Reactions of nickel-group 6 complexes with a bulky terminal alkyne to afford alkyne–carbonyl coupled products: X-ray structure of the heterobimetallic nickelacyclobutenone complex [(η5-C5Me5)Mo(CO)2(η5-C5H4Me)] (Ni–Mo)

The nickel–molybdenum complex [(η5-C5Me5)Nidouble bond; length as m-dashMo(CO)3(η5-C5H4Me)] can be considered to contain a partially dative nickel–molybdenum double bond. This complex reacts with the bulky terminal alkyne HCtriple bond; length of mdashCCPh2(OMe) (DPMP) to afford the alkyne–carbonyl coupled metallacyclic product (3c, R = CPh2(OMe), Ni–Mo) regioselectively and exclusively. No traces of a nickel–molybdenum μ-alkyne complex, analogous to similar complexes isolated with less bulky alkynes, were observed. The structure of complex 3c was established via a single crystal X-ray diffraction study. It exhibits the same connectivity as that observed with a related complex formed with the smaller but-2-yne, but some significant differences are observed between the two structures. Reactions of the nickel–molybdenum and -tungsten species [(η5-C5Me5)Nidouble bond; length as m-dashM(CO)3(η5-C5H5)] (M = Mo, W) with DPMP proceeded analogously and afforded similar products.