Resorcin arene hexamers

Catalysis Within the Self-Assembled Resorcin[4]arene Hexamer... 

Fig. 31.3 (a) Diffusion coefficient of 6e in the absence and presence of THABr as a function of addition of DMSO to the CDCI3 solution [19a], (b) Diffusion coefficients of 6e and H2O in CDCI3 solution at different 6e H20 ratios [19b], (c) Schematic representation of the resorcin[4]arene hexamers in water-saturated CDCI3 solution... 

Self-Sorting and Guest Affinity in Resorcin[4]arene and Pyrogallol[4]arene Hexamers... 

These FRET half-Uves were found to increase more dramatically with the increase in the concentration for pyrogaUol[4]arene hexamers than for the resor-cin[4]arene hexamers. In addition, the FRET experiments also corroborated what was previously known from diffusirMi NMR Pyrogallol[4]arene hexamers are more stable than resorcin[4]arene hexamers and form both in dry and in water-samrated organic solvents, whereas resorcin[4]arene hexamers rally form in water-samrated organic solvents [19, 20, 41]. These results showed that similar conclusions are reached from diffusion NMR [19, 20] and FRET experiments [41]. It should be noted that in the gas phase hetero-hexamers of resorcin[4]arenes and pyrogallol[4] arenes were found [30], a fact that is not easy to reconcile with solution data. In the gas phase, a charged ruthenium complex was added to the solution to allow detection of the hexameric capsule by the MS detector. This ruthenium complex could not be encapsulated in any of these hexamers in solution. In other dimeric cpasules, however, hetero-capsules are observed in solution. For example, heterodimers are observed in which resorcin [4]arene is, in fact, one panel of the heterodimer [42]. 

The first example in which resorcin[4]arene hexamers were used to obtain modest chemo- and region-selectivity of a reaction was reported for the hexamer of 6e encapsulating a gold catalyst (i.e., [chloro[l,3-bis(2,6-diisopropylphenyl) imidazole-2-ylidene]gold(I)], 18) [53a]. In this study, H-NMR clearly indicated that 18 is encapsulated in the hexamers of 6e [53a]. The reaction in hexamers of 6e, shown in Scheme 31.1a, is slower than in the bulk, and the product distribution is different in the presence of 18( 6e6 than in its absence. Interestingly, it was also found that 19 has no affinity for 6eg in the absence of 18. 

Figure 1 (a) General formula for resorcin[4]arenes, 2 (b) hexamer of C-methylresorcin... 

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). 

In the following sections, examples are presented where the synergic effect between transition metal catalysts and the hexamer of resorcin[4]arene imparts unique product and substrate selectivities. In all cases, coencapsulation of the substrate and the catalyst is crucial. 

FIGURE 7.6 The encapsulation of the NHC-Au(I) catalyst within the hexamer of resorcin[4] arene drastically changes the product distrihution in the terminal alkyne hydration of 4-phenyl-l-butyne. (Adapted from Ref. [30].)... 

One of the main motivations for studying the hexameric capsules of resorcin[4] arenes using diffusion NMR was to evaluate the role, in solution, of the water molecules in the self-assembly of such hexameric capsules. Because of the large difference between water molecules in the bulk (Mw =18 Da) and in the hexamer (Mw = 6624 Da) water in these two environments should have very different diffusion coefficients. 

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