Effective transfer hydrogenation of unsaturated compounds by ruthenium dihydride complex in propan-2-ol

Abstract

Ruthenium(II)-hydride complexes were very effective catalysts for the transfer hydrogenation of ketones and imines using propan-2-ol as hydrogen donor in the presence of a base. By using the catalyst dihydridotetrakis(triphenylphosphine)-ruthenium(II), the reduction proceeded effectively in the absence of a base. This ruthenium dihydride catalyst also caused the transfer hydrogenation of benzonitrile to afford benzylamine derivatives albeit in a moderate yield. Isotope labeling experiments in the reaction of N-(2-naphthylmethylidene)benzylamine with this ruthenium dihydride catalyst revealed the hydride transfer from ruthenium hydride to the CN bond of the substrate. In the case of the ruthenium monohydride species, no transfer hydrogenation occurred for ketones, imines and nitrile in the absence of a base except at the CC double bond of conjugated carbonyl compounds.