Mechanism of Nucleophilic Fluorination Facilitated by a Pyrene-tagged Ionic Liquids: Synergistic Effects of Pyrene-Metal Cation π-Interactions

초록

We examine the mechanism of S(N)2 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(double dagger) for both processes. We find that the CIP mechanism is preferred for [PIL + MF + C3H7OMs] (M = Cs, K) system. S(N)2 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 interactions between the metal cation and pyrene, giving G(double dagger) that is smaller (by approximately 1.3 kcal/mol) than that for the [bmim-CsF] system, in excellent agreement with experimental observations.

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