Catalytic Hydroboration in Gas Phase

A new catalytic hydroboration of olefins in the gas phase has been proposed. The kinetics of the reaction of diborane with ethylene or propylene in the presence of a Pd-carbon catalyst was investigated at 30°C to 50°C The initial rate of the reaction, ri, was expressed by ri=kp1/2BPO, where PB and PO denote the initial partial pressures of diborane and ethylene or propylene, respectively, and k the rate constant. The activation energy was 6 and 1.5kcal/mol for ethylene and propylene, respectively. These activation energies were much smaller than those for noncatalytic hydroboration found in literature. The reaction mechanism was interpreted in terms of the rate-determining step which is the attack of the olefin on the dissociated diborane on the catalyst. The reaction mechanism was further confirmed by the adsorptions of diborane, ethylene and propylene.