Electrochemical transformations of catecholate and o-amidophenolate complexes with triphenylantimony(V)

The electrochemical properties of catecholate and o-amidophenolate complexes with triphenylantimony(V) with various substituents in the aromatic ring were examined. Introduction of electron-donating groups into the catecholate ligand or replacement of an O atom (in catecholate) by a N atom (o-amidophenolate) stabilizes the monocationic forms of the complexes obtained by one-electron oxidation. Complexes with electron-withdrawing substituents undergo irreversible two-electron oxidation resulting in the elimination of o-quinone. Complexes containing electron-withdrawing ligands do not form o-semiquinones and are inert to atmospheric oxygen. According to electrochemical data, oxygen can be bound reversibly by catecholate complexes containing the electron-donating methoxy groups in the 3,6-di-tert-butylcatecholate ligand and o-amidophenolate derivatives with half-wave oxidation potentials lower than or equal to 0.70 V (vs. Ag/AgCl), which form relatively stable cationic complexes upon the oxidation.