Redox properties of cobalt(II) and methylcobalt(III) complexes with dianionic macrocyclic polychelate ligands

Redox potentials of a series of complexes of cobalt(II) and organocobalt(III) with tetraazamacrocyclic (N₄) and N₂O₂-noncyclic polychelate ligands have been determined by cyclic voltammetry. Introduction of ano-phenylene fragment instead of an ethylene fragment into an equatorial ligand and/or exchange of an N₄-coordination chromophore for the N₂O₂-analog has been shown to result in the anodic shift of redox potentials of MeCo(IV)L/ MeCo(III)L, MeCo(III)L/MeCo(II)L, and Co(II)L/Co(I)L pairs. It has been established that the solvent effect on redox potential is larger for Co(III)L/Co(II)L than for other pairs. Apparently, this is the first case when quasi-reversible stages of oxidation of MeCo(III)L to MeCo(IV)L⁺ and MeCo(IV)L⁺ to MeCo(IV)L]²⁺ can be simultaneously observed. A. relatively stable complex of methylcobalt(IV) with a long lifetime at 20 °C has been registered by the ESR method.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1029–1033, June, 1993.