Kinetics of the Formation and Decomposition of Carbon-Cobalt(III) Bonds in Aqueous Solutions by the Reaction of Aliphatic Free Radicals with a Coenzyme B-12r Model Cobalt(II) Complex

The reactions of -CH2OH, CH3CHOH, HOCHCH2OH, and -CH2CHO with a CoIIL complex were studied (L=macrocyclic Me6[14]dieneN4). In all systems the product of these reactions is a CoIIIL-RH complex. The mechanism of decomposition of these products depends on the nature of the aliphatic residue-RH. CoIIIL-CH2OH decomposes by a heterolytic cleavage of the carbon metal bond forming CoIL+CH2O. CoIIIL-CH(OH)CH3 seems to decompose by a hydride transfer from the β-carbon yielding CoIIIL-H+CH3CHO. CoIIIL-CH(OH)CH2OH rearranges by loss of water to CoIIIL-CH2CHO, which then hydrolyzes to CoIIIL+CH3CHO. The latter reaction is a model reaction to that of the diol dehydratase enzyme which contains the coenzyme B-12. The mechanism of these reactions and their implication on the chemistry of other systems containing σ carbon-cobalt bonds are discussed.