Cation-π interactions between neutral calix[5]arene hosts and cationic organic guests

✍ Scribed by Ralf Arnecke; Volker Böhmer; Roberta Cacciapaglia; Antonella Dalla Cort; Luigi Mandolini

• Publisher: Elsevier Science
• Year: 1997
• Tongue: French
• Weight: 397 KB
• Volume: 53
• Category: Article
• ISSN: 0040-4020
• DOI: 10.1016/s0040-4020(97)00185-3

✦ Synopsis

The binding properties of the 1,3-bridged calix[5]crowns 1-3 towards a number of quaternary ammonium, phosphonium, and iminium ions have been investigated by 1H NMR in CDCI 3 solution, where the sole driving force for association is provided by cation-n interactions. We have found that the cavity of a calix [5]arene fixed in a cone-like conformation provides a fairly efficient, but rather unselective, receptor site for quaternary salts. The conformationaUy mobile p-tert-butylcalix [5]arene (4) is in general a much less efficient binder than the more preorganized calixerowns, but displays a remarkable selectivity towards N-methylquinuclidinium ion that is believed to arise from a good complementarity between the globe-shaped guest and the highly adaptable host. The adverse effect on complexation of the p-tert-butyl groups at the upper rim has been assessed by comparing the binding properties of 1 vs. its de-tert-butylated analogue 3. Furthermore, some information on the importance nf counterion and solvent effects have been obtained.