The cis influence of the corrin in vitamin B12 models

Density Functional Theory (DFT) and Quantum Theory of Atoms in Molecules (QTAIM) calculations on [NH3[Co(III)(C10-X-corrin)]–CH3]+, where the C10–H of corrin is replaced by electron-donating or –withdrawing groups, X, explore the cis influence in these vitamin B12 models. As the electron donating ability of X increases, a normal trans influence is observed: the Co–NH3 bond weakens while the Co–CH3 bond strengthens. Surprisingly, though, the Co–CH3 bond dissociation energy decreases monotonically as the Co–C bond strengthens. This is found to be a consequence of the extent of shortening of the Co–NH3 during the homolysis reaction.