Fundamental Chlorophosphazene Chemistry
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FUNDAMENTAL CHLOROPHOSPHAZENE CHEMISTRY A Dissertation Presented to The Graduate Faculty of The University of Akron In Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy Zin-Min Tun December, 2011 FUNDAMENTAL CHLOROPHOSPHAZENE CHEMISTRY Zin-Min Tun Dissertation Approved: Accepted: Advisor Department Chair Dr. Claire A. Tessier Dr. Kim C. Calvo Co-Advisor Dean of the College Dr. Wiley J. Youngs Dr. Chand Midha Committee Member Dean of the Graduate School Dr. Peter L. Rinaldi Dr. George R. Newkome Committee Member Date Dr. Chrys Wesdemiotis Committee Member Dr. Edward Evans ii ABSTRACT Even though chlorophosphazene chemistry has been around since the 1800s, it was not until the 1950s when Allcock successfully synthesized the soluble chlorophosphazene polymer that the door to functionalized polyphosphazenes was opened. At present, polyphosphazenes constitute the largest group of inorganic backbone polymers, with their potential applications ranging from elastomers to biomaterials. Most functionalized polyphosphazenes are derived from polychlorophosphazenes. The problems surrounding the synthesis and storage of polychlorophosphazenes hinder the commercial development of functionalized polyphosphazenes. In the quest for a cost- effective synthetic route and for storage solutions, our group focuses on the fundamental chlorophosphazene chemistry. This dissertation discusses our endeavors to understand fundamental chlorophosphazene chemistry, the majority of the work being on the chemistry of [PCl2N]3. The dissertation is divided into six chapters; Introduction, Mechanistic Studies of the Fluxional Behavior of Group 13 Lewis Acid Adducts of [PCl2N]3, Group 13 Super Acid Adducts of [PCl2N]3, Crown ether complexes of HPCl6, Reactions of Group 15 Superacids with Chlorophosphazenes and Conclusion. Chapter I, the introduction, provides the overview of the previous studies of the iii acid-base chemistry of chlorophosphazenes. Chapter II describes a mechanistic study of the fluxional behavior of the Group 13 Lewis acid adducts of [PCl2N]3 and evaluates the likelihood that these adducts are directly involved as intermediates in the ROP process. The synthesis and characterization of Group 13 superacid adducts of [PCl2N]3 are discussed in Chapter III. The fragile acid HPCl6, which can potentially play an important role in chlorophosphazene chemistry, was isolated as complexes of crown ethers. Chapter IV describes the synthesis and characterization of these complexes. The reactivity of Group 15 acids, HPCl6 and HSbCl6 towards cyclic [PCl2N]n (n = 3, 4, 5, and 6) and polymeric [PCl2N]n follows in Chapter V. This chapter also qualitatively compares the acid strengths of the relatively unknown HPCl6 and HSbCl6 acids to the strengths of more commonly known superacids, such as HAlCl4, HAlBr4, HGaCl4 and superacids with carborane anions. iv DEDICATION To my wonderful husband And to all the kind souls who have contributed big or small along the way v ACKNOWLEDGEMENTS First and foremost, I would like to thank my research advisor, Dr. Claire A. Tessier. I can not thank you enough for all that you have done for me and for your guidance both inside and outside of the research lab. You are an advisor, a mentor, a friend, and an inspiration, and I am very fortunate to have you as my chemistry mom. I have grown a lot under your mentorship not just as a chemist but also as a person. I do not think I will ever meet another boss who is more supportive of their employees. I will miss our passionate discussions about anything and everything under the sun. I would also like to thank my co-advisor, Dr. Wiley J. Youngs for his many brilliant ideas and suggestions for my research. I really appreciate the fun and relaxed, yet challenging learning atmosphere that you and Dr. Tessier have created in our group. Thank you very much for letting me and Brian be a part of the fun ‘bible study’ sessions. This is not a goodbye yet though because I will make sure that you two are a part of my life after grad school. A lot of collaborators have contributed greatly to the success of my research project. Dr. Matthew J. Panzner has my deepest gratitude. If it were not for your patience, perseverance and your keen crystallographic skills, I would not have been able to characterize half of my air-sensitive products vi crystallographically. With your thirst for knowledge and your willingness to help others, you are one of the best people to work with. I also would like to thank Dr. Doug Medvetz and Brian Wright for their help with x-ray crystallography. I would like to thank Dr. Peter L. Rinaldi for patiently teaching me about dynamic NMR. I would also like to thank Dr. Venkat Dudipala and Linlin Li for all their gracious help with the NMR over the years. I would like to thank Dr. Chrys Wesdemiotis and Vincenco Scionti for their help with the Mass Spec. Thank you very much, V for willing to go the extra mile and even learn to prepare the air-sensitive samples in the glove-box yourself. I also would like to thank Dr. Amy J. Heston who started this research project in our group. I would like to thank Dr. Chris Allen (The University of Vermont), Dr. Supat Moolsin, Dr. Sujeewani Ekanayake and David J. Bowers for providing me with some of my starting materials. I also would like to thank many chemistry professors that I have met through my graduate and undergraduate years who have been exceptionally inspiring and who cares deeply for the students; thank you very much, Dr. Kim Calvo, Dr. Henry Stevens, Dr. Virginia Pat and Dr. Mark Snider. I also would like to thank the professors on my defense committee who had been kind enough to thoroughly read my dissertation and gave me many useful suggestions and insight. I would like to thank the Tessier-Youngs group members, past and present for all their support and friendship over the years; thank you Dr. Matthew J. Panzner, Dr. Doug Medvetz, Dr. Khadijah Hindi, Dr. Tammy Siciliano, Dr. Amanda Knapp, Dr. Joanna Beres, Nikki Robishaw, Brian Wright, Mike Deblock, vii Pat Wagers, David J. Bowers and Nick Johnson. Thank you, Nick for always being a patient and understanding friend-in-need. I will miss all the fun trips to the Lockview, as well as the ones to the ACS meetings. I also would like to thank Natalie for her friendship that made the Chem seminars almost as fun as the many trips to the lizard. I would like to thank my parents and my two sisters for all their love and support. Even though you have not been by my side physically this past decade because we inhabit four different continents, I have always been able to draw strength from the fact that, where ever we are, we are all resiliently following our own dreams in our own ways. I am grateful to have met my host-parents, Jim and Janelle Collier. I can not thank you enough for all that you have done for me and for all that you have been to me. Last but not least, I would like to thank my wonderful husband, Brian Darby. Thank you, baby for all your love, support and patience that saw me through this long process. Thank you especially for loving the very frustrated, and most probably very frustrating at times :-), me while I was writing this dissertation. I am very grateful to have you as my life partner and I can just hope that I am to you what you are to me. viii TABLE OF CONTENTS Page LIST OF TABLES ................................................................................................ xv LIST OF FIGURES ............................................................................................. xvi LIST OF CHARTS ............................................................................................. xxii LIST OF SCHEMES ......................................................................................... xxiii LIST OF EQUATIONS ...................................................................................... xxiv CHAPTER I. INTRODUCTION ............................................................................................. 1 1.1. Functionalized polyphosphazenes ............................................................. 1 1.2. [PCl2N]n ..................................................................................................... 3 1.2.1. Synthesis of [PCl2N]n ............................................................................ 3 1.2.2. Mechanism of the ROP of [PCl2N]3 ....................................................... 5 1.2.3. Synthesis of [PCl2N]n ............................................................................ 3 1.3. Acid-Base Chemistry of [PCl2N]3 ............................................................. 14 1.3.1. Previously Reported Interactions of Lewis Acids with [PCl2N]3............14 1.3.2. Previously Reported Interactions of Brønsted-Lowry Acids with [PCl2N]3 and [PR2N]3-5............ ............................................................17 1.4. Superacids...............................................................................................19 1.5. Lewis acid/Brønsted acid dichotomy and the protonic impurities affecting the chlorophosphazene chemistry.............................................22 ix 1.6. Topics in this dissertation.........................................................................23 1.7. References..............................................................................................25 II. MECHANISTIC STUDIES OF THE FLUXIONAL BEHAVIOR OF GROUP 13 LEWIS ACID ADDUCTS OF [PCl2N]3 ........................................ 29 2.1. Introduction