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Tri-Tert-Butyl Siloxide Compounds and in the Ephemeral Existence of Destabilized 2-Aza-Allyl Anionic Ligands

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Tri-Tert-Butyl Siloxide Compounds and in the Ephemeral Existence of Destabilized 2-Aza-Allyl Anionic Ligands STUDIES IN ORBITAL SYMMETRY CONSTRAINTS OF THE REACTIVITY OF GROUP (V) TRI-TERT-BUTYL SILOXIDE COMPOUNDS AND IN THE EPHEMERAL EXISTENCE OF DESTABILIZED 2-AZA-ALLYL ANIONIC LIGANDS A Dissertation Presented to the Faculty of the Graduate School of Cornell University in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy by Elliott Baines Hulley May 2011 © 2011 Elliott Baines Hulley STUDIES IN ORBITAL SYMMETRY CONSTRAINTS OF THE REACTIVITY OF GROUP (V) TRI-TERT-BUTYL SILOXIDE COMPOUNDS AND IN THE EPHEMERAL EXISTENCE OF DESTABILIZED 2-AZA-ALLYL ANIONIC LIGANDS Elliott Baines Hulley, Ph.D. Cornell University 2011 2 The olefin complex (silox)3Nb( -trans-1-phenyl-2-vinylcyclopropane) (2- c t PhVi Pr, silox = Bu3SiO) was synthesized as a means of testing the existence a hypothesized biradical transition state for olefin dissociation. The binding of the olefin to (silox)3NbPMe3 (2-PMe3) produces two diastereomeric complexes (2-maj and 2- min) that undergo cyclopropane ring-cleavage and -H atom abstraction to yield isomeric alkylidene-ene products cis/trans-(silox)3Nb=CH-CH=CH-CH2CH2Ph (cis-2- alk and trans-2-alk) upon thermolysis. The two diastereomers rearranged at different rates and kinetic models suggest that trans-2-alk converts to cis-2-alk prior to ring cleavage and rearrangement. Phenomenological kinetic isotope effects were consistent with the kinetic models. Efforts were undertaken to synthesize [(silox)3Ta]2N2 in order to circumvent the apparent kinetic barrier to dinitrogen activation by (silox)3Ta (1). N- aminoazidirines reacted with (silox)3Ta to produce the parent imide (silox)3TaNH (1=NH) and with (silox)3Ta=CH2 to produce alkyl hydrazide complexes. The methyl hydrazide (silox)3Ta(CH3)NHNH2 (3-NHNH2) thermally degraded to the tetraaza- t bimetallacycle [(CH3)(silox)2Ta](-NH-N)(-NHNH)[(CH3)(silox)2Ta]•2 Bu3SiOH t (4●2 Bu3SiOH) with concomitant evolution of CH4. The dinitrogen complex [(silox)2Ta(Cl)]2N2 could be prepared via salt metathesis and methylated to produce [(silox)2Ta(CH3)]2N2. Attempts to oxidatively couple 1=NH or (silox)3TaNLi resulted only in decomposition or production of 1=NH. White phosphorus (P4) was found to react with 1 (at –78 °C) and 2-PMe3 (at room temperature) to produce 1 1 2 [(silox)3M]2( , : )P2 (M = Nb, Ta). When 2-PMe3 was treated with P4 at –78 °C c for 16 h the novel complex [(silox)3Nb( P3)]2 was formed. Attempts to create new ligands containing the 2-aza-allyl anion resulted in CC- coupling chemistry that produced interesting organic frameworks. Both 3- and 5- membered rings and [4.4.0]-bicyclic systems could be constructed from the same precursor ligand, (CH3)2C(CHNCH2Py)2 , upon treatment with different metal complexes. Chromium, cobalt and nickel bis(amide) complexes produced unique metal-metal bonded species as a result of the triple CC-coupling reaction that produces 4,4,8,8-tetramethyl-2,6-di(pyridin-2-yl)-3,7-bis((E)-(pyridin-2-ylmethylene)amino)- octahydro-1,5-naphthyridine (14) as an octadentate ligand. BIOGRAPHICAL SKETCH Elliott Baines Hulley was born in 1983 to Michael and Kathleen Hulley in Washington, D.C. His interest in science was fostered from a very early age by his mother, who quizzed him with algebra problems on the way to elementary school, and by his father, who answered his seven-year-old son’s questions with, “Well, to a first approximation…” His interest in chemistry was first piqued in high school by Mrs. Gayle Meehan, an unusually exuberant and unfailingly encouraging teacher. Having chosen a scientific path, he risked certain doom in the unkempt, wild, and backward lands of the greater Philadelphia area to attend Ursinus College. At Ursinus, he learned the basics of chemical research through studying the oligomerization of aldoketenes. Through the NSF REU program he also had the opportunity to spend a summer studying organic biradicals with Prof. David Shultz at North Carolina State University and another summer attempting to synthesize chiral lactide derivatives with Prof. Mitch Smith at Michigan State University. While at Ursinus he also managed to obtain minor concentrations in Physics and Ancient Greek, although he apparently forgot to turn in the form confirming a minor in the latter. Ursinus played a much more important role in his life than he realized at the time, for it was there he had the fortune to meet his future wife Abigail. He and Abigail both decided to brave the cold and bitter North and make camp in Ithaca for a few years. He had the great honor to join the Wolczanski laboratory and was able to witness the Chadeayne-Marshak dynamic duo. After five-and-a-half years of messing about across the periodic table he completed his degree in December 2010. He and Abigail have now set their sights west, and he will soon join the laboratory of Morris Bullock at Pacific Northwest National Laboratory in Richland, Washington. iii For Dad iv ACKNOWLEDGEMENTS First I would like to thank my advisor Pete Wolczanski, whose guidance and patience for my considerable eccentricities is unrivalled. I have no end of respect for him, both as a scientist and a person, and his clarity of thought breaks down the most complex system into its most essential parts. My sincere gratitude also go to my remaining Committee members, Paul Chirik and Dave Collum. Paul has been exceedingly helpful over the years, both in private conversations and at Tuesday Lit Lunch. On many occasions I was very fortunate to have his input. Dave was also very helpful, particularly on kinetic and mechanistic problems, and the source of some of my most memorable conversations. I would also like to thank Barry K. Carpenter, who helped my understanding of computational chemistry and physical organic chemistry considerably. A great many thanks go to Ivan Keresztes, without whom a great deal of the data in this thesis would not exist. David Zax also deserves tremendous credit for the helping with my understanding of 93Nb NMR, as well as spending two whole days obtaining solid-state NMR spectra. Tom Cundari is also thanked for his calculational contributions, which make their appearance in Chapters 1 and 2. Emil Lobkovsky is thanked for his crystal structure determinations, which, besides the NMR data, make up the bulk of the information in this work. I would also like to thank Denise Wurtenburg and Josh Wakeman for making trips to the stockroom entertaining and enjoyable over the years. Dave Neish and Larry Stull were always helpful and always game for great conversation (particularly about the legislative process). I would also like to thank Pat Hine, Sharon De Roos, Sharon Calhoun, and Vonnie Ellis for the many great interactions I have had with them over the years. v During my graduate school career I have received considerable help from members of the Chirik group, most notably my fellow Ursinus alumnus Jon Darmon. He was always willing to help out with instrumentation or materials, for myself and others in the Wolczanski group, and his contributions to our work are considerable. I wish him the best of luck with his research and look forward to seeing his considerable scientific skill put to work. I would also like to give my thanks to Carsten Milsmann, who put up with my many questions about computational chemistry, Broken Symmetry, and the meaning of . A special thanks goes to the Wolczanski group, past, present and future. Kurt Hirsekorn, Andrew Chadeayne, Mike Marshak, Matt Chambers and Dave Kuiper all ensured that my first few years were unforgettable and chock full of great stories. I would especially give credit to Kurt, who initially trained me and gave me great advice on what to do when I finished at Cornell. My classmates Emily Volpe and Brenda Frazier have been, of course, an integral part of my graduate school experience. In Brenda both Emily and I found a determination and strength of will that helped us put our chemical lives into perspective. Brenda is a wonderful friend and a fantastic labmate, whose attention to detail often counterbalanced my scattered approach to things. Emily is, of course, the most admirable person I have ever met. In Emily both Brenda and I continually found someone who was always willing to listen and help with any particular problem, and she always gave my philosophical and religious questions far more consideration than they likely deserved. I am, for lack of a better word, blessed, to have known the two of them for my entire graduate career and I hope to keep contact with my chemical siblings for as long as they can stand me. Special thanks go to Erika Bartholomew, whom I have gotten to know very well over the past few years. She has come to be one of my closest friends, and I am far more fortunate for it. I have zero doubt she has vi the capability to take all of her predecessors’ strengths to heart and go far in the chemical sciences. I look forward to the day we are colleagues as well as close friends. My final year at Cornell would not have been the same were it not for Wesley Morris and Valerie Williams. They are both very capable scientists and, more importantly, great people. They both ensure that the group dynamic remains positive. I would also like to thank Brian Lindley, the newest group member, whose well-timed comments have proven his ability to change the dynamic of tense situations. Finally, and most importantly, I would like to thank my family for putting up with my flightiness and at-best occasional communication. My mother, without whom none of this would be possible, has allowed her son to put many things on hold in the hope of finishing this program and going on in the sciences, and no amount of gratitude can ever repay her.
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