Isolation and Characterization of a Dihydroxo-Bridged Iron(III,III)(渭-OH)2 Diamond Core Derived from Dioxygen

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• 作者：Michael K. Coggins ; Santiago Toledo ; Julie A. Kovacs
• 刊名：Inorganic Chemistry
• 出版年：2013
• 出版时间：December 2, 2013
• 年：2013
• 卷：52
• 期：23
• 页码：13325-13331
• 全文大小：335K
• 年卷期：v.52,no.23(December 2, 2013)
• ISSN：1520-510X

文摘

Dioxygen addition to coordinatively unsaturated [Fe(II)(O^Me2N₄(6-Me-DPEN))](PF₆) (1) is shown to afford a complex containing a dihydroxo-bridged Fe(III)₂(渭-OH)₂ diamond core, [Fe^III(O^Me2N₄(6-Me-DPEN))]₂(渭-OH)₂(PF₆)₂路(CH₃CH₂CN)₂ (2). The diamond core of 2 resembles the oxidized methane monooxygenase (MMOox) resting state, as well as the active site product formed following H-atom abstraction from Tyr-OH by ribonucleotide reductase (RNR). The Fe-OH bond lengths of 2 are comparable with those of the MMOHox suggesting that MMOHox contains a Fe(III)₂(渭-OH)₂ as opposed to Fe(III)₂(渭-OH)(渭-OH₂) diamond core as had been suggested. Isotopic labeling experiments with ¹⁸O₂ and CD₃CN indicate that the oxygen and proton of the 渭-OH bridges of 2 are derived from dioxygen and acetonitrile. Deuterium incorporation (from CD₃CN) suggests that an unobserved intermediate capable of abstracting a H-atom from CH₃CN forms en route to 2. Given the high C鈥揌 bond dissociation energy (BDE = 97 kcal/mol) of acetonitrile, this indicates that this intermediate is a potent oxidant, possibly a high-valent iron oxo. Consistent with this, iodosylbenzene (PhIO) also reacts with 1 in CD₃CN to afford the deuterated Fe(III)₂(渭-OD)₂ derivative of 2. Intermediates are not spectroscopically observed in either reaction (O₂ and PhIO) even at low-temperatures (鈭?0 掳C), indicating that this intermediate has a very short lifetime, likely due to its highly reactive nature. Hydroxo-bridged 2 was found to stoichiometrically abstract hydrogen atoms from 9,10-dihydroanthracene (C鈥揌 BDE = 76 kcal/mol) at ambient temperatures.