Multi-rotaxanes

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. 

Currently, in the research of CD supermolecule chemistry, besides constant synthesis of new CD derivatives and studying interactions between CDs and guest molecules, new progress has been achieved in the following aspects such as CD molecular recognition and self-assembly, rotaxane design and multi-rotaxane... 

Metallation-demetallation of new multi-porphyrinic [2]rotaxanes in which a gold(III)-porphyrin is part of the ring, has been found to induce a complete changeover of the molecule. ... 

Inorganic templating and self-assembly provide coordination compounds whose geometries make possible the synthesis of complex structures, namely of cyclic multiporphyrin arrays [9.13a, 9.179], of inorganic rotaxanes [9.97a, 9.180], of multi-catenates and catenands (see 181) [8.281, 8.282] and even of molecular knots (see 182) [8.282, 9.77, 9.181] (in 181 and 182 a) with, b) without Cu(l) template). 

Further examples of hybrid pseudorotaxanes containing a linear component incorporating two dialkylammonium centres and a 4,4 -bipyridinium unit associated with an assortment of macrocyclic polyethers have been reported. Both multi-component rotaxanes and polyrotaxanes based on the above tetracationic thread were observed to form. The reversible acid-base-controlled dethreading/rethread-ing of such [n]-rotaxanes has been demonstrated using a combination of NMR, absorption and fluorescence spectroscopies. ... 

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]. 

Advantages of Rotaxanes Compared to Multi-Component Systems... 

In conclusion, these results demonstrate clearly that the rotaxane framework does offer significant performance advantages over multi-component systems for the preparation of switchable molecular assemblies. 

Nakashima et al. developed a multi-mode-driven molecular shuttle (Figure 74) based on [2]rotaxanes using the... 

Figure 74 A multi-mode-driven molecular shuttle based on an azobenzene rotaxane.

Just as the incorporation of two electron-acceptor units in a thread permits the assembly of a two-ringed rotaxane, so the synthesis of multi-electron-acceptor ligsons permits the synthesis of more complicated multi-ring rotaxanes. Thus reaction of LI 107 (Eq. 4.68) with bis- -phenylene-34-crown-10 (L1072) gives a mixture of rotaxanes, with one, two, or three rings on the branches of this three-legged... 

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