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

A series of neutral and cationic Ru(II) complexes (1–10), bearing pyridine-based tridentate (′N ͡N ͡N′), pyridine-based bidentate (N ͡N′), and mixed ′N ͡N ͡N′ + N ͡N′ ligands, were synthesized by starting from [RuCl2(DMSO)4] and [RuCl2(p-cymene)]2 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 N ͡N′ ligands were spontaneously oxidized in air under base-free conditions to give imine-amine bidentate ligands upon replacement of p-cymene by meridional ′N ͡N ͡N′. 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 ′N ͡N ͡N′ and 7, which contain nonsulfonated 2-(aminomethyl)pyridine. However, for complexes 6a–c, containing p-cymene (a facial tridentate ligand), a slower reaction rate was observed.