Synthesis, Characterization and Oxidase Biomimetic Catalytic Activity of Copper(II) Schiff-base Complexes

Abstract

A new series of diimine–Schiff base ligands containing sulfur and nitrogen donor sets and their mononuclear macrocyclic and non-macrocyclic copper(II) complexes were prepared via applying template synthesis technique. The structural characterization was achieved based upon analytical and spectroscopic investigations. The stereochemistry, the nature of the copper(II) chelates, and the catalytic reactivity are markedly dependent upon the type of counter anions and the ligand substituents within the carbonyl moiety of the macrocyclic and non-macrocyclic copper(II) complexes. Catalytic studies demonstrate that the reported copper(II) complexes are suitable as catalysts for the catalytic aerobic oxidation of 3,5-di-tert-butylcatechol (3,5-DTBCH2) to 3,5-di-tert-butyl-benzoquinone (3,5-DTBQ) (catechol oxidase activity), and o-aminophenol (OAPH) to 2-aminophenoxazine-3-one (APX) (phenoxazinone synthase activity) with dioxygen at ambient condition in good yields. From the obtained results, it is also found that the catalytic activity of the investigated copper(II) complexes towards the oxidation of 2-aminophenol is higher than that of catechol oxidation, It was also found that the added triethylamine in both systems greatly accelerates the reaction. On the basis of kinetic data plausible mechanisms were proposed for both systems assuming ternary complex formation between catalyst, substrate and dioxygen, in which the latter one is the rate-determining step.