ArIO (ArI = 2-(^tBuSO₂)C₆H₄I) is an oxidant used to oxidize Fe^II species to their Fe^IV-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)Fe^IVO(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)Fe^IIIOH(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)Fe^IVO(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)Fe^IVO(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)Fe^IIIO(ArIO)]²⁺ that exothermically eliminates ArI and unmasks the reactive Fe^V–dioxo species.

中文翻译：

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揭示 [(Ligand)Fe-OIAr]2+/+ 配合物的铁氧键

ArIO (ArI = 2-( ^t BuSO ₂ )C ₆ H ₄ I) 是一种氧化剂，用于将 Fe ^II物质氧化为其 Fe ^IV -氧代状态，从而实现氢原子转移 (HAT) 和氧原子转移 (OAT)低能垒反应。ArIO 作为配体，生成Fe ^(n-2) -OIAr类型的掩蔽 Fe ^{n =O 物质。}在这里，我们使用气相离子分子反应和 DFT 计算来探索掩蔽的铁氧化合物的性质并了解它们的掩蔽机制。该理论表明，[(TPA)Fe ^IV O(ArIO)] ²⁺ ( 1 ²⁺, TPA = tris(2-pyridylmethyl)amine)) 是高度吸热的；因此，它只能在碰撞诱导的1 ²⁺解离中实现，从而导致未掩蔽的铁 (VI) 二氧络合物。HAT 对1 ²⁺的还原导致 [(TPA)Fe ^III OH(ArIO)] ²⁺降低了 I-O 键断裂的能量需求，但仍然是吸热的。在1 ²⁺的单电子还原后或 OAT 反应后，预计 Fe=O 键的放热暴露。后者导致不饱和烃的 4e ^–氧化：来自 [(TPA)Fe ^IV O(ArIO)] ^{2+的初始 OAT}导致烯烃环氧化并触发仍然在一个碰撞配合物中的第二个Fe = O键的暴露。第二个氧化步骤从 C-H 键的 HAT 开始，然后是 C-自由基和 OH 基团的反弹。从单电子还原开始的过程可以用 [(TQA)Fe ^IV O(ArIO)] ²⁺ ( 2 ²⁺ , TQA = tris(2-quinolylmethyl)amine)) 进行研究，因为它具有足够的电子亲和力与烯烃的电子转移。因此，2 ²⁺与 2-蒈烯的反应导致 [(TQA)Fe ^III O(ArIO)] ²⁺放热消除 ArI 并暴露出反应性的 Fe ^V-二氧化合物。