ISBN: 978-83-60043-10-3 - eurobic9

Eurobic9, 2-6 September, 2008, Wrocław, Poland
Y. Shimazaki
P179. Oxidation Behavior of Metal-Phenolate Complexes and
Characterization of Their Phenoxyl Radical Species
College of Science, Ibaraki University, Bunkyo, 310-8512, Mito, Japan,
e-mail: yshima@mx.ibaraki.ac.jp
The Cu(II)-phenoxyl radical formed during the catalytic cycle of galactose oxidase (GO) attracted much
attention, and the structures and properties of a number of metal-phenoxyl radical complexes have been studied.
As a functional model system of GO, Stack et al. reported that the Cu complex of a distorted salen
(di(salicylidene)ethylenediamine) derivatives showed the catalytic oxidation of primary alcohols to aldehydes,
and formation of the Cu(II)-phenoxyl radical species was revealed in the catalytic cycle.
As an extension of the studies on Metal-phenoxyl radical species, we synthesized Co(II), Co(III), Ni(II), Cu(II),
and Zn(II) complexes of the N3O tripodal ligands with a 2, 4-di(tert-butylphenolate moiety and characterized the
one- and two-electron oxidized complexes. The structures of these phenolate complexes depended on the central
metal ion. Co(II) and Zn(II) complexes were very similar structures while Cu(II) and Ni(II) complexes were
slightly different . Upon one-electron oxidation the Co(II) complexes were converted to the Co(III)-phenolate
species, while the one-electron oxidized species of the Ni(II) complexes were the Ni(II)-phenoxyl radical in the
ground state. The stability of he Ni(II)-phenoxyl radical depends on the N-donor properties; the half-life
increased with the increase of the N-donor ability of the ligands. This characteristic was also observed in the case
of the Zn(II)-phenoxyl radical complexes. Further, the results of the oxidized Co(III) complexes revealed that the
oxidation center is dependent on the properties of the pyridine nitrogen donors. These results illustrate the
control of the oxidation locus that can be reached by modulating the ligand field.
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