Rotaxanes anion templated assembly

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. 

The anion-templated synthesis of rotaxanes first introduced by Vogtle has now been employed by others to produce other interlocked assemblies. Schalley for example [68], has reported an improved yield for the synthesis of rotaxanes by... 

Fig.l Self-assembly of anion templated rotaxane SAM (RC = redox centre). From [46], reproduced by permission of The Royal Society of Chemistry... 

Mullen KM, Mercurio J, Serpell CJ, Beer PD (2009) Exploiting the 1,2,3-triazolium motif in anion-templated formation of a bromide-selective rotaxane host assembly. Angew Chem Int Ed 48 4781... 

Pseudorotaxanes are precursors of both rotaxanes and catenanes they consist of a guest molecule threaded through a macrocyclic host. Stoppering both ends of the threaded molecule gives a rotaxane, cycliza-tion of the thread gives a catenane. Pseudorotaxane formation may occur by spontaneous self-assembly, or may be template-controlled. Anion size can be of paramount importance for such templates - Cl- is effective, Br, I- less good, and PFe ineffective when the recognition motif demands a small template (454). 

Anions have also been used as templates in the synthesis of catenanes and rotaxanes, as recently described by Beer and coworkers [15]. They used the self-assembly of diamides, known as anion receptor molecules, around a chloride anion to produce, for example, [2]- and [3]catenanes by olefin metathesis [16] (Scheme 5.4). In this special example, the template effect was increased by hydrogen bonding between the N-methyl group to the crown ether chain and by n-n stacking interactions. 

The interest in rotaxanes, pseudorotaxanes, and catenanes (i.e., molecules that contain non-covalently interlocked components) stems from their potential use as building blocks in molecular devices. Their syntheses usually rely on some sort of template assistance, such as the preorganization of the assembly s components around a metal center. While cationic templates have been widely used in this context, only a few examples of anion-directed synthesis of interlocked molecules have been reported. In fact, although rotaxanes and pseudorotaxanes have been prepared in this way (as discussed in this section), to date there is no reported example of anion-directed synthesis of catenanes. 

Fluorescence Sensing of Anions, p. 566 Guanidium-Based Anion Receptors, p. (575 Halogen Bonding, p. 628 Macrocyclic Synthesis, p. 830 Molecular Squares, Boxes, and Cubes, p. 909 Naked Anion Effect, p. 939 Organometallic Anion Receptors, p. 1006 Rotaxanes and Pseudorotaxanes, p. 1194 Self-Assembly Definition and Kinetic and Thermodynamic Considerations, p. 1248 The Template Effect, p. 1493... 

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