Self-exchange reactions of cobalt complexes and implications concerning redox reactivity of vitamin B12

Abstract

The self-exchange rates of Co(N₄)(OH₂)₂^3+,2+ complexes, where (N₄) is a tetradentate macrocyclic ligand, have been found to vary by a factor of 10¹⁰; the large reactivity range cannot be related to “spin effects”, but is likely a reflection of ligand reorganizational barriers; the vitamin B_12a–B_12r couple is at the high end of this range—a feature which has significance in the redox mechanisms of B₁₂ and related systems.