Azolium-linked cyclophanes: a comprehensive examination of conformations by 1H NMR spectroscopy and structural studies.
The synthesis and characterization of a series of azolium-linked cyclophanes are reported. The cyclophanes consist of two azolium groups (17 examples) or three imidazolium groups (1 example) linked to two benzenoid units (benzene, naphthalene, p-xylene, mesitylene, 1,2,3,4- and 1,2,4,5-tetramethylbenzene, 2,6-pyridine, and p-tert-butylphenol) via methylene groups. Cyclophanes containing ortho-, meta-, and para-substitution patterns in the benzenoid units were examined. The conformations of the cyclophanes were examined in solution by variable-temperature NMR studies and in the solid state by crystallographic studies. The p-cyclophanes and mesitylene-based m- and o/m-cyclophanes are rigid on the NMR time scale, as indicated by sharp (1)H NMR spectra at all accessible temperatures. The non-mesitylene-based m-cyclophanes and the o-cyclophanes are fluxional on the NMR time scale at high temperatures, but in most cases, specific conformations can be "frozen out" at low temperatures. Many structures deduced from solution studies were consistent with those in the solid state.
Baker
Murray V
MV
Chemistry M313, The University of Western Australia, Crawley, WA 6009, Australia. mvb@chem.uwa.edu.au
Bosnich
Mark J
MJ
Brown
David H
DH
Byrne
Lindsay T
LT
Hesler
Valerie J
VJ
Skelton
Brian W
BW
White
Allan H
AH
Williams
Charlotte C
CC