Issue 1, 2017

Ion-pair recognition by a neutral [2]rotaxane based on a bis-calix[4]pyrrole cyclic component

Abstract

In this work, we report our investigations on the synthesis of a [2]rotaxane based on a bis(calix[4]pyrrole) cyclic component and a 3,5-bis-amidepyridyl-N-oxide derivative axle. We isolated the [2]rotaxane in a significant 50% yield through an optimized “in situ” capping strategy using the copper(I)-catalyzed azide–alkyne cycloaddition reaction. The synthetic precursor of the [2]rotaxane, featuring [2]pseudorotaxane topology, could be quantitatively assembled in solution in the presence of one equivalent of tetrabutylammonium chloride or cyanate salts producing a four-particle aggregate. However, we observed that the addition of the salt was deleterious not only for the isolation of the [2]rotaxane in its pure form but, more important, for the optimal performance of the copper catalyst. We probed the interaction of the prepared [2]rotaxane with tetraalkylammonium salts of chloride, nitrate and cyanate anions by means of 1H NMR titrations and ITC experiments. We show that in chloroform solution the [2]rotaxane functions as an efficient heteroditopic receptor for the salts forming thermodynamically and kinetically highly stable ion-paired complexes with 1 : 1 stoichiometry. At millimolar concentration and using 1H NMR spectroscopy we observed that the addition of more than 1 equiv. of the salt induced the gradual disassembly of the 1 : 1 complex of the [2]rotaxane and the concomitant formation of higher stoichiometry aggregates i.e. 2 : 1 complexes.

Graphical abstract: Ion-pair recognition by a neutral [2]rotaxane based on a bis-calix[4]pyrrole cyclic component

Supplementary files

Article information

Article type
Edge Article
Submitted
09 Aug 2016
Accepted
28 Aug 2016
First published
31 Aug 2016
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY-NC license

Chem. Sci., 2017,8, 491-498

Ion-pair recognition by a neutral [2]rotaxane based on a bis-calix[4]pyrrole cyclic component

J. R. Romero, G. Aragay and P. Ballester, Chem. Sci., 2017, 8, 491 DOI: 10.1039/C6SC03554J

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