Abstract
We examine the mechanism of SN2 fluorination promoted by a pyrene‐tagged ionic liquid (PIL). Comparison is made for contact ion‐pair (CIP) vs. solvent‐separated ion‐pair (SSIP) mechanism by calculating the Gibbs free energies of pre‐reaction complexes and Gibbs free energies of activation G‡ for both processes. We find that the CIP mechanism is preferred for [PIL + MF + C3H7OMs] (M = Cs, K) system. SN2 fluorination of the [1‐Butyl‐3‐methylimidazolium (bmim)‐CsF] system is also studied in order to estimate the efficacy of PIL vs. more conventional ionic liquid [bmim][OMs]. The better promotion of the reaction by PIL is attributed to π interactions between the metal cation and pyrene, giving G‡ that is smaller (by approximately 1.3 kcal/mol) than that for the [bmim‐CsF] system, in excellent agreement with experimental observations.
Published Version
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