Dehydrocoupling Reactions of Dimethylamine-Borane by Pt(Ⅱ) Complexes: A New Mechanism Involving Deprotonation of Boronium Cations

摘要

Coordinatively unsaturated Pt(Ⅱ) complex [Pt(I~tBu')(I~tBu)]~+ stabilized by N-heterocyclic carbene (NHC) ligands dehydrogenates N,N-dimethylaminebor-ane through a mechanism that involves hydride abstraction, assisted by an amine, to yield a platinum-hydride complex [PtH(I~tBu')(I~tBu)] with concomitant formation of the boronium cation [(NHMe_2)_2BH_2]~+. This latter species is very likgly in equilibrium with the THF stabilized borenium cation [(NHMe_2)(THF)BH_2]~+, bearing an acidic NH group that is able to protonate the platinum hydride [PtH(I~tBu')(I~tBu)] releasing H_2, the amino borane H_2B-NMe_2 and regenerating the catalytic [Pt]~+ species.