Functional model oxygenations by nonheme iron complexes - Advances in Catalytic Activation of Dioxygen by Metal Complexes - page 183

efficient oxygenations with the use of molecular oxygen are highly desired. This is
far beyond satisfactory, but very much promising.

4.1 Functional Model Oxygenations by Diiron Complexes
4.1.1 Monooxygenation by Diiron Complexes with Peroxides
By mimicking soluble methane monooxygenases, monooxygenation of
alkanes, alkenes, and arenes by various types of nonheme diiron complexes have
been performed with utilization of activated oxygen species, e.g. m-
chloroperbenzoic acid (m-CPBA) , hydrogen peroxide (TBHP) , cumene
hydroperoxide (CHP) , hydrogen peroxide etc.. The reaction proceeds
catalytically, but discussions focus on the oxygenation mechanisms, especially on
the participation of radicals in the monooxygenation steps and similarity of
mechanisms to that of enzymes. Followings are some of the recent examples.
Kodera et al. synthesized a rigid complex
with 1,2-bis[2-di(pyridyl)methyl-6-pyridyl]ethane that is a dinucleating hexa-
pyridine ligand. 194 The complex monooxygenates alkanes (cyclohexane,
methylcyclohexane, adamantane) in the presence of m-CPBA with a large turnover
frequency and number ( TN ). 195 Radical-rebound mechanism was suggested based
on the reactivity with the additives and kinetic isotope effect. Likewise, the stable
complex
was activated in the presence of acid chloride RCOCl and DMF to
oxygenate hydrocarbons such as cyclohexane. 196 Payra et al. used
diiron(III) bis(benzimidazole) complex for the quantitative and catalytic epoxidation
of styrene in the presence of m-CPBA or NaOCl and N -methylmorpholine N -oxide
as an important additives. 197 In the absence of oxidant under anaerobic conditions,
the reversible oxygen transfer was observed between the
complex and triphenylphosphine.
A complex with bidentate bipyridine (bipy) ligands
was synthesized. 198 The complex possesses Cl ligands that enable the coordination
of substrates. This is modification of the model complexes with a
variety of tridentate N-based ligands (L) that block the terminal binding sites for
substrates. 199-202 Using TBHP hydroxylation of ethane ( TN : 1.2/3 days),
oxygenations of propane ( TN : 13/2 days) and cyclohexane ( TN : 72/3 days) were
performed, resulting in the reactivity sequence of Fish et al. have used
TBHP and for oxygenation of cyclohexane, toluene, adamantane, propane, and
ethane by another complex, (tmima = [{(1-
methylimidazol-2-yl)methyl}amine]), that is characteristic for the polyimidazole
ligands. 203 Formation of intermediate is suggested and the mechanism