On the mechanism of the Co2(CO)8 catalyzed hydroformylation of olefins in hydrocarbon solvents. A high pressure UV and IR study

High pressure IR and UV spectroscopic experiments confirm the Heck and Breslow mechanism of the hydroformylation of 1-octene and cyclohexene with Co₂(CO)₈ as the starting catalyst. The major repeating unit is HCo(CO)₄, which is formed via the reaction of acylcobalt tetracarbonyl with H₂. The rates are 6.7 × 10^?4 mol l^?1 min^?1 and 8.8 × 10^?5 mol l^?1 min^?1 for 1-octene and cyclohexene, respectively at 80°C and 95 bar CO/H₂ = 1 in methylcyclohexane. The alternative reaction of RCOCo(CO)₄ with HCo(CO)₄ is only a minor pathway, with rates of 1.8 × 10^?5 mol l^?1 min^?1 and 1.1 × 10^?5 mol l^?1 min^?1 for 1-octene and cyclohexene, respectively. It represents an exit from the catalytic cycle. The activation of the catalyst precursor Co₂(CO)₈ is the slowest step of the reaction.