Investigation of Anion-pi Interactions Involving Thiophene Walls Incorporated Calix[4]pyrroles

摘要

Thiophene containing two-wall aryl extended calix[4]pyrroles were synthesized for the first time, through acid catalyzed condensation of 2-acetylthiophenes with pyrrole. Isomeric two-walled calix[4]pyrroles (8a-10a and 8b-10b) were obtained in satisfactory yields and their halide anion binding strengths were investigated in the solution phase by H-1 NMR and in the gas phase by computational methods and mass spectrometry. Change in the chemical shifts of thiophene -CH-protons during the course of NMR titrations entailed participation of the thiophene rings in anion binding; this fact was further substantiated by computational methods. The alpha,alpha-(cis)-isomers (8a, 9a, and 10a) showed strong binding toward F- and Cl- anions when compared to their isomeric alpha,beta-(trans)-isomer (8b, 9b, and 10b). In both isomers, binding with F- anion was found to be stronger than that with Cl- anion. Both the solution-phase and gas-phase results revealed that the thiophene rings stabilize the anions through anion-pi interactions.