Mechanism of promotion of S(N)2 fluorination by [Bmim]F in solvent-free environment: Quantum chemical analysis

Quantum chemical analysis is presented for the mechanism of promotion of S(N)2 fluorination by 1-Butyl-3-methylimidazolium fluoride ([Bmim]F) reported by Magnier and co-workers (2014). At [Bmim]F: substrate molar ratio of 2:1, one of the fluorides acts as the nucleophile, but the second F- plays the role as Lewis base on the two counter-cations to facilitate the reaction. We find that the Gibbs free energy(at 80 degrees C) of activation decreases as the [Bmim]F: substrate ratio increases from 1:1 to 2:1, in good agreement with the experimental observations of improved yield from 47 to 84%.