Model Studies for Coenzyme B₁₂ Dependent Enzyme-Catalyzed Rearrangements. Evidence for Cobalt(III)-Olefin π Complexes

Methanolysis of 2-acetoxyethyl-2-¹³C-(pyridine)cobaloxime gave equal amounts of methoxyethyl-l- ¹³C- and -2- ¹³C-(pyridine)cobaloxime. This shows that during the solvolysis both carbon atoms, of the ligand bonded to cobalt, became equivalent, and the intermediate for this can be envisaged as an olefin π complex of cobalt. Further evidence for olefin complexes of trivalent cobalt was obtained from the reaction between cob(III)alamins or cob(III)aloximes and vinyl ethers which gave the corresponding σ-bonded cobalt acetals. By involving such π complexes as intermediates of the reactions which are catalyzed by the B₁₂ coenzyme, one can account for, and generalize, the overall enzymatic rearrangements.