A series of 2,7-functionalized indoles have been synthesized with appended amide and/or urea or thiourea groups. Anion complexation studies show a marked difference in the mode of interaction of carboxylates with indole-ureas vs indole-amides.

No abstract

A novel quinoline‐substituted crown ether has been synthesized as a receptor for ion pairs and its binding behavior was investigated in various solvents. The binding of ion pairs in [D6]DMSO and in mixed [D6]DMSO/CD3CN/CDCl3 solvents was studied and the results revealed positive cooperativity effects. As a novel solubilizing agent, the crown ether can extract halide salts into organic media, especially chloride salts. ESI MS provided evidence for the formation of salt‐receptor complexes. A recycling experiment showed that the receptor can solubilize salts and can be recovered. This process can be performed as a cycle. This study validates the idea that a straightforward combination of a common anion receptor and a well‐studied cation complexation moiety enables the formation of ion‐pair receptors and solubilizers of salts in organic solvents.

Indole‐based anion receptors with an carboxamide unit in 2‐ and an urea in 7‐position were prepared and found to bind halides (as well as acetate and nitrate) in chloroform solutions at room temperature. Investigations of the binding behaviour show that the receptor is selective for chloride. Surprisingly, the truncated receptor 3 without the 2‐carbamoyl substituent shows the highest affinity for Cl–. Thorough 1H, 13C and 15N NMR investigations indicate different binding modes for acetate, nitrate and halides to the receptor 2. The observation of a major conformational change of this receptor during the binding of the halide ions leads to an understanding of the relative binding affinities of 3 > 4 > 2 for chloride. The results of the NMR study are supported by ab initio calculations. In addition, ESI FTICR MS competition experiments of the indole 2 and the quinoline 1 reveal the “self‐aggregation” of the receptors and show that halides have a higher affinity to 2 than to 1.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)