Nuclear Magnetic Resonance Studies of Some Grignard Reagents and Organo- Lithium Compounds

This dissertation has been 64—9547 microfilmed exactly as received ADAMS, David George, 1936— NUCLEAR MAGNETIC RESONANCE STUDIES OF SOME GRIGNARD REAGENTS AND ORGANO- LITHIUM COMPOUNDS. The Ohio State University, Ph.D., 1964 Chemistry, physical University Microfilms, Inc., Ann Arbor, Michigan NUCLEAR MAGNETIC RESONANCE STUDIES OF SOME GRIGNARD REAGENTS AND ORGANOLITHIUM COMPOUNDS DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By David George Adams, S. M. * * * * The Ohio State University 1964 Approved by Adviser Department of Chemistry DEDICATION This dissertation is dedicated to my wife, Barbara, who has aided me immeasurably in many ways in its preparation, and whose complete understanding and belief in me has promoted the task from drudgery to a pursuit of workman ship. ACKNOWLEDGMENTS I wish to thank the McGraw-Hill Book Company, New York, New York, for permission to include portions of the book "High- resolution Nuclear Magnetic Resonance" by J. A. Pople, W. G. Schneider and H. J. Bernstein, copyright 1959. I wish also to thank all of my fellow graduate students, who aided me in my efforts, and especially Englebert Pechhold, as much for his quiet understanding as for his careful synthesis of a necessary compound. My most sincere gratitude to Dr. Gideon Fraenkel, for whose knowledge and dedication I have the deepest respect, and for whose open-mindedness and lack of pedantry in accepting my disputatious nature I have profound admiration. This investigation was supported in part by the Petroleum Research Fund administered by The American Chemical Society, and in part by Public Health Service Fellowship 5 FI GM-17, 815-02 from the Division of General Medical Sciences, Public Health Service. CONTENTS Page DEDICATION 11 ACKNOWLEDGMENTS iii TABLES vi ILLUSTRATIONS vii C hapter ; L INTRODUCTION 1 Historical Background Previous Research Discussion of Problem and Methods Aromatic Grignard Reagents IL EXPERIMENTAL 25 Chemical Reagents Purification and Treatment of Reagents A pparatus P ro ced u res Preparation of organometallic compounds Calibration of spectra n T. RESULTS AND DISCUSSION 47 General Considerations: Aliphatic Grignard Reagents Lithium and Magnesium Organometallic Compounds Mixed Grignard Reagents Asymmetric Grignard Reagents Aromatic Organolithium Compounds and Grignard Reagents iv Chapter Page IV. SUMMARY AND CONCLUSIONS.................................... 84 BIBLIOGRAPHY.................................... 87 AUTOBIOGRAPHY.................................................................................... 92 v TABLES Table Page 1. Chemical Reagents ......................................................... 26 2. Reaction Conditions for the Grignard R eaction ............. 36 3. Chemical Shift of Methyl Groups in Solvents .................... 46 4. Proton Chemical Shifts, RMgBr and RgMg ...................... 48 5. Proton Chemical Shifts, RMgBr and RH ............................ 50 6. Proton Chemical Shifts, RMgBr and R L i ......................... 54 7. Bond Hybridization in MeMgl and M eLi ............................ 55 8. NMR Parameters, 2-bromo- 1-phenylpropane and 2-bromomagnesio- 1-phenylpropane ............... 62 9. NMR Parameters, l-bromo-2-phenylpropane and l-bromomagnesio-2-phenylpropane .................. 66 10. Chemical Shift, 2-bromo-1, 1-dimethylcyclopentane and 2-bromomagnesio-1, 1- dimethylcyclopentane ...................................................... 67 11. NMR Parameters, Aromatic Organometallic C om pounds .......................................................... 69 vi ILLUSTRATIONS Figure Page 1. Magnetic Field Induced by Ring Current .......................... 22 2. Apparatus for Grignard Reaction ...................................... 33 3. Apparatus for Organolithium Preparation ....................... 38 4. Apparatus for Dialkylmagnesium Purification .............. 42 5. NMR Spectrum of 2-bromo-1-phenylpropane ............... 59 6. NMR Spectrum of 2-bromomagnesio-1-phenyl propane .............................................................................. 61 7. NMR Spectrum of l-bromo-2-phenylpropane ............... 63 8. NMR Spectrum of l-bromomagnesio-2-phenyl- p r o p a n e .............................................................................. 65 9. NMR Spectra of ]D-phenyl-di magnesium bromide and ]3-phenyl-di-lithium .............................................. 70 10. Paramagnetic Transitions in Aromatic Organo metallic Compounds ....................................................... 74 11. Paramagnetic Effect in Aromatic Organometallic C om pounds ......................................................................... 80 J CHAPTER I INTRODUCTION Historical Background The direct precursor of the Grignard reagent was the Wagner-Saytzeff reaction. In 1875, Wagner and Saytzeff ^ reported a new synthesis for alcohols. They had mixed zinc, an alkyl iodide, and a carbonyl compound to obtain a complex which gave a low yield of an alcohol on hydrolysis. They characterized the reaction as proceeding through the formation of dialkylzinc, with subsequent addition to the carbonyl compound. Barbier^ substituted magnesium for zinc and obtained higher yields of alcohol in many cases. Victor Grignard (1871-1935), as a student of Barbier, was assigned the problem of studying the mechanism of this type of reaction. His research in this direction finally reached an impasse, and he decided that this reaction might well proceed in two steps. Accordingly, Grignard set out to ^G. Wagner and A. Saytzeff, Ann. 175, 351 (1875). 2p. Barbier, Compt. Rend. 128, 110 (1899). 1 investigate these steps separately. He postulated the first step to be a reaction of magnesium with the organic halide, much the same as Wagner and Saytzeff had suggested. Grignard1 s attempts to react magnesium with an organic halide in ether met with immediate success. A product was formed which would complex with carbonyl compounds to give alcohols on hydrolysis. The scope of these reactions was quickly expanded to include a large variety of halides and solvents in the first step—the formation of the reagent which bears Grignard's name. New reac tions with the Grignard reagent to produce useful products are still being discovered today. In the publication of his work, Grignard^ suggested that the structure of his reagent was RMgX. Grignard and others^? 5 found that a solid precipitated on evaporation, and that one molecule of ether per molecule of alkylmagnesium halide was bound very tenaciously in the solid. This observation was used to support a hypothesis of Baeyer and Villiger, ® who suggested that the Grignard ^V. Grignard, Gompt. Rend. 130, 1322 (1900). ^V. Grignard, Ann. Chim. (Paris) 24, 433 (1901). ^E. -E. Blaise, Compt. Rend. 132, 839 (1901). ®A. Baeyer and V. Villiger, Ber. 35, 1201 (1902). reagent was an oxonium compound; for example, methylmagnesium iodide in diethyl ether would have the structure E t f MeMg — O — I f Et Grignard 7’ ftaccepted the idea of a tetrahedrally coordinated oxygen atom, but preferred the structure E t f Me — O — Mgl I E t The oxonium theory received much attention, but was disproven unequivocally by Thorp and Kamm, ^ who showed that the magnesium compound prepared from diethyl ether and bromobenzene was different from that prepared from ethoxybenzene and bromoethane. During the period in which the oxonium theory enjoyed its greatest popularity, Abegg^ proposed an ionic structure for the Grignard reagent. This theory was largely ignored at that time, but was later revived. He suggested that the Grignard reagent was a ^V. Grignard, Compt. Rend. 136, 1260 (1903). ®V. Grignard, Bull. Soc. Chim. France 29, 944 (1903). ^L. Thorp and O. Kamm, J. Am. Chem. Soc. 36, 1022 (1914). lOR. Abegg, Ber. 38, 4112 (1905). 4 polar compound best represented as an alkylmagnesium halide and that the equilibrium 2 R M gX ^ MgX2 + R-2M^ might exist in solution. Jolibois, H as well as others, prepared dialkylmagnesium by the reaction RgHg + Mg—>R2Mg + Hg. He showed that this compound was more soluble in an ethereal solution of magnesium iodide than in pure ether. From these results, Jolibois suggested the structure MgR2 • Mgl2 to be the best representation for the Grignard reagent. More evidence for this coordination arose from the early work of Menschutkin, 12 who determined the solubility of magnesium bromide dietherate in ether. The solubility of Grignard reagents far exceeds that of magnesium bromide, indicating that the magnesium bromide in Grignard reagents must be coordinated to the rest of the compound to account for its high solubility. Molecular weight determination by Terentjew^ and Grignard^ indicated the molecular weight to be twice that predicted by the single alkylmagnesium halide formula, RMgX; Grignard ascribed this effect Up. Jolibois, Compt. Rend. 155, 353 (1912). 12b . N. Menschutkin, Z. Anorg. Chem. 49, 34 (1906). 13a . P. Terentjew, Z. Anorg. Chem. 156, 73 (1926). 14v. Grignard, Bull. Soc. Chim. France 39, 1285 (1926). to molecular aggregation in solution. Later work showed that the association varied with concentration, from just over one to about four. 15 Thus, the research during the first quarter-century after Grignard's discovery had elucidated the composition of the Grignard reagent in ether solution. However, differentiation between the association of two alkylmagnesium halide molecules and the associa tion of dialkylmagnesium with magnesium bromide was not

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