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Pathways of the Extremely Reactive Iron(IV)‐oxido complexes with Tetradentate Bispidine Ligands
Author(s) -
AbuOdeh Mahmud,
Bleher Katharina,
Johnee Britto Neethinathan,
Comba Peter,
Gast Michael,
Jaccob Madhavan,
Kerscher Marion,
Krieg Saskia,
Kurth Marius
Publication year - 2021
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.202101045
Subject(s) - chemistry , hydrogen atom abstraction , reactivity (psychology) , intramolecular force , reactive intermediate , medicinal chemistry , photochemistry , stereochemistry , radical , catalysis , organic chemistry , medicine , alternative medicine , pathology
The nonheme iron(IV)‐oxido complex trans‐ N3‐[(L 1 )Fe IV =O(Cl)] + , where L 1 is a derivative of the tetradentate bispidine 2,4‐di(pyridine‐2‐yl)‐3,7‐diazabicyclo[3.3.1]nonane‐1‐one, is known to have an S =1 electronic ground state and to be an extremely reactive oxidant for oxygen atom transfer (OAT) and hydrogen atom abstraction (HAA) processes. Here we show that, in spite of this ferryl oxidant having the “wrong” spin ground state, it is the most reactive nonheme iron model system known so far and of a similar order of reactivity as nonheme iron enzymes (C−H abstraction of cyclohexane, −90 °C (propionitrile), t 1/2 =3.5 sec). Discussed are spectroscopic and kinetic data, supported by a DFT‐based theoretical analysis, which indicate that substrate oxidation is significantly faster than self‐decay processes due to an intramolecular demethylation pathway and formation of an oxido‐bridged diiron(III) intermediate. It is also shown that the iron(III)‐chlorido‐hydroxido/cyclohexyl radical intermediate, resulting from C−H abstraction, selectively produces chlorocyclohexane in a rebound process. However, the life‐time of the intermediate is so long that other reaction channels (known as cage escape) become important, and much of the C−H abstraction therefore is unproductive. In bulk reactions at ambient temperature and at longer time scales, there is formation of significant amounts of oxidation product – selectively of chlorocyclohexane – and it is shown that this originates from oxidation of the oxido‐bridged diiron(III) resting state.