Functional model oxygenations by nonheme iron complexes - Advances in Catalytic Activation of Dioxygen by Metal Complexes - page 200

in the synergistic oxidation of cyclohexane 388 and probability of the non-radical
oxidation were reported. 389
Barton et al. used zinc ( Zn ) as a reductant. They isolated a trinuclear iron
complex, from a reaction system containing iron powder,
carboxylic acids, and in aqueous pyridine under 1 atm and found that it
oxidized alkanes in the presence of Zn, pyridine, and acetic acid under 1 atm
(Gif system). Later, the Gif type oxygenations were performed mostly by using
monoiron salts, e.g. Barton et al reported a number of
experiments for application of this system to the more complicated compounds such
as steroids 391-398 and for clarification of mechanism, specially participation of the
radical and nonradical processes. 295, 296, 399-402 Intermediate formation of
alkoxide 403 and was proposed based on the effect of on the
selectivity, cleavage of methylidene olefins into the ketone or aldehyde, or effect of
additives such as thiophenols. 300 Recently, Celenligil-Cetin et al. studied the
reactivity of ferrous and ferric oxo/peroxo pivalate complexes and claimed that the
peroxo species is not directly involved in catalytic Gif-type oxygenation, based on
the low reactivity of the peroxo containing complexes in the oxidation of both cis-
stilbene and adamantane. 405 Kitajima et al. used
for oxygenation of alkanes and arenes in the presence of hexafluoroacetylacetone
(Hhfacac) and Zn hydrotris-1-pyrazolylborate). 229,

230

powder

was isolated and assumed as an active complex. Balavoine et al.
tried to use an electrode in place of zinc in the Gif system for the selective oxidation
of saturated hydrocarbons. 295, 406 - 408
Mimoun and Roch used hydrazobenzene (PhNHNHPh) for oxygenation of
cyclohexane, cyclohexene, and toluene. 409 The most active complex was formed
from and carboxylic acid in the presence of hydrazobenzene. Davis et al.
used and for the same reaction and proposed the hydroperoxide
complex as an active species. 410 Sheu et al. used
complexes (PA: picolinato) for the monooxygenation of
saturated hydrocarbons, especially ketonization of methylenic carbons. 370,411 This
system was applied to the hydroxylation of aromatic hydrocarbons as reaction
mimic for tyrosine hydroxylase. 412 With phenol as a reactant, the dominant product
was catechol.
Funabiki et al. developed an monooxygenation system using hydroquinones
with catecholatoiron(III) complexes in acetonitrile in the presence of pyridine. 413
First the system was applied to hydroxylation of aromatics. 413-416 Catalytic activity
depends greatly on the substituents on hydroquinones (R-HQ) and increases with the
electron-donating property; In the oxygenation of