Kinetics and mechanisms of homogeneous catalytic reactions: Part 1. Hydrogenation of benzaldehyde catalyzed by [RuH(CO)(NCMe) 2(PPh 3) 2]BF 4

Abstract

Kinetic and mechanistic studies of the homogeneous hydrogenation of benzaldehyde were carried out using the cationic complex [RuH(CO)(NCMe) 2(PPh 3) 2]BF 4 ( 1) as the catalyst precursor, which was very efficient under mild reaction conditions in 2-methoxyethanol as the solvent. The experimental rate law was found to be r=( K 1 k 2/1 + K 1[PhCHO])[Ru][PhCHO][H 2] ( K 1 = 1.9 M −1; k 2 = 12.5 M −1 s −1) which can be approximated to r= k cat[Ru][PhCHO][H 2] ( k cat = 20 M −2 s −1). The activation parameters and the kinetic isotope effect were also calculated. The kinetic data and the coordination chemistry related to the hydrogenation of benzaldehyde are consistent with a mechanism involving the addition of hydrogen as the rate-determining step of the catalytic cycle.