Molecular trefoil knot

We shall now see how to apply the theorem to the molecular trefoil knot, which was illustrated in Figure 17. We can create a molecular cell complex G by replacing each isolated benzene ring by a cell and each chain of three fused rings by a single cell. We prove by contradiction that our molecular cell complex is topologically chiral. Suppose that it is topologically achiral. Then there is a defor-... 

The successful synthesis of various catenanes by the strategy depicted in Figure 12 soon brought us to imagine a molecular trefoil knot synthesis by extending the former synthetic concept from one to two copper ions. As shown in Figure 14, two bis-chelating molecular threads (A) can be interlaced on two transition... 

A Synthetic Molecular Trefoil Knot - First Results [89]... 

Figure 28. Principle of the resolution of the dicopper(I) molecular trefoil knot Cu2(K-84) +. The chiral auxiliary used is S-(+)-l,l -binaphthyl-2,2 -diyl phosphate (BNP-).

Ashton, P. R., Matthews, 0. A., Menzer, S., et ai, Molecular meccano, 27 - A template-directed synthesis of a molecular trefoil knot. Liebigs Annalen-Recueil 1997, 2485-2494. 

Trefoil knots are the classic examples of topologically chiral structures. The rational synthesis of molecular trefoil knots, suggested as long ago as 1953,81 was finally achieved in 1989, by Christiane Dietrich-Buchecker and Jean-Pierre Sauvage82 (Figure 18) the enantiomers of this knot were subsequently resolved.83... 

Dietrich-Buchecker CO, Sauvage J-P (1989) A synthetic molecular trefoil knot. Angew Chem Int Ed Engl 28 189-192... 

To our knowledge, topologically chiral molecules have not yet been resolved into enantiomers. However, we may anticipate that their energy barrier to racemization will be extremely high, compared to Euclidean chiral molecules. Therefore they are expected to be useful in enantioselective interactions or reactions. For example, it has been shown that tetrahedral copper(I) bis-2,9-diphenyl-l,10-phenanthroline complexes (which form the catenate subunits) are good reductants in the excited state [97] therefore the chiral Cu(I) catenates could be used for enantioselective electron-transfer reactions. Alternatively, the resolution of topologically chiral molecules would allow to answer fundamental questions, such as what are the chiroptical properties of molecular trefoil knots ... 

We have seen how elegantly transition metals can template the formation of knots, but what about Nature s favourite templating interaction, the hydrogen bond A remarkably efficient molecular trefoil knot synthesis based on this interaction was reported by Vogtle and co-workers, who made a knotane in 20% yield [39]. This amazing route (Fig. 11) was uncovered serendipitously during the synthesis of catenanes. The crystal structure of the compound was the definitive proof for the structure, because neither NMR nor mass spectrometry could tell it apart conclusively from the macrocycles that are also formed. 

Jean-Pierre Sauvage Molecular trefoil knots... 

A synthetic molecular trefoil knot, C. O. Dietrich-Buechecker and J.-P. Sauvage, Angew. Chem. Int. Ed. Engl., 1989, 28, 189. 

Mobius strip were formed exclusively. The synthesis of the more highly twisted belts 42 and 43 would be very interesting because subsequent cleavage of the double bonds by ozonolysis would lead to a catenane 44 and a molecular trefoil knot 45, respectively. 

Figure 3.47 (a) The components used to synthesise a molecular trefoil knot via a macrocyclisation reaction, (b) its X-ray crystal structure and (c) a simplified schematic of the knot. 

Figure 34 (a) Picture of a trefoil knot drawn using POVRAY and (b) a molecular trefoil knot containing two copper(I) centers. 

A remarkably efficient molecular trefoil knot synthesis based on organic templates was reported by VOgtle and coworkers, who serendipitously made and astutely identified the knotane. In the course of the synthesis of [ ]catenanes, reaction of the simple precursors 9 and 10 in the presence of triethylamine under high dilution conditions (10 mM in dichloromethane) produced three colorless products macrocycle 11 (15% yield, 1 1 ratio of reagents... 

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