Cobalt (II) complexes containing bisimine ligands as models for catechol oxidase and Phenoxazinone synthase

The oxidation of 4-tert-butylcatechole (TBC) and 2-aminophenol (OAP) by molecular oxygen in the presence of a catalytic amount of cobalt(II) complexes was studied. The catecholase biomimetic catalytic activity of the cobalt(II) complexes has been determined spectrophotometrically by monitoring the oxidative transformation of 4-tert-butylcatechole and 2-aminophenol to the corresponding light absorbing 4-tert-butylquinone (Q) and 2-amino-3H-phenoxazin-3-one, respectively. The rate of the catalytic oxidation reaction was investigated and correlated with the catalyst structure, time, concentration of catalyst and substrate and finally solvent effects. Addition of Et3N, CH3CN and thiourea showed a dramatic effect on the rate of oxidation reaction. Kinetic investigations demonstrate that the rate of oxidation reaction has a first order dependence with respect to the catalyst and substrate concentration and obeying Lineweaver-Burk Kinetics. It was shown that the catalytic activity depends on the coordination environment of the catalyst created by the ligand.