Rotaxanes directed approaches

A similar template-directed approach was employed (Figure 31) by Anderson et al. [48] to self-assemble azo-dye [2]rotaxanes. The azobenzene diazonium salt 98 is bound by a-cyclodextrin 99 and also by / -cyclodextrin 100 in H20 with pseudorotaxane geometries. Reaction of the terminal diazonium functions with / -naphthol 101 affords the purple [2]rotaxanes 102 and 103 in yields of 12 and 15%, respectively. These two [2]rotaxanes were characterized by electrospray mass spectrometry which revealed peaks corresponding to the loss of all four sodium cations in both cases. By irradiating some of the protons of the dumbbellshaped components of these [2]rotaxanes, enhancement of the resonances of some of the cyclodextrin protons could be observed as a result of an intercomponent... 

A similar template-directed approach has been employed to self-assemble [n]rotaxanes incorporating up to four mechanically-interlocked components and large dendritic stoppers Amabilino, D.B., Ashton, P.R., Balzani, V., Brown, C.L., Credi, A., Frdchet, J.M.J., Leon, J.W., Raymo, F.M., Spencer, N., Stoddart, J.F., Venturi, M., J. Am. Chem. Soc. 1996, 118, 12012-12020. 

A [2]rotaxane containing a 2,6-dioxyanthracene moiety has also been prepared1351 (Figure 20) by employing the usual template-directed approach. Treatment of the bis(hexafluorophosphate) salt IS 2PF6 with the dibromide 16 in the presence of the... 

A similar template-directed approach has been employed to self-assemble [n]rotaxanes incorporating up to four mechanically interlocked components and large dendritic stoppers ... 

Molecular interlocked systems such as catenanes and rotaxanes can also be prepared using anion-directed approaches. Although anionic templates did not make their way into this area until relatively recently, nowadays there are several examples that demonstrate the utility of this approach for the synthesis of this topologically interesting species. 

Fortunately, more efficient methods for the complexation of macrocyclic hosts with acyclic guest molecules have become available with the advent of supramo-lecular chemistry, resulting in higher yields in rotaxane and catenane synthesis. In the following sections, the preparation of different types of interlocked molecules, with the use of host-guest recognition, is discussed. It should be noted that these template-directed methods differ significantly from the above-mentioned stochastic approach [28]. 

The early syntheses of catenanes and rotaxanes were mainly based on statistical threading approaches or on directed methodologies involving chemical conversion [30]. To obtain a catenated molecule, one ring must be closed in the presence of a... 

The first catenanes and rotaxanes were constructed by either statistical [2] or directed [3] synthetic approaches. The statistical method relies [2] on the formation of small quantities of a species in which a cyclic molecule is threaded by an acyclic molecule. After experiencing appropriate covalent bond formation, these threaded species are con-... 

The approaches to heterometaUic systems outlined above all rely upon coordination chemistry, whether to a metal ion or a nanoparticle surface. Supramolecular interactions can also play a role in assembling heterometaUic systems. For instance, Sambrook et al. prepared a pseudo-rotaxane (18) templated around a chloride ion (Fig. 9) in which lanthanide ions are bound to the thread while a luminescent rhenium complex is bound to the macrocycle component [49]. Thus there is no direct link between the donor chromophore and the lanthanide ion, and Dexter exchange is not viable in the absence of bonds enforcing Forster energy transfer. This extreme of behaviour helps to rationalize the behaviour of more conventionaUy... 

The cooperative behaviors of both the anionic and cationic templates are vital for efficient interlocked molecule formation. The anion templation component of this approach, in which the phenolate anion is held within an isophthalamide macrocycle and consumed in the reaction, was pioneered by Vogtle in 1999. " However, the macrobicycle design and presence of the bound alkali metal enabled rotaxane 20 to be synthesized in the polar solvent medium of 5 1 THF DMF in a yield of 20%. Furthermore, the direct templating action of the potassium was demonstrated by the fact that no equivalent reaction occurred in its absence or with the larger cesium cation that was not able to bind efficiently in the crown ether. 

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