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"Synthesis, Structure and Reactivity of Β-Diketiminato Supported

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“Man would not have attained the possible unless time and again he had reached out for the impossible.” — Max Weber THE UNIVERSITY OF CALGARY Synthesis, Structure and Reactivity of β-Diketiminato Supported Organoscandium Cations by Paul George Hayes A DISSERTATION SUBMITTED TO THE FACULTY OF GRADUATE STUDIES IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY DEPARTMENT OF CHEMISTRY CALGARY, ALBERTA APRIL, 2004 © Paul George Hayes 2004 UNIVERSITY OF CALGARY FACULTY OF GRADUATE STUDIES The undersigned certify that they have read, and recommend to the Faculty of Graduate Studies for acceptance, a thesis entitled “Synthesis, Structure and Reactivity of β-Diketiminato Supported Organoscandium Cations” submitted by Paul George Hayes in partial fulfilment of the requirements for the degree of Doctor of Philosophy. ____________________________________________________________ Supervisor, Dr. Warren E. Piers, Department of Chemistry ____________________________________________________________ Dr. Tristram Chivers, Department of Chemistry ____________________________________________________________ Dr. George K. H. Shimizu, Department of Chemistry ____________________________________________________________ Dr. Hans J. Vogel, Department of Biological Sciences ____________________________________________________________ External Examiner, Dr. John E. Bercaw, California Institute of Technology ________________________ Date ii Abstract A variety of β-diketiminato supported mononuclear dialkyl scandium compounds have been synthesized and fully characterized in both the solid and solution states. The 4-coordinate species exhibit fluxional behaviour in solution which has been quantitatively studied and is interpreted as a dynamic process which equilibrates two structures via a C2v symmetric transition state. At elevated temperatures these compounds have been determined to undergo an intramolecular metallation process with loss of RH. Polymerization experiments revealed that several of the organoscandium complexes are effective catalysts for the polymerization of ethylene. The reactivity of the neutral dialkyl organoscandium species was examined leading to the synthesis of a family of highly reactive organoscandium alkyl cations. Deactivation pathways, most notably C6F5 transfer to the metal centre and metallation of an isopropyl group were observed. While C6F5 transfer impeded subsequent reactivity studies, metallation proceeded sufficiently slowly so as not to hinder the development of their organometallic chemistry. Quantitative analysis of ion-pair dynamics established that intermolecular anion exchange likely occurs by way of a highly ordered transition state, most likely a low energy associative anion displacement by an incoming arene molecule. A unique class of isolable solvent separated organoscandium methyl cations was synthesized by reaction of dialkyl scandium compounds with [CPh3][B(C6F5)4]. These complexes have been found to be resistant to both C6F5 transfer and metallation decomposition pathways. The molecular structures show stabilization of the alkyl cations iii through η6 arene binding to the metal centre. These aromatic solvent molecules are bound sufficiently loose to permit the study of their chemistry. Quantitative kinetic experiments for arene exchange imply a partially dissociative mechanism whereby the rate-limiting step involves dissociation to lower hapticity. The mechanism for arene displacement was further investigated upon exploring the reactivity of these compounds with diphenylacetylene. In this situation it was determined that rate-limiting coordination of the alkyne to the metal centre had a slightly higher barrier than arene ring slipping. Preliminary work demonstrated that the β-diketiminato ancillary can also be used to prepare organoyttrium species with potential for further derivatization to the corresponding organoyttrium cations. iv Acknowledgements I would like to thank my supervisor, Dr. Warren Piers, for his direction and mentoring throughout this degree. His enthusiasm and insight have both challenged and inspired me by providing an exceptional scientific environment in which to develop as a chemist. His unrelenting work ethic, scientific integrity and amazing efficiency have made a lasting impression which I will continue to strive towards. He made this thesis possible. Thank you. I would like to extend my gratitude to all my fellow labmates whom have made my time here both productive and fun, especially: Dr. Lawrence (Larry) Lee, Dr. Suobo Zhang, Dr. James Blackwell, Dr. Kevin Cook, Bryon Carpenter (thank you for Easter 2000), Dr. Lisa Knight (my nacnac partner), Dr. Preston Chase, Lee Henderson, Darryl Morrison, Dr. Roland Roesler, Dr. Andy McWilliams, Greg “The Hammer” Welch, Heather Phillips, Glen McInnis, Dr. Ioan Ghesner, Dr. Marcus Schaefer, Allison Kenward, and Mike Bosdet. A significant quantity of time and energy was expended by Dr. Stuart Dubberley, Patricio Romero (my Chilean brother), and Korey “Papa” Conroy (I’ll miss the B&G) proofreading various portions of this thesis. These efforts contributed significantly to the overall quality of this work, and as such, are greatly appreciated. A special thank you is extended to Dr. David Emslie, the eternal postdoc, for countless chemistry discussions, lunches on “the hill”, and for continuously keeping my spirits high. It is impossible not to be excited about science in your presence. I thank Drs. Tristram Chivers, George Shimizu and Hans Vogel for excellent suggestions, numerous reference letters and all else on the extensive list of duties which v sitting on my Ph.D. committee encompassed. I would like to thank Dr. Rupert E. v. H. Spence and Dr. Brian Keay for being members of my Candidacy Committee. Gratitude is extended to Dr. John Bercaw for attending my Ph.D. defence and contributing his knowledge and expertise on mechanistic organometallic chemistry. Many thanks go to Mrs. Dorothy Fox, Ms. Qiao Wu, Mrs. Roxanna Smith, Dr. Raghav Yamdagni, Mark Toonen, Dave Malinsky, Keith Collins, Kim Wagstaff, Mike Siewert and Ed De Bruyn for expert technical assistance. Dr. Masood Parvez is acknowledged for X-ray crystal structure determinations. I am grateful to Ms. Greta Prihodko and Ms. Bonnie King for keeping me organized. I want to thank Dr. Adrien Côté for his assistance with X-ray crystallography and the DSC/TGA analyzer. The University of Calgary, the Natural Sciences and Engineering Research Council of Canada, the Killam Foundation, and the Alberta Heritage Foundation are acknowledged for their generous financial support in the form of teaching assistantships and scholarships throughout my graduate career. Gratitude is extended to Dr. Q. Wang of NOVA Chemicals LTD for performing polymerization experiments. I would like to thank friends Allan MacMillan, Todd Lacey and Drs. Michael and Naomi Kruhlak for extracurricular activities – I owe you my sanity. I am indebted to the excellent teachers in my life: Gus Pike, Michael Gaudet and Dr. Stephen Westcott. Thank you for nurturing my passion for science. Finally I wish to extend my utmost gratitude to my parents, George and Christine, my grandparents, Winston, Madeline, Johnnie and Mabel, my siblings, Stephanie and Ian, and my wife Joanne. Without your continual love, guidance and encouragement I would not be where I am today. Thank you for believing in me. vi Time transcends inequalities, borders and generations equally and unforgivingly; it is the most valuable gift one can give. Thus, I dedicate the following to my eternal supporter and loving wife, Joanne. vii Table of Contents Approval Page………………………………………………………………………..…...ii Abstract………………………………………………………………………………..….iii Acknowledgements……………………………………………………………………......v Dedication………………………………………………………………………………..vii Table of Contents………………………………………………………………………..viii List of Compounds……………………………………………………………………….xi List of Tables…………………………………………………………………………....xiii List of Figures……………………………………………………………………………xv List of Schemes…………………………………………………………………………..xx List of Abbreviations and Symbols………………………………………….………...xxiv Chapter 1: Introduction 1.1 Historical Account of Organoscandium Chemistry and Chapter Content............1 1.2 Scandocene Chemistry..........................................................................................2 1.3 Mixed Cp* - Amido Scandium Chemistry ...........................................................6 1.4 Non-Cp Supported Organoscandium Compounds ...............................................7 1.5 Cationic Organoscandium Compounds ................................................................9 1.6 Thesis Goals........................................................................................................11 Chapter 2: Synthesis, Characterization and Thermal Decomposition of Dialkylscandium Complexes Supported by the β-Diketiminato Ligand 2.1 Introduction – β-Diketiminato Ancillary Ligand................................................13 2.1.1 Synthesis and Structural features of the β-Diketiminato Ligand................13 2.1.2 Electronic Features and Bonding Modes of the β-Diketiminato Ligand....18 2.2 Results.................................................................................................................23 Me 2.2.1 Synthesis of L ScR2(THF)x ......................................................................23 tBu 2.2.2 Synthesis of L ScR2..................................................................................25 2.2.3 X-ray Crystal
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