An Introduction to Rotaxanes and Catenanes (Page 3/3)

Why are they made?

Great strides have been made in the two decades since the first templated catenane synthesis in 1983. Catenanes and rotaxanes can now be constructed in high yields, using a variety of templating interactions: hydrogen bonds, metal-ligand interactions, ∏-∏charge transfer interactions or hydrophobic forces. The acquired understanding of non-covalent interactions and their utility in molecular construction has been a pplied to the synthesis of ever-more complex architectures such as [n]rotaxanes, [n]catenanes (i.e. catenanes and rotaxanes involving several interlocked components) and knots. Synthetic challenges still remain however. The necessity for interactions between components naturally places restrictions on the structural and functional make-up of the final product and the ability to create rotaxanes or catenanes composed of virtually any chemical units is an extremely attractive prospect and one which is being actively pursued in our group. There are also many other interesting architectures still to be reproduced at the molecular level and which are of interest to us.

The main driving-force for research on interlocked molecules today, however, is perhaps not the synthetic challenge but the interesting properties and potential applications of the molecules themselves. Interlocked molecules often exhibit markedly different properties to their non-interlocked analogues. This can include, for example, differences in spectroscopic responses, chemical reactivity or mechanical properties. These differences are a direct result of the interlocked architecture, yet perhaps the most exciting consequence of the mechanical bond, is the unique way in which different parts of the molecule can move with respect to the rest of the system (see Figure 9). Controlling these submolecular motions is a very active area of research in many groups across the world, including our own and it is a goal which is now very much within our grasp. Click here for more information on controlling motion at the molecular level.

Controlled, submolecular motion of components in mechanically interlocked molecules is one approach to the creation of novel functional molecules – molecules which change their properties in response to some external stimulus (e.g. light, electricity or a chemical reagent). Such molecules will form the basis of the molecular machines and molecular devices which are predicted to be the key protagonists in the development of a “bottom-up” nanotechnology for the 21st century.

Figure 9. Mechanically interlocked architectures as components for molecular machines.

References

• 1
  
  a) C. O. Dietrich-Buchecker, J.-P. Sauvage, Chem. Rev. 1987, 87, 795;
  b) S. Anderson, H. L. Anderson, J. K. M. Sanders, Acc. Chem. Res. 1993, 26, 469;
  c) M. C. T. Fyfe, J. F. Stoddart, Acc. Chem. Res. 1997, 30, 393;
  d) R. Jager, F. Vögtle, Angew. Chem. Int. Ed. Engl. 1997, 36, 930;
  e) Templated Organic Synthesis, (Eds.: F. Diederich, P. J. Strang), Wiley-VCH, Weinheim, 1999;
  f) T. J. Hubin, D. H. Busch, Coord. Chem. Rev. 2000, 200-202, 5;
  g) J. F. Stoddart, H. R. Tseng, Proc. Natl. Acad. Sci. U. S. A. 2002, 99, 4797.
• 2
  
  For original papers and accounts from the Strasbourg group, see ref 1a and the following:
  
  a) C. O. Dietrich-Buchecker, J.-P. Sauvage, J. P. Kintzinger, Tetrahedron Lett. 1983, 24, 5095;
  b) C. O. Dietrich-Buchecker, J.-P. Sauvage, J. M. Kern, J. Am. Chem. Soc. 1984, 106, 3043;
  c) J.-P. Sauvage, Acc. Chem. Res. 1990, 23, 319.
• 3
  
  For original papers and accounts from the Los Angeles group, see refs 1d and 1h and the following:
  
  a) P. R. Ashton, T. T. Goodnow, A. E. Kaifer, M. V. Reddington, A. M. Z. Slawin, N. Spencer, J. F. Stoddart, C. Vicent, D. J. Williams, Angew. Chem. Int. Ed. Engl. 1989, 28, 1396;
  b) P. L. Anelli, P. R. Ashton, R. Ballardini, V. Balzani, M. Delgado, M. T. Gandolfi, T. T. Goodnow, A. E. Kaifer, D. Philp, M. Pietraszkiewicz, L. Prodi, M. V. Reddington, A. M. Z. Slawin, N. Spencer, J. F. Stoddart, C. Vicent, D. J. Williams, J. Am. Chem. Soc. 1992, 114, 193;
  c) M. GomezLopez, J. A. Preece, J. F. Stoddart, Nanotechnology 1996, 7, 183.
• 4
  
  a) A. G. Johnston, D. A. Leigh, R. J. Pritchard, M. D. Deegan, Angew. Chem. Int. Ed. Engl. 1995, 34, 1209;
  b) A. G. Johnston, D. A. Leigh, L. Nezhat, J. P. Smart, M. D. Deegan, Angew. Chem. Int. Ed. Engl. 1995, 34, 1212.
• 5
  
  F. G. Gatti, D. A. Leigh, S. A. Nepogodiev, A. M. Z. Slawin, S. J. Teat, J. K. Y. Wong, J. Am. Chem. Soc. 2001, 123, 5983.
• 6
  
  A typical procedure involves simultaneous addition of iosphthloyl dichloride in chloroform and p-xylyene diamine in chloroform to a solution of the thread and triethylamine in chloroform over 4 hours. Insoluble oligomeric material is then filtered off and the rotaxane isolated from salts, unconsumed thread and [2]catenane by chromatography.
• 7
  
  a) D. A. Leigh, A. Murphy, J. P. Smart, A. M. Z. Slawin, Angew. Chem. Int. Ed. Engl. 1997, 36, 728;
  b) G. Brancato, F. Coutrot, D. A. Leigh, A. Murphy, J. K. Y. Wong, F. Zerbetto, Proc. Natl. Acad. Sci. U. S. A. 2002, 99, 4967.
• 8
  
  D. A. Leigh, P. J. Lusby, S. J. Teat, A. J. Wilson, J. K. Y. Wong, Angew. Chem. Int. Ed. 2001, 40, 1538.

Euan Kay, July 10th 2003.