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

A diphenoxido-bridged dinuclear copper­(II) complex, [Cu2L2(ClO4)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, [Cu2L2(OH)]­ClO4 (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 Å (avg.) to 2.798 Å (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 (kcat = 233.4 h–1) than compound 1 (kcat = 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.