INVESTIGATION OF THE REACTIVE OXYGEN INTERMEDIATE IN AN ARENE HYDROXYLATION REACTION PERFORMED BY XYLYL-BRIDGED BINUCLEAR COPPER COMPLEXES

The kinetics of the reaction, via an oxygen-bound intermediate, of [CuI2(NO2-XYL)][ClO4]2·CH3CN to [Cu2(NO2-XYL-O-)(OH)]2+, where the bridging arene is hydroxylated, have been examined with use of resonance Raman spectroscopy. A resonance Raman peak characteristic of peroxide bound in a side-on, μ-η2:η2 geometry is observed upon oxygenation of [CuI2(NO2-XYL)] for both intramolecularly and intermolecularly bridged complexes. The decay of the intramolecularly bridged peroxide stretch at ∼750 cm-1 and the growth of the phenolate stretch of the product at 1320 cm-1 were monitored over time with use of an excitation wavelength of 406.9 nm. Both the decay of the peroxide stretch and the growth of the phenolate stretch were found to be first order, and the rate constants are consistent, within experimental error, with the peroxide intermediate reacting directly to form the hydroxylated product. The possibility of an unobservable amount of a bis-μ-oxo isomer which is in rapid equilibrium with the side-on peroxide...