Oxidative coupling catalyzed by copper complexes of poly(amido-amines)

Abstract

Copper complexes of N, N, N', N'-tetramethylethylenediamine (TMED) are known catalysts for the oxidative coupling of 2,6-dimethylphenol (DMP). In the present study two new poly(amido-amines) (PAA) with TMED-like structures along their backbones were applied as polymeric ligands for the same oxidative coupling in methanol solvent. The polymeric catalysts appeared to be about four times more active than their low-molar mass analog and even than TMED itself. From kinetic and spectrophotometric measurements it could be concluded that the most active polymeric catalysts are probably binuclear copper complexes with one TMED unit per Cu ion and only one bridging OH − between the two Cu ions: {‘TMED’·Cu(OH)ClCu·‘TMED’} 2+·2Cl −, instead of two bridging OH −in the normal TMED complexes in dichlorobenzene solvent. The kinetics demonstrated that the rate of the electron transfer from substrate to Cu 2+ is so rapid in the case of the polymeric catalysts that prior complexation of DMP with the catalyst does not attain an equilibrium value. Thus no substrate saturation was observed and simple first order kinetics both in DMP and CuCl 2 were obtained instead of the usual Michaelis-Menten scheme.