Dual-mode cross-coupling on aromatic imino compounds by dihydridoruthenium catalysts

Abstract

In the catalytic cross-coupling reaction of ketimines, derived from 1-acetonaphthone or acetophenone derivatives and benzylamine, with trialkoxyvinylsilanes RuH2(PPh3)4 or RuH2(CO)(PPh3)3 catalyst caused the selective alkenylation and alkylation on each aromatic ring of the ketimines separately (i.e. dual-mode coupling). Alkenylation occurred at the ortho-position(s) of the benzyl unit and alkylation occurred at the ortho-position(s) of 1-arylethylidene moiety of the substrates. By the stoichiometric reaction of N-1-(4-methylphenyl)ethylidene-4-methylbenzylamine with RuH2(CO)(PPh3)3 in the presence of three equivalents of vinylsilane, a novel ruthenium bismetallacylclic complex with two ruthenium-carbon bonds was isolated. This (C,N,C)-bismetallacycle complex was converted to the alkenylated complex by the reaction with two equiv. of vinylsilane. These observations indicate that the dual-mode coupling proceeds in a sequence of alkenylation followed by alkylation via intermediary bismetallacyclic complex formation.