Applications of transition metal complexes containing 3,3′-bis(diphenylphosphinoamine)-2,2′-bipyridine ligand to transfer hydrogenation of ketones

Hydrogen transfer reduction processes are attracting increasing interest from synthetic chemists in view of their operational simplicity. 3,3′-bis(diphenylphosphinoamine)-2,2′-bipyridine, (Ph2PNH)2C10H6N2, was prepared through a single step reaction of 3,3′-diamino-2,2′-bipyridine with diphenylchlorophosphine. Reaction of (Ph2PNH)2C10H6N2 with [Ru(η6-benzene)(μ-Cl)Cl]2, [Rh(μ-Cl)(cod)]2 or [Ir(η5-C5Me5)(μ-Cl)Cl]2 gave a range of new bridged dinuclear complexes [C10H6N2{NHPPh2Ru(η6-benzene)Cl2}2], 1, [C10H6N2{PPh2NHRh(cod)Cl}2], 2 and [C10H6N2{NHPPh2Ir(η5-C5Me5)Cl2}2], 3, respectively. All new complexes have been fully characterized by analytical and spectroscopic methods. 1H31P-{1H} NMR, 1H13C HETCOR or 1H1H COSY correlation experiments were used to confirm the spectral assignments. 1, 2 and 3 are suitable catalyst precursors for the transfer hydrogenation of acetophenone derivatives. Notably [Ru((Ph2PNH)2C10H6N2)(η6-benzene)Cl2], 1 acts as an excellent catalyst, giving the corresponding alcohols in 98–99% yields in 10 min at 82 °C (TOF ≤600 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.

Graphical abstractThree novel dinuclear transition metal complexes [C10H6N2{NHPPh2Ru(η6-benzene)Cl2}2], [C10H6N2{PPh2NHRh(cod)Cl}2] and [C10H6N2{NHPPh2Ir(η5-C5Me5)Cl2}2] were prepared and characterized. These complexes were evaluated in the transition metal-catalyzed transfer hydrogenation of ketones. Notably [Ru((Ph2PNH)2C10H6N2)(η6-benzene)Cl2] acts as an excellent catalyst, giving the corresponding alcohols in 98–99% yields in 10 min (TOF ≤600 h−1).Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► [Ru(II), Rh(I), Ir(III)] complexes of aminophosphine ligand were synthesized. ► These are suitable catalyst precursors for the TH of acetophenone derivatives. ► 1 gives the corresponding alcohols in 98–99% yields with TOF ≤600 h−1.