Synthesis of ruthenium(II) complexes containing tridentate triamine ('NNN') and bidentate diamine ligands (NN'): As catalysts for transfer hydrogenation of ketones

A series of neutral and cationic Ru(II) complexes (1-10), bearing pyridine-based tridentate ('NNN'), pyridine-based bidentate (NN'), and mixed 'NNN' + NN' ligands, were synthesized by starting from [RuCl 2(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' ligands were spontaneously oxidized in air under base-free conditions to give imine-amine bidentate ligands upon replacement of p-cymene by meridional 'NNN'. 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' 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. © 2011 American Chemical Society