Crystalline inclusion complexes

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). 

Solid-state stability of PAS as a function of molar ratio of a-cyclodexrin (CD) to PAS was complex. At low ratios of CD to PAS, stability decreased because of inhibition of crystallization of PAS during freezing. Higher molar ratios stabilized the PAS because of formation of a crystalline inclusion complex. Again, rapid freezing resulted in higher rates of decarboxylation in the solid state. 

Ibragimov, B. T., Makhkamov, K. K., Beketov, K. M., Polymorphism of crystalline inclusion complexes and unsolvated hosts. Part 8. Endocyclic modification of the cyclotriveratrylene host-guest complex with acetone. J. Incl. Phenom. Macro-... 

For example (+)-43a was obtained after two purifications at 55 % ee and 10 % yield. Treatment of (+)-43a with hydrazine and KOH gave (+)-45a at 55 % ee and 40 % yield. The chiral host (S)-(—)-40 has been found to be extremely effective as a chiral selector towards comparatively bulky molecules of the phthalimide formed from of l- < r -butyl-3-chloro-azetidin-2-one, 47. A crystalline inclusion complex of 1 1 stoichiometry was formed between one mole of (S)-(—)-40 and two moles of rac-47 dissolved in benzene/hexane 1 1 solution. After one recrystallization, the complex was chromatographed on silica gel, and the crystalline product was treated with hydrazine. Optically pure (—)-3-amino-l-ieri-butyl-azetidin-2-one (—)-47, was obtained at 100% ee and 44% yield [51]. Primary diamines, like 1,3-dibromobutane (49), can undergo a similar reaction with potassium phthalimide, yielding diphthalimide, 50. The complexation process between rac-diphthalimide 50 and host (S,S)-(—)-6 gave a 1 1 complex containing (—)-50... 

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... 

The driving forces of complex formation were thought to be the geometric compatibility or fit and intermolecular interaction between hosts and guests. It has been reported that many linear polymeric guests could form inclusion complexes with CDs resulting in main-chain pseudopolyrotaxanes. When the polymers were added into the CD solutions and then sonicated, crystalline inclusion complexes precipitated. As the result of X- ray diffraction study, all crystalline inclusion complexes between CDs and polymeric guests are columnar in structure [27,43],... 

As Tonelli et al. [44,45] have pointed out, the study of crystalline inclusion complexes provides an approach to investigate the behaviors of single polymer chains in isolated and well - defined environments. Then, it is helpful in understanding the mechanism of molecular recognition between hosts and polymeric guests. 

Crystalline inclusion complexes (IC s) have been also formed between polymers and another small-molecules, host clathrated provide a unique environment for observing the solid - state behavior of isolated polymer chains. In their IC s with small-molecule, host clathrates, such as urea (U) [1] and perhydrotriphenylene (PHTP) [57], the included polymer chains are confined to occupy narrow channels (ca. 5.4 A in diameter) where they are extended and separated from neighboring chains by the channel walls, which are composed exclusively of the host clathrate, crystalline matrix. Choi et al. [58] have been studied the behavior of isolated, extended polymer chains included in their IC s with U and PHTP by a combination of molecular modeling [59,60] and experimental observations in an effort to determine their conformations and mobilities in these well-defined, containing environments. 

The next example deals with the enantioselective photocyclization of a-tropolone alkyl ethers [182]. Cyclization occurs through an allowed 4e -disrotation that can result in opposite optical isomers depending on the direction of rotation (Sch. 37). Racemic products are obtained in solution, but irradiation of crystalline inclusion complexes of a-tropolone alkyl... 

It is well known that deoxycholic acid 1 forms inclusion complexes with a number of guest molecules. The crystalline inclusion complexes 87a-c l were obtained from solutions of deoxycholic acid 1 with acetophenone 87a, ra-chloro-acetophenone 87b, or / -fluoroacetophenone 87c in methanol. The host guest molar ratios are 5 2, 3 1, and 8 3, respectively. The guest molecules are... 

In summary, microscopic and thermal observations of PET samples coalesced from their crystalline y-CD-IC suggest crystalline characters and melt-crystallized morphologies that are different from normal samples. After coalescence of their segregated, extended chains from the narrow channels of the crystalline inclusion complex formed with host y-CD, PET chains are much more readily crystalliz-able, and, locally, quickly form small, possibly chain-extended crystals. In addition, the noncrystalline regions of coalesced PET exhibit conformational and motional... 

Insight into the photochemical reactions between deoxycholic or apocholic acid ( choleic acids ) and guest molecules in crystalline inclusion complexes has been obtained by X-rzy studies. The choleic acids form channels with wall structures determined by the nature of the guest molecule. Guest ketones of various types react photochemically by addition to the choleic acid at a site determined by the orientation of the ketone molecule in relation to the host (e.g. deoxycholic acid reacts at C-5 or C-6 with linear aliphatic ketones, but at C-16 with cyclohexanone).12... 

Preparation B. Ault and Kopet2 describe as an introductory organic experiment a procedure for the preparation of adamantane by isomerization of endo-tetrahydrodicyclopentadiene by the method of Schleyer but the product is isolated from a hexane extract of the reaction mixture as the beautifully crystalline inclusion complex with thiourea.3 As noted in 1, 1164, the ratio in this complex is 3.4 molecules of host per molecule of guest hydrocarbon. Although the reaction time is only 1 hour, the yield (15%) is about the same as that reported for a reaction time of 8-12 hours. 

First examples of second-sphere coordination adduct between a CD and such organometallic complexes were observed with the ferrocene and its derivatives. Thus, Breslow was the first to report in 1975 that ferrocene forms a 1 1 adduct with the /3-CD in both A/T-dimethylformamide and dimethyl sulfoxide. Nevertheless, the first crystalline inclusion complexes of ferrocene and its derivatives were prepared by Harada and Takahashi in 1984. The inclusion complexes were obtained by direct addition of crystals of ferrocene or its derivatives into aqueous solutions of CD. The stoichiometry of the inclusion complexes was found to be dependent on the sizes of the CD. The /3-CD and y-CD formed 1 1 stoichiometric inclusion complexes whereas a-CD formed a 2 1 (CD guest) complex with ferrocene. From induced circular dichroism experiments, three structures were proposed for these adducts as shown in Figure... 

A crystalline inclusion complex of 10-(4-f-butylphenyl)-3-(2-ethyl-phenyl)-pyrimido[4,5-fc]quinoline-2,4(3H,10H)-dione/urea/EtOH obtained. X-ray analysis showed that the urea is doubly H-bonded to the pyrimidinone (96TL8905). The proximity of the chiral axis might give interesting applications in chiral recognition. The enantiomers were involved in an enantioselective hydride transfer reaction (Figure 25). 

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