7Li, 31P, and 1H Pulsed Gradient Spin-Echo (PGSE) Diffusion NMR Spectroscopy and Ion Pairing: On the Temperature Dependence of the Ion Pairing in Li(CPh3), Fluorenyllithium, and Li[N(SiMe3)2] amongst Other Salts
✍ Scribed by Ignacio Fernández; Eloísa Martínez-Viviente; Frank Breher; Paul S. Pregosin
- Publisher
- John Wiley and Sons
- Year
- 2005
- Tongue
- English
- Weight
- 209 KB
- Volume
- 11
- Category
- Article
- ISSN
- 0947-6539
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✦ Synopsis
Abstract
^7^Li, ^31^P, and ^1^H variable‐temperature pulsed gradient spin‐echo (PGSE) diffusion methods have been used to study ion pairing and aggregation states for a range of lithium salts such as lithium halides, lithium carbanions, and a lithium amide in THF solutions. For trityllithium (2) and fluorenyllithium (9), it is shown that ion pairing is favored at 299 K but the ions are well separated at 155 K. For 2‐lithio‐1,3‐dithiane (13) and lithium hexamethyldisilazane (LiHMDS 16), low‐temperature data show that the ions remain together. For the dithio anion 13, a mononuclear species has been established, whereas for the lithium amide 16, the PGSE results allow two different aggregation states to be readily recognized. For the lithium halides LiX (X = Br, Cl, I) in THF, the ^7^Li PGSE data show that all three salts can be described as well‐separated ions at ambient temperature. The solid state structure of trityllithium (2) is described and reveals a solvent‐separated ion pair formed by a [Li(thf)~4~]^+^ ion and a bare triphenylmethide anion.