Probing the Mechanism of Coenzyme B 12 : Synthesis, Crystal Structures, and Molecular Modeling of Coenzyme B 12 Model Compounds

Coenzyme B 12 is an organometallic compound that catalyzes biological rearrangement reactions. Homolytic cleavage of the unusual cobalt-carbon bond in the coenzyme initiates the free-radical reaction. In an attempt to understand the factors that might be important in the mechanism, we synthesized a series of model complexes [LCo{(DO)(DOH)bn}R] + with a folded equatorial ligand and determined the crystal structures. Semi-empirical calculations with these and other model compounds provide evidence for a transelectronic influence; when the Co-N bond is shortened, the Co-C bond lengthens. These results are compared to density functional calculations carried out by others.