Synthesis, characterization and catechol oxidase biomimetic catalytic activity of cobalt(II) and copper(II) complexes containing N2O2 donor sets of imine ligands

New tetradentate imine ligands are derived from Schiff base condensation in a 1:2 molar ratio of the 1,2,4,5-tetra-amino benzene with 2-hydroxy benzaldehyde, (L1), 2,4-dihydroxy benzaldehyde (L2) and 2-hydroxy naphthaldehyde (L3). These ligands react with CoCl2 and CuCl2 in refluxing ethanol to yield a series of cobalt(II) and copper(II) complexes of the type [M2IILn] nH2O. The structure of the obtained ligands and their metal(II) complexes were characterized by various physicochemical techniques, viz. elemental analysis, molar conductance, magnetic susceptibility measurements, thermal analysis (TGA & DTG), IR, electronic absorption and ESR spectral studies. Four-coordinate tetrahedral and square-planar structures were proposed for cobalt(II) and copper(II) complex species respectively. The ability of the synthesized complexes to catalyze the aerobic oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC) to the light absorbing 3,5-di-tert-butylquinone (3,5-DTBQ) has been investigated. The results obtained show that all complexes catalyze this oxidation reaction and slight variations in the rate were observed. The probable mechanistic implications of the catalytic oxidation reactions are discussed.