Cluster-Based Catalytic Hydrogenation with High Conversion and Reversible Enantioselectivity

Four tetranuclear ruthenium carbonyl hydrido clusters consisting of the enantiomeric pairs [H4Ru4(CO)10{μ-1,2-(R/S,R/S)-bdpp}] and [H4Ru4(CO)10{1,1-(R/S,R/S)-bdpp}] containing chiral (R,R)- or (S,S)-bdpp [bdpp = (2R/S,4R/S)-2,4-bis(diphenylphosphino)pentane] have been prepared and fully characterized. These clusters catalyze asymmetric hydrogenation of tiglic acid [trans-2-methyl-2-butenoic acid] with high conversion rates (75−100%) under relatively mild reaction conditions. Enantiomeric excesses of 40−46% were observed; the predominating enantiomeric form of the hydrogenated product is dependent on the configuration of the diphosphine ligand, indicating strong chiral induction.