Anion and cation binding by a new indole/pyridine/amine-based ion-pair receptor

Abstract

A new ion-pair receptor bis(3-bromoindol-2-ylmethyl)(2-pyridylmethyl)amine ( 1) was synthesized and studied for its anion and cation binding behavior using ESI-MS and 1H NMR spectroscopy. Among halides, 1 exhibits the strongest binding with Cl − to form a 1:1 adduct ( K a = 1042 ± 21 in CD 3CN). Among alkali metal ions, Li + and Na + showed the strongest binding in the formation of a 1·M + complex. The simultaneous binding of Cl − and Li + to 1 was confirmed by 1H NMR titration of a 1:1 mixture of 1 and Cl − with LiPF 6 in 83:17 v/v mixture of CDCl 3 and DMSO- d 6. DFT-optimized structures of 1·Cl −, 1·Li +, and 1·Li +·Cl − are consistent with the chemical shift changes observed in 1H NMR studies.