PHENOXYL RADICAL COMPLEXES OF ZINC(II)

A series of phenoxyl radical complexes of zinc(II) have been generated in solution and, in one instance, isolated as solid material (5) in o rder to study their spectroscopic features by EPR, resonance Raman, an d UV-vis spectroscopy. They serve as model complexes for the active fo rm of the copper containing fungal enzyme galactose oxidase. The compl exes [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), an d [Zn(L-4)(Me-acac)] (6) were synthesized from solutions of Zn(BF4)(2) . 4H(2)O and the corresponding ligand tert-butyl-2-hydroxybenzyl)-1,4 ,7-triazacyclonane; -5-methoxy-2-hydroxybenzyl)-1,4,7-triazacyclonane; rt-butyl-2-hydroxybenzyl)-1,4,7-triazacyclononane; -methoxy-2-hydroxy benzyl)-1,4,7-triazacyclononane, Ph(2)acac(-)=1,3-diphenyl-1,3-propane dionate, 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 the se complexes in CH3CN and/or CH2Cl2 solution revealed that the coordin ated phenolate ligands undergo reversible one-electron oxidations with formation of coordinated phenoxyl radicals. Synthetically, the microc rystalline, 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 significantl y 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 t he electronic structure of these coordinated phenoxyl radical complexe s.