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Knorr R, Behringer C, Lattke E, et al. How Microsolvation Numbers at Li Control Aggregation Modes, sp(2)-Stereoinversion, and NMR Coupling Constants (2)JH,H of H2C═C in α-(2,6-Dimethylphenyl)vinyllithium. J Org Chem. 2015;80(12):6313-22doi: 10.1021/acs.joc.5b00762.
Knorr, R., Behringer, C., Lattke, E., von Roman, U., & Knittl, M. (2015). How Microsolvation Numbers at Li Control Aggregation Modes, sp(2)-Stereoinversion, and NMR Coupling Constants (2)JH,H of H2C═C in α-(2,6-Dimethylphenyl)vinyllithium. The Journal of organic chemistry, 80(12), 6313-22. https://doi.org/10.1021/acs.joc.5b00762
Knorr, Rudolf, et al. "How Microsolvation Numbers at Li Control Aggregation Modes, sp(2)-Stereoinversion, and NMR Coupling Constants (2)JH,H of H2C═C in α-(2,6-Dimethylphenyl)vinyllithium." The Journal of organic chemistry vol. 80,12 (2015): 6313-22. doi: https://doi.org/10.1021/acs.joc.5b00762
Knorr R, Behringer C, Lattke E, von Roman U, Knittl M. How Microsolvation Numbers at Li Control Aggregation Modes, sp(2)-Stereoinversion, and NMR Coupling Constants (2)JH,H of H2C═C in α-(2,6-Dimethylphenyl)vinyllithium. J Org Chem. 2015 Jun 19;80(12):6313-22. doi: 10.1021/acs.joc.5b00762. Epub 2015 Jun 01. PMID: 26029794.
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J Org Chem. 2015 Jun 19;80(12):6313-22. doi: 10.1021/acs.joc.5b00762. Epub 2015 Jun 01.

How Microsolvation Numbers at Li Control Aggregation Modes, sp(2)-Stereoinversion, and NMR Coupling Constants (2)JH,H of H2C═C in α-(2,6-Dimethylphenyl)vinyllithium.

The Journal of organic chemistry

Rudolf Knorr, Claudia Behringer, Ernst Lattke, Ulrich von Roman, Monika Knittl

Affiliations

  1. Department Chemie, Ludwig-Maximilians-Universität München, Butenandtstrasse 5-13 (Haus F), 81377 München, Germany.

PMID: 26029794 DOI: 10.1021/acs.joc.5b00762

Abstract

The title compound 4 is a trisolvated monomer 4&3THF in THF solution and dimerizes endothermically to form (4&THF)2 with a strongly positive (!) dimerization entropy in toluene as the solvent. In the absence of electron-pair donor ligands, 4 aggregates (>dimer) in hydrocarbon solutions. These results followed from the (13)C-α splitting patterns and the magnitudes of the one-bond (13)C,(6)Li NMR coupling constants in combination with lithiation NMR shifts as secondary NMR criteria. The rate constants of cis/trans sp(2)-stereoinversion could be measured on the (1)H NMR time scale in THF, in which solvent the preinversion lifetime is 0.24 s at 25 °C. This inversion proceeds according to the pseudomonomolecular, ionic mechanism with the typical, strongly negative pseudoactivation entropy. In a different mechanism, the lifetimes are much longer at 25 °C for the dimer (4&t-BuOMe)2 in toluene (ca. 2.5 min) and for donor-free, aggregated 4 in hexane solution (roughly 1 min). The olefinic interproton two-bond coupling constants (2)JH,H of the H2C═CLi part are proposed as an indicator of microsolvation at Li, because they were found to increase linearly with the "explicit" solvation of α-arylvinyllithiums by 0, 1, 2, and 3 electron-pair donor ligands.

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