Tripodi G, Roithová J. Unmasking the Iron-Oxo Bond of the [(Ligand)Fe-OIAr]
2+/+ Complexes.
JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2022;
33:1636-1643. [PMID:
35920859 PMCID:
PMC9460779 DOI:
10.1021/jasms.2c00094]
[Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 03/31/2022] [Revised: 07/26/2022] [Accepted: 07/26/2022] [Indexed: 06/15/2023]
Abstract
ArIO (ArI = 2-(tBuSO2)C6H4I) is an oxidant used to oxidize FeII species to their FeIV-oxo state, enabling hydrogen-atom transfer (HAT) and oxygen-atom transfer (OAT) reactions at low energy barriers. ArIO, as a ligand, generates masked Fen═O species of the type Fe(n-2)-OIAr. Herein, we used gas-phase ion-molecule reactions and DFT calculations to explore the properties of masked iron-oxo species and to understand their unmasking mechanisms. The theory shows that the I-O bond cleavage in [(TPA)FeIVO(ArIO)]2+ (12+, TPA = tris(2-pyridylmethyl)amine)) is highly endothermic; therefore, it can be achieved only in collision-induced dissociation of 12+ leading to the unmasked iron(VI) dioxo complex. The reduction of 12+ by HAT leads to [(TPA)FeIIIOH(ArIO)]2+ with a reduced energy demand for the I-O bond cleavage but is, however, still endothermic. The exothermic unmasking of the Fe═O bond is predicted after one-electron reduction of 12+ or after OAT reactivity. The latter leads to the 4e- oxidation of unsaturated hydrocarbons: The initial OAT from [(TPA)FeIVO(ArIO)]2+ leads to the epoxidation of an alkene and triggers the unmasking of the second Fe═O bond still within one collisional complex. The second oxidation step starts with HAT from a C-H bond and follows with the rebound of the C-radical and the OH group. The process starting with the one-electron reduction could be studied with [(TQA)FeIVO(ArIO)]2+ (22+, TQA = tris(2-quinolylmethyl)amine)) because it has a sufficient electron affinity for electron transfer with alkenes. Accordingly, the reaction of 22+ with 2-carene leads to [(TQA)FeIIIO(ArIO)]2+ that exothermically eliminates ArI and unmasks the reactive FeV-dioxo species.
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