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Rigid Calix[4]arene as a Building Block for the Synthesis of New Quaternary Ammonium Cation Receptors
Author(s) -
Arduini Arturo,
Pochini Andrea,
Secchi Andrea
Publication year - 2000
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/1099-0690(200006)2000:12<2325::aid-ejoc2325>3.0.co;2-e
Subject(s) - calixarene , chemistry , selectivity , stereochemistry , solvent , methylene bridge , cyclophane , proton nmr , nuclear magnetic resonance spectroscopy , crystallography , molecule , organic chemistry , crystal structure , catalysis
The synthesis of a new series of neutral hosts derived from the head ‐ to ‐ head linkage of two calix[4]arene‐bis(crown‐3) units fixed in the rigid cone conformation with bridges of different nature and length is described. The binding abilities of the new receptors towards tetraalkylammonium and N ‐methylpyridinium cations of different size and shape in CDCl 3 solution have been extensively investigated by 1 H NMR spectroscopy. In this solvent, ion‐pairing is found to have a strong effect on the binding efficiency. In the more polar CDCl 3 /CD 3 CN solvent mixture, a substantial decrease in the K ass values is observed, which can be attributed, in part, to CD 3 CN competing for the binding sites of the host. In all cases, the double calixarenes 2 , 7 , 8 , and 9 have been found to exhibit efficiencies much higher than that of the corresponding rigid calix[4]arene‐bis(crown‐3) 1 . The bridge present in these double calix[4]arenes dictates the orientation and distance between the two rigid caps and thus represents a new control element in determining the efficiency and selectivity of binding. The orientation and span imposed by the different bridges to the two calixarene subunits is responsible for the different binding modes observed with N ‐methylpyridinium and isomeric N ‐methylpicolinium cations.