Abnormal N-Heterocyclic Carbene-Phosphine Ruthenium(II) Complexes as Active Catalysts for Transfer Hydrogenation

Abstract

The bifunctional phosphine–abnormal N-heterocyclic carbene ruthenium(II) complex RuBr(OAc)(PPh 3 )(P–aNHC) ( 1 ) has been synthesized in high yield by reaction of Ru(OAc) 2 (PPh 3 ) 2 with a phosphine imidazolium bromide (P–NHC × HBr) and characterized by X-ray diffraction. This compound shows high catalytic activity for the transfer hydrogenation of ketones to alcohols in 2-propanol. Rate and efficiency of 1 can be enhanced by the addition of ethylenediamine or benzylamine, affording TOFs up to 140 000 h –1 . Reaction of 1 with ethylenediamine leads to the Ru carbene/amine complex [Ru(OAc)(PPh 3 )(P–aNHC)(H 2 NCH 2 CH 2 NH 2 )]Br ( 2 ), which displays the same activity of the in situ generated species.