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

The bifunctional phosphine-abnormal N-heterocyclic carbene ruthenium(II) complex RuBr(OAc)(PPh3)(P-aNHC) (1) has been synthesized in high yield by reaction of Ru(OAc)(2)(PPh3)(2) with a phosphine imidazolium bromide (P-NHC X 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)(PPh3)(P-aNHC)-(H2NCH2CH2NH2)]Br (2), which displays the same activity of the in situ generated species.