Electrochemical preparation of stable nickel(III) complexes with tetradentate macrocyclic ligands in aqueous solutions

Stable solution of Ni^III complexes of the 14-membered macrocylic ligands (I), (II), and (III) were obtained by electrochemical oxidation on gold and platinum electrodes of the corresponding Ni^II complexes in mild acidic aqueous solutions in the presence of sulphate; the Ni^III complexes formed represent a new kind of strong, easily accessible, single-electron, oxidizing agent with E° ca. 1 V vs. standard hydrogen electrode (S.H.E.) in aqueous media.