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[22.2.1.1 4,7 .1 11,14 . 1 17,20 ]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 antiferromagnetic interaction between the two neighboring copper ions of two different macrocyclic units. The tetranuclear complex was found to be the major compound present in solution at high concentration levels, but its dissociation into two dinuclear units occurs upon dilution. The dinuclear complex catalyzes the oxidation of 3,5-di-tertbutylcatechol to the respective quinone in methanol by two different pathways, one proceeding via the formation of semiquinone species with the subsequent production of dihydrogen peroxide as a byproduct, and another proceeding via the two-electron reduction of the dicopper(II) center by the substrate, with two molecules of quinone and one molecule 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 ditert-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 electrochemical properties of both the Cu II and the Cu I complexes are also reported.

The reaction of copper(II) perchlorate with the macrocyclic ligand [22]py4pz in the presence of base leads to formation of a dinuclear complex [Cu(2)([22]py4pz)(mu-OH)](ClO(4))(3)xH(2)O, in which two copper ions are bridged by a single mu-hydroxo bridge. Each copper ion is further surrounded by four nitrogen atoms of the ligand. The mu-hydroxo bridge mediates a strong antiferromagnetic coupling (2J = -691(35) cm(-1)) between the metal centers, leading to relatively sharp and well-resolved resonances in the (1)H NMR spectrum of the complex in solution. We herein report the crystal structure, the magnetic properties, and the full assignment of the hyperfine-shifted resonances in the NMR spectrum of the complex, as well as the determination of the exchange coupling constant in solution through temperature-dependent NMR studies.

The monohydroxo-bridged dicopper(II) complex (1), its reduced dicopper(I) analogue (2) and the trans-mu-1,2-peroxo-dicopper(II) adduct (3) with the macrocyclic N-donor ligand [22]py4pz (9,22-bis(pyridin-2'-ylmethyl)-1,4,9,14,17,22,27,28,29,30- decaazapentacyclo -[22.2.1(14,7).1(11,14).1(17,20)]triacontane-5,7(28),11(29),12,18,20(30), 24(27),25-octaene), have been prepared and characterized, including a 3D structure of 1 and 2. These compounds represent models of the three states of the catechol oxidase active site: met, deoxy (reduced) and oxy. The dicopper(II) complex 1 catalyzes the oxidation of catechol model substrates in aerobic conditions, while in the absence of dioxygen a stoichiometric oxidation takes place, leading to the formation of quinone and the respective dicopper(I) complex. The catalytic reaction follows a Michaelis-Menten behavior. The dicopper(I) complex binds molecular dioxygen at low temperature, forming a trans-mu-1,2-peroxo-dicopper adduct, which was characterized by UV-Vis and resonance Raman spectroscopy and electrochemically. This peroxo complex stoichiometrically oxidizes a second molecule of catechol in the absence of dioxygen. A catalytic mechanism of catechol oxidation by 1 has been proposed, and its relevance to the mechanisms earlier proposed for the natural enzyme and other copper complexes is discussed.

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Four new macrocyclic ligands of varying ring size, [22] (D), show the pyrazole groups and the amine nitrogens all to be involved in the coordination of the copper(II) ions. In the mononuclear compound A the copper ion is in a distorted octahedral geometry, with the equatorial plane formed by four nitrogen donor atoms from the ligand and the axial positions occupied by two oxygen atoms from mono-coordinated perchlorate anions. In compound B each copper ion is in a distorted square pyramidal environment, with the three ligand nitrogens and a chloride atom in the equatorial plane and another chloride atom in the axial position. The cation of compound C contains four copper centers. Two bridging Cl atoms connect the two central copper atoms to form a centrosymmetric four membered ring. Two macrocyclic units are present in the cation, each containing two copper atoms bridged by a chloride atom. One copper is fivefold coordinated and the second copper is distorted octahedral. In compound D both copper(II) ions are in a distorted octahedral N 5 O environment, with the equatorial plane formed by the three ligand nitrogens and a nitrogen from an acetonitrile molecule. A second acetonitrile molecule and a mono-coordinated perchlorate anion are weakly bound in the axial positions. The copper nitrate compounds of these new ligands are to some degree active catalysts in the oxidative coupling of 2,6-dimethylphenol with molecular dioxygen to poly(2,6-dimethyl-1,4-phenylene ether). #

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The formation of two new acetal-containing ligands 1,2-bis(3Ј-dimethoxymethylpyrazol-1Ј-yl)ethane (bdmpe) and 1,2-bis(3Ј-diethoxymethylpyrazol-1Ј-yl)ethane (bdepe) in a Cu()-assisted alcoholysis of the initial ligand 1,2-bis(3Ј-formylpyrazol-1Ј-yl)ethane is described. The new ligands form polymeric complexes with Cu() salts of the general formula [Cu(L)X 2 ] x , where L = bdmpe or bdepe, and X = Cl or Br. The single-crystal X-ray structures of [Cu(bdmpe)Cl 2 ] x and [Cu(bdmpe)Br 2 ] x show that two of the four oxygen atoms of the acetal fragments are axially semi-coordinated to the copper() ions, adjusting the coordination sphere around the metal ion to a very distorted octahedron. The coordination of the oxygen atoms of the acetal groups to the metal ion may well be the driving force for the transformation of the initial aldehyde groups into the acetal fragments. The equatorial plane in [Cu(bdmpe)Cl 2 ] x is a trans-CuN 2 Cl 2 chromophore, while in [Cu(bdmpe)Br 2 ] x it is a cis-CuN 2 Br 2 species with a large in-plane distortion.

Page 7711. In the second line of the right column, the cited reference should be 5a instead of 5b. The chiral hybrids reported in ref 5b have amino acids and POM clusters covalently linked.