Insertion of a hydroxido bridge into a diphenoxido dinuclear copper(II) complex: Drastic change of the magnetic property from strong antiferromagnetic to ferromagnetic and enhancement in the catecholase activity

摘要

A diphenoxido-bridged dinuclear copper(II) complex, [Cu _2L _2(ClO _4) _2] (1), has been synthesized using a tridentate reduced Schiff base ligand, 2-[[2-(diethylamino)-ethylamino]methyl] phenol (HL). The addition of triethylamine to the methanolic solution of this complex produced a novel triple bridged (double phenoxido and single hydroxido) dinuclear copper(II) complex, [Cu _2L _2(OH)]ClO _4 (2). Both complexes 1 and 2 were characterized by X-ray structural analyses, variable-temperature magnetic susceptibility measurements, and spectroscopic methods. In 1, the two phenoxido bridges are equatorial-equatorial and the species shows strong antiferromagnetic coupling with J = -615.6(6.1) cm ~(-1). The inclusion of the equatorial-equatorial hydroxido bridge in 2 changes the Cu?Cu distance from 3.018 ? (avg.) to 2.798 ? (avg.), the positions of the phenoxido bridges to axial-equatorial, and the magnetic coupling to ferromagnetic with J = 50.1(1.4) cm ~(-1). Using 3,5-di-tert-butylcatechol as the substrate, the catecholase activity of the complexes has been studied in a methanol solution; compound 2 shows higher catecholase activity (k _(cat) = 233.4 h ~(-1)) than compound 1 (k _(cat) = 93.6 h ~(-1)). Both complexes generate identical species in solution, and they are interconvertible simply by changing the pH of their solutions. The higher catecholase activity of 2 seems to be due to the presence of the OH group, which increases the pH of its solution.