Effect of water on the catalytic oxidation of catechols

A dinuclear copper(II) complex derived from a new water-soluble pentadentate Schiff base backbone ligand has been prepared and characterized in solution and in the solid state. The complex has been found to accelerate the aerobic oxidation of 3,5-di-tert-butylcatechol (DTBC) into 3,5-di-tert-butylquinone (DTBQ) by 5 orders of magnitude, compared to the background reaction in aqueous methanol (K-cat/k(non)= 160 000) at 30 degrees C. The transformation of the model substrate is considerably slower in pure methanol (k(cat)/k(non) = 60 000) under otherwise identical conditions. In-depth investigation of the catalytically active species revealed different structures for the copper(II) complex in methanol and in methanol/water mixtures.