Department of spectroscopy and Catalysis, Institute for Molecules and Materials, Radboud University, Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands.
J Am Soc Mass Spectrom. 2022 Sep 7;33(9):1636-1643. doi: 10.1021/jasms.2c00094. Epub 2022 Aug 3.
ArIO (ArI = 2-(BuSO)CHI) is an oxidant used to oxidize Fe species to their Fe-oxo state, enabling hydrogen-atom transfer (HAT) and oxygen-atom transfer (OAT) reactions at low energy barriers. ArIO, as a ligand, generates masked Fe═O species of the type Fe-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)FeO(ArIO)] (, TPA = tris(2-pyridylmethyl)amine)) is highly endothermic; therefore, it can be achieved only in collision-induced dissociation of leading to the unmasked iron(VI) dioxo complex. The reduction of by HAT leads to [(TPA)FeOH(ArIO)] 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 or after OAT reactivity. The latter leads to the 4e oxidation of unsaturated hydrocarbons: The initial OAT from [(TPA)FeO(ArIO)] 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)FeO(ArIO)] (, TQA = tris(2-quinolylmethyl)amine)) because it has a sufficient electron affinity for electron transfer with alkenes. Accordingly, the reaction of with 2-carene leads to [(TQA)FeO(ArIO)] that exothermically eliminates ArI and unmasks the reactive Fe-dioxo species.
ArIO（ArI=2-（BuSO）CHI）是一种氧化剂，用于将 Fe 物种氧化为其 Fe-氧状态，从而在低能量势垒下进行氢原子转移（HAT）和氧原子转移（OAT）反应。ArIO 作为配体，生成掩蔽的 Fe═O 物种类型 Fe-OIAr。在此，我们使用气相离子-分子反应和 DFT 计算来探索掩蔽铁氧物种的性质，并理解其去掩蔽机制。理论表明，[(TPA)FeO(ArIO)]（，TPA=三（2-吡啶基甲基）胺）中 I-O 键的断裂是高度吸热的；因此，只有在导致未掩蔽铁（VI）二氧配合物的 的碰撞诱导解离中才能实现。通过 HAT 还原 导致 I-O 键断裂的能量需求降低，但仍为吸热反应。预测经过单电子还原 或 OAT 反应后，Fe═O 键的放热去掩蔽。后者导致不饱和烃的 4e 氧化：初始 OAT 从 [(TPA)FeO(ArIO)] 导致烯烃的环氧化，并在一个碰撞络合物中引发第二个 Fe═O 键的去掩蔽。第二个氧化步骤从 C-H 键的 HAT 开始，并伴随着 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)FeO(ArIO)]（，TQA=三（2-喹啉基甲基）胺）来研究，因为它具有足够的电子亲和力，可与烯烃进行电子转移。因此，与 2-蒈烯的反应导致 [(TQA)FeO(ArIO)] 放热地消除 ArI 并暴露反应性的 Fe-二氧物种。
