Proceedings - Interdisciplinary Center for Nanotoxicity

Conference on Current Trends in Computational Chemistry 2009
A DFT Study of the Iron(III)Hydroperoxide Intermediate in
Methane Oxidations Catalyzed by Nonheme Iron Center
Vitaly Solkan
N. D. Zelinski Institute of Organic Chemistry, RAS, 119991 Moscow,
Leninskii pr. 47, Russian Federation; E­mail: solkanvn@ioc.ac.ru
Oxidation is the most important tool to introduce functionality in very unreactive
molecules like alkanes. Ideally these oxidation reactions should be carried out using molecular
oxygen or its reduced form hydrogen peroxide. However, in order to be able to perform these
reactions a catalyst is required. A good starting point for the design of new catalysts is to look at
nature, which has developed highly reactive and selective oxidation enzymes. Many of these
enzymes rely on one or two iron atoms in their active site. A good example of this class is iron
bleomycin (FeBLM), a metalloglycopeptide that is clinically used in cancer treatment owing to
the ability to oxidatively cleave DNA. This mononuclear iron system is also capable of oxidising a
wide range of organic substrates using molecular oxygen or hydrogen peroxide. Spectroscopic
studies of activated bleomycin support its formulation as a low‐spin hydroperoxidoiron(III)
species. Earlier [1] a model for activated BLM has been synthesized that mimics its reactivity
and gives rise to the same optical and EPR spectra. This model is based on iron(II) complex of a
new pentadentate ligand N4Py,(N4Py =N,N‐bis(2‐pyridylmethyl)‐N‐bis(2‐pyridyl)methylamine).
It reacts with H2O2 to generate a transient purple species which is characterized as a low‐spin
hydroperoxoiron(III) complex [(N4Py)FeOOH]. This intermediate is able to oxidize alkanes.
There are several puzzles associated with [(N4Py)FeOOH] chemistry, which still remain
unexplained. In our effort to understand the factor affecting the homolysis of the O‐O bond of
this hydroperoxide intermediate to give two radical type oxidants ( Fe(IV)O and OH ) and to
elucidate the mechanism of N4PyFe(2+) catalysed oxidations of alkanes in presence of H2O2,
we have investigated using quantum chemical methods all intermediates which are involved in
this process: N4Py, [Fe(II)N4Py], [O2Fe(II)N4Py], [HOO Fe(II)N4Py](+), [H2OO Fe(II)N4Py ](+),
(N4Py)Fe(IV)=O , (N4Py)Fe(V)=O , OOH, OH, HO(‐), H2O, Fe(2+), H2O2, and O2. Calculations
have been carried out at the DFT/B3LYP level using 6‐31G(d) basis set. Solvent effects have
been included by means of polarizable continuum model CPCM. Our results indicate two
possible reaction catalytic mechanisms for methane oxidation using [HOO Fe(II)N4Py](+)
complex.
Acknowledgments: This work was supported by the Program of the Department of
Chemistry and Material Sciences of the Russian Academy of Sciences, “Theoretical and
experimental study of nature of chemical bonds and of most important chemical reactions and
processes”.
1. M. Lubben, A. Meetsma, E.C. Wilkinson, B. Feringa, and L. Que, Jr. Angew.Chem. Int.Ed.
Engl. 1995, 34, 1512.
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