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

doi:10.1021/jacs.0c06751

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

School of Chemistry

Research output: Contribution to journal › Article › peer-review

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 language	English
Pages (from-to)	14649-14663
Journal	Journal of the American Chemical Society
Volume	142
Issue number	34
Early online date	27 Jul 2020
DOIs	https://doi.org/10.1021/jacs.0c06751
Publication status	Published - 26 Aug 2020

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García-Domínguez_2020_JACS_Difluorocarbene_AAM
Copyright © 2020 American Chemical Society. This work has been made available online in accordance with publisher policies or with permission. Permission for further reuse of this content should be sought from the publisher or the rights holder. This is the author created accepted manuscript following peer review and may differ slightly from the final published version. The final published version of this work is available at https://doi.org/10.1021/jacs.0c06751
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Craig Paterson Johnston
- cpj3st-andrews.acuk
- School of Chemistry - Royal Society Research Fellow
Person: Academic - Research

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title = "Difluorocarbene generation from TMSCF3: kinetics and mechanism of NaI-mediated and Si-induced anionic chain reactions",

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.",

author = "Andr{\'e}s Garc{\'i}a-Dom{\'i}nguez and West, {Thomas H.} and Primozic, {Johann J.} and Grant, {Katie M.} and Johnston, {Craig P.} and Cumming, {Grant G.} and Leach, {Andrew G.} and Lloyd-Jones, {Guy C.}",

year = "2020",

month = aug,

day = "26",

doi = "10.1021/jacs.0c06751",

language = "English",

volume = "142",

pages = "14649--14663",

journal = "Journal of the American Chemical Society",

issn = "0002-7863",

publisher = "American Chemical Society (ACS)",

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TY - JOUR

T1 - Difluorocarbene generation from TMSCF3

T2 - kinetics and mechanism of NaI-mediated and Si-induced anionic chain reactions

AU - García-Domínguez, Andrés

AU - West, Thomas H.

AU - Primozic, Johann J.

AU - Grant, Katie M.

AU - Johnston, Craig P.

AU - Cumming, Grant G.

AU - Leach, Andrew G.

AU - Lloyd-Jones, Guy C.

PY - 2020/8/26

Y1 - 2020/8/26

N2 - 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.

AB - 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.

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DO - 10.1021/jacs.0c06751

M3 - Article

SN - 0002-7863

VL - 142

SP - 14649

EP - 14663

JO - Journal of the American Chemical Society

JF - Journal of the American Chemical Society

IS - 34

ER -

Difluorocarbene generation from TMSCF3: kinetics and mechanism of NaI-mediated and Si-induced anionic chain reactions

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Craig Paterson Johnston

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Difluorocarbene generation from TMSCF₃: kinetics and mechanism of NaI-mediated and Si-induced anionic chain reactions