Highly selective hydrogenation of carbon-carbon multiple bonds catalyzed by the cation [(C6Me6)2Ru2(PPh 2)H2]+: Molecular structure of [(C 6Me6)2Ru2(PPh2)(CHCHPh)H] +, a possible intermediate in the case of phenylacetylene hydrogenation

Abstract

The dinuclear cation [(C6Me6)2Ru 2(PPh2)H2]+ (1) has been studied as the catalyst for the hydrogenation of carbon-carbon double and triple bonds. In particular, [1][BF4] turned out to be a highly selective hydrogenation catalyst for olefin functions in molecules also containing reducible carbonyl functions, such as acrolein, carvone, and methyljasmonate. The hypothesis of molecular catalysis by dinuclear ruthenium complexes is supported by catalyst-poisoning experiments, the absence of an induction period in the kinetics of cyclohexene hydrogenation, and the isolation and single-crystal X-ray structure analysis of the tetrafluoroborate salt of the cation [(C6Me6)2Ru2(PPh 2)-(CHCHPh)H]+ (2), which can be considered as an intermediate in the case of phenylacetylene hydrogenation. On the basis of these findings, a catalytic cycle is proposed which implies that substrate hydrogenation takes place at the intact diruthenium backbone, with the two ruthenium atoms acting cooperatively in the hydrogen-transfer process. © 2007 Wiley-VCH Verlag GmbH & Co. KGaA.