A kinetic study on asymmetric transfer hydrogenation of unsaturated acids and esters by alcohols with binuclear ruthenium(II) chiral diphosphine complexes

Abstract

Kinetic investigation of the [Ru₂Cl₄{(–)-diop}₃][diop = 2,2-dimethyl-4,5-bis(diphenylphosphinomethyl)-1,3-dioxolane] catalysed transfer hydrogenation of unsaturated acids and esters by alcohols indicated that the catalytically active [RuCl₂{(–)-diop}] complex generated from the [Ru₂Cl₄{(–)-diop}₃]⇌[RuCl₂{(–)-diop}]+[RuCl₂{(–)-diop}₂] reaction afforded chiral hydrogenated products via the reaction of a hydrogen acceptor-[RuCl₂{(–)-diop}](hydrogen donor) complex and of a hydrogen donor-[RuCl₂{(–)-diop}](hydrogen acceptor) complex. ³¹P N.m.r. analysis of [Ru₂Cl₄{(–)-diop}₃] in solution also suggested the possibility of [RuCl₂{(–)-diop}₃] formation from [Ru₂Cl₄{(–)-diop}₃]. The reaction mechanism is also discussed on the basis of isotope effects observed in the [Ru₂Cl₄{(–)-diop}₃] catalysed reaction between deuteriated benzyl alcohols and unsaturated species.