Oxidative coupling polymerization of 2,6-dimethylphenol catalyzed by macrocyclic tetracopper(II) complexes

The macrocyclic ligand of 3,6,9,16,19,22-hexaazatricyclo[22.2.2.2(11,14)]-triaconta-1(26),11(12),13,24,27,29-hexaene(L, BP) was synthesized by [2+2] condensation of p-phthaldehyde and diethylenetriamine. This ligand was used to synthesize dicopper(II) complex [BPCu2(II)](ClO4)(4) (1) and the bis-mu-X bridged tetracopper(II) complexes [BP2Cu4(II)(mu-X)(2)] (X = Ph-COO- (2), CO32- (3) and CH3O- (4)). Complex 3 crystallizes in the triclinic space group P1, with cell constants a = 9.9965(10), b = 13.5887(14), c = 14.0262(7) Angstrom, alpha = 90.317(2), beta = 96.902(2), gamma = 92.691(2)degrees, V = 1889.3(3) Angstrom(3) and Z = 2. Complexes 3 and 4 proved to be effective homogeneous catalysts for oxidative coupling of 2,6-dimethylphenol (DMP) to polyphenylene ether (PPE) by dioxygen. These complexes transform DMP to PPE under mild conditions of atmospheric pressure of O-2 and 298 K. The effectiveness of the catalytic reaction depends upon the type of the mu-X ligand and the concentration of the auxiliary NaOEt. Crystallographic and mechanistic investigation indicated that the catalytic center is the 'dimer-to-dimer' tetranuclear structure, and a novel mechanism for this polymerization reaction was proposed. (C) 2002 Elsevier Science B.V. All rights reserved.