Cluster-Based Catalytic Hydrogenation with High Conversion and Reversible Enantioselectivity<sup>†</sup> HomanenPertti PerssonRoger HaukkaMatti PakkanenTapani A. NordlanderEbbe 2000 Four tetranuclear ruthenium carbonyl hydrido clusters consisting of the enantiomeric pairs [H<sub>4</sub>Ru<sub>4</sub>(CO)<sub>10</sub>{μ-1,2-(<i>R</i>/<i>S</i>,<i>R</i>/<i>S</i>)-bdpp}] and [H<sub>4</sub>Ru<sub>4</sub>(CO)<sub>10</sub>{1,1-(<i>R</i>/<i>S</i>,<i>R</i>/<i>S</i>)-bdpp}] containing chiral (<i>R,R</i>)- or (<i>S,S</i>)-bdpp [bdpp = (2<i>R</i>/<i>S</i>,4<i>R</i>/<i>S</i>)-2,4-bis(diphenylphosphino)pentane] have been prepared and fully characterized. These clusters catalyze asymmetric hydrogenation of tiglic acid [<i>trans</i>-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.