Homogeneous hydrogenation of alkenes catalyzed by the ruthenium-hydride complex (PCy3)2(CO)(Cl)RuH:: Spectroscopic observation of the ruthenium-ethylene-hydride intermediate species

The ruthenium-hydride complex (PCy3)(2)(CO)(Cl)RuH (1a) was found to catalyze the hydrogenation of terminal and cyclic alkenes. For example, the reaction of 1-hexene with 4 atm of H-2 in the presence of 1a (1-hexene:1a = 8300:1) produced the hydrogenation product 2 (TON = 12 000 h(-1)). The treatment of 1a with excess ethylene led to the observation of both the ruthenium-ethyl and ruthenium-ethylene-hydride species 4a and 5a, respectively. The thermodynamic parameters for the equilibria among 1a, 4a, and 5a were estimated from the VT NMR data. These results are consistent with a monohydride mechanistic pathway.