Guest complexes

Fig. 1. Schematic representation of a receptor—substrate (host—guest) complex involving cavity inclusion of the substrate and the formation of different types of weak supramolecular interactions between receptor (hatched) and substrate (dotted).

From the kinetic point of view the facts are different and the order is reverse, ie, the rigid highly preorganized spherands are slow, as contrasted with the flexible barely preorganized podands that are fast both in formation and decomposition of the receptor—substrate (host—guest) complex (20,21). 

F. Viigde and E. Weber, eds., Host-Guest Complex Chemisty—Macroycles, Springer, Bedin-Heidelberg, 1985. 

These molecules are significant in the field of research devoted to host—guest complexation. Synthetic routes to a number of calixarenes have been developed (11). 

Optically active thiiranes have been obtained by resolution of racemic mixtures by chiral tri-o-thymotide. The dextrorotatory thymotide prefers the (5,5)-enantiomer of 2,3-dimethylthiirane which forms a 2 1 host guest complex. A 30% enantiomeric excess of (5,5)-(—)-2,3-dimethylthiirane is obtained (80JA1157). 

Carceplexes and hemicarceplexes, host-guest complexes in which carcerands and hemicarcerands, in particular those including heterocyclic fragments, are hosts 99CRV931. 

Fig. 3-4. (A) Changes in chemical shift of protons of cyclophane -CH - groups between bipyridinium and phenyl in H NMR spectra of 3 as a function of (R)-DOPA concentration (a) 0, (b) 0.111, and (c) 0.272 mol (B) Change in chemical shift plotted against the analytical concentration of (R)- and (5)-DOPA. The solid line is calculated for 1 1 host - guest complexation. (Reprinted with permission from ref. [79]. Copyright 1998, American Chemical Society.)...

Vogtle, F, (ed.) Host Guest Complex Chemistry I, Top. Curr. Chem. 98 (1981), Berlin Heidelberg New York, Springer-Verlag 1982... 

In this chapter we discuss host-guest complexes of arenediazonium salts with crown ethers and related compounds. Transition metal complexes of arenediazonium ions are treated together with those of dinitrogen and of diazoalkanes in our second book (Zollinger, 1995, Sec. 10.1). 

P-Cyclodextrin is assumed to form host-guest complexes with diazonium ions (Fukunishi et al., 1982, 1985), but if so, complexation increases the extent of thermal dediazoniation, i. e., it has the contrary effect to that usually seen. 

In addition to the influence of the complexation equilibrium constant K, the observed reaction rate of arenediazonium salts in the presence of guest complexing reagents is influenced by the intrinsic reaction rate of the complexed arenediazonium ion. This system of reactions can be rationalized as in Scheme 11-1. Here we are specifically interested in the numerical value of the intrinsic rate constant k3 of the complexed diazonium ion relative to the rate constant k2 of the free diazonium ion. 

Checking the literature of the second half of the 1980s for applications of crown complexes of arenediazonium salts for synthetic purposes, one gets the impression that these complexes are not widely used. The two comprehensive reviews by Izatt et al. (1985, 1991) show a definite decline of interest in host —guest complexation of arenediazonium ions in the second half of the 1980s. The subject of arenediazonium... 

HMPT, see Hexamethylphosphoric triamide Host-guest complexation, general 289ff., 293ff., 321, see also Crown ether complexes... 

Another related host-guest complex has been constructed from citric acid, boric acid, and a strontium salt in a 2 1 1 stoichiometry. In this complex the strontium cation is surrounded by four water molecules, two monodentate carboxyl groups and one oxygen atom of the BO4 unit [161]. 

Fig. 30. Compound 118 is a cage-like host-guest complex with the simultaneous inclusion of two metal cations...

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