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 × 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.