Mononuclear and dinuclear (pyridyl) dicarboxamide Ru(II) hydrido complexes: Ligand controlled coordination diversity and catalytic transfer hydrogenation of ketones

Abstract

Reactions of ligand N,N-(1,4-phenylene)-dipicolinamide (H2L1), with [Ru(PPh3)3(CO)HCl] produced the dinuclear complex [Ru2(H2L1)(PPh3)4(CO)2H2]2+[2Cl−]− (Ru1). On the other hand, treatments of ligand N,N-(1,2-phenylene)-dipicolinamide (H2L2), with two and one molar equivalents of [Ru(PPh3)3(CO)HCl] afforded the dinuclear and mononuclear complexes [Ru2(HL2)(PPh3)3(CO)3HCl2] (Ru2) and [Ru(HL2)(PPh3)2(CO)H] (Ru3) respectively. The identities and structures of complexes Ru1-Ru3 were established using NMR, FT-IR spectroscopic techniques, mass spectrometry, and elemental analyses. The complexes Ru1-Ru3 displayed high catalytic activities in the transfer hydrogenation of a wide range of ketones. The hydride complex Ru1 was the most active, while the dinuclear complex Ru2 was more active than the analogous mononuclear complex Ru3. 31P NMR spectroscopic analyses of the reaction intermediates was used to propose a monohydride pathway in the transfer hydrogenation reactions involving dissociation of one PPh3 ligand.