Studies on Grignard reagents. Part I. Fluorine nuclear magnetic resonance spectra of fluoroaryl Grignard reagents

1 January 1967

journal article
research article
Published by Royal Society of Chemistry (RSC) in J. Chem. Soc. A

p. 1643-1648
https://doi.org/10.1039/j19670001643

Abstract

The fluorine resonance spectra of fluoroaryl Grignard reagents, the corresponding bisarylmagnesiums, and mixtures of the two, have been measured over a range of temperature. It has thus been possible to slow the fluoroaryl exchange and distinguish unambiguously between “RMgX” and “R₂Mg” species. Values for the ratio 2[“RMgX”]/[“R₂Mg”] in ether solutions of the pure Grignard reagents are: C₆F₅MgBr, 1·0; C₆F₅MgCl, 2·0; C₆F₅Mgl, 1·4; 3-F,5,4Cl₂C₆H₂·MgBr, ca. 2·5; C₁₀H₆FMgl, 20; p-F·C₆H₄·MgBr, 20; p-F·C₆H₄·Mgl 20. Limited additional information concerning the nature of these “RMgX” and “R₂Mg” species has been obtained from the fluorine chemical shifts. The rates of fluoroaryl exchange qualitatively follow the sequence C₆F₅Mgl < C₆F₅MgBr < C₆F₅MgCl C₁₀H₆FMgl < C₆H₂Cl₂FMgBr < p-F·C₆H₄·Mgl < p-F·C₆H₄·MgBr. For the p-fluorophenyl and pentafluorophenyl systems, mixing the bisarylmagnesium and magnesium iodide rapidly produces a conventional Grignard reagent.

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