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Download The SYNTHESIS AND REACTIVITY OF DINUCLEATING DI(DIAMINO)PHENOLATE LIGANDS FOR ENFORCING COOPERATIVITY by Xiaofang Zhai B.Sc., University of Waterloo, Waterloo, ON, Canada, 2015 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE AND POSTDOCTORAL STUDIES (Chemistry) THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver) December, 2017 © Xiaofang Zhai, 2017 Abstract A new single-frame dinucleating di(diamino)phenolate ligand L has been synthesized and fully characterized, and its coordination chemistry with zinc precursors featuring ethyl, alkoxide, acetate and amide leaving groups has been investigated. Reaction of ligand L with diethyl zinc and Zn[N(SiMe3)2]2 led to the formation of a trinulcear zinc complex 1 (L)Zn3(CH2CH3)4 and a dinuclear zinc amide complex 4 (L)Zn2[N(SiMe3)]2, respectively. Deprotonation of ligand L followed by salt metathesis with Zn(OAc)2 gave rise to a trinuclear zinc complex 3 [(L)Zn3](µ- OAc)4. The alkyl zinc complex 1 reacted with benzyl alcohol to afford a dinuclear alkoxy zinc 1 13 1 complex 2 [(L)Zn2](µ-OCH2Ph)2. Complexes 1-3 were fully characterized by H-NMR, C{ H}- NMR, COSY, NOESY, HSQC and HMBC NMR spectroscopy and elemental analysis. The solid-state structures of Zn complexes 1-4 were characterized by single-crystal X-ray crystallography. The catalytic activities of complex 1 and 2 towards ring opening polymerization of racemic lactide (rac-lactide) have been studied. Complex 2 showed better control over molecular weight and dispersity than complex 1, and generated heterotactically inclined poly(lactic acid). However, complex 2 promoted extensive transesterification and depolymerization reaction. Complex 3 was found to be active to ROP of rac-lactide at high temperatures and it was active to CO2/epoxide copolymerization. ii Lay summary Plastics are playing an indispensable role in our daily life due to their good mechanical properties, lightweight and flexible shapes. However, most plastics are derived from petroleum and they are considered to be non-degradable. The accumulation of the fossil-based plastics has resulted in significant environmental pollution. The development of biodegradable polymers, such as poly(lactic acid)(PLA) has emerged as a sustainable solution to this global challenging. Herein we discuss the production and properties of PLA and other biodegradable polymers. Also, the issues with the synthesis and processing of PLA are discussed. The research presented in this thesis is focused on the design and development of highly active catalysts for the synthesis of biodegradable polymers with good physical and mechanical properties. We have successfully synthesized and characterized three zinc catalysts, and performed preliminary reactivity studies on these catalysts. iii Preface The work presented in this thesis is in collaboration with Prof. Parisa Mehrkhodavandi and Dr. Paul Kelley who was working on the project before I joined the group. Tannaz Ebrahimi and Dr. Brian O. Patrick contributed to the X-ray crystal structure solving. Jakob Marbach conducted the CO2/epoxide copolymerization reactions. Ligand design in Chapter 2 was developed by Prof. Parisa Mehrkhodavandi. Ligand L was synthesized and fully characterized by me (1H-NMR, 13C{1H}-NMR, COSY, NOESY, HSQC and HMBC NMR spectroscopy, mass spectroscopy and elemental analysis). Also, the synthetic procedures were optimized by me. The synthesis and characterization of zinc complexes 1-4 (1H-NMR, 13C{1H}-NMR, 2D NMR, X-ray crystallography, and elemental analysis) in chapter 2, and the polymerization studies in Chapter 3, were conducted by me. iv Table of contents Abstract .......................................................................................................................................... ii Lay summary ................................................................................................................................ iii Preface ........................................................................................................................................... iv Table of contents ........................................................................................................................... v List of tables................................................................................................................................. vii List of figures .............................................................................................................................. viii List of schemes .............................................................................................................................. xi List of abbreviations and symbols ............................................................................................. xii Acknowledgments ....................................................................................................................... xv Chapter 1: General introduction ................................................................................................. 1 1.1. Introduction to poly(lactic acid): a sustainable polymer ............................................ 1 1.2. Synthesis of PLA ............................................................................................................ 2 1.2.1. Mechanism of ring opening polymerization of lactide using metal catalysts ........... 4 1.2.2. Tacticity and microstructure of PLA ........................................................................ 8 1.3. Multi-metallic zinc catalysts for the ROP of lactide ................................................. 11 1.4. Multi-metallic complexes linked to a single-frame ligand: cooperative catalysis in ring-opening polymerization of lactide ................................................................................. 21 1.5. Cooperative catalysis in CO2/epoxide ring-opening copolymerization ................... 26 1.6. Scope of the thesis ......................................................................................................... 31 Chapter 2: Design, synthesis, and characterization of a dinucleating ligand platform and the resulting zinc complexes ....................................................................................................... 33 2.1. Introduction: ligand design for enforcing cooperative effects in catalysis ............. 33 2.2. Synthesis and characterization of ligand L ................................................................ 36 2.3. Synthesis and characterization of zinc complexes supported by chiral dinucleating ligand ....................................................................................................................................... 39 2.3.1. Synthesis of alkyl zinc complex: a trinuclear species ............................................. 39 2.3.2. Synthesis and characterization of alkoxy zinc complex ......................................... 43 2.3.3. Synthesis and characterization of zinc acetate complex ......................................... 48 2.3.4. Attempted synthesis of dinuclear zinc complexes with bulkier functionality ........ 51 2.4. Conclusions ................................................................................................................... 54 Chapter 3: Preliminary studies of the reactivity of multi-metallic zinc complexes .............. 55 Introduction .................................................................................................................. 55 ROP of rac-lactide with alkyl zinc complexes 1 ......................................................... 57 v ROP of rac-lactide with alkoxy zinc complex 2 ......................................................... 58 Reactivity of zinc acetate complex 3 towards lactide polymerization ..................... 63 Conclusions and perspectives ...................................................................................... 65 Experimental procedures ........................................................................................................... 69 References .................................................................................................................................... 76 Appendix A. FTIR spectrum of complex 3. .............................................................................. 81 Appendix B. Characterization of compounds in solution; 1H-NMR, 13C{1H}-NMR and 2D NMR spectra, mass spectra ........................................................................................................ 82 Appendix C. Characterization of polymers ............................................................................ 103 Appendix D. Solid state structure and crystallographic parameters ................................... 107 vi List of tables Table 2.1. Selected bond lengths (Å) and angles (°) for complex 1. ........................................... 43 Table 2.2. Selected bond lengths (Å) and angles (°) for complex 2. ........................................... 47 Table 2.3. Selected bond lengths (Å) and angles (°) for complex 3. ........................................... 51 Table 2.4. Selected bond lengths (Å) and angles (°) for complex 4. ........................................... 54 Table 3.1. Polymerization results of rac-lactide with complex 1a ................................................ 58 Table 3.2. Ring-opening polymerization of rac-lactide with alkoxy zinc complex 2a. ................ 59 Table 3.3. Attempted activation of Zn
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