Catalysis of carbon monoxide hydrogenation by soluble mononuclear complexes

The homogeneous hydrogenation of CO to CH/sub 3/OH, higher primary alcohols and their formate esters in the presence of Co/sub 2/(CO)/sub 8/ using benzene, heptane, and p-dioxane as solvents is reported. The principal rate-determining step is first order in the soluble mononuclear species, HCo(CO)/sub 4/, and the catalysis by cobalt atom dusters or precipitated metal is at most a minor path. Based on paired experiments in benzene (200,220/sup 0/C), and inp-dioxane (182,196/sup 0/C), the apparent activities enthalpy for formation of CO hydrogenation products is 40.7 kcal/mol. This result is compatible with a strongly endothermic rate-determining step in which hydrogen atom transfer to CO yields formyl and cobalt tetracarbonyl radical pairs. Pseudo first-order rate constants for the formation of methanol and total product were found to be 1.3 x 10/sup -5/ s/sup -1/ and 1.46 x 10/sup -5/ s/sup -1/, respectively, and proportionately between hydrogenation rate and concentration of HMn(CO)/sub 5/ was observed.