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Syntheses and Characterization of BH₂ NH₂ Species

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Syntheses and Characterization of BH₂ NH₂ Species This dissertation has been 65—5644 microfilmed exactly as received X HICKAM, Jr., Cecil William, 1939- SYNTHESES AND CHARACTERIZATION OF BHgNHg SPECIES. The Ohio State University, Ph.D., 1964 Chemistry, inorganic I University Microfilms, Inc., Ann Arbor, Michigan SYNTHESES AND CHARACTERIZATION OF BHgNHg SPECIES DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University by Cecil William Hickam, Jr., B.S. The Ohio State University 1964 Approved hy idviser Department of Chemistry ACKNOWLEDGMENTS A grant from the National Science Foundation helped to provide equipment and chemicals for this work. Financial support for myself was given hy E, I. DuPont De Nemours and Company for the summers of 1963 and 1964, and by General Electric for the school year of 1963-64. I would like to thank Dr. Sheldon G, Shore for his continued encouragement throughout my graduate studies, and to gratefully acknowledge his help and guidance in this investigation. I am indebted to my student colleagues, Mr. G. E. McAchran, and Dr. B. Z. Egan, and especially Mr. K. W. Boddeker, who performed some of the molecular weight de­ terminations and analyses reported here; and my uncle and aunt, Mr. and Mrs. W. D. Hedges, and my wife, Lydia, for their financial and moral support. 11 CONTENTS Acknowledgments............................ ii Tables...................... v Illustrations....................................... vil I. INTRODUCTION........................ 1 A, General Background........................ 1 B, Statement of Problem...................... 16 II. EXPERIMENTAL............ 18 A. Apparatus................................ 18 B. Chemicals................................ $6 C. Analytical Procedures.................... 39 D. Determination of the Cryoscopic Constant of Dimethyl Sulfoxide...... 4-3 E. Reactions of Diammoniate of Diborane with Bases in Liquid Ammonia............ 4-8 1. Reactions............. 4-8 2. Properties............................ 53 3. X-ray diffraction patterns............ 54- 4-. Molecular weights......... 56 5, Infrared spectra...................... 57 6. Analyses............... 64- 111 CCjJTENTS (conta.) Page P. Reaction of Iiithinm Amide with Diborane in Diethyl E t h e r ............... 65 1. Reaction.............................. 66 2. Properties............................ 71 5. Protolysis of aminoborane with methanol................ 73 4-. Molecular weights . ................. 78 5. X-ray powder diffraction patterns . 80 6. Infrared spectrum................ 80 7. Reactions of aminoborane............... 81 8. Analysis......... 86 G. Miscellaneous Reactions ............. 87 1. Reaction of lithium methylamide with diborane in diethyl ether .......... 87 2. Reaction of lithium amide diborane in tetrahydrofuran and in dimethyl e t h e r ............................... 88 3. Reaction of sodium amide with diborane in diethyl ether .......... 89 III. DISCUSSION OF RESULTS.......................... 92 BIBLIOGRAPHY........................................... 101 AUTOBIOGRAPHY......................................... 105 IV TABLES Table Page 1. Cryoscopic Constant of Dimethyl Sulfoxide . 4$ 2. Hydrogen Generated from the Reaction of Sodium Amide with Diammoniate of Diborane . 51 3. Hydrogen Generated from the Reaction of Sodium with Diammoniate of Diborane ..... 5^ 4. X-ray Powder Diffraction Pattern of Cyclotriborazane............................. 55 5. X-ray Powder Diffraction Pattern of Cyclopentaborazane........................... 55 5. Apparent Molecular Weight of Cyclotriborazane in Liquid A m m o n i a ........................... 56 7. Apparent Molecular Weight of Cyclopentaborazane in Dimethyl Sulfoxide . .............. 58 8. Infrared Spectrum of (BHgEH^)^................. 61 9. Infrared Spectrum of (BHgNHg)^ ............... 64 10. Analysis of (BHgHHg)^......................... 64 11. Analysis of (BH^m^)^ in 6H HCl at 100°C. 65 12. Analysis of (BHgRHg)^.......... 66 13. Reactions Using the Extractor................. 69 14. Results of Yield Study Reaction ........ 72 15., Results of Protolysis of Aminoborane by Methanol..................................... 7^ 16. Time Study of the Protolysis of Aminoborane by Methanol at 0°C........................... 75 V TABLES (conta.) Table Page 1 7 . Oryoscopic Study of Aminoborane in Dimethyl Sulfoxide............................ 7 8 18. Cryoscopic Study of Aminoborane in Liquid Ammonia............................... 79 19. X-ray Powder Diffraction Pattern of Lithium Borohydride........................ 81 20. Infrared Spectrum of Aminoborane from Ether Reaction............................... 84 21. Analysis of Aminoborane....................... 86 22. X-ray Powder Diffraction Pattern of the Reaction of Sodium Amide with Diborane in Ether................ 91 VI ILLUSTRATIONS Figure Page 1. Freezing Point Cell for Ammonia............ 24 2. Cryostat and Cooling System ................. 26 5. Freezing Point Cell for Dimethyl Sulfoxide. 29 4. Extractor .............................. 32 5. Hydrolysis T u b e .............................. 4C 6. Typical Warming Curve of Solvent DMSC and of Solution................................ 46 7. Infrared Spectrum of ( B H g N H g ) ^ ............ 59 8. Infrared Spectrum of ( B E g N H g ) ^ ............ 62 9. Protolysis of Aminoborane by Methanol at C°C. ................ 76 1C. Infrared Spectrum of Aminoborane from Ether Reaction.............................. 82 vii I. INTRODUCTION A. General Background Because boron chemistry had been limited to research on boric acid and borates, Stock, in 1912, decided to in­ vestigate unexplored areas of boron chemistry, such as the hydrides. His investigations were rewarding, for by 1933 he had isolated the boron hydrides: diborane-6 (BgH^), tetraborane-10 (B^H^q ), pentaborane-9 (B^Hg), pentaborane-11 (B^H^^) , hexaborane-10 (B^H^q ) , and decaborane-14 (1). Although his work produced new and interesting compounds, they possessed structures which were not ex­ plicable in terms of the then existent ideas of structural chemistry. Only within recent years has sufficient informa­ tion been available, so as to be able to discuss, intelli­ gently, the bonding of the boron hydrides. It is remarkable that Stock was able to make contribu­ tions to boron chemistry, since materials available were limited at the time of his researches. Not only was he restricted to the use of soft glass, a difficult substance with which to work and a substance which cannot stand sudden thermal shocks, but he had to use mercury-valves instead of lubricated stopcocks because of the lubricant’s sensitivity to ‘boron liydrides. However, in spite of these difficulties, Stock not only contribnted to boron hydride chemistry, but was responsible for the development of chemical vacuum line techniques. Many of the techniques and procedures used today have originated from Stock’s work. The simplest of the boron hydrides, diborane-6, hence­ forth called diborane, is a bridged structure (2). The four terminal hydrogens define a rectangular plane which contains H H H H The two boron atoms and the two bridged hydrogens lie above and below the plane, respectively. Several descriptions of the bonding in diborane have been given. The most popular of these is that of Eberhardt, Crawford, and Lipscomb (5), who assumed each boron to be an sp^ hybrid. The in plane hydrogens form classical electron pair bonds. The sp^ hybrids, which are directed above and below the plane, and the s orbitals of the hydrogens in the bridge mutually overlap, forming two three-centered orbitals, each containing two electrons-— one from the hydrogen and one 3 from one of the borons* The bridge bond has been called a three-centered or "banana bond," That BHj is not a stable entity is attributed to the fact that in all of the known boron hydrides boron tends to employ all of its low-lying orbitals in bond formation. In diborane, this is accomplished through the formation of the hydrogen bridges; thus all four valence orbitals of boron are occupied. Lewis bases can displace the bridge hydrogens to form molecular addition compounds. In fact, diborane behaves as a Lewis acid. Typical reactions which have been observed are these (4); + 2 M e ^ ------ > 2HjBNMe^ BgHg + EHegO — --- > 2H^B0Me2 BgHg + 2C0 ------- » 2H^B00 In 1926 Stock and Pohland (5) prepared an ammonia- diborane addition compound, which had an empirical formula of BgHg 2KEj, the so-called diammoniate of diborane. Pyrolysis of this compound produced a 30 percent yield of borazine, Eleven years later, by means of an electron diffraction study, Bauer proved that borazine is a structural analogue of benzene because it is a planar, six membered ring (6). Since borazine is isoelectronio as well as structurally analogous to benzene, it has been called inorganic benzene (7); the following Eekule * structures have been proposed (8): H H B B. HN NH NH Contrary to early belief, there is little evidence of aromatic character in the borazine system (9,10). Chemi­ cally, it behaves as though it has the following structure, in which electron pairs are localized on the nitrogen, H B HN: :nh HB BH N H Unlike benzene with its delocalized -rf electron system, borazine forms addition compounds readily. Thus, for example, a complex in the mole ratio 1:5 is formed with HOI, in which a proton adds to a donor atom, nitrogen, and a chloride adds to an acceptor atom, boron (7,11), Ho H"-I 3HCI + B 3 N 3H 6 HgN NH, H Cl H\ / Cl— ►B c X H \ H ' H' Since the
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