Vitamin B12 and the Periodic System

The combination of the corrin macrocycle and of cobalt as the basis for biological organometallic catalysis by the B12-cofactors is very intriguing 1. Replacing the cobalt-center of vitamin B12 derivatives by other metal ions has, thus, been an old dream of chemists working in the B12-field 1-3. Unfortunately, removal of the cobalt-ion from intact corrinoid B12-derivatives has remained futile. However, biosynthetic hydrogenobyric acid, the metal-free corrin ligand of vitamin B12, has now become available 4. This has opened the door to metal-analogues of the natural cobalt-corrins by incorporation of metal ions, selected from the periodic system. In this lecture the intricate structures and chemical properties of metal-analogues of the B12-derivatives are discussed, as well as the special role of the corrin ligand in binding cobalt ions.University Innsbruck