Mechanistic studies of the oxidative coupling polymerization of 2,6-dimethylphenol: 1. Kinetics of polymerization catalysed by a copper(II)-tmed complex

Abstract

A kinetic study of the oxidative coupling polymerization of 2,6-dimethylphenol, catalysed by Cu(II)-tmed § § N, N, N′, N′-tetramethylethylenediamine complexes, is described. The species detected in solution, before the reaction, appeared to be a dinuclear chloro-bridged complex containing one bidentate tmed ligand per copper(II) ion. KInetic experiments in combination with vis spectra suggest that at least a fivefold excess of tmed is needed to obtain a maximum amount of the highly active catalyst. The rate of oxidative coupling is significantly enhanced by the addition of OH −, resulting in a maximum rate at an OH/Cu ratio of ≈1. The role of hydroxide was determined to be that of a ‘co-catalyst’, required for the formation of 2,6-dimethylphenolate anions, allowing these to substitute the chloro-bridges in the dinuclear precursor complex. Under all the experimental conditions used the reaction rates were independent of the dioxygen concentration. A first-order rate dependence on catalyst concentration was found. When varying the 2,6-dimethylphenol (DMP) concentration, Michaelis-Menten behaviour was observed.