New Routes to Pnictogen-Containing Polymers

Sharonna Greenberg

A thesis submitted in conformity with the requirements for the degree of Doctor of Philosophy Graduate Department of Chemistry University of Toronto

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?

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!

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

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

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. 130 4.2 Synthesis of compounds 16. 133 4.3 Synthesis of compounds 17. 136 4.4 Synthesis of compounds 18. 144 4.5 Synthesis of compounds 19. 147 5.1 Proposed routes to zirconium- and/or phosphorus-containing polymers. 167 5.2 Generation of lithium phosphide 20 and zirconium phosphinidene 21. 168

5.3 Generation of lithium phosphide 22-(THF)x. 169 5.4 Generation of zirconium phosphinidene 23. 170 5.5 Attempted synthesis of the proposed zirconium- and phosphorus- containing polymer by (A) direct reaction of 22 with methylchlorozirconocene or (B) treatment of 23 with heat and/or vacuum. 171 5.6 Synthesis of compounds 24. 173 5.7 Polymerization of compounds 24 to give oligomers 25. 174 5.8 Reaction of oligomers 25 with sulfur to give oligomers 26. 181

List of Figures

Figure Page 1.1 Examples of well developed inorganic polymers. 2

1.2 Bonding in polyphosphazenes: 3dπ(P)–2pπ(N) overlap resulting in islands of electronic delocalization. 8 1.3 Polymers related to polyphosphazenes. 10 1.4 Polymers containing nitrogen. 12 1.5 Oligomers and polymers containing trivalent phosphorus. 14 1.6 Zirconium phosphinidene species which have been (a) isolated, (b) detected in solution, or (c) proposed as intermediates on the basis of further reactivity (byproducts are not shown). 23 1.7 Isolated and characterized titanium phosphinidene species. 28 2.1 Resonance contributors of compound 1b. 44 2.2 Molecular structure representation of compounds 1a, 1d, and 1h. 45 2.3 Resonance contributors for aniline and compound 1a. 47

2.4 Calculated structures for anilineopt and 1aopt, with numbering scheme. 49 2.5 Resonance contributors for aniline+• and compound 1a+•. 50

+• 2.6 Dipole moments calculated for (a) 1aopt and (b) 1a opt. Side view is shown. 51

2.7 Selected occupied molecular orbitals for anilineopt and 1aopt showing the front view and the side view. 53

+• +• 2.8 Selected occupied molecular orbitals for aniline opt and 1a opt showing the front view and the side view. 54 2.9 Molecular structure of compound 3a. 60 3.1 Infrared spectra of monomer 1a and oligomer 5. 96 3.2 UV/Vis spectra of monomer 1a and oligomer 5 in acetonitrile. 96

3.3 MALDI-TOF mass spectrum of 5 using Ti(NMe2)4 as the precatalyst. 99

3.4 MALDI-TOF mass spectrum of 5 using Ti(NEt2)4 as the precatalyst. 100 3.5 Molecular structure representation of compounds 7 and 9. 103 3.6 Molecular structure representation of compound 12. 106

3.7 Cyclic voltammogram for compound 1a. 110 3.8 IR spectra of monomer 1a and oligomer 15. 112 3.9 UV/Vis spectra of monomer 1a and oligomer 15 in N,N-dimethylformamide. 112 3.10 MALDI-TOF mass spectrum of 15. 113 4.1 Selected examples of primary phosphines with aryl substituents. 131 4.2 Molecular structure representation of compounds 16a, 16b, and 16d. 135

4.3 Selected examples of (PPh3)m(CuBr)n (m = 1, 2, 3, 4; n = 1, 2, 4) complexes. 139 4.4 Molecular structure representation of compound 17a. 141 4.5 Molecular structure representation of compound 17b. 141 4.6 Molecular structure representation of compounds 18a and 18b. 146 4.7 Molecular structure representation of compound 19b. 148 5.1 IR spectra of monomer 24b and oligomer 25b. 175 5.2 MALDI-TOF mass spectrum for oligomer 25a. 177 5.3 MALDI-TOF mass spectrum for oligomer 25b. 178 5.4 TGA data for oligomer 25a. 179 5.5 EDX data for oligomer 25a. 180 5.6 MALDI-TOF mass spectrum for oligomer 26a. 182 5.7 MALDI-TOF mass spectrum for oligomer 26b. 183 5.8 TGA data for oligomer 26a. 184 5.9 EDX data for oligomer 26a. 184 5.10 UV/Vis spectra of monomer 24a and oligomers 25a and 26a. 186 5.11 B3LYP/6-31G(d) gas phase Gibbs free energy calculations for the hydrophosphination reaction between methylphenylphosphine and diphenylacetylene. 188 5.12 TGA data for oligomer 25b. 208 5.13 EDX data for oligomer 25b. 208 5.14 TGA data for oligomer 26b. 209 5.15 EDX data for oligomer 26b. 209

xii

List of Tables

Table Page 2.1 Selected spectroscopic data for compounds 1. 43 2.2 Selected bond lengths (Å) and angles (°) for 1a, 1d, and 1h. 46

2.3 Selected bond lengths (Å) and angles (°) for aniline, anilineopt, +• +• aniline opt, 1h, 1aopt, and 1a opt. 50

+• +• 2.4 Mulliken charges for anilineopt, aniline opt, 1aopt, and 1a opt. 52 2.5 Selected NMR data for compounds 2. 56 2.6 Selected NMR data for compounds 3 and 4. 59 2.7 Crystallographic parameters for compounds 1a, 1d, 1h, and 3a. 67 3.1 Characteristic data supporting the [2+2] cycloaddition mechanism or the σ-bond insertion mechanism of hydroamination. 89 3.2 Selected bond lengths (Å) and angles (°) for 7 and 9, and a comparison to diagnostic bond lengths and angles typical of imines and enamines. 104 3.3 Crystallographic parameters for compounds 7, 9, and 12. 119 4.1 Selected spectroscopic data for compounds 16. 133 4.2 Selected bond lengths (Å) and angles (°) for 16a, 16b, and 16d. 134 4.3 Selected spectroscopic data for compounds 17. 136 4.4 Selected bond lengths (Å) and angles (°) for 17a and 17b. 142 4.5 A comparison of bond lengths and angles in the copper halide core of complexes 17a and 17b to other [Ar3PCu(μ-X)]2 complexes (Ar = aryl, X = halide). 144 4.6 Selected spectroscopic data for compounds 18. 145 4.7 Selected bond lengths (Å) and angles (°) for 18a and 18b. 146 4.8 Selected spectroscopic data for compounds 19. 148 4.9 Crystallographic parameters for compounds 16a, 16b, 16d, and 17a. 152 4.10 Crystallographic parameters for compounds 17b, 18a, 18b, and 19b. 152 5.1 Selected NMR data for compounds 20, 21, 22, and 23. 170 5.2 Selected spectroscopic data for compounds 24. 174

xiii

5.3 Selected spectroscopic and molecular weight data for oligomers 25a, 25b, 26a, and 26b. 185 5.4 Reaction conditions and experimental data for the attempted oligomerization of compound 24a after a period of 3 weeks at 70 °C. 202 5.5 Selected spectroscopic and molecular weight data for oligomers 25a and 25b with attempted termination by MeOH. 205

xiv

List of Abbreviations

° degrees Å Angstrom, 10-10 m δ chemical shift Δ change ΔG° change in Gibbs free energy (species in standard states) ΔH° change in enthalpy (species in standard states) ΔH‡ enthalpy of activation ΔS° change in entropy (species in standard states) ΔS‡ entropy of activation λmax absorption maximum μL microliter, 10-6 L ν frequency σ standard deviation 6-31G(d) a type of basis set AIBN azobisisobutyronitrile AM anti-Markovnikov Ar aryl ArH tertiary aryl B3LYP a type of DFT exchange-correlational functional ca. circa cat. catalytic CHCA α-cyano-4-hydroxycinnamic acid 5 Cp cyclopentadienyl anion, η -C5H5 5 Cp* pentamethylcyclopentadienyl anion, η -C5Me5 d doublet ddd doublet of doublets of doublets dt doublet of triplets DFT density functional theory DME 1,2-dimethoxyethane, or glyme DMF N,N-dimethylformamide DNA deoxyribonucleic acid DPn number-average degree of polymerization EDX energy dispersive X-ray EI electron impact Epa oxidation potential Eq. equation equiv. equivalents Et ethyl eu entropy units eV electron Volts Fc calculated structure factor Fo observed structure factor xv

FT Fourier transform g gram GPC gel permeation chromatography h hour HOMO highest occupied molecular orbital HMBC heteronuclear multiple bond correlation HRMS high resolution mass spectrometry HSQC heteronuclear single quantum correlation Hz Hertz, s-1 i Bu isobutyl, CH2CH(CH3)2 i Pr isopropyl, CH(CH3)2 IR infrared J coupling constant kcal kilocalorie kJ kilojoule kV kilovolt Ln lanthanide m multiplet m meta M Markovnikov M molarity [M]+ molecular ion Me methyl Mes “mesityl”, 2,4,6-Me3C6H2 t Mes* “supermesityl”, 2,4,6- Bu3C6H2 mg milligram MHz megahertz, 106 s-1 min minute mL milliliter, 10-3 L mm millimeter, 10-3 m mmol millimole, 10-3 mol Mn number-average molecular weight mol mole MS mass spectrometry Mw weight-average molecular weight MW molecular weight m/z mass-to-charge nacnac β-diketiminate anion, CH[C(R)N(R’)]2 nBu n-butyl nm nanometer NMR nuclear magnetic resonance o ortho p para p extent of reaction PDI polydispersity index Ph phenyl, C6H5 xvi

ppm parts per million q quartet quat-Ar quaternary aryl r stoichiometric ratio RNA ribonucleic acid ROP ring-opening polymerization s singlet S Siemens SE semi-empirical t triplet t Bu tert-butyl, C(CH3)3 THF tetrahydrofuran UB3LYP a type of DFT exchange-correlational functional UV ultraviolet UV/Vis ultraviolet/visible V Volts

xvii 1

Chapter 1 Introduction

1.1 Introduction to Polymer Chemistry

Polymer chemistry is ubiquitous, from biological polymers such as

RNA, DNA, and proteins which mark the beginning of life on Earth, to

commodity polymers used in clothing, shelter, and tools, which mark the

progress of humankind. The 19th century is credited with the origin of the

polymer industry through the manipulation of natural polymers, including

mastication and vulcanization of natural rubber, and production of gun

cotton and celluloid from cellulose nitrate.1 These materials are best

described as semi-synthetic, since they are produced from naturally occurring

polymers. The first truly synthetic polymers, made from small molecule

starting materials, emerged in the early 20th century. Nowadays, the most common synthetic polymers have backbones containing carbon, hydrogen, oxygen, and nitrogen. These macromolecules are lightweight, durable, and processible, and are gradually replacing long-established materials such as glass, metal, wood, and natural fibers because of their desirable properties.

The latest trends in polymer science show applications in electroluminescent displays, protective coatings, electronics, chemical sensors, and drug delivery systems.

1.2 An Overview of Inorganic Polymers

The incorporation of inorganic elements into the main chain of a

polymer adds enormous scope to the field of polymer chemistry.2, 3 Indeed,

inorganic polymers combine the molecular architecture of polymers with

advantageous attributes of inorganic elements. They display myriad

interesting and useful properties, including low-temperature flexibility,

thermal, radiative, and oxidative stability, flame retardancy, gas permeability, biocompatibility, novel chemical reactivity patterns, and electrical and electro-optical features.3 These properties are exemplified in

the well developed and commercialized polymers shown in Figure 1.1.

R R R Si O Si PN R R R n n n (a) polysiloxanes(b) polysilanes (c) polyphosphazenes

R Si Lx Fe R M n M = Fe, Ni, Rh, Pt n

(d) polymetallaynes (e) polyferrocenylsilanes

Figure 1.1 Examples of well developed inorganic polymers.

Polysiloxanes (Figure 1.1a), commonly referred to as silicones, are by

far the most widely used and commercially significant inorganic polymer.4, 5

They are synthesized by polycondensation or by anionic or cationic ring-

opening polymerization (ROP) of a cyclic trimer or tetramer. In comparison to typical organic polymers, polysiloxanes possess an exceptionally flexible

backbone even at low temperatures.2 This flexibility is explained by the long

Si–O bond (1.64 Å, compared to a C–C bond length of 1.54 Å) and the large

Si–O–Si bond angle (143°, compared to a C–C–C bond angle of 109°), as well as substituents present on alternating skeletal atoms. Moreover, polysiloxanes have higher thermal and oxidative stability than their organic counterparts as a result of the high Si–O bond strength (450 kJ/mol, compared to 350 kJ/mol for C–C). Additional properties of these polymers

include low surface energy, hydrophobicity, biocompatibility, and high oxygen

permeability. These properties, in conjunction with the very broad range of

operating temperatures, have led to a wide range of highly specialized

applications, such as low temperature seals and lubricants, rubber molds and

caulking, water repellants, bioimplants, and artificial skin and corneas.

Polysilanes (Figure 1.1b) represent another well developed polymer

based on silicon. They are structurally analogous to polyolefins, with

backbones consisting solely of a group 14 element. Unlike the carbon-based

polymer, the silicon congener exhibits interesting electronic and optical

properties as a result of the delocalization of σ-electrons.6 These properties

-1 include conductivities of up to 0.5 S cm upon doping with AsF5, and a σ→σ*

transition that decreases in energy with increasing chain length, up to 300 to

400 nm. Additionally, polysilanes can function as thermal precursors to

silicon carbide ceramics, and they are light- and radiation-sensitive, leading

to applications in microlithography and as polymerization initiators.2

Polysilanes are prepared by Wurtz coupling of an organodichlorosilane with sodium, transition metal-catalyzed dehydrogenative coupling, or ring opening polymerization of a cyclic tetramer.2

Polyphosphazenes (Figure 1.1c, Chapter 1.3.1) represent another

extensively studied polymer with significant commercial applications.7 The

backbone of polyphosphazenes consists of alternating phosphorus and

nitrogen atoms joined by formally unsaturated bonds. Similar to

polysiloxanes, the flexibility of the backbone is explained by long bond

lengths and wide bond angles, in addition to the presence of substituents on

alternating skeletal atoms. Polyphosphazenes are set apart from other

polymers by the way in which side groups are introduced. Whereas the

development of a new polymer typically involves the synthesis of a new

monomer, macromolecular diversity for polyphosphazenes is usually achieved

by carrying out substitution reactions on the pre-formed polymeric

intermediate (see Chapter 1.3.1).7 These substitution reactions allow for the

incorporation of a wide variety of organic groups at phosphorus. In turn,

these side chains dictate the physical and chemical properties of

polyphosphazenes, including fire resistance, flexibility, biomedical

compatibility, near-UV transparency, thermo-oxidative resistance to

homolytic bond cleavage, and stability to γ-radiation.

Polymetallaynes (Figure 1.1d) were first synthesized by copper- catalyzed coupling of a transition metal dihalide with a diacetylide.8, 9 Other

polycondensation routes have since been developed, which allow for the

incorporation of various transition metals into the backbone of the polymer,

including platinum,9, 10 iron,11 nickel,12 and rhodium.10 The rigid-rod

structure and the conjugated backbone have led to potential applications in

liquid crystals13 and electro-optical devices.14

Polyferrocenylsilanes (Figure 1.1e) consist of alternating ferrocene and

organosilane units, and are synthesized by thermal, anionic, transition

metal-catalyzed, or photolytic ring-opening polymerization of a

[1]silaferrocenophane monomer.3 Depending on the organic groups at silicon,

these polymers may be amorphous or semicrystalline with a wide range of

glass transition temperatures. Polyferrocenylsilanes are redox-active,

electrochromic, and semiconducting upon doping, due to the oxidation of

ferrocene units to ferrocenium moieties in the main chain.

Despite the above successes, the development of polymers based on

inorganic elements remains a challenge in polymer science, in contrast to

their well developed organic counterparts.2 This is due to limitations both in

the availability of suitable monomers and in the polymerization strategy

employed. For example, many organic polymers are synthesized by addition

polymerization of an olefin. The analogous route for an inorganic polymer is

difficult: the monomer must possess an element–element multiple bond that

6 is sufficiently inert to be isolated in pure form, yet adequately reactive to be polymerized. As a result, most inorganic polymers, including those shown in

Figure 1.1, are formed by a condensation or a ring-opening strategy; one noteworthy exception involves the research of Derek Gates and coworkers, who synthesized polymethylenephosphines (Chapter 1.3.3) by an addition polymerization strategy.15

1.3 Inorganic Polymers Containing Group 15 Elements

Pnictogens, or group 15 elements, include nitrogen, phosphorus, arsenic, antimony, and bismuth. Several polymers have been synthesized which contain pnictogens, in particular nitrogen and phosphorus, in the main chain.

Polyphosphazenes (Chapter 1.3.1) constitute the most widely used group 15-containing polymer, with applications as biomedical materials, solid battery electrolytes, fuel cell components, fire retardants, optical and electro- optical materials, and membranes.7 Nitrogen-containing polymers (Chapter

1.3.2) with amide linkages are found naturally as proteins and commercially in cables, adhesives, lining materials, and medical tubing.1 Intrinsically conductive polymers such as polypyrrole and polyaniline have commercial applications as sensing devices, electrochromic displays, corrosion inhibitors, and screen coatings.16 Polymers containing phosphorus(III) in the main chain (Chapter 1.3.3) have also attracted attention, due to the diagonal

relationship between carbon and phosphorus,17 with potential applications as

polymer supports18 and π-conjugated materials.19

1.3.1 Polyphosphazenes and Related Polymers

Polyphosphazenes are outlined in Chapter 1.2. A more detailed

account of the polymer is provided in this section, including its structure and

bonding, its polymerization and macromolecular substitution strategies, and

its related polymers.

The phosphorus–nitrogen bonds in polyphosphazenes are roughly

equal, indicating a delocalized P–N π-bonding which arises from

20 3dπ(P)-2pπ(N) overlap. However, this delocalization does not extend for the

entire length of the chain, as indicated by the clear and colourless nature of

the polymer, with no absorptions in the UV or visible range of the spectrum.

The general consensus regarding the bonding in polyphosphazenes is shown

in Figure 1.2. In this model, partial delocalization of electrons extends over a

three-atom “island”, interrupted by a node at each phosphorus center.7, 21

Upon rotation about a P–N bond, various 3d orbitals on phosphorus can interact with the 2p orbital on nitrogen. As a result, polyphosphazenes have a low torsional barrier.

The P–N bonds are fairly long (1.55 to 1.60 Å) compared to typical organic polymers, which places the side groups on phosphorus further apart.

The wide N–P–N and the P–N–P bond angles (ca. 119º and 130–160º, respectively) also allow for a larger separation of lone pairs of electrons on

nitrogen and side groups on phosphorus. This combination of structural parameters results in a highly flexible backbone for polyphosphazenes.

PNP N P N P N P

island of delocalization

Figure 1.2 Bonding in polyphosphazenes: 3dπ(P)–2pπ(N) overlap resulting in islands of electronic delocalization.7

As shown in Scheme 1.1, there are two synthetic routes towards

polyphosphazenes: (A) thermal ring-opening polymerization (ROP) of the

cyclic trimer and (B) polycondensation of a phosphoranimine monomer.

Polyphosphazenes synthesized via Route A typically have high molecular

weights (Mw ≥ 100,000) and broad polydispersities (PDI ≥ 2.0), whereas those

synthesized via Route B have lower molecular weights (Mw ~ 10,000) and

narrower polydispersities (PDI 1.04 to 1.20). Where R = Cl, both Route A22 and Route B23 are believed to occur by a cationic chain growth mechanism.

Route A Route B

R R P R R N N ROP condensation PN X PNSiMe3 R P P R - Me3SiX N R R R R n

Scheme 1.1 Synthesis of polyphosphazenes by (A) ring-opening polymerization; (B) polycondensation.

Although thermal ring-opening polymerization can be carried out for

cyclic trimers where R = alkyl, aryl, alkoxy, and aryloxy substituents,24 this

route is typically performed using hexachlorocyclotriphosphazene (R = Cl).7

The perhalogenated polymer [NPCl2]n can undergo macromolecular substitution (Scheme 1.2) with organic nucleophiles.7 This reaction is

facilitated by the high reactivity of P–Cl bonds as well as the flexibility of the

backbone (vide supra). A variety of nucleophiles can be used, including alkoxides and aryloxides, primary and secondary amines, and organometallic

reagents including organolithium, -magnesium, and -aluminum reagents.

These latter reagents may cause degradation of the polymer backbone. Thus,

the introduction of alkyl or aryl side groups is typically achieved by the

condensation pathway (Scheme 1.1B).

OR PN NaOR OR n -NaCl Cl NRR' RR'NH PN PN - HCl Cl NRR' n n RM - MCl R PN R n

Scheme 1.2 Macromolecular nucleophilic substitution of polydichloro- phosphazene.

Polycondensation of phosphoranimine monomers (Route B in Scheme

1.1) is achieved by elimination of an organosilane, Me3SiX, where X is a

halide, alkoxide, or aryloxide. This route is an effective way to obtain

polyphosphazenes with alkyl or aryl substituents at phosphorus, and can also

be used to synthesize polydihalophosphazenes, which can be further

functionalized by macromolecular substitution.

R' R R R' R R CNP N P N SNP N P N R R R R n n (a) polycarbophosphazenes (b) polythiophosphazenes

R' R R SNP N P N O R R n (c) polythionylphosphazenes

Figure 1.3 Polymers related to polyphosphazenes.

Polycarbophosphazenes (Figure 1.3a), polythiophosphazenes (Figure

1.3b) and polythionylphosphazenes (Figure 1.3c) are structural analogues of polyphosphazenes, in which every third phosphorus atom is replaced with a carbon, sulfur(IV) or sulfur(VI) center, respectively. Like polyphosphazenes,

these polymers are synthesized by thermal ring-opening polymerization of

cyclic trimers, and can undergo macromolecular substitution to replace the

chloride residues for other organic groups. These nucleophilic substitution reactions are regioselective, due to the different reactivity of C–Cl and S–Cl

11 bonds in comparison to P–Cl bonds.2 Thus, substituents can be introduced to the perchlorinated polymer in a stepwise fashion.25

Although polyphosphazenes remain the most widely used pnictogen- containing polymer, there are numerous examples of polymers with nitrogen- or phosphorus-based backbones, which will be discussed in the following two sections.

1.3.2 Polymers Containing Nitrogen

The most well developed polymers containing nitrogen in the backbone are shown in Figure 1.4. Polyamides (Figure 1.4a), polyimides (Figure 1.4b), and polyureas (Figure 1.4c) are all synthesized by a step-growth polycondensation process, and are commercially and/or biologically significant. For example, polyamides are better known to biological chemists as proteins and to materials scientists as Nylons, with applications in fibres, ropes, tents, tires, and garments. Polyimides are lightweight, flexible, and thermally and chemically resistant, with applications as flexible cables, high- temperature adhesives, photoresists, insulating films, and medical tubing.

Polyureas have been commercialized as lining materials due to their abrasion- and corrosion-resistance.

Polypyrrole (Figure 1.4d) and polyaniline (Figure 1.4e) are two examples of intrinsically conductive polymers, for which the 2000 Nobel Prize in Chemistry was awarded to Alan J. Heeger, Alan G. MacDiarmid, and

Hideki Shirakawa.26-28 These polymers have applications as sensing devices,

12 electrochromic displays, antistatic materials, corrosion inhibitors, and screen coatings.16

H H H H H N N N N N O O R R R1 R2 O O O O n n n (a) polyamides (b) polyimides (c) polyureas

H N N H n n

(d) polypyrrole (e) polyaniline

Figure 1.4 Polymers containing nitrogen.

Polypyrrole and polyaniline are synthesized either chemically or electrochemically, by an oxidation process.29 The first step involves the loss of one electron to give a radical cation. Various resonance structures of this radical cation can be drawn for pyrrole30 (Scheme 1.3) and aniline31 (Scheme

1.4). The mechanism of electropolymerization of pyrrole is still a matter of debate,30 but most likely involves coupling of radical cations.32 This is similar to the well established mechanism proposed for aniline.33-36 For pyrrole, the coupling reaction typically occurs between the α-positions of both pyrrole monomers (Scheme 1.3). For aniline, radical coupling occurs in a head-to-tail fashion, forming a new N–C bond between the nitrogen center of one monomer and the para-carbon atom of another (Scheme 1.4). Loss of two protons generates a neutral dimer, which can undergo the same sequence of

steps to generate an oligomeric chain. According to computations,37 each higher oligomer (n-mer) has a lower electrochemical potential, and is consequently more easily oxidized, than the corresponding (n–1)-mer, leading to propagation.

H H H H H H N N N N N - 2H+ N e- N N H H

Scheme 1.3 Initial steps in the polymerization of pyrrole.

H H H H N N

NH2 NH2 NH2 NH2 - 2H+ H e- H N H H N

Scheme 1.4 Initial steps in the polymerization of aniline.

Recently, Manners and coworkers reported a polyaminoborane,

n 38 [RNHBH2]n (R = H, Me, Bu). While Rh-catalyzed dehydrocoupling

reactions generated only cyclic dimers or trimers,39, 40 the related iridium-

catalyzed reactions resulted in polymers.38 The boron- and nitrogen-

containing polymers are direct analogues of polyolefins, and are the first well-

characterized and soluble examples of such polymers. They possess a high

degree of linearity in the chain, and a very high degree of polymerization

(1200 to 3000 repeat units), but copolymers were still soluble and able to be

14 characterized by multinuclear NMR spectroscopy, IR spectroscopy, GPC analysis and dynamic light scattering.

1.3.3 Polymers Containing Phosphorus(III)

E R' P Ph Ph Fe H H PB PC R' R H Mes Ph n n n (a)Polyferrocenyl- (b)Polyphosphino- (c) Polymethylene- phosphines boranes phosphines

R' C R' R' Ph P P P linker C linker P R4 R' Me Me R E n n n (d)Poly-p-phenylene- (e) Polyvinylene- (f) Polyphospholes phosphaalkene phosphines

R P n

(g) Polyarylphosphines (h) P16 macrocycle

Figure 1.5 Oligomers and polymers containing trivalent phosphorus.

Phosphorus-containing polymers are attracting attention because of their flame retardant properties, thermal and oxidative stability, and

potential uses as catalyst supports and π-conjugated materials.19, 41 While

P(V)-containing polymers, particularly polyphosphazenes and

polyheterophosphazenes (Chapter 1.3.1),7 are well developed and commercialized, P(III)-based polymers are considerably less studied.

Examples of such macromolecules are shown in Figure 1.5.

Polyferrocenylphosphines (Figure 1.5a) are synthesized by thermal,42 living anionic,43 or photolytic44 ring-opening polymerization. Living anionic

routes result in homopolymers with controllable chain lengths between 8 and

116 repeat units, or diblock43, 45, 46 or triblock47 copolymers, which can

coordinate via phosphorus to a transition metal such as palladium or iron.43

Manners and coworkers reported the dehydrocoupling of primary and

48, 49 secondary phosphine-BH3 adducts. For a secondary phosphine-borane, linear or cyclic oligomeric species are formed, whereas rhodium(I)-catalyzed

dehydrocoupling of a primary phosphine-borane allows for the formation of

poly(phosphinoborane)s (Figure 1.5b). Elegant mechanistic work on the

secondary phosphine-borane system indicates that the dehydrocoupling

occurs in a homogenous fashion.40, 50 Temperatures of 90 to 130 °C are

i 51 required to polymerize RPH2-BH3 (R = Bu, Ph); however, the phosphine- borane adduct with an electron-withdrawing substituent (R = p-CF3C6H4) undergoes the dehydrocoupling polymerization at a reduced temperature of

60 °C, attributed to the increased acidity of the P–H bond.52

A variety of polymers have been developed containing only phosphorus

and carbon in the backbone. The most well studied of these are

polymethylenephosphines (Figure 1.5c), synthesized by the addition

polymerization of phosphaalkenes under thermal,15 radical,15, 18 or living

anionic53, 54 conditions. Radical copolymerization with styrene generates

polymers which can coordinate palladium via the phosphorus centers in the

backbone, leading to applications in polymer-supported catalysis.18 Anionic

polymerization results in homopolymers with controlled chain lengths

between 20 and 100 repeat units, or block copolymers with styrene.53

Oligomeric π-conjugated poly-p-phenylenephosphaalkenes (Figure

1.5d) were developed independently by Gates and coworkers55, 56 and

Protasiewicz and coworkers.57, 58 These oligomers are synthesized by the

condensation of a bifunctional phosphine with a bis(acyl chloride)55, 56 or a bis(aldehyde), and have number-average degrees of polymerization of about 5 to 20. The π-conjugation in the backbone is indicated by UV/Vis55, 56 and fluorescence measurements.57, 58

Polyvinylenephosphines (Figure 1.5e) are synthesized by anionic ring-

opening polymerization of strained cyclic phosphirenes,59 or by AIBN-

catalyzed ring-collapsed radical alternating copolymerization of a terminal

60 alkyne with P5Me5. In both cases, the resultant polymer contains both cis- and trans-environments of the vinylphosphine. The anionic ROP route results in controlled number-average degrees of polymerization, between 10

and 110 repeat units, depending on the amount of anionic initiator. Radical

alternating copolymerization results in ca. 13 repeat units, and the polymer

displays an emission in the visible region of the spectrum, attributed to the

n→π* transition in the main chain. The ring-collapsed radical alternating

copolymerization strategy61 has also been used to prepare

polyvinylenearsines62 and -stibines.63

Although the parent polyphosphole is as yet unknown, a variety of strategies have been developed for the synthesis of polymers containing phospholes in the main chain (Figure 1.5f).64-70 These polymers exhibit interesting properties such as luminescence64 and π-conjugation,65, 67 and have potential applications in optical devices,68 chemical sensors,66 and solar

cells.70

One final strategy towards phosphorus(III)-containing oligomers or

polymers involves metal-catalyzed P–H bond activation,71 and is represented

by the macromolecules shown in Figures 1.5g and 1.5h. Palladium-catalyzed

cross coupling of primary phosphines and dihaloarenes results in

polyarylphosphines (Figure 1.5f),72 while group 4 metal-catalyzed

73, dehydrocoupling of P–H bonds generates the P16 macrocycle (Figure 1.5g).

Having examined various nitrogen- and phosphorus-containing

polymers, attention is now turned to the small molecule chemistry required

to develop suitable monomers.

1.4 Terminal Group 4 Metal Pnictidene Complexes

Group 4 metal imides and phosphinidenes were first synthesized only

two decades ago, but their importance in organic and inorganic synthesis and

catalysis has stimulated a great deal of research in this area.

1.4.1 Terminal Group 4 Metal Imide Chemistry

Transition metal imides have been reviewed extensively.75-77 For

group 4 transition metals,78, 79 the first terminal imido complexes were

prepared independently in 1988 by the groups of Bergman80 and

Wolczanski.81 Both groups reported that these compounds can induce C–H

bond activation via σ-bond metathesis. The synthesis and reactivity of these

Zr=N compounds is depicted in Schemes 1.5 and 1.6.

RHN R' RHN THF RHN N R Zr Zr NR Zr RHN NHR - R'H RHN RHN O

t R = Si Bu3

CH4

RHN NHR RHN NHR Zr Zr RHN CH3 RHN

t t Scheme 1.5 Generation, trapping, and reactivity of ( Bu3SiNH)2Zr=NSi Bu3.

Wolczanski and coworkers reported the zirconium imido compound shown in Scheme 1.5.81 This species is synthesized by an irreversible α-

abstraction of a hydrocarbon such as methane, benzene, cyclohexane, and

trapped in the presence of THF. The transient zirconium imide exhibits a

very high reactivity towards hydrocarbons: not only does this species

2 3 activate the sp C–H bonds of benzene, but also the sp C–H bonds of

methane.

R H N N R Cp Zr ZrCp Cp Zr 2 N 2 2 N R H R

H2NR

H R N R THF N Cp2Zr Cp2Zr NR Cp2Zr Me - CH4 O

R'C CR'' R" R N N NHR R' H Cp2Zr R' Cp2Zr

R'' R N Cp2Zr R' N R''

Scheme 1.6 Generation, trapping, and reactivity of [Cp2Zr=NR].

Bergman and coworkers reported the imidozirconocene compound

depicted in Scheme 1.6.80 This species is synthesized by α-abstraction of

either an amine or an alkane from the corresponding bis(amido)zirconocene

or alkylamidozirconocene. The Zr=N bond must be sterically protected in

order to suppress the formation of the dimeric species.82 For example, for

t sterically undemanding substituents (e.g. R = p- BuC6H4), thermolysis of

amidomethylzirconcene results in an irreversible formation of the

bis(μ-imido) dimeric product. However, the analogous reaction with sterically

t demanding groups (e.g. R = Bu, 2,6-Me2C6H3) allows for the trapping and isolation of the terminal imidozirconocene species as a THF adduct.

Imidozirconocene species can undergo a wide variety of transformations

(Scheme 1.6),82 including C–H bond activation of arenes and alkenes and insertion reactions with unsaturated organic substrates to generate aza- and diazametallacycles.

These zirconium- and nitrogen-containing metallacycles display interesting stoichiometric and catalytic reactivity. For example, the diazazirconacyclobutane is implicated in the catalytic process of imine metathesis,83-86 the nitrogen analogue of olefin metathesis. The related

azazirconacyclobutene plays a role in catalytic alkyne hydroamination (see

Chapter 1.5.1),87, 88 and undergoes insertion reactions at the Zr–C bond with

aldehydes89, 90 and imines90, 91 to generate six-membered metallacycles

(Scheme 1.7) which are implicated in catalytic alkyne carboamination.90, 91

Finally, azazirconacyclopentadienes participate in metallacycle transfer to a main group reagent to yield isothiazoles (Scheme 1.8).92

R R O 1 2 N Cp Zr R R4 2 3 R1 O N R4 Cp2Zr R2

R1 R2 R R5 3 N N Cp2Zr R3 R4 N R5 R4

Scheme 1.7 Reactivity of azazirconacyclobutenes.

N R1 N R1 S2Cl2 Cp2Zr S

R2 R2 R3 R3

Scheme 1.8 Reactivity of azazirconacyclopentadienes.

Titanium imido chemistry emerged shortly after the first zirconium

imido species were reported. Since the first structurally characterized

terminal titanium imide reported in 1990,93 imidotitanium complexes have

been used stoichiometrically and catalytically in various transformations.

These transformations include C–H bond activation,94-96 olefin

polymerization,97 alkyne iminoamination,98, 99 alkyne carboamination,100, 101 and alkyne or allene hydroamination,102-104 and other reactions with

unsaturated organic molecules.105-107

1.4.2 Terminal Group 4 Metal Phosphinidene Chemistry

Terminal phosphinidenes complexes are known for p-, d-, and f-block

elements, with the majority of research efforts devoted to transition metal

phosphinidenes.108-112 These species are readily characterized by their 31P

chemical shifts, which are in turn influenced by the geometry of the

complex.112 A bent geometry at phosphorus gives rise to a highly deshielded

environment (+650 to +800 ppm), while a linear coordination mode results in

a chemical shift of +150 to +250 ppm. Like the related imide chemistry,

group 4 metal phosphinidene chemistry was first realized for zirconium;113 only recently have titanium phosphinidene species been synthesized and characterized.114

Zirconium-phosphorus chemistry is highly sensitive to reaction

conditions and steric demands.113, 115, 116 To date, very few zirconium

phosphinidenes have been isolated and characterized, all of which contain a

great deal of steric bulk surrounding the phosphorus atom.117-119 Other

zirconium phosphinidenes, notably those which possess less sterically

hindered substituents on phosphorus, have been detected spectroscopically in

solution117, 120, 121 or were proposed as intermediates on the basis of further reactivity117, 122 (Figure 1.6).

(a) Zirconium phosphinidenes, isolated and characterized tBu tBu tBu Mes tBu Cp t Cp P Bu Cp P Mes Zr P tBu Zr Zr Cp PMe3 K(THF) Cp PMe3 Cp H 2 δ = 792.4, -12.0 ppm; 2 δ = 771.0 ppm, -6.7 ppm; JP-P = 23 Hz δ = 565.5 ppm JP-P = 23 Hz

(b) Zirconium phosphinidenes detected in solution Me Me Mes Me Me Cp P Mes Cp Cp* Zr P Me P Me Cp Li Zr Zr H P Li(DME) Cp PMe3 Cp* Cl Mes Mes

δ = 766.1, -2.3 ppm; δ = 537.6 ppm JP-P = 24 Hz δ = 496, -103 ppm

(c) Zirconium phosphinidenes proposed based on further reactivity H Cp* P tBu Zr Cp* tBu Cp* Cp HP tBu Mes Zr P Cp* Zr P tBu P t Cp* Zr Cp Bu P Cp* Mes

Ph Ph Cp* Ph Cp* Cp* P P Zr P Zr Zr P Ph P P Cp* Cp* Cp* Ph Ph

Figure 1.6 Zirconium phosphinidene species which have been (a) isolated, (b) detected in solution, or (c) proposed as intermediates on the basis of further reactivity (byproducts are not shown); Cp* = C5Me5, Mes = 2,4,6- trimethylphenyl.

The reactivity of zirconium phosphinidenes has been well

documented.116 This reactivity includes phosphinidene transfer to organic and other group 14 reagents,123 1,2-additions of polar substrates across the

Zr=P double bond,123 and [2+2] cycloaddition with alkynes.124 This last

reaction generates the phosphazirconacyclobutene Cp2Zr(PMes*)C(R)=C(Ph)

(Mes* = 2,4,6-tri-tert-butylphenyl), and occurs either directly from the

124 transient zirconium phosphinidene or from its PMe3 adduct (Scheme 1.9).

Li H P Mes* Cp t t Cp Cl Bu Bu P Zr + Zr H Me Me Cp Cp

tBu - CH4

Mes* P Mes* Cp RC CPh Cp Mes* PMe3 Cp Zr R P Cp Zr P Zr Cp - PMe3 Cp PMe3 Ph R = Ph, Me, H

Scheme 1.9 Generation and trapping of a zirconium phosphinidene; Mes* = 2,4,6-tri-tert-butylphenyl.

Like zirconium phosphinidene chemistry, the above zirconium- phosphorus metallacycle chemistry is also very sensitive to steric demands.

For example, the reaction between Cp2ZrMeCl and the less sterically

encumbered LiPHMes in the presence of diphenylacetylene does not give the

anticipated phosphazirconacyclobutene Cp2Zr(PMes)C(Ph)=C(Ph), but rather

a diphosphazirconacyclopentene Cp2Zr(PMes)(PMes)C(Ph)=C(Ph) as a minor

product, with several other unidentified byproducts (Scheme 1.10).124 The

mechanism of formation of this minor product is unclear, but may involve the

generation of a diphosphametallacyclopropane [Cp2Zr(PMes)2], which is

trapped through insertion of diphenylacetylene. Although the desired [2+2]

cycloaddition product, Cp2Zr(PMes)C(Ph)=C(Ph), cannot be synthesized by

this direct method, it can be prepared by an entirely different route, involving the reaction of (Cp2ZrCl)2(μ-PMes) with Li2PMes in the presence of

diphenylacetylene (Scheme 1.10).124

Li H Li Li P P Mes Mes Cp Cl PhC CPh Cp P PhC CPh Cp P Cp Zr + Zr Ph + Zr Zr Me Cp Cp Cp Cp Cl Cl Ph

Mes Mes Cp Mes P PhC CPh Cp P P Zr Zr + unidentified products P Cp Cp Mes Ph Ph minor product

Scheme 1.10 Synthetic routes to phospha- and diphosphazirconacycles.

The reactivity of phosphazirconacyclobutenes has also been documented (Scheme 1.11).116 This reactivity includes metallacycle transfer

to various main group reagents such as phosphorus and boron125 and ring

expansion of the phosphazirconacyclobutene with unsaturated organic

substrates to give five-, six-, and seven-membered metallacycles.124, 126

tBu

Mes* Mes* t P P Bu Ph P Ph Ph B Ph PH BH Ph Ph Ph Ph PhPCl2 PhBCl2 - Cp2ZrCl2 - Cp2ZrCl2

O Mes* t-Bu O Ph N Mes* Ph P C N tBu C P Cp Zr Cp Zr Ph Cp Zr 2 P 2 2 Mes* Ph Ph Ph Ph Ph O NCPh R1 R2

R1 Ph R O C 2 N C Cp2Zr P Mes* Cp2Zr P Mes* Ph Ph Ph Ph

Scheme 1.11 Phosphazirconacyclobutene reactivity.

Mindiola and coworkers recently reported the titanium phosphinidene

t species (nacnac)Ti(=PMes*)(CH2 Bu) (nacnac = CH[C(Me)N(Ar)]2, Ar = 2,6-

diisopropylphenyl), synthesized by transmetallation of LiPHMes* with a

titanium alkylidene, followed by rapid α-H-migration to give the Ti=P

multiple bond (Scheme 1.12).127 The titanium phosphinidene was

characterized by X-ray crystallography and by 31P NMR spectroscopy. The

31P NMR spectrum revealed two resonances at 216 and 242 ppm, which may correspond to two isomers which result from deviation of the Ti=PMes* fragment above and below the plane formed by the nacnac ligand.

Ar H Ar H Ar N tBu LiPHMes* N tBu α-migration N tBu Ti Ti Ti - LiOTf N OTf N PHMes* N P Mes* Ar Ar Ar i Ar = 2,6- Pr2C6H3

LiPHR

Ar R tBu N tBu P tBu P Ti Ti N N Et O Ti N P R N Ar 2 ArN Ar Ar Ar OEt2

i R = Cy or 2,4,6- Pr3C6H2

Scheme 1.12 Synthesis of a terminal titanium phosphinidene.

The thermal instability of the titanium phosphinidene precluded further investigations. However, low-temperature reactions with unsaturated organic substrates results in insertion into the Ti–P bond.128

Like the related Zr=P species, titanium phosphinidene chemistry also appears to be sensitive to steric demands. For example, reducing the steric encumbrance at phosphorus to cyclohexyl or 2,4,6-triisopropylphenyl does not allow for isolation of the phosphinidene, instead resulting in a series of intramolecular transformations to give a titanium complex with amidophosphine ligand (Scheme 1.12).127

Using an analogous transmetallation/α-H-migration strategy with a

pincer PNP ligand system, a more stable titanium phosphinidene was

isolated and structurally characterized (Figure 1.7).129 This Ti=P species

exhibits three doublets of doublets in the 31P NMR spectrum, with the peak

at 237 ppm attributed to the phosphinidene. Another titanium

phosphinidene species with cyclopentadienyl and phosphinimide ancillary

ligands was spectroscopically characterized.74 The 31P NMR spectrum also

revealed three resonances, with the peak at 769.9 ppm assigned to the

terminal phosphinidene moiety. This Ti=P species is implicated in P–H and

C–H bond activation reactions.

PiPr 2 Mes* Ar Cp P P N Ti t Ti CH2 Bu N PMe3 i tBu P P Pr2 3

Figure 1.7 Isolated and characterized titanium phosphinidene species.

1.5 Element–Hydrogen Bond Addition across Unsaturated Substrates

The addition of E–H bonds (E = B, Al, Si, N, P, O, S, and Zr) across

unsaturated organic moieties (C=C, C≡C, C=X, and C≡X bonds) represents an

atom-economical methodology towards introducing heteroatoms and often

chirality into a molecule (Scheme 1.13).130

catalyst RnE H H ERn or RnEH + CX CX CX

catalyst RnEH HERn or RnEH + CX CX CX

Scheme 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.

While the direct reaction can be plagued by a high activation energy

barrier, a catalyzed reaction can generate the desired product efficiently and

sometimes chemo-, regio- enantio-, and/or diastereoselectively.130 These

catalytic reactions have applications in asymmetric synthesis and the

preparation of biologically active molecules.

1.5.1 Hydroamination

Much research is currently being conducted on the hydroamination of carbon-carbon multiple bonds.131-137 In the past two decades, just over 1000

references relating to hydroamination have been published,138 more than half

of which have appeared within the last five years.

The direct reaction of ethylene and ammonia is thermodynamically

favourable (ΔG° = -14.7 kJ mol-1, ΔH° = -52.7 kJ mol-1, ΔS° =

-127.3 J mol-1 K-1).139 While experimental thermodynamic data are not

available for the reaction of acetylene and ammonia, semiempirical

computations estimate this reaction to be more exothermic by 63 kJ mol-1 compared to that of ethylene and ammonia.140 Despite the thermodynamic

feasibility, there is a high activation energy barrier due to electrostatic

repulsion of the lone pair of electrons on the amine and electron-rich alkene

or alkyne functionality. Moreover, this high activation energy barrier cannot

be overcome simply by raising the temperature, due to the large negative

entropy value. Consequently, there is a need for catalytic hydroamination.

A variety of hetero- and homogeneous catalysts have been reported to

carry out hydroamination.137, 139, 141 These catalysts include acids137, 142 and bases,137, 143 heavier group 2 complexes,144-148 lanthanides and actinides,134 several group 4 metal species,131-133, 135, 136 other early transition metals such

as vanadium149 and tantalum,150 late transition metals (Ru, Rh, Pd, Pt, Ag,

and Au),139, 141 and heavy metals including mercury and thallium.139

Most early transition metal and f-block element-catalyzed

hydroamination reactions are believed to occur by one of two mechanisms:

(1) [2+2] cycloaddition of the unsaturated organic substrate with a M=N

double bond (Scheme 1.14); (2) σ-bond insertion of an unsaturated organic

substrate into a M–N single bond (Scheme 1.15).

The first pathway was mentioned in Chapter 1.4.1 as one of the

applications of the catalytic applications of group 4 metal-imide species.

Bergman and coworkers have proposed a catalytic cycle for this

transformation,87, 88, 151 which is the most widely accepted mechanism for the

group 4 metal catalyzed inter- and intramolecular hydroamination of alkynes

and allenes.131-133, 135, 136, 152 In the proposed pathway (Scheme 1.14), the group 4 metal imide species reacts with an alkyne in a [2+2] cycloaddition fashion to afford the azametallacyclobutene. Reaction of this species with an incoming amine generates an (amido)(enamido)metal compound. Release of the enamine then regenerates the active catalytic species.

NHR [M] NHR

H NR 2 R' CCR' [M] N R R N H NHR [M] R'

R' R' R'

R R R' N N [M] R' R' [M] NHR H R'

H2NR

Scheme 1.14 Hydroamination of an alkyne using a group 4 catalyst ([M] = X2Ti or X2Zr) via a [2+2] cycloaddition pathway.

The second pathway, based on detailed mechanistic studies by Marks

et al.,153 is typical for lanthanide-catalyzed hydroamination cyclization of

aminoalkenes and -alkynes (Scheme 1.15).134 The metal amide active

catalyst, formed by metathesis, reacts in an intramolecular fashion with the

pendant alkene or alkyne. This step is turnover-limiting, with a postulated

four-membered transition state, to achieve an organometallic complex.

Reaction of this organometallic species with an additional equivalent of

amine results in release of the enamine and regeneration of the active metal

amide catalyst.

R" R' N n + [M] X H R R HX R'

R" [M] N n H N R" R R

R' R R n R R" R N [M] R" R' n N n H R R R' R" N R [M] n R R'

Scheme 1.15 Hydroamination cyclization of an aminoalkene or aminoalkyne using a lanthanide catalyst ([M] = X2Ln, Ln = lanthanide) via a σ-bond insertion pathway.

1.5.2 Hydrophosphination

The addition of a P–H bond across an unsaturated organic molecule is

a powerful tool for the synthesis of phosphorus-containing compounds,154-156 and is sometimes possible without the use of a catalyst.156 However, the

presence of a catalyst offers improvements in the rate, selectivity, and

stereocontrol. It should be noted that this reactivity has been studied in

greater detail for P(V) than for P(III).156 Indeed, hydrophosphination, which

refers specifically to P(III) substrates, is often limited to activated

unsaturated organic molecules, and the reaction mixture typically contains

various byproducts.156 Nonetheless, within the last decade, a variety of

catalysts have been reported to carry out the hydrophosphination reaction.

These catalysts include complexes of lanthanides,157 heavier group 2

elements,158, 159 and late transition metals such as Co,160 Rh,161 Ni,162-164

Pd,164-167 and Cu.168, 169 The reaction can also be carried out in the presence of

radical initiators,170-173 bases,169, 172, 174 and microwave irradiation.166, 175

R P + [M] X H n

[M] P R n P R

n R P n [M] R P H n R P [M] n

Scheme 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).

For the most part, the mechanism of hydrophosphination is not well

understood. One notable exception involves the intramolecular lanthanide-

mediated hydrophosphination cyclization of primary and secondary

phosphinoalkenes and phosphinoalkynes (Scheme 1.16).157, 176 The catalytic

cycle is very similar to that proposed for hydroamination cyclization. The active phosphidolanthanide catalyst is generated by protonolysis of the lanthanide alkyl or amide precursor. The next step, which is turnover-

limiting, involves the insertion of the C=C or C≡C multiple bond into the Ln–

P bond to generate the Ln–C species. Rapid protonolysis gives the

phosphorus-containing heterocycle and regenerates the active catalytic

species.

1.5.3 Element–Hydrogen Bond Addition across Unsaturated Substrates as a Route to Inorganic Polymers

The addition of an E–H bond across an unsaturated organic substrate has been used as a strategy towards oligomers and polymers containing heteroatoms such as boron,177-179 aluminum,180 silicon,181, 182 and

phosphorus(V).183

The hydroboration polymerization strategy was developed by Chujo

and coworkers (Scheme 1.17).177-179 Oligomers containing cyclodiborazane

178 B2N2 moieties in the backbone are prepared by a hydroboration reaction

between a primary borane and a dicyano compound.184-189 An analogous

strategy furnishes an organoaluminum polymer with a four-membered Al2N2 ring in the main chain.180 The boron-containing polymers exhibit modest

degrees of polymerization (5 to 20 repeat units, by GPC relative to

polystyrene), and interesting properties, including π-conjugation and

luminescence.189, 190 Other boron-containing polymers are synthesized by hydroboration of carbon–carbon multiple bonds. For example, the reaction of

a primary borane with a bisallene191 or a diene192-194 leads to oligomers or

polymers with ca. 5 to 25 repeat units, and B–C bonds in the backbone. The

related reaction with a diyne195, 196 leads to π-conjugated fluorescent

polymers. Finally, reacting BH3 with an olefin bearing a pendant amine or

pyridine group results in a polymeric material containing C–B covalent bonds

and N→B coordination bonds.197

H R R B R"2 R' N N N B B N R' N R' NR"2 R' R H H n n R B H H

. R' . R'

R' R R' B B R R' n n R B R' n

Scheme 1.17 Hydroboration polymerization.

Hydrosilylation polymerization has been described by Rickle181 and by

Itsuno et al.182 In the former report, a hydrosilylation reaction occurs between a dihydrosilane and a terminal bisalkene or -alkyne.181 In order to

achieve a maximal degree of polymerization, an exact 1 : 1 stoichiometry is

required according to the Carothers equation (vide infra). In practice, this is

difficult to achieve, so a small amount of trifunctional trisalkene is added to

ensure high molecular weight polymer. With this strategy, degrees of

polymerization of approximately 100 are obtained. In the latter report, the

authors utilize a bifunctional monomer containing both the vinyl and the

tertiary silane groups.182 Degrees of polymerization were found to be ca. 10

to 40, as measured by end group analysis in the 1H NMR spectrum, GPC, and

vapour pressure osmometry.

A hydrophosphorylation strategy was used to prepare P(V)-containing

polymers by reaction of a bisphosphoroyl compound with a diyne (Scheme

1.18). The P–H bond addition is regio- and stereoselective, depending on the

metal catalyst: catalytic RhBr(PPh3)3 gives the trans-vinylidene product,

while Ni(PPhMe2)4 and PdMe2(PPhMe2)2 catalysts result in the gem-

vinylidene polymer. Degrees of polymerization of 40 to 110 are obtained,

with polydispersity indices in the range 1.21–2.43.

O O PArP R R Ph Ph + cat. [M] n O O O O H PArP H PArP R Ph Ph Ph Ph n

Scheme 1.18 Phosphorus(V)-containing polymers via hydrophosphorylation.

One final species is worthy of mention, although very low degrees of

polymerization were reported. In studying the polymerization of substituted

styrenes, Hamaya noticed that two different polymers are obtained from a

para-aminostyrene monomer under different reaction conditions (Scheme

1.19).142, 198 Radical polymerization resulted in the polyolefin, while acid-

37 catalyzed conditions resulted in hydroamination dimers, trimers, tetramers, and pentamers.

AIBN

NH2 CF3COOH n

NH2 NH2 NH n-1

Scheme 1.19 Nitrogen-containing polymers or oligomers via olefin polymerization or hydroamination.

1.6 Research Objectives

The chemistry of group 4-imides and -phosphinidenes, as well as that of hydroamination and hydrophosphination all have one thing in common: reactivity with unsaturated organic molecules such as alkynes. In this

Thesis, this reactivity is exploited for the synthesis of new nitrogen- and phosphorus-containing polymers.

1+ r DP = (Eq 1) n 1+ r − 2rp

In order to achieve a maximal degree of polymerization via a step- growth process, precise control of the stoichiometry is required. This dependence is illustrated by the Carothers equation (Eq 1), where even if the extent of the reaction (p) is high, the number-average degree of

polymerization (DPn) is dramatically reduced when the stoichiometric ratio

(r) deviates from unity.

Therefore, a bifunctional monomer was targeted which contains both

an amine or phosphine moiety (–EH2, E = N or P) and a pendant alkyne fragment (e.g. –C≡CPh). These two functional groups are substituted about a central arene ring in a para-fashion. This geometry would preclude an intramolecular reaction, favouring instead the intermolecular reaction to form oligomers or polymers.

Cp2 Zr E C ion dit C ad clo R2 Ph Cy n 2] [2+

H Hydroamination or Hydrophosphination H C C E R2 E C H R2 C O H xid n at ion H C C N

Scheme 1.20 Proposed routes to nitrogen- or phosphorus-containing polymers.

Stoichiometric reactivity with zirconocene species is expected to provide a [2+2] cycloaddition polymer containing both zirconium and a pnictogen, while catalytic hydroamination or hydrophosphination should

39 furnish pnictogen-containing polymers. One final strategy involves an oxidative polymerization in direct analogy to polyaniline. These proposed polymerization routes are summarized in Scheme 1.20.

With these pnictogen-containing polymers in mind, the objectives of this Ph.D. work are the following:

(1) To synthesize and characterize amines and phosphines bearing

pendant alkynes (Chapters 2 and 4, respectively).

(2) To examine [2+2] cycloaddition polymerization as a route to new

zirconium- and pnictogen-containing polymers (Chapters 3 and 5).

(3) To investigate hydroamination and hydrophosphination strategies

towards new nitrogen- or phosphorus-containing polymers (Chapters

3 and 5, respectively).

(4) To prepare new polyaniline derivatives with an extended para-

phenylethynyl backbone (Chapter 3).

All syntheses and characterization were performed by the candidate, with the following exceptions. Gregory L. Gibson (a summer student working under the candidate’s guidance) helped in the synthesis of compounds 24a and 24b, and the initial polymerization studies to generate 25a and 25b. Dr.

Richard Jagt (group of Professor Mark Nitz, University of Toronto) instructed the candidate on the use of the MALDI-TOF instrument. Dr. Kevin J. T.

Noonan (group of Professor Derek Gates, University of British Columbia) performed triple-detection GPC measurements on polymers 5 and 25a.

Jeffrey McDowell (group of Professor Geoffrey Ozin, University of Toronto) performed EDX measurements on polymers 25a, 25b, 26a, and 26b.

Portions of these chapters have been published: Greenberg, S.; Gibson,

G. L.; Stephan, D. W., Chem. Commun. 2008, 304-306; Greenberg, S.;

Stephan, D. W., Inorg. Chem. 2009, 48, 8623-8631.

Chapter 2 Amines Bearing Pendant Alkyne Substituents

2.1 Abstract

A series of primary amines of the form H2NC6H2R2C≡CR’, 1 (a R = H,

n R’ = Ph; b R = H, R’ = SiMe3; c R = H, R’ = Bu; d R = H, R’ = p-C6H4Me; e R = i i i n i Pr, R’ = Ph; f R = Pr, R’ = SiMe3; g R = Pr, R’ = Bu; h R = Pr, R’ = p-

n C6H4Me) is reported. Lithiation with BuLi generates the lithium amides

LiNHC6H2R2C≡CR’ (2a to 2h). Reaction of compounds 2 with Cp2ZrMeCl or

Cp2Zr(CH2CH2CMe3)Cl yields compounds 3 Cp2ZrMe(NHC6H2R2C≡CR’) or 4

Cp2Zr(CH2CH2CMe3)(NHC6H2R2C≡CR’), respectively. Characterization is achieved by multinuclear NMR spectroscopy, IR spectroscopy, high-resolution mass spectrometry, elemental analysis, and X-ray crystallography.

2.2 Introduction

Chapters 1.3.2 and 1.4.1 describe the synthesis and utility of polyaniline and of group 4 imido compounds, respectively. Our goal is to explore the rich chemistry of these compounds in order to access new polymeric systems. These results are presented in Chapter 3. Prior to accessing new macromolecules, however, the small molecule chemistry of the monomeric species must first be developed. Thus, in this Chapter, a series of

42 primary amines bearing pendant alkynes will be described, and their reactivity with zirconocene sources to give amidozirconocene complexes will be presented.

2.3 Results and Discussion

2.3.1 Synthesis of Amines Bearing Pendant Alkynes

Sonogashira coupling of an aryl iodide and a terminal alkyne199-201

(Scheme 2.1) affords compounds 1, H2NC6H2R2C≡CR’ (a R = H, R’ = Ph; b R =

n i H, R’ = SiMe3; c R = H, R’ = Bu; d R = H, R’ = p-C6H4Me; e R = Pr, R’ = Ph; f

i i n i R = Pr, R’ = SiMe3; g R = Pr, R’ = Bu; h R = Pr, R’ = p-C6H4Me). Compound

1a has been previously synthesized and characterized.202 Some other amine- alkynes (1b, 1c, 1d) have been reported and/or utilized,203-206 but characterization data are sparse. Thus, all of compounds 1 were fully characterized by multinuclear NMR and IR spectroscopy, mass spectrometry, and, where possible, elemental analysis and X-ray crystallography.

NH2 NH2 1.15 equiv. 1 mol % trans-Pd(PPh3)2Cl2 R R H R R 1 mol % CuI + o NEt3, 18 h, 25 C I R' R' 1

Scheme 2.1 Synthesis of compounds 1 (a R = H, R’ = Ph; b R = H, R’ = SiMe3; n i i c R = H, R’ = Bu; d R = H, R’ = p-C6H4Me; e R = Pr, R’ = Ph; f R = Pr, R’ = i n i SiMe3; g R = Pr, R’ = Bu; h R = Pr, R’ = p-C6H4Me).

Table 2.1 Selected spectroscopic data for compounds 1. IR stretch (cm-1) 1H NMR (ppm) 13C{1H} NMR (ppm) cmpd N–H C≡C NH2 m-C6H2R2 o-C6H4 CN C≡C 1a 3475, 3380 2211 2.73 7.40 6.11 147.4 91.3, 88.1 1b 3480, 3380 2145 2.69 7.38 6.02 147.5 107.3, 91.3 1c 3457, 3372 2224 2.74 7.38 6.14 146.8 88.1, 82.2 1d 3467, 3379 2209 2.73 7.44 6.13 147.3 90.6, 88.2 1e 3494, 3410 2200 3.27 7.51 - 141.8 92.8, 88.0 1f 3494, 3410 2140 3.23 7.41 - 141.6 108.5, 90.8 1g 3491, 3406 2224 3.20 7.44 - 140.9 87.5, 83.3 1h 3489, 3409 2204 3.27 7.52 - 141.3 92.0. 87.8

Spectroscopic data confirm the formulation of compounds 1 (Table 2.1).

For example, IR spectra of compounds 1 show two N–H bands at ca. 3480 and

3400 cm-1 (asymmetrical and symmetrical stretching modes, respectively),207 as well as a C≡C stretch at ca. 2200 cm-1. In the 1H NMR spectra of compounds 1a to 1d, the NH2 signal is observed at ca. 2.7 ppm; compounds

1e to 1h, which possess ortho-isopropyl groups, show a noticeable downfield shift in this signal to ca. 3.2 ppm. The same downfield shift by approximately

0.4 to 0.5 ppm is observed for the NH2 protons of other arylamines such as aniline and 2,6-diisopropylaniline (2.79 and 3.19 ppm) and 4-iodoaniline and

2,6-diisopropyl-4-iodoaniline (2.57 ppm and 3.05 ppm), where all NMR shifts

13 1 are reported in C6D6. The opposite trend is observed in the C{ H} NMR for the ipso-C–N carbon atom: this carbon center resonates further downfield in aniline derivatives 1a to 1d compared to 2,6-diisopropylaniline derivatives 1e to 1h.

The alkyne carbon atoms are located in a diagnostic region of the

13C{1H} NMR spectrum, from 80 to 95 ppm, with the exception of those alkynes possessing trimethylsilyl substituents, namely 1b and 1f. For these compounds, the carbon atom beta to silicon is deshielded by ca. 20 ppm compared to other alkyne carbon resonances. This is explained by invoking a significant ground state contribution from resonance form II for compound 1b

(Figure 2.1).208, 209

NH2 NH2

Cβ Cβ

Cα Cα

SiMe3 SiMe3

III

Figure 2.1 Resonance contributors of compound 1b.

Few primary amines bearing pendant alkyne substituents have been characterized by X-ray crystallography;210, 211 the molecular structures of compounds 1a, 1d, and 1h were thus determined (Figure 2.2, Table 2.2). For compound 1a, the most chemically reasonable model is obtained when C1 is constrained to be isotropic and the arene ring containing C1 is modeled as benzene. Compound 1d shows an end-to-end disorder with respect to the p-

CH3 and NH2 groups, thereby creating a pseudo center of symmetry in the molecule. Consequently, the N1–C1 bond distances in compounds 1a and 1d should not be taken as exact values. Compound 1h crystallizes with four

45 molecules in the asymmetric unit, with slight deviations in metrical parameters that are not statistically different from one another; average bond lengths and angles are given for 1h.

1a 1d 1h

Figure 2.2 Molecular structure representation of compounds 1a, 1d, and 1h (ellipsoids drawn at the 50 % probability level). All hydrogen atoms have been omitted for clarity. Selected bond lengths (Å) and angles (°) are given in Table 2.2.

In the alkyne fragment of 1a, 1d, and 1h, the bond distances and angles are indicative of a triple bond, and fall within the range typical of diphenylacetylene derivatives.212, 213 The N1–C1 distances in 1h (1.376(5) to

1.400(4) Å) are similar to those reported for H2NC6H4-p-(C≡C)n-p-C6H4NO2,

214 t 215 (1.368(9) to 1.384(5) Å), o-(H2N)2C6(C≡C Bu)4 (1.400(7), 1.413(7) Å), and

46 aniline (1.402(2) Å, determined by microwave spectroscopy).216 In general, arylamines have substantially shorter N–C bond distances than alkylamines

(ca. 1.40 versus 1.45 Å)210, 211 which is ascribed to a certain degree of double bond character.216

Table 2.2 Selected bond lengths (Å) and angles (°) for 1a, 1d, and 1h. 1a 1d 1ha N1–C1 1.352 1.46(2) 1.389(8) C1–C2, C1–C6 1.390 1.398(6) 1.41(1) C2–C3, C5–C6 1.390 1.378(6) 1.39(1) C3–C4, C4–C5 1.390 1.402(6) 1.40(1) C4–C7 1.440(7) 1.432(6) 1.44(1) C7–C8 1.207(8) 1.203(8) 1.197(9) C8–C9 1.426(9) 1.432(6) 1.44(1) C9–C10, C9–C14 1.38(1) 1.404(6) 1.39(1) C10–C11, C13–C14 1.38(1) 1.386(6) 1.39(1) C11–C12, C12–C13 1.38(1) 1.402(6) 1.39(1) C4–C7–C8 178.3(5) 178.7(6) 177.9(8) C7–C8–C9 178.2(6) 178.7(6) 176.2(8) b ∠out-of-plane 5.6 to 35.6 Σ ∠ at N 344.7 to 359.7 a Data are averaged over four molecules, except for the out-of-plane angle and the sum of angles at nitrogen. The estimated error is given by the square root of the sum of the squares of each error. b The out-of-plane angle at N is defined as the angle between the NH2 plane and the C6H5N plane.

The degree of double bond character is described not only by bond lengths, but also by the sum of the angles about N and the out-of-plane angle at N. These angles give an indication of the planarity at N, where the N atom approaches planarity if the sum of the angles about N approaches 360° and the out-of-plane angle approaches 0°. The H atoms were not located or refined for compounds 1a or 1d due to disorder issues. However, in compound 1h, the hydrogen atoms on nitrogen were located and refined for

47 the four molecules in the asymmetric unit. The sum of the angles about nitrogen ranges from 344.7 to 359.7°, while the out-of-plane angle ranges from 5.6 to 35.6°; in comparison, the out-of-plane angle in aniline is 37.5°.216

Therefore, compounds 1 likely possess a similar or slightly greater degree of

C=N double bond character than aniline, which can be rationalized by the electron donating effect of the amino substitutent.217 This effect is depicted in Figure 2.3 for the resonance contributors of aniline and 1a.

NH2 NH2 NH2 NH2

I II III IV

NH2 NH2 NH2 NH2 NH2 NH2 NH2 NH2

C C C C C C C C C C C C C C C C

I II III IV V VI VII VIII

Figure 2.3 Resonance contributors for aniline (above) and compound 1a (below).

Canonical structures (I) of aniline and compound 1a imply a pyramidal nitrogen center, while the various resonance contributors of aniline (II to IV) and compound 1a (II to VIII) imply shortened N–C bond lengths, increased planarity at nitrogen, a distortion of the aromatic rings, and cumulene

48 character in the linking fragment. Some of these features are observed in the molecular structure of compound 1h. For example, the N–C bond length is shorter than a typical alkylamine and the N atom approaches planarity.

However, distortions in the aniline-containing aromatic ring are not statistically significant when averaged over four molecules. In addition, cumulene character is not evident in the linking fragment, which clearly consists of a triple bond flanked by two single bonds, as determined by bond lengths. The nature of these molecules will be examined further in the following section with the use of computations.

2.3.2 A Computational Study of Compound 1a

In order to assess the electronic structure of compound 1a, density functional theory (DFT) studies were carried out at the B3LYP/6-31G(d) level of theory. The crystal structure of 1a served as an initial prediction for the optimized structure 1aopt, which in turn served as a starting point for the

+• structure of the radical cation 1a opt. (This latter calculation will relate to nitrogen-containing oligomer 15 described in Chapter 3.3.4.) A comparison of

+• bond lengths and angles for aniline, 1h, 1aopt and 1a opt is given in Table 2.3, with reference to the microwave structure determined for aniline,216 and the

218 semi-empirical (SE) calculations performed for 1aopt by Rosseto et al.

Although 1h is not the best analogue for 1a, it was chosen for comparison purposes because there is no disorder in the crystallographic model. The numbering scheme is shown in Figure 2.4, bond distances and angles are

49 given in Table 2.3, computed dipole moments are illustrated in Figure 2.6, the highest occupied molecular orbitals (HOMOs) of anilineopt and 1aopt are

+• +• depicted in Figure 2.7, and the HOMOs of aniline opt and 1a opt are depicted in Figure 2.8.

Figure 2.4 Calculated structures for anilineopt and 1aopt, with numbering scheme.

The crystallographically determined structure 1h and the DFT optimized structure 1aopt are similar in terms of bond lengths and angles.

For the optimized structures 1aopt, both by DFT and SE methods, the resonance structures II to VIII shown in Figure 2.3 clearly contribute a great deal to the overall structure. This is observed in the C–C bond distances of the arene rings: C2–C3 and C10–C11 are slightly shorter than the other carbon–carbon bond distances in the arene rings.

Table 2.3 Selected bond lengths (Å) and angles (°) for aniline, anilineopt, +• +• aniline opt, 1h, 1aopt, and 1a opt; numbering scheme is shown in Figure 2.4. aniline anilineopt aniline+•opt 1ha 1aopt 1aopt 1a+•opt

(μ-wave)216 (DFT) (DFT) (X-ray) (DFT) (SE)218 (DFT) N1–C1 1.402(2) 1.400 1.336 1.389(8) 1.393 1.428 1.343 C1–C2b 1.397(4) 1.405 1.436 1.41(1) 1.406 1.402 1.428 C2–C3b 1.394(6) 1.393 1.374 1.39(1) 1.387 1.386 1.369 C3–C4b 1.396(3) 1.397 1.416 1.40(1) 1.410 1.399 1.431 C4–C7 1.44(1) 1.422 1.414 1.388 C7–C8 1.197(9) 1.217 1.195 1.231 C8–C9 1.44(1) 1.424 1.414 1.400 C9–C10b 1.39(1) 1.411 1.399 1.421 C10–C11b 1.39(1) 1.392 1.389 1.385 C11–C12b 1.39(1) 1.397 1.391 1.402 C4–C7–C8 177.9(8) 179.89 180.00 C7–C8–C9 176.2(8) 179.92 180.00 ∠out-of-plane 37.5 41.0 0.0 5.6-35.6 38.2 0.0 344.7- Σ ∠ at N 340.19 360.00 342.8 360.00 359.7 a Data is averaged over four molecules, except for the angles at nitrogen and the out-of-plane angle. b Experimentally determined data for aniline and 1h are averaged over the two symmetry-related positions. The estimated errors are given by the square root of the sum of the squares of each error.

NH2 NH2 NH2 NH2

I II III IV

NH2 NH2 NH2 NH2 NH2 NH2 NH2 NH2

C C C C C C C C C C C C C C C C

I II III IV V VI VII VIII

Figure 2.5 Resonance contributors for aniline+• (above) and compound 1a+• (below).

In comparison to 1a and 1aopt, the structure of the radical cation

+• 1a opt shows a shortened N1–C1 bond, accompanied by pronounced distortions in the arene rings: the C2–C3 and C10–C11 bond distances are

+• now significantly shorter than the other arene bond distances. In 1a opt, the

C7–C8 alkyne bond is lengthened, while the C4–C7 and C8–C9 bonds have gained substantial double bond character. Finally, the nitrogen atom is

+• planar in 1a opt, while it is pyramidal in 1aopt. Thus, of all the resonance contributors shown in Figure 2.5, drawn by extension to those of aniline, the

+• calculated structure of 1a opt clearly has a large contribution from forms V to

VIII.

+• (a) 1aopt (b) 1a opt +• Figure 2.6 Dipole moments calculated for (a) 1aopt and (b) 1a opt. Side view is shown.

+• The side views of 1aopt and 1a opt shown in Figure 2.6 clearly indicate the geometry at nitrogen: 1aopt possesses a pyramidal nitrogen center, while

+• that of 1a opt is planar. By the same token, the dipole moment of 1aopt is at a

+• slight angle relative to the diphenylacetylene plane, while that of 1a opt is exactly in line with the diphenylacetylene plane. In both cases, the dipole points away from the aniline ring towards the phenyl ring of the tolane derivative. This can also be explained with reference to resonance contributors shown in Figure 2.3 (for 1a) and Figure 2.5 (for 1a+•), in which a formal positive charge is placed on nitrogen.

+• +• Table 2.4 Mulliken charges for anilineopt, aniline opt, 1aopt, and 1a opt; numbering scheme is shown in Figure 2.4. +• * +• * atom anilineopt aniline opt Δ(charge) 1aopt 1a opt Δ(charge) N1 -0.786 -0.704 +0.082 -0.790 -0.765 +0.025 C1 +0.306 +0.377 +0.071 +0.326 +0.403 +0.077 C2 -0.172 -0.124 +0.048 -0.179 -0.159 +0.020 C3 -0.135 -0.118 +0.017 -0.140 -0.112 +0.028 C4 -0.139 -0.082 +0.057 +0.003 -0.019 -0.022 C7 -0.031 +0.039 +0.070 C8 -0.049 +0.052 +0.101 C9 +0.014 -0.017 -0.031 C10 -0.137 -0.109 +0.028 C11 -0.132 -0.123 +0.009 C12 -0.127 -0.102 +0.025 * Δ(charge) is taken as the difference between the atom’s Mulliken charge in the radical cation relative to the neutral species.

While the individual numbers given by the Mulliken charges (Table

2.4) are not particularly meaningful, there are some interesting trends in the data. Consistent with the formation of a radical cation, almost all atoms gain positive charge (Δ(charge) > 0) upon losing an electron in the neutral species

53 to form the radical cation. The positive charge gained by nitrogen is more substantial for aniline (Δ(charge) = +0.082) than for compound 1a (Δ(charge)

= +0.025). This can be explained by the extended backbone of 1a which allows for greater delocalization. In fact, a substantial amount of positive charge appears to be delocalized onto the alkyne carbon atoms C7 and C8

(Δ(charge) = +0.070 and +0.101), so much so that the neighbouring carbon atoms C4 and C9 become negatively charged.

For anilineopt:

(a) HOMO–2 (b) HOMO–1 (c) HOMO

For 1aopt:

(a) HOMO–1 (b) HOMO–2 and HOMO–3 (c) HOMO

Figure 2.7 Selected occupied molecular orbitals for anilineopt (above) and 1aopt (below) showing the front view (left) and the side view (right).

The occupied frontier molecular orbitals for aniline and 1aopt (Figure

2.7) are similar, except for the relative ordering of the molecular orbitals.

(The HOMO–1, HOMO–2, and HOMO–3 for 1aopt are within 0.013 Hartrees of one another.) In both aniline and 1aopt, there is a substantial amount of electron density on both the amine and the para-C atom of the phenyl group;

1aopt also shows electron density on the alkyne fragment. The distortion seen in the arene rings, where C2–C3 and C10–C11 are slightly shorter than the other C–C arene distances (Table 2.3), is also indicated by the occupied molecular orbitals: substantial C2–C3 overlap is found in the HOMO–1 of anilineopt and the HOMO–3 of 1aopt, while C10–C11 overlap is found in the

HOMO–2 of 1aopt.

+• For aniline opt:

(a) HOMO–2 (b) HOMO–1 (c) HOMO

+• For 1a opt:

(a) HOMO–2 (b) HOMO–1 and HOMO–3 (c) HOMO

+• Figure 2.8 Selected occupied molecular orbitals for aniline opt (above) and +• 1a opt (below) showing the front view (left) and the side view (right).

For the radical cations (Figure 2.8), the HOMO is expected to be similar to the respective neutral species, except for the fact that the removal of an electron renders the molecule planar. This is reflected in the electron density about nitrogen (see side views): the neutral species both show an asymmetric electronic environment about N corresponding to the lone pair of electrons, while the radical cations show a symmetric electron density. The distortion of the arene rings, with shorter C2–C3 and C10–C11 bond distances (Table 2.3), is also indicated in the molecular orbitals of the radical

+• cations. The highest occupied molecular orbitals of 1aopt and 1a opt are qualitatively similar; the only difference is that there is slightly more

+• electron density on the para-C atom in the phenyl ring of 1a opt. Compared to this para-carbon atom, there is less electron density located at the ortho- and meta-positions of the aniline and phenyl rings. The molecular orbitals presented herein will have important consequences for the observed reactivity discussed in Chapter 3.3.4.

2.3.3 Synthesis of Lithium Amides

Treatment of compounds 1 with nBuLi (Scheme 2.2) results in lithium amides 2, LiNHC6H2R2C≡CR’ (a R = H, R’ = Ph; b R = H, R’ = SiMe3; c R = H,

n i i R’ = Bu; d R = H, R’ = p-C6H4Me; e R = Pr, R’ = Ph; f R = Pr, R’ = SiMe3; g R

i n i = Pr, R’ = Bu; h R = Pr, R’ = p-C6H4Me). These compounds have not been previously characterized (Table 2.5).

Li H NH2 N R R R R nBuLi

Et2O 25 oC, 2 h R' R' 1 2

Scheme 2.2 Synthesis of compounds 2 (a R = H, R’ = Ph; b R = H, R’ = SiMe3; n i i c R = H, R’ = Bu; d R = H, R’ = p-C6H4Me; e R = Pr, R’ = Ph; f R = Pr, R’ = i n i SiMe3; g R = Pr, R’ = Bu; h R = Pr, R’ = p-C6H4Me).

Table 2.5 Selected NMR data for compounds 2. 1H NMR (ppm) 13C{1H} NMR (ppm) cmpd NHLi m-C6H2R2 o-C6H4 CN C≡C 2aa 3.07 7.48 6.47 165.6 95.1, 86.6 2bb 2.61 7.38 6.12 159.8 108.1, 90.9 2ca ~3.5c 7.35 6.50 164.7 84.6, 84.5 2da 3.04 ~7.44d 6.46 165.7 94.3, 86.4 2ea 3.16 7.54 - 158.4 95.0, 86.8 2fa 3.11 7.45 - e e 2ga 3.20 7.42 - e e 2ha 3.24 7.42 - 159.0 95.0, 86.2 a NMR data acquired in C6D6 with 3 drops d8-THF. b NMR data acquired in C6D6. c Signal is buried under coordinated Et2O. d Peak overlaps with other signals. e Partial spectrum was obtained.

Compounds 2 can either be isolated or used in situ. In the 1H NMR spectra of compounds 2, the NH peak is slightly shifted in comparison to 1.

The ortho-protons on the central arene ring of 2a to 2d are shifted downfield by ca. 0.3 ppm relative to 1, but the resonances of meta-protons in the central arene ring in compounds 2 are unchanged. In the 13C{1H} NMR spectrum, the most significant shift for compounds 2 in comparison to compounds 1 is observed for the ipso-C–N carbon atom, which resonates further downfield by

15-20 ppm. IR measurements were not possible due to air and moisture sensitivity: the IR spectra of compounds 2 are identical to compounds 1, likely due to hydrolysis.

2.3.4 Synthesis of Zirconium Amides

Zirconium-nitrogen bonds are primarily formed in one of two ways

(Scheme 2.3): (1) metathesis between a lithium amide and a zirconium chloride species; (2) protonolysis with an amine and a suitable zirconium precursor such as an alkylzirconium compound. For zirconocenes, the former route can be carried out at room temperature, while the latter route may require thermal duress.219 Higher temperatures are expected to give rise to various byproducts, including [2+2] cycloaddition as a result of the pendant alkyne fragment, which will be presented in Chapter 3. Thus, to achieve precise control of the reaction and clean isolation of zirconium amides, the metathesis route was favoured.

LnZr Cl LnZr R' + + LnZr NR2 - LiCl - R'H R2N Li R2N H

Scheme 2.3 Formation of zirconium amides by metathesis (left) or protonolysis (right).

Reaction of compounds 2 with chlorozirconocene precursors

(Cp2ZrMeCl or Cp2Zr(CH2CH2CMe3)Cl) results in metathesis to give the alkylamidozirconocene species 3 (Cp2ZrMe(NHC6H2R2C≡CR’) or 4,

(Cp2Zr(CH2CH2CMe3)(NHC6H2R2C≡CR’)), respectively (Scheme 2.4).

R H Me N R' Cp2Zr Zr H H Li H Cl Me N N R R R R R THF, 3 25 oC, 2 d nBuLi Cl THF Cp2Zr tBu R R' R' THF, H 1 2 25 oC, 2 d N R' Zr R tBu 4

Scheme 2.4 Synthesis of compounds 3 and 4 (a R = H, R’ = Ph; b R = H, R’ = n i SiMe3; c R = H, R’ = Bu; d R = H, R’ = p-C6H4Me; e R = Pr, R’ = Ph; f R = i i n Pr, R’ = SiMe3; g R = Pr, R’ = Bu).

Compounds 3 and 4 display diagnostic chemical shifts in the 1H and

13C{1H} NMR spectra (Table 2.6). Those compounds where R = iPr were not always isolated cleanly; partial characterization is given in these cases. Like for compounds 2, IR data for 3 and 4 showed only the presence of compounds

1, likely due to air and moisture sensitivity. NMR data for compounds 3 and

4 correlate well with anilidozirconocenes synthesized by Walsh et al.219 The resonances for the zirconocene fragment are shifted upfield from the

1 corresponding starting materials ( H NMR of Cp2ZrMeCl in C6D6: 5.76 (Cp)

1 and 0.45 (CH3); H NMR of Cp2Zr(CH2CH2C(CH3)3)Cl in C6D6: 5.78 (Cp)).

The protons in the anilido ligand are all shifted downfield in compounds 3 and 4, relative to starting materials 1. For example, the o-C6H4 protons in the series a, b, c, and d are located ca. 0.4 ppm downfield of 1. The most substantial downfield shift by ca. 3 ppm is observed for the anilido proton in

59 compounds 3 and 4, similar to other alkylanilidozirconocenes (5.73 to 6.55 ppm).219 In the 13C{1H} NMR, a considerable shift is observed for the ipso-C–

N carbon atom, ca. 10-15 ppm downfield of compounds 1. This is consistent with metal complex formation, and the carbon resonances are similar to other anilidozirconocene compounds.219

Table 2.6 Selected NMR data for compounds 3 and 4. 1H NMR (ppm) 13C{1H} NMR (ppm)

Cp Zr–CHn NH m-C6H2R2 o-C6H4 Cp CN C≡C 3a 5.67 0.19 6.26 7.47 6.53 110.3 156.9 91.9, 88.8 3b 5.57 0.17 6.19 7.47 6.43 110.2 156.9 107.8, 91.6 3c 5.66 0.18 6.17 7.42 6.53 110.2 156.0 88.5, 82.3 3d 5.68 0.20 6.28 ~7.49a 6.54 110.3 156.7 91.2, 88.9 3e 5.60 0.19 6.11 7.60 - 110.1 153.4 b 3f 5.57 0.16 6.08 7.55 - 110.1 153.6 108.1, 91.9 4a 5.63 0.85-0.83 6.22 7.51 6.52 110.3 156.8 91.8, 88.6 4b 5.65 0.86-0.80 6.19 7.37 6.41 110.3 156.8 107.8, 92.0 4c 5.62 0.86-0.79 6.27 7.48 6.52 110.2 156.0 88.4, 82.3 4d 5.69 0.85-0.79 6.29 ~7.49# 6.53 110.3 156.6 91.0, 88.7 4e 5.61 0.83-0.79 6.01 7.60 - 110.2 b b 4f 5.58 0.79-0.76 6.02 7.55 - 110.2 153.7 92.0b 4g 5.60 0.82-0.77 6.00 7.52 - 110.1 152.5 88.3, 82.6 a Peak overlaps with other signals. b Compound was not isolated cleanly.

The molecular structure of 3a was determined by X-ray crystallography (Figure 2.9). The methyl/chloride position is disordered; the best structural solution is obtained with 70 : 30 occupancy for Me : Cl. The presence of the byproduct, Cp2ZrCl(NHC6H4C≡CPh), may be accounted for in one of two ways. First, the starting material Cp2ZrMeCl may contain some residual Cp2ZrCl2 required in its synthesis. Reaction of Cp2ZrCl2 with

60 lithium amide 2a would result in the observed byproduct. Second, if the lithiation reaction to form compound 2a is incomplete, the remaining 1a may react via protonolysis with Cp2ZrMeCl to give the observed byproduct.

N1 C12 C15 Zr1 C18 C19 C20

C1/Cl1

Figure 2.9 Molecular structure of compound 3a (ellipsoids drawn at the 50 % probability level). All hydrogen atoms have been omitted for clarity. Selected bond lengths (Å) and angles (°): Zr1–N1 2.107(4), Zr1–C1 2.34(4), Zr1–Cl1 2.54(2), N1–C12 1.388(5), C15–C18 1.444(7), C18–C19 1.199(7), C19–C20 1.439(7), N1–Zr1–C1 98.0(9), N1–Zr1–Cl1 96.4(4), Cpcentroid–Zr1– Cpcentroid 129.73, Zr1–N1–C12 143.8(3), C15–C18–C19 177.3(6), C18–C19–C20 179.4(6).

In the 1H NMR spectrum of 3a, it is difficult to compare the integral of the methyl group in order to determine the site occupancy. This is because all the other protons in the molecule are either aryl or cyclopentadienyl protons, which are known to integrate at lower values, or the NH proton which is fairly broad. Unfortunately, crystals were not obtained reproducibly from the crude reaction mixture; consequently, further NMR studies could not be carried out with longer relaxation delays in order to reliably integrate the 1H NMR spectrum.

The general connectivity of compound 3a is as expected. Given the

Me/Cl disorder and the resultant large standard deviations in the Zr–C and

Zr–Cl bond lengths, these bond lengths are similar to those reported for alkylzirconocenes (Zr–C 2.270 to 2.289 Å)220, 221 and chlorozirconocenes (Zr–Cl

2.435 to 2.476 Ǻ).220, 222-225 The metrical parameters of the anilido ligand are similar to previously reported zirconocenes (Zr–N 2.075 to 2.238 Ǻ; Zr–N–Ar

117.8 to 141.3°),226, 227 while the alkyne fragment is linear, with typical bond lengths and angles.212, 213

The synthesis of alkylamidozirconium compounds 3 and 4 provides access to the rich stoichiometric and catalytic chemistry of imidozirconium species, which will be presented in Chapter 3.

2.4 Summary

In this chapter, several amines, lithium amides, and zirconium amides incorporating alkynyl substituents were presented. The unique combination of C≡C functional groups with Zr–N and/or N–H moieties in a single molecule can be exploited towards the synthesis of new nitrogen-containing polymers.

Indeed, alkylamidozirconium compounds 3 and 4 can give rise to imidozirconium species, which can potentially undergo intermolecular [2+2] cycloaddition to prepare Zr- and N-containing polymers. Alternately, amines

1 are potential substrates for intermolecular hydroamination polymerization.

Finally, the electronic structure of compound 1a is similar to aniline, in that it exhibits extensive delocalization along the backbone, as indicated by

62 computational studies. This electronic feature can be used in the synthesis of polyaniline-like materials. The reactivity of compounds 1 to 4 will be discussed in Chapter 3, as pertaining to the synthesis of nitrogen-containing polymers.

2.5 Experimental Section

2.5.1 General Considerations

All manipulations of air- and/or water-sensitive compounds were carried out under an atmosphere of dry oxygen-free nitrogen using standard

Schlenk techniques or a Vacuum Atmospheres inert atmosphere glovebox.

1H, 13C{1H}, 29Si{1H} and 7Li{1H} NMR spectra were acquired on a Bruker

Avance 300 MHz spectrometer, a Bruker Avance 400 MHz spectrometer, a

Bruker SpectroSpin 500 MHz spectrometer, a Varian Mercury 300 MHz spectrometer, or a Varian Mercury 400 MHz spectrometer. 1H resonances were referenced internally to the residual protonated solvent resonances, 13C resonances were referenced internally to the deuterated solvent resonances,

29 7 Si resonances were referenced externally to SiMe4 in C6D6, and Li

1 13 resonances were referenced externally to LiCl in D2O. H- C HSQC and

HMBC experiments were carried out using conventional pulse sequences to aid in the assignment of peaks in the 13C{1H} NMR. 1H-29Si HMBC experiments were carried out using conventional pulse sequences, and

referenced externally to SiMe4. Coupling constants (J) are reported as absolute values.

Mass spectra were recorded with a VG 70-250S mass spectrometer in positive ion electron impact (EI) mode. Calculated isotopic distribution for each ion matched with experimental values. Infrared spectra were recorded using a Perkin-Elmer Spectrum One FT-IR spectrometer at 25 °C, either as a

Nujol mull or deposited onto the NaCl plate from a CH2Cl2 or C6D6 solution.

Elemental analyses were performed using a Perkin-Elmer 2400 C/H/N analyzer. UV/Vis spectra were acquired on a double-beam Lambda 12 UV-

Visible spectrometer, using the solvent as the external standard. Samples were scanned at a rate of 100 nm/min.

Calculations were performed with the Gaussian03 program using

228 density functional theory (DFT). The geometry of compound 1aopt was fully optimized starting from the X-ray structure of 1a using B3LYP exchange- correlational functional with the 6-31G(d) basis set. The geometry of

+• compound 1a opt was fully optimized starting from 1aopt using the UB3LYP exchange-correlational functional with the 6-31G(d) basis set. The

+• geometries of anilineopt and aniline opt were fully optimized using the B3LYP and UB3LYP (respectively) exchange-correlational functionals, with the

6-31G(d) basis set. Optimizations were performed without (symmetry) constraints, and the resulting structures were confirmed to be minima on the potential energy surface by frequency calculations (the number of imaginary

64 frequencies is zero). Visualization of the computed structures and molecular orbitals was achieved using the program WebMO.229

2.5.2 Starting Materials and Reagents

Anhydrous solvents including toluene, pentane, hexanes, ether, tetrahydrofuran, and dichloromethane were purchased from Aldrich and purified using Grubbs’ column systems manufactured by Innovative

230 Technology. C6D6 was purchased from Cambridge Isotopes Laboratories, vacuum distilled from Na/benzophenone, and freeze-pump-thaw degassed

(x3). Diethylamine was purchased from Aldrich and degassed by sonication prior to use. Hyflo Super Cel® (Celite) was purchased from Aldrich and dried for at least 12 h in a vacuum oven or on a Schlenk line prior to use. Molecular sieves (4 Å) were purchased from Aldrich and dried at 100 ºC under vacuum using a Schlenk line. Unless otherwise noted, starting materials were purchased from Aldrich and used as received. nBuLi (1.6 M in hexanes) and tBuLi (1.7 M in pentane) were titrated prior to use for concentration

231 determination. Phenylacetylene was vacuum distilled from CaH2, and stored in the dark at -35 °C. trans-Pd(PPh3)2Cl2 was purchased from Strem.

The following compounds were synthesized according to literature procedure:

232 80 233 Cp2ZrMe2, Cp2ZrMeCl, and Cp2Zr(CH2CH2CMe3)Cl. The former two compounds were purified by recrystallization from hexanes at -35 °C, and if the recrystallized product was found to contain more than 5 % impurity by 1H

NMR in the Cp region, then they were further purified by sublimation at

80 °C. The latter compound was obtained cleanly by 1H NMR without the need for recrystallization or any other means of purification. Compounds

1a,202 1b,203, 205 and 1f234 are known. Compound 1c is reported in the literature, in low yield (by NMR), contaminated with inseparable byproducts, and no characterization data are given.235 Compounds 1c and 1d are used as reagents, but no record of their synthesis or characterization data is given.206

2.5.3 Crystallography

X-ray data collection and reduction. Crystals were manipulated and suspended in Paratone or mounted in capillaries in a glovebox, thus maintaining a dry, O2-free environment for each crystal. Diffraction experiments were performed on a Siemens SMART System CCD diffractometer. The data (4.5°< 2θ <45-50.0°) were collected in a hemisphere of data in 1329 frames with 10 second exposure times. The observed extinctions were consistent with the space groups in each case. A measure of decay was obtained by re-collecting the first 50 frames of each data set. The intensities of reflections within these frames showed no statistically significant change over the duration of the data collections. The data were processed using the SAINT and SHELXTL processing packages. An empirical absorption correction based on redundant data was applied to each data set. Subsequent solution and refinement was performed using the

SHELXTL solution package.

Structure solution and refinement. Non-hydrogen atomic scattering factors were taken from the literature tabulations.236 The heavy atom positions were determined using direct methods employing the SHELXTL direct methods routine. The remaining non-hydrogen atoms were located from successive difference Fourier map calculations. The refinements were carried out by using full-matrix least squares techniques on F, minimizing

2 2 2 the function ω (Fo-Fc) where the weight ω is defined as 4F o /2σ (Fo ) and Fo and Fc are the observed and calculated structure factor amplitudes, respectively. In the final cycles of each refinement, all non-hydrogen atoms were assigned anisotropic temperature factors in the absence of disorder or insufficient data. In the latter cases atoms were treated isotropically. Unless otherwise noted, C–H atom positions were calculated and allowed to ride on the carbon to which they are bonded assuming a C–H bond length of 0.95 Å.

H-atom temperature factors were fixed at 1.10 times the isotropic temperature factor of the C-atom to which they are bonded. The H-atom contributions were calculated, but not refined. The locations of the largest peaks in the final difference Fourier map calculation as well as the magnitude of the residual electron densities in each case were of no chemical significance.

In the crystallographic model of 1a, the most chemically reasonable model is obtained by constraining C1 (adjacent to N) to be isotropic, and fixing this arene ring (C1 to C6) to be a perfect hexagon with bond distances

67 of 1.390 Ǻ. In the crystallographic model of 1d, there is an end-to-end disorder with respect to the p-CH3 and NH2 groups, thereby creating a pseudo center of symmetry in the molecule. In the crystallographic model of

1h, the hydrogen atoms on nitrogen were located and refined. The thermal parameters of these H atoms were fixed, but the positions were allowed to vary. All other H atoms were calculated and allowed to ride on the carbon to which they are bonded assuming a C–H bond length of 0.95 Å. In the crystallographic model of 3a, the most chemically reasonable model is obtained with a 70 : 30 methyl : chloride occupancy.

Table 2.7 Crystallographic parameters for compounds 1a, 1d, 1h, and 3a. 1a 1d 1h 3a Formula C14H11N C15H13N C21H25N C24.7H22.1Cl0.3NZr Formula weight 193.24 207.26 291.42 434.79 Crystal system orthorhombic monoclinic triclinic monoclinic Space group Pna21 P21/n P-1 P21/n a (Å) 18.064(4) 13.5949(14) 9.1172(18) 9.5164(15) b (Å) 5.7756(12) 5.8193(6) 19.016(4) 15.446(3) c (Å) 10.248(2) 14.3821(14) 21.101(4) 13.740(2) α (deg) 97.87(3) β (deg) 93.887(4) 99.75(3) 92.992(2) γ (deg) 91.13(3) V (Å3) 1069.2(4) 1135.2(2) 3568.0(12) 2016.8(6) Z 4 4 8 4 dcalc (g·cm-3) 1.200 1.213 1.085 1.432 Abs coeff, μ (cm-1) 0.070 0.071 0.062 0.593 Data collected 9661 11835 26626 22677 Rint 0.0395 0.0423 0.0724 0.1007 Data Fo2 > 3σ(Fo2) 1023 3453 11922 4729 No. of parameters 113 193 817 256 R1(a) 0.0610 0.1004 0.0732 0.0626 wR2(b) 0.1847 0.2709 0.2213 0.1257 Goodness of fit 1.092 1.149 1.017 0.990 ∑ F − F 2 2 2 (a) o c (b) ∑ w(Fo − Fc ) R1 = wR2 = 2 2 ∑ Fo ∑ w(Fo )

Molecular structure representations of compounds 1a, 1d, and 1h are shown in Figure 2.2 with selected bond distances and angles given in Table

2.2. The molecular structure representation of compound 3a is shown in

Figure 2.9, with selected bond distances and angles given in the caption.

Crystallographic parameters for these compounds are given in Table 2.7.

2.5.4 Synthesis and Characterization

Synthesis of compounds 1

Synthetic and/or spectroscopic data concerning compounds 1 are sparse; thus, these compounds are reported herein with full synthetic and spectroscopic characterization. The general procedure is as follows. To a

NEt3 solution of 4-iodoaniline or 2,6-diisopropyl-4-iodoaniline was added 1.0 mol % trans-Pd(PPh3)2Cl2 and 1 mol % CuI. The brown mixture was stirred and 1.15 equiv. of HC≡CR’ was added. The mixture turned red-orange in colour and was stirred overnight at room temperature. The solvent was removed in vacuo, and the residue extracted with Et2O and filtered through

Celite. Removal of Et2O in vacuo resulted in a brown oil, which was then extracted with a 3 : 1 solution of CH2Cl2 : hexanes, filtered, and the solvent evaporated, to give a brown solid.

NH2 For 1a: 2.190 g 4-iodoaniline (10.00 mmol), 50 mL NEt3, 1.175 g

freshly distilled phenylacetylene (11.50 mmol, 1.15 equiv.), 70 mg

trans-Pd(PPh3)2Cl2 (0.010 mmol, 0.010 equiv.), 19 mg CuI (0.10 mmol,

1 0.010 equiv.). Yield: 1.785 g (92.3 %). H NMR (C6D6, 25 ºC,

300 MHz) δ: 7.54 (m, 2H, o-C6H5), 7.40 (m, 2H, m-C6H4), 7.01–6.98

13 1 (m, 3H, m- and p-C6H5), 6.11 (m, 2H, o-C6H4), 2.73 (br s, 2H, NH2). C{ H}

NMR (C6D6, 25 ºC, 75.5 MHz) δ: 147.4 (ipso-CN), 133.3 (ArH), 131.8 (ArH),

128.6 (ArH), 127.7 (ArH), 124.9 (quat-Ar), 114.7 (ArH), 112.9 (quat-Ar), 91.3

+ (C≡C), 88.1 (C≡C). EI-MS (m/z): 193.1 (100 %) [M] . HRMS: C14H11N mass

193.0892, calcd mass 193.0891, fit 0.5 ppm. FT-IR (25 ºC, evaporation of a

-1 C6D6 solution, cm ): ν(N–H) 3475, 3380 (medium, sharp), ν(C≡C) 2211

(medium, sharp). UV/Vis (CH3CN, 25 ºC): λmax = 311 nm; UV/Vis (DMF,

25 ºC): λmax = 325 nm. Anal. Calcd for C14H11N: C, 87.01; H, 5.74; N, 7.25.

Found: C, 86.88; H, 5.92; N, 6.82. Crystals suitable for X-ray crystallography were obtained upon evaporation of a solution in Et2O.

NH2 For 1b: 2.190 g 4-iodoaniline (10.00 mmol), 50 mL NEt3, 1.130 g

trimethylsilylacetylene (11.50 mmol, 1.15 equiv.), 70 mg

trans-Pd(PPh3)2Cl2 (0.010 mmol, 0.010 equiv.), 19 mg CuI

1 SiMe3 (0.010 mmol, 0.010 equiv.). Yield: 1.727 g (91.2 %). H NMR (C6D6,

25 ºC, 300 MHz) δ: 7.38 (m, 2H, m-C6H4), 6.02 (m, 2H, o-C6H4), 2.69 (br s, 2H,

13 1 NH2), 0.28 (s, 9H, Si(CH3)3). C{ H} NMR (C6D6, 25 ºC, 75.5 MHz) δ: 147.5

(ipso-CN), 133.7 (C6H4), 114.5 (C6H4), 112.7 (quat-Ar), 107.3 (Ar-C≡C-Si), 91.3

29 1 (Ar-C≡C-Si), 0.3 (s, Si(CH3)3). Si{ H} NMR (C6D6, 25 ºC, 79.5 MHz) δ: -18.8.

+ + EI-MS (m/z): 189.1 (37 %) [M] ; 174.1 (100 %) [M] – Me. HRMS: C11H15NSi mass 189.0972, calcd mass 189.0974, fit -1.1 ppm. FT-IR (25 ºC, evaporation

-1 of a C6D6 solution, cm ): ν(N–H) 3480, 3380 (medium, sharp), ν(C≡C) 2145

(very strong, sharp). Anal. Calcd for C11H15NSi: C, 69.78; H, 7.99; N, 7.40.

Found: C, 69.04; H, 8.30; N, 7.07.

NH2 For 1c: 2.190 g 4-iodoaniline (10.00 mmol), 50 mL NEt3, 0.945 g

1-hexyne (11.50 mmol, 1.15 equiv.), 70 mg trans-Pd(PPh3)2Cl2

(0.010 mmol, 0.010 equiv.), 19 mg CuI (0.010 mmol, 0.010 equiv.).

1 Yield: 1.687 g (97.4 %). H NMR (C6D6, 25 ºC, 300 MHz) δ: 7.38

(m, 2H, m-C6H4), 6.14 (m, 2H, o-C6H4), 2.74 (br s, 2H, NH2), 2.28 (t,

3 2H, C≡CCH2CH2CH2CH3, JH-H = 7 Hz), 1.49–1.33 (m, 4H,

3 C≡CCH2CH2CH2CH3), 0.80 (t, 3H, C≡CCH2CH2CH2CH3, JH-H = 7 Hz).

13 1 C{ H} NMR (C6D6, 25 ºC, 100.7 MHz) δ: 146.8 (ipso-CN), 133.3 (m-C6H4),

115.0 (o-C6H4), 114.1 (quat-Ar), 88.1 (C≡C), 82.2 (C≡C), 31.8

(C≡CCH2CH2CH2CH3), 22.6 (C≡CCH2CH2CH2CH3), 19.7

(C≡CCH2CH2CH2CH3), 14.1 (C≡CCH2CH2CH2CH3). EI-MS (m/z): 173.1

+ + + (48 %) [M] ; 158.1 (26 %) [M] – CH3; 144.1 (28 %) [M] – CH2CH3; 130.1

+ (100 %) [M] – CH2CH2CH3. HRMS: C12H15N mass 173.1201, calcd mass

-1 173.1204, fit -1.7 ppm. FT-IR (25 ºC, evaporation of a CH2Cl2 solution, cm ):

ν(N–H) 3457, 3372 (strong, broad), ν(C≡C) 2224 (weak). Suitable elemental analysis could not be obtained on the oily product.

NH2 For 1d: 2.190 g 4-iodoaniline (10.00 mmol), 50 mL NEt3, 1.326 g

p-tolylacetylene (11.40 mmol, 1.14 equiv.), 70 mg trans-Pd(PPh3)2Cl2

(0.010 mmol, 0.010 equiv.), 19 mg CuI (0.10 mmol, 0.010 equiv.). The

product was recrystallized at -35 °C from dichloromethane and

hexanes. Yield of crystalline product: 1.180 g (56.9 %). 1H NMR

(C6D6, 25 ºC, 300 MHz) δ: 7.52 (m, 2H, o- or m-C6H4Me), 7.44 (m, 2H,

m-NC6H4), 6.83 (m, 2H, o- or m-C6H4Me), 6.13 (m, 2H, o-NC6H4), 2.73 (br s,

13 1 2H, NH2), 1.99 (s, 3H, CH3). C{ H} NMR (C6D6, 25 ºC, 100.7 MHz) δ: 147.3

(ipso-CN), 137.7 (quat-Ar), 133.3 (m-NC6H4), 131.8 (C6H4Me), 129.5

(C6H4Me), 121.9 (quat-Ar), 114.8 (o-NC6H4), 113.1 (quat-Ar), 90.6 (C≡C), 88.2

+ (C≡C), 21.6 (CH3). EI-MS (m/z): 207.1 (100 %) [M] . HRMS: C15H13N mass

207.1043, calcd mass 207.1048, fit -2.4 ppm. FT-IR (25 ºC, evaporation of a

-1 C6D6 solution, cm ): ν(N–H) 3467, 3379 (very strong, broad), ν(C≡C) 2209

(weak). Anal. Calcd for C15H13N: C, 86.92; H, 6.32; N, 6.76. Found: C, 86.97;

H, 6.91; N, 6.80. Crystals suitable for X-ray diffraction were obtained from a dichloromethane and hexanes solution at -35 °C.

NH2 For 1e: 3.032 g 2,6-diisopropyl-4-iodoaniline (10.00 mmol),

50 mL NEt3, 1.175 g freshly distilled phenylacetylene

(11.50 mmol, 1.15 equiv.), 70 mg trans-Pd(PPh3)2Cl2

(0.010 mmol, 0.010 equiv.), 19 mg CuI (0.010 mmol,

1 0.010 equiv.). Yield: 2.504 g (90.4 %) H NMR (C6D6, 25 ºC,

300 MHz) δ: 7.62 (m, 2H, o-C6H5), 7.51 (s, 2H, C6H2), 7.02–6.96 (m, 3H, m-

3 and p-C6H5), 3.27 (br s, 2H, NH2), 2.48 (septet, 2H, CH(CH3)2, JH-H = 7 Hz),

3 13 1 1.05 (d, 12H, CH(CH3)2, JH-H = 7 Hz). C{ H} NMR (C6D6, 25 ºC, 75.5 MHz and 100.7 MHz) δ: 141.8 (ipso-CN), 132.6 (quat-Ar), 132.1 (o-C6H5), 129.1

(quat-Ar), 129.0 (m- or p-C6H5), 128.0 (m- or p-C6H5), 127.6 (m-C6H2), 125.4

(quat-Ar), 92.8 (C≡C), 88.0 (C≡C), 28.4 (CH(CH3)2), 22.6 (CH(CH3)2). EI-MS

+ + (m/z): 277.2 (100 %) [M] ; 262.2 (94 %) [M] – Me. HRMS: C20H23N mass

277.1836, calcd mass 277.1830, fit 2.2 ppm. FT-IR (25 ºC, evaporation of a

-1 C6D6 solution, cm ): ν(N–H) 3494, 3410 (strong, sharp), ν(C≡C) 2200 (strong, sharp). Anal. Calcd for C20H23N: C, 86.59; H, 8.36; N, 5.05. Found: C, 86.87;

H, 8.21; N, 4.54.

NH2 For 1f: 1.512 g 2,6-diisopropyl-4-iodoaniline (5.000 mmol),

25 mL NEt3, 0.565 g trimethylsilylacetylene (5.75 mmol,

1.15 equiv.), 35 mg trans-Pd(PPh3)2Cl2 (0.0050 mmol,

SiMe3 0.010 equiv.), 10 mg CuI (0.005 mmol, 0.010 equiv.). Yield:

1 1.310 g (95.9 %) H NMR (C6D6, 25 ºC, 300 MHz) δ: 7.41 (s, 2H, C6H2), 3.23

3 (br s, 2H, NH2), 2.41 (septet, 2H, CH(CH3)2, JH-H = 7 Hz), 0.97 (d, 12H,

3 13 1 CH(CH3)2, JH-H = 7 Hz), 0.30 (s, 9H, Si(CH3)3). C{ H} NMR (C6D6, 25 ºC,

75.5 MHz) δ: 141.6 (ipso-CN), 132.1 (quat-Ar), 128.0 (m-C6H2), 113.0

(quat-Ar), 108.5 (Ar-C≡C-Si), 90.8 (Ar-C≡C-Si), 28.0 (CH(CH3)2), 22.2

29 1 (CH(CH3)2), 0.5 (Si(CH3)3). Si{ H} NMR (C6D6, 25 ºC, 79.5 MHz) δ: -18.2.

+ + EI-MS (m/z): 273.2 (67 %) [M] ; 258.2 (100 %) [M] – Me. HRMS: C17H27NSi mass 273.1902, calcd mass 273.1913, fit -4.0 ppm. FT-IR (25 ºC, evaporation

-1 of a CH2Cl2 solution, cm ): ν(N–H) 3494, 3410 (strong, broad), ν(C≡C) 2140

(very strong, sharp). Suitable elemental analysis data could not be obtained.

NH2 For 1g: 3.032 g 2,6-diisopropyl-4-iodoaniline (10.00 mmol),

50 mL NEt3, 0.945 g 1-hexyne (11.50 mmol, 1.15 equiv.),

70 mg trans-Pd(PPh3)2Cl2 (0.010 mmol, 0.010 equiv.), 19 mg

CuI (0.010 mmol, 0.010 equiv.). Yield: 2.324 g (90.4 %) 1H

NMR (C6D6, 25 ºC, 300 MHz) δ: 7.44 (s, 2H, C6H2), 3.20 (br s, 2H, NH2), 2.50

3 3 (septet, 2H, CH(CH3)2, JH-H = 7 Hz), 2.38 (t, 2H, C≡CCH2CH2CH2CH3, JH-H

= 7 Hz), 1.55–1.45 (m, 2H, C≡CCH2CH2CH2CH3), 1.45–1.37 (m, 2H,

3 C≡CCH2CH2CH2CH3), 1.05 (d, 12H, CH(CH3)2, JH-H = 7 Hz), 0.81 (t, 3H,

3 13 1 C≡CCH2CH2CH2CH3, JH-H = 7 Hz). C{ H} NMR (C6D6, 25 ºC, 75.5 MHz) δ:

140.9 (ipso-CN), 132.5 (quat-Ar), 127.4 (m-C6H2), 114.7 (quat-Ar), 87.5 (C≡C),

83.3 (C≡C), 32.0 (C≡CCH2CH2CH2CH3), 28.4 (CH(CH3)2), 22.7

(C≡CCH2CH2CH2CH3), 22.6 (CH(CH3)2), 20.0 (C≡CCH2CH2CH2CH3), 14.2

+ + (C≡CCH2CH2CH2CH3). EI-MS (m/z): 257.2 (64 %) [M] ; 242.2 (100 %) [M] –

+ i Me, 214.2 (58 %) [M] – Pr. HRMS: C18H27N mass 257.2148, calcd mass

-1 257.2144, fit 1.6 ppm. FT-IR (25 ºC, evaporation of a C6D6 solution, cm ):

ν(N–H) 3491, 3406 (strong, sharp), ν(C≡C) 2224 (weak). Anal. Calcd for

C18H27N: C, 83.99; H, 10.57; N, 5.44. Found: C, 83.39; H, 10.62; N, 5.46.

NH2 For 1h: 3.032 g 2,6-diisopropyl-4-iodoaniline (10.00 mmol),

50 mL NEt3, 1.330 g p-tolylacetylene (11.40 mmol,

1.14 equiv.), 70 mg trans-Pd(PPh3)2Cl2 (0.010 mmol,

0.010 equiv.), 19 mg CuI (0.010 mmol, 0.010 equiv.). The

compound was recrystallized from dichloromethane and hexanes at -35 °C. Yield of crystalline product: 1.753 g (60.2 %). 1H NMR

(C6D6, 25 ºC, 300 MHz) δ: 7.58 (m, 2H, C6H4), 7.52 (s, 2H, C6H2), 6.85 (m, 2H,

3 C6H4), 3.27 (br s, 2H, NH2), 2.49 (septet, 2H, CH(CH3)2, JH-H = 7 Hz), 2.00 (s,

3 13 1 3H, C6H4CH3), 1.06 (d, 12H, CH(CH3)2, JH-H = 7 Hz). C{ H} NMR (C6D6,

25 ºC, 75.5 MHz and 100.7 MHz) δ: 141.3 (ipso-CN), 137.5 (quat-Ar), 132.3

(quat-Ar), 131.7 (ArH), 129.5 (ArH), 127.2 (ArH), 122.2 (quat-Ar), 113.5

(quat-Ar), 92.0 (C≡C), 87.8 (C≡C), 28.1 (CH(CH3)2), 22.3 (CH(CH3)2), 21.3

+ + (C6H4CH3). EI-MS (m/z): 291.2 (5 %) [M] ; 276.2 (4 %) [M] – Me, 177.2

+ + (29 %) [M] – C≡CC6H4Me, 162.1 (100 %) [M] – C≡CC6H4Me – Me. HRMS:

C21H25N mass 291.1986, calcd mass 291.1987, fit -0.3 ppm. FT-IR (25 ºC,

-1 evaporation of a C6D6 solution, cm ): ν(N–H) 3489, 3409 (medium, sharp),

ν(C≡C) 2204 (medium, sharp). Anal. Calcd for C21H25N: C, 86.55; H, 8.65; N

4.81. Found: C, 86.89; H, 8.54; N, 4.98. Crystals suitable for X-ray diffraction were obtained from a dichloromethane and hexanes solution at -35 °C.

Synthesis of compounds 2

Compound 1 was dissolved in Et2O, and 1.00 equiv. of freshly titrated nBuLi in hexanes was added with stirring at room temperature. The mixture was allowed to stir overnight, and the product was isolated on a frit as a brown powder. Compounds 2 were either isolated as described above, or synthesized and utilized in situ using THF as the solvent. IR data for compounds 2 is identical to compounds 1: these samples were likely protonated by residual water present in air during the time taken to walk from the glovebox to the IR spectrometer.

Li H For 2a: 193 mg 1a, 10 mL Et O, 0.625 mL of 1.598 M nBuLi in N 2

1 hexanes. Yield: 151 mg (75.9 %). H NMR (C6D6 + 3 drops d8-THF,

25 ºC, 400 MHz) δ: 7.55 (m, 2H, o-C6H5), 7.48 (m, 2H, m-C6H4), 7.03

(m, 2H, m-C6H5), 6.94 (m, 1H, p-C6H5), 6.47 (br, 2H, o-C6H4), 3.07 (s,

13 1 1H, NH). C{ H} NMR (C6D6 + 3 drops d8-THF, 25 ºC, 100.7 MHz) δ:

165.6 (ipso-CN), 133.6 (m-C6H4), 131.1 (o-C6H5), 128.5 (m-C6H5), 126.6

(p-C6H5), 126.4 (quat-Ar) 116.3 (o-C6H4), 102.1 (quat-Ar), 95.1 (C≡C), 86.6

7 1 (C≡C). Li{ H} NMR (C6D6 + THF-d8, 25 ºC, 155.5 MHz) δ: 0.66 (s).

n Li H For 2b: 189 mg 1b, 10 mL Et2O, 0.625 mL of 1.598 M BuLi in N

1 hexanes. Yield: 186 mg (95.4 %). H NMR (C6D6, 25 ºC, 400 MHz)

δ: 7.38 (br, 2H, m-C6H4), 6.12 (br, 2H, o-C6H4), 2.61 (br, 1H, NH),

13 1 0.34 (s, 9H, Si(CH3)3). C{ H} NMR (C6D6, 25 ºC, 100.7 MHz, SiMe3 partial) δ: 159.8 (ipso-CN), 134.8 (m-C6H4), 116.7 (o-C6H4), 108.1 (Ar-C≡C-Si),

7 1 90.9 (Ar-C≡C-Si), 0.6 (Si(CH3)3). Li{ H} NMR (C6D6, 25 ºC, 155.5 MHz) δ:

0.50 (s).

Li H For 2c: 173 mg 1c, 5 mL Et2O, 2 mL toluene and 5 mL THF, N 0.625 mL of 1.598 M nBuLi in hexanes. Yield: 120 mg (67.1 %). 1H

NMR (C6D6 + 3 drops d8-THF, 25 ºC, 400 MHz) δ: 7.35 (m, 2H,

m-C6H4), 6.50 (m, 2H, o-C6H4), ca. 3.5 (NH, shoulder of THF peak),

3 2.37 (t, 2H, C≡CCH2CH2CH2CH3, JH-H = 7 Hz), 1.65–1.36 (m, 4H,

3 C≡CCH2CH2CH2CH3), 0.80 (t, 3H, C≡CCH2CH2CH2CH3, JH-H = 7 Hz).

13 1 C{ H} NMR (C6D6 + 3 drops d8-THF, 25 ºC, 100.7 MHz, partial) δ: 164.7

(ipso-CN), 133.2 (o-C6H4), 129.3 (m-C6H4), 84.6 (C≡C), 84.5 (C≡C), 32.1

(C≡CCH2(CH2)2CH3), ca. 25 (C≡CCH2(CH2)2CH3, buried under THF-d8), 19.9

7 1 (C≡CCH2CH2CH2CH3), 13.9 (C≡CCH2CH2CH2CH3). Li{ H} NMR (C6D6 +

THF-d8, 25 ºC, 155.5 MHz) δ: 0.84 (s).

n Li H For 2d: 207 mg 1d, 10 mL Et2O, 0.625 mL of 1.598 M BuLi in N

1 hexanes. Yield: 153 mg (71.9 %). H NMR (C6D6 + 3 drops d8-THF,

25 ºC, 400 MHz) δ: 7.46–7.42 (m, 4H, o- or m-C6H4Me and

m-NC6H4), 6.87 (m, 2H, o- or m-C6H4Me), 6.46 (m, 2H, o-NC6H4),

13 1 3.04 (br s, 2H, NH2), 2.03 (s, 3H, CH3). C{ H} NMR (C6D6 + 3 drops

d8-THF, 25 ºC, 100.7 MHz) δ: 165.7 (ipso-CN), 135.9 (quat-Ar), 133.5

(m-NC6H4), 131.1 (o- or m-C6H4Me), 129.2 (o- or m-C6H4Me), 127.9 (quat-Ar),

7 1 123.6 (quat-Ar), 116.3 (o-NC6H4), 94.3 (C≡C), 86.4 (C≡C), 21.2 (CH3). Li{ H}

NMR (C6D6 + THF-d8, 25 ºC, 155.5 MHz) δ: 0.61 (s).

n Li H For 2e: 277 mg 1e, 10 mL Et2O, 0.625 mL of 1.598 M BuLi N

1 in hexanes. Yield: 230 mg (81.3 %). H NMR (C6D6 + 3

drops THF-d8, 25 ºC, 300 MHz) δ: 7.60 (m, 2H, o-C6H5), 7.54

(s, 2H, C6H2), 7.07–6.94 (m, 3H, m- and p-C6H5), 3.16 (br,

3 3H, NH and CH(CH3)2), 1.32 (d, 12H, CH(CH3)2, JH-H = 7

13 1 Hz). C{ H} NMR (C6D6 + 3 drops THF-d8, 25 ºC, 75.5 MHz, partial) δ: 158.4

(ipso-CN), 132.1 (quat-Ar), 131.3 (o-C6H5), 127.5 (m-C6H2), 126.8 (m- or p-C6H5), 126.1 (quat-Ar), 123.4 (m- or p-C6H5), 95.0 (C≡C), 86.8 (C≡C), 28.4

7 1 (CH(CH3)2), 23.4 (CH(CH3)2). Li{ H} NMR (C6D6 + THF-d8, 25 ºC, 116.6

MHz) δ: 1.57 (s).

n Li H For 2f: 273 mg 1f, 10 mL Et2O, 0.625 mL of 1.598 M BuLi N

1 in hexanes. Yield: 198 mg (72.5 %). H NMR (C6D6 + 2

drops THF-d8, 25 ºC, 300 MHz) δ: 7.45 (s, 2H, C6H2), 3.11 (br,

3 3H, NH and CH(CH3)2), 1.22 (d, 12H, CH(CH3)2, JH-H = 7 SiMe3 13 1 Hz), 0.31 (s, 9H, Si(CH3)3). C{ H} NMR (C6D6 + 2 drops THF-d8, 25 ºC,

75.5 MHz, partial) δ: 127.7 (C6H2), 28.2 (CH(CH3)2), 23.2 (CH(CH3)2), 0.7

7 1 (Si(CH3)3). Li{ H} NMR (C6D6 + THF-d8, 25 ºC, 116.6 MHz) δ: 1.65 (s).

n Li H For 2g: 257 mg 1a, 10 mL Et2O, 0.625 mL of 1.598 M BuLi N in hexanes. Yield: 120 mg (45.6 %). Partial characterization

1 is as follows. H NMR (C6D6 + 3 drops THF-d8, 25 ºC,

300 MHz) δ: 7.42 (s, 2H, C6H2), 3.2 (br, 1H, NH), 3.00 (q,

Et2O), 2.9 (br, 2H, CH(CH3)2), 2.42 (br, 2H,

C≡CCH2CH2CH2CH3), 1.55–1.39 (m, 4H, C≡CCH2CH2CH2CH3), 1.24 (d, 2H,

3 CH(CH3)2), JH-H = 6), 1.06 (b, 3H, C≡CCH2CH2CH2CH3), 0.82 (t, Et2O).

n Li H For 2h: 291 mg 1a, 10 mL Et2O, 0.625 mL of 1.598 M BuLi N

1 in hexanes. Yield: 143 mg (48.2 %). H NMR (C6D6 + 3

drops THF-d8, 25 ºC, 400 MHz) δ: 7.46 (m, 2H, o- or m-

C6H4Me), 7.42 (s, 2H, C6H2), 6.86 (m, 2H, o- or m-C6H4Me),

ca. 3.24 (NH and CH(CH3)2, with residual Et2O), 2.04 (s, 3H,

3 13 1 C6H4CH3) 1.29 (d, 12H, CH(CH3)2, JH-H = 7 Hz). C{ H}

NMR (C6D6 + THF-d8, 25 ºC, 100.7 MHz) δ: 159.0 (ipso-CN), 135.9 (quat-Ar),

131.9 (quat-Ar), 131.1 (o- or m-C6H4Me), 129.3 (o- or m-C6H4Me), 127.9 (quat-

Ar), 127.0 (C6H2), 123.7 (quat-Ar), 95.0 (C≡C), 86.2 (C≡C), 28.1 (CH(CH3)2),

7 1 23.4 (CH(CH3)2), 21.2 (C6H4CH3). Li{ H} NMR (C6D6 + THF-d8, 25 ºC, 155.5

MHz) δ: 0.96 (s).

Synthesis of compounds 3

A solution of 2 was generated in situ by addition of 1.05 equiv. nBuLi

(0.665 mL of a 1.579 M solution, 1.05 mmol) to a solution of 1 (1.00 mmol) in

5 mL THF, and stirred 0.5 to 1 h. The solution of 2 was added dropwise to a solution of 0.95 equiv. Cp2ZrMeCl (258 mg, 0.95 mmol) in 5 mL THF at room temperature. The reaction was stirred overnight, filtered through a plug of

Celite, and the solvent removed in vacuo to afford a brown oil. Compounds 3 were contaminated by residual solvents and small amounts of a cyclopentadienyl-containing byproduct, thereby precluding elemental analysis. Yields are therefore given as NMR yields, based on disappearance of signals corresponding to 1 or 2. For 3e and 3f, the product was not obtained cleanly; partial characterization is given for these compounds.

H For 3a: 1.00 mmol in situ generated 2a in N Zr Me 5 mL THF, 258 mg Cp2ZrMeCl (0.95 mmol,

0.95 equiv.) in 5 mL THF. By NMR, > 95 % consumption of 1a. 1H NMR

(C6D6, 25 ºC, 300 MHz) δ: 7.55 (m, 2H, o-C6H5), 7.47 (m, 2H, m-C6H4), 7.08–

6.99 (m, 3H, m- and p-C6H5), 6.53 (m, 2H, o-C6H4), 6.26 (s, 1H, NH), 5.67 (s,

13 1 10H, C5H5), 0.19 (s, 3H, Zr-CH3). C{ H} NMR (C6D6, 25 ºC, 75.5 MHz) δ:

156.9 (ipso-CN), 132.7 (m-C6H4), 131.7 (o-C6H5), 128.7 (m- or p-C6H5), 127.7

(m- or p-C6H5), 124.7 (quat-Ar), 119.6 (o-C6H4), 113.1 (quat-Ar), 110.3 (Cp),

91.9 (C≡C), 88.8 (C≡C), 23.5 (Zr-CH3).

H For 3b: 1.00 mmol in situ generated 2b in 5 mL N SiMe Zr 3 Me THF, 258 mg Cp2ZrMeCl (0.95 mmol,

0.95 equiv.) in 5 mL THF. By NMR, > 95 % consumption of 1b. 1H NMR

(C6D6, 25 ºC, 300 MHz) δ: 7.47 (m, 2H, m-C6H4), 6.43 (m, 2H, o-C6H4), 6.19 (s,

1H, NH), 5.57 (s, 10H, C5H5), 0.29 (s, 9H, Si(CH3)3), 0.17 (s, 3H, Zr-CH3).

13 1 C{ H} NMR (C6D6, 25 ºC, 75.5 MHz) δ: 156.9 (ipso-CN), 133.0 (m-C6H4),

119.4 (o-C6H4), 113.2 (quat-Ar), 110.2 (Cp), 107.8 (Ar-C≡C-Si), 91.6

(Ar-C≡C-Si), 23.4 (Zr-CH3), 0.5 (Si(CH3)3).

H For 3c: 1.00 mmol in situ generated 2c in N Zr Me 5 mL THF, 258 mg Cp2ZrMeCl (0.95 mmol,

0.95 equiv.) in 5 mL THF. By NMR, > 95 % consumption of 1c. 1H NMR

(C6D6, 25 ºC, 300 MHz) δ: 7.42 (m, 2H, m-C6H4), 6.53 (m, 2H, o-C6H4), 6.17 (s,

3 1H, NH), 5.66 (s, 10H, C5H5), 2.31 (t, 2H, C≡CCH2CH2CH2CH3, JH-H = 7 Hz),

1.47–1.35 (m, 4H, C≡CCH2CH2CH2CH3), 0.82 (t, 3H, C≡CCH2CH2CH2CH3,

3 13 1 JH-H = 7 Hz), 0.18 (s, 3H, ZrCH3). C{ H} NMR (C6D6, 25 ºC, 75.5 MHz) δ:

156.0 (ipso-CN), 132.5 (C6H4), 119.7 (C6H4), 113.0 (quat-Ar), 110.2 (Cp), 88.5

(C≡C), 82.3 (C≡C), 31.5 (C≡CCH2(CH2)2CH3), 22.7 (Zr–CH3), 22.3

(C≡CCH2(CH2)2CH3), 19.6 (C≡CCH2CH2CH2CH3), 13.9

(C≡CCH2CH2CH2CH3).

H For 3d: 1.00 mmol in situ generated 2d in N Zr Me 5 mL THF, 258 mg Cp2ZrMeCl (0.95 mmol,

0.95 equiv.) in 5 mL THF. By NMR, > 95 % consumption of 1d. 1H NMR

(C6D6, 25 ºC, 300 MHz) δ: 7.51–7.47 (m, 4H, o-C6H4Me and m-NC6H4), 6.87

(m, 2H, m-C6H4Me), 6.54 (m, 2H, o-NC6H4), 6.28 (s, 1H, NH), 5.68 (s, 10H,

13 1 C5H5), 2.04 (s, 3H, C6H4CH3), 0.20 (s, 3H, Zr-CH3). C{ H} NMR (C6D6,

25 ºC, 75.5 MHz, partial) δ: 156.7 (ipso-CN), 137.7 (quat-Ar), 132.6 (o-C6H4Me or m-NC6H4), 131.7 (o-C6H4Me or m-NC6H4), 129.5 (m-C6H4Me), 121.8

(quat-Ar), 119.6 (o-NC6H4), 113.5 (quat-Ar), 110.3 (Cp), 91.2 (C≡C), 88.9

(C≡C), 23.3 (Zr-CH3), 21.4 (C6H4CH3).

iPr For 3e: 1.00 mmol in situ generated 2e in H N 5 mL THF, 258 mg Cp ZrMeCl (0.95 mmol, Zr 2 Me i Pr 0.95 equiv.) in 5 mL THF. This compound was

1 not isolated cleanly; partial characterization is as follows. H NMR (C6D6,

25 ºC, 300 MHz) δ: 7.62 (m, 2H, o-C6H5), 7.60 (s, 2H, C6H2), 7.05–6.99 (m, 3H, m- and p-C6H5), 6.11 (br s, 1H, NH), 5.60 (s, 10H, C5H5), 3.26 (m, 2H,

3 13 1 CH(CH3)2), 1.15 (d, 2H, CH(CH3)2, JH-H = 7 Hz, 0.19 (s, 3H, ZrCH3). C{ H}

NMR (C6D6, 25 ºC, 75.5 MHz, partial) δ: 153.4 (ipso-CN), 110.1 (Cp), 92.2

(C≡C), 89.9 (C≡C).

iPr For 3f: 1.00 mmol in situ generated 2f in 5 mL H N SiMe Zr 3 THF, 258 mg Cp2ZrMeCl (0.95 mmol, Me i Pr 0.95 equiv.) in 5 mL THF. This compound was

1 not isolated cleanly; partial characterization is as follows. H NMR (C6D6,

25 ºC, 300 MHz) δ: 7.55 (s, 2H, C6H2), 6.08 (br s, 1H, NH), 5.57 (s, 10H,

3 C5H5), 3.22 (m, 2H, CH(CH3)2), 1.08 (d, 12H, CH(CH3)2, JH-H = 7 Hz), 0.33 (s,

13 1 9H, Si(CH3)3), 0.16 (s, 3H, ZrCH3). C{ H} NMR (C6D6, 25 ºC, 75.5 MHz, partial) δ: 153.6 (ipso-CN), 110.1 (Cp), 108.1 (C≡C), 91.9 (C≡C), 0.5

(Si(CH3)3).

Synthesis of compounds 4

A solution of 2 (1.00 mmol, in 5 mL THF, generated in situ and stirred

0.5 to 1 h) was added dropwise to a solution of Cp2Zr(CH2CH2C(CH3)3)Cl

(0.95 equiv.) in 5 mL THF at room temperature. The reaction was stirred overnight, filtered through a plug of Celite, and the solvent removed in vacuo to afford a brown oil. Compounds 4 were contaminated by residual solvents and small amounts of a cyclopentadienyl-containing byproduct, thereby precluding elemental analysis. Yields are therefore given as NMR yields, based on disappearance of signals corresponding to 1 or 2. For 4e, 4f, and 4g, the product was not obtained cleanly; partial characterization is given for these compounds.

H For 4a: 1.00 mmol in situ generated 2a in N Zr 5 mL THF, 342 mg Cp2Zr(CH2CH2C(CH3)3)Cl tBu

(0.95 mmol, 0.95 equiv.) in 5 mL THF. By NMR, > 95 % consumption of 1a.

1 H NMR (C6D6, 25 ºC, 300 MHz) δ: 7.59 (m, 2H, o-C6H5), 7.51 (m, 2H, m-C6H4), 7.05–6.96 (m, 3H, (m- and p-C6H5), 6.52 (m, 2H, o-C6H4), 6.22 (br s,

1H, NH), 5.63 (s, 10H, C5H5), 1.48–1.45 (m, 2H, CH2), 1.01 (s, 9H, C(CH3)3),

13 1 0.85–0.83 (m, 2H, CH2). C{ H} NMR (C6D6, 25 ºC, 75.5 MHz, partial) δ:

156.8 (ipso-CN), 132.7 (m-C6H4), 131.7 (o-C6H5), 128.7 (m- or p-C6H5), 124.8

(quat-Ar), 119.6 (o-C6H4), 113.1 (quat-Ar), 110.3 (Cp), 91.8 (C≡C), 88.6 (C≡C),

48.1 (CH2), 38.9 (CH2), 32.9 (ZrCH2CH2C(CH3)3), 29.4 (ZrCH2CH2C(CH3)3).

H For 4b: 1.00 mmol in situ generated 2b in 5 mL N SiMe Zr 3 THF, 342 mg Cp2Zr(CH2CH2C(CH3)3)Cl tBu (0.95 mmol, 0.95 equiv.) in 5 mL THF. By NMR,

1 > 95 % consumption of 1b. H NMR (C6D6, 25 ºC, 300 MHz) δ: 7.37 (m, 2H, m-C6H4), 6.41 (m, 2H, o-C6H4), 6.19 (s, 1H, NH), 5.65 (s, 10H, C5H5), 1.42–

1.37 (m, 2H, CH2), 0.95 (s, 9H, C(CH3)3), 0.80–0.75 (m, 2H, CH2), 0.27 (s, 9H,

13 1 Si(CH3)3). C{ H} NMR (C6D6, 25 ºC, 75.5 MHz) δ: 156.8 (ipso-CN), 133.1

(C6H4), 119.4 (C6H4), 113.3 (quat-Ar), 110.3 (Cp), 107.8 (Ar-C≡C-Si), 92.0

(Ar-C≡C-Si), 48.1 (CH2), 38.9 (CH2), 32.9 (ZrCH2CH2C(CH3)3), 29.4

(ZrCH2CH2C(CH3)3), 0.5 (Si(CH3)3).

H For 4c: 1.00 mmol in situ generated 2c in N Zr 5 mL THF, 342 mg Cp2Zr(CH2CH2C(CH3)3)Cl tBu (0.95 mmol, 0.95 equiv.) in 5 mL THF. By NMR,

1 > 95 % consumption of 1c. H NMR (C6D6, 25 ºC, 300 MHz) δ: 7.48 (m, 2H,

m-C6H4), 6.52 (m, 2H, o-C6H4), 6.27 (br s, 1H, NH), 5.62 (s, 10H, C5H5), 2.32

3 (t, 2H, C≡CCH2CH2CH2CH3, JH-H = 7 Hz), 1.52–1.38 (m, 6H,

C≡CCH2CH2CH2CH3 and Zr(CH2)2C(CH3)3), 1.00 (s, 9H, ZrCH2CH2C(CH3)3),

3 0.83 (t, 3H, C≡CCH2CH2CH2CH3, JH-H = 7 Hz), 0.86–0.79 (m, 2H,

13 1 Zr(CH2)2C(CH3)3). C{ H} NMR (C6D6, 25 ºC, 75.5 MHz) δ: 156.0 (ipso-CN),

132.5 (m-C6H4), 119.7 (o-C6H4), 114.6 (quat-Ar), 110.2 (Cp), 88.4 (C≡C), 82.3

(C≡C), 48.1 (Zr(CH2)2C(CH3)3), 38.1 (Zr(CH2)2C(CH3)3), 32.9

(ZrCH2CH2C(CH3)3), 31.5 (C≡CCH2(CH2)2CH3), 29.4 ((ZrCH2CH2C(CH3)3),

22.3 (C≡CCH2(CH2)2CH3), 19.6 (C≡CCH2CH2CH2CH3), 13.9

(C≡CCH2(CH2)2CH3).

H For 4d: 1.00 mmol in situ generated 2d in N Zr 5 mL THF, 342 mg Cp2Zr(CH2CH2C(CH3)3)Cl tBu (0.95 mmol, 0.95 equiv.) in 5 mL THF. By

1 NMR, > 95 % consumption of 1d. H NMR (C6D6, 25 ºC, 300 MHz) δ: 7.53–

7.44 (m, 4H, o-C6H4Me and m-NC6H4), 6.87 (m, 2H, m-C6H4Me), 6.53 (m, 2H, o-NC6H4), 6.29 (s, 1H, NH), 5.69 (s, 10H, C5H5), 2.00 (s, 3H, C6H4CH3), 1.46–

1.41 (m, 2H, CH2), 0.98 (s, 9H, CH2CH2C(CH3)3), 0.85–0.79 (m, 2H, CH2).

13 1 C{ H} NMR (C6D6, 25 ºC, 75.5 MHz, partial) δ: 156.6 (ipso-CN), 137.6

(quat-Ar), 132.7 (o-C6H4Me), 131.7 (m-NC6H4), 129.5 (m-C6H4Me), 119.7

(o-NC6H4), 110.3 (Cp), 91.1 (C≡C), 88.9 (C≡C), 48.2 (CH2), 38.8 (CH2), 33.0

(ZrCH2CH2C(CH3)3), 29.4 (ZrCH2CH2C(CH3)3), 21.4 (C6H4CH3).

iPr For 4e: 1.00 mmol in situ generated 2e in H N 5 mL THF, 342 mg Cp Zr(CH CH C(CH ) )Cl Zr 2 2 2 3 3 i Pr (0.95 mmol, 0.95 equiv.) in 5 mL THF. tBu Compound was not isolated cleanly; partial characterization is as follows. 1H

NMR (C6D6, 25 ºC, 500 MHz) δ: 7.63 (m, 2H, o-C6H5), 7.60 (s, 2H, C6H2),

7.04–6.97 (m, 3H, m- and p-C6H5), 6.01 (br s, 1H, NH), 5.61 (s, 10H, C5H5),

3.23 (br, 2H, CH(CH3)2), 1.54–1.51 (m, 2H, CH2), 1.15 (d, 12H, CH(CH3)2,

3 JH-H = 7 Hz), 1.08 (s, 9H, C(CH3)3), 0.83–0.79 (m, 2H, CH2).

iPr For 4f: 1.00 mmol in situ generated 2f in 5 mL H N SiMe3 THF, 342 mg Cp Zr(CH CH C(CH ) )Cl Zr 2 2 2 3 3 i Pr (0.95 mmol, 0.95 equiv.) in 5 mL THF. tBu Compound was not isolated cleanly; partial characterization is as follows. 1H

NMR (C6D6, 25 ºC, 500 MHz) δ: 7.55 (s, 2H, C6H2), 6.02 (br s, 1H, NH), 5.58

(s, 10H, C5H5), 3.2 (br, 2H, CH(CH3)2), 1.51–1.48 (m, 2H, CH2), 1.08 (d, 12H,

3 CH(CH3)2, JH-H = 7 Hz), 1.05 (s, 9H, C(CH3)3), 0.79–0.76 (m, 2H, CH2), 0.32

13 1 (s, 9H, Si(CH3)3). C{ H} NMR (C6D6, 25 ºC, 75.5 MHz, partial) δ: 153.7

(ipso-CN), 110.2 (Cp), 92.0 (Ar-C≡C-Si), 0.5 (Si(CH3)3).

iPr For 4g: 1.00 mmol in situ generated 2g in H N 5 mL THF, 342 mg Cp2Zr(CH2CH2C(CH3)3)Cl Zr i Pr (0.95 mmol, 0.95 equiv.) in 5 mL THF. tBu Compound was not isolated cleanly; partial characterization is as follows. 1H

NMR (C6D6, 25 ºC, 500 MHz) δ: 7.52 (s, 2H, C6H2), 6.00 (br s, 1H, NH), 5.60

(s, 10H, C5H5), 3.20 (br, 2H, CH(CH3)2), 2.37 (t, 2H, C≡CCH2CH2CH2CH3,

3 JH-H = 7 Hz), 1.54–1.38 (m, 6H, C≡CCH2CH2CH2CH3 and Zr(CH2)2C(CH3)3),

3 1.14 (d, 2H, CH(CH3)2, JH-H = 7 Hz), 1.07 (s, 9H, CH2CH2C(CH3)3), 0.81 (t,

3 3H, C≡CCH2CH2CH2CH3, JH-H = 7 Hz), 0.82–0.77 (m, 2H, Zr(CH2)2C(CH3)3).

13 1 C{ H} NMR (C6D6, 25 ºC, 75.5 MHz, partial) δ: 152.5 (ipso-CN), 110.1 (Cp),

88.3 (C≡C), 82.6 (C≡C).

Chapter 3 New Routes towards Nitrogen-Containing Polymers

3.1 Abstract

In an effort to form nitrogen-containing polymers, three strategies were attempted: (1) [2+2] cycloaddition chemistry using compounds 3a,

Cp2ZrMe(NHC6H4C≡CPh), and 4a, Cp2Zr(CH2CH2CMe3)(NHC6H4C≡CPh); (2) hydroamination of compound 1a, H2NC6H4C≡CPh, using a titanium(IV) catalyst; (3) electrochemical or chemical oxidation of compound 1a. The first strategy, involving thermolysis of zirconium amides 3a or 4a, did not generate zirconium- and nitrogen-containing polymers, but rather oligomers of the parent amine 1a. By the second strategy, compound 1a was heated at

70 °C in the presence of 10 mol % Ti(NR2)4 (R = Me or Et) for 4 days, resulting in the formation of oligomeric chains (5). Oligomer 5 was characterized by NMR, IR, and UV/Vis spectroscopy, and by matrix-assisted laser desorption/ionization – time-of-flight (MALDI-TOF) mass spectrometry and gel permeation chromatography (GPC). These data indicate up to 15 repeat units in the chain. Model reactions were performed using phenylacetylene or diphenylacetylene and aniline or 2,6-diisopropylaniline, which generated a variety of enamines and imines (compounds 6 to 14), three of which were characterized by X-ray crystallography. The proposed

87 mechanism of hydroamination polymerization most likely follows the widely accepted catalytic cycle developed by Bergman and coworkers,87, 88, 151 as well as an extra step of σ-bond insertion of an alkyne into a Ti–N bond.237-241 The third and final strategy towards nitrogen-containing polymers involves an oxidation polymerization of compound 1a. Cyclic voltammetry of 1a indicates

0/+ an irreversible oxidation wave at 0.60 V (relative to Cp2Fe , while chemical oxidation of 1a using Ce(SO4)2 and catalytic CF3COOH in dimethylformamide gives oligomer 15, which possesses up to 9 repeat units in the chain.

3.2 Introduction

Polymers containing nitrogen are ubiquitous: all living matter is composed of amide-linked proteins, while commodity products include polyamides, polyimides, and polyurethanes (Chapter 1.3.2). In 2000, the

Nobel Prize in Chemistry was awarded to Alan J. Heeger, Alan G.

MacDiarmid, and Hideki Shirakawa for the discovery and development of conductive polymers.26-28 Two examples of intrinsically conductive polymers include polyaniline and polypyrrole, with commercial applications as antistatic materials, corrosion inhibitors, and computer screen coatings.

Polyaniline is particularly unique among conducting polymers due to its chemical and environmental stability, its tunable electrical conductivity and its unique optical properties.27, 242

The group 4 metal-nitrogen chemistry discussed in Chapters 1 and 2 provides a basis for our attempts at preparing nitrogen-containing polymers.

For example, imidozirconocene compounds react with alkynes in a [2+2] cycloaddition reaction to generate an azazirconacyclobutene (Chapter 1.4.1,

Scheme 1.6).80 Compounds 3 and 4 are ideal precursors to extend this small molecule chemistry to that of oligomers and polymers, since they possess a

Zr–N functionality and a C≡C moiety. The proposed [2+2] cycloaddition polymerization of compounds 3 and 4 is expected to afford a daisy chain zirconium- and nitrogen-containing polymer (Scheme 3.1). Such a polymer is expected to display interesting reactivity typical of Zr–N metallacycles

(Chapter 1.4.1, Schemes 1.7 and 1.8), including ring expansion reactions89 and metallacycle transfer from zirconocene to a main group reagent.92

R R H N R' 2n Zr 2n Zr N R' R'' - R"H R R 3 or 4

R R' R Cp2 Zr N N Zr Cp R 2 R R' n

Scheme 3.1 Proposed route towards a daisy chain polymer containing zirconium and nitrogen.

This [2+2] cycloaddition chemistry also has applications in catalysis.

Bergman and coworkers have proposed a catalytic cycle for the hydroamination of an alkyne using group 4 metal species (Chapter 1.5.1,

Scheme 1.14).87, 88, 151 This catalytic cycle is widely accepted for the inter- and intramolecular hydroamination of alkynes and allenes using group 4 metal catalysts.131-133, 135, 136

Recently, however, researchers have proposed some exceptions to this mechanism: certain cationic238, 239 and neutral240, 241 group 4 complexes are known to catalyze intramolecular hydroamination cyclization of alkenes238-241 or alkynes241 with evidence for a M–N σ-bond insertion mechanism like that proposed for lanthanide catalysts (Chapter 1.5.1, Scheme 1.15).134

Computational studies support this pathway for the hydroamination cyclization of alkenes,243 although the analogous computations for allenes suggest a [2+2] cycloaddition route.244

Table 3.1 Characteristic data supporting the [2+2] cycloaddition mechanism or the σ-bond insertion mechanism of hydroamination. M=NR M–N [2+2] cycloaddition σ-bond insertion

(intermolecular (intramolecular hydroamination) hydroamination) 1 -1 1 1 0 Rate Law [M] [N–H] [alkyne] [M] [alkyne(CH2)nN–H] Induction period? Yes No High [amine] Rate decrease No effect Low [amine] Rate increase No effect High [Product] No effect Rate decrease ΔH‡ ~12 kcal/mol* ~ 10 kcal/mol ΔS‡ ~-45 eu* ~ -30 eu 2° amine substrates? No Yes * Measured for Cp’2AnMe2-catalyzed intermolecular alkyne hydroamination, An = actinide.

Unique characteristics of each hydroamination mechanism are given in

Table 3.1.241 Kinetic parameters can clearly distinguish between the two mechanisms. However, the most telling evidence comes from the reactivity with secondary amines: the [2+2] cycloaddition pathway involves a metal- imide intermediate, which is limited to primary amine substrates. In contrast the σ-bond insertion mechanism can be operative for both primary and secondary amines.

Our goal is to use hydroamination chemistry to prepare oligomers and polymers. Compounds 1, which possess both a primary amine and a C≡C moiety para-substituted about the central arene ring, are therefore ideal candidates for this purpose.

Another route to nitrogen-containing polymers can be envisaged based on the similarity of the electronic structure of compound 1a to that of aniline, as discussed in Chapter 2.3.2. As aniline is polymerized by an oxidation process (Chapter 1.3.2), this prompted interest in the oxidative polymerization of compound 1a.

For the polymerization of aniline, Scheme 1.4 in Chapter 1.3.2 shows the first few mechanistic steps. The first step involves formation of a radical cation, for which various resonance structures can be drawn. Theoretically, all of these resonance structures can participate in the radical coupling reaction. In actuality, polyaniline almost exclusively consists of head-to-tail

(N–para-C) linkages. For example, for electrochemically prepared

91 polyaniline, no N–ortho-C or N–meta-C linkages are detected by resonance

Raman spectroscopy.245 Similar results are obtained by X-ray photoelectron spectroscopy; however, the experimental error in this technique may be as high as 15 %, leading the authors to propose a maximum of 15 % branching in polyaniline.246 Semiempirical calculations suggest that N–para-C coupling is significantly more probable than N–N, N–ortho-C, N–meta-C, and para-C– para-C coupling,37, 247 especially in an acidic medium.248 Similar conclusions relating the pH to the degree of N–para-C versus N–ortho-C linkages were obtained experimentally.249, 250

Given that the N–para-C radical coupling reaction is the chief means of propagation, substituents in the para-position are problematic for the polymerization of aniline. In fact, there are very few reports in the literature describing the electropolymerization of a para-substituted aniline.34, 251

These experiments were conducted merely to demonstrate the existence of N– ortho-C linkages and no molecular weight data are given for the resultant polymer.

Clearly, substituents in the para-position of aniline thwart the head- to-tail radical coupling step of the polymerization. Compound 1a, which bears a substituent in its para-position, is nonetheless a prime candidate for polymerization, because of the various resonance structures that can be drawn for the radical cation formed from 1a (Figure 2.5, Chapter 2.3.2). In one of these resonance structures (structure VII in Figure 2.5), the unpaired

92 electron resides on the para-position of the pendant phenylethynyl moiety, which can potentially be involved in a similar type of head-to-tail radical coupling reaction as that required to form polyaniline.

We therefore envisioned three new routes to nitrogen-containing polymers, which will be discussed in this Chapter: (1) [2+2] cycloaddition polymerization using amidozirconocene compounds 3 or 4; (2) hydroamination polymerization of compounds 1 using a group 4 catalyst; (3) electrochemical or chemical oxidation of compound 1a.

3.3 Results and Discussion

3.3.1 Proposed [2+2] Cycloaddition Polymerization

The proposed [2+2] cycloaddition polymerization of compounds 3 and 4 to afford a daisy chain zirconium- and nitrogen-containing polymer is shown in Scheme 3.1. Under thermal duress, amidozirconium compounds 3 or 4

(Cp2ZrMe(NHC6H2R2C≡CR’) or Cp2Zr(CH2CH2CMe3)(NHC6H2R2C≡CR’), respectively) are expected to liberate one equivalent of alkane (R”H = CH4 or

CH3CH2CMe3) to generate an imidozirconocene species. Subsequent [2+2] cycloaddition with an alkyne fragment of a neighbouring molecule generates the polymer.

Thermolysis reactions of 3a and 4a in toluene-d8 at 100 °C were monitored for 3 weeks by 1H NMR spectroscopy and by electron impact (EI) and MALDI-TOF mass spectrometry. The 1H NMR spectrum of 3a indicates

93 a shift in resonances, while that of 4a reveals a broadening of signals suggestive of the formation of oligomers. The EI and MALDI-TOF mass spectra reveal no evidence of the anticipated daisy chain oligomers.

Interestingly, peaks are observed in the MALDI-TOF mass spectra at 579,

772, and 965 m/z, corresponding to trimers, tetramers, and pentamers of compound 1a.

Two possible explanations can account for the formation of oligomers of

1a from the thermolysis of compound 3a or 4a. First, the anticipated daisy chain polymers may in fact form, but subsequently hydrolyze during the sample preparation for MALDI-TOF mass spectrometry. Second, the amidozirconocene compound may catalyze the intermolecular hydroamination of the alkyne.87, 88 In other words, the group 4 compound is functioning as a catalyst, rather than a monomer, which gives rise to nitrogen-containing oligomers, rather than zirconium- and nitrogen-based daisy chain polymers. In both cases, compounds 3a and 4a mediate intermolecular alkyne hydroamination. These results prompted interest in polymerization via hydroamination, which is the subject of the following section.

3.3.2 Hydroamination Polymerization

Thermolysis of amidozirconocene compounds does not generate Zr- and

N-containing polymers; however, the catalytic hydroamination of compounds

1 could present a viable route towards N-containing polymers. Zirconocene

94 compounds 3 and 4 are not particularly feasible as precatalysts, for the following two reasons: (1) their synthesis requires multiple synthetic and purification steps; (2) hydroamination using these catalysts requires long reaction times (≥ 13 d) at high temperatures (≥ 110-120 °C).87 In addition to zirconocene-based compounds, a wide variety of catalysts are reported to carry out hydroamination of alkynes,139, 141 including other group 4 metal species, early and late transition metals, main group compounds, and lanthanide and actinide species. The most well-studied of these are the group 4 transition metal compounds,136 because they are inexpensive, nontoxic, and commercially available or relatively easy to synthesize. In addition, these catalysts are typically not restricted to reactions of activated substrates (e.g. styrenes, terminal alkynes, aromatic amines), and they mediate intermolecular reactivity in addition to intramolecular hydroamination. Therefore, the commercially available Ti(IV) species

Ti(NMe2)4 was tested for the hydroamination polymerization of compound 1a.

Reaction of 1a with 0.10 equiv. of Ti(NMe2)4, at 70 °C in toluene for ca.

80-90 h results in hydroamination polymerization to give 5 (Scheme 3.2).

Oligomer 5 was isolated in 35.8 % yield upon precipitation into a vortex of hexanes, and was characterized by NMR, IR, and UV/Vis spectroscopy, as well as GPC and MALDI-TOF mass spectrometry.

H H N

0.10 equiv. H C H Ti(NMe2)4 H H n C C N C o C Toluene, 70 C, Ph C N 80-90 h x Ph y n 5 1a

Scheme 3.2 Hydroamination polymerization of compound 1a to synthesize oligomer 5.

In the 1H NMR spectrum, the broad peaks are indicative of an oligomer. Signals attributed to enamine CH and imine CH2 moieties are observed at 6.1 and 3.8 ppm, respectively, in a ratio of 0.73 : 0.27 (x : y in

Scheme 3.2). The corresponding peaks in the 13C NMR spectrum are observed at 167 (C=N), 101 (PhCH), and 36 ppm (CH2), assigned by HSQC and HMBC experiments. The IR spectrum of oligomer 5 shows important differences compared to monomer 1a (Figure 3.1). For example, the absence of peaks between 2700 and 1650 cm-1 indicates a lack of C≡C fragments. The peaks at 3384 and 1620 cm-1 are attributed, respectively, to the N–H stretch of a secondary amine and the C=N stretch of an imine moiety.217, 252 The peaks at 1592 and 1515 cm-1 are assigned to ring stretching modes.242, 253, 254

The UV/Vis spectrum of oligomer 5 is very similar to that of monomer 1a

(Figure 3.2), indicating minimal conjugation along the oligomer chain.

Figure 3.1 IR spectra of monomer 1a (blue) and oligomer 5 (red).

Figure 3.2 UV/Vis spectra of monomer 1a (blue) and oligomer 5 (red) in acetonitrile.

Relative to polystyrene standards, GPC data indicate Mn = 730, Mw =

1540, corresponding to a number-average degree of polymerization (DPn) of 4.

Using laser light scattering detection, GPC data indicate a higher DPn of 6

(Mn = 1230, Mw = 1680). It should be noted that these values may be underestimated since GPC data were acquired under air in THF. Indeed, the residual water present in air may hydrolyze the backbone,252 leading to chain degradation; furthermore, samples of 5 were not completely soluble in THF and were filtered to remove insoluble material prior to GPC analysis.

Literature precedent suggests that the mechanism of hydroamination follows a [2+2] cycloaddition pathway (Chapter 1.5.1, Scheme 1.14).102, 131-133,

135, 136 In the proposed mechanism (Scheme 3.3), the active catalytic species is presumed to be the terminal titanium-imide, generated by reaction of the

Ti(NMe2)4 precatalyst with amine 1a, with loss of two equivalents of HNMe2.

Reaction of the Ti=N species with the alkyne portion in another molecule of

1a results in [2+2] cycloaddition to generate the azatitanacyclobutene. An additional equivalent of amine 1a opens the metallacycle to produce the

(amido)(enamido)titanium species, which then eliminates enamine and regenerates the active titanium-imide catalyst. (For simplicity, only one regioisomer is shown, but conceivably either carbon atom in the alkyne moiety could bind α- to the metal center. In addition, only the enamine is shown, although spectroscopic data indicate the presence of both the imine and the enamine.) The released product can reenter the catalytic cycle since it contains a primary amine functional group, which can form a new

98 titanium-imide species. This is the step in the catalytic cycle which would result in growth of the oligomeric chain.

H2N Ph Ph NMe [Ti] 2 [Ti] N Ar NMe2 2 equiv. HNMe2

NH2 Ar NH H Ar = Ph

Ph H or N NH Ph H 2 n Ar N Ar Ph [Ti] Ph N NH2 [Ti] NH H

NH2

Ph H2N Ph

Scheme 3.3 Hydroamination polymerization mechanism using the group 4 precatalyst Ti(NMe2)4.

The above mechanism, however, does not account for an important feature revealed in the MALDI-TOF mass spectrum of 5 (Figure 3.3). The minor peaks in the mass spectrum (highlighted in purple) are located at an integral number of monomer units, 193n m/z, where 193 Daltons is the mass of compound 1a, and n is an integer. However, the major peaks (highlighted in blue) are located at an integral number of monomer units plus 45 m/z.

That is, each peak corresponds to a species with 193n + 45 m/z, where n is an

99 integer between 5 and 15. The extra 45 m/z, which occurs exactly once at every oligomeric chain, may result from the addition of HNMe2 (molecular weight = 45 Daltons) to every oligomeric chain. The presence of NMe2 is in fact indicated in the 1H NMR spectrum with a peak at 1.7 ppm. Using this peak, as well as the fact that HNMe2 is added exactly once to every chain, end group analysis is possible. End group analysis indicates approximately

10 repeat units in the chain.

Figure 3.3 MALDI-TOF mass spectrum of 5 using Ti(NMe2)4 as the precatalyst. Peaks highlighted in purple correspond to the minor product at 193n m/z, where n is an integer. Peaks highlighted in blue correspond to the major product, at 193n + 45 m/z, where n is an integer.

To test this hypothesis of HNMe2 adding to every chain, the same reaction was carried out for monomer 1a using Ti(NEt2)4 as the precatalyst.

100

In this case, the MALDI-TOF mass spectrum (Figure 3.4) reveals patterns of peaks spaced by 193 m/z, corresponding to one monomer fragment. Here, again, the major peaks (highlighted in blue) are located at an integral number of monomer units plus 73 m/z (molecular weight of HNEt2 = 73

1 Daltons). In the H NMR spectrum, signals attributed to N(CH2CH3)2 occur at ca. 3.0 and 0.9 ppm. End group analysis indicates that this oligomer contains ca. 12 repeat units.

Figure 3.4 MALDI-TOF mass spectrum of 5 using Ti(NEt2)4 as the precatalyst. Peaks highlighted in purple correspond to the minor product at 193n m/z, where n is an integer. Peaks highlighted in blue correspond to the major product, at 193n + 73 m/z, where n is an integer.

101

As discussed in Chapter 3.2 (Table 3.1), reactivity with a secondary amine (HNR2, R = Me, Et) is incompatible with a [2+2] cycloaddition mechanism (Schemes 1.14 and 3.3), and is instead indicative of σ-bond insertion (Scheme 1.15). However, the hydroamination polymerization may occur entirely via a σ-bond insertion mechanism, or by a combination of the

[2+2] cycloaddition and the σ-bond insertion mechanisms. The following section describes the small molecule model chemistry that helps distinguish between these two alternatives.

3.3.3 Model Compounds for Hydroamination Polymerization

Model reactions were performed to further probe the structure of oligomer 5 and glean information regarding its mechanism of formation.

These model reactions use diphenylacetylene or phenylacetylene as the alkyne, and aniline, 2,6-diisopropylaniline, N-methylaniline or diethylamine as the primary or secondary amine.

No reaction was observed for either alkyne with N-methylaniline or diethylamine in the presence of Ti(NMe2)4 at 70 °C for 3-4 days. The crude mixture consisted largely of unreacted starting materials. The lack of reactivity using a secondary amine is inconsistent with a mechanism that relies solely on σ-bond insertion. Thus, the [2+2] cycloaddition mechanism is likely operative for this titanium(IV) catalyst.

Reactions using diphenylacetylene and aniline or

2,6-diisopropylaniline are shown in Scheme 3.4, while reactions of

102 phenylacetylene with aniline or 2,6-diisopropylaniline are shown in Scheme

3.5. In all cases, imines and enamines may be formed. In latter case, the asymmetrical nature of the alkyne may result in products with Markovnikov

(M) or anti-Markovnikov (AM) regiochemistry.141 In general, the regiochemistry depends not only on the catalyst,255-262 but also on the amine259, 260, 262 and alkyne141, 255-258, 262 substrates.

NH2 R R + Ph Ph

0.1 equiv. Ti(NMe2)4 Toluene, 70 oC

R R H H N H N H Ph Ph R Ph Ph R

6: R = H 7: R = H i i 8: R = Pr 9: R = Pr

Scheme 3.4 Synthesis of model compounds: hydroamination of diphenylacetylene with aniline or 2,6-diisopropylaniline.

In the hydroamination reaction between diphenylacetylene and aniline or 2,6-diisopropylaniline (Scheme 3.4) imines 7 and 9 are formed preferentially relative to enamines 6 and 8. The relative ratios of 6 : 7 and 8 :

9 are 47 : 53 and 5 : 95, respectively. In contrast, many literature studies on the hydroamination of diphenylacetylene with an arylamine report the preferential formation of the enamine.87, 256, 257, 263 It should be noted that

103 interconversion of the imine and enamine does not occur under these reaction conditions. Indeed, samples of imine 9 in C6D6 were heated at 70 °C for 4

1 days, either with or without Ti(NMe2)4, and monitored by H NMR spectroscopy. Spectra indicate only the presence imine 9, without any enamine 8.

Imines 7 and 9 crystallized from their respective reaction mixtures and were characterized by single-crystal X-ray diffraction studies (Figure 3.5;

Table 3.2); these structures have not been reported previously.210, 211

Figure 3.5 Molecular structure representation of compounds 7 and 9 (ellipsoids drawn at the 50 % probability level). All hydrogen atoms except those on C2 have been omitted for clarity. Selected bond lengths and angles are given in Table 3.2.

The hydrogen atoms on C2 were unambiguously located and refined in these compounds, with C–H distances of 0.97(2) to 1.03(2) Å, indicating that compounds 7 and 9 are in fact imines rather than enamines. This

104 designation is also supported by the bond distances and angles in the central core (Table 3.2), as well as NMR data on the crystalline sample.

Table 3.2 Selected bond lengths (Å) and angles (°) for 7 and 9, and a comparison to diagnostic bond lengths and angles typical of imines and enamines.210, 211 7 9 Range for Range for imines210, 211 enamines210, 211 N1–C1 1.282(2) 1.279(1) 1.275 to 1.297 1.398 to 1.477 N1–C3 1.423(2) 1.420(1) C1–C2 1.517(2) 1.512(1) 1.486 to 1.527 1.305 to 1.365 C1–C9/C21 1.500(2) 1.494(1) C2–C15 1.514(2) 1.523(1) C1–C2–C15 114.3(1) 115.81(8) 116.0 to 119.5 122.4 to 126.9 C2–C1–N1 124.2(1) 124.16(9) C2–C1–C9/C21 118.6(1) 118.86(8) 115.7 to 119.4 120.9 to 126.3 N1–C1–C9/C21 117.2(1) 116.86(8) C1–N1–C3 120.9(1) 124.43(8)

NH2 R R + Ph H

0.1 equiv. Ti(NMe2)4 Toluene, 70 oC

R R R R

H HN H HN H N H N H H HPhR Ph H R H Ph R Ph H R

10-M: R = H 10-AM: R = H 11-M: R = H 11-AM: R = H i i i i 13-M: R = Pr 13-AM: R = Pr 14-M: R = Pr 14-AM: R = Pr

Scheme 3.5 Synthesis of model compounds: hydroamination of phenylacetylene using aniline or 2,6-diisopropylaniline. M = Markovnikov addition, AM = anti-Markovnikov addition.

105

Reaction of aniline and phenylacetylene results in a mixture of compounds, due to the presence of imines and enamines, as well as

Markovnikov (M) and anti-Markovnikov (AM) regiochemistry. In the EI mass spectrum, the peak at 195 m/z is indicative of the expected products

10-M, 10-AM, 11-M, and/or 11-AM (Scheme 3.5), while the peaks at 147 and

297 m/z correspond to unexpected products. The former peak is consistent with a reaction between phenylacetylene and dimethylamine, presumably derived from the Ti(NMe2)4 catalyst. This product, H2C=C(NMe2)(Ph) (or its anti-Markovnikov regioisomer), has been observed in an analogous reaction.237 The latter peak at 297 m/z (compound 12) implicates a 2 : 1 reaction between phenylacetylene : aniline. This compound subsequently crystallized from the mixture (vide infra). Presumably, compound 12 results from the reaction of enamine 10-AM or imine 11-AM with an additional equivalent of phenylacetylene. It is important to note that these unexpected products are formed from the reaction of a secondary amine (dimethylamine) or an enamine/imine (10-AM/11-AM) with phenylacetylene. These results, like the addition of HNR2 (R = Me, Et) to oligomer 5, implicate a σ-bond insertion mechanism (Chapter 1.5.1, Scheme 1.15) in which phenylacetylene inserts into a Ti–N bond.

In the 1H NMR spectrum of the mixture of products, compounds 10-M,

10-AM, 11-M, 11-AM, and 12 are found in a ratio of ca. 2 : 48 : 11 : 15 : 24.

Peaks for 10 and 11 were assigned on the basis of literature comparisons256

106 and two-dimensional NMR experiments for both the crude mixture and crystalline compound 12. IR spectroscopy of the mixture indicates N–H,

C=N, C=C, and C–N stretches.

Crystals which grew from the mixture were confirmed to be compound

12 by single crystal X-ray diffraction (Figure 3.6). While compounds 10 and

11 are known products of other hydroamination reactions,237 compound 12 has not been previously reported.

C17 C3 C2 C11 N1

C4 C1

Figure 3.6 Molecular structure representation of compound 12 (ellipsoids drawn at the 50 % probability level). All hydrogen atoms have been omitted for clarity. Selected bond lengths (Å) and angles (°): N1–C5 1.506(4), N1–C2 1.393(3), N1–C3 1.415(3), C1–C2 1.357(3), C3–C4 1.346(3), C1–C11 1.423(3), C4–C17 1.436(3), C2–N1–C5 120.9(2), C3–N1–C5 119.9(2), C2–N1–C3 119.2(2) N1–C2–C1 126.3(3), N1–C3–C4 125.5(3), C2–C1–C11 125.0(2), C3– C4–C17 126.7(2).

The bond distances and angles in 12 are typical of enamines (see Table

3.2).264, 265 The nitrogen atom is planar, which is not often the case for enamines.264, 265 For example, semiempirical calculations performed on the simplest tertiary enamine, N,N-dimethylaminoethene, indicate that forcing a

107 planar geometry at nitrogen raises the energy by 5.6 kcal/mol compared to a pyramidal configuration.265 Only those enamines with an electron withdrawing substituent such as NO2 or CN trans- to the nitrogen atom were optimized to be planar, presumably due to the push/pull of electrons.265

In compound 12, not only is the nitrogen atom planar, but the backbone from C11 to C17 is also very nearly planar, including the two phenyl rings containing C11 and C17. There is no evidence of π-stacking in the packing model, so the planarity of compound 12 cannot be explained by packing effects. Rather, this planarity is suggestive of participation from the lone pair on nitrogen to the π-system along the backbone of the molecule.

This is supported by the UV/Vis spectrum of 12, in which λmax = 357 nm; in comparison, aniline shows λmax at 230 nm. Another indication of the electronic delocalization is given by the C1–C11 and C4–C17 bond lengths of

1.423(3) and 1.436(3) Å, respectively, which are significantly shorter than a typical C–C single bond (1.54 Å).217 With delocalization, the C1–C2 and C3–

C4 bonds might be expected to lengthen in comparison to a typical C=C double bond. In fact, this is not the case for compound 12 or for other structurally characterized enamines,264, 265 in which the C=C bond length is essentially constant at 1.34 Å regardless of the n-π participation of nitrogen.

The related reactions to form compounds 13 and 14 proceed in a similar manner; however, there is no evidence for any 2 : 1 products like 12, or any reactivity with dimethylamine, as judged by EI-MS. In the 1H NMR

108 spectrum, peaks were assigned based on literature comparisons,256 and the product distribution was determined to be 13-M : 13-AM : 14-M : 14-AM = 3 :

11 : 40 : 46. Thus, the imine is formed preferentially compared to the enamine, as observed for compounds 7 and 9, and the anti-Markovnikov product is slightly favoured over the Markovnikov product. In general, there is minimal control over the tautomer and the regiochemistry; in contrast, other catalyst systems offer much greater control.141, 255-257, 259-261, 263

The purpose of synthesizing model compounds 6 to 14 was to deduce the structure of oligomer 5 and garner information on the hydroamination mechanism. In this vein, there are four important points to summarize this section. First, both imines and enamines are formed in all hydroamination reaction, with a preference for imines. Thus, it is reasonable that oligomer 5 consists of both imine and enamine fragments, and the spectroscopic data for oligomer 5 support this formulation. In contrast to the small molecule model compounds in which the imine is the preferred tautomer, there is a slight preference for enamines in oligomer 5. Second, there is minimal regioselectivity for the Markovnikov and anti-Markovnikov products in the formation of compounds 10, 11, 13 and 14. A similar lack of regioselectivity may also exist for oligomer 5, which is supported by the width of the peaks in the 1H NMR spectrum of 5. Third, in the reaction of phenylacetylene and aniline, the observation of H2C=C(NMe2)(Ph) (or its regioisomer) and compound 12 supports the same type of σ-bond insertion step as implicated in

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the reaction of oligomer 5 with HNR2 (R = Me, Et). Finally, while the σ-bond insertion pathway is clearly operative, it is not the only mechanism in the formation of 5. This is indicated by the lack of reactivity between phenylacetylene or diphenylacetylene and a secondary amine

(N-methylaniline or diethylamine). Thus, oligomer 5 is likely formed by a combination of the [2+2] cycloaddition (Schemes 1.14 and 3.3) and the σ-bond insertion (Scheme 1.15) pathways, with the former resulting in the growth of the oligomeric species, and the latter resulting in capping of the alkyne moiety.

3.3.4 Oxidation Polymerization

As discussed in Chapters 2.3.2 and 3.2, the electronic structure of compound 1a is similar to that of aniline. A cyclic voltammetric experiment was conducted in order to assess whether compound 1a could undergo chemical or electrochemical polymerization, in direct analogy to polyaniline.

An irreversible oxidation wave is observed at +0.60 V relative to ferrocene/ferrocenium (Figure 3.7). This value is similar to the one-electron oxidation of aniline (1.06 V relative to standard calomel electrode ≈ 0.56 V

0/+ 245 relative to Cp2Fe ).

The fact that 1a can be irreversibly oxidized prompts the question of whether it can also undergo a chemical oxidation polymerization. Indeed,

31 chemical oxidation of 1a in acidic conditions (CF3COOH) using 1 equiv.

Ce(SO4)2 in N,N-dimethylformamide results in oligomer 15 (Scheme 3.6).

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Figure 3.7 Cyclic voltammogram for compound 1a (CH2Cl2, 0.1 M n 0/+ [ Bu4N][PF6], 0.25 V/s at 25 °C; potentials were calibrated against Cp2Fe as an internal standard). Epa(A) = 0.60 V.

NH2

CF3COOH H n C + 2n Ce(SO4)2 C C N DMF C 25 oC, 18 h n 15

+ n Ce2(SO4)3 + n H2SO4 1a

Scheme 3.6 Oxidative polymerization of 1a to synthesize oligomer 15.

Oligomer 15 is insoluble in most organic solvents, marginally soluble

1 in THF, and slightly soluble in DMF. The H NMR spectrum in DMF-d7 displays very broad resonances. The broad peaks may be indicative of an oligomer, or may be caused by residual paramagnetic Ce(III) as a byproduct.

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End group analysis is not possible due to the breadth of the peaks. The poor solubility of 15 impedes efforts to obtain 13C NMR data. However, according to MacDiarmid and coworkers,266 13C NMR spectra of soluble oligoanilines are not always informative. Indeed, spectra are typically of much greater complexity than expected, with more signals than there are carbon atoms in the postulated repeat unit, which is rationalized by the slow interchange of many conformational isomers.

The IR spectrum of 15 shows certain similarities to 1a (Figure 3.8): the peaks at 2221, 1460, and 1375 cm-1 are assigned to the C≡C, benzene ring, and C–N stretching modes, respectively.253, 254 Differences occur in the ring breathing region: the peaks at 1595 and 1512 cm-1 are assigned to the quinoid phenyl ring stretch and the benzenoid phenyl ring stretch, respectively, by analogy to the IR spectra of oligomeric aniline derivatives

(peaks at 1587 and 1510 cm-1, respectively).242, 253, 254 The band at 1644 cm-1 is tentatively assigned to an N–H bending vibration; the related peak for aniline occurs at 1628 cm-1.267

The UV/Vis spectra of 1a and 15 (Figure 3.9) are very similar, with absorption maxima for both species observed at ca. 320 nm, indicating that both species have a similar degree of conjugation along the backbone.

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Figure 3.8 IR spectra of monomer 1a (blue) and oligomer 15 (red).

Figure 3.9 UV/Vis spectra of monomer 1a (blue) and oligomer 15 (red) in N,N-dimethylformamide.

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GPC data on the soluble fraction of 15 in THF indicate Mn = 350, Mw =

750; these results may be underestimated due to the poor solubility of 15 in

THF. The MALDI-TOF mass spectrum of 15 (Figure 3.10) shows patterns of peaks spaced by 191 m/z, the mass of one monomer fragment, up to 9 repeat units.

Figure 3.10 MALDI-TOF mass spectrum of 15.

+• DFT computations for 1a opt were presented in Chapter 2.3.2. The

HOMO and HOMO–2 have a high degree of electron density on the nitrogen center, in the alkyne spacer, and at the para-carbon atom of the phenyl ring.

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These qualitative pictures suggest that the radical coupling of 1a to form oligomer 15 (Scheme 3.7) may occur in a similar manner to that of aniline

(Chapter 1.3.2, Scheme 1.4).

H H N C C N C C H H - e- - e-

H H N C C N C C H H

H H N C C N C C H H H

- 2H+

H H N C C N C C H

Scheme 3.7 First steps in the proposed mechanism of formation of 15.

To conclude this section, it is interesting to note that oligomers 5 and

15 represent different macromolecules derived from exactly the same monomer. This is evidenced by the distinct spectroscopic data for each oligomer. For example, the IR spectra show the presence of an alkyne stretch for oligomer 15 and a notable absence of this stretch for oligomer 5. In addition, the MALDI-TOF mass spectra of the two oligomers are different: peaks for 15 are spaced by 191 m/z, while peaks for 5 are spaced by 193 m/z.

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This corresponds to loss of two hydrogen atoms per repeat unit for oligomer

15 in comparison to 5.

Thus, although certain lanthanides are known to catalyze the

134, 141 hydroamination of alkenes and alkynes, in this case, Ce(SO4)2 is acting as an oxidant rather than as a hydroamination catalyst. (In fact, there are only two references in which cerium is used as a hydroamination catalyst,268,

269 but both of these reports use trivalent cerium, rather than Ce(IV).)

3.4 Summary

In this chapter, two new routes to nitrogen-containing oligomers were successfully established: (1) hydroamination polymerization of a bifunctional amine-alkyne; (2) oxidative polymerization of an aniline-like derivative. In both cases, the monomer employed was compound 1a. This compound is rare in its ability to generate two different oligomers from the same monomer.142

Oligomer 5, formed by hydroamination, contains up to 15 repeat units in the chain, and is capped by one molecule of dialkylamine which originates from the tetrakisdialkylamidotitanium(IV) catalyst. Model chemistry suggests that this species contains both imine and enamine moieties, and that there is minimal regioselectivity in the reaction. In the formation of 5, a combination of the [2+2] cycloaddition mechanism (Chapter 1.5.1, Scheme

1.14) and the σ-bond insertion mechanism (Chapter 1.5.1, Scheme 1.15) are operative.

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Oligomer 15, formed by oxidation, contains up to 9 repeat units in the chain. Certain spectroscopic properties are similar to polyaniline. This is the first well-characterized example of a polyaniline derivative with a substituent in the para-position.

3.5 Experimental Section

3.5.1 General Considerations

General experimental considerations are given in Chapter 2.5.1, with the following additions. MALDI-TOF mass spectra were acquired using a

Waters Micromass MALDI micro MX. Spectra were acquired using the following conditions: positive polarity mode, reflectron flight path, 12 kV flight tube voltage, 10 Hz laser firing rate, 10 shots per spectrum, pulse 1950

V, detector 2350 V. The instrument was calibrated using polyethyleneglycol

(PEG). The matrix consisted of 6 mg of α-cyano-4-hydroxycinnamic acid

(CHCA) in 1 mL of a 6 : 3 : 1 mixture of CH3CN : CH3OH : H2O plus one drop of CF3COOH. The analyte solution consisted of 3-5 mg of polymer in 1 mL of

270 CH2Cl2. Samples were prepared using the layer method: 1 μL of matrix was spotted onto the sample plate under an atmosphere of air, the sample plate was allowed to dry, then the plate was brought into an inert atmosphere,271 whereupon 1 μL of analyte was spotted onto the sample plate and the plate was allowed to dry again.

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Polymer molecular weights were determined by gel permeation chromatography (GPC) using one of two instruments. Absolute and relative molecular weights were determined by triple detection GPC using a Waters liquid chromatograph equipped with a Waters 515 HPLC pump, Waters 717 plus autosampler, Waters Styragel columns (4.6x300 mm), HR2 x 2 and HR4,

Waters 2410 differential refractometer (refractive index detector, λ = 940 nm), Wyatt tristar miniDAWN (laser light scattering detector, λ = 690 nm) and a Wyatt ViscoStar viscometer. A flow rate of 0.5 mL/min was used and samples were dissolved in THF (ca. 2 mg/mL), and prepared in air. Relative molecular weights were determined using a Waters liquid chromatograph equipped with a Waters 1515 HPLC pump, Waters Styragel columns

(4.6x300 mm), HR 4E x 3, Waters 2414 differential refractometer (refractive index detector, λ = 880 nm). A flow rate of 1.0 mL/min was used and samples were dissolved in THF (ca. 2 mg/mL) and prepared in air. Polystyrene standards were purchased from Polymer Laboratories, with molecular weights varying between 580 and 283,300 g mol-1.

Cyclic voltammetry studies were performed in a BASi RDE-2 cell stand for rotating disk electrochemical experiments, using a glassy carbon working electrode with a disk diameter of 3.0 mm, an aqueous Ag/AgCl reference electrode and a Pt wire auxiliary electrode. The working electrode was polished with alumina (0.05 μm) and rinsed with deionized water prior to

n use. The supporting electrolyte used was [ Bu4N][PF6], 0.1 M solution; all

118 potentials were referenced versus ferrocene/ferrocenium. All electrochemical data were acquired with a computer-controlled BASi Epsilon EC potentiostat, using the Epsilon EC software.

3.5.2 Starting Materials and Reagents

General considerations for starting materials and reagents are given in

Chapter 2.5.2. Aniline, 2,6-diisopropylaniline and N-methylamine were degassed by sparging with N2; diethylamine was degassed by sonication.

Ti(NMe2)4 and Ti(NEt2)4 were purchased from Strem and used as received.

3.5.3 Crystallography

General considerations for crystallography are given in Chapter 2.5.3.

For compounds 7 and 9, the H atoms on C2 were located and refined; all other H atoms were calculated and allowed to ride on the carbon to which they are bonded assuming a C–H bond length of 0.95 Å. Molecular structure representations of compounds 7 and 9 are shown in Figure 3.6 with selected bond distances and angles given in Table 3.2. The molecular structure representation of compound 12 is shown in Figure 3.7, with selected bond distances and angles given in the caption. Crystallographic parameters for compounds 7, 9, and 12 are given in Table 3.3.

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Table 3.3 Crystallographic parameters for compounds 7, 9, and 12. 7 9 12 Formula C20H17N C26H29N C22H19N Formula weight 271.35 355.50 297.38 Crystal system monoclinic monoclinic orthorhombic Space group P21/n P21/c Pbca a (Å) 5.5976(11) 11.2839(5) 16.1137(8) b (Å) 8.3168(6) 11.8464(5) 8.8958(4) c (Å) 31.769(3) 15.6094(7) 22.9830(12) α (deg) β (deg) 92.784(4) 94.908(2) γ (deg) V (Å3) 1477.2(2) 2078.91(16) 3294.5(3) Z 4 4 8 dcalc (g·cm-3) 1.220 1.136 1.199 Abs coeff, μ (cm-1) 0.070 0.065 0.069 Data collected 9575 44347 11649 Rint 0.0386 0.0445 0.0418 Data Fo2 > 3σ(Fo2) 2584 6382 2900 No. of parameters 198 252 208 R1(a) 0.0410 0.0461 0.0566 wR2(b) 0.1009 0.1320 0.1711 Goodness of fit 1.029 1.032 1.040 ∑ F − F 2 2 2 (a) o c (b) ∑ w(Fo − Fc ) R1 = wR2 = 2 2 ∑ Fo ∑ w(Fo )

3.5.4 Synthesis and Characterization

Thermolysis of compounds 3a and 4a

Compound 3a or 4a (ca. 0.5 mmol) was placed in an NMR tube with

1.0 mL toluene-d8. The dark brown samples were heated at 100 °C in a temperature-controlled oil bath, and monitored periodically by 1H NMR spectroscopy, and EI and MALDI-TOF mass spectrometry. Thermolysis of 4a resulted in a thick mixture after 1 week. After 3 weeks, the following data

1 were observed. For thermolyzed 3a. H NMR (toluene-d8, 25 ºC, 400 MHz)

δ: 7.7–7.3, 7.1–7.0, and 6.2–5.3 (ArH and C5H5), 0.2 (CH3). EI-MS: highest

MW peak at 399.4 m/z. MALDI-TOF MS: highest MW peak at 818.7 m/z

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(100 %); peaks at 579.9 (60 %) and 773.0 (82 %) correspond to trimer and

1 tetramer of 1a, respectively. For thermolyzed 4a. H NMR (toluene-d8,

25 ºC, 400 MHz) δ: 7.5–7.6.5 and 6.2–5.5 (br, ArH and C5H5), 1.5–0.5 (alkyl).

EI-MS: highest MW peak at 386.2 m/z. MALDI-TOF MS: highest MW peak at 1066.1 m/z, hexamer of 1a, (5 %); peaks at 579.9 (24 %), 773.0 (100 %), and

966.2 (9 %) correspond to trimer, tetramer and pentamer of 1a, respectively.

Synthesis of oligomer 5

Compound 1a (640 mg, 3.31 mmol), Ti(NMe2)4 H N Ph (74 mg, 0.33 mmol, 0.10 equiv.), and 40 mL C C N toluene were placed in a 100 mL bomb, to give a H C C H Ph H brown mixture. After heating at 70 °C for 3.5 n days, the mixture was evacuated to about 5-10 mL, then precipitated into a vortex of 75 mL hexanes. The solid brown precipitate was isolated on a frit.

An identical protocol was used for polymerization with Ti(NEt2)4 as the catalyst.

1 Using Ti(NMe2)4 as the precatalyst, yield: 229 mg (35.8 %). H NMR

3 (C6D6, 25 ºC, 300 MHz) δ: 8.0–6.3 (br, 15H, ArH), 6.1 (d, 1.3H, =CH, JH-H =

8 Hz), 3.8 (br, 1H, CH2), 2.8 (br, 1.1H, NH), 1.7 (br, 1.1H, N(CH3)2). The integration data suggests that the ratio of enamine (=CH) : imine (CH2) is ca.

2.7 : 1, and that the ratio of enamine + imine : NMe2 end group is ca. 10 : 1.

13 1 C{ H} NMR (C6D6, 25 ºC, 75.5 MHz, partial) δ: 167.4 (C=N), 138.7 (Ar),

133.3 (Ar), 132.9 (Ar), 131.9 (Ar), 131.8 (Ar), 128.9 (Ar), 128.6 (Ar), 128.2 (Ar),

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124.8 (Ar), 101.7 (=CH), 48.8 (N(CH3)2), 36.0 (CH2). FT-IR (25 ºC, deposited

-1 from CH2Cl2 solution, cm ): ν(N–H) 3384 (weak), no peaks detected from

2700 to 1650, ν(C=N) 1620 (medium, sharp), ν(phenyl ring) 1592 (strong,

-5 sharp), ν(phenyl ring) 1515 (medium, sharp). UV/Vis (CH3CN, ca. 10 M,

25 ºC): λmax = 311 nm. For GPC analysis, oligomer 5 was placed in THF under air and filtered to remove insoluble particulates prior to acquiring GPC data. Since 5 is partially soluble in THF, some of the sample was removed upon filtration. GPC (versus polystyrene standards): Mn 730, Mw 1540. GPC

(laser light scattering detection): Mn 1230, Mw 1680. MALDI-TOF MS: highest MW peak 2944 m/z ([5]15 + 45).

1 Using Ti(NEt2)4 as the precatalyst, yield: 494 mg (77.2 %). H NMR

3 (C6D6, 25 ºC, 300 MHz) δ: 8.0–6.2 (br, 15H, ArH), 6.1 (d, 1H, =CH, JH-H = 8

Hz), 3.8 (br, 1H, CH2), 3.0 (q, 0.5H, N(CH2CH3)2), 2.8 (br, 1H, NH), 1.0–0.8

(m, 0.8H, N(CH2CH3)2). The integration data suggests that the ratio of enamine (=CH) : imine (CH2) is ca. 2 : 1, and that the ratio of enamine +

13 1 imine : NEt2 end group is ca. 12 : 1. C{ H} NMR (C6D6, 25 ºC, 75.5 MHz, partial) δ: 165.0 (C=N), 133.3 (Ar), 131.9 (Ar), 131.8 (Ar), 128.9 (Ar), 128.6

(Ar), 126.5 (Ar), 101.7 (=CH), 44.7 (N(CH2CH3)2), 31.5 (CH2), 21.8

-1 (N(CH2CH3)2). FT-IR (25 ºC, deposited from CH2Cl2 solution, cm ): ν(N–H)

3384 (weak), no peaks detected from 2700 to 1650, ν(C=N) 1620 (weak),

ν(phenyl ring) 1592 (weak), ν(phenyl ring) 1515 (weak). MALDI-TOF MS: highest MW peak 2005 m/z ([5]10 + 73).

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Synthesis of compounds 6 to 9

Reactions were carried out under identical conditions.

Diphenylacetylene (891 mg, 5.00 mmol) and Ti(NMe2)4 (112 mg, 0.500 mmol) were combined in a 50 mL bomb which was wrapped in aluminum foil.

Freshly degassed aniline (0.46 mL, 0.47 mg, 5.0 mmol) or diisopropylaniline

(0.94 mL, 0.88 g, 5.0 mmol) was added via syringe. The reaction mixture was heated at 70 °C for 65 h, and volatile materials were removed in vacuo to afford a brown oil.

For the reaction mixture of 6 and 7

H After exposure to vacuum, H N H N H diphenylacetylene and aniline are

still present in the mixture, as 67 indicated by NMR spectra. The relative ratio of compounds 6 : 7 is ca. 47 : 53. X-ray quality crystals which were obtained from the brown residue upon standing were determined to be

7. Compounds 6 and 7 have been previously synthesized and characterized,150 but no IR data was given, nor is the molecular structure of compound 7 known.

The presence of compounds 6 and 7 is confirmed by the following

1 resonances in the H NMR (C6D6, 25 ºC, 300 MHz and 400 MHz). For 6:

7.61–7.55 (m, C6H5), 7.17–7.12 (m, C6H5), 6.88–6.82 (m, C6H5), 6.69–6.65 (m,

C6H5), 6.34 (s, C6H5), 5.61 (s, =CHPh), 5.09 (s, NH). For 7: 8.27–8.20 (m,

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C6H5), 7.73–7.67 (m, C6H5), 7.21–7.16 (m, C6H5), 3.83 (s, CH2). EI-MS (m/z):

+ + 271.1 (2 %) [M] ; 180.1 (17 %) [M] – CH2Ph; 178.1 (100 %) PhC≡CPh.

HRMS: C20H17N mass 271.1366, calcd mass 271.1361, fit 1.8 ppm. FT-IR

-1 (25 ºC, mixture of 6 and 7, deposited from C6D6 solution, cm ): ν(N–H) 3392

(medium, broad), ν(C=N) 1626 (strong, sharp), ν(C=C) 1600 (very strong, sharp).

For the mixture of 8 and 9

After exposure to vacuum,

H diphenylacetylene and 2,6-diisopropyl- H N H N H aniline are still present in the

mixture, indicated by the NMR data. 89 The relative ratio of compounds 8 : 9 is ca. 5 : 95. X-ray quality crystals grew from the brown residue upon standing; these were determined to be 9 by single crystal X-ray diffraction.

Compound 8 has been previously synthesized and characterized by multinuclear NMR spectroscopy,256 but no IR data was given. Compound 9 has not been characterized, nor is its molecular structure known.

The presence of compounds 8 and 9 is confirmed by the following

1 resonances in the H NMR (C6D6, 25 ºC, 300 MHz and 400 MHz). For 8:

7.53–7.51 (m, 2H, ArH), 7.1–6.9 (m, 11H, ArH), 5.30 (s, 1H, =CHPh), 4.38 (br s, 1H, NH), 3.39 (septet, 2H, CH(CH3)2), 1.45 (d, 6H, CH(CH3)a(CH3)b), 1.30

(d, 6H, CH(CH3)a(CH3)b). For 9: 8.07–8.05 (m, 2H, C6H5), 7.20–7.12 (m, 5H,

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NC6H3 and C6H5), 6.91–6.81 (m, 6H, C6H5), 3.86 (s, 2H, CH2), 2.88 (septet,

2H, CH(CH3)2), 1.21 (d, 6H, CH(CH3)a(CH3)b), 1.10 (d, 6H, CH(CH3)a(CH3)b).

13 1 C{ H} NMR of crystalline 9 (C6D6, 25 ºC, 100.6 MHz, partial) δ: 165 (C=N),

135 (N-ipso-C), 131.6 (ArH), 130.1 (ArH), 128.9 (ArH), 128.3 (ArH), 128.0

(ArH), 126.1 (ArH), 123.8 (ArH), 123.0 (ArH), 36.4 (CH2), 28.5 (CH(CH3)2),

23.6 (CH(CH3)a(CH3)b), 21.8 (CH(CH3)a(CH3)b). EI-MS (m/z): 355.2 (7 %)

+ + [M] ; 264.2 (100 %) [M] – CH2Ph, 178.1 (82 %) PhC≡CPh. HRMS: C26H29N mass 355.2307, calcd mass 355.2300, fit 2.0 ppm. FT-IR (25 ºC, mixture of 8

-1 and 9, deposited from C6D6 solution, cm ): ν(N–H) 3399 (weak), ν(C=N) 1627

(medium, sharp), ν(C=C) 1600 (medium, sharp). FT-IR (25 ºC, crystalline 9

-1 deposited from C6D6 solution): ν(C=N) 1627 cm (very strong, sharp).

Synthesis of compounds 10 to 14

Phenylacetylene (511 mg, 5.00 mmol) and Ti(NMe2)4 (112 mg,

0.500 mmol) were combined in a 50 mL bomb which was wrapped in aluminum foil. Freshly degassed aniline (0.46 mL, 0.47 mg, 5.0 mmol) or diisopropylaniline (0.94 mL, 0.88 g, 5.0 mmol) was added via syringe. The reaction mixture was heated at 70 °C for 22 h, and volatile materials were removed in vacuo to afford a brown oil. For these reactions, M =

Markovnikov; AM = anti-Markovnikov.

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For the reaction mixture containing compounds 10, 11, and 12

H H Upon standing, X-ray quality crystals grew, Ph N H H N Ph which were determined to be 12 by single Ph H Ph H 10-M 10-AM crystal X-ray diffraction. The relative ratio of

Ph N H H N Ph compounds 10-M : 10-AM : 11-M : 11-AM : 12 H H Ph H Ph H is ca. 2 : 48 : 11 : 15 : 24. Compounds 10 and 11 11-M 11-AM have been previously synthesized,237 but there Ph N are no reports of compound 12 concurrent with Ph Ph 12 the synthesis of 10 and/or 11. Thus, the presence of compounds 10 and 11 was confirmed by 1H NMR and EI-MS, while crystalline compound 12 was characterized fully.

The presence of compounds 10 and 11 is confirmed by the following

1 resonances in H NMR (C6D6, 25 ºC, 300 MHz and 400 MHz). For 10-M: 4.49

2 (d, JH-H = 2 Hz, =CHaHb); the corresponding peak for =CHaHb is buried under

3 3 other signals. For 10-AM: 6.50 (dd, JH-H = 14 Hz, JH-H = 7 Hz, =CHNH),

3 5.47 (d, JH-H = 14 Hz, =CHPh). For 11-M: 2.88 (s, CH3). For 11-AM: 3.46

3 + (d, JH-H = 8 Hz, CH2). EI-MS for mixture of products (m/z): 297.2 (2 %) [12] ;

+ 195.1 (92 %) [10 and/or 11] , 147.1 (9 %) [H2C=C(Ph)(NMe2) or

+ PhCH=CH(NMe2)] . FT-IR (25 ºC, mixture of 10, 11 and 12, deposited from

-1 C6D6 solution, cm ): ν(N–H) 3401 (medium, broad), ν(C=N) 1634 (very strong, sharp), ν(C=C) 1595 (very strong, sharp), ν(C–N) 1275 (medium, sharp).

126

1 For crystalline 12: H NMR (C6D6, 25 ºC,

N 300 MHz and 400 MHz) δ: 7.28–7.25 (m, 4H,

CC6H5), 7.03–6.99 (m, 4H, CC6H5), 7.01–6.95 (m, 2H,

3 m-NC6H5), 6.72–6.69 (d, 2H, PhC(H)=C(H)N, JH-H = 12 Hz; buried under this peak is 1H, p-NC6H5), 6.25–6.20 (m, 2H, CC6H5), 6.21–6.18 (m, 2H, o-NC6H5),

3 13 1 5.75 (d, 2H, PhC(H)=C(H)N, JH-H = 12 Hz). C{ H} NMR (C6D6, 25 ºC,

75.5 MHz and 100.6 MHz, partial) δ: 142.2 (ipso-NC6H5), 131.6 (m-NC6H5),

130.8 (C6H5), 129.7 (C6H5), 128.9 (p-NC6H5), 127.8 (C6H5), 126.4 (C6H5), 126.0

(C6H5), 124.0 (C6H5), 120.5 (PhC(H)=C(H)N), 118.6 (ipso-CC6H5), 114.3

+ (o-NC6H5), 105.2 (PhC(H)=C(H)N). EI-MS (m/z): 297.2 (22 %) [M] ; 295.1

+ (100 %) [M] – 2H. HRMS: C22H19N mass 297.1513, calcd mass 297.1517, fit

-1.3 ppm. FT-IR (25 ºC, crystalline compound 12, deposited from C6D6 solution): ν(C=C) 1594 cm-1 (very strong, sharp), ν(C–N) 1275 cm-1 (very strong, sharp). Anal. Calcd for C22H19N (crystalline compound 12): C, 87.85;

H, 6.44; N, 4.71. Found: C, 88.46; H, 6.48; N, 5.27.

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For the reaction mixture of 13 and

14 H H N H H N After exposure to vacuum,

Ph H Ph H 2,6-diisopropylaniline is still present in

13-M 13-AM the mixture, as indicated by NMR

spectroscopy. The relative ratio of

N H H N compounds 13-M : 13-AM : 14-M : 14- H H Ph H Ph H AM is ca. 3 : 11 : 40 : 46. Compounds 13- 14-M 14-AM AM and 14-AM have been previously synthesized and characterized,256 but no IR data were given.

The presence of compounds 13 and 14 is confirmed by the following

1 resonances in H NMR (C6D6, 25 ºC, 300 MHz and 400 MHz). For 13-M: 5.36

2 2 (d, JH-H = 2 Hz, =CHaHb), 4.38 (d, JH-H = 2 Hz, =CHaHb). For 13-AM: 6.65

3 3 3 (dd, JH-H = 14 Hz, JH-H = 7 Hz, =CHNH), 5.19 (d, JH-H = 14 Hz, =CHPh),

3 4.16 (br, NH). For 14-M: 2.35 (s, CH3). For 14-AM: 7.41 (t, JH-H = 5 Hz,

3 + CHN), 3.51 (d, JH-H = 5 Hz, CH2). EI-MS (m/z): 279.2 (3 %) [M] ; 264.2 (5 %)

+ + [M] – Me; 188.1 (19 %) [M] – CH2Ph; 177.2 (29 %) 2,6-diisopropylaniline;

162.1 (100 %) 2,6-diisopropylaniline – Me. HRMS: C20H25N mass 279.1981, calcd mass 279.1987, fit -2.1 ppm. FT-IR (25 ºC, mixture of 13-M, 13-AM, 14-

-1 M and 14-AM, deposited from C6D6 solution, cm ): ν(N–H) 3401 (weak),

ν(C=N) 1620 (strong, sharp), ν(C–N) 1264 (medium, sharp).

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Synthesis of oligomer 15

To an orange suspension of Ce(SO4)2 (664 mg, H N C C n 2.00 mmol) in 5 mL N,N-dimethylformamide with two drops of CF3COOH was added 1a (193 mg, 1.00 mmol) in 5 mL dimethylformamide, under air. The resultant brown mixture was stirred for

18 h at room temperature, then precipitated into a vortex of rapidly stirring hexanes to afford a brown precipitate. Yield: 120 mg (62.2 %). 1H NMR

13 1 (DMF-d7, 25 ºC, 400 MHz) δ: 8.3–6.3 (very broad, Ph). C{ H} NMR (DMF-d7,

25 ºC, 100.7 MHz) δ: Poor solubility results in the observation of signals for the solvent only. FT-IR (25 ºC, Nujol mull, cm-1): ν(N–H) 3346 (medium, broad), ν(C≡C) 2221 (weak), ν(N–H bend) 1644 (medium, sharp), ν(C=N) 1620

(medium, sharp), ν(phenyl ring, quinonoid) 1595 (medium, sharp), ν(phenyl ring, benzenoid) 1512 (medium, sharp). UV/Vis (DMF, 25 ºC): λmax = 320 nm.

GPC (versus polystyrene standards; oligomer 15 is marginally soluble in

THF, thus a large amount of the sample was removed upon filtration):

Mn 350, Mw 750. MALDI-TOF MS (dried droplet method, deposited from

DMF solution): highest MW peak 1719 m/z ([15]9).

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Chapter 4 Phosphines Bearing Pendant Alkyne Substituents

4.1 Abstract

The synthesis of a series of phosphines bearing pendant alkyne substituents is reported. Sonogashira coupling furnishes arylbromides 16,

i i BrC6H2R2C≡CR’ (a R = Me, R’ = Ph; b R = Pr, R’ = Ph; c R = Pr, R’ = SiMe3;

i d R = Pr, R’ = p-C6H4Me). The phosphine center is then introduced using a dialkylamido protecting group, to yield phosphines of the form

i i (Et2N)2PC6H2R2C≡CR’, 17 (a R = Me, R’ = Ph; b R = Pr, R’ = Ph; c R = Pr, R’

= SiMe3). In the solid state, compounds 17 are isolated as dimeric complexes with bridging CuBr. Conversion to the dichloroarylphosphine is achieved via reaction with HCl(g) to yield compounds 18, Cl2PC6H2R2C≡CR’ (a R = Me, R’ =

i i Ph; b R = Pr, R’ = Ph; c R = Pr, R’ = SiMe3). Subsequent reduction using

LiAlH4 gives primary arylphosphines 19, H2PC6H2R2C≡CR’ (a R = Me, R’ =

i i Ph; b R = Pr, R’ = Ph; c R = Pr, R’ = SiMe3). These phosphines are relatively

“user-friendly”272 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. All compounds are characterized by multinuclear NMR spectroscopy, IR spectroscopy, high-resolution mass spectrometry, elemental analysis, and X-ray crystallography.

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4.2 Introduction

Primary phosphines (RPH2) are versatile reagents for many chemical reactions. For example, Scheme 4.1 shows the reaction of primary phosphines with a variety of substrates to generate a functionalized organophosphines.273 These compounds have applications in a wide variety of fields such as catalysis, nuclear imaging, materials science, environmental chemistry, biological chemistry, and biomedicine.273, 274 However, access to the rich chemistry of primary phosphines is precluded by their highly air- sensitive, toxic, malodorous and often pyrophoric nature.

R' RP R' Z O RPOH RP OH R'X Z [O] Z O O S O O R' HN NH R' R' N R' n R' N n R' R' P R PH2 P R R' R

HNR'2, HCHO O O O

R' R" O NR' O 2 O RP P NR' R" 2 R R' OH RP OH R' R"

Scheme 4.1 Reactions demonstrating the versatility of primary phosphines; byproducts are not shown.

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PH2 PH2 PH2

AB C

PH2 PH2 PH2

DEF

Figure 4.1 Selected examples of primary phosphines with aryl substituents.

One strategy to kinetically stabilize primary phosphines involves the use of bulky substituents. Consider the primary arylphosphines shown in

Figure 4.1. The parent compound, phosphine (PH3), is an extremely toxic, volatile gas (bp -87.8 °C), spontaneously flammable upon exposure to air.

Phenylphosphine (Compound A in Figure 4.1) is a highly air-sensitive pyrophoric liquid (bp 154 to 157 °C) with an offensive odour.275, 276 Upon addition of sterically bulky substituents, the relative reactivity and toxicity dramatically decrease. For example, 2,4,6-trimethylphenylphosphine

(MesPH2, Compound B in Figure 4.1) shows moderate oxidative stability in air and a less pronounced stench,277 and was the first primary phosphine to be characterized by X-ray crystallography.278 Greater steric protection is observed for 2,4,6-triethylphenylphosphine (Compound C in Figure 4.1),279

2,4,6-tri-iso-propylphenylphosphine (Compound D in Figure 4.1),279 and

2,6-diisopropylphenylphosphine (Compound E in Figure 4.1).280 These

132 arylphosphines are colourless liquids (bp 77 °C at 3 mbar for C and D, 73 to

85 °C at 0.5 mbar for E), and Compound E is reported to have very little

280 odour, but must stored below room temperature under N2. Thus, methyl, ethyl, and isopropyl groups about the central arene ring provide a certain degree of steric stabilization; in comparison, bulky tert-butyl groups, particularly in the ortho-positions impart a great deal of kinetic stability.

Indeed, 2,4,6-tri-tert-butylphenylphosphine (Mes*PH2, Compound F in Figure

4.1) is a crystalline solid (mp 114 °C) which oxidizes over several months upon exposure to air.281, 282

We are interested in the synthesis of new phosphorus-containing polymers, which are presented in Chapter 5. However, as highlighted in

Chapter 1.2, one of the major challenges surrounding the field of inorganic polymers is the preparation of suitable monomers. These monomers must be stable enough to be isolated and purified, but reactive enough to allow for polymerization. Towards this goal, we envisioned the synthesis of a primary arylphosphine which is sterically protected by bulky groups in the ortho-positions, yet also possesses a pendant alkyne moiety to promote further reactivity. In this Chapter, the synthesis of a series of phosphines bearing pendant alkyne moieties is reported. The primary phosphines are solids or highly viscous liquids, with low volatility and minor stench, and can be prepared in a sequence of generally high-yielding steps.

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4.3 Results and Discussion

4.3.1 Synthesis of Aryl Bromides

Sonogashira coupling of an aryl iodide and a terminal alkyne199-201

(Scheme 4.2) affords compounds 16, BrC6H2R2C≡CR’ (a R = Me, R’ = Ph; b R

i i i = Pr, R’ = Ph; c R = Pr, R’ = SiMe3; d R = Pr, R’ = p-C6H4Me) in excellent yields. Mass spectrometric data indicate that the coupling reaction takes place exclusively between the terminal alkyne and the aryl iodide, rather than the bromide. In general, the Sonogashira coupling reaction occurs much less readily and requires more forcing conditions for aromatic bromides than for the corresponding iodides.201

Br 1.3 equiv. 2.5 mol % trans-Pd(PPh3)2Cl2 R R H R R 1 mol % CuI + o HNEt2, 18 h, 25 C I R' R' 16

Scheme 4.2 Synthesis of compounds 16 (a R = Me, R’ = Ph; b R = iPr, R’ = i i Ph; c R = Pr, R’ = SiMe3; d R = Pr, R’ = p-C6H4Me).

Table 4.1 Selected spectroscopic data for compounds 16 (a R = Me, R’ = Ph; i i i b R = Pr, R’ = Ph; c R = Pr, R’ = SiMe3; d R = Pr, R’ = p-C6H4Me). IR stretch (cm-1) 1H NMR (ppm) 13C{1H} NMR (ppm) Cmpd C≡C m-C6H2R2 C≡C 16a 2213 7.11 90.7, 89.9 16b 2210 7.46 90.2, 90.1 16c 2160 7.42 105.9, 94.7 16d 2208 7.48 90.7, 89.5

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Selected spectroscopic data are provided in Table 4.1. The presence of the alkyne functionality is indicated by diagnostic peaks in the IR and

13C{1H} NMR spectra. For compound 16c, the signal corresponding to the alkyne carbon Ar-C≡C-SiMe3 is shifted significantly downfield, as was observed for the trimethylsilylalkynyl compounds discussed in Chapter 2

(Figure 2.1).208, 209

The solid state structures of compounds 16a, 16b, and 16d were determined by X-ray crystallography (Figure 4.2, Table 4.2). The Br–Cipso distances are similar to previously reported structures of the form

212 212 BrC6H4C≡CR (R = Ph 1.884(4) Å, R = C6H4Br 1.891(6) Å, and R =

213 C6H2Br2C≡CC6H4Br 1.887(4) Å ), with a slight elongation for 16d. This lengthening is also observed in other bromobenzene derivatives with 2,6- dialkyl substituents (Br–C 1.913 to 1.931 Å).283-285 The alkyne fragment is linear in all three molecules, with bond distances that fall within the typical range for diphenylacetylene derivatives (1.16 to 1.20 Å).212, 213

Table 4.2 Selected bond lengths (Å) and angles (°) for 16a, 16b, and 16d. 16a 16b 16d Br1–C1 1.898(3) 1.907(3) 1.917(2) C4–C7 1.450(5) 1.447(4) 1.436(3) C7–C8 1.190(5) 1.191(4) 1.200(3) C8–C9 1.439(5) 1.433(4) 1.440(3) C4–C7–C8 174.1(4) 176.3(4) 178.5(3) C7–C8–C9 176.9(4) 177.2(3) 179.2(3)

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16a 16b 16d

Figure 4.2 Molecular structure representation of compounds 16a, 16b, and 16d (ellipsoids drawn at the 50 % probability level). All hydrogen atoms have been omitted for clarity. Selected bond lengths and angles are given in Table 4.2.

4.3.2 Synthesis of Bisamidophosphines

The synthesis of compounds 17 is shown in Scheme 4.3, with diagnostic spectroscopic data given in Table 4.3. The introduction of a phosphorus center is clearly indicated in the 31P{1H} NMR spectra, as well as by the coupling to phosphorus observed for certain peaks in the 13C{1H} NMR spectra. Spectroscopic data for the alkyne fragment are essentially unchanged relative to starting materials 16.

136

1.9 equiv. tBuLi NEt2 Br Et2N Cu 1.2 equiv. CuCl P Br R R R R 1.0 equiv. ClP(NEt2)2 THF, 18 h -78 oC to 25 oC

R' R' 2 16 17

Scheme 4.3 Synthesis of compounds 17 (a R = Me, R’ = Ph; b R = iPr, R’ = i Ph; c R = Pr, R’ = SiMe3).

Table 4.3 Selected spectroscopic data for compounds 17 (a R = Me, R’ = Ph; i i b R = Pr, R’ = Ph; c R = Pr, R’ = SiMe3). IR stretch 31P{1H} 1H NMR 13C{1H} NMR (ppm) (cm-1) NMR (ppm) (ppm) cmpd C≡C m-C6H2R2 CP C≡C 17a 2210 86.2 7.21 140.9 (d) 91.0, 90.1 17b 2209 88.9 7.64 153.3 (d) 91.0, 90.4 17c 2157 85.0 7.57 153.1 (d) 106.3, 95.2

Based on literature precedent,286-290 this reaction likely proceeds by lithium/bromide exchange, followed by in situ generation of an organocopper reagent, followed by carbon–phosphorus bond formation. Organocopper reagents are often synthesized from a copper(I) salt and an organolithium or

Grignard reagent and utilized in situ;291 these compounds are known to mediate carbon–carbon290 and carbon–heteroatom287, 288 coupling reactions with greater selectivity than Grignard or organolithium reagents.

The use of CuCl is necessary in the synthesis of compounds 17: in the presence of this reagent, a single broad peak is observed in the 31P{1H} NMR spectrum at ca. 87 ppm; in the absence of CuCl, multiple peaks are observed

137 in the 31P{1H} NMR spectrum of the product after work-up. High resolution mass spectral data for compounds 17 are consistent with the liberation of copper halide to give (Et2N)2PC6H2R2C≡CR’ in the gas phase. In the solid state, however, phosphines 17 are observed to be complexes of copper bromide, as confirmed by elemental analysis and X-ray crystallographic data for 17a and 17b (vide infra). Halide exchange accounts for the isolation of

CuBr complexes rather than CuCl, and has been documented in the literature.292-296

It is not uncommon to observe copper-phosphine complexes in the solid state,297-301 free phosphine in the gas phase,302 and rapid phosphine exchange and/or dissociation in solution, the extent of which depends on the nature of the phosphine, the temperature, the solvent, and the concentration.302-304 For example, Morse and coworkers examined the gas phase and solution equilibria of various tertiary phosphine complexes of copper(I) halides (CuX, where X = Cl, Br, I) using several characterization techniques.302 While mass spectrometry shows only free phosphine in the gas phase, vapour pressure osmometry and UV spectrophotometry data indicate increased dissociation of the phosphine ligand upon dilution. In a related study, copper(I) halide complexes of tri-p-tolylphosphine (L) were examined by low temperature 31P

NMR spectroscopy.304 At -100 °C, the major species is the 2 : 1 dimer of the form [L2CuX]2; at -80 to -70 °C, ligand dissociation results in the presence of the 3 : 2 species [L3(CuX)2], the 1 : 1 dimer [LCuX]2 and the 2 : 1 monomeric

138

species [L2CuX]. Collectively, these results suggest that the structural integrity observed in the solid state for phosphine complexes of copper(I) halides is not necessarily retained in the gas phase or in solution.

Given this literature precedence, it is therefore not surprising that compounds 17 are observed to be free phosphine in the gas phase but dimeric complexes of copper bromide in the solid state. In contrast, the solution behaviour of compounds 17 is not entirely clear. For example, the relatively broad signal in the 31P{1H} NMR spectrum may suggest coordination to a quadrupolar nucleus such as 63Cu or 65Cu (S = 3/2 for both nuclei). However, the chemical shift of ca. 87 ppm observed for compounds 17 is similar to other bisamidoarylphosphines that are not coordinated to copper ((Et2N)2PPh 99.0;

i 305 ( Pr2N)2Ph 59.2 ppm; NMR data acquired in CDCl3).

4.3.2.1 X-Ray Crystal Structures of Bisamidophosphines

The coordination chemistry and solid state structures of copper(I) phosphine complexes are well documented.306, 307 Because of the d10 electronic configuration of Cu(I) and the resultant absence of ligand field control, Cu(I)-phosphine complexes can exist in a wide variety of structures and stoichiometries, in which the copper atoms may be di-, tri-, or tetracoordinate. The structure obtained depends on the starting material copper salt and its oxidation state prior to forming the Cu(I) species, the steric bulk of the phosphine, the solvent, the reaction conditions, and the crystallization conditions.307-309 In some cases, recrystallization of an

139 analytically pure sample results in a mixture of products with different stoichiometries.302

Br Br Br PPh3 Ph3P Ph3P Cu Cu Cu Cu PPh3 PPh3 Ph3P PPh3 Ph3P Br AB C

Ph3P PPh3 Ph3P Cu Br Cu Br Cu Br Br Cu Br Br Cu PPh3 Cu Br Cu PPh3 Cu Br PPh3 PPh3 Ph3P DE

Figure 4.3 Selected examples of (PPh3)m(CuBr)n (m = 1, 2, 3, 4; n = 1, 2, 4) complexes.

The extensive structural diversity of Cu(I)-phosphine complexes is demonstrated in the reaction of triphenylphosphine with copper bromide

(Figure 4.3). Under different reaction conditions and/or crystallization conditions, the reaction could lead to the following products: a tetracoordinate copper center in the 3 : 1 complex (Ph3P)3CuBr (Complex A in

297 Figure 4.3); a tricoordinate copper center in the 2 : 1 complex (Ph3P)2CuBr

310 (Complex B in Figure 4.3); a 3 : 2 complex (Ph3P)2Cu(μ-Br)2Cu(PPh3) in which one copper center is tetracoordinate and the other is tricoordinate

309, 311 (Complex C in Figure 4.3); a 1 : 1 complex [Ph3PCuBr]4 with a cubane structure in which all copper atoms are tetracoordinate (Complex D in Figure

312 4.3); a 1 : 1 complex [Ph3PCuBr]4 with a stepped tetrameric arrangement in which the outer two copper atoms are tricoordinate while the inner two are

140 tetracoordinate (Complex E in Figure 4.3).309 In one unique case,313 mixing a

2 : 1 ratio of phosphine : copper halide in benzene or chloroform did not result in the 2 : 1 complex (Ph3P)2CuBr (Complex A in Figure 4.3), but rather in a mixture of the 3 : 1 complex (Ph3P)3CuBr (Complex B in Figure 4.3) and the

3 : 2 complex (Ph3P)2Cu(μ-Br)2Cu(PPh3) (Complex C in Figure 4.3), isolated by fractional crystallization from ethanol.

Clearly, this wide variety of complexes makes it difficult to predict the solid state structure of copper(I)-phosphine complexes. However, as a general rule, coordination numbers of three or less about the copper center are only possible with ligands possessing steric bulk, particularly in the ortho-position of the triarylphosphine. For example, the copper(I) bromide adduct of tri(p-methoxy)phenylphosphine adopts a cubane arrangement,314 while tri(o-methoxy)phenylphosphine assumes a dimeric configuration with bridging bromides315 and tris(2,4,6-trimethoxy)phenylphosphine is monomeric316 with a dicoordinate copper center.

The molecular structures of compounds 17a and 17b are shown in

Figures 4.4 and 4.5, respectively, and bond lengths and angles are given in

Table 4.4. The dimeric core of compounds 17a and 17b is suggestive of the bulky nature of the phosphine.

141

Figure 4.4 Molecular structure representation of compound 17a (ellipsoids drawn at the 50 % probability level). All hydrogen atoms have been omitted for clarity. Selected bond lengths and angles are given in Table 4.4.

Figure 4.5 Molecular structure representation of compound 17b (ellipsoids drawn at the 50 % probability level). All hydrogen atoms have been omitted for clarity. Selected bond lengths and angles are given in Table 4.4.

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Table 4.4 Selected bond lengths (Å) and angles (°) for 17a and 17b. 17a 17b Cu1–Br1 2.389(2) 2.393(1) Cu1–Br1a 2.406(1) 2.447(1) Cu1–P1 2.194(2) 2.206(1) P1–N1 1.667(6) 1.701(4) P1–N2 1.679(7) 1.672(4) P1–C1 1.856(7) 1.862(4) C4–C7 1.46(1) 1.452(7) C7–C8 1.17(1) 1.187(7) C8–C9 1.45(1) 1.444(7) Cu1–Br1–Cu1a 81.34(4) 78.48(3) Br1–Cu1–Br1a 98.66(4) 101.52(3) P1–Cu1–Br1 133.05(7) 133.17(4) P1–Cu1–Br1a 128.24(7) 125.28(5) N1–P1–Cu1 115.6(2) 109.2(1) N2–P1–Cu1 108.8(2) 116.6(2) C1–P1–Cu1 110.3(2) 110.1(1) N1–P1–N2 107.2(3) 107.7(2) N1–P1–C1 101.0(3) 109.8(2) N2–P1–C1 113.9(3) 103.1(2) C4–C7–C8 178.5(9) 177.7(6) C7–C8–C9 176(1) 179.1(6)

Compounds 17a and 17b are the sole examples of structurally characterized bisamidoorganophosphines coordinated to a copper halide.

Other structurally characterized compounds involving trisamidophosphines or monoamidodiarylphosphines coordinated to a copper halide do not show the dimeric geometry, [(R3P)Cu(μ-X)]2. Instead, these compounds display a wide variety of geometries, including a 2 : 1 structure (Complex B in Figure

4.3),317 a 1 : 1 cubane structure (Complex D in Figure 4.3),318 and a 2 : 1 dimeric structure with a chelating phosphine.319 Other geometries are also possible for cationic complexes.320, 321 Despite the lack of related structures, compounds 17a and 17b can nonetheless be compared with certain related

143

X-ray crystal structures, including triarylphosphine complexes of copper halides and copper-free bisamidoarylphosphines.

There are four important points concerning the molecular structures of

17a and 17b. First, although copper chloride was used as the coupling agent, compounds 17a and 17b are isolated as copper bromide adducts. This is verified by the bond distances and angles in the copper halide core, in relation to other complexes of the form [(Ar3P)Cu(μ-X)]2, where X = Cl or Br

(Table 4.5).307, 322, 323 Second, the P–Cu bond distances in 17a and 17b fall within the range typical for copper(I)-phosphine complexes (2.183 to 2.369

Å).210, 211, 297, 324 This P–Cu distance is often independent of halide, the geometry of the complex, and the coordination number about the copper center. Third, for the (R2N)2PAr portion, the geometry about phosphorus correlates well with other bisamidoarylphosphine that are not coordinated to copper (P–Cipso 1.841 Å to 1.875 Å; P–N 1.665 Å to 1.740 Å; N–P–N 105° to

109°).305, 325-328 This suggests that phosphine coordination to copper does not affect the spatial or electronic configuration of the phosphorus center. The only exception may be in regards to the N–P–Cipso angles of 101.0(3)° and

113.9(3)° in 17a and 103.1(2)° and 109.8(2)° in 17b which are slightly larger than previously characterized structures (97.5° and 101.7°). This could be a result of crystal packing or steric effects. Fourth, the metrical parameters of the alkyne fragment are typical of diarylalkynes.212, 213

144

Table 4.5 A comparison of bond lengths and angles in the copper halide core of complexes 17a and 17b to other [Ar3PCu(μ-X)]2 complexes (Ar = aryl, X = halide).307, 322, 323 Cu–X (Å) X–Cu–X (°) 17a 2.389(2), 2.406(1) 98.66(4) 17b 2.393(1), 2.447(1) 101.52(3) [(Ar3P)Cu(μ-Br)]2 2.391(7) to 2.438(5) 97.0(2) to 100.8(1) [(Ar3P)Cu(μ-Cl)]2 2.281(3) to 2.342(3) 95.26(5) to 96.44(5)

4.3.3 Synthesis of Dichlorophosphines

Treatment of compounds 17 with hydrogen chloride gas generates dichlorophosphines 18 (Scheme 4.4) accompanied by a white precipitate. The

31P{1H} NMR spectrum of the reaction mixture shows a single peak at ca. 163 ppm, typical of dihaloarylphosphines.280 Compounds 18 are extracted with ether and toluene, and their elemental analyses and X-ray crystallographic data (vide infra) are consistent with loss of coordinated copper. Thus, the

1 precipitate must consist of [H2NEt2]Cl (detected by H NMR spectroscopy) as well as copper salts.

NEt2 Et2N Cu Cl Cl P Br P R R R R HCl(g)

Et2O/toluene 10 min, 0 oC R' R' 2 17 18

Scheme 4.4 Synthesis of compounds 18 (a R = Me, R’ = Ph; b R = iPr, R’ = i Ph; c R = Pr, R’ = SiMe3).

145

Spectroscopic data (Table 4.6) are consistent with this formulation. In contrast to the 31P{1H} spectrum, which shows a dramatic downfield shift for compounds 18 in comparison to 17, the signals in the 1H and 13C{1H} NMR do not change significantly.

Table 4.6 Selected spectroscopic data for compounds 18 (a R = Me, R’ = Ph; i i b R = Pr, R’ = Ph; c R = Pr, R’ = SiMe3). IR stretch 31P{1H} NMR 1H NMR 13C{1H} NMR (ppm) (cm-1) (ppm) (ppm) cmpd C≡C m-C6H2R2 CP C≡C 18a 2212 165.2 ~7.03* 143.7 (d) 92.7, 89.1 18b 2209 162.7 ~7.53* 155.1 (d) 92.6, 89.6 18c 2160 162.5 7.48 155.2 (d) 105.3, 97.4 * Peak overlaps with other signals.

X-ray crystallographic data (Figure 4.6, Table 4.7) for 18a and 18b indicate that the species are monomeric in the solid state, and have lost the coordinated copper(I) salt. For both 18a and 18b, bond lengths and angles about the phosphorus centers correlate well with previously reported dichloroarylphosphines,288, 329-332 and the alkyne fragments are linear with typical C≡C bond distances.212, 213

146

Figure 4.6 Molecular structure representation of compounds 18a and 18b (ellipsoids drawn at the 50 % probability level). All hydrogen atoms have been omitted for clarity. Selected bond lengths and angles given in Table 4.7.

Table 4.7 Selected bond lengths (Å) and angles (°) for 18a and 18b. 18a 18b P1–C1 1.822(2) 1.832(3) P1–Cl1 2.059(1) 2.066(1) P1–Cl2 2.064(1) 2.072(1) C4–C7 1.437(4) 1.440(4) C7–C8 1.194(4) 1.202(4) C8–C9 1.433(3) 1.437(4) Cl1–P1–Cl2 100.43(5) 101.62(5) C1–P1–Cl1 102.56(9) 101.8(1) C1–P1–Cl2 102.40(9) 101.7(1) C4–C7–C8 179.8(3) 177.6(3) C7–C8–C9 178.7(3) 178.4(3)

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4.3.4 Synthesis of Primary Phosphines

Reduction of dichlorophosphines 18 with LiAlH4 yields primary phosphines 19 (Scheme 4.5). In the 31P NMR spectrum of compounds 19, the

1 272 triplet at ca. -155 ppm ( JP-H = 207 Hz) is typical of a primary phosphine; the corresponding doublet is present in the 1H NMR spectrum at ca. 3.5 to 3.8

1 ppm ( JP-H = 207 Hz). The presence of a P–H bond is also clearly indicated in the IR spectrum with an intense peak at approximately 2300 cm-1. Other spectroscopic data (Table 4.8) are also consistent with this formulation, showing only slight differences compared to starting materials 18.

Under these conditions, the alkyne bond is not reduced: typically such reduction only occurs under thermal duress or using catalytic amounts of a titanium(IV) compound.333, 334 The molecular structure of 19b was determined by X-ray crystallography, and the bond lengths and angles are typical of other primary phosphines.332, 335, 336

Cl Cl H H P P R R R R LiAlH4

Et2O/toluene 18 h, -78 oC to 25 oC

R' R' 18 19

Scheme 4.5 Synthesis of compounds 19 (a R = Me, R’ = Ph; b R = iPr, R’ = i Ph; c R = Pr, R’ = SiMe3).

148

Table 4.8 Selected spectroscopic data for compounds 19 (a R = Me, R’ = Ph; i i b R = Pr, R’ = Ph; c R = Pr, R’ = SiMe3). IR stretch 31P NMR 1H NMR (ppm) 13C{1H} NMR (ppm) (cm-1) (ppm) cmpd C≡C P–H PH2 m-C6H2R2 CP C≡C 19a 2211 2306 -153.8 (t) 3.50 (d) 7.21 141.0 (d) 90.2 19b 2209 2315 -156.3 (t) 3.77 (d) 7.54 152.3 (d) 90.9, 90.3 19c 2158 2320 -156.2 (t) 3.72 (d) 7.50 152.1 (d) 106.7, 94.7

Figure 4.7 Molecular structure representation of compound 19b (ellipsoids drawn at the 50 % probability level). All hydrogen atoms have been omitted for clarity. Selected bond lengths (Å) and angles (°): P1–C1 1.838(2), C4–C7 1.442(3), C7–C8 1.192(3), C8–C9 1.433(3), C4–C7–C8 175.3(2), C8–C9–C10 176.0(2).

Primary phosphines bearing pendant alkene, alkyne, and allene functionalities have been previously reported. For example, the parent compound, ethynylphosphine, HC≡CPH2, was first synthesized in 9 % yield by low-pressure silent electric discharge of a mixture of acetylene and

149 phosphine.337 Higher yielding (20 – 40 %) synthetic routes towards

n ethynylphosphines (RC≡CPH2; R = H, Me, SiMe3, Bu), as well as the preparation of allenylphosphines (R2C=C=C(R’)PH2; R, R’ = H, Me) and the heavier group 15 analogues were reported by Guillemin et al.338, 339 These syntheses rely on the in situ-generated reducing agent AlHCl2 and require constant evacuation of the low boiling unsaturated phosphines onto a cold trap. Primary alkenyl- and alkynylphosphines with a methylene spacer group were reported by Norman and coworkers,340 synthesized in good yields

(60 to 75 %) by halide displacement from an alkenylhalide using the phosphinating agent LiAl(PH2)4. Primary phosphines with alkene and alkyne functional groups separated by a three- or four-carbon alkyl chain were synthesized by Marks and coworkers157, 176 in order to study their hydrophosphination cyclization behaviour.

These primary phosphines with pendant unsaturated hydrocarbon moieties are liquids and have not been characterized by X-ray crystallography, and in some cases these compounds are not even isolated but rather stored and characterized in solution.176, 338, 340 In contrast to these earlier reports, phosphines 19 synthesized herein are isolated in pure form without the need for distillation, are highly viscous liquids (19a and 19c) or even solid and crystalline (19b), and are not pyrophoric or particularly malodorous. Additionally, compounds 19 are stable in the solid or liquid state, or in solution, in an N2 atmosphere; for example, a C6D6 solution of the

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phosphine 19b can be stored under N2 for over a month without decomposition. Therefore, phosphines 19 are considered relatively “user- friendly”.272

4.4 Summary

In this chapter, a synthetic route to a series of phosphines incorporating alkynyl substituents was presented. These compounds represent unique bifunctional building blocks with potentially interesting reactivity. While the “user-friendly” primary arylphosphines described in

Chapter 4.2, Figure 4.1 do not contain any substituents which can be further functionalized, primary phosphines 19 contain a reactive P–H functional group in conjunction with the C≡C moiety. The way in which these two functionalities can be exploited towards the synthesis of new polymers is the subject of Chapter 5.

4.5 Experimental Section

4.5.1 General Considerations

General experimental considerations are given in Chapter 2.5.1 and

3.5.1, with the following additions. 31P{1H} NMR spectra were acquired on a

Bruker Avance 300 MHz spectrometer, a Bruker Avance 400 MHz spectrometer, a Varian Mercury 300 MHz spectrometer, or a Varian Mercury

400 MHz spectrometer, and referenced externally to 85 % H3PO4.

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4.5.2 Starting Materials and Reagents

General considerations for starting materials and reagents are given in

Chapters 2.5.2 and 3.5.2. The following compounds were synthesized according to literature procedures: 1-bromo-2,6-dimethyl-4-iodobenzene,341 1-

289 342 bromo-2,6-diisopropyl-4-iodobenzene, and ClP(NEt2)2.

4.5.3 Crystallography

General considerations for crystallography are given in Chapter 2.5.3.

Molecular structure representations of compounds 16(a, b, d), 17a, 17b,

18(a, b), and 19b are shown in Figures 4.2, 4.4, 4.5, 4.6, and 4.7, respectively, with selected bond distances and angles given in Tables 4.2, 4.4, 4.4, 4.7 and the caption to Figure 4.7, respectively. Crystallographic parameters for all of these compounds are given in Tables 4.9 and 4.10.

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Table 4.9 Crystallographic parameters for compounds 16a, 16b, 16d, and 17a. 16a 16b 16d 17a Formula C16H13Br C20H21Br C21H23Br C48H66Br2Cu2N4P2 Formula weight 285.17 341.28 355.30 1047.89 Crystal system orthorhombic monoclinic monoclinic monoclinic Space group Pna21 P21/c C2/c P21/c a (Å) 8.4825(3) 12.984(3) 20.104(4) 10.2751(16) b (Å) 24.5415(11) 10.408(2) 9.0615(18) 13.845(2) c (Å) 6.1744(3) 13.080(3) 20.509(4) 17.689(3) α (deg) β (deg) 104.12(3) 104.68(3) 92.000(2) γ (deg) V (Å3) 1285.35(10) 1714.2(6) 3614.1(12) 2515.0(7) Z 4 4 8 2 dcalc (g·cm-3) 1.474 1.322 1.306 1.384 Abs coeff, μ (cm-1) 3.172 2.390 2.270 2.533 Data collected 5519 12780 12519 23493 Rint 0.0270 0.0770 0.0408 0.0533 Data Fo2 > 3σ(Fo2) 2161 3009 3170 4418 No. of parameters 154 190 199 262 R1(a) 0.0250 0.0401 0.0293 0.0626 wR2(b) 0.0578 0.0939 0.0723 0.2213 Goodness of fit 1.037 1.018 1.040 1.030

Table 4.10 Crystallographic parameters for compounds 17b, 18a, 18b, and 19b. 17b 18a 18b 19b Formula C56H82Br2Cu2N4P2 C16H13Cl2P C20H21Cl2P C20H23P Formula weight 1160.10 307.13 363.24 294.35 Crystal system monoclinic triclinic monoclinic monoclinic Space group P21/c P-1 P21/c P21/c a (Å) 12.210(3) 7.7142(14) 10.696(2) 12.8438(18) b (Å) 12.162(3) 8.2249(15) 9.761(2) 10.7033(15) c (Å) 20.067(5) 12.280(2) 18.094(4) 13.4456(19) α (deg) 81.541(2) β (deg) 104.265(4) 82.734(2) 90.33(3) 103.084(2) γ (deg) 86.607(2) V (Å3) 2888.2(13) 763.8(2) 1889.0(7) 1800.4(4) Z 2 2 4 4 dcalc (g·cm-3) 1.334 1.335 1.277 1.086 Abs coeff, μ (cm-1) 2.213 0.513 0.425 0.145 Data collected 27122 7340 11697 16748 Rint 0.0600 0.0270 0.0525 0.0236 Data Fo2 > 3σ(Fo2) 5090 2683 4286 3177 No. of parameters 298 172 208 198 R1(a) 0.0505 0.0439 0.0584 0.0523 wR2(b) 0.1532 0.1239 0.1454 0.1610 Goodness of fit 1.009 1.048 1.027 1.032 ∑ F − F 2 2 2 (a) o c (b) ∑ w(Fo − Fc ) R1 = wR2 = 2 2 ∑ Fo ∑ w(Fo )

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4.5.4 Synthesis and Characterization

Synthesis of compounds 16

All compounds were prepared in a similar manner, thus a generic procedure is reported. To a solution of 1-bromo-2,6-dialkyl-4-iodobenzene in

100 mL HNEt2 was added 2.5 mol % trans-Pd(PPh3)2Cl2 and 1 mol % CuI.

The yellow mixture was stirred for 10 minutes, then 1.3 equiv. of HC≡CR was added by syringe. The mixture was allowed to stir at room temperature overnight then all volatiles were removed in vacuo. The residue was extracted with Et2O, filtered through a frit, and all volatiles were removed in vacuo.

Br For 16a: 3.110 g 1-bromo-2,6-dimethyl-4-iodobenzene

(10.00 mmol), 1.328 g phenylacetylene (13.00 mmol, 1.30 equiv.),

175 mg trans-Pd(PPh3)2Cl2 (0.249 mmol, 0.025 equiv.), 21 mg

CuI (0.11 mmol, 0.011 equiv.). Yield: 2.809 g (98.5 %). 1H NMR

(C6D6, 25 ºC, 300 MHz) δ: 7.55 (m, 2H, o-C6H5), 7.11 (s, 2H,

13 1 C6H2), 7.06–7.00 (m, 3H, m- and p-C6H5), 2.13 (s, 6H, CH3). C{ H} NMR

(C6D6, 25 ºC, 100.6 MHz) δ: 139.1 (quat-Ar), 132.2 (o-C6H5), 131.9 (C6H2),

129.6 (quat-Ar), 129.1 (m- or p-C6H5), 128.9 (m- or p-C6H5), 124.3 (quat-Ar),

122.6 (quat-Ar), 90.7 (C≡C), 89.9 (C≡C), 24.0 (CH3). EI-MS (m/z): 286 and

+ + 79 284 (100 %, 97 %) [M] ; 205 (15 %) [M] – Br. HRMS: C16H13 Br mass

284.0200, calcd mass 284.0201, fit -0.4 ppm. FT-IR (25 ºC, evaporation of a

-1 CH2Cl2 solution, cm ): ν(C≡C) 2213 (weak). Anal. Calcd for C16H13Br: C,

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67.39; H, 4.59. Found: C, 67.74; H, 4.91. Crystals suitable for X-ray crystallography were obtained from the oil upon standing.

Br For 16b: 4.440 g 1-bromo-2,6-diisopropyl-4-iodobenzene

(12.10 mmol) 1.602 g phenylacetylene (15.68 mmol, 1.30

equiv.) 211 mg trans-Pd(PPh3)2Cl2 (0.301 mmol, 0.025 equiv.)

and 24 mg CuI (0.13 mmol, 0.011 equiv.). Yield: 4.016 g

1 (97.6 %). H NMR (C6D6, 25 ºC, 300 MHz) δ: 7.58–7.54 (m,

2H, o-C6H5), 7.46 (s, 2H, C6H2), 7.02–6.99 (m, 3H, m- and p-C6H5), 3.50

3 3 (septet, 2H, CH(CH3)2, JH-H = 7 Hz), 1.07 (d, 12H, CH(CH3)2, JH-H = 7 Hz).

13 1 C{ H} NMR (C6D6, 25 ºC, 100.6 MHz) δ: 148.6 (quat-Ar), 131.9 (o-C6H5),

128.8 (m- or p-C6H5), 128.6 (m- or p-C6H5), 128.0 (C6H2), 127.4 (quat-Ar),

123.8 (quat-Ar), 123.3 (quat-Ar), 90.2 (s, C≡C), 90.1 (s, C≡C), 33.9 (s,

+ CH(CH3)2), 22.8 (s, CH(CH3)2). EI-MS (m/z): 342 and 340 (100 %, 99 %) [M] ;

+ 79 327 and 325 (48 %, 52 %) [M] – Me. HRMS: C20H21 Br mass 340.0829, calcd mass 340.0827, fit 0.6 ppm. FT-IR (25 ºC, Nujol mull, cm-1): ν(C≡C)

2210 (weak). Anal. Calcd for C20H21Br: C, 70.39; H, 6.20. Found: C, 70.31; H,

6.17. Crystals suitable for X-ray crystallography were obtained from the oil upon standing.

Br For 16c: 1.000 g 1-bromo-2,6-diisopropyl-4-iodobenzene

(2.724 mmol), 0.348 g trimethylsilylacetylene (3.54 mmol,

1.30 equiv.), 48 mg trans-Pd(PPh3)2Cl2 (0.068 mmol,

SiMe3 0.025 equiv.), 5 mg CuI (0.026 mmol, 0.01 equiv.). Yield:

155

1 0.872 g (94.9 %). H NMR (C6D6, 25 ºC, 300 MHz) δ: 7.42 (s, 2 H, C6H2), 3.44

3 3 (septet, 2H, CH(CH3)2, JH-H = 7 Hz), 0.99 (d, 12H, CH(CH3)2, JH-H = 7 Hz),

13 1 0.26 (s, 9H, SiMe3). C{ H} NMR (C6D6, 25 ºC, 75.5 MHz and 100.6 MHz) δ:

148.6 (quat-Ar), 128.6 (C6H2), 127.2 (quat-Ar), 123.2 (quat-Ar), 105.9

(Ar-C≡C-SiMe3), 94.7 (s, Ar-C≡C-SiMe3), 33.9 (s, CH(CH3)2), 22.7 (s,

29 1 CH(CH3)2), 0.0 (Si(CH3)3. Si{ H} NMR (C6D6, 25 ºC, 79.5 MHz) δ: -17.8.

EI-MS (m/z): 338 and 336 (32 %, 33 %) [M]+; 323 and 321 (95 %, 100 %) [M]+

79 – Me. HRMS: C17H25 BrSi mass 336.0910, calcd mass 336.0909, fit 0.3 ppm.

-1 FT-IR (25 ºC, evaporation of a CH2Cl2 solution, cm ): ν(C≡C) 2160 (very strong, sharp). Anal. Calcd for C17H25BrSi: C, 60.52; H, 7.47. Found: C,

60.38; H, 7.40.

Br For 16d: 1.470 g 1-bromo-2,6-diisopropyl-4-iodobenzene

(4.00 mmol), 0.605 g 1-ethynyl-4-methylbenzene (5.21 mmol,

1.30 equiv.), 70 mg trans-Pd(PPh3)2Cl2 (0.10 mmol,

0.025 equiv.), 8 mg CuI (0.042 mmol, 0.01 equiv.). Yield:

1 1.309 g (92.0 %). H NMR (C6D6, 25 ºC, 300 MHz) δ: 7.53–

7.51 (m, 2H, o-C6H4CH3), 7.48 (s, 2H, C6H2), 6.84–6.82 (m, 2H, m-C6H4CH3),

3 3.50 (septet, 2H, CH(CH3)2, JH-H = 7 Hz), 1.98 (s, 3H, C6H4CH3), 1.07 (d, 12H,

3 13 1 CH(CH3)2, JH-H = 7 Hz). C{ H} NMR (C6D6, 25 ºC, 75.5 MHz and

100.6 MHz) δ: 148.6 (quat-Ar), 138.7 (quat-Ar), 131.9 (o-C6H4CH3), 129.6

(m-C6H4CH3), 127.9 (C6H2), 127.2 (quat-Ar), 123.6 (quat-Ar), 120.9 (quat-Ar),

90.7 (C≡C), 89.5 (C≡C), 33.9 (CH(CH3)2), 22.8 (CH(CH3)2), 21.3 (C6H4CH3).

156

EI-MS (m/z): 356 and 354 (99 %, 100 %) [M]+; 341 and 339 (27 %, 29 %)

+ 79 [M] – Me. HRMS: C21H23 Br mass 354.0977, calcd mass 354.0983, fit -1.7

-1 ppm. FT-IR (25 ºC, evaporation of a CH2Cl2 solution, cm ): ν(C≡C) 2208

(weak). Anal. Calcd for C21H23Br: C, 70.99; H, 6.52. Found: C, 71.16; H, 6.41.

Crystals suitable for X-ray analysis were obtained by slow diffusion of pentane into a dichloromethane solution of 1d at room temperature.

Synthesis of compounds 17

All compounds were prepared in a similar manner, thus a generic procedure is reported. A dark red solution of 16 in 300 mL THF was cooled to

-78 ºC, and 1.9 equiv. tBuLi (1.7 M in pentane) was added via syringe over ca.

30 min to give a dark brown-purple mixture. The mixture was stirred at

-78 ºC for 3 h, then the cold bath was removed and the dark purple mixture was stirred at room temperature for 1 h. At room temperature, 1.2 equiv.

CuCl was added, then the mixture was cooled again to -78 ºC, whereupon

1.0 equiv. ClP(NEt2)2 was added via syringe over ca. 15 min. The mixture was stirred overnight while warming to room temperature. All volatile materials were removed in vacuo to give a green-brown residue, which was extracted with 100 mL toluene, filtered through Celite, and all volatiles were removed in vacuo once again. The residue was washed with 50 mL of toluene to give a beige solid, which was isolated and dried on a frit. An additional crop was isolated from the filtrate by removing the toluene in vacuo, adding

20 mL pentane, and isolating the beige solid on a frit.

157

For 17a: 5.667 g 16a (19.87 mmol), 22.2 mL tBuLi (1.7 M, Et2N Br Et2N Cu P 37.7 mmol, 1.9 equiv.), 2.361 g CuCl (23.85 mmol, 1.2 equiv.),

4.187 g ClP(NEt2)2 (19.87 mmol, 1.0 equiv.). Yield: 6.114 g

1 (58.7 %). H NMR (C6D6, 25 ºC, 300 MHz) δ: 7.60–7.57 (m,

2H, o-C6H5), 7.21 (m, 2H, C6H2), 7.03–7.00 (m, 3H, m- and

2 p-C6H5), 2.96–2.86 (m, 8H, N(CH2CH3)2), 2.55 (s, 6H, CH3),

3 31 1 0.95 (t, 12H, N(CH2CH3)2, JH-H = 7 Hz). P{ H} NMR (C6D6, 25 ºC,

13 1 121.5 MHz) δ: 86.2. C{ H} NMR (C6D6, 25 ºC, 75.5 MHz and 100.5 MHz,

1 partial) δ: 140.9 (d, ipso-CP, JP-C = 13 Hz), 134.9 (quat-Ar), 133.5 (s, C6H2),

132.0 (s, o-C6H5), 128.7 (m- or p-C6H5), 128.3 (m- or p-C6H5), 124.1 (d, quat-Ar, JP-C = 14 Hz), 91.0 (s, C≡C), 90.1 (s, C≡C), 44.2 (d, P(N(CH2CH3)2)2,

2 3 JP-C = 11 Hz), 22.6 (d, P(N(CH2CH3)2)2, JP-C = 11 Hz), 14.9 (s, CH3). MS (70

+ + eV, EI) m/z (%): 380 (35) [M] , 308 (90) [M – N(CH2CH3)2] , 237 (100) [M –

+ (N(CH2CH3)2)2 + H] . HRMS (70 eV, EI): calcd for C24H33N2P 380.2381, found 380.2389, fit 2.1 ppm. FT-IR (25 ºC, Nujol mull, cm-1): ν(C≡C) 2210

(weak). Anal. Calcd for C24H33BrCuN2P: C, 55.02; H, 6.35; N, 5.35. Found: C,

54.87; H, 6.54; N 5.26. Crystals suitable for X-ray diffraction were obtained from a toluene solution.

For 17b: 6.154 g 16b (18.03 mmol), 20.2 mL tBuLi (1.7 M, 34.34 mmol, 1.9 equiv.), 2.142 g CuCl (21.64 mmol, 1.2 equiv.), 3.80 g ClP(NEt2)2 (18.0 mmol,

1 1.0 equiv.) Yield: 7.976 g (76.3 %). H NMR (C6D6, 25 ºC, 300 MHz) δ: 7.65–

7.64 (m, 2H, C6H2), 7.60–7.57 (m, 2H, o-C6H5), 7.01–6.98 (m, 3H, m- and

158

p-C6H5), 4.30–4.24 (m, 2H, (CH(CH3)2), 3.15–2.95 (m, 8H, Et2N Br Et N Cu 2 3 P N(CH2CH3)2), 1.31 (d, 12H, CH(CH3)2, JH-H = 7 Hz), 1.01 (t, iPr iPr 3 31 1 12H, N(CH2CH3)2, JH-H = 7 Hz). P{ H} NMR (C6D6, 25 ºC,

13 1 121.5 MHz) δ: 88.9. C{ H} NMR (C6D6, 25 ºC, 75.5 MHz

1 and 100.6 MHz, partial) δ: 153.3 (d, ipso-CP, JP-C = 12 Hz),

132.0 (s, ArH), 128.7 (s, ArH), 128.5 (s, ArH), 127.2 (s, 2 quat-Ar), 125.3 (s, quat-Ar), 124.0 (s, quat-Ar), 91.0 (s, C≡C), 90.4 (s, C≡C),

2 43.4 (d, P(N(CH2CH3)2)2, JP-C = 12 Hz), 30.2 (s, CH(CH3)2), 28.4 (d,

3 P(N(CH2CH3)2)2, JP-C = 13 Hz), 25.8 (s, CH(CH3)2). EI-MS (m/z): 436.3 (7 %)

+ + + [M] – CuBr; 364.2 (100 %) [M] – CuBr – NEt2; 292.1(28 %) [M] – CuBr –

+ 2NEt2; 175.1 (37 %) [P(NEt2)2] . HRMS: C28H41N2P mass 436.3010, calcd mass 436.3007, fit 0.7 ppm. FT-IR (25 ºC, Nujol mull, cm-1): ν(C≡C) 2209

(weak). Anal. Calcd for C28H41BrCuN2P: C, 57.98; H, 7.12; N, 4.83. Found: C,

58.35; H, 7.08; N, 5.24. Crystals suitable for X-ray diffraction were obtained by slow evaporation of a toluene solution.

For 17c: 0.581 g of 16c (1.72 mmol), 2.0 mL tBuLi (1.7 M, Et2N Br Et2N Cu P 3.4 mmol, 2.0 equiv.), 0.205 g CuCl (2.07 mmol, 1.2 equiv.), iPr iPr

0.363 g ClP(NEt2)2 (1.72 mmol, 1.0 equiv.). Yield: 0.196 g

1 (19.8 %). H NMR (C6D6, 25 ºC, 300 MHz) δ: 7.57 (d, 2H,

4 3 SiMe3 C6H2, JP-H = 3 Hz), 4.18 (d of septets, 2H, (CH(CH3)2, JH-H = 2 4 7 Hz, JP-H = 3 Hz), 3.10–2.91 (m, 8H, N(CH2CH3)2), 1.21 (d, 12H, CH(CH3)2,

3 3 JH-H = 7 Hz), 0.98 (t, 12H, N(CH2CH3)2, JH-H = 7 Hz), 0.28 (s, 9H, Si(CH3)3).

159

31 1 13 1 P{ H} NMR (C6D6, 25 ºC, 121.5 MHz) δ: 85.0. C{ H} NMR (C6D6, 25 ºC,

1 100.6 MHz) δ: 153.1 (d, ipso-CP, JP-C = 13 Hz), 132.0 (s, quat-Ar), 128.2

(C6H2), 125.0 (s, quat-Ar), 106.3 (s, C≡C), 95.2 (s, C≡C), 43.3 (d,

2 3 P(N(CH2CH3)2)2, JP-C = 11 Hz), 28.3 (d, CH(CH3)2, JP-C = 13 Hz ), 25.6 (s,

29 1 CH(CH3)2), 14.5 (s, P(N(CH2CH3)2)2), 0.0 (s, Si(CH3)3). Si{ H} NMR (C6D6,

25 ºC, 79.5 MHz) δ: -17.7. MS (70 eV, EI) m/z (%): 432 (7) [M]+, 360 (100)

+ + [M – N(CH2CH3)2] , 330 (12) [M – N(CH2CH3)2 – CH3CH2 – H] , 287 (39) [M –

+ + (N(CH2CH3)2)2 – H] , 175 (19) [P(N(CH2CH3)2)2] . HRMS (70 eV, EI): calcd for C25H45N2PSi 432.3090, found 432.3097, fit 1.6 ppm. FT-IR (25 ºC,

-1 evaporation of a CH2Cl2 solution, cm ): ν(C≡C) 2157 (medium, sharp). Anal.

Calcd for C25H45BrCuN2PSi: C, 52.12; H, 7.78; N, 4.86. Found: C, 52.14; H,

7.89; N 4.91.

Synthesis of compounds 18

All compounds were prepared in a similar manner, thus a generic procedure is reported. A yellow solution of 17 in 150 mL Et2O/toluene was cooled in an ice-water bath, and HCl(g) was bubbled through the solution for 5 to 10 min., during which time a fine white precipitate was generated. The yellow solution was filtered through a Schlenk frit containing Celite, 75 mL toluene was added to the original flask, and the suspension was bubbled with

HCl(g) for a further 3 min. This solution was also filtered through the

Schlenk frit, and the precipitate was extracted with a further 50 mL toluene.

All volatiles were removed from the filtrate in vacuo to give a yellow solid.

160

Cl Cl For 18a: 1.731 g 17a (4.549 mmol). Yield: 1.397 g (82.1 %). 1H P

NMR (C6D6, 25 ºC, 300 MHz) δ: 7.56–7.52 (m, 2H, o-C6H5), 7.06–

3 7.00 (m, 5H, C6H2 and m- and p-C6H5), 2.40 (d, 6H, CH3, JP-C =

31 1 13 1 4 Hz). P{ H} NMR (C6D6, 25 ºC, 121.5 MHz) δ: 165.2. C{ H}

NMR (C6D6, 25 ºC, 75.5 MHz and 100.6 MHz, partial) δ: 143.7 (d,

1 ipso-CP, JP-C = 26 Hz), 132.8 (s, C6H2 or m-C6H5 or p-C6H5), 132.1 (s, o-C6H5),

129.0 (s, C6H2 or m-C6H5 or p-C6H5), 128.8 (s, C6H2 or m-C6H5 or p-C6H5),

3 123.3 (s, quat-Ar), 92.7 (s, C≡C), 89.1 (s, C≡C), 21.3 (d, CH3, JP-C = 26 Hz).

Suitable mass spectral data could not be obtained. FT-IR (25 ºC, evaporation

-1 of a CH2Cl2 solution, cm ): ν(C≡C) 2212 (weak). Anal. Calcd for C16H13Cl2P:

C, 62.57; H, 4.27. Found: C, 63.23; H, 4.79. Crystals suitable for X-ray diffraction were obtained from a toluene solution.

Cl Cl For 18b: 9.161 g 17b (15.79 mmol). Yield: 5.111 g (89.4 %). P

1 H NMR (C6D6, 25 ºC, 300 MHz) δ: 7.56–7.54 (m, 2H, o-C6H5)

7.54–7.52 (m, 2H, C6H2), 6.99–6.97 (m, 3H, m- and p-C6H5),

3 4.12–4.06 (m, 2H, CH(CH3)2), 1.12 (d, 12H, CH(CH3)2, JH-H =

31 1 7 Hz). P{ H} NMR (C6D6, 25 ºC, 121.5 MHz) δ: 162.7.

13 1 C{ H} NMR (C6D6, 25 ºC, 75.5 MHz and 100.6 MHz) δ: 155.1 (d, ipso-CP,

1 JP-C = 23 Hz), 135.6 (s, quat-Ar), 134.6 (s, quat-CC≡CC6H5), 132.1 (s, o-C6H5), 129.1 (s, m-C6H5 or p-C6H5), 128.8 (s, m-C6H5 or p-C6H5), 128.2 (s,

i C6H2), 123.2 (s, quat-CC≡CC6H2 Pr2), 92.6 (s, C≡C), 89.6 (s, C≡C), 30.9 (d,

3 + CH(CH3)2, JP-C = 27 Hz), 24.4 (s, CH(CH3)2). EI-MS (m/z): 362.1 (27 %) [M] ;

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+ 327.1 (100 %) [M] – Cl. HRMS: C20H21Cl2P mass 362.0753, calcd mass

362.0758, fit -1.4 ppm. FT-IR (25 ºC, Nujol mull, cm-1): ν(C≡C) 2209 (weak).

Anal. Calcd for C20H21Cl2P: C, 66.13; H, 5.83. Found: C, 66.32; H, 5.90.

Crystals suitable for X-ray diffraction were obtained from the oil upon standing.

Cl Cl For 18c: 0.817 g of 17c (1.42 mmol). Yield: 0.465 g (91.3 %). P

1 4 H NMR (C6D6, 25 ºC, 300 MHz) δ: 7.48 (d, 2H, C6H2, JP-H =

3 3 Hz), 4.03 (m, 2H, CH(CH3)2), 1.02 (d, 12H, CH(CH3)2, JH-H =

31 1 7 Hz), 0.26 (s, 9H, Si(CH3)3). P{ H} NMR (C6D6, 25 ºC, 121.5 SiMe3 13 1 MHz) δ: 162.5. C{ H} NMR (C6D6, 25 ºC, 75.5 MHz and 100.6 MHz) δ: 155.2

1 (d, ipso-CP, JP-C = 22 Hz), 129.3 (s, quat-Ar), 128.6 (s, C6H2), 125.7 (s, quat-Ar), 105.3 (s, ArC≡CSiMe3), 97.4 (s, ArC≡CSiMe3), 30.9 (d, CH(CH3)2,

3 29 1 JP-C = 27 Hz), 24.3 (s, CH(CH3)2), 0.0 (s, Si(CH3)3. Si{ H} NMR (C6D6, 25 ºC,

79.5 MHz) δ: -17.4. MS (70 eV, EI) m/z (%): 358 (48) [M]+, 343 (79) [M –

+ + + CH3] , 323 (100) [M – Cl] , 307 (35) [M – CH3 – Cl – H] . HRMS (70 eV, EI): calcd for C17H25Cl2PSi 358.0840, found 358.0823, fit –4.7 ppm. FT-IR (25 ºC,

-1 evaporation of a CH2Cl2 solution, cm ): ν(C≡C) 2160 (medium, sharp). Anal.

Calcd for C17H25Cl2PSi: C, 56.82; H, 7.01. Found: C, 56.85; H, 6.93.

Synthesis of compounds 19

All compounds were prepared in a similar manner, thus a generic procedure is reported. A yellow-orange solution of 18 in 20 mL Et2O and

20 mL toluene was added dropwise via cannula over 30 min. to a -78 ºC

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slurry of ca. 4-5 equiv. LiAlH4 in 100 mL Et2O. The mixture was stirred overnight while warming to room temperature. The brown mixture was cooled again in an ice-water bath, and 10 mL degassed water was added dropwise with much bubbling. The organic layer was transferred by cannula to a flask containing MgSO4. The aqueous layer was washed with two portions of 20 mL Et2O and all organic portions were combined in the flask containing MgSO4. The yellow solution was then cannula transferred to a

Schlenk frit and filtered. Upon removal of all volatiles in vacuo, a yellow residue was obtained.

H H For 19a: 0.471 g 18a (1.53 mmol), 0.325 g LiAlH4 (8.56 mmol, 5.6 P

1 equiv.). Yield: 0.349 g (95.5 %). H NMR (C6D6, 25 ºC, 300 MHz)

δ: 7.58–7.56 (m, 2H, o-C6H5), 7.21 (s, 2H, C6H2), 7.04–6.98 (m, 3H,

1 m- and p-C6H5), 3.50 (d, 2H, PH2, JP-H = 207.5 Hz), 2.03 (d, 6H,

4 31 CH3, JP-H = 9 Hz). P NMR (C6D6, 25 ºC, 121.5 MHz) δ: -153.8

1 13 1 (t, JP-H = 207.5 Hz). C{ H} NMR (C6D6, 25 ºC, 75.5 MHz and 100.6 MHz

1 partial) δ: 141.0 (d, ipso-CP, JP-C = 11 Hz), 131.9 (s, Ar), 130.9 (s, Ar), 124.1

3 (s, Ar), 122.7 (s, Ar), 90.2 (s, C≡C), 22.9 (d, CH3, JP-C = 10 Hz). EI-MS (m/z):

+ + 238.1 (100 %) [M] ; 223.1 (60 %) [M] – CH3. HRMS: C16H15P mass 238.0911, calcd mass 238.0902, fit -3.8 ppm. FT-IR (25 ºC, Nujol mull, cm-1): ν(C≡C)

2211 (weak), ν(P–H) 2306 (very strong, broad). Despite repeated attempts, suitable elemental analytical data could not be obtained.

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H H For 19b: 1.760 g 18b (4.845 mmol), 1.014 g LiAlH4 P (26.72 mmol, 5.5 equiv.). Yield: 1.002 g (70.3 %). 1H NMR

(C6D6, 25 ºC, 300 MHz) δ: 7.60–7.57 (m, 2H, o-C6H5), 7.54 (d,

4 2H, C6H2, JP-H = 2 Hz), 7.00–6.89 (m, 3H, m- and p-C6H5),

1 3.77 (d, 2H, PH2, JP-H = 206 Hz), 3.23 (d of septets, 2H,

3 4 3 CH(CH3)2, JH-H = 7 Hz, JP-H = 3 Hz), 1.08 (d, 12H, CH(CH3)2, JH-H = 7 Hz).

31 1 13 1 P NMR (C6D6, 25 ºC, 121.5 MHz) δ: -156.3 (t, JP-H = 207 Hz). C{ H} NMR

1 (C6D6, 25 ºC, 75.5 MHz and 100.6 MHz, partial) δ: 152.2 (d, ipso-CP, JP-C =

9 Hz), 132.0 (s, o-C6H5), 128.7 (s, m-C6H5 or p-C6H5), 128.4 (s, m-C6H5 or

i p-C6H5), 126.5 (s, C6H2), 124.0 (quat-Ar), 90.9 (s, C6H2 Pr2C≡CC6H5), 90.3 (s,

i 3 C6H2 Pr2C≡CC6H5), 33.1 (d, CH(CH3)2, JP-C = 11 Hz), 23.4 (s, CH(CH3)2).

+ + EI-MS (m/z): 294.2 (100 %) [M] ; 251.1 (83 %) [M] – CH(CH3)2. HRMS:

C20H23P mass 294.1542, calcd mass 294.1537, fit 1.74 ppm. FT-IR (25 ºC,

Nujol mull, cm-1): ν(C≡C) 2209 (weak), ν(P–H) 2315 (strong, broad). Anal.

Calcd for C20H23P: C, 81.60; H, 7.88. Found: C, 81.10; H, 8.12.

H H For 19c: 1.238 g 18c (3.445 mmol), 0.510 g LiAlH4 P (13.4 mmol, 3.9 equiv.). Yield: 0.551 g (55.1 %). 1H NMR

4 (C6D6, 25 ºC, 300 MHz) δ: 7.50 (d, 2H, C6H2, JP-H = 2 Hz),

1 3.72 (d, 2H, PH2, JP-H = 207 Hz), 3.23 (d of septets, 2H, SiMe3

3 4 3 CH(CH3)2, JH-H = 7 Hz, JP-H = 3 Hz), 1.01 (d, 12H, CH(CH3)2, JH-H = 7 Hz),

31 1 0.28 (s, 9H, Si(CH3)3). P NMR (C6D6, 25 ºC, 121.5 MHz) δ: -156.2 (t, JP-H =

13 1 207 Hz). C{ H} NMR (C6D6, 25 ºC, 75.5 MHz and 100.6 MHz) δ: 152.1 (d,

164

1 ipso-CP, JP-C = 9 Hz), 128.3 (s, quat-C(CH(CH3)2)), 126.7 (s, C6H2), 123.7 (s, quat-CC≡CSiMe3), 106.7 (s, ArC≡CSiMe3), 94.7 (s, ArC≡CSiMe3), 33.1 (d,

3 29 1 CH(CH3)2, JP-C = 11 Hz), 23.3 (s, CH(CH3)2), 0.1 (s, Si(CH3)3). Si{ H} NMR

+ (C6D6, 25 ºC, 79.5 MHz) δ: -18.4. MS (70 eV, EI) m/z (%): 290 (100) [M] , 275

+ (72) [M – CH3] . HRMS (70 eV, EI): calcd for C17H27P 290.1620, found

-1 290.1606, fit –4.8 ppm. FT-IR (25 ºC, evaporation of a CH2Cl2 solution, cm ):

ν(C≡C) 2158 (strong, sharp), ν(P–H) 2320 (medium, broad). Anal. Calcd for

C17H27PSi: C, 70.30; H, 9.37. Found: C, 70.58; H, 8.73.

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Chapter 5 New Routes towards Phosphorus-Containing Polymers

5.1 Abstract

Reaction of 2,4,6-triisopropylphenylphosphine with tert-butyllithium

i yields lithium phosphide LiPHC6H2 Pr3 20. This species reacts with methylchlorozirconocene in the presence of trimethylphosphine to give the

i zirconium phosphinidene species Cp2Zr(=PC6H2 Pr3)(PMe3) 21. In an analogous manner, primary phosphine 19b can be converted to lithium

i phosphide 22, LiPHC6H2 Pr2C≡CPh, and subsequent treatment with methylchlorozirconocene in the presence of trimethylphosphine affords the

i zirconium phosphinidene species Cp2Zr(=PC6H2 Pr2C≡CPh)(PMe3) 23.

Efforts to form zirconium- and phosphorus-containing polymers are unsuccessful to date. Compound 22 reacts with alkyl bromides RBr to

i generate secondary phosphines RPHC6H2 Pr2C≡CPh (24a: R =

CH2CH(CH3)2, 24b: R = CH2Ph). Treating compounds 24a or 24b with a catalytic amount of n-butyllithium results in the formation of phosphorus(III)-containing oligomers 25a or 25b via hydrophosphination.

Spectroscopic data suggest that oligomers 25 are cyclic. By MALDI-TOF mass spectrometry, up to 8 repeat units are observed for 25a, and up to 5 repeat units for 25b. By GPC relative to polystyrene standards, oligomer 25a

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shows Mn 3600 and Mw 9200, while 25b shows Mn 2300 and Mw 10800. These results may be underestimates: GPC with laser light scattering detection for

25a indicates Mn 21000 and Mw 25000. Reaction of oligomers 25 with elemental sulfur generates oligomers 26 (a: R = CH2CH(CH3)2, b: R =

CH2Ph). GPC relative to polystyrene indicates Mn 3000 and Mw 9600 for 26a, and Mn 2300 and Mw 11860 for 26b, while MALDI-TOF mass spectrometry shows up to 6 or 4 repeat units for 26a or 26b, respectively.

Thermogravimetric analysis (TGA) and energy dispersive X-ray (EDX) analysis of 25 and 26 indicate phosphorus-containing particles are formed by heating to 800 °C. The discussion of the hydrophosphination mechanism is augmented with gas phase DFT calculations.

5.2 Introduction

Our efforts are focused on preparing zirconium- and/or phosphorus- containing polymers. Such polymers are expected to display interesting reactivity typical of zirconium-phosphorus species (Chapter 1.4.2, Scheme

1.11),113, 116 and have potential applications as flame retardants, catalyst supports,18 and π-conjugated materials.19

Towards this goal, we envisioned two routes to phosphorus-containing polymers (Scheme 5.1): (1) [2+2] cycloaddition of a zirconium phosphinidene with an alkyne (see Chapter 1.4.2); (2) hydrophosphination of an alkyne (see

Chapter 1.5.2). These two strategies are analogous to the attempts at nitrogen-containing polymers discussed in Chapter 3, and both routes rely on

167 bifunctional phosphines 19 described in Chapter 4. These phosphines possess P–H and C≡C functional groups para-substituted about the central arene ring. Such an arrangement of functional groups precludes intramolecular reactivity; instead, an intermolecular reaction is expected to afford oligomers.

ZrCp2 P R Cp2 R R Zr P C C R" H P R" = H C R R' n R R C R'

C C R R' H P R" R' R n

Scheme 5.1 Proposed routes to zirconium- and/or phosphorus-containing polymers.

5.3 Results and Discussion

5.3.1 Synthesis of Zirconium-Phosphorus Compounds

To extend the small molecule zirconium-phosphorus chemistry to that of oligomers and polymers necessitates an arylphosphine with a high degree of steric bulk. This is because the zirconium phosphinidene chemistry and the subsequent metallacycle chemistry are very sensitive to steric demands

(Chapter 1.4.2).113, 116 It was anticipated that phosphine 19b,

168

i H2PC6H2 Pr2C≡CPh, would be an ideal precursor for zirconium-phosphorus chemistry.

1.0 equiv. Cp Me Cp PMe Zr 3 Cl Zr H H H Li Cp P P Cp P i t Pr iPr iPr 1.0 equiv. BuLi iPr iPr excess PMe3 iPr pentane C6H6 or C6D6 o o 3 h, -35 C to 25 C o 24 h, 25 C i iPr iPr Pr 20 21

Scheme 5.2 Generation of lithium phosphide 20 and zirconium phosphinidene 21.

To investigate this hypothesis, a test reaction was carried out for

2,4,6-triisopropylphenylphosphine (Scheme 5.2, Table 5.1). Reaction with tert-butyllithium in pentane affords the lithium phosphide 20, isolated as a

31 1 yellow powder. The P NMR spectrum shows a doublet at -171.2 ppm ( JP-H

= 180 Hz), upfield from the primary phosphine starting material (-157.8, t,

1 117 JP-H = 203 Hz), and comparable to other lithium arylphosphides.

Subsequent reaction with methylchlorozirconocene and excess trimethylphosphine in benzene generates zirconium phosphinidene 21

(Scheme 5.2). By analogy to other isolated zirconium phosphinidenes

(Chapter 1.4.2, Figure 1.6),117, 119, 120 compound 21 is readily characterized by its extremely downfield doublet peak in the 31P{1H} NMR at 785.6 ppm, with

2 coupling to the bound trimethylphosphine (δ = -7.7 ppm, JP-P = 21 Hz). The strongly deshielded resonance indicates a bent geometry at phosphorus.112

169

This geometry is corroborated by the 1H NMR spectrum, in which separate resonances are observed for the two inequivalent cyclopentadienyl ligands.

Similar spectroscopic data are found for the crystallographically

117 characterized species Cp2Zr(=PMes*)(PMe3).

Given that 2,4,6-triisopropylphenylphosphine is a viable precursor to zirconium phosphinidene 21, compound 19b should also behave accordingly.

Primary phosphine 19b can be converted to lithium phosphide 22 by reaction with nBuLi or tBuLi (Scheme 5.3, Table 5.1). Compound 22 can be generated and utilized in situ with hexanes or toluene as the solvent. Alternatively, when the reaction is performed in THF, compound 22 can be isolated and characterized as a THF adduct by multinuclear NMR spectroscopy. The 31P

1 NMR spectrum of compound 22-(THF)x shows a doublet at -162.5 ppm ( JP-H

= 182 Hz), upfield from compound 19b, and similar to compound 20 and other lithium phosphides.117 In the 13C{1H} NMR spectrum, the alkyne carbon atoms resonate at 93.8 and 88.2 ppm.

H H H Li(THF) P P x iPr iPr iPr iPr 1.0 equiv. nBuLi or tBuLi

THF or hexanes/toluene 3 h, -35 oC to 25 oC

19b 22-(THF)x

Scheme 5.3 Generation of lithium phosphide 22-(THF)x.

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Reaction of isolated 22-(THF)x or in situ-generated 22 with methylchlorozirconocene in the presence of excess trimethylphosphine in benzene (Scheme 5.4, Table 5.1) results in a dark red-brown solution. The

31P{1H} NMR spectrum of the reaction mixture shows a doublet at 756.7 ppm, characteristic of the Zr=P species 23, coupled to bound trimethylphosphine (δ

-7.9 ppm), with a coupling constant of 22 Hz. Like compound 21 and

Cp2Zr(=PMes*)(PMe3), two resonances are observed for the inequivalent cyclopentadienyl group, suggesting a bent geometry of the phosphinidene fragment.117 This NMR data correlates well with that observed for 21 and

117, 119, 120 other PMe3 adducts of zirconium phosphinidenes.

H Li Cp PMe3 P Zr iPr iPr P Cp iPr Cp iPr Me excess PMe3 Zr + Cl Cp C6H6 or C6D6 24 h, 25 oC

22 23

Scheme 5.4 Generation of zirconium phosphinidene 23.

Table 5.1 Selected NMR data for compounds 20, 21, 22, and 23. 1H NMR 13C{1H} NMR Cmpd 31P or 31P{1H} NMR (ppm) (ppm) (ppm) Cp C≡C 1 20 -167.7 (d, JP-H = 180 Hz) 1 21 785.6 (d), -8.3 (d) ( JP-P = 21 Hz) 5.59, 5.58 1 22-(THF)x -162.5 (d, JP-H = 182 Hz) 93.8, 88.2 1 23 756.7 (d), -7.9 (d) ( JP-P = 22 Hz) 5.54, 5.53 91.6, 90.2

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5.3.2 Proposed [2+2] Cycloaddition Polymerization

Formation of the proposed daisy chain oligomer was attempted by two routes (Scheme 5.5): (A) direct reaction of lithium phosphide 22 with

Cp2ZrMeCl; (B) exposure of zirconium phosphinidene 23 to heat or vacuum.

Reactions were monitored by 31P{1H} spectroscopy: the anticipated [2+2] cycloaddition reaction should give rise to a diamagnetic species, with a peak in the region 30 to 85 ppm,124 which is broadened as a result of oligomer formation.1

Route A Route B

Cp PMe3 H Li Zr P P i i Cp iPr Pr Pr Cp Me iPr Zr R' R R Cl Cp2 heat and/or Cp Zr vacuum P P - LiCl Zr - PMe3 Cp 2 R R' R n

22 23

Scheme 5.5 Attempted synthesis of the proposed zirconium- and phosphorus-containing polymer by (A) direct reaction of 22 with methylchlorozirconocene or (B) treatment of 23 with heat and/or vacuum.

The direct reaction of methylchlorozirconocene with lithium phosphide

31 1 22 in C6H6 or C6D6 results in a mixture of products: P{ H} spectra reveal several peaks, none of which are in the expected range 30 to 85 ppm.

In the second proposed route to form oligomeric species, zirconium- phosphinidene 23 was exposed to heat and/or vacuum in an attempt to

172

remove the low-boiling PMe3 trapping agent and force an intermolecular reaction. Initially, the 31P{1H} NMR spectrum revealed a number of phosphorus-containing species, including the free phosphine 19b. However, after two to three days, no signal was observed in the 31P{1H} NMR spectrum from +900 to -900 ppm.

The lack of signals might be explained by the formation of paramagnetic zirconium(III) species, for which there is literature precedent.

For example, a paramagnetic bridging phosphide (P3-) coordinated to three zirconium centers is obtained from the reaction of H2PMes* with two equivalents of Schwartz’ reagent.120 The related paramagnetic species,

(Cp*2Zr)2(μ-P), is obtained as a byproduct in 10 % yield from the reaction of

118 Cp*2Zr(PHMes*)Cl with KH. Electron paramagnetic resonance (EPR) as well as X-ray crystallographic data confirm the mixed valent nature of these complexes. For both of these products, the mechanism of formation is unknown, but must involve P–H and P–C bond cleavage, which may be sterically induced due to the steric demands of the supermesityl substituent.

The synthetic routes attempted herein are not promising for the synthesis of zirconium- and phosphorus-containing oligomers. However, by direct analogy to the nitrogen-containing polymers discussed in Chapter

3.3.2, phosphines 19 can also potentially give rise to polymers via hydrophosphination. The synthesis of suitable monomers is the subject of the next section, and hydrophosphination polymerization follows thereafter.

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5.3.3 Synthesis of Secondary Phosphines

Reaction of lithium phosphide 22 (either isolated or generated in situ) with isobutyl bromide or benzyl bromide yields 24a or 24b, respectively, both of which are viscous oils (Scheme 5.6). Spectroscopic data (Table 5.2) are consistent with the formulation of compounds 24. For example, the 31P NMR spectra are similar to other secondary phosphines,343, 344 with a doublet downfield from the primary phosphine and a coupling constant of ca. 210 Hz.

Peaks in the 1H NMR spectra are also indicative of the P–H fragment. For compound 24a, the configurational rigidity at phosphorus renders the methylene and methyl protons diastereotopic; similar results have been reported in the literature.280 The presence of the alkyne fragment is indicated in the 13C{1H} NMR and IR spectra (ca. 2200 cm-1); the latter spectra also show the P–H stretch at ca. 2300 cm-1.

H Li H R P P iPr iPr iPr iPr RBr

hexanes/toluene 18 h, 25 oC

22 24

Scheme 5.6 Synthesis of compounds 24 (a R = CH2CH(CH3)2; b R = CH2Ph).

174

Table 5.2 Selected spectroscopic data for compounds 24. 31P NMR 1H NMR Cmpd IR stretch (cm-1) 13C{1H} NMR (ppm) (ppm) (ppm) C≡C P–H PH CP C≡C 24a 2209 2320 -99.0 (d) 4.36 (ddd) 153.5 (d) 90.9, 90.4 24b 2208 2313 -80.9 (d) 4.54 (dt) 153.6 (d) 90.9, 90.5

5.3.4 Hydrophosphination Polymerization

As described in Chapter 1.5.2, hydrophosphination can be achieved using a variety of catalysts, co-catalysts, solvents, and temperatures.154, 155

Many of these reaction conditions were tested on an NMR scale in an effort to form oligomers (see Table 5.4, Chapter 5.5.3).

i Pr2 H R H R P P i i R Pr Pr P H Ph Ph n 0.2 equiv. BuLi i n Pr2 iPr THF, 18 h, 25 oC 2 Ph Ph H P P R R H i Pr2 n-3 24 25

Scheme 5.7 Polymerization of compounds 24 to give oligomers 25 (a R = CH2CH(CH3)2; b R = CH2Ph).

Synthesis of oligomers 25 is achieved by treating monomers 24 with

0.2 equiv. nBuLi in THF (Scheme 5.7). Monitoring the reaction by 31P{1H}

NMR spectroscopy indicates almost complete conversion after 1.5 h at room temperature: essentially all starting material is consumed, and a new peak

175 at -20 ppm or -8 ppm (for 25a or 25b, respectively) emerges; after 18 h, all starting material is consumed. A brown gummy residue is obtained upon repeated precipitation of the polymer into hexanes. In the 1H NMR spectra, the very broad resonance attributable to the alkene proton is indicative of variations in the regiochemistry of addition and/or the stereochemistry at phosphorus. In the 31P{1H} NMR spectra, the absence of peaks corresponding to an end group, which would be expected to resonate close to that of the monomer, is suggestive of a cyclic product. This is supported by the IR spectra (Figure 5.1), which show a notable absence of peaks in the region from 2750 to 1650 cm-1, indicating a lack of P–H and C≡C fragments.

Figure 5.1 IR spectra of monomer 24b (blue) and oligomer 25b (red).

176

In related experiments, the hydrophosphination polymerization of 24a or 24b was carried out under identical conditions, followed by the addition of one drop of methanol. The 31P{1H} NMR data and IR data are identical to

25a and 25b, and no signals were observed corresponding to methoxide in the

1H NMR. Molecular weight data (vide infra) are unchanged with respect to

25a and 25b. Collectively, these data support the formulation of oligomers

25 as cyclic species.

The molecular weights of oligomers 25 were estimated using MALDI-

TOF mass spectrometry and GPC (Table 5.3). These techniques do not provide exact molecular weights: calculating Mn or Mw from the MALDI mass spectrum is not advisable for samples with broad polydispersity,270 while GPC measurements are typically calibrated with polystyrene standards and therefore rely on the polymer under investigation having a similar hydrodynamic volume to polystyrene.1 Although these techniques do not give exact molecular weights, they are nonetheless benchmark characterization tools for molecular weight analysis of oligomers and polymers.

For oligomer 25a, GPC relative to polystyrene standards indicates Mn

3600 and Mw 9200, corresponding to a number-average degree of polymerization of 10. These values may be underestimated, by analogy to other phosphorus-containing polymers;15 indeed, GPC employing light scattering detection suggests higher molecular weights of Mn 21000 and Mw

25000. The MALDI-TOF mass spectrum of 25a (Figure 5.2) shows patterns

177 of peaks spaced by 350 m/z units, the mass of one monomer fragment, from

1050 to 2800 m/z, corresponding to 3 to 8 repeat units. At each major signal, a fine structure is observed in which extra peaks are located at 16n m/z units

(n = 1, 2, 3, etc.) from the major signal. These higher molecular weight species most likely correspond to oxidation of phosphorus centers in the oligomer to give phosphine oxide moieties.

Figure 5.2 MALDI-TOF mass spectrum for oligomer 25a.

178

For oligomer 25b, GPC versus polystyrene standards indicates Mn

2300 and Mw 10800, corresponding to a number-average degree of polymerization of 6. The MALDI-TOF mass spectrum of 25b (Figure 5.3) shows independent patterns of peaks spaced by 384 m/z units, the mass of one monomer fragment. One of these patterns of peaks corresponds to an integral number of monomer units, while the other patterns are offset from the first pattern and from each other by ca. 90 m/z units.

Figure 5.3 MALDI-TOF mass spectrum for oligomer 25b.

179

The origin of the other peak patterns is unclear. Although fragmentation is atypical for the soft ionization offered by MALDI, it is nonetheless known to occur for broadly polydisperse samples.270

Fragmentation at the phosphorus–benzyl bond (CH2Ph m/z = 91) during mass spectrometric analysis may account for this second set of peaks.

Another possibility involves phosphide abstraction of a benzyl group during polymerization, as an alternative termination pathway; P–C bond cleavage has been described in the literature.118, 120, 345, 346 One final possibility is a backbiting mechanism, which has been proposed for other phosphorus- containing polymers.347

100%

80%

60%

Weight (%) 40%

20%

0% 0 200 400 600 800 1000 Temperature (°C)

Figure 5.4 TGA data for oligomer 25a.

180

Thermogravimetric analysis (TGA) of oligomer 25a (Figure 5.4) indicates that the sample is relatively thermally stable to approximately

300 °C. The majority of weight loss occurs from 300 to 475 °C, and the remaining 20 % of the original sample is thermally robust up to

850 °C. The resultant particles are not soluble in common organic solvents, precluding characterization by solution NMR. However, energy dispersive

X-ray (EDX) analysis (Figure 5.5) indicates that there is phosphorus and carbon present in the material, in addition to oxygen which may result from the solvent (methanol) used to prepare the sample. Similar results are obtained for oligomer 25b (Chapter 5.5.3, Figures 5.12 and 5.13).

Figure 5.5 EDX data for oligomer 25a.

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Oligomers 25 react with sulfur in THF to give oligomers 26 (Scheme

5.8) with corresponding resonances in the 31P{1H} NMR spectrum at 46.2 ppm

(26a) and 45.4 ppm (26b). The MALDI-TOF mass spectrum of 26a (Figure

5.6) shows patterns of peaks spaced by 382 m/z units, the mass of one sulfurized monomer fragment, up to 2292 m/z which corresponds to 6 repeat units. The MALDI-TOF mass spectrum of 26b (Figure 5.7 is similar, showing up to 4 repeat units.

i i Pr2 Pr2 H R H S R P R P R P H S P H Ph Ph Ph Ph i 1 equiv. S8 i Pr2 Pr2 iPr iPr 2 THF, 18 h, 25 oC 2 Ph Ph Ph Ph H P H P S P R R P R R H S H i i Pr2 Pr2 n-3 n-3 25 26

Scheme 5.8 Reaction of oligomers 25 with sulfur to give oligomers 26 (a R = CH2CH(CH3)2; b R = CH2Ph).

182

GPC data relative to polystyrene standards indicates Mn 3000 and Mw

9600 for 26a, and Mn 2300 and Mw 11860 for 26b. These values correspond to a number-average degree of polymerization of 8 and 5.5 for 26a and 26b, respectively. Taken together, the data obtained by MALDI-TOF mass spectrometry and GPC suggest that there is minimal chain degradation upon sulfurization.

Figure 5.6 MALDI-TOF mass spectrum for oligomer 26a.

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Figure 5.7 MALDI-TOF mass spectrum for oligomer 26b.

TGA of oligomer 26a (Figure 5.8) indicates that the sample is thermally stable to approximately 300 °C. The majority of weight loss occurs from 300 to 500 °C, and the remaining 20 to 30 % of the original sample is thermally robust up to 800 or 900 °C. The resulting particles contain both phosphorus and sulfur, according to EDX analysis (Figure 5.9). Similar results are obtained for oligomer 26b (Chapter 5.5.3, Figures 5.14 and 5.15).

184

100%

80%

60%

Weight (%) 40%

20%

0% 0 200 400 600 800 1000 Temperature (°C)

Figure 5.8 TGA data for oligomer 26a.

Figure 5.9 EDX data for oligomer 26a.

185

Spectroscopic and molecular weight data are summarized in Table 5.3.

The electronic structures of oligomers 25 and 26 were probed using UV/Vis spectroscopy in THF, and compared to similar studies of monomers and oligomers of phosphaalkenes (Figure 1.5d)55-58, 348 and arylphosphines (Figure

1.5g).72

Table 5.3 Selected spectroscopic and molecular weight data for oligomers 25a, 25b, 26a, and 26b. 31P{1H} GPC relative to polystyrene MALDI- UV/Visd Cmpd c NMR standards TOF λmax (nm) Mn Mw PDI DPn 24a -99.0a 293 24b -80.9a 294 25a -20.0b 3600 9200 2.5 10.3 decamer 313 25b -8.2b 2300 10800 4.7 6.0 hexamer 316 26a 46.2b 3000 9600 3.2 7.9 hexamer 301 26b 45.4b 2300 11900 5.2 5.5 tetramer 300 a NMR data were acquired in C6D6. b NMR data were acquired in C6D6 + THF-d8. c MALDI-TOF data represent the highest molecular weight species observed. d UV/Vis data were acquired in THF solution, ca. 10-5 M.

In relation to other phosphorus-containing polymers,55-58, 72, 348 the

UV/Vis spectra (Figure 5.10) of oligomers 25 and 26 show absorption maxima that are intermediate between arylphosphine monomers and oligomers (λmax

72 = 250 to 291 nm) and phosphaalkene monomers and oligomers (λmax = 310 to 445 nm).55-58, 348 The absorption maxima for oligomers 25 are red-shifted by 20-22 nm relative to the λmax of monomers 24. This bathochromic shift is

56 similar to that observed for oligomeric phosphaalkenes (Δλmax = 18-28 nm)

72 and oligomeric arylphosphines (Δλmax = 21-22 nm) compared to their

186

monomeric counterparts. A red shift in the λmax may indicate a certain degree of conjugation along the backbone of oligomers 25. In comparison, oligomers 26 show absorption maxima that are blue shifted compared to the

λmax of oligomers 25. This hypsochromic shift suggests that the presence of

P=S moieties partially impedes the conjugation in the oligomer.

Figure 5.10 UV/Vis spectra of monomer 24b and oligomers 25b and 26b (ca. 10-5 M in THF).

Mechanistically, hydrophosphination of an alkene or alkyne can follow a radical process,174, 349-352 an ionic route,169, 174 or a transition metal-155, 160-169 or lanthanide-mediated157 pathway. Heavier group 2 elements158 can also serve as catalysts, and the reaction can be effected by thermolysis or microwave irradiation.166, 175 For the hydrophosphination polymerization reaction described herein, the radical pathway is ruled out based on the lack

187 of reactivity with known radical initiators such as benzoyl peroxide and azobis(isobutyronitrile) (AIBN). Indeed, treating a sample of 24a in benzene-

31 1 d6 with benzoyl peroxide resulted in no change in the P{ H} NMR spectrum after 3-4 days at room temperature. After 3 weeks at 70 °C, the reaction mixture consists mainly of unreacted secondary phosphine. A small amount

(6 %) of byproduct is observed with spectroscopic data suggestive of a secondary phosphine oxide,353-355 but there is no signal at -20 ppm corresponding to oligomer 25a. Similar results are obtained using AIBN.

Thus, the hydrophosphination polymerization does not follow a radical route.

Instead, the mechanism of hydrophosphination polymerization most likely follows an ionic route. This process was probed employing gas phase

DFT calculations at the B3LYP/6-31G(d) level of theory. For simplification, the phosphine and alkyne were modeled separately as methylphenylphosphine and diphenylacetylene. In order to illustrate the initial steps of the polymerization process, the reactants, products, and transition state were optimized, and their Gibbs free energies were computed. The Gibbs free energy was chosen as the best model for the energy since it includes the entropy contribution, which is clearly important in a polymerization process. In contrast, other calculations of electronic and thermal energies or enthalpies neglect the change in entropy. However, it should be noted that Gibbs free energy calculations in the gas phase overestimate the entropy change of the reaction.356.

188

Gibbs free energy Me kcal/mol P Ph Ph

Ph +11 H Me P Ph

+3 Me 0 Ph P Me H Me Ph Ph Me P P Me Ph P P Ph Ph H Ph H Me Ph Ph Ph P Ph -8 Ph -12 H Me Me P P Ph Ph Ph Ph

Figure 5.11 B3LYP/6-31G(d) gas phase Gibbs free energy calculations for the hydrophosphination reaction between methylphenylphosphine and diphenylacetylene.

The proposed reaction pathway (Figure 5.11) shows an overall exothermic process. Initial attack of the phosphide on the alkyne generates an alkenylphosphine anion, with a transition state located as a saddle point on the potential energy surface. Subsequent exothermic protonation of the alkenylphosphine anion by the secondary phosphine regenerates the phosphide for further reaction, as well as resulting in the hydrophosphination product. Of the two possible products that can be envisioned, the syn addition product is favoured slightly over the anti addition product.

189

5.4 Summary

In this chapter, various routes towards phosphorus- and/or zirconium- containing polymers were presented, based on bifunctional phosphine 19b, which contains both P–H and C≡C functional groups. New terminal zirconium-phosphinidenes 21 and 23 were prepared, but the proposed [2+2] cycloaddition chemistry of compound 23 did not result in the daisy chain zirconium- and phosphorus-containing polymer. In an alternate strategy, phosphorus-containing oligomers were synthesized by a hydrophosphination polymerization reaction of secondary phosphines 24. This reaction furnishes cyclic oligomeric species 25, which are sulfurized to give oligomers 26.

Oligomers 25 and 26 have number-average degrees of polymerization of 6 to

10, which may be underestimates due to the cyclic nature of the oligomers, and the relative nature of GPC measurements. Oligomers 25 and 26 are thermally stable up to 300 °C with ca. 20 % weight retention at 800 °C and phosphorus present in the resultant material. DFT calculations indicate that the hydrophosphination polymerization follows an exothermic anionic route.

5.5 Experimental Section

5.5.1 General Considerations

General experimental considerations are given in Chapters 2.5.1, 3.5.1, and 4.5.1, with the following additions. In the MALDI-TOF analysis of oligomers 25a, 25b, and 26b, samples were prepared using the layer

190 method;270 samples of 26a were prepared using the dried droplet method.270

The matrix solution for 25a and 25b consisted of 6 mg CHCA in 1 mL of a

6 : 3 : 1 mixture of CH3CN : CH3OH : H2O plus one drop of CF3COOH. The matrix for 26b was prepared in an identical fashion, plus an additional 6 mg

CuBr. Analyte solutions for 25a, 25b, and 26b were prepared by dissolving

3-5 mg of sample in 1 mL THF. In the layer method, the matrix solution was spotted under air, the target plate was allowed to dry, then the plate was brought into an inert atmosphere,271 whereupon 1 μL of analyte solution was spotted onto the sample plate and the plate was allowed to dry again. The matrix solution for 26a consisted of 20 mg pyrene in 1 mL THF plus one drop of CF3COOH, while the analyte solution consisted of 1 mg/mL 26a in THF.

The two solutions were mixed in a 9 : 1 ratio of matrix solution : analyte solution, and 1.5 μL of the resultant mixture was spotted onto the sample plate under an atmosphere of air.

Thermogravimetric analyses (TGA) were performed using a TA

Instruments SDT Q600 simultaneous TGA/DSC, under an atmosphere of pre- purified nitrogen gas at a heating rate of 10 °C/min. After performing TGA to

800 °C, samples were suspended in methanol and placed on a transmission electron microscopy (TEM) grid for energy dispersive X-ray (EDX) analysis.

EDX analyses were acquired on a Hitachi S-5200 scanning electron microscope using an acceleration voltage of 15 kV with a current of 20 μA.

The microscope was equipped with an Oxford instruments Inca x-Sight EDX

191

system. The intensity of phosphorus Kα and sulfur Kα X-ray emission lines at

2.0134 keV and 2.3075 keV were used to gauge the relative abundance of these elements in the material.

5.5.2 Starting Materials and Reagents

General considerations for starting materials and reagents are given in

Chapters 2.5.2, 3.5.2, and 4.5.2. Isobutylbromide was generously donated by the Chemical Control Center, Department of Chemistry and Biochemistry,

University of Windsor. Methanol was dried over sodium in a sacrificial manner and distilled under N2.

5.5.3 Synthesis and Characterization

Generation of compound 20

H Li 2,4,6-triisopropylphenylphosphine (241 mg, 1.02 mmol) was P iPr iPr placed in a 20 mL scintillation vial inside a brass plate designed

to surround the bottom and walls of the vial. 10 mL pentane iPr was added, and the entire assembly was cooled to -35 ºC. tBuLi in pentane

(0.63 mL of 1.7 mol/L, 1.07 mmol, 1.05 equiv.) was added to the stirred solution. After 1 h, the reaction mixture appeared slightly yellow and opaque. The entire assembly was warmed to room temperature over 4 hours, and the yellow-white precipitate was collected on a frit, washed with 10 mL more pentane, and dried in vacuo. This compound can also be generated and utilized in situ for further reactions, with pentane or hexanes as the solvent.

192

1 Yield: 212 mg (87.5 %). H NMR (C6D6 + THF-d8, 25 ºC, 300 MHz) δ: 7.09 (s,

3 2H, C6H2), 4.10 (m, 2H, o-CH(CH3)2), 2.91 (septet, 1H, p-CH(CH3)2, JH-H =

1 3 7 Hz), 2.76 (d, 1H, PH, JP-H = 180 Hz), 1.54 (d, 12H, o-CH(CH3)2, JH-H = 7

3 31 Hz), 1.35 (d, 6H, p-CH(CH3)2, JH-H = 7 Hz). P NMR (C6D6 + THF-d8, 25 ºC,

1 121.5 MHz) δ: -167.7 (d, JP-H = 180 Hz).

Generation of compound 21

iPr Compound 20, either isolated or generated in situ, (for iPr Cp P isolated 20, 0.250 g, 1.03 mmol) was suspended in 6 mL Zr Cp iPr PMe3 benzene, and excess PMe3 (ca. 0.5 mL, 5 mmol) was added to the pale yellow mixture. A solution of Cp2ZrMeCl (0.280 g,

1.03 mmol, 1.00 equiv.) in 4 mL benzene was added dropwise. The mixture turned dark green immediately, and was stirred for an additional 18 h.

31 1 P{ H} NMR for the reaction mixture (C6H6, 25 ºC, 121.5 MHz) δ: -158.4

(compound 5; peak height ~5 % relative to peak at -8.3), -61.9 (free PMe3),

2 -8.3 (d, PMe3 in compound 21, JP-P = 21 Hz), 267.3 (peak height ~10 %

2 relative to peak at 785.6), 785.6 (d, Zr=PAr in compound 21, JP-P = 21 Hz).

The reaction mixture was filtered through Celite and all volatiles were removed in vacuo. Diethyl ether was added to the green residue, and the solvent was again evaporated under reduced pressure. Phosphorus- containing byproducts (ca. 15 % by 31P{1H} NMR) were obtained alongside compound 21, which have similar solubility in diethyl ether, THF, pentane, hexanes, benzene, and toluene. Although compound 21 cannot be isolated

193 cleanly, peaks in the NMR spectra can be assigned by integration in the 1H

1 13 1 NMR and by H– C HSQC experiments. H NMR (C6D6, 25 ºC, 300 MHz) δ:

7.38 (s, 2H, C6H2), 5.59 and 5.58 (two singlets, 10H, Cp), 3.36 (septet, 2H,

3 3 o-CH(CH3)2, JH-H = 7 Hz), 3.10 (septet, 1H, p-CH(CH3)2, JH-H = 7 Hz), 1.48

3 3 (d, 6H, p-CH(CH3)2, JH-H = 7 Hz), 1.39 (d, 12H, o-CH(CH3)2, JH-H = 7 Hz),

2 31 1 0.72 (d, 9H, P(CH3)3, JP-H = 6 Hz). P{ H} NMR (C6H6, 25 ºC, 121.5 MHz) δ:

13 1 exactly as for the reaction mixture. C{ H} NMR (C6D6, 25 ºC, 100.7 MHz, partial) δ: 143.9 (quat-Ar), 142.2 (quat-Ar), 119.7 (m-C6H2), 104.3 (s, Cp),

34.8 (s, p-CH(CH3)2), 33.7 (s, o-CH(CH3)2), 25.0 (s, p-CH(CH3)2, 23.7 (s,

1 o-CH(CH3)2), 18.7 (d, JP-C = 20 Hz, P(CH3)3). Because compound 21 cannot be isolated cleanly, suitable elemental analysis could not be obtained; moreover, its extreme sensitivity to air and moisture precludes mass spectrometric techniques.

Generation of compound 22

H Li (THF) (i) Compound 19b (200 mg, 0.680 mmol) was placed in a P x iPr iPr 20 mL scintillation vial inside a brass plate designed to

surround the bottom and walls of the vial, and 10 mL THF

was added. The entire assembly was cooled to -35 ºC, and

tBuLi in pentane (0.44 mL of 1.7 mol/L, 0.75 mmol,

1.1 equiv.) was added to the stirred solution to generate a red solution. The entire assembly was warmed to room temperature over 4 hours, and all volatiles were removed in vacuo to give a red residue. Yield: 350 mg (89.7 %,

194

1 based on x = 3.8 by NMR). H NMR (C6D6, 25 ºC, 300 MHz) δ: 7.58–7.54 (m,

4H, o-C6H5 and C6H2), 7.03–6.94 (m, 3H, m- and p-C6H5), 3.90 (m, 2H,

1 CH(CH3)2), 3.52 (m, ca. 7.6H, THF), 2.92 (d, 2H, PH, JP-H = 182 Hz), 1.41 (d,

3 31 12H, CH(CH3)2, JH-H = 7 Hz), 1.37 (m, ca. 7.6H, THF). P NMR (C6D6, 25 ºC,

1 13 1 121.5 MHz) δ: -162.5 (d, JP-H = 182 Hz). C{ H} NMR (C6D6, 25 ºC,

1 75.5 MHz) δ: 147.8 (d, ipso-C, JP-C = 6 Hz), 132.0 (s, Ar), 131.7 (s, Ar), 127.3

(s, Ar), 125.5 (s, Ar), 124.9 (s, Ar), 114.4 (s, Ar), 93.8 (s, C≡C), 88.2 (s, C≡C),

3 68.1 (THF), 33.0 (d, CH(CH3)2, JP-C = 14 Hz), 25.7 (THF), 23.9 (s, CH(CH3)2).

7 1 Li{ H} NMR (C6D6, 25 ºC, 116.6 MHz) δ: -0.7.

(ii) Using 10 mL pentane as the solvent, instead of 10 mL THF, compound 22 can be isolated on a frit, washed with 10 mL more pentane, and dried in vacuo, to give a yellow-orange powdery precipitate.

(iii) Using 10 mL pentane as the solvent, instead of 10 mL THF, compound

22 can be generated in situ and utilized without purification.

(iv) Using nBuLi instead of tBuLi, compound 22 or 22-(THF)x can be isolated or generated in situ, in either pentane or THF, and utilized without purification.

Generation of compound 23

Compound 22 isolated from pentane (90 mg, iPr 0.30 mmol) was placed in a vial with a brass Cp P Zr Cp iPr plate described above, suspended in 1 mL PMe3 toluene and cooled to -35 °C. A toluene solution (2 mL) of PMe3 (5 drops) and

195

Cp2ZrMeCl (82 mg, 0.30 mmol) was cooled to -35 °C, then added to the solution of compound 22 with stirring. The reaction mixture turned dark brown, and was stored at -35 °C for 7 d. The mixture was then allowed to warm to room temperature for 5 h, and 31P{1H} NMR for the reaction mixture

(toluene, 25 ºC, 121.5 MHz) indicated the following peaks: -156.3 (s, 19b; peak height ~10 % relative to peak at -7.9), -61.9 (free PMe3), -7.9 (d, PMe3 of

2 2 compound 23, JP-P = 22 Hz), 756.7 (d, Zr=PAr of compound 23, JP-P = 22 Hz).

The reaction mixture was evaporated to give a red residue, C6D6 was added, and the reaction mixture filtered through Celite into an NMR tube. Despite byproducts present in the mixture, peaks corresponding to 23 in the NMR spectra can be tentatively assigned on the basis of integration in the 1H NMR

1 13 1 and H– C HSQC experiments. H NMR (C6D6, 25 ºC, 300 MHz) δ: 7.80–

7.63 (m, 4H, C6H2 and o-C6H5), 7.06–6.99 (m, 3H, m- and p-C6H5), 5.54 and

5.53 (two singlets, 10H, Cp), 3.26 (m, 2H, CH(CH3)2), 1.30 (d, 12H, CH(CH3)2,

3 2 31 1 JH-H = 7 Hz), 0.67 (d, 9H, P(CH3)3, JP-H = 6.5 Hz). P{ H} NMR (C6H6, 25 ºC,

13 1 121.5 MHz) δ: exactly as for the reaction mixture. C{ H} NMR (C6D6, 25 ºC,

75.5 MHz, partial) δ: 150.8 (s, Ar), 142.8 (s, Ar), 132.0 (s, Ar), 126.5 (s, Ar),

125.2 (s, Ar), 122.5 (s, Ar), 118.4 (s, Ar), 104.3 (s, Cp), 91.6 (s, C≡C), 90.2 (s,

3 C≡C), 33.7 (d, CH(CH3)2, JP-C = 8 Hz), 24.1 (s, CH(CH3)2), 18.4 (d, P(CH3)3,

1 JP-C = 20 Hz). Because compound 23 cannot be isolated cleanly, suitable elemental analysis could not be obtained; moreover, its extreme sensitivity to air and moisture precludes mass spectrometric techniques. It should be

196 noted that performing this reaction at room temperature instead of -35 °C results in an unidentified phosphorus-containing byproduct (peak height ~20

% relative to the peak at 756.7 ppm) with a singlet in the 31P NMR at δ

259.5 ppm.

Attempted Formation of Zirconium- and Phosphorus-Containing

Polymers

Route A, (i). To a C6D6 solution (1.5 mL) of compound 22-(THF)x (124 mg,

0.216 mmol based on 3.8 equiv. THF in the NMR spectrum) was added solid

Cp2ZrMeCl (59 mg, 0.22 mmol). The solution was stirred at room temperature for 4 d, monitored periodically by 31P{1H} NMR spectroscopy, scanned from -350 to +250 ppm (unless otherwise noted). The sample was then divided into two equal portions, one of which remained at room temperature and was monitored periodically, while the other was transferred to a J-Young’s tube, heated at 80 °C for 11 d, and monitored periodically.

Complex mixtures of products were obtained, and the products were not

31 1 identified. P{ H} NMR (C6D6, 25 ºC, 121.5 MHz): after 3 h at room temperature, δ: -156 (compound 19b; 13 %), -135 (16 %), -63 (8 %), -13 (63 %); after 24 h at room temperature, δ: -135 (73 %), -63 (21 %), -13 (6 %); after 4 d at room temperature (scanned from -900 to +900 ppm), δ: -135 (58 %), -63

(11 %), +20 (10 %), +330 (10 %), +466 (11 %); after 10 d at room temperature,

δ: -135 (62 %), -63 (13 %), -5 (14 %), +20 (11 %); after 23 d at room temperature, δ: -135 (67 %), -5 (33 %); after 4 d at room temperature and

197

12 h at 80 °C, δ: -135 (weak signal, 100 %); after 4 d at room temperature and 36 h at 80 °C, δ: -135 (weak signal, 39 %), -5 (weak signal, 61 %); after

4 d at room temperature and 6 d at 80 °C, δ: -5 (weak signal, 100 %); after

4 d at room temperature and 11 d at 80 °C, δ: -5 (weak signal, 100 %).

Route A, (ii). To a C6D6 solution (1 mL) of compound 22-(THF)x (43 mg,

0.075 mmol based on 3.8 equiv. THF in the NMR spectrum) was added

Cp2ZrMeCl (20 mg, 0.075 mmol). The solution was stirred at room temperature for 6 weeks and monitored periodically by 31P{1H} NMR spectroscopy, scanned from -250 to +350 ppm. Complex mixtures of products

31 1 were obtained, and the products were not identified. P{ H} NMR (C6D6,

25 ºC, 121.5 MHz): after 2 h at room temperature, δ: -167 (86 %), -67 (14 %); after 2 d at room temperature, δ: -164 (100 %), after 10 d at room temperature, δ: -164 (18 %), -95 (59 %), -67 (23 %); after 21 d at room temperature, δ: -63 (100 %); after 42 d at room temperature, δ: -67 (100 %).

Route A, (iii). To a C6H6 solution (2 mL) of compound 22 (84 mg, 0.28 mmol), isolated from pentane, was added solid Cp2ZrMeCl (72 mg, 0.26 mmol). The solution was stirred at room temperature for 8 d and monitored by 31P{1H}

31 1 NMR spectroscopy, scanned from -350 ppm to +850 ppm. P{ H} NMR (C6D6,

25 ºC, 121.5 MHz): after 5 h at room temperature, δ: -156 (compound 19b;

18 %), -13 (56 %), +9 (17 %), +259 (9 %); after 22 h at room temperature, δ:

+9 (71 %), +259 (29 %); after 8 d at room temperature, no signals are observed.

198

Route B, (i). A solution of compound 23 in C6D6 was exposed to vacuum overnight, then C6H6 was added, the solution was filtered through a

Kimwipe, transferred to an NMR tube, and allowed to stand at room temperature for 2 weeks. No signals were observed in the 31P{1H} NMR from

-900 to +900 ppm.

Route B, (ii). A solution of compound 23 in C6D6 was heated at 80 °C for 2 d.

No signals were observed in the 31P{1H} NMR from -900 to +900 ppm.

Route B, (iii). A solution of compound 23 in C6D6 was exposed to vacuum overnight, then C6H6 was added, the solution was filtered through a

Kimwipe, transferred to an NMR tube and heated at 80 °C for 3 d. No signals were observed in the 31P{1H} NMR from -900 to +900 ppm.

Synthesis of compounds 24a, 24b

All compounds were prepared in a similar manner, thus a generic procedure is reported. Compound 19b and 6 mL hexanes were placed in a 20 mL scintillation vial inside the brass plate described above, and the entire assembly was cooled to -35 ºC. Freshly titrated nBuLi in hexanes

(1.00 equiv.) was added to the stirred solution to generate an orange opaque mixture. The entire assembly was warmed to room temperature over

4 hours, then RBr was added dropwise, as well as 4 mL toluene, and the reaction mixture was stirred overnight. The orange-brown mixture was filtered through Celite, and all volatiles were removed in vacuo to give a brown oil. This reaction can also be performed using isolated compound 22.

199

For 24a: 190 mg 19b (0.645 mmol), 0.41 mL nBuLi (1.578

H P mol/L, 0.647 mmol, 1.00 equiv.), 88 mg BrCH2CH(CH3)2 (0.64 iPr iPr 1 mmol, 1.0 equiv.) Yield: 179 mg (79.2 %). H NMR (C6D6,

25 ºC, 300 MHz) δ: 7.62–7.57 (m, 4H, o-C6H5 and C6H2), 7.03–

1 6.97 (m, 3H, m- and p-C6H5), 4.36 (ddd, 1H, PH, JP-H = 212 Hz,

3 3 JH-H = 9 Hz, JH-H = 6 Hz), 3.73 (m, 2H, ArCH(CH3)2), 1.81 (m,

1H, PCHaHb), 1.69 (m, 1H, PCH2CH(CH3)2), 1.43 (m, 1H, PCHaHb), 1.20 (d,

3 3 6H, ArCH(CH3)a(CH3)b, JH-H = 7 Hz), 1.13 (d, 6H, ArCH(CH3)a(CH3)b, JH-H =

3 7 Hz), 0.97 (d, 3H, PCH2CH(CH3)a(CH3)b, JH-H = 4 Hz), 0.94 (d, 3H,

3 31 PCH2CH(CH3)a(CH3)b, JH-H = 4 Hz). P NMR (C6D6, 25 ºC, 121.5 MHz) δ:

1 13 1 -99.0 (d, JP-H = 212 Hz). C{ H} NMR (C6D6, 25 ºC, 75.5 MHz) δ: 153.5 (d,

1 ipso-CP, JP-C = 11 Hz), 133.9 (s, Ar), 133.6 (s, Ar), 132.0 (s, Ar), 128.7 (s, Ar),

126.9 (s, Ar), 124.6 (s, Ar), 124.1 (s, Ar), 90.9 (s, C≡C), 90.4 (s, C≡C), 34.2 (d,

1 3 PCH2CH(CH3)2, JP-C = 13 Hz), 33.0 (d, ArCH(CH3)2, JP-C = 13 Hz), 28.4 (d,

2 PCH2CH(CH3)2, JP-C = 12 Hz), 24.7 (s, ArCH(CH3)a(CH3)b), 24.3 (s,

ArCH(CH3)a(CH3)b), 23.94 (s, PCH2CH(CH3)2), 23.86 (s, PCH2CH(CH3)2).

+ + EI-MS (m/z): 350.2 (37 %) [M] ; 293.1 (100 %) [M] – CH2CH(CH3)2. HRMS:

C24H31P mass 350.2164, calcd mass 350.2163, fit 0.3 ppm. FT-IR (25 ºC,

Nujol mull): ν(C≡C) 2209 cm-1 (weak), ν(P–H) 2320 cm-1 (medium, broad).

-5 UV/Vis (THF, ca. 10 M, 25 °C): λmax = 293 nm. Despite repeated attempts, suitable elemental analysis could not be obtained.

200

For 24b: 110 mg 22 (0.366 mmol), 85 mg BrCH2C6H5

1 (0.50 mmol, 1.0 equiv.) Yield: 71 mg (50.3 %). H NMR (C6D6, H P iPr iPr 25 ºC, 300 MHz) δ: 7.58–7.56 (m, 4H, ArH), 7.03–6.91 (m, 8H,

1 3 ArH), 4.54 (dt, 1H, PH, JP-H = 214 Hz, JH-H = 7 Hz), 3.47 (m,

2H, CH(CH3)2), 2.89 (m, 2H, PCH2Ph), 1.09 (d, 12H, CH(CH3)2,

3 31 JH-H = 6 Hz). P NMR (C6D6, 25 ºC, 121.5 MHz) δ: -80.9 (d,

1 13 1 JP-H = 214 Hz). C{ H} NMR (C6D6, 25 ºC, 75.5 MHz, partial) δ: 153.6 (d,

1 ipso-CP, JP-C = 11 Hz), 139.9 (s, Ar), 132.0 (s, Ar), 129.3 (s, Ar), 128.7 (s, Ar),

126.8 (s, Ar), 126.1 (s, Ar), 125.7 (s, Ar), 124.8 (s, Ar), 124.0 (s, Ar), 90.9 (s,

3 1 C≡C), 90.5 (s, C≡C), 32.9 (d, CH(CH3)2, JP-C = 13 Hz), 31.6 (d, PCH2Ph, JP-C

= 16 Hz), 24.4 (s, CH(CH3)a(CH3)b), 24.1 (s, ArCH(CH3)a(CH3)b). EI-MS (m/z):

+ + 384.2 (51 %) [M] ; 293.1 (100 %) [M] – CH2Ph. HRMS: C27H29P mass

384.2013, calcd mass 384.2007, fit 1.6 ppm. FT-IR (25 ºC, Nujol mull):

ν(C≡C) 2208 cm-1 (weak), ν(P–H) 2313 cm-1 (strong, broad). UV/Vis (THF, ca.

-5 10 M, 25 °C): λmax = 294 nm. Despite repeated attempts, suitable elemental analysis could not be obtained.

Attempted Hydrophosphination Polymerization

An NMR tube was charged with compound 24a (ca. 30 mg,

0.085 mmol) and 0.8 mL solvent. Those experiments conducted in a non- deuterated solvent were spiked with a few drops of C6D6 as per the requirements of the Varian NMR spectrometers. Reactions were maintained a room temperature for 4-5 days and heated in a temperature-controlled oil

201 bath at 70 °C for 3 weeks. Reactions were periodically monitored by electron impact mass spectrometry (EI-MS; samples assembled in the glovebox) and

31P{1H} NMR spectroscopy. Although EI-MS is not the best technique for oligomeric samples, the highest molecular weight peak provides information about the minimum number of repeat units present in the oligomeric species.

In the 31P NMR spectra, up to five peaks were observed with chemical

1 1 1 shifts of -156 (t, JP-H = 207 Hz), -100 (d, JP-H = 212 Hz), -99 (d, JP-H =

1 212 Hz), -19 (s), and +20 ppm (d, JP-H = 489 Hz). These peaks are assigned, respectively, to compound 19b, an “end group” resulting from hydrophosphination (designated 25aend), unreacted 24a, a “middle group” resulting from hydrophosphination (designated 25amid), and an oxidation product of compound 24a (designated 24a(O), tentatively assigned by analogy to other secondary phosphine oxides).271, 354, 355, 357 The results after 3 weeks are compiled in Table 5.4.

202

Table 5.4 Reaction conditions and experimental data for the attempted oligomerization of compound 24a after a period of 3 weeks at 70 °C. En- Catalyst, 31P{1H} NMR EI-MS: highest Solvent try additive 24a:25amid:25aend:24a(O):19b MW species DME,* 1 None 85 : 2 : 2 : 4 : 7 Dimer C6D6 Benzoyl DME, 2 94 : 0 : 0 : 6 : 0 Dimer peroxide C6D6 THF, 3 AIBN 76 : 0 : 0 : 24 : 0 Dimer C6D6

4 NaH C6D6 85 : 7 : 8 : 0 : 0 Dimer NaH, 5 C D 87 : 4 : 5 : 0 : 0 Dimer 15-crown-5 6 6 NaH, 6 C D 89 : 5 : 6 : 0 : 0 Dimer 18-crown-6 6 6

7 KH C6D6 93 : 4 : 3 : 0 : 0 Dimer KH, 8 C D 70 : 13 : 17 : 0 : 0 Dimer 18-crown-6 6 6 DME, 9 KOtBu 89 : 1 : 1 : 2 : 7 Dimer C6D6 DME, 10 nBuLi 90 : 1 : 1 : 1 : 7 Dimer C6D6 THF, 11 nBuLi 0 : 100 : 0 : 0 : 0 Trimer C6D6 nBuLi, 12 C D 14 : 0 : 0 : 86 : 0 Dimer 12-crown-4 6 6

13 LiPPh2 C6D6 83 : 7 : 10 : 0 : 0 Dimer * DME = 1,2-dimethoxyethane

203

Synthesis of oligomers 25a, 25b

i Pr2 All compounds were prepared in a similar H R R P manner, thus a generic procedure is reported. P H Ph Ph Compound 24 and 3 mL THF were placed in a iPr 2 i Pr2 20 mL scintillation vial, to which 0.2 equiv. Ph Ph H P n P R freshly titrated BuLi in hexanes was added R H i Pr2 with stirring at 25 °C. The resultant dark n-3 brown mixture was stirred overnight, then precipitated into a vortex of hexanes or pentane. The brown supernatant was decanted to give a dark brown gummy residue, which was then dissolved in 2 mL THF and re- precipitated into hexanes or pentane. This step was repeated (3 or 4 precipitations in total). The dark brown gummy residue was then dried in vacuo to give a dark brown solid.

For 25a (R = CH2CH(CH3)2): 0.999 g 24a (2.85 mmol), 0.365 mL nBuLi (1.578 mol/L in hexanes, 0.576 mmol, 0.200 equiv.). Yield: 0.380 g

1 (38.0 %). H NMR (THF-d8, 25 ºC): 7.7–5.9 (br, 7H, ArH), 4.1–3.6 (br, 2H,

31 1 ArCHMe2), 1.6–0.5 (br, 21H, PCH2CH(CH3)2 and ArCH(CH3)2). P{ H} NMR

13 1 (C6D6, 25 ºC): -20.0 (br). C{ H} NMR (C6D6, partial): 156 (br, Ar), 148 (br,

Ar), 143 (br, Ar), 130 (b, Ar), 129 (br, Ar), 126 (br, Ar), 37 (br, alkyl), 35.6 (s, alkyl), 33 (br, alkyl), 32 (s, alkyl), 30 (s, alkyl), 29 (br, alkyl), 25 (br, alkyl), 24

(s, alkyl), 19 (s, alkyl), 15 (s, alkyl), 10 (s, alkyl). FT-IR (25 ºC, deposited from

THF solution): no peaks between 2750 and 1640 cm-1. UV/Vis (THF, ca.

204

-5 -1 10 M, 25 °C): λmax = 313 nm. GPC (triple detection): Mn 3600 g mol ,

-1 Mw 9200 g mol . GPC (refractive index detection, versus polystyrene

-1 -1 standards): Mn 3300 g mol , Mw 13800 g mol . GPC (laser light scattering

-1 -1 detection): Mn 21000 g mol , Mw 25000 g mol . MALDI-TOF MS (layer method, CHCA matrix, THF solution) highest molecular weight peak: decamer.

n For 25b (R = CH2Ph): 0.320 g (0.832 mmol) 24b, 0.11 mL BuLi

(1.579 mol/L, 0.17 mmol, 0.20 equiv.). The reaction mixture was dark purple in colour, and a brown precipitate isolated by precipitation into hexanes.

1 Yield: 0.153 g (47.8 %). H NMR (C6D6, 25 ºC): 7.4–6.7 (br, 12H, ArH), 4.1–3.9 and 3.3–3.1 (br, 4H, ArCH(CH3)2 and CH2Ph), 1.2–0.8 (br, 12H, ArCH(CH3)2).

31 1 13 1 P{ H} NMR (C6D6, 25 ºC): -8.2 (br). C{ H} NMR (C6D6 and THF-d8, partial):

157 (br, Ar), 147 (br, Ar), 142 (br, Ar), 140 (br, Ar), 130 (br, Ar), 126 (br, Ar),

33 (br, alkyl). FT-IR (25 ºC, deposited from a THF solution): no peaks

-1 -5 between 2700 and 1700 cm . UV/Vis (THF, ca. 10 M, 25 °C): λmax = 316 nm.

GPC (refractive index detection, versus polystyrene standards): Mn 2300 g

-1 -1 mol , Mw 10800 g mol . MALDI-TOF MS (layer method, CHCA matrix, THF solution) highest molecular weight peak: hexamer.

Synthesis of oligomers 25a, 25b with attempted termination by

MeOH

Compound 24 and 3 mL THF were placed in a 20 mL scintillation vial, to which 0.2 equiv. freshly titrated nBuLi in hexanes was added with stirring

205 at 25 °C. The resultant dark brown mixture was stirred overnight, then one drop of methanol was added to the reaction mixture. Precipitation into a vortex of hexanes or pentane yielded a fine beige precipitate (for 25a) or a brown precipitate (for 25b), which was isolated on a frit and dried in vacuo.

Compared to non-terminated oligomers 25 described above, 31P{1H} NMR spectra are identical, GPC data (refractive index detection versus polystyrene standards) are similar, and MALDI-TOF mass spectra show similar repeating patterns of peaks. These results are summarized in Table 5.5.

Table 5.5 Selected spectroscopic and molecular weight data for oligomers 25a and 25b with attempted termination by MeOH. GPC relative to MALDI-TOF: Termin Yield 31P{1H} Cmpd polystyrene standards highest MW -ation (%) NMR Mn Mw PDI DPn species 25a None 38.0 -20.0 3300 13800 4.2 9.4 decamer 25a MeOH 88.9 -20.0 2300 6400 2.8 6.6 decamer 25b None 47.8 -8.2 2300 10800 4.7 6.0 hexamer 25b MeOH 24.5 -8.2 6400 12400 1.9 16.7 pentamer

Synthesis of oligomers 26a, 26b

i Pr2 All oligomers were prepared in a similar H S R P R manner, thus a generic procedure is reported. S P H Ph Ph Oligomer 25 (or 25 with attempted iPr 2 i Pr2 termination by MeOH, D2O, or Me3SiCl) and Ph Ph H P S R P R 4 mL THF were placed in a 20 mL S H i Pr2 scintillation vial, to which elemental sulfur n-3 was added. The reaction mixture was stirred overnight at 25 °C. The brown

206 solution was precipitated into a vortex of hexanes, and the resulting beige solid was isolated from the supernatant by decanting, and dried in vacuo.

For 26a (R = CH2CH(CH3)2): 50 mg 25a (0.14 mmol), 6 mg S8

1 (0.2 mmol, 1 equiv.). Yield: 45 mg (82 %). H NMR (THF-d8, 25 ºC): 7.9–6.5

(br, 7H, ArH), 4.3–4.0 (br, 2H, ArCHMe2), 2.3–0.3 (br, 21H, PCH2CH(CH3)2

31 1 13 1 and ArCH(CH3)2). P{ H} NMR (C6D6, 25 ºC): 46.2 (br). C{ H} NMR (C6D6,

25 ºC, partial): 157 (br, Ar), 139 (br, Ar), 133 (br, Ar), 131 (b, Ar), 129 (br, Ar),

128 (br, Ar), 36 (s, alkyl), 33 (s, alkyl), 31 (br, alkyl), 30 (s, alkyl), 28 (s, alkyl),

24 (s, alkyl), 21 (s, alkyl), 14 (s, alkyl), 12 (s, alkyl). FT-IR (25 ºC, deposited from a THF solution): no peaks between 2800 and 1620 cm-1. UV/Vis (THF,

-5 ca. 10 M, 25 °C): λmax = 301 nm. GPC (refractive index detection, versus

-1 -1 polystyrene standards): Mn 3000 g mol , Mw 9600 g mol . MALDI-TOF MS

(dried droplet method, CHCA matrix, THF solution) highest molecular weight peak: hexamer.

For 26b (R = CH2Ph): 72 mg 25b (0.19 mmol), 6 mg S8 (0.19 mmol,

1 equiv.). The dark purple-blue solution turned orange in colour within

10 min of addition of elemental sulfur. Precipitation into hexanes yielded a

1 slightly off-white powdery precipitate. Yield: 47 mg (65 %). H NMR (C6D6,

25 ºC, 300 MHz) δ: 7.8–6.7 (br, 12H, ArH), 4.6–4.3 and 3.8–3.6 (br, 5H,

31 1 ArCH(CH3)2, PCH2Ph, and alkene), 1.2–0.8 (br, 12H, ArCH(CH3)2). P{ H}

13 1 NMR (C6D6 and THF-d8, 25 ºC, 121.5 MHz) δ: 45.4 (br). C{ H} NMR (C6D6 and THF-d8, partial): 132 (Ar), 129 (Ar), 115 (C=C), 35 (alkyl), 31 (alkyl), 23

207

(alkyl), 14 (alkyl). FT-IR (25 ºC, deposited from a THF solution): no peaks

-1 -5 between 2780 and 1610 cm . UV/Vis (THF, ca. 10 M, 25 °C): λmax =

300 nm. GPC (refractive index detection, versus polystyrene standards):

-1 -1 Mn 2300 g mol , Mw 11900 g mol . MALDI-TOF MS (layer method, CHCA matrix, THF solution) highest molecular weight peak: tetramer.

TGA and EDX for oligomers 25a, 25b, 26a, 26b

For each of oligomers 25a, 25b, 26a, and 26b (or those samples with attempted termination by MeOH), two TGA experiments were conducted: (1)

TGA data were acquired up to 1000 °C; (2) TGA data were acquired up to

800 °C, and the subsequent pyrolyzed sample was collected from the pan and used for EDX measurements (solution NMR measurements were not possible due to insolubility of the material). TGA and EDX data for oligomer 25a are shown in Figures 5.4 and 5.5, and for oligomer 26a in Figures 5.8 and 5.9.

TGA and EDX data for oligomers 25b and 26b are shown below in Figures

5.12 to 5.15.

208

100%

80%

60%

Weight (%) 40%

20%

0% 0 200 400 600 800 1000 Temperature (°C)

Figure 5.12 TGA for oligomer 25b.

Figure 5.13 EDX data for oligomer 25b.

209

100%

80%

60%

Weight (%) Weight 40%

20%

0% 0 200 400 600 800 1000 Temperature (°C)

Figure 5.14 TGA data for oligomer 26b.

Figure 5.15 EDX data for oligomer 26b.

210

Chapter 6 Summary and Future Work

New nitrogen- and phosphorus-containing polymers have been prepared by hydroamination or hydrophosphination polymerization and by oxidation polymerization of an aniline derivative. These polymers enhance the growing body of literature on macromolecules containing heteroelements in the main chain.358 Moreover, the general strategy of element–hydrogen bond addition across a carbon–carbon multiple bond adds scope to the field of inorganic polymers. Although the hydroboration approach to boron- containing polymers is well developed (Chapter 1.5.3),178, 179 an analogous strategy based on other main group elements has received little attention.

Thus, the hydroamination and hydrophosphination polymerization methodologies reported herein represent a significant contribution to this area of research. With synthetic methodologies constantly being developed and tested for hydroboration, -alumination, -silylation, -amination, and

-phosphination,130 this heterofunctionalization route to novel inorganic polymers will undoubtedly flourish.

The first goal was to synthesize and characterize various amines and phosphines bearing pendant alkynes. Various compounds were synthesized with primary amine and alkyne functionalities para-substituted about a central arene ring (compounds 1). These amines were investigated by a combination of spectroscopic, crystallographic, and computational techniques.

211

A similar series of phosphines bearing pendant alkynes was prepared in a multi-step synthesis involving aryl bromides (compounds 16), bisamidoarylphosphines (compounds 17), dichloroarylphosphines (compounds

18), and primary arylphosphines (compounds 19).

The second goal was to examine a new strategy for the synthesis of zirconium- and pnictogen-containing polymers: [2+2] cycloaddition of a terminal zirconium pnictidene with an alkyne. Towards this target, a number of zirconium amides (compounds 3 and 4), as well as two new zirconium phosphinidenes (compounds 21 and 23), were synthesized and characterized. Unfortunately, attempts at [2+2] cycloaddition polymerization of these compounds were unsuccessful to date. For zirconium phosphinidene chemistry, this is not surprising given the sensitivity of these complexes towards steric demands and reaction conditions.113, 115, 116 In the related nitrogen chemistry, the zirconium-nitrogen species may be mediating a hydroamination reaction rather than acting as a monomer.87, 88

The third objective was to investigate hydroamination and hydrophosphination as strategies towards new nitrogen- or phosphorus- containing polymers. Titanium-catalyzed hydroamination of primary amine

1a furnishes oligomer 5, which contains up to 15 repeat units in the chain and is capped by one molecule of dialkylamine originating from the catalyst.

Characterization of oligomers and model compounds suggest that the mechanism of hydroamination involves a combination of the [2+2]

212 cycloaddition (Chapter 1.5.1, Scheme 1.14) and the σ-bond insertion mechanisms (Chapter 1.5.1, Scheme 1.15). Base-catalyzed hydrophosphination of secondary phosphines 24 provides cyclic oligomers 25, which are derivatized by treatment with sulfur to give oligomers 26.

Phosphorus-containing oligomers 25 and 26 have modest degrees of polymerization (ca. 6 to 10 repeat units), which may be underestimated as a result of GPC relative to polystyrene and the cyclic nature of the macromolecules.

The fourth and final goal was to prepare new polyaniline derivatives from compound 1a. According to DFT calculations, compound 1a and aniline have similar electronic structures, as do the radical cations formed by one- electron oxidation. Oxidative polymerization of 1a generates oligomer 15, which contains up to 9 repeat units in the chain and shows similar spectroscopic properties to polyaniline.

Bifunctional amines or phosphines bearing pendant alkynes can be further exploited. For example, a terminal alkyne can be synthesized from a trimethylsilyl-substituted precursor,252, 359-362 such as compound 1b, 1f, 16c,

17c, 18c, or 19c, and would be expected to display greater reactivity than an internal alkyne,252 especially for element–hydrogen bond addition.136 Using these derivatives, hydroamination or hydrophosphination may be possible with a wide variety of catalysts.137, 139, 141, 154, 155 The reaction may allow for

213 greater regioselectivity,141 and may occur to a greater extent, and would therefore give higher degrees of polymerization (see Chapter 1.6, Eq. 1).1

Additional future work in this area should examine electrochemical polymerization as a route to nitrogen-containing oligomers 15. In comparison to chemical polymerization, the electrochemical route is advantageous due to precise control over the initiation and termination steps, as well as the stoichiometry.31 In addition, oligomers 15 are expected to display interesting electronic properties, in direct analogy to polyaniline. For example, polyaniline is unique amongst conducting polymers for the numerous ways in which it can be doped. Whereas all conducting polymers are doped chemically or electrochemically by changing the number of electrons, polyaniline can also be doped via acid/base chemistry by changing the number of protons.27, 28 It would therefore be instructive to examine the different ways to dope oligomer 15, as well as the resultant properties and applications of the macromolecule. By analogy to other conducting polymers, these properties may include metallic-like conductivity (approaching that of copper), 1D nonlinear optical phenomena, and electrochromism.

Phosphorus-containing oligomers 25 may show interesting π- conjugation, since the UV/Vis spectra of oligomers 25 are red-shifted compared to monomers 24. This may lead to applications in light-emitting diodes and solar cells.19 Another potential application involves polymer- supported synthesis,18, 363-365 by coordination to a transition metal such as

214 palladium. This may be possible for oligomer 25, or for a copolymer based on compound 24 and a suitable comonomer such as styrene and/or divinylbenzene. The resultant polymer-supported catalyst would be tested for its ability to carry out organic coupling reactions,364 and for the cleavage and recycling of the catalyst.

In conclusion, this research has established the synthesis and polymerization abilities of amines and phosphines bearing pendant alkyne substituents. Three new routes to nitrogen- and phosphorus-containing polymers have been successfully employed, which lays the foundation for further progress in the synthesis and applications of these polymers.

215

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