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

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 C=N 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 C=C double bond of conjugated carbonyl compounds. (C) 1999 Elsevier Science B.V. All rights reserved.