Synthesis of Ruthenium(II) Complexes Containing Tridentate Triamine ('(NNN)over-cap ') and Bidentate Diamine Ligands ((NN)over-cap '): as Catalysts for Transfer Hydrogenation of Ketones

A series of neutral and cationic Ru(II) complexes (1-10), bearing pyridine-based tridentate ('(NNN) over cap'), pyridine-based bidentate ((NN) over cap'), and mixed '(NNN) over cap' + (NN) over cap' 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 (NN) over cap' ligands were spontaneously oxidized in air under base-free conditions to give imine-amine bidentate ligands upon replacement of p-cymene by meridional '(NNN) over cap'. 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 '(NNN) over cap' and 7, which contain nonsulfonated 2-(aminomethyl)pyridine. However, for complexes 6(a-c), containing p-cymene (a facial tridentate ligand), a slower reaction rate was observed.