Ruthenium, rhodium and iridium complexes of the furfuryl-2-(N-diphenylphosphino)methylamine ligand: Molecular structure and catalytic activity

The reaction of furfurylamine with two equivalents of PPh2Cl in the presence of Et3N affords furfuryl-2-(N,N-bis(diphenylphosphino)amine), (Ph2P)(2)NCH2-C4H3O (1). The corresponding ruthenium(II) complex trans-[Ru((PPh2)(2)NCH2-C4H3O)(2)Cl-2] (3) was synthesized by reacting 1 with [Ru(eta(6)-p-cymene)(mu-Cl)Cl](2). The reaction of furfurylamine with one equivalent of PPh2Cl gives Ph2PNHCH2-C4H3O (2). The reaction of 2 with [Ru(eta(6)-p-cymene)(mu-Cl)Cl](2), [Ru(eta(6)-benzene)(mu-Cl)Cl](2), [Rh(mu-Cl)(cod)](2) and [Ir(eta(5)-C5Me5)(mu-Cl)Cl](2) yields the complexes [Ru(Ph2PNHCH2-C4H3S)(eta(6)-p-cymene)Cl-2] (4), [Ru(Ph2PNHCH2-C4H3O)(eta(6-)benzene)Cl-2] (5), [Rh(Pb2PNHCH2-C4H3O)(cod)Cl] (6) and [Ir(Ph2PNHCH2-C4H3O)(eta(5)-C5Me5)Cl-2] (7), respectively. All the complexes were isolated from the reaction solution and fully characterized by analytical and spectroscopic methods. The structure of [Ru(Ph2PNHCH2-C4H3O)(eta(6)-p-cymene)Cl-2] (4) was also determined by single crystal X-ray diffraction. Complexes 3-7 are suitable precursors forming highly active catalysts in the transfer hydrogenation of a variety of simple ketones. Notably, the catalysts obtained by using the ruthenium complexes [Ru(Ph2PNHCH2-C4H3O)(eta(6)-p-cymene)Cl-2] (4) and [Ru(Ph2PNHCH2-C4H3O)(eta(6)-benzene)Cl-2] (5) are much more active in the transfer hydrogenation, converting the carbonyls to the corresponding alcohols in 97-99% yields (TOF <= 300 h(-1)), compared to analogous rhodium and iridium complexes and the trans-Ru(II)-p-cymene bis(phosphino)amine complex. (c) 2012 Elsevier Ltd. All rights reserved.