Benzo[h]quinoline Pincer Ruthenium and Osmium Catalysts for Hydrogenation of Ketones

Chiral orthometalated osmium complexes [OsCl(CN'N)(PP)] {PP = (S,R)-Josiphos type diphosphane} based on 2-aminomethylbenzo[h]quinoline ligands (HCN'N) were prepared by reaction of [OsCl2(PPh3)(3)] with a Josiphos diphosphane and a HCN'N ligand in the presence of NEt3. Ruthenium and osmium complexes [MX(CN'N)(PP)] (M = Ru, Os; X = Cl, OCH(p-C6H4F)(2); PP = dppb, (S,R)-Josiphos), in the presence of KOtBu, efficiently catalyze the chemoselective hydrogenation (H-2 = 5 atm) of aromatic and aliphatic ketones to secondary alcohols in methanol or methanol/ethanol mixtures, when a S/C ratio of 10000-50000 is used. With use of these chiral phosphanes, alkyl aryl ketones have been reduced with ee values up to 99% and turnover frequencies (TOFs) up to 5.6 x 10(4) h(-1).