A Nickel(II)-Containing Vitamin B₁₂ Derivative with a Cofactor-F430-type π-System

F430 is a unique enzymatic cofactor in the production and oxidation of methane by strictly anaerobic bacteria. The key enzyme methyl coenzyme M reductase (MCR) contains a hydroporphinoid nickel complex with a characteristic absorption maximum at around 430 nm in its active site. Herein, the three-step semisynthesis of a hybrid Ni^II -containing corrinoid that partly resembles F430 in its structural and spectroscopic features from vitamin B₁₂ is presented. A key step of the route is the simultaneous demetalation and ring closure reaction of a 5,6-secocobalamin to metal-free 5,6-dihydroxy-5,6-dihydrohydrogenobalamin with cobaltocene and KCN under reductive conditions. Studies on the coordination chemistry of the novel compound support an earlier hypothesis why nature carefully selected a corphin over a corrin ligand in F430 for challenging nickel-catalyzed biochemical reactions.