Development of aryl-containing dipyrrolyldiketone difluoroboron complexes (BONEPYs): Tune the hydrogen bond o–C[sbnd]H···F for fluoride recognition

Abstract

Dipyrrolyldiketone difluoroboron complexes (BONEPYs) were synthesized by condensation of the corresponding pyrroles and malonyl chloride followed by treatment with BF3·OEt2. The aryl-substituted pyrrole is introduced to form a cyclic system in order to investigate anion binding studies. In BONEPYs 1–3 the o-H of the aryl group forms hydrogen bonding with F− to give a more table complex. In contrast, the intramolecular hydrogen-bonded BONEPY endo-4 is more stable than its exo isomer. While adding F−, the hydrogen bonds must be broken first to give 4·(3)F−. Owing to the electron-rich group (-OMe), the o-H of the phenyl group can hardly interact with F−via hydrogen bonding to give the less stable complex 4·(5)F−. The energy differences between the different conformations were calculated using DFT methods, which is consistent to the experimental observations.