Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 106, Issue 26, Pages 10455-10459Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.0809612106
Keywords
calixpyrroles; hydrogen bonding; N-oxides
Categories
Funding
- Direccion General de Investigacion, Ministerio de Ciencia y Tecnologia [CTQ2005-08989-C02/BQU, CTQ2008-00222/BQU]
- Consolider Ingenio [CSD2006-0003]
- Institute of Chemical Research of Catalonia Foundation
- Generalitat de Catalunya DURSI [2005SGR00108]
- ICREA Funding Source: Custom
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Calix[4]pyrroles having extended aromatic cavities have been functionalized with 4 ureas in the para position of their meso phenyl substituents. This elaboration of the upper rim was completed in 2 synthetic steps starting from the alpha, alpha, alpha, alpha-tetranitro isomer of the calix[ 4] pyrrole obtained in the acid catalyzed condensation of p-nitrophenyl methyl ketone and pyrrole. In dichloromethane solution and in the presence of 4,4'-bipyridine N-N'-dioxide the tetraurea calix[4]pyrrole dimerizes reversibly forming a cyclic array of 16 hydrogen bonds and encapsulating 1 molecule of bis-N-oxide. The encapsulated guest is bound in the cavity by hydrogen bonding to the 2 endohedral calix[4]pyrrole centers. Further evidence for dimerization of the tetraurea calix[4]pyrroles is provided by (1)H-NMR experiments and by the formation of mixed capsules.
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