Science of Synthesis

2003 Georg Thieme Verlag 

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Science of Synthesis 

Houben–Weyl Methods of Molecular Transformations 

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 

1

2 



Science of Synthesis 

Houben–Weyl Methods of Molecular Transformations 

Editorial Board D. Bellus E. Schaumann 

S. V. Ley I. Shinkai 

R. Noyori E. J. Thomas 

M. Regitz B. M. Trost 

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Managing Editor M. F. Shortt de Hernandez


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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 

Science of Synthesis : Houben–Weyl methods 

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 

3 

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4 



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 ..................... 7 

1.1.1 Product Subclass 1: Nickel Complexes of 1,3-Dienes ...................... 8 

Synthesis of Product Subclass 1 ............................................ 8 

1.1.1.1 Method 1: Ligand Exchange with Bis(ç 4 -cycloocta-1,5-diene)nickel(0) ... 8 

Applications of Product Subclass 1 in Organic Synthesis ..................... 9 

1.1.1.2 Method 2: Diene–Diene Cycloadditions ................................ 9 

1.1.1.3 Method 3: Diene–Alkyne Cycloadditions ............................... 10 

1.1.1.4 Method 4: Diene–Aldehyde Reductive Cyclizations ..................... 11 

1.1.1.4.1 Variation 1: Triethylsilane-Mediated Reactions ........................... 11 

1.1.1.4.2 Variation 2: Triethylborane-Mediated Reactions ......................... 12 

1.1.1.5 Method 5: 1,4-Dialkylation of Dienes .................................. 12 

1.1.1.6 Method 6: Hydrocyanation of Dienes .................................. 13 

1.1.2 Product Subclass 2: Nickel–Allyl Complexes ............................... 13 


1.1.2.1 Method 1: Oxidative Addition of Nickel(0) with Allylic Electrophiles ...... 13 

1.1.2.2 Method 2: Addition of Allylmagnesium Halides to Nickel(II) Salts ........ 14 

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

the Presence of Lewis Acids ................................. 15 

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

Conjugated Dienes ......................................... 16 


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

with Alkyl Halides and Other Electrophiles ................... 17 

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

with Alkyl Halides and Other Electrophiles ................... 18 

1.1.2.7 Method 7: Coupling of Nickel–Allyl Complexes with 

Main Group Organometallics ............................... 20 

1.1.2.7.1 Variation 1: Allylic Ether Derived ð-Allyl Complexes ...................... 20 

1.1.2.7.2 Variation 2: Enal-Derived ð-Allyl Complexes ............................. 22 

1.1.2.7.3 Variation 3: Allylic Alcohol Derived ð-Allyl Complexes .................... 22 

1.1.2.8 Method 8: Addition of Stabilized Nucleophiles to Nickel–Allyl Complexes 23 

1.1.2.9 Method 9: Alkyne Insertions with Nickel–Allyl Complexes ............... 23 

1.1.2.10 Method 10: Alkene Insertions with Nickel–Allyl Complexes ............... 25 

1.1.3 Product Subclass 3: Nickel–Alkyne Complexes ............................ 25 


1.1.3.1 Method 1: Ligand Exchange with Nickel–Alkene Complexes ............. 26 


1.1.3.2 Method 2: Coupling of Alkynes with Carbon Dioxide .................... 27 

1.1.3.3 Method 3: Coupling of Alkynes with Isocyanides ....................... 28 



5

6 

1.1.3.4 Method 4: Coupling of Alkynes with Aldehydes ......................... 28 

1.1.3.5 Method 5: Coupling of Two Alkynes ................................... 31 

1.1.3.6 Method 6: Coupling of Alkynes with Alkenes ........................... 32 

1.1.3.7 Method 7: [2 +2+2] Cycloadditions .................................... 34 

1.1.3.8 Method 8: Alkyne Carbonylation ...................................... 36 

1.1.3.9 Method 9: Alkyne Hydrocyanation ..................................... 36 

1.1.3.10 Method 10: Alkyne Hydrosilylation ...................................... 36 

1.1.3.11 Method 11: Alkyne Carbozincation ..................................... 37 

1.1.4 Product Subclass 4: Nickel–Alkene Complexes ............................ 38 


1.1.4.1 Method 1: Ligand Exchange with Nickel(0) Complexes .................. 38 

Applications of Product Subclass 4 in Organic Synthesis 39 

1.1.4.2 Method 2: Conjugate Addition to Electrophilic Double Bonds ........... 39 

1.1.4.2.1 Variation 1: Organoaluminums ......................................... 39 

1.1.4.2.2 Variation 2: Organozincs ............................................... 40 

1.1.4.2.3 Variation 3: Organozirconiums ......................................... 42 

1.1.4.2.4 Variation 4: Direct Conjugate Addition of Alkyl Halides ................... 43 

1.1.4.3 Method 3: Coupling of Two Alkenes ................................... 44 

1.1.4.4 Method 4: Alkene Carbonylation ...................................... 47 

1.1.4.5 Method 5: Alkene Hydrocyanation ..................................... 48 

1.1.4.6 Method 6: Alkene Hydrosilylation ..................................... 49 

1.1.4.7 Method 7: Alkene Hydroalumination .................................. 49 

1.1.4.8 Method 8: Alkene Hydrozincation ..................................... 51 

1.1.4.9 Method 9: Alkene Carbozincation ..................................... 52 

1.1.4.10 Method 10: Homo-Diels–Alder Cycloadditions ........................... 53 

1.1.4.11 Method 11: Alkene Polymerization ...................................... 53 


www.science-of-synthesis.com

1.1 Product Class 1: 

Organometallic Complexes ofNickel 

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 



Ph3P, AcOH, rt, 24 h 

84% 

NiCl2(PPh3) 2 

3 

7

8 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 08C 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: 1.28 g (40%). 

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

A soln of NiCl 2 •6H 2O (2.38 g, 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%). 

1.1.1 Product Subclass 1: 

Nickel Complexes of1,3-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 ofProduct 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] 



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

Ni(cdt) 

+ 

P P 

Pri Pri Pri Pri + 

Et2O −78 oC 85% 

Pr 

4 

i 

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 ofProduct 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. 



1.1.1 Nickel Complexes of 1,3-Dienes 9 

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 

Ni 

P 

P 

Pr i 

Pr i 

for references see p 55


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 858C 

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

(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 Variation 1: 

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 



1.1.1 Nickel Complexes of 1,3-Dienes 11 

CHO 

20 mol% Ni(cod)2 2 

40 mol% Ph3P Et3SiH (5 equiv), THF 

O 

H 

N 

40% 

OTES 

+ 

O 

H 

N 

38% 

OTES 



1.1.1.4.2 Variation 2: 

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; 12.8 mg, 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-Dialkylation ofDienes 

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 13 

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 ofDienes 

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 Addition ofNickel(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: 

Addition ofAllylmagnesium 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 ofNickel(0) with Enones in the Presence ofLewis 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 

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 

(8 mL) 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 



27 



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 

08C. A second 100-mL Schlenk tube containing Na metal strips (1.03 g, 44.8 mmol, 

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 

(1.88 mL, 22.4 mmol, 1.00 equiv) and TBDMSCl (3.38 g, 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 ofNickel(0) Complexes ofConjugated 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] 

MeO2C 

CO2Me + Ni(cod)2 + Ph3P 

Ph3P Ni 

2 

MeO2C CO 2Me 

+ Ni(cod) 2 + bipy 

2 

MeO2C 

MeO 2C 

Ni(bipy)


1.1.2.5 Method 5: 

Coupling ofAllyl 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 Br 

Ni Ni 

Br 

R 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 ofEnal-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, 44.8 mmol, 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 

(1.88 mL, 22.4 mmol, 1.00 equiv) and TBDMSCl (3.38 g, 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 ofNickel–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 Variation 1: 

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, NiCl 2(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 R 

91% 

Et 

73% ee 

( ) 5 

36 major isomer 

38 99:1 regioselectivity 

Ph 

( ) 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 228C for 18 h under argon. The mixture was cooled to 0 8C and quenched by the 

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




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%). 

1.1.2.7.2 Variation 2: 

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, 0.148 mmol), TBDMSCl (168 mg, 

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, 0.098 mmol), 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 

48 h, 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. 

1.1.2.7.3 Variation 3: 

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] 

Bu 

OH 

MeMgBr, NiCl2(PPh3) 2 3 

50% 

+ 

40 

41 4:1 

42 

t But But 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: 

Addition ofStabilized 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 CO + H H 

CO, MeOH 

O Ni 

Cl 

Cl 

R 1 

Cl 

Ni Ni 

Cl 

TMSO R 1 

OTMS 

+ 

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 

O 

R 2 

43 

O 

H 

R 1 

OMe 

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 0 8C, 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

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 



1.1.3 Nickel–Alkyne Complexes 25 

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 


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 

47 

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 ofAlkynes 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% 

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 (1.8 mL), a soln of Cy 3P (0.05 g, 0.18 mmol) 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%). 




R 1 

H 

52 

R 1 

CO 2H 

53 

Et 

Et 

O 

O 

Et 

O 



1.1.3.3 Method 3: 

Coupling ofAlkynes 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 

80% 

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 110–1358C 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 ofAlkynes 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] 



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 

LnNi 

R 1 

H 

R 4 

O 

H 

OH R 4 

R2 56 

L L 

Ni 

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 

Et3SiH 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 0 8C. 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 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). 

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 258C 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 08C. 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 ofTwo 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 

H 

SiX 3 

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 

R 1 

SiX3 

Ln 

Ni 

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, 1.8 mmol) 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 ofAlkynes 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 

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] 



LnNi 

R 2 

H 

R 1 

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 

R3 = 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 

O 

O 

R 3 

H 

R 2 

R 2 

OTBDMS 

HO 

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 08C. 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 ∗ 

R2 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 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. 




52% 

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 08C 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 

(0.8 g, 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 18 h. 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 

2. 

1. CuCN 2LiCl 

2. R2COCl R 1 

Ph 

Br 

CO2Et 

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 (3.8 mL) 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, 8 equiv) 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 

69 

CO 2Me 

CO 2Me

1.1.4 Nickel–Alkene Complexes 39 

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] 

1.1.4.2.1 Variation 1: 

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 

67% 

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; 128 mg, 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 08C. 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. 

1.1.4.2.2 Variation 2: 

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, ZnBr2 Ni(acac) 2 1, ))) 

50−90% 

N 

R 1 

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 

Me2Zn, LiBr 

Ni(acac) 2 1, Et2O 

78% 

1. Me2Zn, Ni(acac)2 1 

2. TMSCl, Et3N 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 (2.5–4.8 mmol) 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; 18 mg, 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: 348 mg (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 0 8C, 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, 0.018 mmol) 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%). 

1.1.4.2.3 Variation 3: 

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, 6.48 mmol) were dissolved 

in THF (30 mL) and cooled to 0 8C. [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

1.1.4.2.4 Variation 4: 

Direct Conjugate Addition ofAlkyl 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 2003 Georg Thieme Verlag 



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 (2.38 g, 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 238C 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: 5.28 g 

(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 ofTwo 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 R2 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 

OR1 PPh2 

[NiBr(H2C CHCH 2)] 2, NaBAr 4, L ∗ 

Scheme 69 Cycloisomerization of Dienes [160] 

R 1 

R 1 

92 



Ar 1 

O 

[NiBr(H2C CHCH2)] 2, R 

O 

1 3P 

81% 

[NiHL n] + 

R 1 

R 1 

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 558C 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 (0.08 g, 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 0 8C. 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 

Ar2 2P 

O 

O 

Ar 2 2P 

94 

OPh 

NiL 

CN 

Ar1 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 

AlBu i 2 

H 

R 1 = 4-MeOC6H4 90% 

R 

96 

1OH + 

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. 




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: 68 mg 

(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 

L nNi Et 

Zn 

R 1 = (CH 2) 5Me 38% 

acac 

ZnEt 2 

LnNi 

L nNi 

acac 

H 

acac 

Zn 

1 R + 

2 

97 

R 1 

R 1 

LnNi H 

2 H 2C CH 2 

acac 

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 08C, 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 

OR1 R2 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 16–48 h. 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 1 

N + 

Ni 

N 

Ar 1 

Ar 

N 

Ni 

N 

1 

+ Me 

n 

Ar 1 

polyethene

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