Rotaxane cationic

The PFg anion is frequently employed as a counter ion in the preparation of stable crystalline salts with cations of special interest. Among the advantages claimed is the tendency to exclude solvent molecules on crystallisation and the formation of highly soluble salts which dissociate easily. Examples are the first organic superconductor (TMTSF)J PFg, the recently discovered helical sexipyridyl complexes [39,40] and several complex catenane and rotaxane cations. 

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... 

An original approach to assemblies of rotaxanes was suggested by Schalley et al. [56], The authors synthesized a rotaxane 40 containing the bis-quinoline unit in its wheel component. Subsequent exo-coordination of copper cations leads to a copper-bridged bis(rotaxane) 41 with perpendicularly oriented axles. 

Shukla, R., Deetz, M.J., Smith, B.D. [2]Rotaxane with a cation-binding wheel, Chem. Commun. (2000), 2397-2398. 

For a number of years the research interests of the Beer group have covered many areas of macrocychc coordination and supramolecular chemistry. This article reviews our latest results of current research by focusing on three major sections sensing of cations and anions anion templated assembly of pseudorotaxanes and rotaxanes, and metal-directed self-assembly using the dithiocaibamate ligand. 

Ordering suitably tailored molecules in two dimensions at interfaces and then transferring them onto surfaces is a widely used technique. A series of investigations111-113 have shown that cationic rotaxanes and catenanes such as 134+ (Fig. 17.12) can be self-organized at the air-water interface when the PF6... 

However, preorganization by reversible interactions via hydrogen bonds does not necessarily need a further template such as an anion. Direct intermolecular hydrogen bonds between derivatives of isophthalic acid and 2,6-pyridine diacid were used to synthesize a series of new catenanes [17,18], rotaxanes [18c,19], and trefoil knots [20]. The interaction of dibenzylammonium cations and dibenzo[24]crown[8] [21] led to the preparation of rotaxanes by the attachment of stoppers to the thread ends (Scheme 5.5) [22], or similarly by clipping of the crown ether chain wrapped around the ammonium dumbbell [23]. Recently, several novel catenanes were synthesized via the macrocydic connection of three ammonium cations threaded through three crown ether rings attached to a triptycene core [24]. 

Scheme 5.5 A pseudorotaxane is formed by hydrogen bonding between benzylic protons and the -NH2- protons of the ammonium cation with the oxygens of a crown ether. The introduction of bulky residues to appropriately functionalized thread ends produces a rotaxane, while catenanes are accessible by a cyclic connection of the ends.

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