Journal
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
Volume 140, Issue 43, Pages 14391-14400Publisher
AMER CHEMICAL SOC
DOI: 10.1021/jacs.8b08950
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Funding
- European Research Council (ERC CoG) [682275]
- Czech Ministry of Education, Youth and Sports [LTAUSA17026]
- COST action ECOSTBio
- MINECO of Spain [CTQ2015-70795-P]
- Catalan DIUE of the Generalitat de Catalunya [2009SGR637]
- ICREA-Academia award
- University of Minnesota
- US National Science Foundation [CHE1665391]
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Terminal non-heme iron(IV)-oxo compounds are among the most powerful and best studied oxidants of strong C-H bonds. In contrast to the increasing number of such complexes (>80 thus far), corresponding one-electron-reduced derivatives are much rarer and presumably less stable, and only two iron(III)-oxo complexes have been characterized to date, both of which are stabilized by hydrogen-bonding interactions. Herein we have employed gas-phase techniques to generate and identify a series of terminal iron(III)-oxo complexes, all without built-in hydrogen bonding. Some of these complexes exhibit similar to 70 cm(-1) decrease in nu(Fe-O) frequencies expected for a half-order decrease in bond order upon one-electron reduction to an S = 5/2 center, while others have nu(Fe-O) frequencies essentially unchanged from those of their parent iron(IV)-oxo complexes. The latter result suggests that the added electron does not occupy and orbital with Fe=O antibonding character, requiring an S = 3/2 spin assignment for the nascent Fe-III-O- species. In the latter cases, water is found to hydrogen bond to the Fe-III-O- unit, resulting in a change from quartet to sextet spin state. Reactivity studies also demonstrate the extraordinary basicity of these iron(III)-oxo complexes. Our observations show that metal-oxo species at the boundary of the Oxo Wall are accessible, and the data provide a lead to detect iron(III)-oxo intermediates in biological and biomimetic reactions.
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