The ligand α,α-bis{bis[1-(1-methyl-2-benzimidazolyl)- methyl]amino}-m-xylene (L-55) forms the complexes [CuI 2(L- 55)(MeCN)2](PF6)2 (1) and [CuII 2(L-55)(OMe)2][ClO4]2 (2), in which an extremely weak axial amine interaction is imposed by the small five-membered benzimidazole chelating ring units. This structural feature has been characterized by Xray crystal structure determination. In 1, the CuI centers are three-coordinate with ligation from two benzimidazolyl and one acetonitrile N-donors, in a slightly distorted trigonal arrangement. In 2, each CuII center has a distorted squareplanar geometry and coordinates to the benzimidazolyl N atoms and the bridging methoxy groups in the basal positions, with a much weaker interaction with the tertiary amine N in an apical position. These structural features affect the reactivities of the copper(I)− and copper(II)−L-55 complexes Introduction The interactions between synthetic copper complexes and dioxygen have become increasingly important in the last decade,[14] in connection with the enzymatic reactions catalyzed by copper enzymes,[59] particularly tyrosinase, and potential applications in catalytic transformations of organic substrates.[10,11] In the best characterized systems, the μ-η2:η2-peroxodicopper() or bis(μ-oxo)dicopper() complexes have been found to be able to effect CH bond cleavage of the ligand[1218] or an exogenous substrate[19,20] with insertion of an oxygen atom. In other dinuclear copper systems the putative copperdioxygen intermediate could not be characterized, due to high reactivity even at [a] Dipartimento di Chimica Generale, Universita` di Pavia, Via Taramelli 12, 27100 Pavia, Italy Fax: (internat.) 39-0382/528544 E-mail: bioinorg@unipv.it [b] Dipartimento C.I.M.A., Universita` di Milano, Centro CNR, Via Venezian 21, 20133 Milano, Italy [c] Dipartimento di Scienze Chimiche, Universita` di Trieste, Via L. Giorgieri 1, 34127 Trieste, Italy [d] Institute of Inorganic Chemistry, University of Erlangen- Nürnberg, Egerlandstraße 1, 91058 Erlangen, Germany Eur. J. Inorg. Chem. 2003, 11971205  2003WILEY-VCH Verlag GmbH & Co. KGaA, 69451Weinheim 14341948/03/03061197 $ 20.00.50/0 1197 toward dioxygen and hydrogen peroxide, respectively. [CuI 2(L-55)(MeCN)2]2+ does not produce a stable peroxo complex, but undergoes an irreversible oxidation to copper( II) species, while [CuII 2(L-55)(H2O)2]4+ reacts slowly with hydrogen peroxide to undergo regiospecific hydroxylation of the ligand at one benzylic carbon atom, which causes decomposition of the complex. [Cu2(L-55)(H2O)2]4+ is easily converted into its bis(μ-hydroxo) adduct [Cu2(L-55)(OH)2]2+. This pH-driven equilibrium was monitored by paramagnetic 1H NMR spectroscopy, and the solution magnetic properties of the complexes were determined by the Evans susceptibility method

Structure and Reactivity Studies on Dinuclear Copper Complexes of the Ligand a,a’-Bis{bis[1-(1’-methyl-2’-benzimidazolyl)-methyl]amino}-m-xylene

CASELLA L
;
MONZANI, ENRICO;
2003-01-01

Abstract

The ligand α,α-bis{bis[1-(1-methyl-2-benzimidazolyl)- methyl]amino}-m-xylene (L-55) forms the complexes [CuI 2(L- 55)(MeCN)2](PF6)2 (1) and [CuII 2(L-55)(OMe)2][ClO4]2 (2), in which an extremely weak axial amine interaction is imposed by the small five-membered benzimidazole chelating ring units. This structural feature has been characterized by Xray crystal structure determination. In 1, the CuI centers are three-coordinate with ligation from two benzimidazolyl and one acetonitrile N-donors, in a slightly distorted trigonal arrangement. In 2, each CuII center has a distorted squareplanar geometry and coordinates to the benzimidazolyl N atoms and the bridging methoxy groups in the basal positions, with a much weaker interaction with the tertiary amine N in an apical position. These structural features affect the reactivities of the copper(I)− and copper(II)−L-55 complexes Introduction The interactions between synthetic copper complexes and dioxygen have become increasingly important in the last decade,[14] in connection with the enzymatic reactions catalyzed by copper enzymes,[59] particularly tyrosinase, and potential applications in catalytic transformations of organic substrates.[10,11] In the best characterized systems, the μ-η2:η2-peroxodicopper() or bis(μ-oxo)dicopper() complexes have been found to be able to effect CH bond cleavage of the ligand[1218] or an exogenous substrate[19,20] with insertion of an oxygen atom. In other dinuclear copper systems the putative copperdioxygen intermediate could not be characterized, due to high reactivity even at [a] Dipartimento di Chimica Generale, Universita` di Pavia, Via Taramelli 12, 27100 Pavia, Italy Fax: (internat.) 39-0382/528544 E-mail: bioinorg@unipv.it [b] Dipartimento C.I.M.A., Universita` di Milano, Centro CNR, Via Venezian 21, 20133 Milano, Italy [c] Dipartimento di Scienze Chimiche, Universita` di Trieste, Via L. Giorgieri 1, 34127 Trieste, Italy [d] Institute of Inorganic Chemistry, University of Erlangen- Nürnberg, Egerlandstraße 1, 91058 Erlangen, Germany Eur. J. Inorg. Chem. 2003, 11971205  2003WILEY-VCH Verlag GmbH & Co. KGaA, 69451Weinheim 14341948/03/03061197 $ 20.00.50/0 1197 toward dioxygen and hydrogen peroxide, respectively. [CuI 2(L-55)(MeCN)2]2+ does not produce a stable peroxo complex, but undergoes an irreversible oxidation to copper( II) species, while [CuII 2(L-55)(H2O)2]4+ reacts slowly with hydrogen peroxide to undergo regiospecific hydroxylation of the ligand at one benzylic carbon atom, which causes decomposition of the complex. [Cu2(L-55)(H2O)2]4+ is easily converted into its bis(μ-hydroxo) adduct [Cu2(L-55)(OH)2]2+. This pH-driven equilibrium was monitored by paramagnetic 1H NMR spectroscopy, and the solution magnetic properties of the complexes were determined by the Evans susceptibility method
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11571/110633
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