Statistical Approaches to Catenanes and Rotaxanes

8 Schalley, C. A., Beizai, K. and Vogtle, F., On the way to rotaxane-based molecular motors Studies in molecular mobility and topological chirality , Acc. Chem. Res. 2001, 34, 465-476. 

We have already seen (Section 3.12.6) how strong r-stacking interactions occur with the aryl corands 3.116 and 3.117 and the herbicide paraquat (3.113) (e.g. 3.116 + 3.113, = 730 in Me2CO), result- 

It is a tribute to the templating effect of the electronically matched pairs of reactants that the [2] catenane 

The electrochemistry of catenane 10.76 can be studied by cyclic voltammetry (Box 4.1). The compound possesses very different redox properties in comparison with the two isolated components. 

This difference is a direct result of the close Jt-stacking interactions. Electrochemical reduction of the bis(bipyridinium) cyclophane occurs in three distinct stages  

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The early syntheses of catenanes and rotaxanes were mainly based on statistical threading approaches or on directed methodologies involving chemical conversion [30]. To obtain a catenated molecule, one ring must be closed in the presence of a... 

Frisch, H.L. and Wasserman, E. (1961) Chemical topology, J. Am. Chem. Soc. 83, 3789-3794. Schill, G. (1971) Catenanes, rotaxanes and knots. Academic Press, New York. Walba, D.M. (1985) Topological stereochemistry. Tetrahedron 41, 3161-3212. Dietrich-Buchecker, C.O. and Sauvage, J.P. (1987) Interlocking of molecular threads From the statistical approach to the templated synthesis of catenands, Chem. Rev. 87, 795-810. Philp, D. and Stoddart, J.F. (1991) Self-assembly in organic synthesis, Synlett 445-458. 

It was not only for the basic scientific knowledge but also for the new challenges in the synthesis and the beauty of the final structures that nearly half a century ago, chemists started to investigate intertwined macrocyclic supramolecules such as rotaxanes and catenanes [4], Earlier, when the syntheses of such structures were at their infancy, the routes to such systems were troublesome. The statistical methods [5] proved to be low-yield processes. Multistep procedures [6] involving a covalent junction which is formed between two parts that are needed to stay together until the structure is complete were not convenient as well. The use of non-covalent templates thus provided a more straightforward and high-yield approach to the problem. 

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