Mechanistic aspects of coenzyme b12-dependent rearrangements. Organometallics as free radical precursors

Abstract

The mechanistic aspects of coenzyme B12-dependent rearrangements are discussed. At the present stage it appears that the principal, if not the only, role of coenzyme is B12 to serve as the precursor for an organic free radical, generated by homolytic dissociation of the cobalt-carbon bond, which triggers the substrate rearrangement. The determination of cobalt-alkyl bond dissociation energies in organo-cobalt compounds related to coenzyme B12 and the electronic and structural factors that influence such bond dissociation energies, are discussed. An analogy is developed between the role of coenzyme B12 in biological systems as a reversible “free radical carrier” and the role of hemes as reversible dioxygen carriers. 0033-4545/83 $3.00+0.00 Pergamon Press Ltd. © 1983 IUPAC