Enantioselective hydride transfer hydrogenation of ketones catalyzed by [(η6-p-cymene)Ru(amino acidato)Cl] and [(η6-p-cymene)Ru(amino acidato)]3(BF4)3 complexes

The new complexes (RRuSC, SRuSC)-[(η6-pCym)Ru(l-Aze)Cl] (6a, b), (RRuSC, SRuSC)-[(η6-pCym)Ru(l-Pip)Cl] (7a, b), (RRuRRuRRuSCSCSCSNSNSN, SRuSRuSRuSCSCSCSNSNSN)-[{(η6-pCym)Ru(l-Aze)}3](BF4)3 (8a, b) and (RRuRRuRRuSCSCSCSNSNSN, SRuSRuSRuSCSCSCSNSNSN)-[{(η6-pCym)Ru(l-Pip)}3](BF4)3 (9a, b) (l-Aze=l-2-azetidinecarboxylate, l-Pip=l-2-piperidinecarboxylate) were prepared, characterized and used, together with the known [{(η6-pCym)Ru(l-Pro)}3](BF4)3, 5 and [{(η6-pCym)Ru(l-Ala)}3](BF4)3, 10 (l-Pro=l-prolinate, l-Ala=l-alaninate), in hydride transfer reduction of acetophenone, a series of substituted acetophenones and several other ketones with moderate to high conversions and enantioselectivities up to 86% e.e.