Synthesis, structure, magnetism, and hydrolase and catecholase activity of a new trinuclear copper(II) complex

Abstract

In this paper we report the synthesis of the new multidentate N,O-donor ligand H3L_2pyald=(N,N′-bis-(2-pyridylmethyl)-(2-hydroxy-3-carbonyl-5-methylbenzyl)-1,3-propanediamine-2-ol) and its first trinuclear copper(II) complex, [Cu3(L_2pyald)(μ-OAc)](ClO4)2 (1). The structure of 1 was determined by X-ray crystallography and variable-temperature magnetic data in the temperature range of 4–300K indicate weak antiferromagnetism (J1,2≅−1.0cm−1) between the Cu(1) and Cu(2) centers bridged by the μ-alkoxo and μ-acetate groups and weak ferromagnetic coupling (J1,3=J2,3≅+4.0cm−1) involving the {Cu(1)(μ-phenoxo)Cu(3)} and {Cu(2)(μ-phenoxo)Cu(3)} structural units. Complex 1 shows significant catalytic activity towards the hydrolysis of the model substrate bis(2,4-dinitrophenyl)phosphate (2,4-BDNPP) as well as catechol oxidase activity since it efficiently catalyzes the oxidation of 3,5-di-tert-butylcatechol to 3,5-di-tert-butyl-o-benzoquinone by dioxygen. A comparison of the catalytic efficiency of 1 with its dinuclear parent complex [Cu2(H2bbppnol)(μ-OAc)]2+ (H3bbppnol=N,N′,N,N′-bis[(2-hydroxybenzyl)(2-methylpyridyl)]-1,3-propanediamine-2-ol) reveals that the hydrolase efficiency (kcat/KM) is 12 times higher for 1, while the catecholase efficiencies of these two compounds are similar.