Synthetic Studies of Sodium Aminodiboranate Salts with Electron- Withdrawing Substituents

SYNTHETIC STUDIES OF SODIUM AMINODIBORANATE SALTS WITH ELECTRON- WITHDRAWING SUBSTITUENTS BY CONNOR I. DALY THESIS Submitted in partial fulfillment of the requirements for the degree of Master of Science in Chemistry in the Graduate College of the University of Illinois at Urbana-Champaign, 2020 Urbana, Illinois Adviser: Professor Gregory S. Girolami ABSTRACT Magnesium diboride, MgB2, has the highest superconducting critical temperature of all traditional superconductors and is being considered for the fabrication of superconducting integrated circuits that can operate at higher temperatures than analogous niobium alloy circuits. A significant barrier to preparing superconducting MgB2 thin films, however, is that the films must be deposited below 300 °C to prevent Mg from subliming out of the film and causing loss of the superconducting properties. One approach to solve this problem is to prepare low- temperature chemical vapor deposition (CVD) precursors which would enable deposition of MgB2 at temperatures low enough to prevent loss of Mg from the thin film. In chapter 1, we describe the synthesis of three new sodium aminodiboranate salts, Na(BH3)2NRR′, with trimethylsilyl groups on nitrogen. These compounds – sodium N,N-bis- (trimethylsilyl)aminodiboranate, sodium N-trimethylsilylaminodiboranate, and sodium N- methyl-N-trimethylsilylaminodiboranate – were prepared by the reaction of μ-aminodiborane(6) species with sodium hydride. IR, 1H NMR, 13C NMR, and 11B NMR spectra are reported for all of these compounds, along with the crystal structures of N-trimethylsilylaminodiboranate and N- methyl-N-trimethylsilylaminodiboranate. Comparisons of 11B NMR chemical shifts suggest that steric, inductive, and hyperconjugative effects of the substituents on nitrogen are all in competition in these systems. In chapter 2 we describe the preparation of fluorinated aminodiborantes, although here the longer reaction times required for their synthesis lead to undesirable production of butoxyborate species through the ring-opening reaction of thf with BH3. To circumvent this problem, we employed non-cyclic ethers such as diglyme and cyclopentyl(methyl)ether to investigate the preparation of μ-aminodiborane(6) species from the fluorinated amines N,N- ii bis(2,2,2-trifluoroethyl)amine, N-(2,2,2-trifluoroethyl)amine, and N-methyl-N-(2,2,2-trifluoroethyl)amine. We find that there is a correlation between the pKa of the ammonium form of the amine with the relative stabilities of the μ-aminodiborane(6) and aminoborane: N,N-bis(2,2,2- trifluoroethyl)amine forms the aminoborane preferentially, whereas both N-(2,2,2- trifluoroethyl)amine and N-methyl-N-(2,2,2-trifluoroethyl)amine form the µ-aminodiborane(6) in good yields. Sodium N-methyl-N-(2,2,2-trifluoroethyl)aminodiboranate was prepared and characterized by 11B NMR spectroscopy, although efforts to isolate it were unsuccessful. iii ACKNOWLEDGMENTS It becomes all the more apparent at the end of this work, that its completion was something that I would never have been capable of on my own. If I were to choose one lesson that completing my thesis work has taught me, outside of numerous chemical lessons, it would be that collaboration with other skilled individual is crucial for any successful endeavor both inside and outside the sciences, and I would like to take this moment to thank them. First and foremost, I would thank my advisor, Professor Gregory Girolami, for serving as my mentor over the course of this degree, and for taking a chance on me and accepting me into his group after I left the Makri group halfway through my graduate career. I hold his wisdom, patience, compassion, and gift to foster interest in chemistry to the highest of standards and, moving forward, I aspire one day in the future to become an educator of similar skill to serve my future students. Thank you for allowing me to work with you and the talented members of your group, and I wish for you to find success in many interesting scientific problems in the future. I would like to thank all Girolami group members who have worked with me during my tenure here. I would especially like to thank both Brian Trinh and Sumeng Liu for mentoring me and helping me refine almost everything I know about synthetic air-free chemistry, Nels Anderson for his help orienting myself to the group and for our many discussions about more rudimentary inorganic chemistry, as well as the use of his former fume hood where I finished the last of my experiments for this thesis, Chris Caroff for his incredible depth of knowledge on boron chemistry and his initiative which saw me learn more than I ever would have on my own, Nathan Edmonsond his enduring nature, constructive conversations and criticisms, and his patience as I learned how to properly spell his last name, and Joe Wright for his patience in having me as his student mentor. iv I thank our collaborators in the materials department, Dr. John Abelson and his lab members for all the help on CVD, I especially thank Xiaoqing Chu for characterizing thin films grown in their lab and helping me learn more about CVD then I ever could have on my own. I would also like to thank Nancy Makri, my mentor and research advisor before joining the Girolami group, for her patience and continued support when it became apparent that her research was not a good fit for my interests. I thank the help of the SCS facilities staff, specifically Beth Eves and Kiran Subedi from the Microanalysis Laboratory and Dean Olsen, who not only provided excellent conversation during those few times where I was waiting on a particularly long data collection and he was free, but also answered all of my questions regarding the NMR instruments and methodologies, and was always free regardless of the time of day to address issues with their upkeep or functionality. I would also like thank Danielle Grey and especially Toby Woods of the X-ray laboratory for being quick enough to collect crystal structure data on my air-sensitive crystals, helping me install olex2, and giving me ideas on how to crystallize my compounds. I would like to thank all of the members of the IMP office, past and present, who were always willing to work with me, bring my attention to free food, and provide interesting conversations while waiting for things to print. I would like to especially thank Katie Trabaris for her numerous talks about our shared interests in fiction, and for her ability to untangle any of my scheduling conflicts, Lisa Johnson for introducing me to new kinds of music, Theresa Struss for her sarcastic quips and Raegan Smith for her positive attitude and helping me schedule meetings. Finally, I thank my friends and family who helped me cope with the emotional burdens of graduate school. Without them, I would not be here writing this. I thank David Eury, David Craig, and Nick McGarrell for being three of the best friends anyone could ever wish for. I thank v Amartya Bose, Sohang Kundu, and Reshmi Dani for their support when I changed groups and their continued friendship afterwards. And last, but certainly not least, I thank my parents Kevin Daly and Leah Mann-Daly for the unconditional love and support they have consistently given to me over the years, and for encouraging me to always work hard, challenge myself, and pursue excellence. I give special thanks to my younger sister, Fionuala (Nuala) Daly for her enduring belief in me, and her endless attempts at sarcasm; I look forward to supporting you in the future, and hope to have the honor of receiving your acknowledgment one day when you reach the heights only you know that you can reach. vi TABLE OF CONTENTS CHAPTER 1: SYNTHESIS AND CHARACTERIZATION OF SODIUM AMINODIBORANATE SALTS PREPARED FROM SILYLAMINES ................................. 1 1.1 Introduction ................................................................................................................. 1 1.2 Results and Discussion ................................................................................................ 5 1.3 Experimental .............................................................................................................. 15 1.4 References .................................................................................................................. 22 CHAPTER 2: SYNTHETIC AND 11B NMR STUDIES OF AMINODIBORANATE SALTS PREPARED FROM PRIMARY AND SECONDARY FLUOROAMINES ......................... 29 2.1 Introduction ............................................................................................................... 29 2.2 Results and Discussion .............................................................................................. 31 2.3 Experimental .............................................................................................................. 37 2.4 References .................................................................................................................. 40 APPENDIX A: SYNTHESIS OF Mo[H3BNMe2BH3]2 WITH TIN AS A CO-REDUCTANT ....................................................................................................................... 45 A.1 Introduction .............................................................................................................. 45 A.2 Experimental ............................................................................................................. 46 A.3 References ................................................................................................................. 49 vii

Load more