials are susceptible 

to photodegradation. [29] 

A number of methods have been utilized successfully to synthesize polymeric aryland 

heteroarylgermanes. These include Wurtz coupling, [30] coupling of Grignard reagents 

with dihalogermanes, [31] treatment of organolithiums with dichlorogermylene–dioxane 

complex, [28] zirconium-mediated dehydrogenative coupling [32] and ruthenium-mediated 

demethanative coupling. [33] 

The reactivity of heteroarylgermanes [34] has been investigated only to a limited extent. 

Cycloadditions involving furans 4 (Scheme 2) [35,36] and thiophene 1,1-dioxides [37] 

have been reported. In these examples, the presence of germanium does not affect the expected 

course of the reactions. Although the electrophilic chemistry of arylgermanes has 

been well-documented, [38–43] the reactivity of heteroarylgermanes in this respect remains 

to be established except in the case of furylgermanes 4 (Scheme 2). [44] 

Scheme 2 Reactions of Furylgermanes [44] 

O 

O 

Br 

Cl 

GeMe3 

GeMe3 

F 3C 

chloramine-T 

O 

O 

NBS 

TFAA 

GeMe3 

O 

O 

4 

Br 

Br2 •dioxane 

GeMe3 

Br Br 

O 

CCl2, MeOH 

Cl 

Me3C + 

O 

O 

O 

MeO O GeMe3 GeMe 3 

Redistribution reactions between aryl- and halogermanes can readily be achieved using 

Lewis acid catalysis and microwave irradiation. [45] This process requires strict stoichiometric 

control and often results in complex mixtures, detracting from its use as a preparative 

technique. Attempts to synthesize arylgermanes from simple aromatics by direct Friedel– 

Crafts germylation, [45] or high temperature condensation with trichlorogermane [46] generally 

result only in low yields of the desired products. In contrast, polyfluorinated arenes 

readily react with halogermanes in the presence of tris(diethylamino)phosphine to give 

the corresponding polyfluoroarylgermanes in moderate to good yields. [47] 

SAFETY: Appropriate safety precautions and procedures should be taken when handling 

and disposing of germanium compounds. For further information about the toxicity 

of organogermanium compounds please see Section 5.1. 

Bu t 


170 Science of Synthesis 5.1 Germanium Compounds 


5.1.22.1 Method 1: 

From Halogermanes by Substitution with Arylmetals 

Ge-C bonds are usually formed by reaction of halogermanes with organometallics. This 

process generally provides the most efficient and convenient entry into this class of compound, 

and remains the standard method for their synthesis where applicable. 

5.1.22.1.1 Variation1: 

Using Preformed Arylmetals 

The use of preformed aryl Grignard reagents 5 and organolithium reagents (e.g., those 

generated from 7 and butyllithium)with halogermanes is the most common method for 

the introduction of aromatic ligands around germanium (Scheme 3). [1] Attempts to effect 

selectively monoarylation of polyhalogenated germanium substrates can be achieved 

using stoichiometric quantities of reagent, [48] although this process can be substrate dependent. 

[49] Synthesis of fully arylated germanes using a large excess of Grignard reagent 

requires forcing conditions, otherwise the reaction stops at the triarylated stage when 

employing hindered aromatics. [1] Moreover, a total absence of free magnesium from the 

reaction mixture is required under thermal conditions to avoid the competitive formation 

of hexaaryldigermanes. [3] Use of organolithium reagents is often found to be inferior 

to the use of the corresponding Grignard reagents, [1] but can give superior results in 

specific cases. [49] Pyrrolyl-, furyl-, and thienylgermanes 8 are synthesized predominantly 

using organolithium precursors due to their ease of preparation by selective deprotonation 

at the 2-position using alkyllithiums (Scheme 3). [34,50,51] 

Scheme 3 Use of Preformed Organometallics in the Synthesis of Aryland 

Heteroarylgermanes [1,34,50,51] 

R 1 

5 

MgX 

X = Cl, Br; R 1 = alkyl, aryl; R 2 = Me, Et, Ph 

R 1 

Y 

7 

Y = O, NMe, S; R 1 = alkyl, aryl; R 2 = Me, Et 

R 2 nGeX4−n 

50−95% 

1. BuLi 

2. R2 3GeX 

40−80% 

R 1 

R 1 

Y 

8 

6 

GeR 2 3 

GeR 2 nX 3−n 

(Chloromethyl)methylphenyl(2-tolyl)germane [6, R 1 = 2-Me; GeR 2 nX 3–n = Ge(CH 2Cl)MePh]; 


CAUTION: Inhalation, ingestion, or absorption of iodomethane (MeI) through the skin may be 

fatal. It affects the central nervous system, causes irritation to the skin, eyes, and respiratory 

tract, and is a suspected carcinogen. Appropriate safety precautions and procedures should be 

taken during all stages of its handling and disposal. 

2-Tolylmagnesium bromide prepared from 2-bromotoluene (13.5 g, 79 mmol)and Mg 

(2.1 g, 87 mmol)in Et 2O (80 mL)was added to a mixture of dichloro(chloromethyl)phenylgermane 

(21.3 g, 79 mmol)in Et 2O (50 mL)at 0 8C with stirring. The mixture was stirred at 

rt for 3 h. The Grignard reagent prepared from MeI (13.3 g, 87 mmol)and Mg (2.3 g, 

95 mmol)in Et 2O (70 mL)was added to the mixture at 0 8C with stirring. The mixture was


stirred at rt for 3 h, and then refluxed for 1 h. Aq 3 M HCl (40 mL)was added to the mixture 

at 0 8C. The organic layer was separated and the aqueous layer extracted with Et 2O 

(2 ” 30 mL). The combined organic layer and extracts were dried (Na 2SO 4), and evaporated. 

Distillation of the residue gave the product as a colorless oil; yield: 17.2 g (71%); bp 141 8C/ 

0.18 Torr. 

5.1.22.1.2 Variation2: 

Using Barbier-Type Reactions 

Attempts to synthesize monoarylgermanes using stoichiometric quantities of tetraethoxygermane 

or germanium(IV)halides with aryl halides and magnesium metal (Barbier conditions)generally 

result in poor yields, often due to low selectivity. [4] This can be improved 

in some instances by switching to copper, with the best results being achieved 

using germanium(IV)chloride and aryl bromides under forcing conditions. [53] Synthesis 

using Barbier conditions under thermal conditions are also plagued by competitive formation 

of hexaphenyldigermanes, although yields can be improved using hexacoordinate 

tris(benzene-1,2-diolato)germanates in place of germanium(IV) halides when preparing 

tetraarylgermanes. [54] Although Wurtz–Fittig coupling using sodium (or lithium)has 

been used in the synthesis of tetraarylgermanes, [55] treatment with zinc also results in 

modest conversion of germanium(IV)iodide to tetraphenylgermane. [56] 

Ultrasound has been used successfully to induce Barbier reactions involving trialkylhalogermanes, 

[36] and gives superior yields and avoids digermane side products often observed 

under thermal conditions. [57] 

Scheme 4 Synthesis of Arylgermanes Using Barbier Conditions [36] 

R 1 

9 

X 

R 2 3GeX, Mg, BrCH 2CH 2Br, ))), rt 

X = Br; R 1 = 4-CH CH 2; R 2 = Et 74% 

R 1 

10 

GeR 2 3 

4-(Triethylgermyl)styrene (10,R 1 = 4-CH=CH 2;R 2 = Et); Typical Procedure: [57] 

A Schlenk tube containing Mg turnings (0.60 g, 25 mmol), 1,2-dibromoethane (0.54 mL, 

6.22 mmol), Et 3GeBr (3.0 g, 12.5 mmol), and 4-bromostyrene (9, X = Br; R 1 = 4-CH=CH 2; 

2.28 g, 12.5 mmol)in THF (25 mL)was placed in a commercial ultrasonic cleaning bath 

(Branson B1200 E1, working frequency: 47 kHz)and sonicated for 2 h. The mixture was 

washed with brine (20 mL)and extracted with Et 2O (2 ” 20 mL). The organic layers were 

dried (MgSO 4), the solvents removed in vacuo, and the residue purified by column chromatography 

(silica gel, petroleum ether/Et 2O 95:5)to give the product as an oil; yield: 2.4 g 

(74%); 1 H NMR (CDCl 3, ä): 0.9–1.2 (m, 15H), 2.24 (dd, J = 2, 11 Hz, 1H), 5.79 (dd, J = 2, 11 Hz, 

1H), 6.73 (dd, J = 11, 17.5 Hz, 1H), 7.39 (d, J = 8.5 Hz, 2H), 7.43 (d, J = 8.5 Hz, 2H); 13 CNMR 

(CDCl 3, ä): 4.4, 9.0, 113.8, 125.9, 134.6, 137.3, 140.1. 

5.1.22.2 Method 2: 

From Aryl Halides by Palladium(0)-Mediated Coupling with Digermanes 

Initial studies carried out by Eaborn demonstrated that hexaalkyldigermanes, like other 

group 14 metal analogues, [58] undergo palladium(0)-mediated coupling with aryl bromides, 

albeit in low-to-modest yields due to competing formation of the corresponding 

biaryl derivatives. [59] This problem was resolved by the use of aryl iodides such as iodobenzene 

(11)and 1,2-dichloro-1,1,2,2-tetramethyldigermane, [60] which resulted in excellent 

yields of the desired germylated aromatics, in this case iododimethylphenylgermane 

(12)and chlorodimethylphenylgermane (13)(Scheme 5). [61] This method is also suitable 



for the synthesis of derivatives such as bis(halodimethylgermyl)thiophene 15 synthesized 

from 2,5-dibromothiophene (14), [30] which can be difficult to synthesize using conventional 

organometallic procedures due to their tendency to participate in oligomerization 

i.e. reaction of 16 to give 17 (Scheme 5). [62] The major drawback with this methodology is 

the availability of 1,2-dichloro-1,1,2,2-tetramethyldigermane, [63] which is currently not 

commercially available and requires synthesis before use. 

Scheme 5 Palladium(0)-Mediated Coupling of Digermanes with Aryl Halides [30,61,62] 

PhI 

(Me2ClGe)2, Pd(PPh3)4 

benzene, 120 o C 

Ph I 

Ge 

Me2 11 12 31% 

Br 

S 

16 

+ 

Ph Ge Cl 

Me2 13 68% 

S 

Br 

(Me2ClGe)2, Pd(PPh3)4, 

benzene, 120 

X = Br, Cl 56% after treatment with MeLi to give X = Me 

14 15 

oC X 

Ge 

Me2 S 

1. BuLi, TMEDA 

2. (Me2ClGe) 2 

80% 

Me2Ge 

S 

GeMe2 S S 

S 

Me 2Ge GeMe 2 

Iododimethylphenylgermane (12) and Chlorodimethylphenylgermane (13); 


A soln of iodobenzene (11; 82 mg, 0.4 mmol)in benzene (0.8 mL)(CAUTION: carcinogen!) 

was treated with 1,2-dichloro-1,1,2,2-tetramethyldigermane (0.4 mmol)in the presence of 

Pd(PPh 3) 4 (23 mg, 0.02 mmol)at 1208C for 5 h. Purification by fractional distillation led to 

the isolation of 12; yield: 38 mg (31%)and 13; yield: 59 mg (68%)(yields calculated by GC). 

5.1.22.3 Method 3: 

From Aryl Halides by Insertion of Dichlorogermylene 

Insertion of germylenes into aryl carbon–halogen bonds of simple aromatics generally 

proceeds in moderate yield using elevated temperatures (>150 8C)and sealed reaction vessels. 

[64,65] A modification of this procedure involving the use of the most readily accessible 

dichlorogermylene source, dichlorogermylene–dioxane complex, [66] and catalytic quantities 

of anhydrous aluminum trichloride allows these reactions to be conducted under relatively 

mild conditions (~80 8C, atmospheric pressure)giving insertion in excellent yields 

(Scheme 6). [4] The tolerance of this methodology towards other functionalities however 

remains to be established. 

Scheme 6 Germylene Insertion into Aromatic Halides [4] 

R 1 

18 

Br 

GeCl2 dioxane 

AlCl3, 80 oC R 1 = 4-Me 98%; (19/20) 64:32 

17 

R 1 

19 

GeCl 3 

+ 

R 1 

20 

X 

Ge 

Me2 GeBr 3


Trichloro(4-tolyl)germane (19,R 1 = 4-Me) and Tribromo(4-tolyl)germane (20,R 1 = 4-Me); 


A mixture of 4-bromotoluene (250 mL), GeCl 2 •dioxane (10 g, 43.2 mmol), and anhyd AlCl 3 

(0.29 g, 2.17 mmol)was heated to 808C for 24 h with continuous stirring. After the mixture 

was cooled to rt, it was filtered, the dioxane removed in vacuo, and the unreacted 4bromotoluene 

removed by vacuum distillation (43 8C/5”10 –4 Torr)to leave the product as 

a white solid; yield: 13.33 g (98%); ratio 19/20 64:32 (by GC/MS). 

5.1.22.4 Method 4: 

Heteroarylgermanes by Cycloaddition 

Cycloaddition reactions involving alkynylgermanes (Section 5.1.20)are generally analogous 

to those observed using nonmetalated alkynes. Hence, nitrogen-based heterocycles 

such as pyrazoles 22, triazoles 23, and pyridazines 24 can be readily accessed in high yield 

by treatment of alkynylgermanes 21 with diazomethane, [67] azides, [68] or tetrazines, [69] respectively 

(Scheme 7). 

Scheme 7 Nitrogen Heterocycles from Alkynylgermanes by Cycloaddition [67–70] 

R 2 

21 

GeR 1 3 

CH 2N 2 

R3N3 R1 = Me, Et; 

R3 R 

= Na, Ph, 4-Tol, 4-O2NC6H4 

32−84% 

2 = CH NR4 N N 

N N 

R1 = Me; R2 = H 80% 

R1 = Me; R2 = GeMe3 93% 

R 1 3Ge R 2 

22 

N 

N 

N 

N 

H 

R 1 3Ge R 2 

R 2 

23 

24 

GeR 1 3 

4-(Trimethylgermyl)pyridazine (24, R 1 = Me; R 2 = H); Typical Procedure: [70] 

Tetrazine (82.0 mg, 1.0 mmol)and (ethynyl)trimethylgermane (21,R 1 =Me;R 2 = H; 300 mg, 

1.80 mmol, contains approx. 20% THF)in MeCN were heated to reflux for 90 min. The 

resulting pale yellow soln was concentrated in vacuo. The residual brown liquid was 

purified by column chromatography (silica gel, Et 2O)to afford the product as colorless 

oil (which turned yellow quite rapidly in air); yield: 158 mg (80%); 1 H NMR (CDCl 3, ä): 

0.45 (s, 9H), 7.50 (dd, J = 4.9, 1.8 Hz, 1H), 9.06 (dd, J = 4.9, 1.4 Hz, 1H), 9.17 (dd, J = 1.8, 

1.4 Hz, 1H); 13 C NMR (CDCl 3, ä): –2.43, 131.29, 142.43, 150.64, 154.98. 

N N 

NR 3 




5.1.22.5 Method 5: 

Arylgermanes as Linkers for Solid-Phase Synthesis 

Group 14 metals have been utilized as key functional elements in a number of linker 

strategies for solid-phase organic synthesis. [71] Arylsilane linkers have been shown to be 

stable towards a relatively wide range of reaction conditions and can be cleaved via ipsoprotodesilylation 

with acid to liberate aromatics from the resin in a traceless fashion. [72] 

Cleavage with concomitant diversification has also been achieved via ipso-halodesilylation 

using bromine and iodine chloride to liberate aryl bromides and iodides, respectively. 

[73] However, one limitation to the use of arylsilane linkers for solid-phase organic synthesis 

is the necessity for harsh conditions (e.g., neat HF)when cleaving electron-deficient 

aromatics. One tactic that addresses this problems involves increasing the susceptibility 

towards electrophilic ipso-demetalation by exchanging silicon for germanium (Scheme 

8). [74] This is as a result of the increasing â-effect observed down the periodic group (i.e., 

Si < Ge < Sn)in the rate-determining electrophilic ipso-addition step. [10,38,75–77] Treatment 

of the arylgermanium linkers 25 with halogen sources also permits diversification at the 

point of cleavage giving 26, [78] and these linkers have been used to synthesize chemical 

libraries based on benzodiazapines [74] and pyrazoles. [49] 

Scheme 8 Arylgermanes as Diversification Linkers for Solid-Phase Organic Synthesis [78] 

R 1 

25 

E = H, Br, Cl, I 

Me2 Ge 

E + 

R 1 

26 

E


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Abbreviations 

Chemical 

Name Used in Text Abbreviation Used 

in Tables and on Arrow 

in Schemes 

Abbreviation Used 

in Experimental 

Procedures 

(R)-1-amino-2-(methoxymethyl)pyrrolidine RAMP RAMP 

(S)-1-amino-2-(methoxymethyl)pyrrolidine SAMP SAMP 

ammonium cerium(IV) nitrate CAN CAN 

2,2¢-azobisisobutyronitrile AIBN AIBN 

barbituric acid BBA BBA 

benzyltriethylammonium bromide TEBAB benzyltriethylammonium 

bromide 

benzyltriethylammonium chloride TEBAC benzyltriethylammonium 

chloride 

N,O-bis(trimethylsilyl)acetamide BSA BSA 

9-borabicyclo[3.3.1]nonane 9-BBNH 9-BBNH 

borane–methyl sulfide complex BMS BMS 

N-bromosuccinimide NBS NBS 

tert-butyldimethylsilyl chloride TBDMSCl TBDMSCl 

tert-butyl peroxybenzoate TBPB tert-butyl peroxybenzoate 

10-camphorsulfonic acid CSA CSA 

chlorosulfonyl isocyanate CSI chlorosulfonyl isocyanate 

3-chloroperoxybenzoic acid MCPBA MCPBA 

N-chlorosuccinimide NCS NCS 

chlorotrimethylsilane TMSCl TMSCl 

1,4-diazabicyclo[2.2.2]octane DABCO DABCO 

1,5-diazabicyclo[4.3.0]non-5-ene DBN DBN 

1,8-diazabicyclo[5.4.0]undec-7-ene DBU DBU 

dibenzoyl peroxide DBPO dibenzoyl peroxide 

dibenzylideneacetone dba dba 

di-tert-butyl azodicarboxylate DBAD di-tert-butyl azodicarboxylate 

2,3-dichloro-5,6-dicyanobenzo- 

1,4-quinone 

DDQ DDQ 

dichloromethyl methyl ether DCME DCME 

dicyclohexylcarbodiimide DCC DCC 

N,N-diethylaminosulfur trifluoride DAST DAST 

diethyl azodicarboxylate DEAD DEAD 

diethyl tartrate DET DET 

2,2¢-dihydroxy-1,1¢-binaphthyllithium 

aluminum hydride 

BINAL-H BINAL-H 

diisobutylaluminum hydride DIBAL-H DIBAL-H 

177

178 Abbreviations 

Chemical (cont.) 



in Schemes 



Procedures 

diisopropyl tartrate DIPT DIPT 

1,2-dimethoxyethane DME DME 

dimethylacetamide DMA DMA 

dimethyl acetylenedicarboxylate DMAD DMAD 

2-(dimethylamino)ethanol Me2N(CH2) 2OH 2-(dimethylamino)ethanol 

4-(dimethylamino)pyridine DMAP DMAP 

dimethylformamide DMF DMF 

dimethyl sulfide DMS DMS 

dimethyl sulfoxide DMSO DMSO 

di-tert-butyl peroxide DTBP DTBP 

1,3-dimethyl-3,4,5,6-tetrahydropyrimidin-2(1H)-one 

DMPU DMPU 

ethyl diazoacetate EDA EDA 

ethylenediaminetetraacetic acid edta edta 

hexamethylphosphoric triamide HMPA HMPA 

hexamethylphosphorus triamide HMPT HMPT 

iodomethane MeI MeI 

N-iodosuccinimide NIS NIS 

lithium diisopropylamide LDA LDA 

lithium hexamethyldisilazanide LiHMDS LiHMDS 

lithium isopropylcyclohexylamide LICA LICA 

lithium 2,2,6,6-tetramethylpiperidide LTMP LTMP 

lutidine lut lut 

methylaluminum bis(2,6-di-tert-butyl-4-methylphenoxide) 

MAD MAD 

methyl ethyl ketone MEK methyl ethyl ketone 

methylmaleimide NMM NMM 

4-methylmorpholine N-oxide NMO NMO 

1-methylpyrrolidin-2-one NMP NMP 

methyl vinyl ketone MVK methyl vinyl ketone 

petroleum ether PEa petroleum ether 

N-phenylmaleimide NPM NPM 

polyphosphoric acid PPA PPA 

polyphosphate ester PPE polyphosphate ester 

potassium hexamethyldisilazanide KHMDS KHMDS 

pyridine pyridineb pyridine 

pyridinium chlorochromate PCC PCC 

pyridinium dichromate PDC PDC 

pyridinium 4-toluenesulfonate PPTS PPTS 

a Used to save space; abbreviation must be defined in a footnote. 

b pyused on arrow in schemes.

Chemical (cont.) 

Abbreviations 179 



in Schemes 



Procedures 

sodium bis(2-methoxyethoxy)aluminum hydride Red-Al Red-Al 

tetrabutylammonium bromide TBAB TBAB 

tetrabutylammonium chloride TBACl TBACl 

tetrabutylammonium fluoride TBAF TBAF 

tetrabutylammonium iodide TBAI TBAI 

tetracyanoethene TCNE tetracyanoethene 

tetrahydrofuran THF THF 

tetrahydropyran THP THP 

2,2,6,6-tetramethylpiperidine TMP TMP 

trimethylamine N-oxide TMANO trimethylamine N-oxide 

N,N,N¢,N¢-tetramethylethylenediamine TMEDA TMEDA 

tosylmethyl isocyanide TosMIC TosMIC 

triethylbenzylammonium bromide TEBAB TEBAB 

triethylbenzylammonium chloride TEBAC TEBAC 

trifluoroacetic acid TFA TFA 

trifluoroacetic anhydride TFAA TFAA 

trimethylsilyl cyanide TMSCN TMSCN 

Ligands 

acetylacetonato acac 

2,2¢-bipyridyl bipy 

1,2-bis(dimethylphosphino)ethane DMPE 

2,3-bis(diphenylphosphino)bicyclo[2.2.1]hept-5-ene NORPHOS 

2,2¢-bis(diphenylphosphino)-1,1¢-binaphthyl BINAP 

1,2-bis(diphenylphosphino)ethane dppe (not diphos) 

1,1¢-bis(diphenylphosphino)ferrocene dppf 

bis(diphenylphosphino)methane dppm 

1,3-bis(diphenylphosphino)propane dppp 

1,4-bis(diphenylphosphino)butane dppb 

2,3-bis(diphenylphosphino)butane Chiraphos 

bis(salicylidene)ethylenediamine salen 

cyclooctadiene cod 

cyclooctatetraene cot 

cyclooctatriene cte 

ç 5 -cyclopentadienyl Cp 

dibenzylideneacetone dba 

6,6-dimethylcyclohexadienyl dmch 

2,4-dimethylpentadienyl dmpd 

ethylenediaminetetraacetic acid edta 

isopinocamphenyl Ipc


Ligands (cont.) 

2,3-O-isopropylidene-2,3-hydroxy-1,4bis(diphenylphosphino)butane 

Diop 

norbornadiene (bicyclo[2.2.1]hepta-2,5-diene) nbd 

ç 5 -pentamethylcyclopentadienyl Cp* 

Radicals 

acetyl Ac 

aryl Ar 

benzotriazol-1-yl Bt 

benzoyl Bz 

benzyl Bn 

benzyloxycarbonyl Cbz 

benzyloxymethyl BOM 

9-borabicyclo[3.3.1]nonyl 9-BBN 

tert-butoxycarbonyl Boc 

butyl Bu 

sec-butyl s-Bu 

tert-butyl t-Bu 

tert-butyldimethylsilyl TBDMS 

tert-butyldiphenylsilyl TBDPS 

cyclohexyl Cy 

3,4-dimethoxybenzyl DMB 

ethyl Et 

ferrocenyl Fc 

9-fluorenylmethoxycarbonyl Fmoc 

isobutyl iBu 

mesityl Mes 

mesyl Ms 

4-methoxybenzyl PMB 

(2-methoxyethoxy)methyl MEM 

methoxymethyl MOM 

methyl Me 

4-nitrobenzyl PNB 

phenyl Ph 

phthaloyl Phth 

phthalimido NPhth 

propyl Pr 

isopropyl iPr 

tetrahydropyranyl THP 

tolyl Tol 

tosyl Ts 

triethylsilyl TES 

triflyl, trifluoromethanesulfonyl Tf 

triisopropylsilyl TIPS 

trimethylsilyl TMS 

2-(trimethylsilyl)ethoxymethyl SEM 

trityl [triphenylmethyl] Tr

Abbreviations 181 

General 

absolute abs 

anhydrous anhyd 

aqueous aq 

boiling point bp 

catalyst no abbreviation 

catalytic cat. 

chemical shift ä 

circular dichroism CD 

column chromatographyno abbreviation 

concentrated concd 

configuration (in tables) Config 

coupling constant J 

dayd 

density d 

decomposed dec 

degrees Celsius 8C 

diastereomeric ratio dr 

dilute dil 

electron-donating group EDG 

electron-withdrawing group EWG 

electrophile E + 

enantiomeric excess ee 

enantiomeric ratio er 

equation eq 

equivalent(s) equiv 

flash-vacuum pyrolysis FVP 

gas chromatographyGC 

gas chromatography-mass spectrometry GC/MS 

gas–liquid chromatographyGLC 

gram g 

highest occupied molecular orbital HOMO 

high-performance liquid chromatographyHPLC 

hour(s) h 

infrared IR 

in situ in situ 

in vacuo in vacuo 

lethal dosage, e.g. to 50% of animals tested LD 50 

liquid liq 

liter L 

lowest unoccupied molecular orbital LUMO 

mass spectrometryMS 

medium-pressure liquid chromatographyMPLC 

melting point mp 

milliliter mL 

millimole(s) mmol 

millimoles per liter mM 

minute(s) min 

mole(s) mol 

nuclear magnetic resonance NMR 

nucleophile Nu – 

optical purityop 

phase-transfer catalysis PTC 

proton NMR 

1H NMR


General (cont.) 

quantitative quant 

reference (in tables) Ref 

retention factor (for TLC) R f 

retention time (chromatography) t R 

room temperature rt 

saturated sat. 

solution soln 

temperature (in tables) Temp (8C) 

thin layer chromatography TLC 

ultraviolet UV 

volume (literature) Vol. 

via via 

vide infra vide infra 

vide supra vide supra 

yield (in tables) Yield (%)

ca01 only detailed ToC 1..24

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