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Russian Chemical Bulletin, International Edition, Vol. 62, No. 5, pp. 1201—1209, May, 2013
1201
Binuclear iron complexes with acyclic Schiff bases
based on 4ꢀtertꢀbutylꢀ2,6ꢀdiformylphenol: synthesis,
properties, and use in catalytic partial oxidation of isobutane
L. I. Rodionova, N. E. Borisova, A. V. Smirnov, V. V. Ordomsky, A. A. Moiseeva, and D. A. Pankratov
Chemical Department, M. V. Lomonosov Moscow State University,
Building 3, 1 Leninskie Gory, 119991 Moscow, Russian Federation.
Fax: +7 (495) 939 3570. Eꢀmail: ludmilarodionova@mail.ru
New binuclear iron complexes with acyclic Schiff bases based on 4ꢀtertꢀbutylꢀ2,6ꢀdiꢀ
formylphenol and amino acids methionine and histidine were synthesized. The composition
and inferred structure of the complexes were studied by elemental analysis, IR spectroscopy,
Mössbauer spectroscopy, and electrochemical methods. The synthesized complexes were studꢀ
ied in catalytic reactions of partial oxidation of isobutane to tertꢀbutyl alcohol and decomposiꢀ
tion of tertꢀbutyl hydroperoxide. The activity and selectivity of the complex depend on the
nature of the bridging group between two iron ions and are independent of the amino acid
environment.
Key words: binuclear iron complexes, Schiff base, partial isobutane oxidation.
Binuclear iron complexes of various structure are widely
used in organic chemistry as oxidation catalysts. Based on
biological processes such as methane oxidation with methꢀ
ane monooxygenase,1 oxidation of steroids, and synthesis
of prostaglandin on metalloenzyme cytochrome P450,2
new catalysts for the oxidation of alkanes, cycloalkanes,
and alcohols, in particular, iron porphyrins,3,4 Fenton´s
reagents,5 and monoꢀ and binuclear metal complexes with
diverse ligands were developed.6—8 Since Robson type
complexes with Schiff bases are structural analogs of some
active biological molecules, it can be assumed that they
are highly active in oxidation processes.
octane additive to gasoline. In the industrial nonꢀcatalytic
oxidation,9 isobutane is oxidized under high pressures and
the major product is ButOOH. A low selectivity to ButOH
(about 30 mol.%) prompted researchers to develop new
catalytic processes and to search for catalysts capable of
efficient performance under milder conditions compared
to the nonꢀcatalytic method.
In this work, the binuclear iron complexes with Schiff
bases based on amino acids, viz. histidine and methionine,
were synthesized. These complexes were studied in the
partial aerobic oxidation of isobutane to ButOH.
One of the new and important directions of alkane
oxidation is the oxidation of isobutane with air oxygen to
form tertꢀbutyl alcohol (ButOH) and tertꢀbutyl hydroꢀ
peroxide (ButOOH) (Scheme 1).
Results and Discussion
The binuclear iron complexes were synthesized from
the corresponding sodium salts of chiral ligands by the
reaction with the iron salts in a solution of anhydrous
methanol via Scheme 2.
Depending on the nature of the bridging group binding
two iron ions, the complexes can be divided into two
groups. In the first group (compounds 1a,b), the iron ions
are bonded through the methoxy group. In compounds of
the second group (compounds 2a,b), bonding occurs
through the oxygen bridge.
Scheme 1
The compositions of the synthesized complexes were
determined by elemental analysis, IR spectroscopy, and
1Н NMR spectroscopy.
i. Air, T = 130 C, p = 35 atm.
The latter is used in the largeꢀtonnage epoxidation of
propylene, and ButOH is used in the synthesis of methyl
methacrylate and methylꢀtertꢀbutyl ether and as a highꢀ
The IR spectra (Table 1) of all complexes show a strong
band at 1620 cm–1, which is characteristic of the С=N
bond of Schiff bases. This band is shifted to lower frequenꢀ
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1201—1209, May, 2013.
1066ꢀ5285/13/6205ꢀ1201 © 2013 Springer Science+Business Media, Inc.