Properties and reactivities of nonheme iron(iv)–oxo versus iron(v)–oxo: long-range electron transfer versus hydrogen atom abstraction

Abstract

Recent work of Nam and co-workers [J. Yoon, S. A. Wilson, Y. K. Jang, M. S. Seo, K. Nehru, B. Hedman, K. O. Hodgson, E. Bill, E. I. Solomon and W. Nam, Angew. Chem., Int. Ed., 2009, 48, 1257] on a biomimetic iron complex implicated a mixture of iron(IV)-oxo and iron(V)-oxo intermediates but the latter could not be spectroscopically characterized, hence its involvement was postulated. To gain insight into the relative activity of these iron(IV)-oxo versus iron(V)-oxo intermediates, we have performed an extensive density functional theory (DFT) study on the chemical properties of the chemical system of Nam et al., namely [Fe(O)(BQEN)(NCCH3)](2+/3+) with BQEN = N,N'-dimethyl-N,N'-bis(8-quinolyl)ethane-1,2-diamine and their reactivity in hydrogen atom abstraction from ethylbenzene. We show that the perceived iron(V)-oxo species actually is an iron(IV)-oxo ligand cation radical, similar to cytochrome P450 compound I. Moreover, this intermediate has an extremely large electron affinity and therefore can abstract electrons from substrates readily. In our particular system, this means that prior to the hydrogen atom abstraction, an electron is abstracted to form an iron(IV)-oxo species, which subsequently abstracts a hydrogen atom from the substrate. Thus, our calculations show for the first time how some nonheme iron complexes react by long-range electron transfer and others directly via hydrogen atom abstraction. We have rationalized our results with detailed thermochemical cycles that explain the observed reactivity patterns.

Mechanism of Photoinduced Triplet Intermolecular Hydrogen Transfer between Cycloxydim and Chlorothalonil

“…In addition, for pathway 3, the proton transfer following electron transfer was barrierless, enabling it the preferred reaction pathway. The conclusion that intermolecular electron transfer facilitates subsequent proton migration is in agreement with previous computational research on hydrogen atom abstraction of nonheme iron dioxygen compounds from substrate as well as the study on intermolecular hydrogen transfer from phenols to triplet diketones …”

Development of an efficient magnetically separable nanocatalyst: theoretical approach on the role of the ligand backbone on epoxidation capability

“…15c,d The generation of Fe V ]O species is very common that were conrmed previously both experimentally an theoretically. [31][32][33][34][35][36] Theoretical investigation Theoretical investigation on the effect of halogen substituent on the oxidation of iron complex catalysts Geometry and charge distribution of the non-oxidized Fe(III) complexes. All the initial complexes are electrically neutral and only differ in the halogen at the ortho and para positions of the two benzene rings of the Schiff base bonded to the Fe(III) center (Fig.…”

Computational Insight into the Mechanism of Alkane Hydroxylation by Non-heme Fe(PyTACN) Iron Complexes. Effects of the Substrate and Solvent

“…An alternative to the HAT for the first step of the mechanism is a long-range electron transfer from the substrate to the high-valent [Fe V (O)­(OH)­(PyTACN)] 2+ . This ET first step mechanism was computationally determined by de Visser et al as the most viable for [Fe­(O)­(BQEN)­(NCCH 3 )] 3+ (BQEN = N,N ′-dimethyl- N,N ′-bis­(8-quinolyl)­ethane-1,2-diamine), an iron­(IV)-oxo ligand cation radical which has an extremely large electron affinity . The same charge transfer first step mechanism was also proposed on the basis of computational studies for Cpd I of P450 and non-heme iron­(IV)-tosylimido species .…”

“…radical which has an extremely large electron affinity and therefore can abstract electrons from substrates. 61 The same charge transfer first step mechanism was also found for Cpd I of P450 62 and non heme iron(IV)-tosylimido species. 63 However, for…”