Mechanism of a dinuclear copper complex catalyzed autoxidation of 3,5-di-tert-butylcatechol

The autoxidation of 3,5-di-tert-butylcatechol (H2DTBC) was catalyzed by the dicopper (II) complex, Cu2(dppn)(OH)Cl3·H2O (Cu2(dppn)(OH)3+). Kinetic studies determined that the reactants were first order in the concentrations of the catalytic dinuclear copper species, molecular oxygen, and H2DTBC and inverse first order in the proton concentration. An experimental rate law, consistent with the kinetic data, was proposed and suggested that both O2 and HDTBC− were associated with the dinuclear copper complex in the transition state. The second order rate constant was calculated to be 189 ± 19 M−1 s−1. Furthermore, the stoichiometry of the catalyzed reaction was the same as tyrosinase-catalyzed oxidations and O2 was reduced to water in a four electron process. The 3,6-bis(2′-pyridyl)pyridazine (dppn) chelate served as the binucleating ligand and provided a rigid and sterically unencumbered platform for catalytic interaction of the dicopper core with O2 and HDTBC−. The dppn chelate also afforded the dicopper core the necessary coordination flexibility required for each copper ion to simultaneously cycle between square pyramidal cupric and tetrahedral cuprous ligand field geometries.

The autoxidation of 3,5-di-tert-butylcatechol (H2DTBC) was catalyzed by the dicopper (II) complex, Cu2(dppn)(OH)Cl3·H2O (Cu2(dppn)(OH)3+). Kinetic studies determined that the reactants were first order in the concentrations of the catalytic dinuclear copper species, molecular oxygen, and H2DTBC and inverse first order in the proton concentration. An experimental rate law, consistent with the kinetic data, was proposed and suggested that both O2 and HDTBC− were associated with the dinuclear copper complex in the transition state. The second order rate constant was calculated to be 189 ± 19 M−1 s−1. Furthermore, the stoichiometry of the catalyzed reaction was the same as tyrosinase-catalyzed oxidations and O2 was reduced to water in a four electron process. The 3,6-bis(2′-pyridyl)pyridazine (dppn) chelate served as the binucleating ligand and provided a rigid and sterically unencumbered platform for catalytic interaction of the dicopper core with O2 and HDTBC−. The dppn chelate also afforded the dicopper core the necessary coordination flexibility required for each copper ion to simultaneously cycle between square pyramidal cupric and tetrahedral cuprous ligand field geometries.Figure optionsDownload as PowerPoint slide