Versatile Activity of a Copper(II) Complex Bearing a N4-Tetradentate Schiff Base Ligand with Reduced Oxygen Species

Abstract

The reactivity of the Cu(II) complex of N,N’-bis(pyridin-2-ylmethylene)propane-1,3-diamine (py2pn), [Cu(py2pn)(ClO4)2], toward O2.− and H2O2 has been examined. The complex reacts with O2.− with fast second order kinetics, kMcF=4.05×106 M−1 s−1, employing the Cu(II)/Cu(I) couple proved by spectroscopic detection of the reduced form at low temperature. At −40 °C in DMF, the reaction of the complex with H2O2/Et3N yields an stable end-on Cu(II)-hydroperoxide, with kOOH=0.31 min−1, the formation of which has been established by DFT calculations, electronic and EPR spectra. At room temperature, the end-on Cu(II)-hydroperoxide reacts with a second Cu(II) complex to evolve O2, with kCAT=83.2 M−2 s−1. The Cu(II)-hydroperoxide can mediate phenol oxidation, probably through a trigonal bipyramidal ternary transition state based on DFT analysis, favored over catalase activity when low proportion of catalyst is used. In these reactions, structural constraints imposed by the ligand distort the coordination geometry of the metal and controls reactivity.