Cluster-based catalytic hydrogenation with high conversion and reversible enantioselectivity

Four tetranuclear ruthenium carbonyl hydride clusters consisting of the ena ntiomeric pairs [H4Ru4(CO)(10){mu -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,4 R/S)-2,4-bis(diphenylphosphino)pentane] have been prepared and fully charac terized. These clusters catalyze asymmetric hydrogenation of tiglic acid [t rans-2-methyl-2-butenoic acid] with high conversion rates (75-100%) under r elatively mild reaction conditions. Enantiomeric excesses of 40-46% were ob served; the predominating enantiomeric form of the hydrogenated product is dependent on the configuration of the diphosphine ligand, indicating strong chiral induction.