Contact vs solvent-separated ion pairs: a 7Li and 13C solid-state NMR study of organolithium compounds
✍ Scribed by Martin Kühnen; Harald Günther; Jean-Paul Amoureux; Christian Fernandéz
- Publisher
- John Wiley and Sons
- Year
- 2001
- Tongue
- English
- Weight
- 237 KB
- Volume
- 40
- Category
- Article
- ISSN
- 0749-1581
- DOI
- 10.1002/mrc.980
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✦ Synopsis
Abstract
^7^Li and ^13^C solid‐state magic angle spinning NMR spectra were measured for three benzyllithium systems, α‐(phenylthio)benzyllithium, α‐phenyl‐α‐lithiodithiane and α‐(trimethylsilyl)benzyllithium, stabilized by different ligands (THF, PMDTA, TMEDA, [12]crown‐4). They were analyzed with respect to the ^7^Li quadrupole parameters χ(^7^Li) and η(^7^Li) and the chemical shifts δ(^6,7^Li) and δ(^13^C), respectively. On the basis of X‐ray and solution NMR data from the literature, it is shown that solvent‐separated ion pairs (SIP) can be distinguished from contact ion pairs (CIP) by the different magnitudes of χ(^7^Li) and typical shifts for δ(^6,7^Li) and δ(^13^C). Systems with 2 mol equiv. crown ether ligand [12]crown‐4 exist exclusively as SIP structures and show χ(^7^Li) values < 50 kHz, whereas for CIP structures we find χ(^7^Li) > 80 kHz. Copyright © 2001 John Wiley & Sons, Ltd.