Cation Complexation by Chemically Modified Calixarenes. 11. Complexation and Extraction of Alkali Cations by Calix[5]- and -[6]arene Ketones. Crystal and Molecular Structures of Calix[5]arene Ketones and Na⁺ and Rb⁺ Complexes

Abstract

A series of four calix[5]arenes and three calix[6]arenes (R-calixarene-OCH(2)COR(1)) (R = H or Bu(t)) with alkyl ketone residues (R(1) = Me or Bu(t)) on the lower rim have been synthesized, and their affinity for complexation of alkali cations has been assessed through phase-transfer experiments and stability constant measurements. The conformations of these ketones have been probed by (1)H NMR and X-ray diffraction analysis, and by molecular mechanics calculations. Pentamer 3 (R = R(1) = Bu(t)) possesses a symmetrical cone conformation in solution and a very distorted cone conformation in the solid state. Pentamer 5 (R = H, R(1) = Bu(t)) exists in a distorted 1,2-alternate conformation in the solid state, but in solution two slowly interconverting conformations, one a cone and the other presumed to be 1,2-alternate, can be detected. X-ray structure analysis of the sodium and rubidium perchlorate complexes of 3 reveal the cations deeply encapsulated by the ethereal and carbonyl oxygen atoms in distorted cone conformations which can be accurately reproduced by molecular mechanics calculations. The phase-transfer and stability constant data reveal that the extent of complexation depends on calixarene size and the nature of the alkyl residues adjacent to the ketonic carbonyls with tert-butyl much more efficacious than methyl.

Synthesis, structures and full characterization of p-tert-butylcalix[5]arene mono-, di-, tri- and pentaanionic ligand precursors

“…Bu t C5 has a cavity size with an ideal balance between constraint and flexibility [18,19], compared to its calix [4,6,8]arene analogues. It is larger and more flexible than calix [4]arene, but it still favors the cone conformation of C 5v symmetry [14].…”

“…These modifications (e.g. addition of ester, amide, carboxylic acid, or ketone groups) [7,[12][13][14] have been of great interest in organic and organometallic [5] chemistry of calixarene derivatives. Deprotonated calixarene derivatives, ''calixanions", have also attracted interest in a number of fields.…”

“…The crystal structures of the Na + and Rb + salts of a functionalized calix [5]arene were obtained by McKervey and coworkers during extraction studies of chemically modified calix [5]arenes [14]. No crystal structures of lithium or cesium salts of Bu t C5 have been reported.…”

Alkali and alkaline-earth metal cation complexation and transport properties by tetraphenyl ketone ofp-tert-butyldihomooxacalix[4]arene

“…A large number of calix[n]arenes (mainly n = 4, 5 and 6) chemically modified at the lower rim with ester, [3][4][5][6][7][8][9][10] amide, 6,[9][10][11][12] ketone, 5,6,13,14 carboxylic acid, 15 crown ether [16][17][18][19][20] and thioamide 21,22 groups as substituents have been synthesized and their cation binding and transport properties studied. The ionophoric activity of these calixarene derivatives has especially been analysed towards alkali and alkaline earth metal cations.…”

Structure of p-Phenylcalix[5]arene Dichloroform Solvate

“…The conformational characteristics and complexation properties of calix [5]arenes have been extensively investigated by diffraction, [1][2][3][4][5] organic synthesis [6][7][8][9][10] and computation methods. [11][12][13] The calix [5]arenes may posses a greater propensity to completely include small organic molecules than analogous calix [4]arenes due to their larger cavity size.…”