Conformational studies of host-guest interactions in calixarenes using dynamic NMR spectroscopy, X-ray crystallography and pseudo-cavity volume analysis.

Abstract

The compound 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrakis( N,N-diethylaminocarbonyl)methoxycalix[4]arene, 1, forms a 1:1 complex with both the sodium and potassium cations in a binary mixture of chloroform-d and acetonitrile-d3. Kinetic and mechanistic solution studies are analyzed using 1H, 23Na and 39K NMR in order to compare the binding modes of the guests Na+ and K+. Both the sodium and potassium complexes exhibit a quantitative complexation (Kf > 10 4 M-1) in the temperature range of 238 to 320 K. The exchange between the complexed and solvated sodium cations is very slow on the 23Na NMR time scale at 320 K. Similarly, results for the exchange between the complexed and solvated potassium cations at 320 K were found to be slow to moderately slow on the 39K NMR time scale. Dynamics of the ethyl moiety are probed using 1H NMR and EXSY techniques. Analysis of 2-D EXSY 1H NMR data for the interconversion of the methylene protons from the N(CH2CH3)2 moiety of the (Na,1)+ and (K;1) + complexes exhibit slow exchange at 320 K. (Abstract shortened by UMI.)