Threaded rotaxane-type compounds

The hydrogen bonding of ammonium ions to crown ethers has also been used to assemble a range of rotaxanes andp. eMd/orotaxanes. The inclusion of a secondary ammonium thread into dibenzo[24]crown-8 followed by covalent capping to give a rotaxane is shown in Scheme 10.19. This kind of approach can result in some interesting multiply threaded rotaxane type compounds, Figure 10.63. 

Rotaxanes and polyrotaxanes are another type of compound consisting of string-like components threaded through ring-like components without covalent bonding (Fig. 11.19) and have received attention for a long time.46 Reported ring parts of... 

Metalation of free rotaxanes. One of the special features of the rotaxanes presently described is that their coordination sites comprise two dpp-type chelates, both of which being incorporated in different subunits, i.e. die ring and the dumbbell thread. The compounds thus contain a coordinating tetradentate site well suited for tetrahedral... 

A classic example of the formation of a macrocycle by a neutral template is that of the versatile host compound and component of molecular machines, the so-called blue box, or cyclobis paraquat-para-phenylene. Reaction of the horseshoe precursor with dibromo-para-xylene leads to the formation of a tricationic intermediate that is capable of binding the template molecule (Scheme 3), which closes the macrocycle to form the tetracationic cyclophane. The jT-ir interactions of the charge-transfer variety (the complex of the product and template is colored, whereas the components are not) assisted by the charge on ihe product are a major driving force in the process, as revealed in X-ray structures of complexes. It should be noted that the interaction is of the jr-n type assisted by the complementary positive charge on the bipyridinium residues and r-electron-rich nature of the template. This supramolecu-lar synthon can be used for other cyclophanes, catenanes, and rotaxanes (see Self-Assembly of Macromolecular Threaded Systems, Self-Assembled Links Catenanes, and Rotaxanes—Self-Assembled Links, Self-Processes). 

A further type of threading is involved in amide (pseudo)rotaxanes. In this class of compounds both components are amides (e.g. L1097 with L1098 Eq. 4.64) [204]. There are many sites for hydrogen-bonding and n-n (stacking, donor-acceptor) non-covalent interactions between the components [205]. 

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