STUDY OF THE REACTION MECHANISM OF CYCLOHEXENE HYDROGENATION CATALYZED BY RhCl(PPh_3)_3

The hydrogenation rate of styrene in benzene using RhCI(PPh_3)_3 as catalyst increases with the concentration of styrene. But the hydrogenation rate of cyclohexene is rather different, It shows a maximum. So we inquire into the reaction mechanism of cyclohexene hydrogenation catalyzed by RhCI(PPh_3)_3. The rate of hydrogenation was measured at 25±0.15℃, as a function. of catalyst concentration, olefin concentration, triphenylphosphine concentration and hydrogen pressure. The maximum of the reaction rate is interpreted by the formation of RhClL_2S_2. The rate determining step is considered to be the reaction of olefin insertion into one of the Rh-H bonds formed by hydrogenation of RhClL3 to H_2RhClL_3. The hydrogenation rate of the substrate can be described by a third order equation in terms of concentration of H_2RhClL_3. Average error between the results evaluated by this equation and experimental results is about 4.9％. The quantum chemistry calculation gives support to the present mechanism.