Catechol oxidation promoted by bridging phenoxo moieties in a bis(μ-phenoxo)-bridged dicopper() complex

A dinuclear copper( ii ) complex [Cu 2 (papy) 2 (CH 3 OH) 2 ] has been synthesized by reaction of one equiv. of Cu(OAc) 2 ·2H 2 O with one equiv. of the tetradentate tripodal ligand H 2 papy [ N -(2-hydroxybenzyl)- N -(2-picolyl)glycine] and has been characterized by various spectroscopic techniques and its solid state structure has been confirmed by X-ray crystal structure analysis. The single-crystal structure of the complex reveals that the two copper centers are hexa-coordinated and bridged by two O-atoms of the phenoxo moieties. The variable temperature magnetic susceptibility measurement of the complex reveals weak ferromagnetic interactions among the Cu( ii ) ions with a J value of 1.1 cm −1 . The catecholase activity of the complex has been investigated spectrophotometrically using 3,5-di- tert -butyl catechol as a model substrate in methanol solvent under aerobic conditions. The Michaelis-Menten kinetic treatment has been applied using different excess substrate concentrations. The parameters obtained from the catecholase activity by the complex are K M 2.97 × 10 −4 M, V max 2 × 10 −4 M s −1 , and k cat 7.2 × 10 3 h −1 . A reaction mechanism has been proposed based on experimental findings and theoretical calculations. The catechol substrate binds to dicopper( ii ) centers and subsequently two electrons are transferred to the metal centers from the substrate. The bridging phenoxo moieties participate as a Brønsted base by accepting protons from catechol during the catalytic cycle and thereby facilitating the catechol oxidation process. A bis(μ-phenoxo)-bridged dicopper( ii ) complex capable of oxidizing catechol with the highest efficiency amongst any bis(μ-phenoxo)-bridged dicopper( ii ) complexes is reported.