Abnormal Mesoionic Carbene Silver Complex: Synthesis, Reactivity, and Mechanistic Insight on Oxidative Fluorination

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• 作者：Qilun Liu ; Zheliang Yuan ; Hao-yang Wang ; Yang Li ; Yichen Wu ; Tao Xu ; Xuebing Leng ; Pinhong Chen ; Yin-long Guo ; Zhenyang Lin ; Guosheng Liu
• 刊名：ACS Catalysis
• 出版年：2015
• 出版时间：November 6, 2015
• 年：2015
• 卷：5
• 期：11
• 页码：6732-6737
• 全文大小：517K
• ISSN：2155-5435

文摘

A silver-catalyzed intramolecular amination of alkynl-imine substrates has been extensively studied to build various isoquinoline derivatives efficiently. However, most of these transformations are limited to hydroamination, and the related oxidative reaction is quite rare. Importantly, the mechanistic details are still unknown, which retarded further progress in the field. In this work, a novel abnormal mesoionic carbene silver complex (MIC)_nAg(I) was isolated and fully characterized as the key intermediate. Further investigation on the oxidative transformation of the silver complex reveals that successful oxidative halogenation could be achieved with NXS (X = Cl, Br, and I), as well as F⁺ reagent. Surprisingly, the fluorination reaction occurred in the presence of both strong (SelectFluor) and weak (NFSI) fluorinating reagents, although the F-Py-type reagent, whose oxidative potential lies between, is ineffective. Further mechanistic studies disclosed that (1) from kinetic data, the (MIC)Ag(I) complex was proved to be the reactive intermediate in the fluorination reaction, and pyridyl-oxazoline (Pyox) ligand could significantly improve this transformation; (2) from DFT calculation results, two different mechanistic pathways were suggested to be involved, a metathesis process in the case of NFSI promoted by the chelation of sulfonyl group toward the silver center and a redox process in the case of SelectFluor due to its strong oxidative potential.