Interlocked catenanes

Figure 78 Two preformed Pd11 cage compounds that are reorganized into the three-dimensionally interlocked catenane in high yield when they are mixed in an aqueous solution.

A highly unusual air-stable Ni species has been produced using an interlocking catenane ligand (40). The NF precursor... 

Instead of using a metal ion as a clasp , it is also possible to use weak interactions between ring components for catenane interlocking. In the example shown in Fig. 3.25, a C-shaped precursor containing viologen-type cyclophane was complexed to a cyclophane with benzene ring moieties. The cationic bipyridine moiety in the C-shaped component was then sandwiched by electron-rich benzene units. Cyclization of the C-shaped precursor using a dibromo compound resulted in interlocked catenanes. This electronic interaction between two kinds of species results in more efficient catenane formation. 

Catenane synthesis can be also achieved by dynamic molecular association. Figure 3.27 shows an example of catenane preparation through the dynamic formation of a palladium (Pd) complex. Mixing the Pd complex with pyridine-type ligands in water induces the formation of both a monocyclic structure and an interlocked catenane. An equilibrium exists between these two structures, and the catenane structures are more favorable at higher concentrations. In the catenane structure, the benzene rings stack next to each other due to favorable... 

This strategy has been further extended to the synthesis of a triply twisted tris[bis(phenanthroline)copper(I)] complex analogous to (35) which, after correct linking of the termini and demetalation, leads to a doubly interlocked catenane structure [46]. 

Figure 33 Strategy for the synthesis of a doubly interlocked catenane. Reproduced with permission from reference 96.

Illustrated in Fig. 2 is one of the most famous examples of a metal-mediated, thermodynamically self-assembled catenane. The reaction of 1 (M = Pd) with the angled bipyridyl ligand 2 was found by Fujita and coworkers to lead to the formation of cycle 3, along with the interlocked catenane The nature of the self-assembly process... 

Fig. 1 Multiple molecular recognition Free metallocycle 1 is formed in dilute solution because of the enthalpy of formation of the Pd—N coordination bonds. When the solution is concentrated from 2-50 mM, the lability of these bonds allows the in situ formation of the interlocked catenane 2. This is driven by hydrophobic interactions to minimize the contact of the metallocycle cavities with the water solvent, the formation of 7t-stacking interactions between two such rings, and an entropic effect due to a decline in the number of species present in solution after interlocking.

Like rotaxanes, catenanes are mechanically interlocked molecules. However, instead of interlocking one ring shaped macrocycle and a dumbbell shape, catenanes consist of interlocked macrocycles. The number of macrocycles contained in a catenane is indicated by the numeral that precedes it. Catenanes have bistable and multistable forms and a switchable, bistable [2]catenane is commonly exploited in nanotechnology and molecular electronics because its behavior can be controlled by electrochemical processes [89]. Collier et al. was the first to demonstrate the electroactivity of interlocked catenanes [90]. The authors affixed phospholipid counterions to a monolayer of [2]catenanes and then sandwiched this system between two electrodes. This work resulted in a molecular switching device that opened at a positive potential of 2 V and closed at a negative potential of 2 V. 

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