Solvent-driven selective π-cation templating in dynamic assembly of interlocked molecules†
Both bispyridinium (BPY) and trispyridinium (TPY) have been used to template the formation of linear or triply threaded rotaxanes through imine-based dynamic clipping reactions. In this paper, we report contrasting solvent dependence between these two templated clipping reactions when two different solvents, namely CDCl3 and CD3CN, are used. The solvent dependence is elucidated based on 1H NMR studies, and structural features are revealed by single crystal X-ray analyses of the respective linear and triply threaded interlocked molecules. We have shown that although both clipping reactions are affected by hydrogen-bonding and aromatic–aromatic interactions in general, the nature of the aromatic–aromatic interactions is quite different, which is responsible for the different solvent response. The BPY-based clipping reaction is driven by electrostatic interactions between aromatic surfaces, while the TPY-based reaction is mainly governed by the solvation/desolvation effect (solvophobic interactions). These findings led us to design a rare solvent switchable system. In competition clipping experiments employing both BPY and TPY as the templates, exclusive formation of the BPY-based linear rotaxane can be achieved in pure CDCl3, while in pure CD3CN, a 6.7 : 1 selectivity is achieved in favor of the TPY-based triply threaded rotaxane. The detailed structural analysis of the two rotaxanes as well as the solvent-dependent selectivity, may encourage more integrated approaches for the design of complex molecular architectures.
- This article is part of the themed collection: HOT articles in Organic Chemistry Frontiers for 2014