Synthesis of Ruthenium(II) Complexes Containing Tridentate Triamine (′ňňn′) and Bidentate Diamine Ligands (Ňn′): As Catalysts for Transfer Hydrogenation of Ketones

Abstract

A series of neutral and cationic Ru(II) complexes (1-10), bearing pyridine-based tridentate (′ŇŇN′), pyridine-based bidentate (ŇN′), and mixed ′ŇŇN′ + ŇN′ ligands, were synthesized by starting from [RuCl <inf>2</inf>(DMSO)<inf>4</inf>] and [RuCl<inf>2</inf>(p-cymene)]<inf>2</inf> precursors. Solid-state structures of mixed-ligand complexes 9 and 10 were determined by single-crystal X-ray diffraction. Both complexes are unusual in that ŇN′ ligands were spontaneously oxidized in air under base-free conditions to give imine-amine bidentate ligands upon replacement of p-cymene by meridional ′ŇŇN′. The complexes 1-10 were screened for transfer hydrogenation (TH) of aryl ketones with 2-propanol. The highest catalytic activity was obtained with the complexes containing tridentate ′ŇŇN′ and 7, which contain nonsulfonated 2-(aminomethyl)pyridine. However, for complexes 6<inf>a-c</inf>, containing p-cymene (a facial tridentate ligand), a slower reaction rate was observed. © 2011 American Chemical Society.