Mechanistic implications of an asymmetric intermediate in catalytic C-C coupling by a dinuclear nickel complex

An asymmetric nickel-nickel bonded intermediate was isolated in the reaction of biphenylene with bis(1,5-cyclooctadiene) nickel and i-Pr(3)P, where three of the four carbons are sigma-bonded to one nickel. Mechanistic investigations support reactivity as a formal Ni(III)-Ni(I) complex; reductive elimination of cis-disposed Ni-C bonds from a single nickel centre directly provides a dinuclear Ni(I)-Ni(I) complex, a reaction relevant to dinuclear catalysis.