Pyrogallol arene

Recently, Atwood and coworkers reported a series of metal-organic analogs of multimeric nanocapsules based on resor-cin[4]arenes (76) and pyrogallol[4]arene units (77). These containers contain several metal atoms in the hydrogen-bonded seam connecting the capsule units and it was demonstrated that metal... 

Fig. 6. The structures of pyrogallol[4]arene L4 and capsule complexes 4a,b (77). The encapsulated 3-methylpyridine in 4a,b is omitted for clarity.

Self-assembly of nanocapsules with pyrogallol[4]arene macrocycles... 

Crystal structures for several of the corresponding pyrogallol[4]arenes 50 (Figure 3.23) have been solved. These also form hexameric capsules, which now contain an array of 72 hydrogen bonds (48 are intramolecular and 24 intermolecular, HB/ (N— 1) =4) and have no structural water molecules [64]. The increase in the ITm HB/(N— 1) value agrees very well with the fact that nanocapsules based on pyrogallol 50a are more stable in polar media than those derived from resorcinarene 49a. 

Solid State Formation of the Hexameric Capsule Derived from Pyrogallol[4]arene (50c) [74]... 

A different neutral hexameric coordination cage structure was assembled from six either C-propyl- or C-pentyl-pyrogallol[4]arene units and 12 Ga(III) ions [51]. In both cases the centroids of the macrocyclic ligand components reside on the vertices of a squeezed octahedron enclosing a space of approximately 1150 A3. Only a total of 20... 

Besides these covalently constructed cage-type receptors a number of self-assembled capsules with hydrogen bond donors protruding to the inside have also been described. An early example was reported by Atwood et al. This system makes use of the well known properties of resorcin[4]arene 30a and pyrogallol[4]arene 30b to form hexameric spherical capsules in the solid state and, in the case of 30b, also in solution. 

Figure 8 (a) General forumla for pyrogallol[4]arene, 7 (b) structure of the hexamer, 8, C-propylresorcin[4]arene with the oxygen atoms shown in red, (see also Plate 20). 

There has been a recent report of a very interesting, large supramolecular assembly related to the resorcin[4]arene work. The synthesis of several pyrogallol [4]arenes, 7, has been accomplished under mild conditions [32]. However, the authors report that they obtained the hexamer of C-isobutylpyrogallol[4]arene, 8, only one time out of many attempts (Figure 8). 

Figure 12 (a) The spherical capsule consisting of six pyrogallol[4]arene molecules shown in... 

Plate 22 (Figure 3.12). (a) he spherical capsule consisting of six pyrogallol[4]arene molecules shown in the capped-stick metaphor, and (b) with the carbon and hydrogen atoms removed. Hydrogen bonds are shown as thin, solid red lines. Parts (c) and (d) show the remarkable correspondence of the hydrogen bonded pattern with the Archimediean solid, the small rhombicuboctahedron. 

The examples given here employ two routes Hogberg s original method and Mattay s [18] extended reflux method. The products are simple C-methyl[4] re-sorcinarene derivatives and a heptyl pyrogallol[4]arene as shown in Figure 3.30. 

Other linear aldehydes may be used to prepare pyrogallol[4]arenes though some, such as pentanal, have unpleasant odours. 

Whereas the examples in Chapter 1 are all essentially linear and those in Chapter 2 cyclic, the compounds described in Chapter 3 introduce a third dimension to supramolecular chemistry. Cyclotriveratrylenes, [4]resorcinarenes and pyrogallol[4]arenes, as exemplified by compounds 23, 35 and 36, are all prepared through the reaction of an aldehyde with an aromatic dialcohol, or derivative, in the presence of acid. Many variations on both the compounds and the... 

Figure 15 Chanical structure of a pyrogallol[4]arene host and the betaine guest.

On this basis, calix[4]arene 1, thiacalix[4]arene 2, cahx[4]resorcinarene 3, and calix[4]pirogallolarene 4 (Scheme 4.1), which are cyclocondensation products of p-alkylphenols with formaldehyde or sulfur in alkaline medium and of acid-catalyzed reaction of resorcinol or pyrogallol with aldehydes, are used as basic blocks for the construction of host molecules. 

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