New Routes to Pnictogen-Containing Polymers by Sharonna Greenberg A thesis submitted in conformity with the requirements for the degree of Doctor of Philosophy Graduate Department of Chemistry University of Toronto © Copyright by Sharonna Greenberg 2010 New Routes to Pnictogen-Containing Polymers Sharonna Greenberg Doctor of Philosophy Graduate Department of Chemistry University of Toronto 2010 Abstract New synthetic routes to nitrogen- and phosphorus-containing polymers have been investigated. These routes rely on amine- and phosphine- containing monomers bearing pendant alkyne substituents, and subsequent hydroamination, oxidation, or hydrophosphination polymerization. i A series of primary amines of the form H2NC6H2R2C≡CR’ (R = H or Pr; n R’ = Ph, SiMe3, Bu, or p-C6H4Me) is reported. These amines are deprotonated with nBuLi to give lithium amides, which react with zirconocene compounds to provide amidozirconium complexes. Characterization is achieved by multinuclear NMR spectroscopy, IR spectroscopy, high-resolution mass spectrometry, elemental analysis, X-ray crystallography, and DFT calculations. Three routes were attempted towards nitrogen-containing oligomers: (1) thermolysis of amidozirconium complexes to afford [2+2] cycloaddition polymers; (2) Ti(IV)-catalyzed hydroamination of H2NC6H4C≡CPh; (3) chemical oxidation of H2NC6H4C≡CPh. The latter two strategies resulted in ii distinct nitrogen-containing oligomers. The oligomer formed by Ti(NR2)4- catalyzed hydroamination (R = Me, Et) contains up to 15 repeat units in the chain, with both imine and enamine moieties, and is capped by a molecule of HNR2 (R = Me or Et) originating from the catalyst. The oligomer formed by chemical oxidation contains up to 9 repeat units in the chain. A series of phosphines of the form X2PC6H2R2C≡CR’ is reported (X = i NEt2, Cl, H; R = Me, Pr; R’ = Ph, SiMe3). Characterization is achieved by multinuclear NMR spectroscopy, IR spectroscopy, high-resolution mass spectrometry, elemental analysis, and X-ray crystallography. The primary phosphines, H2PC6H2R2C≡CR’, are relatively “user-friendly” in that they are not particularly malodorous, they are isolated as solids or highly viscous liquids, and they are stable when stored under N2 in the solid state and in solution. i The primary phosphine H2PC6H2 Pr2C≡CPh serves as a precursor for a zirconium phosphinidene and for the secondary phosphines i i RP(H)C6H2 Pr2C≡CPh (R = CH2 Pr, CH2Ph). Hydrophosphination polymerization gives cyclic P(III)-containing oligomers, which are converted to P(V)-based macromolecules by treatment with sulfur. The oligomers contain ca. 5 to 10 repeat units, and heating to 800 °C gives rise to phosphorus-containing ceramics. The mechanism of hydrophosphination is discussed with the use of DFT calculations. iii Dedication To the memory of my dearly beloved grandfather Yehoram “Poopsie” Ben Shachar Did I ever tell you how beautiful you are? Did I ever tell you how much I love you? iv Acknowledgements I owe a special thanks to my supervisor, Professor Douglas W. Stephan, whose friendship, enthusiasm, and endless supply of ideas are an inspiration to me. I am grateful to the past and present Stephan group members for the parties, squash games, movies nights, Spanish lessons, and countless discussions about chemistry (and other unrelated topics). Professor James Green, Dr. Richard Jagt, Professor Mark Nitz, Dr. Kevin Noonan, Professor Derek Gates, and Jeffrey McDowell helped me with instrumentation and measurements. Hanna Thorup and Greg Gibson are two very talented students who have contributed to my research. The support staff (NMR lab, mass spectrometry lab, Analest lab, chemistry stores, machine shop, glass blowing shop, and administration) are essential for the smooth functioning of the department both at the University of Windsor and at the University of Toronto, and I appreciate their expertise and assistance. Andrea Corrente, Dr. Edwin Otten, and Dr. Alberto Ramos performed editorial magic, and this thesis is much better as a result. One final word of appreciation: I would never have reached this point without my family, who show their love and support every day in every way. They taught me the value of hard work and persistence, and they always believed in me even when (especially when) I did not. Thank you! v Table of Contents Page Abstract ii Dedication iv Acknowledgements v List of Schemes ix List of Figures xi List of Tables xiii List of Abbreviations xv Chapter 1: Introduction 1 1.1 Introduction to Polymer Chemistry 1 1.2 An Overview of Inorganic Polymers 2 1.3 Inorganic Polymers Containing Group 15 Elements 6 1.3.1 Polyphosphazenes and Related Polymers 7 1.3.2 Polymers Containing Nitrogen 11 1.3.3 Polymers Containing Phosphorus(III) 14 1.4 Terminal Group 4 Metal Pnictidene Complexes 18 1.4.1 Terminal Group 4 Metal Imide Chemistry 18 1.4.2 Terminal Group 4 Metal Phosphinidene Chemistry 21 1.5 Element–Hydrogen Bond Addition across Unsaturated Substrates 28 1.5.1 Hydroamination 29 1.5.2 Hydrophosphination 32 1.5.3 Element–Hydrogen Bond Addition across Unsaturated Substrates as a Route to Inorganic Polymers 34 1.6 Research Objectives 37 Chapter 2: Amines Bearing Pendant Alkyne Substituents 41 2.1 Abstract 41 2.2 Introduction 41 vi 2.3 Results and Discussion 42 2.3.1 Synthesis of Amines Bearing Pendant Alkynes 42 2.3.2 A Computational Study of Compound 1a 48 2.3.3 Synthesis of Lithium Amides 55 2.3.4 Synthesis of Zirconium Amides 57 2.4 Summary 61 2.5 Experimental Section 62 2.5.1 General Considerations 62 2.5.2 Starting Materials and Reagents 64 2.5.3 Crystallography 65 2.5.4 Synthesis and Characterization 68 Chapter 3: New Routes towards Nitrogen-Containing Polymers 86 3.1 Abstract 86 3.2 Introduction 87 3.3 Results and Discussion 92 3.3.1 Proposed [2+2] Cycloaddition Polymerization 92 3.3.2 Hydroamination Polymerization 93 3.3.3 Model Compounds for Hydroamination Polymerization 101 3.3.4 Oxidation Polymerization 109 3.4 Summary 115 3.5 Experimental Section 116 3.5.1 General Considerations 116 3.5.2 Starting Materials and Reagents 118 3.5.3 Crystallography 118 3.5.4 Synthesis and Characterization 119 Chapter 4: Phosphines Bearing Pendant Alkyne Substituents 129 4.1 Abstract 129 4.2 Introduction 130 4.3 Results and Discussion 133 4.3.1 Synthesis of Aryl Bromides 133 vii 4.3.2 Synthesis of Bisamidophosphines 135 4.3.2.1 X-ray Crystal Structures of Bisamidophosphines 138 4.3.3 Synthesis of Dichlorophosphines 144 4.3.4 Synthesis of Primary Phosphines 147 4.4 Summary 150 4.5 Experimental Section 150 4.5.1 General Considerations 150 4.5.2 Starting Materials and Reagents 151 4.5.3 Crystallography 151 4.5.4 Synthesis and Characterization 153 Chapter 5: New Routes towards Phosphorus-Containing Polymers 165 5.1 Abstract 165 5.2 Introduction 166 5.3 Results and Discussion 167 5.3.1 Synthesis of Zirconium-Phosphorus Compounds 167 5.3.2 Proposed [2+2] Cycloaddition Polymerization 171 5.3.3 Synthesis of Secondary Phosphines 173 5.3.4 Hydrophosphination Polymerization 174 5.4 Summary 189 5.5 Experimental Section 189 5.5.1 General Considerations 189 5.5.2 Starting Materials and Reagents 191 5.5.3 Synthesis and Characterization 191 Chapter 6: Summary and Future Work 210 References 215 viii List of Schemes Scheme Page 1.1 Synthesis of polyphosphazenes by (A) ring-opening polymerization; (B) polycondensation. 8 1.2 Macromolecular nucleophilic substitution of polydichloro- phosphazene. 9 1.3 Initial steps in the polymerization of pyrrole. 13 1.4 Initial steps in the polymerization of aniline. 13 t t 1.5 Generation, trapping, and reactivity of ( Bu3SiNH)2Zr=NSi Bu3. 18 1.6 Generation, trapping, and reactivity of [Cp2Zr=NR]. 19 1.7 Reactivity of azazirconacyclobutenes. 21 1.8 Reactivity of azazirconacyclopentadienes. 21 1.9 Generation and trapping of a zirconium phosphinidene. 24 1.10 Synthetic routes to phospha- and diphosphazirconacycles. 25 1.11 Phosphazirconacyclobutene reactivity. 26 1.12 Synthesis of a terminal titanium phosphinidene. 27 1.13 E–H bond addition across multiple bonds C=X (X = CR2, NR, O) and C≡X (X = CR, N), where E = B, Al, Si, N, P, O, S, Zr. 29 1.14 Hydroamination of an alkyne using a group 4 catalyst ([M] = X2Ti or X2Zr) via a [2+2] cycloaddition pathway. 31 1.15 Hydroamination cyclization of an aminoalkene or aminoalkyne using a lanthanide catalyst ([M] = X2Ln, Ln = lanthanide) via a σ-bond insertion pathway. 32 1.16 Proposed catalytic cycle for the hydrophosphination cyclization of phosphinoalkenes and -alkynes using a lanthanide catalyst ([M] = X2Ln, where X = E(SiMe3)2, Ln = lanthanide, E = CH, N, P). 33 1.17 Hydroboration polymerization. 35 1.18 Phosphorus(V)-containing polymers via hydrophosphorylation. 36 1.19 Nitrogen-containing polymers or oligomers via olefin polymerization or hydroamination. 37 1.20 Proposed routes to nitrogen- or phosphorus-containing polymers. 38 2.1 Synthesis of compounds 1. 42 2.2 Synthesis of compounds 2. 56 ix 2.3 Formation of zirconium amides by metathesis or protonolysis. 57 2.4 Synthesis of compounds 3 and 4. 58 3.1 Proposed route towards a daisy chain polymer containing zirconium and nitrogen. 88 3.2 Hydroamination polymerization of compound 1a to synthesize oligomer 5. 95 3.3 Hydroamination polymerization mechanism using the group 4 precatalyst Ti(NMe2)4. 98 3.4 Synthesis of model compounds: hydroamination of diphenylacetylene with aniline or 2,6-diisopropylaniline. 102 3.5 Synthesis of model compounds: hydroamination of phenylacetylene using aniline or 2,6-diisopropylaniline. M = Markovnikov addition, AM = anti-Markovnikov addition. 104 3.6 Oxidative polymerization of 1a to synthesize oligomer 15. 110 3.7 First steps in the proposed mechanism of formation of 15. 114 4.1 Reactions demonstrating the versatility of primary phosphines; byproducts are not shown.