Resorcarene

M. Vazquez, J. Bobacka, M. Luostarinen, K. Rissanen, A. Lewenstam, and A. Ivaska, Potentiometric sensors based on poly(3,4-ethylenedioxythiophene) (PEDOT) doped with sulfonated calix[4]arene and calix[4]resorcarenes. J. Solid State Electrochem. 9, 312-319 (2005). 

In view of the greater reactivity of resorcinol, its cyclic tetramers are synthesized by the acid catalized condensation with less reactive aldehydes (Fig. 7.2.4) [lc]. However, in contrast with calixarenes 221, only hexamer resorcarene has been reported [8]. In view of different relative configurations at the CHR bridges, 225 can exist in form of four diastereomers [lc]. 

Figure 6.3 Upper- and lower-rim intramolecular hydrogen-bonding interactions in calix[4] arenes and [4] resorcarenes, which stabilise the cone conformations.

Table 6.1 Binding constants for sulfonated resorcarenes with various alcohol guests.

Cavitand 6.29 has a vase-shaped cavity that is large enough to accommodate Me2NCHO in the solid state. In solution, the most effective host is the dimethylsilyl derivative (6.28e), which has a tall, narrow cavity suitable for inclusion of linear guests such as those listed above. Compound 6.28e is prepared readily from the octol [4] resorcarene 6.3 by treatment with SiMe2Cl2. The X-ray crystal structure of the CS2 complex of 6.28e is shown in Figure 6.7, indicating clearly the neat fit of the linear... 

Since the preparation of 6.97, an enormous range of carcerand and hemicarcerand species have been prepared based upon both [n]resorcarenes and calix[n]arenes (n = 4,5), all of which exhibit interesting binding behaviour and intra-cavity reactivity, as we will see in the next sections. 

Scheme 6.20 Reaction of a resorcarene triol with dihaloalkanes to give a hemicarcerand with a portal for guest exchange.

Figure 6.51 Synthesis of a trimeric carcerand from a resorcarene trimer precursor.76...

Figure 6.52 Molecular models viewed along the C4 (a and c) and C I (b and d) axes of the 1700 A3 resorcarene hexamer formed in an 18-component, one-pot synthesis. (Copyright Wiley VCH Verlag GmbH Co. KGaA. Reproduced by permission).

Explain why careerism is not observed for small carcerands based purely on [4] resorcarenes, such as 6.98. 

Work by Paul Beer et al. in Oxford on dithiocarbamate-functionalised resorcarenes has resulted in resorcarene trimers termed molecular loops and molecular tetrahedra composed of four resorcarene units. The molecular loops (pyridine-capped Cd(II) and Zn(II) complexes) can bind C60 which fits neatly into the 16.4 A wide central cavity.35 The slightly larger tetrahedral tetramer which has a 19.4 A edge length, compared to 19.1 A for the loop, is bridged by square planar copper(III) ions, a very unusual oxidation state of copper that is obtained from iodine oxidation of an intermediate copper(II) complex. The solid-state structures of examples of the loop and tetrahedron are shown in Figure 10.35. 

Resorcarene hexamers bridged either by 24 Cu(II) ions or 12 Ga(III) ions have also been prepared.36 37 These compounds are closely analogous to hydrogen-bonded resorcarene and pyrogallolarene hexamers (indeed the metal-bridged compounds can be prepared by substitution of 2H+ for Cu2+) and we will look at these systems as a whole in Section 10.6.3. 

While the role of the propan-2-ol in the capsule shown in Figure 10.44 is serendipitous, a number of designer heterocapsules of this type with linkers such as 4,4 bipyridine and 2-aminopyrimidine have been prepared, Figure 10.45.49,50 These kinds of materials, and indeed [4] resorcarenes in general have found significant application as molecular containers, particularly in isolating and protecting... 

Figure 10.44 X-ray crystal structure of the capsular, propan-2-ol linked Ms([4] resorcarene) portion of the co-crystal of 6.3 (R = CH2CH2Ph) with C60.48...

Figure 10.45 Multi-component, hydrogen-bonded capsules (a) C-methyl[4]resorcarene 4,4 -bipyri-dine capsule with two included p-nitrobenzene guests,49 (b) rigidified [4]resorcarene tetracarboxylic acid held together by 2-aminopyrimidine with two included p-nitrobenzene guests.50...

Atwood et al. have gone on to prepare a truly enormous molecular capsule along these principles, which conforms to the geometry of a snub cube (structure (1) in Figure 10.47). Reaction of six equivalents of the octol [4] resorcarene (with either methyl or undecyl feet ) with eight water molecules results in... 

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