Anion inclusion

The (3-keto sulfoxides can be alkylated via their anions. Inclusion of an alkylation step prior to the reduction provides a route to ketones with longer chains. 

All these studies serve to illustrate the dominant importance of hydrogen bonding in stabilizing particular anion inclusion complexes of the type just discussed. The relative importance of any direct electrostatic attraction between the positive cavity and the anionic guest is more difficult to define. Nevertheless, interactions of the latter type are of crucial importance in other systems. 

It can be seen that the anion inclusion selectivity in the cavity of the OD cationic cage is mainly dependent on the size and shape of the anion fitted with the size and shape of the cavity of the cage. 

Typically, the cumulative electron-withdrawing effect of metallating more than half of the arenes of the macrocycle is required in order to observe anion inclusion. Thus, we have focused on tetrametallated derivatives of calix[4]arene and di- or trimetalated derivatives of the related orr/io-cyclophane, cyclotriveratrylene (CTV). The X-ray crystal structure of the BF salt of the water soluble bear trap 51 demonstrates the suitability of the narrow calix[4]arene cavity for small tetra-... 

Graf, E., Lehn, J.-M., Anion cryptates-highly stable and selective macrotricyclic anion inclusion complexes. J. Am. Chem. Soc. 1976, 98, 6403-6405. 

Schmidtchen, F. P., Muller, G., Anion inclusion without auxiliary hydrogen bonds X-ray structure of the iodide cryptate of a macrotricyclic tetra-quaternary ammonium receptor. J. Chem. Soc., Chem. Commun. 1984, 1115-1116. 

Xu, W., Vital, J. J., Puddephatt, R. J., Selective anion inclusion in calix[4]arene complexes driven by face-bridging mu-4 halide binding. J. Am. Chem. Soc. 1993, 115, 6456-6457. 

Another class of metal-employing anion receptors is represented by structure 24 [23]. Its function is based on the incorporation of positively charged transition metal complexes directly into the calixarene skeleton. Such calixarenes with enhanced electron deficiency of the aromatic walls provide well-preor-ganised cavities suitable for anion inclusion. The corresponding rhenium [24], ruthenium, rhodium or iridium complexes of this type were prepared and studied for anion recognition [25,26]. 

It is worth noting that this anion inclusion by the [Ag3(l)2]3 + cylindrical cage is also an anion recognition process. As illustrated in Figure 11.4, the same [Ag3(l)2]3 +... 

The data for mixed metal zeolites as first prepared by Scherzer and Fort (18) shown in Tables I and XI are quite extensive. The reported isomer shifts and quadrupole splittings are for the iron atoms in the anionic state. Each of these unreduced samples show Mossbauer spectra that are in close agreement with literature values of the corresponding iron coordination complexes. Typical examples of unreduced and reduced samples are shown in Figures 3 and 4. We note here that preparations 16 through 22 are new and are developments of our laboratory and that 9 through 15 are preparations based on the work of Scherzer and Fort (18). Samples 16 and 17 show that this method can be extended to other zeolites like ZSM-5. If no transition metal cation is used in the synthesis, no Mossbauer spectrum for the corresponding anion is observed. Therefore, the nature of the cation is critical and complexation of the anion to a cation is necessary for anion inclusion. Certain transition metal cations (Ru + for instance) do not seem to bind the anion. 

Fig. 21 Katapinand a triple-stranded diammonium alkane, which, in a 50% trifluoroacetic acid aqueous solution, swallows a chloride ion. Anion inclusion is preceded by a structural reorganisation of the diammonium receptor from the out,out isomer (o+o+, the two N-H fragments pointing outside of the cavity) to the in,in isomer (i+i+, N-H fragments pointing inside)...

Fig. 36 Anion inclusion in the [Cu2n(20)]2+ cryptate in aqueous solution. The stability of the ternary inclusion complex, expressed by log K for the equilibrium [Cun2(20)]4++ X- [Cun2(20)(X)]3+, at pH = 7 and 25 °C, is related to the bite length of the anion X-, with a sharp peak selectivity. The N3- ion has the right bite length to encompass the Cun-Cun distance, without inducing any serious conformational rearrangement of the dimetallic cryptate [73, 74]...

Anion inclusion selectivity can be modulated by varying the nature of the spacers of the dimetallic cryptate used as a receptor. An example is provided by the dicopper(II) complex of the bistren derivative 21, whose crystal structure is shown in Fig. 37 [75]. The tetranitrate complex salt was crystallised from water and contained two water molecules apically coordinated to the two metal centres. The complex displays selectivity for the inclusion of linear aliphatic dicarboxylates, as shown in Fig. 38. In particular it is observed that the most stable inclusion... 

A study has also been made of the theoretical propensity of organoboron macrocyclic hosts for anion binding (84). This study indicated that for the hypothetical hosts studied, anion inclusion occurred with cavity shrinkage and partial boron rehybridization. This effect would be expected for these anion receptors, which are dependent on orbital overlap interactions for their mode of action. 

Puddephatt and co-workers (153, 154) reported a novel use of a calixresor-cinarene for anion binding. Receptor 61 was synthesized and tetracopper(I) and tetrasilver(I) complexes were isolated. In each case, an electron deficient cavity is formed with an array of four metal ions around its upper rim. These metal ions are capable of coordinating an anion between them. Crystal structures [Fig. l(a and b) of two such anion inclusion complexes were resolved and a discussion of highest occupied molecular orbital/lowest unoccupied molecular orbital (HOMO/LUMO) overlap was provided. The nature of the cavity was shown to... 

Computation in the gas phase did not locate a concerted TS, but indicated instead that the reactions proceed by dissociation-reassociation. The reassociation process has no barrier, whereas the dissociation has a very small one (2.4-2.6 kcal/mol). For the oxy anion, inclusion of a Li+ counterion resulted in a concerted process with a barrier of about 12 kcal/mol. Since this more closely approximates solution conditions, it suggests that a concerted mechanism is feasible in solution. The dissociation mechanism is favored for both nitrogen and carbon. 

Urea/Thiourea/Selenourea-Anion Inclusion Compoimds. 202... 

III. CRYSTAL STRUCTURES OF SOME UREA/THIOUREA/SELENOUREA-ANION INCLUSION COMPOUNDS... 

UREA/THIOUREA/SELENOUREA-ANION INCLUSION COMPOUNDS... 

The results of our studies on urea/thiourea/selenourea-anion inclusion compounds have demonstrated that the classical urea or thiourea hydrogen-bonded host lattice can be modified in interesting ways by the incorporation of various anionic moieties, with or without cocrystallized water or other uncharged molecules, and that novel host frameworks bearing different urea, thiourea, or selenourea/guest molar ratios are generated by variation in size of the hydrophobic, pseudo-spherical R4N guest species. The stoichiometric formulas of 46 inclusion compounds and their structural details are listed in Table 10. For convenient description of stoichiometric ratios, the letters u, a, and c are used to denote the urea/thiourea/se-lenourea molecule, the anion, and the cocrystallized neutral molecule, respectively. 

We now present results illustrating that the N-H- 0 and N-H -S hydrogen bonds play an instrumental role in the structures of a novel class of urea/thiourea inclusion compounds. The average lengths of 84 measured N-H - O hydrogen bonds in 16 urea-anion inclusion complexes and 114 measured N-H—S hydrogen bonds in 23 thiourea-anion host lattices are listed in Table 11. 

Our studies on the generation of novel urea, thiourea, and selenourea-anion inclusion compounds have shown that novel anionic host lattices can be constructed from urea derivatives and many types of anions as building blocks. The versatility of urea, thiourea, or selenourea as a key component in the construction of novel host lattices is clearly demonstrated by the occurrence of many new types of linkage modes, which include various discrete units, chains or ribbons, and composite ribbons with corresponding anions. These motifs are shown in Tables 14, IS, and 16, respectively. 

Table 16. Typical Composite Ribbons in Urea/Thiourea-Anion Inclusion...

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