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.
UR - https://www.scopus.com/pages/publications/85090076194
U2 - 10.1021/jacs.0c06751
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 -
