Copper-dioxygen complexes and their roles in biomimetic oxidation reactions - Advances in Catalytic Activation of Dioxygen by Metal Complexes - page 108

functional aspects of the alcohol to aldehyde conversion. There also have
been successful efforts to generate and physically characterize Cu(II)-
phenoxyl radical complexes or their zinc(II) analogues. 106,114-117

Here, we focus on some recent developments in the catalytic
oxidation of alcohols to aldehydes or ketones using copper catalysts. Stack
and co-workers 118 reported on one of the first functional models for galactose
oxidase, in which the catalytic oxidation of benzylic and allylic alcohols to
their corresponding aldehydes or ketones occurs using under mild
conditions; moreover, the mechanism observed appears to faithfully replicate
that observed for galactose oxidase. The copper Schiff-base ligand complexes
possess two phenolate donors, each with bulky ortho and para substituents. A
representative complex, [Cu(II)(BSP)], which contains o -thiophenyl and p-

tert -butyl groups in its ligand, is shown in Scheme 11.
The key feature of the [Cu(II)(L)] (L = dianionic tetradentate ligand)
complexes is their distorted non-square-planar structure, deduced from an x-
ray structure and solution EPR spectra. One-electron oxidation (i.e., using
leads to EPR silent Cu(II)-phenoxyl radical complexes, as
corroborated by Cu K-edge x-ray absorption spectra and EPR spectra on
analogous one-electron oxidized zinc(II) phenoxyl radical complexes. The
radical cation complexes bind alcoholates in a 1:1 stoichiometry to
form pentacoordinate alkoxide species, and for
anaerobic conversion to benzaldehyde and a copper(I) complex occurs.