Calcium Bistriflimide-Mediated Sulfur (VI)–Fluoride Exchange (SuFEx): Mechanistic Insights toward Instigating Catalysis
Researcher ORCID Identifier
Anions, calcium bistriflimide, S(VI) fluoride, SuFEx, computational chemistry, transition states, kinetics, catalysis
We report a mechanistic investigation of calcium bistriflimide-mediated sulfur(VI)–fluoride exchange (SuFEx) between sulfonyl fluorides and amines. We determine the likely pre-activation resting state─a calcium bistriflimide complex with ligated amines─thus allowing for corroborated calculation of the SuFEx activation barrier at ∼21 kcal/mol, compared to 21.5 ± 0.14 kcal/mol derived via kinetics experiments. Transition state analysis revealed: (1) a two-point calcium-substrate contact that activates the sulfur(VI) center and stabilizes the leaving fluoride and (2) a 1,4-diazabicyclo[2.2.2]octane additive that provides Brønsted-base activation of the nucleophilic amine. Stable Ca–F complexes upon sulfonamide formation are likely contributors to inhibited catalytic turnover, and a proof-of-principle redesign provided evidence that sulfonamide formation is feasible with 10 mol % calcium bistriflimide.
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Ball, Nicholas; Han, Brian; Khasnavis, Samuel R.; Nwerem, Matthew; Bertagna, Michael; and Ogba, O Maduka, "Calcium Bistriflimide-Mediated Sulfur (VI)–Fluoride Exchange (SuFEx): Mechanistic Insights toward Instigating Catalysis" (2022). Pomona Faculty Publications and Research. 492.