1,1,6,6-tetraphenylhexa-2,4-diyne-1,6-diol

The wheel-and-axle design as source for host-guest compounds was originally proposed by Toda and Hart in 1981 for hosts containing hydroxyl functions 481 (see Ch. 3, Sect. 2.1 of Vol. 140). The l,l,6,6-tetraphenylhexa-2,4-diyne-l,6-diol (24) provides a representative compound. It forms 1 2 crystalline inclusion complexes with a large number of small guest molecules, including a variety of ketones, amines, amides and a sulfoxide 48). 

One of the first examples is the use of achiral l,l,6,6-tetraphenylhexa-2,4-diyne-l,6-diol (1) for resolution of a mixture of o-, m- and p-methylbenzalde-hydes (56-58). It showed that an inclusion complex at a 1 1 ratio was formed selectively with the p-isomer 58. The complexant was effectively separated from the complex by heating in vacuo, and p-m e(hy I benzaIdeIn de was obtained at 100% purity and 96% yield [59],... 

However, an equimolar sample starting at the centre of the triangle would move approximately as indicated in Figure 3. Results of this kind were obtained in the selectivity experiments carried out with the host l,l-bis(4-hydroxyphenyl)cyclo-hexane with the isomers of benzenediol [9], picoline [10] and lutidine [11], When the selectivity for a pair of guests is concentration dependent, this will be reflected in the three component experiment. In Figure 4 we show the case in which the selectivity of the host A > B with Ka.b = 5, B C with KB.c 1, and A C is concentration dependent. In this case, samples of the three-component mixture will give a split result which is dependent on their initial concentrations. This outcome occurred in the selectivity by the host 1,1,6,6-tetraphenylhexa-2,4-diyne-l,6-diol of mixtures of lutidines [12], and the host dinaphthol with... 

Figure 6 Host = 1,1,6,6-tetraphenylhexa-2,4-diyne-l,6-diol. Guest = 4-,3- and 2-ami-nobenzonitrile. Correlation between lattice energies (ron — Tm) and AH of guest release.

In 1986, we have found that l,l,6,6-tetraphenylhexa-2,4-diyne-l,6-diol (1) includes various guest molecules in a stoichiometrical ratio and forms crystalline inclusion complexes.1 X-ray analysis of a 1 2 inclusion complex of 1 and acetone showed that the guest molecules are accommodated in inclusion crystalline cavity by the formation of hydrogen bond with the hydroxyl groups of l.2 It was also found that inclusion complexation with 1 occurs selectively, and a mixture of isomers can be separated by the selective inclusion process.3 This suggests that racemic guest compound can be separated into enantiomers by inclusion... 

When a mixture of finely powdered l,l,6,6-tetraphenylhexa-2,4-diyne-l,6-diol 1 and an equimolar amount of finely powdered benzophenone 2 was agitated using a test-tube shaker for 0.2 h at room temp., a 1 1 complex 3 involving these two compounds was formed. 

Here, the chiral clathrate former l,6-bis(u-chlorophenyl)-l,6-diphenylhexa-2,4-diyn-l,6-diol (138), derived froml,l,6,6-tetraphenylhexa-2,4-diyn-l,6-diol and developed by Toda shall be presented. Using this host compound, numerous guest substances, e.g. cychc ketones and lactones which constitute important synthetic building blocks, have been successfully separated into enantiomers 55-57)... 

In 1968, we found that l,l,6,6-tetraphenylhexa-2,4-diyne-l,6-diol la) and 1,1,4,4-tetraphenylbut-2-yne-l,4-diol lb) form crystal inclusions with a wide variety of guest compounds, as shown in Table 1 In most cases, la and lb include guest species in 1 2 and 1 1 ratios, respectively. The vOH absorption band of all inclusion compounds appears at lower frequencies than those of uncomplexed la and Ib -. This suggests the presence of strong hydrogen bonding between host and guest (inclusion complexes ). 

Figure 5(c) is the result obtained when the selectivity is concentration dependent and the host favors the guest in greater concentration. This is exemplified by the selectivity profile exhibited by the host l,l,6,6-tetraphenylhexa-2,4-diyne-l,6-diol with the isomeric guests 3-aminobenzonitrile and 4-aminobenzonitrile. It is noteworthy that, in this case, the same result is obtained when the competition is carried out in solution or fi-om direct solid-solid reactions. 

Figure 1 Molecular structures of some organic molecules that form the host structures in solid inclusion compounds (these specific host structures are encountered freqnently in this chapter) urea, thiourea, tri-orfto-thymotide (TOT), perhydrotriphenylene (PHTP), deoxycholic acid (DCA) and varions molecules related to deoxycholic acid, host A (l,l,6,6-tetraphenylhexa-2,4-diyne-l,6-diol), host B (frans-2,3-bis(hydroxydiphenylmethyl)-l,4-dioxaspiro[5.4]decane), and host C (irans-2,3-bis(hydroxydiphenylmethyl)-l,4-dioxaspiro[5.4]nonane).

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