SELECTIVITY FOR HYDROGENATION OR HYDROFORMYLATION OF OLEFINS BY HYDRIDOPENTACARBONYLMANGANESE(I) IN SUPERCRITICAL CARBON-DIOXIDE

The stoichiometric and catalytic hydrogenation and hydroformylation of activated olefins by MnH(CO)(5) are generally believed to proceed by a free radical caged pair mechanism, the selectivity of which is affected by solvent. However, the stoichiometric reaction with a test olefin in. supercritical CO2 (scCO(2)), with its low viscosity, gives a selectivity for hydrogenation almost identical to that found in alkanes or without solvent. Aside from the possibility of coincidentally equal cage strengths, the most likely explanation is that the aldehydes are primarily formed by nonradical pathways which are independent of solvent viscosity.