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

Abstract

The reaction of furfurylamine with two equivalents of PPh2Cl in the presence of Et3N affords furfuryl-2-(N,N-bis(diphenylphosphino)amine), (Ph2P)2NCH2-C4H3O (1). The corresponding ruthenium(II) complex trans-[Ru((PPh2)2NCH2-C4H3O)2Cl2] (3) was synthesized by reacting 1 with [Ru(η6-p-cymene)(μ-Cl)Cl]2. The reaction of furfurylamine with one equivalent of PPh2Cl gives Ph2PNHCH2-C4H3O (2). The reaction of 2 with [Ru(η6-p-cymene)(μ-Cl)Cl]2, [Ru(η6-benzene)(μ-Cl)Cl]2, [Rh(μ-Cl)(cod)]2 and [Ir(η5-C5Me5)(μ-Cl)Cl]2 yields the complexes [Ru(Ph2PNHCH2-C4H3S)(η6-p-cymene)Cl2] (4), [Ru(Ph2PNHCH2-C4H3O)(η6-benzene)Cl2] (5), [Rh(Ph2PNHCH2-C4H3O)(cod)Cl] (6) and [Ir(Ph2PNHCH2-C4H3O)(η5-C5Me5)Cl2] (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)(η6-p-cymene)Cl2] (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)(η6-p-cymene)Cl2] (4) and [Ru(Ph2PNHCH2-C4H3O)(η6-benzene)Cl2] (5) are much more active in the transfer hydrogenation, converting the carbonyls to the corresponding alcohols in 97–99% yields (TOF ≤300h−1), compared to analogous rhodium and iridium complexes and the trans-Ru(II)-p-cymene bis(phosphino)amine complex.