Activation of dioxygen by copper complexes incorporated in molecular sieves

Abstract

The activation of dioxygen, at ambient conditions, by dimeric copper acetate complexes incorporated in molecular sieves Y, MCM-22 and VPI-5, in the oxidation of phenols to ortho diphenols and diphenols to o-quinones is reported. l-tyrosine is oxidised to l-DOPA, phenol to catechol, catechol to ortho benzoquinone and cresols to the corresponding ortho dihydroxy and o-quinone compounds. The incorporated copper complexes have been characterized by IR, UV and ESR spectroscopies. A linear correlation between the concentration of the copper acetate dimer in the molecular sieve (from ESR) and the conversion of l-tyrosine suggests that the dimeric copper atoms are the active sites in the activation of dioxygen. The catalytic efficiency (turnover numbers) of the copper atoms are higher in the incorporated state compared to that in ‘neat’ copper acetate. Our results indicate that copper acetate dimers in molecular sieves mimic both the monophenolase and diphenolase catalytic activity of the monooxygenase enzyme, tyrosinase.