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The Use of Functionalized Zirconocenes As Precursors to Silica-Supported Zirconocene Olefin Polymerization Catalysts

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The Use of Functionalized Zirconocenes As Precursors to Silica-Supported Zirconocene Olefin Polymerization Catalysts THE USE OF FUNCTIONALIZED ZIRCONOCENES AS PRECURSORS TO SILICA-SUPPORTED ZIRCONOCENE OLEFIN POLYMERIZATION CATALYSTS by Cheng, Xu A Dissertation Submitted to the Faculty of the Virginia Polytechnic Institute and State University in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in Chemistry Paul A. Deck, Chairman Karen J. Brewer Brian E. Hanson Timothy E. Long James M. Tanko Dec. 10th, 2001 Department of Chemistry Virginia Tech Blacksburg, Virginia Keywords: Synthesis, Organometallic, Zirconocene, Stannyl, Silyl, Electrophilic Substitution, Hydrolysis, Polyolefin Catalyst, MAO, Immobilization, Silica, Leaching Copyright 2001, Cheng, Xu Abstract Me3Si substituents adjacent to Cp2MCl2 (M = Ti, Zr, Hf) are converted to BrMe2Si groups using BBr3. The high reactivity of the Si-Br bonds toward nucleophiles such as water suggested that these substituents could react with hydroxylated silica surfaces, immobilizing the metallocenes. This dissertation concerns the syntheses of electrophile-functionalized zirconocene dihalide complexes and their use as precursors to silica-supported metallocene olefin polymerization catalysts. First we extended the metallocene “functionalization” chemistry to obtain substituents bearing more than one electrophilic bond. (Me3Sn)2C5H4 combined with CpZrCl3 in toluene to 5 afford (h -Me3Sn-C5H4)CpZrCl2 (A). Reactions of A with electrophiles (E-X = Cl2B-Cl, I-Cl, 5 and I-I) afforded (h -XMe2Sn-C5H4)CpZrCl2 (and E-Me) cleanly. The reaction of A with BBr3 5 5 afforded either (h -BrMe2Sn-C5H4)CpZrBr2 (25 °C, 10 min) or (h -Br2MeSn-C5H4)CpZrBr2 (25 5 °C, 15 h). Ph2MeSi-C5H4Li combined with ZrCl4•2THF to afford (h -Ph2MeSi-C5H4)2ZrCl2 (B). The reaction of B with BCl3 led to incomplete cleavage of the Ph-Si bonds, however treatment of 5 5 B with BBr3 afforded (h -Br2MeSi-C5H4)2ZrBr2 (C) efficiently. X-ray crystal structures of (h - 5 ClMe2Sn-C5H4)CpZrCl2•½toluene, (h -Br2MeSn-C5H4)CpZrBr2•THF, B, and C were obtained. Metallocene C reacts with water to afford an oligosiloxane-supported zirconocene dibromide. Spectroscopic characterization suggested a stereoregular structure in which the metallocene units have meso symmetry. The oligomeric substance showed high activity for homogeneous ethylene polymerization. Supported metallocene olefin polymerization catalysts were prepared by combining a functionalized metallocene precursor (Cp2ZrBr2 bearing either BrMe2Si or Br2MeSi groups) and partially dehydroxylated silica. The activities of the immobilized zirconocene catalysts ii decreased and the stabilities increased with increasing number of tethers. The immobilized 5 catalyst prepared from (h -Br2MeSi-C5H4)2ZrBr2, which is assumed to form two “double- tethers” to silica, was significantly more active than the catalyst prepared from [h5-1,3- (BrMe2Si)2C5H3]2ZrBr2, which is assumed to form four “single-tethers” to silica. Catalyst leaching was observed in all the immobilized zirconocene catalysts. Finally we report model studies on the stability of the Si-O-Si bonds toward 5 t methylaluminoxane (MAO). The reaction of (h -BrMe2Si-C5H4)CpZrBr2 with BuMe2SiOH results in the formation of Si-O-Si bonds; addition of NEt3 results in further reaction to afford Si- O-Zr bonds. The reaction of Me3Si-O-SiMe3 with MAO showed that Si-O-Si bonds can be cleaved under the conditions of our polymerization reactions. iii Acknowledgements I sincerely thank my advisor, Prof. Paul A. Deck, for his great support and guidance in my graduate research for the Ph. D. degree at Virginia Tech. Under his supervision, I learned a lot of synthetic organometallic methods and techniques, as well as methods and techniques for heterogeneous catalytic olefin polymerization. It has been a great opportunity and experience for me to work in his group. I sincerely appreciate his great help. I am grateful to my committee members, Professors Karen Brewer, Brian Hanson, Timothy Long, and James Tanko, for their kind help during the course of my research and graduate study. I also want to thank William Bebout and Tom Glass of the Analytical Service for their help with the NMR instrument, and Ms. Judy Gunderson of Dow Chemical for her kind work in obtaining the GPC data of polyethylene samples. I also got a lot of help in my research from my group partners in the past two years. They are Francisco Cavadas, Eric Hawrelak, Owen Lofthus, Matthew Thornberry, and Andrea Warren. Their friendship encouraged me to overcome many difficulties. I wish to take this opportunity to thank them. This research was supported by the National Science Foundation (CHE-9875446) and Research Corporation (CS0567). I appreciate their financial support. Finally, without the edification, support, and endless love from my parents, I would not have been the person I am. They were, are, and will be forever the most important source of encouragement to me. This dissertation is dedicated to them. iv Table of Contents Chapter 1 Introduction................................................................................................................. 1 1.1 Polyethylenes and Methods to Produce Polyethylenes.......................................................... 1 1.1.1 Classification of Polyethylenes and Their Applications............................................... 1 1.1.2 Free Radical Polymerization......................................................................................... 3 1.1.3 Coordination Polymerization Using Ziegler-Natta Catalysts ....................................... 5 1.1.3.1 The Solution Polymerization Process ..................................................................... 9 1.1.3.2 The Bulk Polymerization Process........................................................................... 9 1.1.3.3 The Slurry Polymerization Process......................................................................... 9 1.1.3.4 The Gas-Phase Polymerization Process................................................................ 10 1.2 Metallocene Catalysts.......................................................................................................... 13 1.2.1 Development of Metallocene Catalysts ...................................................................... 13 1.2.2 Synthesis, Structure and Property of Aluminoxanes .................................................. 15 1.2.2.1 Synthesis of Aluminoxanes................................................................................... 15 1.2.2.2 Structures and Properties of Aluminoxanes.......................................................... 17 1.2.3 Advantages of Metallocene Catalysts......................................................................... 20 1.2.4 Disadvantages of Metallocene Catalysts .................................................................... 24 1.2.5 Mechanism of Metallocene Catalyzed Olefin Polymerization ................................... 26 1.2.5.1 Some Proposed Mechanisms ................................................................................ 26 1.2.5.2 Formation of Active Sites and the Role of MAO ................................................. 29 1.3 Supported Metallocene Catalysts......................................................................................... 31 1.3.1 Supported Metallocene Catalysts on Silica................................................................. 32 1.3.1.1 General Features of Silica..................................................................................... 33 1.3.1.2 Direct Deposition.................................................................................................. 37 1.3.1.3 Pre-alumination..................................................................................................... 39 1.3.1.4 Covalent Tethering................................................................................................ 42 1.3.2 Metallocene Catalysts Supported on Other Materials ................................................ 48 1.4 New Immobilization Strategy and Goals of the Research................................................... 56 1.4.1 Proposal for a New Immobilization Method Using Multiple Short Covalent Tethers56 1.4.2 Achievements in the Syntheses of Group 4 Metallocene Compounds Containing Multiple Halosilyl Groups ............................................................................................. 58 1.4.3 Goals of the Research ................................................................................................. 61 Chapter 2 Synthesis and Reactivity of Trimethylstannyl Zirconocene Dichloride [(h5- Me3Sn-C5H4)CpZrCl2].......................................................................................................... 63 2.1 Introduction: Comparison between Silicon and Tin............................................................ 63 5 2.2 Synthesis of (h -Me3Sn-C5H4)CpZrCl2 ............................................................................... 66 v 2.2.1 Discussion of the Synthetic Route.............................................................................. 66 5 2.2.2 Synthesis and Characterization of (h -Me3Sn-C5H4)CpZrCl2 .................................... 69 2.2.3 Discussion of the Synthetic Conditions and Origins of Some Impurities .................. 70 5 2.3 Reactivity of (h -Me3Sn-C5H4)CpZrCl2 with Electrophiles................................................ 73 5 2.3.1 Reaction of (h -Me3Sn-C5H4)CpZrCl2 with BCl3 ...................................................... 73 5 2.3.2 Reaction of (h -Me3Sn-C5H4)CpZrCl2
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