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
posted on 1998-01-16, 00:00authored bySteven E. J. Bell, Julie K. Browne, Vickie McKee, M. Anthony McKervey, John F. Malone, Maeve O'Lear, Andrew Walker, Francoise Arnaud-Neu, Olivier Boulangeot, Olivier Mauprivez, Marie-Jose Schwing-Weill
A series of four calix[5]arenes and three
calix[6]arenes
(R-calixarene-OCH2COR1) (R = H or
But)
with alkyl ketone residues (R1 = Me or But)
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
1H NMR and X-ray diffraction analysis, and by molecular
mechanics calculations. Pentamer 3 (R
= R1 = But) possesses a symmetrical cone
conformation in solution and a very distorted cone
conformation in the solid state. Pentamer 5 (R = H,
R1 = But) 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.