Ruthenium(II) complexes bearing pyridine-based tridentate and bidentate ligands: catalytic activity for transfer hydrogenation of aryl ketones

Ru(II) complexes of the general formula [RuCl2('NNN??')(L)] (1: 'N?=?Nb, L?=?MeOH; 2: 'N?=?Nb, L?=?CH3CN; 3: 'N?=?Nd, L?=?CH3CN; 4: 'N?=?Np, L?=?CH3CN), [Ru(p-cymene)(NN?ab)Cl]Cl (5a: N?Na?=?2,2'-bipyridine; 5b: N?Nb?=?4,4'-dimethyl2,2'-bipyridine), [Ru('NNN??')(NN?ab)Cl]Cl (6a: 'N?=?Nb, NN?a?=?2,2'-bipyridine; 6b: 'N?=?Nb, NN?b?=?4,4'-dimethyl-2,2'-bipyridine; 7a: 'N?=?Nd, NN?a?=?2,2'-bipyridine; 7b: 'N?=?Nd, NN?b?=?4,4'-dimethyl-2,2'-bipyridine; 8a: 'N?=?Np, NN?a?=?2,2'-bipyridine; 8b: 'N?=?Np, NN?b?=?4,4'-dimethyl-2,2'-bipyridine) and [Ru('NNN??')(NN?a)Cl]BF4 (9a: 'N?=?Nb; NN?a?=?2,2'-bipyridine) were synthesized from the corresponding [RuCl2(p-cymene)]2 dimer, 'NNN??' and NN?ab ligands. The compounds were characterized by elemental analysis, IR and NMR. Complex 9a was studied by X-ray diffraction, confirming its cationic-mononuclear [RuCl(bNNN??b)(NN?a)]+ nature. The synthesized Ru(II) complexes (18) were employed as catalysts for the transfer hydrogenation of ketones to secondary alcohols in the presence of KOH using 2-propanol as a hydrogen source at 82 degrees C. The rates of the transfer hydrogenation reactions strongly depended on the type of NNN?? and ancillary ligands. Copyright (C) 2012 John Wiley & Sons, Ltd.