Copper-dioxygen complexes and their roles in biomimetic oxidation reactions - Advances in Catalytic Activation of Dioxygen by Metal Complexes - page 97

that experimentally, the dicopper side-on peroxo isomer is a better
oxygen-atom transfer reagent while the isomer is a better

hydrogen-atom acceptor.
Recently, Meyer and Pritzkow 9 3 reported on the X-ray
crystallographic characterization of a novel complex using a
multidentate pyrazolate ligand by treating the pyrazolate ligand with 2
equivalents of and excess and allowing the product to
crystallize. The tetranuclear complex with a central peroxo ligand has four
copper(II) centers in Jahn-Teller-distorted square-pyramidal environments,
and the O-O bond distance of 1.497(5) is within the range for known

peroxo structures. However, it is the longest O-O bond distance reported to
date on structurally characterized copper-peroxo complexes. No resonance
Raman data was reported for this peroxo compound.

Å

3. COPPER OXYGENASE CHEMISTRY

3.1 Aromatic Hydroxylation

The enzyme tyrosinase functions by utilizing a complex
to hydroxylate an arene. In a model system for copper hydroxylases from our
own laboratories, dicopper(I) complex reacts with
(reversibly), giving an intermediate possessing a bridged
side-on bound ligand which transforms to the xylyl-ligand
hydroxylated dicopper(II) complex (Scheme 5).
Thus, an unactivated arene (XYL-H) is converted to the phenol XYL-OH.
Detailed mechanistic studies indicate that the hydroxylatton reaction occurs
by electrophilic attack of the xylyl substrate by a side-on bound peroxo group
(in As in an enzyme active site, the XYL-H substrate is
held in ideal proximity to the reacting species. Although
stoichiometric, this monooxygenase model remains as one of very few
chemical systems where an unactivated C-H bond substrate is rapidly
hydroxylated under very mild conditions using dioxygen

(-80 °C;

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