Mechanism
The coordination of the remote double bond to the nickel center is crucial for the cross-coupling reaction (Scheme 6).
Scheme 6
The presence of a remote carbonyl and cyano groups in the alkyl halides also facilitates their cross-coupling with diorganozincs. For example, functionalized diorganozincs and alkyl iodides can be cross-coupled using m - or p -trifluoromethyl styrene as a promotor and Ni(acac)2 as a catalyst (Scheme 7).
Scheme 7
11.9.3.2 Kumuda Coupling
The coupling of Grignard reagents with alkyl, vinyl or aryl halides under Ni-catalysis provides an effective route for carbon-carbon bond formation. For example, the synthesis of unsymmetrical biaryls can be accomplished from phenylmagnesium bromide and 1-chloro-4-methoxybenzene using Ni(COD)2 which is an example for low cost production of biaryl compounds (Scheme 8).
Scheme 8
Scheme 9