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

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 H-1 NMR spectroscopy. Among halides, 1 exhibits the strongest binding with Cl- to form a 1:1 adduct (K-a = 1042+/-21 in CD3CN). 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 H-1 NMR titration of a 1:1 mixture of 1 and Cl- with LiPF6 in 83:17 viv mixture of CDCl3 and DMSO-d(6). DFT-optimized structures of 1.Cl-, 1.Li+, and 1.Lr+.Cl- are consistent with the chemical shift changes observed in H-1 NMR studies. (C) 2010 Elsevier Ltd. All rights reserved.