Synthesis, characterization, and redox behavior of new dicobalt complexes having monoanionic imine/oxime-type ligands

New dicobalt complexes, [Co^III₂LBr₄], with monoanionic ligands (L) have been synthesized by the reaction of a tetraamine and oximes, followed by an aerobic reaction with CoBr₂·6H₂O. The complexes were characterized by elemental analyses, IR, ESR, and NMR as well as mass spectroscopies. The redox behavior of the complexes was examined in DMF by means of cyclic voltammetry in comparison with that of the corresponding mononuclear complex. Redox waves identified to Co^III/Co^II and Co^II/Co^I for [Co^III₂L] were observed at -0.19 V and -0.69 V vs Ag/AgCl, respectively. These potentials are quite similar to those for the corresponding mononuclear complex. An electrogenerated [Co¹₂L] species reacts with methyl p-toluenesulfonate to give an organocobalt complex. Two-electron reduction of the dinuclear organocobalt compound yields an unstable intermediate that undergoes rapid decomposition by cleavage of the cobalt-carbon bond. The dimethylated complex, which has cobalt-carbon bonds at one axial site of each cobalt, was disproportionated to a tetramethylated complex, involving two cobalt-carbon bonds at both axial sites, and a dicobalt(I) species by two-electron reduction. The tetramethylated cobalt complex was inactive for an electrochemical reduction, but transformed into the dimethylated complex via cleavage of the cobalt-carbon bonds upon electrochemical oxidation.