Catenanes multi

The principal idea of this present essay was to show how the unique preorganization of functional groups in self-assembled dimers of tetra-urea calix[4]arenes can be used to prepare novel multi-rotaxanes and -catenanes or topologically even more complex molecules and supramolecular structures. We will conclude by summarizing some related studies in which calixarenes were used in a different way as building blocks for the construction of such structures or assemblies. 

Based on the chemistry discussed so far, two-step procedures for the assembly of [4]- and [5]-catenanes have also been developed. In part, the success of these syntheses reflects the use of the intermediate ring size crown, tris-/ -phenylene-[51]-crown-15 which provides two non-equivalent templating sites for the catenation reactions. The strategies employed for the construction of these extraordinary multi-linked systems are given in Figure 5.15. The respective products were characterised by means of FAB-MS and LSI-MS, with the fragmentation patterns... 

Many other catenane species have been synthesised. These range from further simple [2]-catenanes, other [2]- as well as [3]-catenane species incorporating redox-active tetrathiafulvalene groups, other multi-ring derivatives, through to polymeric species incorporating catenane domains as part of a larger macromole-... 

A Helical System Leading to a Multi-intertwined [2]-Catenane... 

Rotaxanes [a name derived from the Latin words rota (wheel) and axis (axle)] [1] and catenanes [from the Latin word catena (chain)] [1] are supramolecular (multi-component) species [1-10] strictly related (Figure 1) to pseudorotaxanes, which were described in Volume III, Part 2, Chapter 6. Whereas pseudorotaxanes can undergo dissociation into their wire-like and macrocyclic components, rotaxanes and catenanes are interlocked species, whose dissociation requires breaking of a covalent bond. It should be pointed out, however, that, as discussed in detail in the previous chapter 6, the boundary between rotaxanes and pseudorotaxanes is somewhat fuzzy because, for example, when the stoppers are not extremely bulky compared to the hole of the macrocyclic component, a rotaxane at low temperature might well be a pseudorotaxane at elevated temperature [11]. 

The foniiation of 4, therefore, involved several different noncovalent interactions. The cyclization step was brought about by the formation of Pd—N coordinate bonds that is, by a metal-mediated process. The interlocking step involved n- and hydrophobie/hydrophilic-mediated processes, along with an entropic effect. Catenane 4 can. therefore, be considered an example of a multi-mediated,"" multiple-interaction self-assembly. Fujita referred to such processes as ""double-molecular recognition"" procedures, in which the two interlocking molecules bind each other in their cavities. 

Figure L Principle of the hypothetical multi-threading reaction. The coordinating fragments are indicated in thick line. The assembling metal centre is a black circle, (a) the well established quantitative threading of a monochelate with formation of a precursor to various catenanes [2] (b) and (c) possible generalisation of the reaction to multi-metallic threaded systems.

Multi-ring catenanes may also be prepared by the cyclophane approach. The polyether LI 160 (Eq. 4.89), the trinaphtho-analogue of L1094, is a large ring and... 

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