Cyclohexyne nickel complex

Reactions of 250 with four electrophiles are recorded in Scheme 31. In general, the products are more stable than those from complexes with monodentate ligands. Reaction of 249 with CS2, 249 or 250 with alkynes, and 249-251 with ethylene gives products in which the C6H8 has been lost but its fate has not been determined attempts to trap free cyclohexyne failed.93 Loss of the organic ligand appears to occur more readily in nickel complexes than in those with platinum. 

The insertion of CS2 into a Ni-C coordination bond is proposed in the reaction of the cyclohexyne nickel(O) complex 45, as in the case of the reaction with CO2, although the product 46 could not be separated from the byproduct (Scheme 12) [95]. 

Cyclohexyne nickel(O) complex 19, prepared by the reductive elimination of 1,2-dibromocyclohexene with sodium amalgam in the presence of Ni(C2H4)L2 (L2 = Cy2PCH2CH2PCy2), also reacts with carbon dioxide or carbon disulfide to give complexes 20 and 21, respectively (Eq.ll). ... 

Generally, cyclohexyne is an unstable molecule because of its ring strain. However, it can be stabilized by coordination to transition metals.35 The reduction of 1,2-dibromocyclohexene by sodium/mercury in the presence of a nickel-bromide complex afforded the Ni-alkyne complex 66 as a thermally stable and isolable compound (Scheme 22).36 Complex 66 smoothly reacted with C02 under atmospheric pressure to give nickelacycle 67 in good yield. Dimethyl acetylenedicarboxylate was inserted into the vinyl-nickel bond in 67 to give the seven-membered oxanickelacycle 68. 

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