Anion templated synthesis

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... 

Scheme 21 Anion-templated synthesis of [2]rotaxanes first introduced by Vogtle...

Figure 51. Anionic template synthesis of rotaxane 118 with a bis(phenyl ether) axle. The mechanical bond is formed by reaction of the phenolate-macrocycle complex [32-115] (supramolecular nucleophile) with the semiaxle intermediate 117. 

The procedure of the anion-templated synthesis was later used for the preparation of various rotaxanes by the groups of Smith [41] and Schalley [34-36], The anion-templation technique was carefully tested by Schalley et al. Altering the length of the axle-center pieces and the size of stopper groups they synthesized a variety of rotaxanes and analysed their yields and de-slipping rates [34, 35],... 

More recently, Beer and his group developed a high-yielding anion-templated synthesis of the chloride-selective receptor 62. This was done by carrying out two identical cyclizations of two macrocyclic rings in the presence of chloride anion,... 

Abstract This review presents an overview of the area of anion-templated synthesis of molecules and supramolecular assemblies. The review is divided into two main sections the first part deals with anion-templated systems where the final products are linked by bonds that are not reversible under the conditions of the experiment Several recent examples of macrocycles, cages and interlocked species are presented in this section. The second part of the chapter, presents a discussion of anion-templation in systems containing reversible bonds that give rise to dynamic combinatorial libraries (either by formation of coordination metal-ligand bonds or by reversible covalent bonds). 

This chapter aims to provide an update on the role of anions as templates. The review is divided in two main sections (a) anion-templated synthesis of assemblies linked together by irreversible bonds (or bonds that are inert under mild experimental conditions) (b) anion templates in systems where the bonds linking the components are reversible and lead to anion-controlled dynamic combinatorial libraries. Since some comprehensive reviews in the area of anion temptation have appeared over the past few years [5-7], this chapter will mainly focus on papers published recently and will aim to show the principles of anion temptation rather than being a comprehensive account of the literature. In addition, the scope of the chapter will be restricted to finite assemblies (molecular or supramolecular) and not polymeric (for a review on molecularly imprinted polymers using anions see Steinke s chapter in this volume). 

Scheme 6 Schematic representation of the anion templated synthesis of rotaxanes based on tetralactam macrocycles and a phenolate anions...

Using the same general strategy described above. Beer reported the first anion-templated synthesis of catenanes [43,44]. Mixing macrocycle 21 with... 

Elegant examples o/anion-templated synthesis are the penta- and hexanuclear circular helicates reported by Lehn (see Fig. In this work it was demonstrated that the... 

Cheng, S. T. Doxiadi. E. Vilar, R. White. A.J.P. Williams- D.J. Anion templated synthesis of Ni/Pd containing metalla-macrocycles. J. Chem. Soc. Dalton Trans. 2001.2239-2244. "... 

One of the most successful approaches to the synthesis of metalla-supramolecular systems has been by templated self-assembly processes. Most of the templating agents used by synthetic chemists are either cationic or neutral species. Anions, on the other hand, have only fairly recently been successfully utilized as templates. The new metalla-macrocycles [Pd2Ni2(atu)4(PPh3)4X]3+ (atu = deprotonated amidinothiourea, X = C1, Br, I) have been prepared using anion templated syntheses. Only in the presence of each of these three halides are the metalla-macrocycles... 

The binary representation is applicable to various other oxide materials. However, an important distinction can be made between borates and other main group element oxide systems, such as aluminates and silicates. In the latter systems cations predominantly reside at sites created by the demands of rigid anionic oxide frameworks. Although some degree of structural control may be obtained by varying cations or by use of template synthesis, the oxide frameworks of these systems tend to be relatively inflexible in comparison with... 

Our template synthesis of knots implies that the target molecules are obtained as cationic dicopper(I) complexes. Therefore we considered the possibility of interconverting both enantiomers into a pair of diastereomeric salts [137, 138] by combining them with an optically active anion. Binaphthyl phosphate (BNP") [139] drew our attention because its chirality arises from the binaphthyl core, which is twisted. This helical structure is of the same type as that of die copper double helix, precursor of the knot. Besides, both compounds are aromatic and, thus, we could expect some potentially helpful stacking interactions [87],... 

This seems to be the first rotaxane synthesis based on an anionic template and latest results indicate that this new strategy can be extended to ester- and acetal-based axles [70]. Hence the anionic procedure represents a powerful alternative to the rotaxane synthesis assisted by a neutral template. 

Scheme 16 anion-templated rotaxane synthesis via a Michael addition reaction. 

Such complexes form a precursor to a full discussion of the vast and highly topical field of self-assembly (Chapter 10). We consider them here since they resemble structurally the types of compounds discussed in Section 4.7, but unlike metal-based anion receptors the simple thermodynamic equilibrium between host, anion and complex is not the only process occurring in solution. In fact multiple equilibria are occurring covering all possible combinations of interaction between anions, cations and ligands. These systems have the appeal that the formation of particular metal coordination complexes are thus subject to thermodynamic anion templating (cf. the thermodynamic template effect in macrocycle synthesis, Section 3.9.1) and vice versa. 

Schalley, C.A, Silva, G., Nising, C.F., Linnartz, P. Analysis and improvement of an anion-templated rotaxane synthesis, Helv. Chim. Acta, 85 (2002), 1578-1596. 

Scheme 6.5.3. Anion template effect for efficient rotaxane synthesis. 

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