Model Studies for Coenzyme B12 Dependent Enzyme-Catalyzed Rearrangements. Evidence for Cobalt(III) Olefin Complexes
Silverman, R.B. and David Dolphin
J. Am. Chem. Soc.
Methanolysis of 2-acetoxyethyl-2-13C-(pyridine)cobaloxime gave equal amts. of methoxyethyl-1-13C- and -2-13C-(pyridine)cobaloxime. This shows that during the solvolysis both C atoms, of the ligand bonded to Co, became equivalent, and the intermediate (I) for this can be envisaged as an olefin π-complex of Co. Further evidence for olefin π-complexes of trivalent Co was obtained from the reaction between cob(III)alamins or cob(III)aloximes and vinyl ethers which gave the corresponding σ-bonded Co 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 enzymic rearrangements.