Difluorocarbene Generation from TMSCF3: Kinetics and Mechanism of NaI-Mediated and Si-Induced Anionic Chain Reactions

Andrés García-Domínguez, Thomas H. West, Johann J. Primozic, Katie M. Grant, Craig P. Johnston, Grant G. Cumming, Andrew G. Leach, Guy C. Lloyd-Jones

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Abstract

The mechanism of CF2 transfer from TMSCF3 (1), mediated by TBAT (2–12 mol %) or by NaI (5–20 mol %), has been investigated by in situ/stopped-flow 19F NMR spectroscopic analysis of the kinetics of alkene difluorocyclopropanation and competing TFE/c-C3F6/homologous perfluoroanion generation, 13C/2H KIEs, LFERs, CF2 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 CF3 anionoid to TMSCF3 (1) 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 TMSCF3 (1) 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.
Original languageEnglish
Pages (from-to)14649-14663
Number of pages15
JournalJournal of the American Chemical Society
Volume142
Issue number34
Early online date27 Jul 2020
DOIs
Publication statusPublished - 13 Aug 2020

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