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Phenoxyl radical complexes of zinc(II)
Citation key ISI:A1997XX82000017
Author Sokolowski, A and Muller, J and Weyhermuller, T and Schnepf, R and Hildebrandt, P and Hildenbrand, K and Bothe, E and Wieghardt, K
Pages 8889-8900
Year 1997
ISSN 0002-7863
Address 1155 16TH ST, NW, WASHINGTON, DC 20036
Journal J. Am. Chem. Soc
Volume 119
Number 38
Month SEP 24
Publisher AMER CHEMICAL SOC
Abstract A series of phenoxyl radical complexes of zinc(II) have been generated in solution and, in one instance, isolated as solid material (5) in order to study their spectroscopic features by EPR, resonance Raman, and UV-vis spectroscopy. They serve as model complexes for the active form of the copper containing fungal enzyme galactose oxidase. The complexes [Zn((LH2)-H-1)]BF4 . H2O (1), [Zn((LH2)-H-2)]BF4 . H2O (2), [Zn((LH)-H-2)] (2a), [Zn(L-3)(Ph(2)acac)] (3), [Zn(L-4)(Ph(2)acac)] (4), and [Zn(L-4)(Me-acac)] (6) were synthesized from solutions of Zn(BF4)(2) . 4H(2)O and the corresponding ligand ((LH3)-H-1=1,4,7-tris(3,5-tert-butyl-2-hydroxybenzyl)-1,4,7-triazacyclon ane; (LH3)-H-2=1,4,7-tris(3-tert-butyl-5-methoxy-2-hydroxybenzyl)-1,4,7-triaz acyclonane; (LH)-H-3=1,4-dimethyl-7-(3,5-di-tert-butyl-2-hydroxybenzyl)-1,4,7-triaza cyclononane; (LH)-H-4=1,4-dimethyl-7-(3-tert-butyl-5-methoxy-2-hydroxybenzyl)-1,4,7-t riazacyclononane, Ph(2)acac(-)=1,3-diphenyl-1,3-propanedionate, and Me-acac(-)=3-methyl-2,4-pentanedionate). Complexes 2, 3.0.5 toluene.1n-hexane, and 4 were structurally characterized by single-crystal X-ray crystallography. An electrochemical investigation of these complexes in CH3CN and/or CH2Cl2 solution revealed that the coordinated phenolate ligands undergo reversible one-electron oxidations with formation of coordinated phenoxyl radicals. Synthetically, the microcrystalline, paramagnetic (mu(eff)=1.7 mu(B)), solid material of [Zn(L-4)(Ph(2)acac)]PF6 (5) was produced by one electron oxidation of 4 by 1 equiv of ferrocenium hexafluorophosphate in dry CH2Cl2. Oxidation of coordinated phenol pendent arms in 1, 2, and 2a occurs at significantly higher potentials and is irreversible. Electronic (UV-vis), electron paramagnetic resonance (EPR), and resonance Raman (RR) spectra of the radicals have been studied in solution and allow the description of the electronic structure of these coordinated phenoxyl radical complexes.
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