The cis influence of the corrin in vitamin B12 models

► DFT calculations explore the cis influence of corrins on Co-CH3 bond homolysis. ► There is normal trans influence between Co-CH3 and Co-NH3 bond lengths. ► Increasing electron donation from the corrin causes the Co-CH3 BDE to decrease. ► Differences in BDE arises from differential stabilization between 6C-Co(III) and 5(C)-Co(II).