A Macrobicyclic Calix[6]arene Phosphocine: Conformational Studies Involving High-Resolution NMR Analysis and Molecular Modeling

Autor: Stéphane Pellet-Rostaing, Bernard Fenet, Alain Cartier, Jean-Bernard Regnouf-de-Vains
Rok vydání: 2005
Předmět:
Zdroj: Helvetica Chimica Acta. 88:1110-1125
ISSN: 1522-2675
0018-019X
Popis: The solution structure of the phosphorylated hexa(tert-butyl)calix[6]arene 1a was elucidated through a series of high-resolution, one- and two-dimensional 1H- and 13C-NMR experiments, in combination with 31P-NMR measurements. The NMR results were cross-checked and refined with partial structural information obtained from a poorly resolved X-ray crystal-structure analysis. The latter, that could not be upgraded due to the low quality of the crystals and due to strong thermal motions, confirmed that 1a was a racemate in which two adjacent phenol units are bridged by a mono-ethyl phosphate moiety, generating a macrocyclic dibenzo[1,3,2]dioxaphosphocine substructure, while the four residual aromatic rings bear regular diethyl phosphate arms. One of these rings is inverted, generating the main asymmetry in the molecule, which gives rise to the racemic nature of the macrobicycle. The two enantiomers, however, do not interconvert on the NMR time scale in solution and resemble the solid-state structure, as expected from the steric hindrance due to the pendant phosphoesters and the high intramolecular tension due to the presence of the phosphocine substructure. The most-probable conformation of 1a in solution was determined, starting from the NMR and X-ray data, by means of semi-empirical PM3 calculations with the GEOMOS program, including an unprecedented large number of 232 atoms.
Databáze: OpenAIRE
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