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

Abstract

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 [BPCu 2(II)](ClO 4) 4 ( 1) and the bis-μ-X bridged tetracopper(II) complexes [BP 2Cu 4(II)(μ-X) 2] (X=PhCOO − ( 2), CO 3 2− ( 3) and CH 3O − ( 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) Å, α=90.317(2), β=96.902(2), γ=92.691(2)°, V=1889.3(3) Å 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 μ-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.