Interactions of Organic Halide and Nitrate Salts with meso-Octamethylcalix[4]pyrrole

Abstract

Proton NMR titrations have been performed with meso-octamethylcalix[4]pyrrole and a variety of organic chloride and bromide salts in dichloromethane-d ₂ . The results show apparently increasing chloride stability constants within each set of anion salts (tetrabutylammonium < imidazolium < pyridinium). Addition of 1-ethyl-3-methylimidaolium (EMIM) nitrate to dichloromethane-d ₂ solutions of calix[4]pyrrole caused significantly larger downfield shifts of the pyrrole NH protons of calix[4]pyrrole than addition of equimolar quantities of tetrabutylammonium nitrate. The first crystal structure of a nitrate complex of a calix[4]pyrrole is also presented.

Keywords:

• Anion receptors
• Pyrrole
• Crystallography

Acknowledgements

We would like to thank the EPSRC and Crystal Faraday for a studentship (GWB) and the EPSRC together with Professor Mike Hursthouse for access to the crystallographic facilities at the University of Southampton.