Hydrogen Bonding in SN2 Reactions Promoted or Inhibited by Ionic Liquids: Effects of Side Chain

Quantum chemical analysis is presented for the origin of promotion and inhibition of SN2 fluorination by [bmim][PF6](1) and [hexaEGmim][PF6](2), respectively, experimentally observed by Kim and co‐workers [Tetrahedron 2014; 70: 533–542]. We show that hydrogen bonding of OH in hexaEGmim+ causes complete suppression of SN2 fluorination by positioning the nucleophile F− far off the electropositive C atom in prereaction complex. On the other hand, in SN2 fluorination under the influence of [bmim][PF6], the nucleophile F− is in proximity to the electropositive C for facile nucleophilic attack by F−. Comparisons are made for SN2 fluorination by [hexaEGmim][OMs], which gave the largest rate constant in experiments. The use of ionic interactions and hydrogen bonding for controlling the chemical transformation is illustrated for developing and designing the efficient and task‐specific organocatalysts. SN2 Reactions promoted or Inhibited by Ionic Liquids