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

1967; Royal Society of Chemistry; Linguagem: Inglês

10.1039/j19670001643

2050-5582

D. F. Evans, Muhammad S. Khan,

Synthesis and Reactions of Organic Compounds

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.