Synthesis and reactivities of novel η 2-(C,O) alkylphenylketene complexes of nickel. Coordination-mode switching reaction of the ketene ligand

Abstract

A series of bis(tertiary phosphine)(alkylphenylketene)nickel complexes, Ni[(C 6H 5(R)CCO)L 2 [R  CH 3 ( a), C 2H 5 ( b); L  P(C 6H 5) 3 ( 1), P(C 6H 5) 2( p-CH 3C 6H 4) ( 2)], were isolated from the reaction of bis(1,5-cyclooctadiene)nickel with alkylphenylketene in the presence of the corresponding tertiary phosphines. The spectroscopic analyses of 1 and 2 suggest η 2-(C,O) to be a ketene structure close to the structure of oxanickelacyclopropane. Based on their chemical reactivities and fluxional behaviors in 1H and 13C NMR, the ketene moieties of 1 and 2 switch their coordination-mode from η 2-(C,O) to η 2-(C,C) type via an associative process involving binuclear μ-ketene intermediates prior to undergoing further reactions.