Protonation of Tetrapropoxy-4-tert-butylcalix[4]arene: NMR Study of Interaction and Probable Structures of the Product

Jaroslav Kriz (1) , Jiri Dybal (2) , Emanuel Makrlik (3) , Jan Budka (4) , Petr Vanura (4)

1 Structure Analysis
2 Structure Analysis
3 University of West Bohemia [Plzeň ]
4 ICT - Institute of Chemical Technology [Prague]

Using 1H and 13C NMR spectroscopy, the interaction of tetrapropoxy-p-tert-butyl-calix[4]arene (1) with H3O+ ions produced by hydrogen bis(1,2-dicarbollyl) cobaltate (HDCC) and traces of water was studied in nitrobenzene-d5. It was shown that 1 readily forms an equimolecular complex with H3O+. The equilibrium constant K of its formation is 2.6 at 296 K. Exchange between bound and free 1 is fast even under mild excess of HDCC, the correlation time Τex being about 0.13 ms. NMR shows that H3O+ is bound to the aryl-oxygen atoms and this binding forces the calixarene cup to adopt a more open and symmetrical conformation. This conclusion is in a full accord with high precision quantum DFT calculations which find one structure of the complex corresponding to a global energy minimum, in which the H3O+ ion is bound to three of the oxygen atoms by strong hydrogen bonds and to the remaining oxygen by two weaker hydrogen bonds. The calixarene part is forced into a C4 symmetrical opened form. When stored for weeks, the complex gradually transforms into other forms, most probably its hydrates, according to spectral evidence and DFT calculations.

Mots clés: Physical Sciences

Jaroslav Kriz, Jiri Dybal, Emanuel Makrlik, Jan Budka, Petr Vanura. Protonation of Tetrapropoxy-4-tert-butylcalix[4]arene: NMR Study of Interaction and Probable Structures of the Product. Supramolecular Chemistry, 2008, 20 (05), pp.487-494. ⟨10.1080/10610270701422065⟩. ⟨hal-00513513⟩