EaStChem, University of Edinburgh, Joseph Black Building, David Brewster Road, Edinburgh EH9 3FJ, U.K.
School of Health Sciences, Stopford Building, The University of Manchester, Oxford Road, Manchester M13 9PT, U.K.
J Am Chem Soc. 2020 Aug 26;142(34):14649-14663. doi: 10.1021/jacs.0c06751. Epub 2020 Aug 13.
The mechanism of CF transfer from TMSCF (), mediated by TBAT (2-12 mol %) or by NaI (5-20 mol %), has been investigated by in situ/stopped-flow F NMR spectroscopic analysis of the kinetics of alkene difluorocyclopropanation and competing TFE/CF/homologous perfluoroanion generation, C/H KIEs, LFERs, CF transfer efficiency and selectivity, the effect of inhibitors, and density functional theory (DFT) calculations. The reactions evolve with profoundly different kinetics, undergoing autoinhibition (TBAT) or quasi-stochastic autoacceleration (NaI) and cogenerating perfluoroalkene side products. An overarching mechanism involving direct and indirect fluoride transfer from a CF anionoid to TMSCF () has been elucidated. It allows rationalization of why the NaI-mediated process is more effective for less-reactive alkenes and alkynes, why a large excess of TMSCF () is required in all cases, and why slow-addition protocols can be of benefit. Issues relating to exothermicity, toxicity, and scale-up are also noted.
已通过原位/停流 F NMR 光谱分析研究了由 TBAT（2-12 mol%）或 NaI（5-20 mol%）介导的 TMSCF () 与 CF 的转移机制，分析了烯烃双氟环丙烷化反应和竞争性 TFE/CF/同系全氟阴离子生成的动力学、C/H KIEs、LFERs、CF 转移效率和选择性、抑制剂的影响以及密度泛函理论（DFT）计算。这些反应的动力学差异很大，经历了自动抑制（TBAT）或准随机自动加速（NaI），并产生了全氟烯烃副产物。已经阐明了一种涉及直接和间接从 CF 负离子向 TMSCF () 转移氟化物的总体机制。它可以解释为什么 NaI 介导的过程对反应性较低的烯烃和炔烃更有效，为什么在所有情况下都需要大量过量的 TMSCF ()，以及为什么缓慢添加方案可能有益。还注意到了与放热、毒性和放大相关的问题。
