New light on the Co–C bond activation in B12-dependent enzymes from density functional theory

Density functional theory (DFT) is applied to the calculation of activation of the Co–CR bond in models of vitamin B12, B–[CoIII(corrin)]–R. It is shown that there is a positive correlation of the bond lengths between the Co atom and the two axial ligands, B and R. The electron donation from axial ligands to the cobalt atom either by electron donating substituents or by a properly oriented external electric field caused by external electric charges is argued to be the main trigger for the activation of the Co–CR bond.