Département de chimie moléculaire

We report the structure, properties and a mechanism for the catecholase activity of a tetranuclear carbonato-bridged copper(II) cluster with the macrocyclic ligand [22]pr4pz (9,22-dipropyl-1,4,9,14,17,22,27,28,29,30-decaazapentacyclo[22.2.1.14.7.111,14.117,20]triacontane-5,7(28),11(29),12,18,20(30),24(27),25-octaene). In this complex, two copper ions within a macrocyclic unit are bridged by a carbonate anion, which further connects two macrocyclic units together. Magnetic susceptibility studies have shown the existence of a ferromagnetic interaction between the two copper ions within one macrocyclic ring, and a weak anti-ferromagnetic interaction between the two neighboring copper ions of two different macrocyclic units. The tetranuclear complex was found to be the major compd. present in soln. at high concn. levels, but its dissocn. into two dinuclear units occurs upon diln. The dinuclear complex catalyzes the oxidn. of 3,5-di-tert-butylcatechol to the resp. quinone in methanol by two different pathways, one proceeding via the formation of semiquinone species with the subsequent prodn. of hydrogen peroxide as a byproduct, and another proceeding via the two-electron redn. of the dicopper(II) center by the substrate, with two mols. of quinone and one mol. of water generated per one catalytic cycle. The occurrence of the first pathway was, however, found to cease shortly after the beginning of the catalytic reaction. The influence of hydrogen peroxide and di-tert-butyl-o-benzoquinone on the catalytic mechanism has been investigated. The crystal structures of the free ligand and the reduced dicopper(I) complex, as well as the electrochem. properties of both the CuII and the CuI complexes are also reported. [on SciFinder(R)]