Abstract
The pyrolysis of several dialkylphosphate ester derivatives of calix[4]arenes yielded the same phosphorus bridged compound 7. Under the pyrolytic conditions the phosphate groups may be cleaved or intermolecularly transferred. X-ray crystallography of the bridged calixarenes 7 and 8 shows that they exist in a chiral 'flattened cone' (fc) conformation. The bridged calixarenes undergo in solution a dynamic process with a barrier of about 10.1 kcal mol-1 for 7 and 8 and 13.1 kcal mol-1 for 10, respectively. The dynamic processes result in enantiomerization of the systems. Pyrolysis of partially phosphorylated calix[6]arenes resulted in the formation of two products (11 and 12), each consisting of two subunits of three proximal rings bridged by a phosphate group. The rotational barriers for 11 and 12 are 14.4 and 8.8 kcal mol-1, indicating that the bridged calix[6]arene system 12 is appreciably more flexible than 11.
Original language | English |
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Pages (from-to) | 237-256 |
Number of pages | 20 |
Journal | Journal of Inclusion Phenomena and Molecular Recognition in Chemistry |
Volume | 19 |
Issue number | 1-4 |
DOIs | |
State | Published - Mar 1994 |
Keywords
- Calixarenes
- conformation
- dynamics
- preparation