New dicobalt complexes, [CoIII 2LBr4], 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 CoIII/CoII and CoII/CoI for [CoIII 2L] 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 [Co1 2L] 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.
All Science Journal Classification (ASJC) codes
- 化学 (全般)