Aerobic oxidative coupling of 2-naphthol derivatives catalyzed by a hexanuclear bis(μ-hydroxo)copper(II) catalyst

A novel hexanuclear bis(μ-hydroxo)copper(II) complex, [L₃(Cu₂(μ-OH)₂)₃](ClO₄)₆ (1), was synthesized with dinucleating ligand N,N,N,N-tetra(pyridin-2-ylmethyl)-m-xylene diamine (L). Complex 1 is fully characterized by X-ray crystallography and magnetic susceptibility in the solid state and UV-vis and electron paramagnetic resonance spectroscopy in solution. The molecular structure of 1 possesses three dicopper cores, in which two copper centers are bridged by two hydroxide groups and separated by a distance ranging from 2.8852(15) to 2.8937(10) Å. In addition, the three dicopper cores are linked by the dinucleating ligand between each pair of adjacent dicopper cores. Importantly, aerobic oxidative coupling of 2,4-di-tert-butylphenol, 2-naphthol, and six 2-naphthol derivatives was achieved in 33-96% yield using complex 1 as a catalyst.