Rotaxanes statistical approach

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. 

Figure 13.8 Schematic operation of a two-station rotaxane as a controllable molecular shuttle, and idealized representation of the potential energy of the system as a function of the position of the ring relative to the axle upon switching off and on station A. The number of dots in each position reflects the relative population of the corresponding coconformation in a statistically significant ensemble. Structures (a) and (c) correspond to equilibrium states, whereas (b) and (d) are metastable states. An alternative approach would be to modify station through an external stimulus in order to make it a stronger recognition site compared to station A.

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. 

The first rotaxanes were prepared by a statistical synthetic approach. The threading of a macrocycle around a linear chain is based purely on chance no specific... 

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... 

The first catenanes and rotaxanes were constructed by either statistical [2] or directed [3] synthetic approaches. The statistical method relies [2] on the formation of small quantities of a species in which a cyclic molecule is threaded by an acyclic molecule. After experiencing appropriate covalent bond formation, these threaded species are con-... 

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