Functional model oxygenations by nonheme iron complexes - Advances in Catalytic Activation of Dioxygen by Metal Complexes - page 189

less electron-rich pyridine analogue, was found

inactive towards these substrates.

4.3 Functional Model Oxygenations by Iron Species in the
Polyoxometalate and Heterogeneous Matrix
4.3.1 Oxygenation by Iron Species in the Homogeneous System
In the aim to overcome the catalytic instability towards activated oxygen
species (particularly organic ligands), the use of the iron species without organic
ligands has been tried for the catalytic system. One of these systems was developed
by Zhang et al. who used and p -cyano- N , N -dimethylaniline N -oxide
as an oxygen source 251 and by Mizuno et al. who used polyoxometalates, specially
di-iron-substituted silicotungstate, (Fig. 14) and as

an oxygen source. 252-254

Homogeneous oxidation reactions were carried out in the presence of 30 %
in acetonitrile under Ar. It was shown that the
efficiency of utilization to oxygenated products reached to ca. 100% for the
oxygenation of cyclohexane. The catalytic system was applied to other alkanes such
as n-hexane, n-pentane, and adamantane 253 and alkenes such as cyclooctene, 2-
octene, 1-octene, cyclohexene, styrene and trans -stilbene. 254 It is noteworthy that
epoxides are selectively (or mainly) formed in the oxygenation of alkenes. Non-
radical process is suggested by the fairly stereospecific epoxidation of cis -stilbene.
Mizuno et al. found that a water soluble potassium salt of di-iron-substituted
silicotungstate, catalyzes the conversion of methanol to
methylformate (10.2%) > methanol (0.3%) > formic acid (0.2%) together with
(16.6%). 255 The work was attempted to demonstrate catalytic oxidation of methane
with hydrogen peroxide in water. Interestingly, mono- and tri-iron-substituted
silicotungstates is much less active and nonselective for the oxidation. The catalyst