Draft:Pi-Stacking (chemistry)

Use of pi-pi.CH-pi, and pi-cation interactions in supramolecular assembly

$\pi$ systems are important building blocks in supramolecular assembly because of their versatile noncovalent interactions with various functional groups. Particularly, $\pi -\pi$ , $CH-\pi$ and $\pi -$cation interactions are widely used in supramolecular assembly and recognition.

$\pi -\pi$ concerns the direct interactions between two $\pi -$systems; and cation-$\pi$ interaction arises from the electrostatic interaction of a cation with the face of the $\pi$-system. Unlike these two interactions, the CH-$\pi$ interaction arises mainly from charge transfer between the C-H orbital and the $\pi$-system.

Figure 1. Examples of $\pi -\pi$, CH-$\pi$, and $\pi$-cation interactions.

A notable example of applying $\pi -\pi$ interactions in supramolecular assembly is the synthesis of catenane. The major challenge for the synthesis of catenane is to interlock molecules in a controlled fashion. Stoddart and co-workers developed a series of systems utilizing the strong $\pi -\pi$ interactions between electron-rich benzene derivatives and electron-poor pyridinium rings$^{1}$.[2]Catanene was synthesized by reacting bis(pyridinium) (A), bisparaphenylene-34-crown-10 (B), and 1, 4-bis(bromomethyl)benzene C (Fig. 2). The $\pi -\pi$ interaction between A and B directed the formation of an interlocked template intermediate that was further cyclized by substitution reaction with compound C to generate the [2]catenane product.

Figure 2. The Stoddart synthesis of [2] catenane...

References

1. Ashton, P. R., Goodnow, T. T., Kaifer, A. E., Reddington, M. V., Slawin, A. M. Z., Spencer, N., Stoddart, J. F., Vicent, Ch. and Williams, D. J. Angew. Chem. Int. Ed. 1989, 28, 1396–1399.

External links

• www.example.com