Dinuclear complexes [NAPH (Cu II) 2 (μ-X) (bipy) 2]ClO 4: synthesis, characterization and Tyr-like activity

Abstract

Four μ-X-bridged dicopper(II) complexes have been synthesized, namely [NAPH Cu 2 (μ-X) (bipy) 2]ClO 4 (X=OH ( 1), OAc ( 2), Cl ( 3) and Br ( 4); NAPH denotes 1,8-naphthalate dianion). NAPH was found to have the ability to form dinuclear complexes with X as an additional ligand. Based on the elemental analysis, infrared and electronic spectra, these complexes were found to have heterocyclic structure with both DPHA and μ-X as bridging ligands. The temperature dependence of magnetic susceptibilities of complexes 1 and 4 have been studied, giving the exchange integral of J=−189.7 and −187.9 cm −1, respectively. This result is in agreement with proposed μ-X-bridged structure. In methanolic solution and excess dioxygen, these complexes were found to be effective catalysts for catechol oxidizing to benzoquinone. The rate constant for these complexes is in the order of 1>2–3>4. The oxidation is first order in Cu 2 complex and zero in substrate. In the same conditions and in the presence of sodium ethoxide, the rates of catalytic reactions for these complexes were found to be 2–4 times greater than for the formal oxidation. On the basis of these observations, a catalytic scheme based on the dicopper(II) complex as the initial active species is proposed.