Catenanes, rotaxanes and knots

Rouvray, D. H. and King, R. B. (Eds), Topology in Chemistry - Discrete Mathematics of Molecules, Horwood Publishing, Chichester, UK, 2002. 

Suavage, J.-P. and Dietrich-Buchecker, C. (Eds), Molecular Catenanes, Rotax-anes and Knots - A Journey Through the World cf Molecular Topology, Wiley-VCH, Weinheim, Germany, 1999. 

Topological Connection The interlocking of two or more species or the knotting of a single entity without the need for a chemical bond between the components - a mechanical interlocking rather than a chemical one. 

Topological Isomers Compounds that have the same covalent connectivity but are topologically unique. Inter-conversion cannot occur with any amount of deformation without bonds being broken. 

Rotaxanes Interpenetrating compounds in which one or more macrocycles are threaded onto a linear molecule and secured in place by the use of bulky terminal groups. 

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A useful summary of the various and numerous types of rotaxanes, catenanes, and knots can be found in a review of template routes to interlocked molecular structures 468). Inorganic chemistry is centrally involved in the templating involved in self-assembly and in controlled synthesis of such species. 

III. Template Effects for the Syntheses of Rotaxanes, Catenanes, and Knots 177... 

Schalley, C.A, Reckien, W., Peyerimhoff, S., Vogtle, F. Theory and experiment in concert templated synthesis of amide rotaxanes, catenanes and knots, Chem. Eur. J. in press. 

The amide-based template synthesis of rotaxanes, catenanes and knots were first discovered by Vogtle and coworkers when they tried to synthesize macrocycle 3 [13], The cyclization to yield the tetralactam ring was carried out under high-dilution... 

Scheme 1 illustrates the simplest structures of rotaxane, catenane, and knot besides polyrotaxane and polycatenane. From the fact that the main chain-type polyrotaxane at the left side is the only interlocked polymer synthesized so far among the three polymers shown at the bottom of the scheme, progress in synthesis of interlocked polymers appears to be sluggish judging from the level of activity in synthetic polymer chemistry in the world. 

Fig. 1 Rotaxanes, catenanes, and knots formed by template reactions.

Since the work of Pedersen, Lehn and Cram, an enormous amount of research has been conducted using macrocycles for binding cation, anion and neutral species, sensing and catalysis, as well as the synthesis of self-assembled rotaxanes, catenanes and knots (see Chapter 3). Subsequent sections give a brief overview of some of the most important classes of compound. 

A wide range of instrumental techniques are needed to characterise products fully - X-ray crystallography, mass spectrometry (especially FAB-MS and electrospray MS), H and NMR, UV-Vis spectroscopy, and electrochemistry - in the solid state and in solution. As much information as possible is needed in order to establish both the exact nature and long-range structural features (superstructure) of rotaxanes, catenanes and knots. As noted at appropriate points in the text, there is considerable interest in applications for these classes of compounds, particularly in respect to molecular switching devices. 

The copper(I) ion is characterised by tetrahedral coordination in complexes, and this plays a key role in the assembly of rotaxanes, catenanes and knots. 

Figure I Cartoons of the simplest rotaxane, catenane, and knot.

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