ca01 only detailed ToC 1..24

50 Science of Synthesis 1.1 Organometallic Complexes of Nickel
steps of alkyne cyclooligomerizations have been further documented by Eisch. [66] Alternatively,
many selective transformations have been reported in which one alkyne and a different
unsaturated unit couple in an oxidative cyclization. Oxidative cyclizations of this
class form the basis of many useful procedures. [187] An outstanding review on the formation
of oxa- and azametallacycles has appeared. [9]
Scheme 29 Oxidative Cyclization of an Alkyne
and a Second Unsaturated Unit [9,187]
R 1
L L
Ni
Y
X
R1 Ni
R
Y
X
1
R1 L L
47
Synthesis of Product Subclass 3
1.1.3.1 Method 1:
Ligand Exchange with Nickel–Alkene Complexes
Nickel–alkyne complexes are typically unstable owing to their propensity to catalyze alkyne
polymerization to yield polyacetylenes. The most common preparative method involves
the displacement of alkenes under conditions in which the stoichiometry is carefully
controlled. Numerous bis(ligand)nickel(0)–mono(alkyne) complexes (e.g., 48) have
been reported and fully characterized by Pörschke (Scheme 30). [67] Further treatment of
the monoalkyne complex with alkyne leads to formation of the bis(alkyne) complex. (ç 6 -
Cyclododeca-1,5,9-triene)nickel(0) [Ni(cdt)] [68] is a common starting nickel(0) complex for
the preparation of alkyne complexes. Bis(alkyne)nickel(0) complexes 50 have also been
prepared by Rosenthal and Pörschke from nickel(0) complexes of hepta-1,6-diene (e.g.,
49) by ligand displacement (Scheme 31). [69]
Scheme 30 Preparation of Nickel(0)–Alkyne Complexes [67]
Ni(cdt) + H 2C
CH2 + Cy 3P Cy 3P Ni
Scheme 31 Preparation of Nickel(0)–Bis(alkyne) Complexes [69]
N Ni
49
+
Ph
TMS
80%
H H
82%
TMS
N Ni
TMS
50
Ph
Ph
Cy 3P Ni
(Acetylene)(ethene)(tricyclohexylphosphine)nickel(0) (48): [67]
Acetylene (50 mL, 6 mmol) was added at –508C without stirring to an Et 2O soln (40 mL) of
[Ni(C 2H 4) 2(PCy 3)] (5.0 mmol) [prepared from Ni(cdt) (1.165 g, 5.0 mmol Ni), ethene, and
Cy 3P (1.40 g, 5.0 mmol)]. The color of the yellow soln changed to light red, and at –788C
over the course of 2 d small yellow crystals formed. The mother liquor was decanted,
and the crystals were washed with cold Et 2O (2 ”) and dried in vacuo at –308C to afford
48; yield: 1.62 g (82%).
48