Copper-dioxygen complexes and their roles in biomimetic oxidation reactions - Advances in Catalytic Activation of Dioxygen by Metal Complexes - page 107

However, it is highly unlikely that the active oxygenation species is a discrete
copper-dioxygen adduct in this system. In fact, the authors suggest that it is
probably a Cu(II)-catalyzed autoxidation reaction that leads to the
oxygenation of a methine position in the ligand.

Yoshizawa and co-workers recently reported on the characterization
of a transient copper(II) hydroperoxo species
= bis{2-N,N-bis(2-pyridylethyl)-amino]-1,1-dimethylethyl}
disulfide) by treating the disulfide-bridged dicopper(I) complex
with (see diagram). 150 This hydroperoxo species has
absorption maxima at 295 nm, 325 nm, and 670 nm and exhibits resonance
Raman features with

and close to that of
observed for a structurally characterized hydroperoxo-copper(II) complex. 89
The of is red-shifted to 781 and
when is used, indicating that two kinds of hydroperoxo species are
formed, possibly differing between having trans or cis Cu-OOH moieties.
Because is thought to be the intermediate

responsible for the catalyzed oxidation of cyclohexane to

cyclohexanol with it may serve as a useful functional model for

understanding PHM or D β M activities, both of which have S-donors to their

copper centers.

4. COPPER OXIDASE MODELS; CATALYTIC

ALCOHOL OXIDATION

Galactose oxidase, a mononuclear copper enzyme, catalyzes the two-
electron oxidation of alcohols to aldehydes, coupled with the reduction of
to through a Cu(II) phenoxyl-radical active species. Modeling this
biological reaction is of great interest from the perspective of its importance
as an organic transformation. The crystal structure of the enzyme shows that
the copper ion is square pyramidal, with two tyrosine phenolate, two histidine
imidazole ligands and one exogenous ligand. The equatorial tyrosinate
has the unusual thioether linkage to a nearby cysteine via an ortho C-S bond.
Many research groups have carried out efforts to model the structure and
ligation of the protein copper center and develop systems mimicking