Reactivity of Bi2-Derivatives in Organometallic Reactions

The formation and cleavage of the Co-C bond in organometallic B12-cofactors are crucial steps in the reactions catalyzed by B12-derivatives and by B -dependent enzymes [1,6,25,26,115-118]. The reactivity of B12-derivatives in organometallic reactions also holds the key to much of the 

In solution cleavage and formation of the Co - C bond have been observed to occur in all of the basic oxidation levels for the cobalt center of the corrin core [115-118]. Two main paths for these organometallic reactions have been found  

The homolytic mode is formally a one-electron reduction/oxidation of the corrin-bound cobalt center and involves the cleavage or formation of a single axial bond, as is typical of the reactivity of coenzyme B12 [119-123)  

For the particular case of AdoCbl (2) it was found that the contribution of nucleotide coordination to the ease of homolytic cleavage was relatively small. On the basis of available thermodynamic data concerning the coordination of the nucleotide in 2 and of the homolysis product cob(II)alamin (23), the coordination of the nucleotide was estimated to weaken the Co - C bond by only 0.7 kcal/mol [75,86]. In contrast to that, the intramolecular coordina- 

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