A P-31 dynamic NMR study of the bond shift rearragement in solid Li3P7
by Sen, T.; Poupko, R.; Fleischer, U.; Zimmermann, H.; Luz, Z.
Phosphorus-31 NMR measurements are reported on solid Li3P7(monoglyme)(3) in the temperature range -90 to +70 degrees C, under both, nonspinning and magic angle spinning (MAS) conditions. At low temperatures (<-30 degrees C) the spectra correspond to a static situation, exhibiting a superposition of three subspectra due to the epical, equatorial, and basal phosphorus atoms in the P-7-cage. Analysis of these spectra provided information on the principal values of the chemical shift tensors of the various P atoms in their respective principal axis systems. Their orientations in the molecular frame were obtained from quantum mechanical calculations. In the temperature range -30 to +70 degrees C the spectra exhibit dynamic effects, which at high temperatures result in a line shape corresponding to a single average axially symmetric chemical shift tensor. This is interpreted in terms of a bond shift rearrangement similar to the Cope rearrangement process in bullvalene. Analysis of the results yields approximate kinetic parameters for the reaction, At room-temperature the rate constant is about 10(5) s(-1), and the activation energy lies between 7 and 12 kcal/mol. Due to the amorphous nature of the sample used and the incomplete fit of the experimental and simulated spectra, the possibility of a heterogeneous reaction with a distribution of rates and an independent 3-fold jumps process, cannot be ruled out.
- Journal
- Journal of the American Chemical Society
- Volume
- 122
- Issue
- 5
- Year
- 2000
- Start Page
- 889-896
- URL
- https://dx.doi.org/10.1021/ja992452l
- ISBN/ISSN
- 1520-5126; 0002-7863
- DOI
- 10.1021/ja992452l