Applications of transition metal complexes containing aminophosphine ligand to transfer hydrogenation of ketones

Abstract

Hydrogen transfer reduction processes are attracting increasing interest from synthetic chemists in view of their operational simplicity. Reaction of [Ph2PNHCH2-C4H3S] with [Ru(eta(6)-benzene)(mu-Cl)Cl](2), [Rh(mu-Cl)(cod)](2) and [Ir(eta(5)-C5Me5)(mu-Cl)Cl](2) gave a range of new monodendate complexes [Ru(Ph2PNHCH2-C4H3S)(eta(6)-benzene)Cl-2], 1, [Rh(Ph2PNHCH2-C4H3S)(cod)Cl], 2, and [Ir(Ph2PNHCH2-C4H3S)(eta(5)-C5Me5)Cl-2], 3, respectively. All new complexes were fully characterized by analytical and spectroscopic methods. H-1-P-31 NMR, H-1-C-13 HETCOR or H-1-H-1 COSY correlation experiments were used to confirm the spectral assignments. 1-3 are suitable catalyst precursors for the transfer hydrogenation of acetophenone derivatives. Notably [Ru(Ph2PNHCH2-C4H3S)(eta(6)-benzene) Cl-2], 1, acts as an excellent catalyst, giving the corresponding alcohols in 98-99% yields in 30 min at 82 degrees C (TOF <= 200 h(-1)) for the transfer hydrogenation reaction in comparison to analogous rhodium or iridium complexes. This transfer hydrogenation is characterized by low reversibility under these conditions. Copyright (C) 2011 John Wiley & Sons, Ltd.