Oxidation of alkanes by cobalt(II) salts of weakly coordinating anions

Abstract

Catalysts which effect the selective oxidation of alkanes under mild reaction conditions are highly desired. Commercial processes exist which involve the oxidation of alkanes by O{sub 2} with cobalt carboxylate catalysts. Elevated temperatures and pressures are required, and the metal ion function is to decompose hydroperoxides formed in a radical-chain process. The authors have demonstrated that a weakly solvated cobalt-acetonitrile complex (Co(NCCH{sub 3}){sub 4})(PF{sub 6}){sub 2}, with a weakly coordinating anion catalyzes the air oxidation of alkanes under mild conditions (75C and 3 atm). Cyclohexane and adamantane are converted to the corresponding alcohol and ketone products. The commercial catalyst for cyclohexane oxidation does not function under these milder conditions. Experiments indicate a mechanism in which the metal ion functions both as an initiator and as a hydroperoxide decomposition catalyst.