Generation of Ferryl Species through Dioxygen Activation in Iron/EDTA Systems: A Computational Study
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- 作者：Leonardo Bernasconi ; Evert Jan Baerends
- 刊名：Inorganic Chemistry
- 出版年：2009
- 出版时间：January 19, 2009
- 年：2009
- 卷：48
- 期：2
- 页码：527-540
- 全文大小：465K
- 年卷期：v.48,no.2(January 19, 2009)
- ISSN：1520-510X
文摘
The ferryl species (oxidoiron(IV), FeO2+) is a ubiquitous, highly oxidative intermediate in oxidation catalysis. We study theoretically its abiotic generation, in the form of the singularly active complex of FeO2+ with the EDTAHn−4+n, n = 0−4 ligands, from O2 and Fe2+−EDTA complexes. The calculations are for the gas phase using generalized gradient corrected (BLYP and OPBE) Density Functional Theory (DFT). We examine the effects of ligand protonation on the coordination geometry and electronic structure of the chelated Fe2+ ion, on its affinity to bind dioxygen, and on the generation of dinuclear Fe/EDTA/O2 complexes, whose formation has been hypothesized on the basis of kinetic measurements of FeII/FeIII autoxidation reactions in aqueous solution. We also consider the homolytic cleavage of the O−O bond within one such complex, [Fe·EDTAH·O2·EDTAH·Fe]2−, and we show that this reaction leads to a pair of FeIVO/EDTA systems with an energetic barrier comparable to those computed for model systems of active sites of enzymes involved in dioxygen activation, such as methane monooxygenase. Our study supports the recently advanced hypothesis that high valent iron compounds capable of oxidizing organic substrates may be produced as a byproduct of the FeII/FeIII autoxidation in aqueous Fe/EDTA/O2 solutions at ambient conditions. We also identify the origin of the enhanced O2 activation ability in the monoprotonated [Fe·EDTAH]− complex, compared to other ligand protonation states, which has been observed in kinetic measurements.