Functional model oxygenations by nonheme iron complexes - Advances in Catalytic Activation of Dioxygen by Metal Complexes - page 204

As for the formation of high-valent oxo species of nonheme iron complexes,
Lange et al. reported about evidence for a nonheme Fe(IV)=O species. 434 No direct
spectroscopic evidence for the species has been obtained, but the intramolecular
hydroxylation of a ligand phenyl moiety was explained by its involvement in the
mechanism. This supports the hypothesis that Fe(IV)=O species can be the active
species responsible for substrate oxidation in the class of oxygen-activating
nonheme iron enzymes. Wada et al. have isolated and characterized
species from the reaction of
with Reactions of the species with cyclohexene and
cyclohexane in the stoichiometric oxidation gave alcohols as the main product with
a trace amount of ketones. A higher efficiency was observed in oxidation of
to rather than in the case of to indicating that the active
species not only acts as a two-electron oxidant but also displays nucleophilicity. It
is suggested that the homolytic O-O bond cleavage generates both of and
HO, both of which cooperatively perform a C-H bond cleavage step with a
subsequent C-O bond formation step in the hydroxylation.
5. FROM FUNCTIONAL MODEL TO CATALYSIS
Goals for biomimetic chemistry on oxygenases are clarification of active
species, e.g. Fe-OOH or Fe=O, involved in the enzymatic and model oxygenations,
development of catalytic systems for the selective oxygenations using as the
oxidant, and so on. Efforts for these topics in the last ten years have given rise to
various types of nonheme iron complexes that stabilize iron-oxygen species and
oxygenate substrates in the di- and mono-oxygenase-like fashion.
The high-valent iron-oxo species became popular in the great development of
cytochome P450 chemistry. These species was first thought characteristic to heme