Molecular recognition. Anion cryptates of a macrobicyclic receptor molecule for linear triatomic species

Abstract

Ward, J. Am. Chem. Soc., 94, 552 (1972). (11) The carboxyl inversion product (4b) is formed in 18% yield but does not exhibit CIDNP in either the 1 *H or ,3C NMR. This supports a nonradical mechanism for formation of this product. Furthermore, 4b is stable under the reaction conditions and is thus not a precursor of 3b or 5-7. The relative yields of 3b and 5-7 are also insensitive to the concentration of 1b (0.045-0.5 M) and to the addition of excess m-chlorobenzoic acid (saturated in ODCB at 0.2 M). This makes it unlikely that either induced decomposition or acid promoted ionization of 1b contribute significantly to the reaction under these conditions. (12) (a)

A Fluorine-Containing Cryptand for the Complexation of Anions and the Utility of 19F NMR Spectroscopy for the Determination of Host-Guest Association

“…The stability constants for the m onovalent ions relative to perchlorate are as follows: log K 2.1 (Cl~), 2.4 (B r_), 1.4 (I-). The values for Cl-and B r-are comparable to those determ ined for related ligands [12].…”

“…Since related macrocycles had been utilized by Lehn et al to coordinate anions within the posi tively charged cavity [12], we were intrigued whether this was also possible with fluorine-con taining 4-6 H C 1 04 and if incorporation of anions tion of anions, the 19F NMR resonances are shifted with respect to those of 4-6H C 104 (Scheme 3). In the series of the halides the complexation-induced shifts of the 19F NMR signal are correlated to the size of the anions since iodide generates the largest effect on the posi tion of the 19F NM R signal, even though it is only weakly bonded.…”

“…The condensation product (1.3 g, 2 m mol) was suspended in 50 ml of ethanol and stirred with NaBH4 (0.5 g, 13 mmol) for 12 h. The solvent was evaporated in vacuo, 10 ml of water added to the residue, and the suspension ex tracted with C H 2C12 three times. The organic layer was separated, dried over M gS 04, evaporated, and the oily residue dried in vacuo for 12 …”

Aspects of Anion Coordination from Historical Perspectives

“…However, while investigations on crown ethers rapidly evolved and many of these compounds were prepared and their chemistry widely explored, studies on anion coordination chemistry remained at the initial stage. Further development waited until Lehn and his group revisited this point in the late 1970s and beginning of the 1980s [56][57][58][59][60][61][62]. Nevertheless, evidence that anions interact with charged species, modifying their properties, in particular their acid-base behavior, was known from the early times of the development of speciation techniques in solution, when it was noted that …”

“…Receptor 18 (C5-BISTREN) prepared by Lehn's group was studied along with 11 by potentiometry in collaboration with Martell and coworkers. Such studies, and the crystal structure of the azide complex [57], gave the first indications of the possibility of the formation of binuclear or higher nuclear anionic complexes with two encapsulated anions or, even better, with the hydrogen bifluoride anion (HF 2 − ) (see below for …”