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

The macrocyclic ligand of 3,6,9,16,19,22-hexaazatricyclo[22.2.2.211,14]-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-μ-X bridged tetracopper(II) complexes [BP2Cu4(II)(μ-X)2] (X=PhCOO− (2), CO3 2− (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) Å, α=90.317(2), β=96.902(2), γ=92.691(2)°, V=1889.3(3) Å3 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 O2 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.