Metal-Templated Synthesis of Catenanes

Figure 2.22. Strategies for the transition metal-templated synthesis of catenanes. The metal (in) predisposes two fragments as open chelates (A) (strategy I) or as a macrocyclic chelate (E) and an open chelate (strategy II) in intermediates (B) and (F), respectively. Cyclization of these intermediate complexes with the chain fragments (C) provides the [2]-catenate complex (D).

Figure 26 Strategies for the transition metal-templated synthesis of catenanes. The metal...

Figure 3-9 Metal-templated synthesis of the [2]catenane 36 under thermodynamic control.

Fig. 17 Two strategies for the transition metal-templated synthesis of a [2]catenane made with Zn and Au porphyrin-incorporating interlocked macrocycles. The thick lines represent chelating fragments, the black disk symbolises copper(I), the empty diamonds are Zn(II) porphyrins, and the hatched diamonds are Au(III) porphyrins...

Figure 9 Active metal template synthesis of [2]catenanes (a) schematic of theory and (b) example of synthesis nsing Glaser coupling.

Figure 10 Active metal template synthesis of a [2]catenane using CuAAC reaction.

The use of metal coordination in the template-directed synthesis of knots and links is one of the earliest successful strategies employed by chemists. The first example of metal-templated synthesis of a [2]catenane was reported in Strasbourg by Sauvage et al. who first used the method to assemble two phenanthroline-based strands around a tetrahedral copper(I) cation (Scheme 17.1). 

Sauvage, J.-P. Dietrich-Buchecker, C. O. Chambron, J.-C. Transition metals as assembling and templating species synthesis of catenanes and molecular knots. In Comprehensive Supramolecular Chemistry, Sauvage, J.-P. Hosseini, M.W., Ed., Publisher Elsevier, Oxford, UK 1996 Vol. 2, p 43. 

The functionalisation also allows extending the complexity of intertwined molecular assemblies involving molecular catenanes, rotaxanes and knots. Elaborate interlocked assemblies constructed by means of metal-templation techniques and ji-ji-stacking preorganisation were reviewed [3, 11], Our last survey was devoted to the hydrogen bond templated synthesis of amide-based catenanes and rotaxanes [32], Since then a considerable advancement in elucidation of mechanisms of templation and derivatisation of the amide-based interlocked structures has been reached. Moreover, in 2000 we reported a one pot synthesis of amide-based knots such as 8 [21], which is so far the easiest preparation of molecular knots. In the following, specific possibilities of functionalisation of amide-based catenanes, rotaxanes and knots will be discussed. 

Fig. 27. Principle of the template synthesis of a catenane. The U fragment is a metal-chelating ligand and the black dot is a transition-metal ion with a pseudo-tetrahedral coordination geometry...

In the early 1980s, a transition-metal template strategy for the synthesis of catenanes was developed in our laboratory.9 It is based on the ability of Cu(I) to entwine two diphenylphenanthroline molecules in such a way that the coordination geometry around the metal is tetrahedral. Thus catenanes... 

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. 

At present, the known catenanes can be divided into two categories - those prepared by metal template synthesis and those synthesised in the absence of a metalion influence. A considerable number of catenanes of the first type have been prepared by Sauvage et al. as well as by a number of other workers. However, discussion on these important metal-ion-directed systems is deferred to the next chapter in which particular supramolecular assemblies produced by metal-ion-controlled procedures are discussed. 

The interest in rotaxanes, pseudorotaxanes, and catenanes (i.e., molecules that contain non-covalently interlocked components) stems from their potential use as building blocks in molecular devices. Their syntheses usually rely on some sort of template assistance, such as the preorganization of the assembly s components around a metal center. While cationic templates have been widely used in this context, only a few examples of anion-directed synthesis of interlocked molecules have been reported. In fact, although rotaxanes and pseudorotaxanes have been prepared in this way (as discussed in this section), to date there is no reported example of anion-directed synthesis of catenanes. 

SYNTHESIS OF INTERLOCKING RINGS USING TWO DIFFERENT TRANSITION METALS AS TEMPLATING AND CONNECTING CENTERS RuCu(20.4) -", RuZn(20.4), AND RuAg(20.4) CATENANES TEMPLATE SYNTHESIS OF A 5-COORDINATE ZINC(1I) CATENANE,... 

Figure 19 Template synthesis of a [2]catenane. The U-shaped fragment contains a bidentate coordinating moiety, and the black dot represents a tetrahedrally coordinating metal ion. (Reproduced from Ref. 56. Springer, 1993.)...

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