Synthesis, structure and diverse coordination chemistry of cobalt(III) complexes derived from a Schiff base ligand and their biomimetic catalytic oxidation of o-aminophenols

Abstract

This paper deals with the syntheses and structural characterizations of four new cobalt(III) compounds (1–4) derived from a N3O donor Schiff base ligand and their catalytic activity towards the aerobic oxidation of o-aminophenols. Both counter ions and solvents used for the synthesis have significant influence on structural diversity of the resulting complexes. X-ray crystallography reveals that although the geometry of cobalt(III) centres are octahedral in all the cases but the coordination environments are significantly different in them. All these complexes show diverse reactivity towards the catalytic oxidation of o-aminophenols in which availability of substitutionally labile sites at the metal centre for substrate o-aminophenols binding is the main reason for higher catalytic activity in 2 and 3 than others. Furthermore, we have examined the detailed kinetic studies of the aerobic oxidation of one substituted o-aminophenol, namely 2-amino-5-methylphenol, using 2 and 3 as catalysts in which facile oxidation of the substituted o-aminophenol was noticed. ESI mass spectral study has been carried out in order to get insight into mechanistic pathway of functioning such catalytic activity.