STUDIES ON THE DYNAMICS OF PHOSPHORYLATED P-TERT-BUTYLCALIX[6]ARENES BY USING 2D NMR-SPECTROSCOPY

Citation
Rg. Janssen et al., STUDIES ON THE DYNAMICS OF PHOSPHORYLATED P-TERT-BUTYLCALIX[6]ARENES BY USING 2D NMR-SPECTROSCOPY, Journal of the American Chemical Society, 118(15), 1996, pp. 3666-3675
Citations number
58
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Chemistry
ISSN journal
0002-7863
Volume
118
Issue
15
Year of publication
1996
Pages
3666 - 3675
Database
ISI
SICI code
0002-7863(1996)118:15<3666:SOTDOP>2.0.ZU;2-8
Abstract
The overall dynamics of partially phosphorylated and thiophosphorylate d p-tert-butylcalix[6]arenes has been studied by NMR spectroscopy. Whe n p-tert-butylcalix[6]arene is monosubstituted with a phosphate or thi ophosphate group, the calix[6]arene skeleton is remarkably rigidified. The 1,3- and 1,4-(thio)phosphorylated p-tert-butylcalix[6]arenes are more flexible. 2D NMR spectroscopy showed that these calix[6]arenes ad opt syn conformations. A combination of H-1 and P-31 NMR spectroscopy revealed that the calix[6]arene (thio)phosphates are involved in at le ast three dynamic processes, viz., macrocyclic ring interconversion, h ydrogen bond array reversal, and pinched conformer interconversion. Th e activation barrier (Delta G(h)(double dagger)) for macrocyclic ring interconversion depends on the type and number of substituents and ran ges from 67 to 86 kJ . mol(-1). The activation barrier (Delta G(h)(dou ble dagger)) for hydrogen bond array reversal depends on the number of hydroxyl groups and ranges from 31 to 45 Id mol-l For the pinched con former interconversion an activation barrier (Delta G(h)(double dagger )) ranging from 44 to 55 kJ . mol(-1) was found. Pinched conformations have been frequently observed in the solid state, for example, for mo no- and 1,4-bis(thiophosphorylated) p-tert-butylcalix[6]arene. These s tudies, however, show for the first time that these conformations also exist in solution and that differently pinched conformers may rapidly interconvert.