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From main group to transition metal-containing Brønsted acid initiators for the cationic polymerization… Hazin, Khatera 2018

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   From Main Group to Transition Metal-containing Brønsted Acid Initiators for the Cationic Polymerization of Olefin Monomers by  Khatera Hazin  M.Sc., Freie Universität Berlin, 2010  A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF  Doctor of Philosophy in THE FACULTY OF GRADUATE AND POSTDOCTORAL STUDIES (Chemistry)  THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver)   July 2018  © Khatera Hazin, 2018  ii  The following individuals certify that they have read, and recommend to the Faculty of Graduate and Postdoctoral Studies for acceptance, the dissertation entitled:  From Main Group to Transition Metal-containing Brønsted Acid Initiators for the Cationic Polymerization of Olefin Monomers  submitted by Khatera Hazin  in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Chemistry  Examining Committee: Derek Gates Supervisor  Laurel Schafer Supervisory Committee Member   Supervisory Committee Member Mark MacLachlan University Examiner Glenn Sammis University Examiner   Additional Supervisory Committee Members: Chris Orvig Supervisory Committee Member George Sawatzky Supervisory Committee Member   iii  Abstract   This dissertation outlines the development of Brønsted acids and their application as single-component initiators for the cationic polymerization of olefins. Solid weighable Brønsted acids are of particular interest in the generation and stabilization of highly reactive cations. Weakly coordinating anions (WCAs) facilitate the isolation of Brønsted acids and play a critical role in the carbocationic polymerization of vinyl monomers.   Chapter 1 gives an introduction to the mechanism of cationic polymerization and the challenges associated with it. The chapter also describes important initiator systems that are used in cationic polymerization and provides an overview of main group element-based WCAs that have been previously reported.   Chapter 2 outlines the application of the known tris(tetrachlorobenzenediolato)phosphate, [P(1,2-O2C6Cl4)3]–, as a WCA in the stabilization of reactive cations. The isolated Brønsted acids H(L)2[P(1,2-O2C6Cl4)3] (L = THF, DMF) were employed as effective single-component initiators for the cationic polymerization of n-butyl vinyl ether and p-methoxystyrene at various temperatures. Notably, high molecular weight poly(p-methoxystyrene)                                                  was obtained with an unexpected branched structure.   Chapter 3 describes three potential routes to afford Hellwinkel’s salt, [P(C12H8)2][P(C12H8)3]. A pentavalent phosphorane, P(C12H8)2(C12H9), and an unprecedented product, [P(C12H8)(C24H16)][P(C12H8)3], were isolated and characterized. The cation [P(C12H8)(C24H16)]+ is formally derived from the insertion of an additional biphenyl unit into the known [P(C12H8)2]+.  iv   Chapter 4 highlights the synthesis and characterization of several amine salts and an alkali metal salt featuring a hexacoordinate anion, [P(C6H4CO2)3]–. The basicity of [P(C6H4CO2)3]– was examined using IR spectroscopy and found to be comparable to [ClO4]– and [N(SO2CF3)2]–.  Chapter 5 describes the synthesis and characterization of two different Brønsted acids with the cation moiety [H(OEt2)2]+. The Brønsted acids were employed as highly effective single-component initiators for the cationic polymerization of n-butyl vinyl ether, styrene,                    -methylstyrene and isoprene at different temperatures. Remarkably, high molecular weight polystyrene and poly(-methylstyrene) were obtained. A predominantly rich syndiotactic poly(-methylstyrene) (rr up to 90%) was isolated from a polymerization at –78 °C.  Chapter 6 provides a summary of the thesis work and postulates future considerations in the field.     v  Lay Summary  Polymers are produced by a process in which monomers are chemically combined to form long chain molecules composed of many repeated units. Rubber, a synthetic polymer, is produced by a process called cationic polymerization and requires an initiator to start the polymerization. The initiator is comprised of a cation (positively charged ion) and an anion (negatively charged ion). Industrial processes utilize a chemical, in combination with water, as an activator to generate such an initiator. This dissertation details the preparation and characterization of initiators that contain the cation and anion in one system. In order for the initiator to provide desired long polymer chains, the interaction between the cation and anion is of particular interest. The interaction should neither be too strong nor too weak, but just right. There are only a few such systems known due to the challenge in preparing and handling these initiators.    vi  Preface  Sections of this dissertation have been previously published in peer reviewed journals.       Chapter 2 has been published as a full paper in Dalton Transactions. Khatera Hazin, Spencer C. Serin, Brian O. Patrick, Maria B. Ezhova, Derek P. Gates. [HL2][P(1,2-O2C6Cl4)3] (L = THF, DMF): Brønsted acid initiators for the polymerization of n-butyl vinyl ether and                          p-methoxystyrene. Dalton Trans. 2017, 46, 5901–5910. I have performed the syntheses, polymerizations, and characterizations. I wrote the manuscript in collaboration with my supervisor Prof. Derek P. Gates. Dr. Maria B. Ezhova assisted in the collection of the low temperature 2D 1H-NOESY and 1H-ROESY NMR spectra. Dr. Spencer C. Serin collected X-ray crystallographic data for compounds H(DMF)2[2.1], H(THF)2[2.1] and H(THF)(CH3CN)[2.1]. The refinements of these three structures were performed by Dr. Spencer C. Serin and Dr. Brian O. Patrick.   Chapter 3 has been published as a full paper in Canadian Journal of Chemistry. Khatera Hazin and Derek P. Gates. A twist on Hellwinkel’s salt, [P(2,2'-biphenyl)2]+[P(2,2'-biphenyl)3]–. Can. J. Chem. 2018, 96, 526-533. I performed all synthetic work and characterizations. I wrote the manuscript in collaboration with Prof. Derek P. Gates. X-ray crystallographic data for the structures [3.1'][3.2] and 3.3 were collected by Dr. Spencer C. Serin and solved by both Dr. Spencer C. Serin and Dr. Brian O. Patrick.   A version of Chapter 4 will be submitted as a full paper to a peer reviewed journal. Khatera Hazin, Brian O. Patrick, Derek P. Gates. To be submitted. I performed the syntheses and characterizations of the complexes. The manuscript is written in collaboration with Prof. Derek P. Gates. X-ray crystallographic data for the structure [PhNMe2H]–rac–mer–[4.1] was collected and solved by Dr. Spencer C. Serin, while data for the structures [(–)-brucineH]–Λ–mer–[4.1],  vii  [isoquinolineH]–rac–mer–[4.1], [pyH]–rac–mer–[4.1], and K–rac–mer–[4.1] were collected and solved by Dr. Brian O. Patrick.  A version of Chapter 5 will be submitted for publication to a peer reviewed journal. Khatera Hazin and Derek P. Gates. To be submitted. I performed the syntheses, polymerizations, and characterizations. The manuscript is written in collaboration with Prof. Derek P. Gates. The collection of the 13C{1H} NMR spectrum of polyisoprene at 44 °C was performed by Dr. Maria B. Ezhova. X-ray crystallographic data for the structure H(OEt2)2[5.1] was collected and solved by Dr. Brian O. Patrick.  Chapter 6 was written by me.      viii  Table of Contents  Abstract ......................................................................................................................................... iii Lay Summary .................................................................................................................................v Preface ........................................................................................................................................... vi Table of Contents ....................................................................................................................... viii List of Tables .............................................................................................................................. xiii List of Figures ...............................................................................................................................xv List of Schemes .............................................................................................................................xx List of Symbols and Abbreviations ......................................................................................... xxii Acknowledgements .................................................................................................................. xxix Dedication ................................................................................................................................. xxxi Chapter 1: Introduction ................................................................................................................1 1.1 Butyl Rubber ................................................................................................................. 1 1.2 Mechanism of Cationic Polymerization ...................................................................... 4 1.2.1 Initiation ...................................................................................................................... 5 1.2.2 Propagation ................................................................................................................. 7 1.2.3 Termination and Chain Transfer ................................................................................. 8 1.3 Initiators Used in Cationic Polymerization .............................................................. 10 1.3.1 Binary Initiators ........................................................................................................ 10 1.3.2 Single-component Initiators ...................................................................................... 10 1.4 Weakly Coordinating Anions (WCAs)...................................................................... 12 1.4.1 Development and Application of WCAs in Cationic Olefin Polymerization ........... 14  ix  1.5 Group 15 Element Based WCAs ............................................................................... 26 1.6 Outline of Thesis ......................................................................................................... 28 Chapter 2: [HL2][P(1,2-O2C6Cl4)3] (L = THF, DMF): Brønsted Acid Initiators for the Polymerization of n-Butyl Vinyl Ether and p-Methoxystyrene* .............................................30 2.1 Introduction ................................................................................................................. 30 2.2 Results and Discussion ................................................................................................ 32 2.2.1 Synthesis and Characterization of Initiators ............................................................. 32 2.2.2 Metrical Parameters Determined by X-ray Crystallography .................................... 38 2.2.3 H(DMF)2[2.1] and H(THF)2[2.1]-initiated Cationic Polymerization ....................... 44 2.3 Summary ...................................................................................................................... 52 2.4 Experimental ............................................................................................................... 53 2.4.1 General Procedures ................................................................................................... 53 2.4.2 Synthesis of H(DMF)2[2.1] ....................................................................................... 55 2.4.3 Synthesis of H(THF)2[2.1] ........................................................................................ 55 2.4.4 Synthesis of (CH3CN)(THF)[2.1] ............................................................................. 56 2.4.5 Representative H(DMF)2[2.1]-initiated Polymerization of n-Butyl Vinyl Ether ..... 56 2.4.6 Representative H(DMF)2[2.1]-initiated Polymerization of p-Methoxystyrene ........ 57 2.4.7 X-ray Structure Determination ................................................................................. 57 Chapter 3: A Twist on Hellwinkel′s Salt, [P(2,2'-biphenyl)2]+[P(2,2'-biphenyl)3]– * .............60 3.1 Introduction ................................................................................................................. 60 3.2 Results and Discussion ................................................................................................ 62 3.3 Summary ...................................................................................................................... 73 3.4 Experimental ............................................................................................................... 74  x  3.4.1 General Procedures ................................................................................................... 74 3.4.2 Synthesis of [P(C12H8)(C24H16)]+ ([3.1']+), [P(C12H8)2]+ ([3.1]+), [P(C12H8)3]– ([3.2]–) and P(C12H8)2(C12H9) (3.3) ................................................................................................... 75 3.4.3 Synthesis of [P(C12H8)(C24H16)][3.2]........................................................................ 76 3.4.4 Synthesis of 3.3 ......................................................................................................... 77 3.4.5 X-ray Structure Determination ................................................................................. 77 Chapter 4: Ammonium and Potassium Salts of a Hexacoordinate Phosphorus(V) Anion Featuring P–O and P–C Bonds ...................................................................................................79 4.1 Introduction ................................................................................................................. 79 4.2 Results and Discussion ................................................................................................ 81 4.2.1 Synthesis and Characterization of Ammonium Salts of mer–[4.1]– ......................... 81 4.2.2 Metrical Parameters Determined by X-ray Crystallography .................................... 85 4.2.3 Placement of mer–[4.1]– on IR Scale for WCAs ...................................................... 88 4.2.4 Preparation of K+ and H+ Salts of mer–[4.1]– ........................................................... 89 4.3 Summary ...................................................................................................................... 93 4.4 Experimental ............................................................................................................... 94 4.4.1 General Procedures ................................................................................................... 94 4.4.2 X-ray Structure Determination ................................................................................. 95 4.4.3 Synthesis of [PhNMe2H]–mer–[4.1] ......................................................................... 96 4.4.4 Synthesis of [PhNH3]–mer–[4.1] .............................................................................. 97 4.4.5 Synthesis of [pyH]–mer–[4.1] .................................................................................. 98 4.4.6 Synthesis of [isoquinolineH]–mer–[4.1] ................................................................... 99 4.4.7 Synthesis of [(–)-brucineH]–mer–[4.1] .................................................................. 100  xi  4.4.8 Synthesis of [(n-C8H17)3NH]–mer–[4.1] ................................................................. 102 4.4.9 Synthesis of K–mer–[4.1] ....................................................................................... 103 4.4.10 Attempted Synthesis of H(DMF)n[4.1] ............................................................... 104 Chapter 5: Brønsted Acids with Hexacoordinate Tantalum(V) Weakly Coordinating Anions as Highly Effective Initiators for the Cationic Polymerization of Vinyl Monomers106 5.1 Introduction ............................................................................................................... 106 5.2 Results and Discussion .............................................................................................. 109 5.2.1 Synthesis and Characterization of Initiators ........................................................... 109 5.2.2 Metrical Parameters Determined by X-ray Crystallography .................................. 115 5.2.3 H(OEt2)2[5.1] and H(OEt2)2[5.2]-initiated Cationic Polymerization ...................... 119 5.3 Summary .................................................................................................................... 134 5.4 Experimental ............................................................................................................. 135 5.4.1 General Procedures ................................................................................................. 135 5.4.2 Synthesis of H(OEt2)2[5.1]...................................................................................... 136 5.4.3 Synthesis of H(OEt2)2[5.2]...................................................................................... 137 5.4.4 Representative H(OEt2)2[5.1]-initiated Polymerization of n-Butyl Vinyl Ether .... 138 5.4.5 Representative H(OEt2)2[5.1]-initiated Polymerization of Styrene ........................ 138 5.4.6 Representative H(OEt2)2[5.1]-initiated Polymerization of -Methylstyrene ......... 139 5.4.7 Representative H(OEt2)2[5.1]-initiated Polymerization of Isoprene ...................... 139 5.4.8 Representative H(OEt2)2[5.2]-initiated Polymerization of n-Butyl Vinyl Ether .... 140 5.4.9 Representative H(OEt2)2[5.2]-initiated Polymerization of -Methylstyrene ......... 141 5.4.10 X-ray Structure Determination of H(OEt2)2(H2O)[5.1] ...................................... 141 Chapter 6: Conclusion and Future Work ................................................................................143  xii  6.1 Introduction ............................................................................................................... 143 6.2 Hexacoordinate WCAs ............................................................................................. 143 6.3 Concluding Remarks ................................................................................................ 148 References ...................................................................................................................................149 Appendices ..................................................................................................................................166 Appendix A ............................................................................................................................ 166 A.1 Supplementary Spectra for Chapter 2 ................................................................ 166 Appendix B ............................................................................................................................ 173 B.1 Supplementary Spectra for Chapter 3 ................................................................ 173 Appendix C ............................................................................................................................ 176 C.1 Supplementary Spectra for Chapter 4 ................................................................ 176 Appendix D ............................................................................................................................ 189 D.1 Supplementary Spectra for Chapter 5 ................................................................ 189   xiii  List of Tables  Table 2-1. Cationic polymerization of n-butyl vinyl ether using H(DMF)2[2.1] and H(THF)2[2.1] as initiator...................................................................................................................................... 48 Table 2-2. Cationic polymerization of p-methoxystyrene using H(DMF)2[2.1] and H(THF)2[2.1] as initiator...................................................................................................................................... 50 Table 2-3. X-ray crystallographic data and refinement details for compounds H(DMF)2[2.1], H(THF)2[2.1] and H(THF)(CH3CN)[2.1]. .................................................................................... 59 Table 3-1. X-ray crystallographic data for [3.1'][3.2] and 3.3. .................................................... 78 Table 4-1. 31P{1H} and 1H-NMR chemical shifts of [NbaseH]–rac–mer–[4.1]. ............................ 83 Table 4-2. N–H frequencies for [(n-C8H17)3NH]+[Anion]– salts in CCl4 and solid state. .......... 89 Table 4-3. X-ray crystallographic data for [PhNMe2H]–rac–mer–[4.1], [pyH]–rac–mer–[4.1], [isoquinolineH]–rac–mer–[4.1], [(–)-(brucineH]–Λ–mer–[4.1], and K–rac–mer–[4.1]. .......... 105 Table 5-1. Temperature dependencies of H(OEt2)2[5.1]-initiated cationic polymerizations of n-butyl vinyl ether, -methylstyrene, styrene, and isoprene in CH2Cl2. The results shown are representative of multiple repeat runs. ........................................................................................ 123 Table 5-2.Temperature dependencies of H(OEt2)2[5.2]-initiated cationic polymerizations of n-butyl vinyl ether and -methylstyrene in CH2Cl2. ...................................................................... 124 Table 5-3. H(OEt2)2[5.1]-initiated cationic polymerizations of n-butyl vinyl ether and styrene in CH2Cl2 with varying monomer-to-initiator ratio. ....................................................................... 133 Table 5-4. H(OEt2)2[5.1]-initiated cationic polymerizations of styrene in CH2Cl2 with varying amounts of added H2O (L). ....................................................................................................... 134  xiv  Table 5-5. X-ray crystallographic parameters for H(OEt2)(H2O)[5.1]. ...................................... 142 Table C-1. Selected bond lengths [Å] and bond angles [°] of [PhNMe2H]–rac–mer–[4.1], [pyH]–rac–mer–[4.1], [isoquinolineH]–rac–mer–[4.1], [(–)-brucineH]–Λ–mer–[4.1], and K–rac–mer–[4.1]. ............................................................................................................................................ 188   xv  List of Figures  Figure 1.1. Microstructure of natural rubber contains cis-1,4-polyisoprene units. ......................... 1 Figure 1.2. Solvation association of the carbocation (A ) and counter anion (B ). ..................... 7 Figure 1.3. Examples of Brønsted acids used as single-component initiators for cationic polymerization of olefins. ............................................................................................................. 12 Figure 1.4. Electrostatic interactions between a carbocation and a counterion. ........................... 13 Figure 2.1. Examples of isolable Brønsted acids that have successfully been employed as single-component initiator systems for olefins. ....................................................................................... 31 Figure 2.2.1H NMR (400 MHz, CD2Cl2, –85 °C) spectrum of (a) H(THF)2[2.1] and (b) H(DMF)2[2.1]. .............................................................................................................................. 35 Figure 2.3. 2D 1H–NOESY(400 MHz, CD2Cl2, –85 °C) experiment of H(THF)2[2.1]. .............. 37 Figure 2.4. Molecular structure of H(DMF)2–rac–[2.1]·0.2 CH2Cl2 (Δ isomer is shown; molecule 1 of 5 unique molecules). .............................................................................................................. 40 Figure 2.5. Molecular structure of H(THF)2–rac–[2.1]·C6H2O2Cl4·THF (Λ isomer is shown)... 41 Figure 2.6. Molecular structure of H(THF)(MeCN)–rac–[2.1]·3.35 MeCN·1.52 THF (Δ isomer is shown). ...................................................................................................................................... 43 Figure 2.7. Comparison of C–O and C–C bond length of [H(THF)2]+ in H(THF)2[2.1], H(THF)2[CHB11H5Br6], H(THF)2[Al{OC(CF3)3}4] and H(THF)2[MnCl4(THF)2]. ..................... 44 Figure 2.8. 1H NMR (400 MHz, CDCl3, 25 °C) spectra of poly(n-butyl vinyl ether) polymerized using (a) H(DMF)2[2.1] at 18 °C, (b) H(THF)2[2.1] at 18 °C and (c) H(DMF)2[2.1] at –50 °C.. 46 Figure 2.9. Refractive index traces of poly(n-butyl vinyl ether) initiated by H(DMF)2[2.1] (Table 2.1, entry 5) and H(THF)2[2.1] (Table 2.1, entry 14). .................................................................. 47  xvi  Figure 2.10. 1H NMR (400 MHz, CDCl3, 25 °C) spectrum of poly(p-methoxystyrene) prepared using H(DMF)2[2.1] at 18°C. ....................................................................................................... 52 Figure 3.1. Selected examples of boron(III)–, aluminum(III)– and phosphorus(V)–containing WCAs. ........................................................................................................................................... 60 Figure 3.2. Hellwinkel’s spiro-compound [3.1][3.2]. ................................................................... 61 Figure 3.3. 31P{1H} NMR (162 MHz, 25 °C) spectra of: (a) the reaction mixture obtained by reacting PCl5 with 2,2'–lithiobiphenyl [obtained from biphenyl, n-BuLi and TMEDA] in THF/Et2O – Route A in Scheme 3.1; (b) the reaction mixture obtained by reacting a portion of isolated reaction mixture from Route A (above) with 2,2'-dilithiobiphenyl in Et2O; (c) crystals of isolated [3.1'][3.2] dissolved in THF/Et2O solution; and (d) crystals of isolated 3.3 dissolved in THF/Et2O. ..................................................................................................................................... 64 Figure 3.4. Spiro–compound [P(C12H8)(C24H16)][P(C12H8)3] ([3.1'][3.2]). ................................. 67 Figure 3.5.Molecular structure of the salt (S)–[3.1']–Δ–[3.2]·1.73 THF·0.27·Et2O. ................... 67 Figure 3.6. Pentacoordinate phosphorane 3.3, [P(C12H8)2(C12H9)]. ............................................. 69 Figure 3.7. Molecular structure of 3.3. ......................................................................................... 69 Figure 3.8. 31P{1H} NMR (162 MHz, 25 °C) spectrum of [3.1][3.2] and [3.1'][3.2] via (a) dilithiated 2,2'–diiodobiphenyl recorded in THF/Et2O solution (Route B); (b) dilithiated 2,2'–dibromobiphenyl recorded in THF/Et2O solution (Route C). ....................................................... 71 Figure 4.1. Examples of hexacoordinate phosphorus(V) weakly coordinating anions. ............... 80 Figure 4.2. 31P{1H} NMR (162 MHz, 25 °C) spectra of a) [(–)-brucineH]–rac–mer–[4.1] recorded in (CD3)2SO and b) [(–)-brucineH]–rac–mer–[4.1] recorded in CD2Cl2 solvent. ......... 83  xvii  Figure 4.3. Molecular structures of (a) [PhNMe2H]–rac–mer–[4.1]·Me2C=O (Λ isomer is shown); (b) [pyH]–rac–mer–[4.1]·0.5 Me2C=O (Δ isomer is shown); (c) [isoquinolineH]–rac–mer–[4.1]·(C9H7N) (Δ isomer is shown); (d) [(–)-brucineH]–Λ–mer–[4.1]·2.02 CH2Cl2. .......... 86 Figure 4.4. Extended structure showing the coordination polymer formed by K–rac–mer–[4.1]·3 CH3OH (K–Δ,Δ–mer–[4.1] is shown). ......................................................................................... 91 Figure 4.5. 31P{1H} NMR (162 MHz, 25 °C) spectra of a) reaction mixture of H(DMF)n–mer–[4.1] recorded after 2 days and b) reaction mixture of H(DMF)n–mer–[4.1] recorded after ca. 4 weeks. 4.2 is phosphorane P(C6H4CO2)2(C6H4COOH)…………….…………………..……………91 Figure 5.1. Examples of characterized tantalum(V)-containing complexes. .............................. 108 Figure 5.2. Brønsted acids H(OEt2)2[5.1] and H(OEt2)2[5.2]. .................................................... 109 Figure 5.3. 1H NMR (400 MHz, CD2Cl2, –85 °C) spectrum of H(OEt2)2[5.1]. ......................... 111 Figure 5.4. Molecular structure of H(OEt2)(H2O)–cis–[5.1]·OEt2·0.17 CH2Cl2. ....................... 112 Figure 5.5. 1H NMR (400 MHz, CD2Cl2, –85 °C) spectrum of H(OEt2)2[5.2]. ......................... 114 Figure 5.6. 13C{1H} NMR (400 MHz, CD2Cl2, 25 °C) spectrum of H(OEt2)2[5.2]. .................. 115 Figure 5.7. Metrical parameters [Å] for the cation in H(OEt2)(H2O)[5.1]·OEt2·0.17 CH2Cl2. .. 117 Figure 5.8. 1H NMR (400 MHz, CDCl3, 25 °C) spectrum of poly(n-butyl vinyl ether); polymerization performed (a) with initiator H(OEt2)2[5.1] at 18 °C, (b) with initiator H(OEt2)2[5.2] at 19.3 °C, (c) with initiator H(OEt2)2[5.1] at –84 °C. ........................................ 122 Figure 5.9. 1H NMR (400 MHz, CDCl3, 25 °C) spectrum of syndiotactic-rich poly(-methylstyrene) (rr = 90%); polymerization performed with initiator H(OEt2)2[5.1] at –78 °C. 127 Figure 5.10. 1H NMR (400 MHz, CDCl3, 25 °C) spectrum of polystyrene; polymerization performed with initiator H(OEt2)2[5.1] at –50 °C. ...................................................................... 129  xviii  Figure 5.11. 13C{1H} NMR (101 MHz, CDCl3, 45 °C) spectrum of oligoisoprene; polymerization performed with initiator H(OEt2)2[5.1] at 18 °C. ........................................................................ 132 Figure A.1. 31P{1H} NMR (121 MHz, CD3CN, 25 °C) spectrum of H(THF)2[2.1]. ................. 166 Figure A.2. 31P{1H} NMR (121 MHz, CD3CN, 25 °C) spectrum of H(DMF)2[2.1]. ................ 167 Figure A.3. 13C{1H} NMR (75 MHz, CD3CN, 25 °C) spectrum of H(THF)2[2.1]. ................... 168 Figure A.4. 13C{1H} NMR (75 MHz, CD3CN, 25 °C) spectrum of H(DMF)2[2.1]. .................. 169 Figure A.5. 1H–1H NOESY (400 MHz, CD2Cl2, –85 °C) spectrum of H(DMF)2[2.1]. ............. 170 Figure A.6. 1H–1H ROESY (400 MHz, CD2Cl2, –85 °C) spectrum of H(DMF)2[2.1]. ............. 171 Figure A.7. 1H–1H ROESY (400 MHz, CD2Cl2, –85 °C) spectrum of H(THF)2[2.1]. .............. 172 Figure B.1. LRMS (ESI; positive mode) mass spectrum of [3.1]+ and [3.1']+ via Route A. ...... 173 Figure B.2. LRMS (ESI; negative mode) mass spectrum of [3.2]– via Route A . ...................... 174 Figure B.3. Crystal packing of the molecular structure of [3.1'][3.2] is shown with 2 unit cells along the b axis (x,y,z). ............................................................................................................... 175 Figure C.1. 31P{1H} NMR (162 MHz, (CD3)2CO, 25 °C) spectra of: a) [PhNMe2H]–mer–[4.1], b) [pyH]–mer–[4.1], c) [isoquinolineH]–mer–[4.1], and d) [(n-C8H17)3NH]–mer–[4.1]. .......... 176 Figure C.2. 31P{1H} NMR (162 MHz, (CD3)2SO, 25 °C) spectra of a) [PhNH3]–mer–[4.1] and b) [(–)-brucineH]–rac–mer–[4.1]. 4.2 is phosphorane P(C6H4CO2)2(C6H4COOH). ...................... 177 Figure C.3. 1H NMR (400 MHz, (CD3)2CO, 25 oC) spectrum of [PhNMe2H]–mer–[4.1]......... 177 Figure C.4. 13C{1H} NMR (101 MHz, (CD3)2CO, 25 oC) spectrum of [PhNMe2H]–mer–[4.1]...................................................................................................................................................... 178 Figure C.5. 1H NMR (400 MHz, (CD3)2SO, 25 oC) spectrum of [PhNH3]–mer–[4.1]. ............. 179 Figure C.6. 13C{1H} NMR (101 MHz, (CD3)2SO, 25 oC) spectrum of [PhNH3]–mer–[4.1]. .... 179 Figure C.7. 1H NMR (400 MHz, CD2Cl2, 25 oC) spectrum of [pyH]–mer–[4.1]. ...................... 180  xix  Figure C.8. 13C{1H} NMR (101 MHz, CD2Cl2, 25 oC) spectrum of [pyH]–mer–[4.1]. ............. 181 Figure C.9. 1H NMR (400 MHz, CD2Cl2, 25 oC) spectrum of [isoquinolineH]–mer–[4.1]. ...... 182 Figure C.10. 13C{1H} NMR (101 MHz, CD2Cl2, 25 oC) spectrum of [isoquinolineH]–mer–[4.1]...................................................................................................................................................... 182 Figure C.11. 1H NMR (400 MHz, CD2Cl2, 25 oC) spectrum of [(–)-brucineH]–Λ–mer–[4.1]. . 183 Figure C.12. 13C{1H} NMR (101 MHz, CD2Cl2, 25 oC) spectrum of [(–)-brucineH]–Λ–mer–[4.1]. ............................................................................................................................................ 184 Figure C.13. 1H NMR (400 MHz, (CD3)2CO, 25 oC) spectrum of [(n-C8H17)3NH]–mer–[4.1]. 185 Figure C.14. 13C{1H} NMR (101 MHz, (CD3)2CO, 25 oC) spectrum of [(n-C8H17)3NH]–mer–[4.1]. ............................................................................................................................................ 186 Figure C.15. 1H NMR (400 MHz, CD3OD, 25 oC) spectrum of K–mer–[4.1]. .......................... 187 Figure C.16. 13C{1H} NMR (101 MHz, CD3OD, 25 oC) spectrum of K–mer–[4.1]. ................. 187 Figure D.1. 1H–13C HMBC NMR (400 MHz for 1H, CD2Cl2, –85 °C) spectrum of H(OEt2)2[5.1]...................................................................................................................................................... 189 Figure D.2. 13C{1H} NMR (400 MHz, CD2Cl2, –85 °C) spectrum of H(OEt2)2[5.1]. ............... 190 Figure D.3.1H NMR (400 MHz, CD2Cl2, –85 °C) spectrum of H(OEt2)2[5.1]: a) day 1; b) day 2; c) day 3; d) day 5; e) day 8 (addition of CD2Cl2 ca. 0.9 mL); f) day 12 and g) day 15. † indicates free Et2O...................................................................................................................................... 191 Figure D.4.1H NMR (400 MHz, CDCl3, 25 °C) spectrum of syndiotactic-rich poly(-methyl- styrene) (rr = 86 %); polymerization performed with initiator H(OEt2)2[5.2] at –78 °C ........... 192   xx  List of Schemes  Scheme 1.1. Commercial synthetic process for the production of butyl rubber. ............................ 2 Scheme 1.2. General mechanism of cationic chain polymerization of vinyl monomers. ............... 4 Scheme 1.3. General formation of an active initiator (A B ). ........................................................ 5 Scheme 1.4. Trend in monomer reactivity in cationic polymerization. .......................................... 6 Scheme 1.5. The carbocation can be stabilized by resonance (top) and inductive effect (bottom). 6 Scheme 1.6. Combination of the propagating species with a fragment of the counterion. ............ 8 Scheme 1.7. Chain transfer reaction can occur via (a) -proton transfer to monomer and (b) chain transfer to counterion, respectively. ................................................................................................ 9 Scheme 1.8. Side reaction in styrene polymerization can occur via (a) chain transfer to growing polymer chain or (b) branching or cross-linking of styrene during cationic polymerization. ........ 9 Scheme 1.9. Motifs of different interaction between the carbocation and counter anion during cationic polymerization. ................................................................................................................ 14 Scheme 1.10. Different types of cationic polymerization and their general mechanisms; (a) reveals the mechanism of cationic chain polymerization; (b) shows the mechanism of cationic coordination polymerization, and (c) illustrates the mechanism of cationic ring-opening polymerization. ............................................................................................................................. 16 Scheme 2.1. Synthesis of Brønsted acid H(L)2[2.1] (L = DMF, THF)......................................... 33 Scheme 2.2. Synthesis of Brønsted acid H(THF)(MeCN)[2.1]. ................................................... 38 Scheme 2.3. H(L)2[2.1] (L = DMF, THF) initiated cationic polymerization of n-butyl vinyl ether........................................................................................................................................................ 45 Scheme 3.1. Synthesis of [3.1][3.2] via route A–C. ..................................................................... 63  xxi  Scheme 4.1. General synthetic route of [NbaseH][4.1] with Nbase = PhNMe2, PhNH2, py, isoquinoline, (–)-brucine and N(n-C8H17)3. 4.2 is phosphorane P(C6H4CO2)2(C6H4COOH)....... 81 Scheme 4.2. Synthetic route of K–rac–mer–[4.1]. ....................................................................... 90 Scheme 4.3. Proposed route to H(DMF)n–mer–[4.1] (n ≥ 1). ...................................................... 92 Scheme 5.1. Synthesis of Brønsted acid H(OEt2)2[5.1]. ............................................................. 109 Scheme 5.2. Synthesis of Brønsted acid H(OEt2)2[5.2]. ............................................................. 113 Scheme 5.3. H(OEt2)2[5.1] and H(OEt2)2[5.2]-initiated cationic polymerization of n-butyl vinyl ether............................................................................................................................................. 120 Scheme 5.4. H(OEt2)2[5.1] and H(OEt2)2[5.2]-initiated cationic polymerization of -methylstyrene. ............................................................................................................................. 125 Scheme 5.5. H(OEt2)2[5.1]-initiated cationic polymerization of styrene. .................................. 127 Scheme 5.6. H(OEt2)2[5.1]-initiated cationic polymerization of isoprene. ................................ 130 Scheme 6.1. Synthesis of Brønsted acid H(L)2[6.1] (L = DMF, THF)....................................... 144 Scheme 6.2. Proposed synthetic route of compound Li[6.4] and H(L)2[6.4] (L = DMF or Et2O)...................................................................................................................................................... 145 Scheme 6.3. Synthesis of Brønsted acids H(OEt2)2[6.6] and H(OEt2)2[6.7]. ............................. 147  xxii  List of Symbols and Abbreviations   alpha Å Angstrom (1 x 10–10 meters) anal. analysis Ar aryl avg. average ax axial  beta br broad or broadened (spectra) BR butyl rubber nBu n-butyl tBu tert-butyl C Celsius c centi (10–2) ca. circa (about) calcd calculated cf. compare cis same side CCDC Cambridge Crystallographic Data Centre COSY correlation spectroscopy Cp cyclopentadienyl ligand  xxiii  Cp* pentamethylcyclopentadienyl ligand  Δ  delta (configurational) ° degree (angle or temperature) δ NMR chemical shift in parts per million (ppm) d day(s); doublet (NMR spectroscopy) d deuterated D dimensional D1 relaxation delay (NMR spectroscopy) d7 inversion recovery delay (NMR spectroscopy) DLS dynamic light scattering DMF dimethylformamide, (CH3)2NCH DMSO dimethyl sulfoxide, (CH3)2SO2 Đ dispersity dn/dc refractive index increment ed. edition ed. eds. editor(s) e.g. exempli gratia (for example) elem. elemental ESI electrospray ionization eq equatorial equiv equivalent Et ethyl or CH3CH2–  xxiv  et al. and others Et2O diethyl ether or (C2H5)2O etc. and so forth eV electron Volt fac facial (configuration) FT fourier transform FW free weight fwhm full width at half maximum g gram GOF goodness of fit (crystallography) GPC gel permeation chromatography h hour {1H} proton decoupled (NMR spectroscopy) HPLC high-performance liquid chromatography HMBC heteronuclear multiple bond correlation HRMS high resolution mass spectrometry Hz Hertz (s–1) i iso (as in i-Pr) i.e. id est (in other words) int internal (X-ray) in situ in place or in the reaction in vacuo in a vacuum  xxv  IR infrared J coupling constant (NMR spectroscopy) K Kelvin K spectral line ki rate constant of initiation kp rate constant of propagation ktr rate constant of termination KH potassium hydride  wavelength Λ lambda (configuration) L generic ligand; liter  LA Lewis acid LLS laser light scattering LRMS low resolution mass spectrometry v wavenumber M generic metal; molarity (mol per liter) M+ molecular ion m milli (10–3); multiplet (NMR spectroscopy); meter  micro (10–6); absorption coefficient (X-ray) MAO methylaluminoxane, (–[O–Al(CH3)]n–) MALDI-TOF matrix-assisted laser desorption ionization - time of flight MALS multi angle light scattering  xxvi  Me methyl or CH3– MeOH methanol MeOSt methoxystyrene mer meridonial (configuration) MHz megahertz M/I monomer to initiator ratio min minute Mn number average molecular weight Mw weight average molecular weight MW molecular weight mol mole MS mass spectrometry m/z mass-to-charge ratio n number; normal (in n-butyl); nano  NA not available η hapticity; intrinsic viscosity NMR nuclear magnetic resonance NOE nuclear Overhauser effect NOESY nuclear Overhauser effect spectroscopy o ortho p para % percent (parts per hundred)  xxvii  Ph phenyl pH negative logarithm of hydrogen ion concentration Phen phenanthryl PhNH2 aniline, C6H5NH2  PhNMe2 N,N-dimethylaniline, C6H5N(CH3)2 pKa pK for association ppm parts per million py pyridine iPr isopropyl q quartet R generic substituent; residual factor (X-ray) R rectus (configuration) rac racemic mixture or racemate  refln reflection Rh hydrodynamic radius ROESY rotating-frame overhauser effect spectroscopy rr syndiotactic triad RT room temperature rvdw van der Waals radii s second; singlet (spectra); strong (spectra) S sinister (configuration) SADABS Siemens area detector absorption correction program  xxviii    t tertiary; triplet (NMR spectroscopy); time T temperature Tc ceiling temperature Tg glass transition temperature THF tetrahydrofuran, C4H8O Tm melting temperature TMEDA N,N,N’,N’-tetramethylethylenediamine trans opposite side trifyl trifluoromethanesulfonyl TRISPHAT tris(tetrachlorobenzenediolato)phosphate anion UBC University of British Columbia V volume  vibration vide infra see below vol% volume percent w weak (spectra) WCA weakly coordinating anion wt % weight percent vw very weak (spectra) X generic halogen Z number of units in a cell (X-ray)  xxix  Acknowledgements  First, I would like to express my sincere gratitude to my PhD supervisor Prof. Derek P. Gates for his support, insight, patience and dedication to this project over the years. I appreciate and cherish our talks about science and life.  I thank my supervisory committee members Prof. Laurel L. Schafer and Prof. Chris Orvig for reviewing my thesis and their insightful advice.  My PhD journey was not a walk in a park and I am thankful for having the support of so many great people around me, who helped me get to this point.  I would like to thank Khaleda Hazin, Anna Bennett, Ben Rawe, Linus Chiang, Kerim Samedov, and Zeyu Han for proofreading parts of my thesis. To the past and present Gates group members, who made the time in the lab enjoyable (in no particular order): Ben Rawe, Spencer Serin, Paul Siu, Anna Bennett, Harvey MacKenzie, Sonja Gerke, Andrew Priegert, Tom Hsieh, Shuai Wang, Zeyu Han, Leixing Chen, Chuantian Zhan, Jeffery Suen, Kerim Samedov, Kaoru Adachi, and Henry Walsgrove.  To Anna Bennett, Renad Al-Debasi and Ania Sergeenko for their hard work while working under my supervision.  I would like to thank the NMR, Mass Spec, and Chemistry Shops and Services for their help over the years. In particular, Dr. Maria Ezhova, Brian Ditchburn, Dr. Paul Xia, Dr. Emily Seo, Patrick Olsthoorn, and Marshall Lapawa. Further, I would like to thank Dr. Brian O. Patrick, Spencer Serin and Zeyu Han for their efforts in X-ray crystallography. I thank my family and friends, near and far, for their encouragement. Special thanks to my husband Sal for his patience and support through the highs and lows of my PhD.   xxx  Finally, I would like to thank my sister Khaleda and especially my parents, Maliha and Amin, for believing in me and for their unconditional support in every stage of my life.     xxxi  Dedication  To my family for their unconditional love and encouragement.    1  Chapter 1: Introduction  1.1 Butyl Rubber Rubber is one of mankind’s inimitable discoveries that has become an essential part of daily life. Natural and synthetic rubbers are elastomeric materials. Depending on the type of rubber, the additives, as well as the degree of vulcanization, widely different properties can be harvested. For instance, the degree of elasticity, hardness and strength are readily tunable.1,2 Vulcanization is a process that alters the chemical structure of the rubber by forming cross-linked segments that enhance mechanical properties. This process is enabled by the reaction of the carbon double bonds (C=C) present in the rubber pre-polymer.  The microstructure of natural rubber mainly consists of high molecular weight             cis-1,4-polyisoprene units (Figure 1.1; Mw = 106 g mol–1; Mw = weight average molecular weight) and represents ca. 40% of the total global elastomer consumption. Natural rubber is commercially obtained from a fluid secretion of the rubber tree, Hevea brasiliensis, which is called latex. More than 90% of the cultivated Hevea brasiliensis trees are located in South and Southeast Asia as it must be grown in a tropical climate.3-6 Natural rubber possesses ideal     high-performance properties such as elasticity and heat dispersion when compared to synthetic rubber and is irreplaceable in automobile and aircraft tires, and surgical gloves.7   Figure 1.1. Microstructure of natural rubber contains cis-1,4-polyisoprene units.  2   However, the global natural rubber production is highly dependent on specific climate conditions, where the rubber tree may be grown, mainly tropical regions. Natural rubber is sensitive to ozone surface cracking and organic solvents that cause a loss in physical strength.1 Therefore, synthetic rubber has been developed to replace or supplement natural rubber in many industrial applications. Synthetic butyl rubber (1.4) is a copolymer of isobutene and isoprene (ca. 2 mol%) and must be produced by cationic polymerization (Scheme 1.1). Butyl rubber (BR) exhibits excellent heat, chemical and oxygen resistance.8 It is susceptible to vulcanization through the residual C=C bonds that are introduced from the incorporation of isoprene moieties. The microstructure illustrates trans-1,4 polyisoprene units, which predominate over the 1,2- and 3,4-enchainments.9 Synthetic butyl rubber is particularly intriguing for the automobile industry due to its impermeability to air. Over 70% of the BR polymer produced is incorporated into inner liners of tire and tube products.2 The global market size of synthetic butyl rubber was valued at US$ 2.9 billion in 2016 and is predicted to reach US$ 5.2 billion by 2025.10  Scheme 1.1. Commercial synthetic process for the production of butyl rubber. In 1844, the rubber industry was launched by Goodyear’s landmark discovery of the vulcanization of natural rubber to produce a durable material with high mechanical strength.11 Synthetic butyl rubber was first prepared by Otto and Müller-Cunradi, who in 1931 reported homopolymers of isobutene initiated by the Lewis acid BF3. The polymerization of isobutene followed a cationic polymerization mechanism and afforded high molecular weight  3  polyisobutene (Mw ≥ 106 g mol–1).12,13 However, the polymer was non-curable, or crosslinkable, due to the absence of unsaturated units. In 1937, the production of synthetic BR was pioneered by Thomas and Sparks at Standard Oil Development Company (Exxon Research and Engineering Company). The copolymerization of isobutene and 1,3-butadiene with AlCl3 as catalyst afforded an insoluble, colorless rubbery polymer.13 Remarkably, Thomas and Sparks isolated a vulcanizable polymer by utilizing isoprene as a co-monomer in small amounts        (0.5–4 mol %) with AlCl3 as catalyst in methyl chloride solution at –100 °C to produce a slurry copolymer. This process was first commercialized in 1943.14 The low polymerization temperature is crucial in order to avoid side reactions during polymerization, thereby permitting access to high molecular weight BR. Notably, the introduction of halogen to synthetic butyl rubber 1.4 led to commercially available chlorinated or brominated BR with faster curing rates.1 The composition of BR makes it particularly interesting for a variety of applications in industrial and household products ranging from tire products, gloves, sealants and medical stoppers to food-grade chewing gum products.6,15   The goal of this dissertation involves the development of improved synthetic methods for the isolation of single-component initiator systems for cationic polymerization of olefin monomers. In particular, the objective is to develop new initiators that will provide access to high molecular weight polymers at higher temperatures than –100 C. The cationic polymerization of butyl rubber is a challenging and complex reaction. Current methodology necessitates low temperature (–100 C) for industrial scale polymerizations. In order to overcome these challenges, one needs to understand the mechanism of cationic polymerization.   4  1.2 Mechanism of Cationic Polymerization The cationic polymerization of olefins is an ionic chain polymerization. This type of polymerization involves a positively charged carbocation at the growing polymer chain end. Cationic polymerization proceeds in three steps: initiation, propagation and termination.16 The initiation step is induced via protic acids by protonation of the olefin monomer 1.5 to generate a carbocation 1.6 as illustrated in Scheme 1.2. The carbocation is charge-balanced by the counter anion. Propagation is realized by the successive addition of a monomer to the reactive carbocation chain end to form a polymer 1.7.17  Scheme 1.2. General mechanism of cationic chain polymerization of vinyl monomers.  Cationic polymerization proceeds at rapid rates greater than those of radical and anionic polymerization, within a matter of seconds (typical polymerization times: anionic = minutes; radical: ~1h).18,19 For comparison, the propagation rate constant in radical polymerization is       ~102-104 L mol–1 s–1 and –ca. 104 L mol–1 s–1 in anionic polymerization, whereas the propagation rate of cationic polymerization is several orders of magnitude higher (for styrene: kp ~104–6  L mol–1 s–1; isobutene: kp ~108 L mol–1 s–1).20-24 The rapid rates in cationic polymerization, with kp>>ki and ktr>kp, affect the stability of the propagating carbocation and lead to uncontrolled polymerization causing side reactions including chain transfer and termination. Therefore,  5  cationic polymerization remains the most challenging polymerization among radical and ionic chain polymerization.25   1.2.1 Initiation  Cationic polymerization necessitates carefully designed initiators with a cation source    (A ) and a charge-balancing anion (B ).26,27 For instance, protic acids (e.g. HSO3CF3 and HClO4) are used as initiators in cationic polymerization.28-30 Alternatively, active initiators are generated in situ by binary systems, in which a co-initiator is required. Binary initiators are comprised of a proton donor like water 17 and a neutral Lewis acid (LAn) (e.g. AlCl3, BF3, SnCl4, SbCl5 and TiCl4).22,31-34 The activation of H2O results in an H+, whereas the activation of a cationogen (RX) (e.g. alkyl and alkylaryl halides) generates a carbenium ion (R3C+) as the active cationic initiator (Scheme 1.3).   Scheme 1.3. General formation of an active initiator (A B ).  Vinyl monomers are utilized in cationic polymerization. The reactivity of the monomer depends on the electron-donating ability of the substituent. For example, vinyl ethers, 1.8, are more reactive than styrene derivatives, 1.9, 1.20 and 1.21, while isobutene, 1.23, and               1,3-butadiene, 1.24, are less reactive monomers used in cationic polymerization (Scheme 1.4).  6  Scheme 1.4. Trend in monomer reactivity in cationic polymerization.  Vinyl monomers with substituents that possess electron donating ability can stabilize the resulting reactive carbocation 1.6. The stability of the carbocation increases with the number of substituents on the monomer. Therefore, tertiary carbocations are more stable than secondary (R3C >R2C >RC ). Monomers with -heteroatoms such as alkoxy groups, 1.9, can stabilize the carbocation through resonance. Aryl monomers with electron-donating groups delocalize the positive charge through resonance as illustrated in Scheme 1.5. The carbocation is mainly stabilized by hyperconjugation.26 Monomers with alkyl substituents also stabilize the carbocation via an inductive effect.  Scheme 1.5. The carbocation can be stabilized by resonance (top) and inductive effect (bottom).  7  1.2.2 Propagation The rate of propagation is influenced by the temperature, solvent and counterion used. High molecular weight polymers are dependent on the formation of a stable propagating species for successive monomer addition. The application of low temperatures during polymerization lowers the rate of termination by suppressing the termination of chain growth and chain transfer, leading to the formation of a growing propagating chain.17,19 Likewise, solvent effects also influence the rate of propagation. Polar hydroxylic solvents, for example water and alcohols, most likely react with the initiator and prevent initiation. Therefore, cationic polymerization is performed in solvents with low to moderate polarity. In solvents such as tetrahydrofuran and 1,2-dichloroethane the propagating species (~~~AB) can adopt different arrangements ranging from a covalent bond (I), contact ion pair (II), and the solvent-separated or so called loose ion pair (III) to free ions (IV) (Figure 1.2). The carbocation (A ) has a counter anion (B ) in the contact ion pair, and thus forms an inactive or dormant species. In contrast, in the solvent seperated ion pair, the ions are partially separated by a solvent molecule. Increased solvent polarity favors the loose ion pair (III), while in solvents with lower polarity the contact ion pair (II) is preferred.17,18,35  Figure 1.2. Solvation association of the carbocation (A ) and counter anion (B ).  The size of the counter anion has a significant effect on the rate of propagation. Small counterions with high charge density possess a strong electrostatic interaction with the propagating carbocation and render it unreactive. For comparison, large charge delocalized  8  counterions demonstrate a weaker coordination to the carbocation and facilitate the stabilization of the propagating carbocation.36  1.2.3 Termination and Chain Transfer  The complexity of the fast uncontrolled cationic polymerization is also indicated by termination and chain transfer reactions. One method of termination involves the combination of the propagating species with the counterion as illustrated in Scheme 1.6.13,17,37  Scheme 1.6. Combination of the propagating species with a fragment of the counterion.  Cationic polymerization is prone to side reactions due to a faster termination rate than the propagation rate (ktr > kp). Chain transfer reactions act to terminate the growing propagating species; however, they do not terminate the polymerization since a new propagating active center is generated.18 Chain transfer reactions can occur by means of -proton transfer to monomer, chain transfer to counterion, or chain transfer to polymer.17 -Proton transfer is the main side reaction in cationic polymerization. Due to the stabilization of the carbocation through hyperconjugation, the positive charge is partially delocalized onto the C-H proton. Thus, the propagating species is prone to -proton elimination by the monomer or counter anion during cationic polymerization, generating a new propagating species and resulting in the formation of an unsaturated polymer chain end (Scheme 1.7, (a)). Another possible side reaction is chain transfer to counter anion, also called spontaneous termination, which involves a -proton transfer to the counterion. Subsequently, this process leads to a dormant polymer, while the initiator is regenerated (Scheme 1.7, (b)).17,38  9   Scheme 1.7. Chain transfer reaction can occur via (a) -proton transfer to monomer and (b) chain transfer to counterion, respectively.  In the presence of aromatic groups, such as styrene and styrene derivatives, intramolecular electrophilic aromatic substitution (or backbiting) is often observed that results in terminal indanyl or cyclized structures as illustrated in Scheme 1.8 (a).39-41 Branching or cross-linking has also been observed in the cationic polymerization of styrene through intermolecular aromatic substitution by a propagating carbocation onto the aromatic ring of another polymer chain (Scheme 1.8, (b)).42-44   Scheme 1.8. Side reaction in styrene polymerization can occur via (a) chain transfer to growing polymer chain or (b) branching or cross-linking of styrene during cationic polymerization.   10  1.3 Initiators Used in Cationic Polymerization 1.3.1 Binary Initiators  More and more studies have led to the development of initiators based on Lewis acid precursors that are suitable for the cationic polymerization of vinyl monomers. The development of binary systems bearing Lewis acids and a proton donor as active initiators for cationic polymerization was pioneered by Higashimura and Kennedy. For example, initiator systems for the polymerization of vinyl ethers (e.g. HI/I2 and HCl/ZnCl2)45,46 and isobutene (e.g. BCl3/acetate, 1,4-bis(1-azido-1-methylethyl)benzene/Et2AlCl, AlCl3/OBu2, AlCl3/OiPr2) have been reported.47,48 Styrene and styrene derivatives have been polymerized by the HI/I2 and HI/ZnI2 initiating system in the presence of nBu4NX (X= Cl, Br, I) and other binary systems (e.g. 1-chloroethylbenzene/SnCl4, BF3OEt2/alcohol, cumyl acetate/BCl3).49-54 In addition, isoprene and 1,3-butadiene have been polymerized by [Ph3C][B(C6F5)4] in combination with a co-initiator (C5Me5)2Ln[(í-Me)AlMe2(í-Me)]Ln(C5Me5)2/Al(iBu)3 (Ln = Sm, Gd) or (C5Me5)Sc(BH4)2(THF).55-57 A key disadvantage of these types of two-component initiators is that the nature and concentration of the initiaing species, presumably H+, is not well defined or easily studied.  1.3.2 Single-component Initiators  The development of single component initiators is of emergent interest. Single component initiators incorporating weakly coordinating anions (WCAs) of group 13 and 14 elements include [Al(η5-Cp)2][Al{OC(CF3)3}4],58 [Al(η5-Cp)2][MeB(C6F5)3],59 [Ga(C6H5F)2][Al{OC(CF3)3}4],60 [EtZn(arene)2][Al{OC(CF3)3}4] (arene = toluene, mesitylene),61 [Cp*Ti(CH3)2][CH3B(C6F5)4].36,62 When employed to polymerize isobutene, these  11  systems afford low to high molecular weight polyisobutene (Mn = 290 g mol–1 to 270,000            g mol–1; Mn = number average molecular weight). Further, [Ni(C12H19)][B{3,5-(CF3)2C6H3}4] has been shown to be an effective initiator in the polymerization of 1,4-butadiene.63   Single-component initiators based on Brønsted acids are less common. Although in principle H+ represents the ideal initiator, the challenge remains in the synthesis, isolation and necessity to handle these systems at lower temperatures. Examples for single component initiators for the cationic polymerization of vinyl monomers are illustrated in Figure 1.3. The Brønsted acid 1.25 has been studied in the cationic ring opening polymerization of 2–alkyl–2–oxazoline and carbocationic polymerization of isobutene, while the single component initiator 1.26 is an effective initiator for the polymerization of vinyloxazolidinones and isobutene.58,64,65 The compounds 1.27 and 1.28 were shown to be effective initiators for the cationic polymerization of isobutyl vinyl ether and styrene.33,66,67 The proton of the water molecule in the cation moiety of 1.27 initiates the polymerization. Single component initiators are solid and weighable and therefore give a better control over the monomer-to-initiator ratio during cationic polymerization than binary systems.  12   Figure 1.3. Examples of Brønsted acids used as single-component initiators for cationic polymerization of olefins.  1.4 Weakly Coordinating Anions (WCAs) The capability to control the interaction between the counter anion and the carbocation during cationic polymerization is challenging and critical. The objective is to retain the electrophilicity at the cation center by applying WCAs.68 The development of WCAs necessitates low overall charge and charge delocalization over a large number of ligand atoms to minimize the electrostatic interaction between the cation and anion motif (V; Figure 1.4). Hence, the larger the anion, the more delocalized the charge will be and therefore, the more weakly coordinating the anion will be. Reducing the Coulombic interaction will facilitate the stabilization of reactive cations. WCAs should be chemically robust against oxidation, electrophilic attack and should not possess basic coordination sites.69,70  13   Figure 1.4. Electrostatic interactions between a carbocation and a counterion. The degree of coordination of the counter anion to the carbocation has an impact on the formation of the ion-pair and therefore on the cationic polymerization step as illustrated in Scheme 1.9.71 The search for the “just right” interaction between the carbocation and the counterion that is neither too strong nor too weak, refers to the Goldilocks effect derived from the fairy tale “Goldilocks and the Three Bears”. Small and nucleophilic anions such as VI (Figure 1.4) will coordinate to the carbocation and render it unreactive. Subsequently, this will suppress the propagation step, leading to chain transfer and termination of the polymerization (Scheme 1.9 (a)). An anion that is too weakly coordinating will not be able to stabilize the reactive carbocation during cationic polymerization and will lead to termination (Scheme 1.9 (b)). Preferably, a WCA that is charge delocalized and non-nucleophilic will stabilize the propagating carbocation during polymerization; such ideal “just right” interaction is elucidated in Scheme 1.9 (c). Therefore, high molecular-weight polymers are dependent on the formation of a stable carbocation for successive propagation.   14   Scheme 1.9. Motifs of different interaction between the carbocation and counter anion during cationic polymerization.  1.4.1 Development and Application of WCAs in Cationic Olefin Polymerization  This section of Chapter 1 deals with the evolution of the “classical anion” to larger and more charge delocalizing WCAs. In addition, the application of WCAs in cationic olefin polymerization is highlighted. Therefore, a general mechanism of the different types of cationic olefin polymerization (e.g. cationic chain polymerization, cationic coordination polymerization, as well as cationic ring-opening polymerization) is warranted.   Cationic chain polymerization involves a protic acid as initiator to generate a positively charged carbocation 1.6 at the growing polymer chain end (Scheme 1.10 (a)) and is discussed in section 1.2. Coordination polymerization is a type of addition polymerization that involves an unsaturated metal-based complex as the active site (Scheme 1.10 (b)).72,73 For example, a homogeneous metallocene catalyst [LnMR2; M = metal, L = ligand, R = alkyl, aryl] is used in the presence of a Lewis or Brønsted acidic co-initiator (e.g.: MAO (–[O–Al(CH3)]n–), Al(C2H5)3,  15  Al(C2H5)2Cl, B(C6F5)3, H(OEt2)2[B(C6F5)4]) to generate a metal-alkyl cation with a vacant coordination site (1.29).68,74 Propagation is realized by successive insertion of the C=C bond of   –olefin monomers (e.g. ethylene, propene, 1–hexene, 1–octene) into the metal-alkyl bond at each active site 1.30 to form a polymer.75,76 The mechanism of cationic ring-opening polymerization is illustrated in Scheme 1.10 (c). In general, initiation proceeds via activation of a heterocyclic monomer (e.g. oxazoline, lactone, ether) by a Brønsted acid or carbocation (1.31) (cation source = H+, R3C+). Propagation is achieved by the addition of a cyclic monomer to the cationic species at the chain end 1.32, and thereby opening the ring system resulting in a linear polymer.77   About three decades ago the term “non-coordinating anion”78,79 was used when a coordinating anion such as a halide was replaced by a complex anion for example [BF4]–,78 [ClO4]–,80 [SO3CF3]–, [SO3F]–,81 [PF6]–82 or [AsF6]–.83 Their application as counter anions was fostered with the advancement of X-ray crystallographic techniques. With the help of X-ray crystallography, the structural characterization of the coordination of these anions with various metal complexes was enabled.84 In the early 1990s the term “weakly coordinating anion” (WCA) was coined, which describes the interaction between the cation and anion species.69,79 Since then, the research of WCAs has been widely explored with the focus to design large charge delocalized and stable counter anions with respect to oxidation.70 WCAs based on group 13 elements have received considerable attention, while anions of group 15 elements are less common. In addition, WCAs are mainly used to stabilize reactive cations and are widely employed in pericyclic rearrangement and Diels-Alder reactions,85-91 olefin polymerization,92-95 electrochemistry96-101 or lithium ion batteries.102-107  16     Scheme 1.10. Different types of cationic polymerization and their general mechanisms; (a) reveals the mechanism of cationic chain polymerization; (b) shows the mechanism of cationic coordination polymerization, and (c) illustrates the mechanism of cationic ring-opening polymerization.  17   The scope of this section is confined to WCAs applied in cationic olefin polymerization including mainly coordination polymerization and a few examples in cationic chain polymerization. Rather than to separate this discussion into the two separate polymerization types (i.e. coordination and cationic), the progress in this field will be discussed in roughly chronological order in an effort to draw attention to the advances in WCA design.  The evolution of [1.33]– to larger WCAs began in the 1960s, when Massey and Park isolated a lithium salt containing the tetraphenylborate anion, [BPh4]–, [1.34]–.108  The WCA [1.34]– is applied as a counter anion in the Ziegler-Natta catalyst for ethylene       polymerization.109-111 Although, the anion was resistant to hydrolysis it was found that the phenyl groups are relatively strongly coordinating. X-ray crystallography revealed that [1.34]– coordinated to the metal via -interaction with one of the phenyl rings. Therefore, attempts to reduce the coordinating ability of the anion to the metal center were achieved by applying electron withdrawing groups, such as bulky fluorinated substituents (e.g. C6F5 or                  C6H3-3,5-(CF3)2). The addition of fluorinated aryl moieties to the Lewis acidic boron center gave rise to bulkier and more charge delocalized WCAs [B(C6F5)4]–, [1.36]–, and [B(ArF)4]– (ArF = C6H3–3,5–(CF3)2), [1.37]–.112  In the 1990s, Marks and co-workers studied the reactivity of the related Lewis acid B(C6F5)3 and demonstrated the isolation of a “cation-like” zirconocene catalyst for propene polymerization. It was shown that B(C6F5)3 abstracts a methyl group of zirconocene dimethyl complexes (L2ZrMe2 with L = η5-C5H5, η5-1,2-(CH3)2C5H3, η5-(CH3)5C5) that generated a zwitterionic complex [L2ZrMe][1.35].94,113-116 The complex [Al(η5–C5H5)2][1.35] has been employed as an initiator for isobutene polymerization.59 This sparked an interest in the application of tetrakis(pentafluorophenyl)borate, [1.36]–, as a WCA for metallocene  18  polymerization catalysts.117 Particularly, an alkyl abstraction reagent [Ph3C][1.36] was synthesized and reacted with an zirconocene dimethyl complex that yielded a highly effective catalyst for propene polymerization.118   Effective metallocene catalysts for olefin polymerization are also formed through protonolysis, by reacting (η5–Me5Cp)2ThMe2 with [HNnBu3][1.36] to yield                            [(η5–Me5Cp)2ThMe][1.36].113,117 Brookhart’s Brønsted acid, H(OEt2)2[1.37], has proven to be a potent protic reagent for the protonolysis of [(phen)Pd(CH3)2] to form a cationic palladium catalyst, [(phen)Pd(CH3)NCCH3][1.37], that is utilized in the copolymerization of ethylene and carbon monoxide.119,120 Despite the widespread use of [1.36]– as a WCA, the perfluorinated tetraphenylborate anion is prone to acid induced B–C bond cleavage.121    The quest for larger and more charge delocalized WCAs spearheaded the design of bridged borane anions to reduce the cation anion interaction. This led to the development of WCAs [1.38]–,122 [1.39]–,123,124 and [1.40]–,125 where the negative charge is distributed over two boron centers. These WCAs are utilized as activators for metallocene olefin polymerization catalysts.126-129 Furthermore, Baird and co-workers were able to generate a Brønsted acid in situ by reacting stearic acid (C17H35CO2H) with two B(C6F5)3 moieties. The resulting complex, H[1.41], is a highly effective initiator for the carbocationic polymerization of isobutene and isoprene to afford butyl rubber.130,131  19     The successful application of tetrafluoroarylborates has led to the development of aluminum containing WCAs. For example, Marks and co-workers reported the complex [Ph3C][1.42] that is utilized as a coactivator of zirconium complexes for ethylene and propene polymerization.132-134 However, studies have shown that their catalytic activities are lower than the catalysts containing [1.35]– and [1.36]–, indicating that [1.42]–  might be more coordinating than the latter anions.132,135    The search for weaker coordinating anions led to the design of bridged anions and the delocalization of the negative charge over multiple Lewis acid centers. Marks and co-workers isolated the fascinating perfluoroarylaluminate anions [1.43]–, [1.44]– and [1.45]2– as co-catalysts for the zirconium metallocene mediated propene polymerization. Increasing the anion size from  20  [1.43]– to [1.44]– demonstrated an increase in activity in propene polymerization, while increasing the anion size further to three bridged aluminum centers resulted in a decrease in polymerization activity. This is due to the increase in negative charge of the dianion            [1.45]2–.136-138 The WCA [1.46]–, an analog of [1.38]–, with an imidazole fragment as linking group between two aluminum centers, has been employed in a titanium catalyst for the copolymerization of ethylene and 1-octene. The catalyst system with the anion [1.46]– revealed higher activity and higher molecular weight polymer than that of  [1.38]–.122     In addition, perfluoroalkoxide or perfluoroaryloxide aluminate anions were explored as effective WCAs.139-148 Substantial efforts have been made to increase the stability from OC6F5 to (CF3)3 groups. For instance, Marks and co-workers reported zirconocene complexes of [Al(OC6F5)4]– ([1.47]–) and [Al{OC(CF3)3}4]– ([1.48]–) that are effective catalysts for ethylene polymerization.149,150 The complex [Al(η5–C5H5)2][1.48] is a more effective initiator for the cationic polymerization of isobutene than [Al(η5–C5H5)2][1.35].58,59 The WCA [1.48]– has been pioneered by Krossing and co-workers with the substitution of OArF for steric ORF alkoxy ligands [e.g. OC(CF3)3], shaping a very stable and WCA due to the strong aluminum-oxygen  21  bonds. However, the nucleophilicity of the oxygen bonds is evaded by the incorporation of electron withdrawing fluorine groups. The electronic stabilization of [1.48]– was demonstrated by perfluorination resulting in an increase of acidity from non-fluorinated HO-C(CH3)3               (pKa = 19.3) to partially fluorinated HO-C(H)(CF3)2 (pKa = 9.5) and perfluorinated HO-C(CF3)3 (pKa = 5.5) alcohol.151 The WCA [1.48]– stabilizes several highly reactive cations {e.g. [PX4]+ (X = F–I), [P2I5]+, [P5X2]+ (X = Br, I), [AsBr4]+, [CX3]+ (X = Cl, Br), [CI3]+, Li+, Ag+, [M(L)]+ (M = Ag, Cu; L = P4, P4S3 S8, C2H4), [Ga(C6H5F)2]+, Cs+, [Ph3C]+, [NR4]+                                           (R = Me, Et)}.60,139,141,146,152-164 Further, the anion is stable towards hydrolysis in H2O and nitric acid due to the steric shielding of the oxygen atom by the bulky C(CF3)3 ligands.148 The anion [1.48]– has been utilized in electrochemistry as a supporting electrolyte containing WCAs for the stabilization of reactive organometallic radical cations and as a WCA in ionic liquids.61,144,151,165 In addition, the perhalogenated WCA [1.49]– has been recently reported to stabilize lithium and trityl cations.166    22   The Brønsted acid [H(OEt)2][1.48] is an effective cationic single-component initiator for the ring-opening polymerization of 2-alkyl-2-oxazolines and for the carbocationic polymerization of isobutene.58,65 Krossing and co-workers have applied the complex [Ga(L)2][1.48] (L = C6H5F, PhC2H4Ph, 1,4-Me2C6H4) as an efficient initiator for the polymerization of isobutene.60,167 Further, the Brønsted acids H(OEt2)2[1.47] and H(OEt2)2[1.48], and trityl salts of [1.48]– and [1.50]– were investigated as co-catalysts in combination with a chromium catalyst for the oligomerization of ethylene to 1–hexene and 1–octene.168 The chromium complex of [1.48]– showed higher activity than the larger fluoro-bridged [1.50]–. The anion [1.50]– has been suggested as the “least coordinating anion”. However, it was found that [1.50]– was prone to dissociation in the presence of donor solvents into [FAl{OC(CF3)3}3]– and Al{OC(CF3)3}3.151,155,169  Gallium-containing WCAs such as [1.51]– and [1.52]– have also been applied in polymerization. The iodonium and triphenylcyclopropenium salts of [1.51]– have been investigated as photo-initiator for the cationic polymerization of epoxides and demonstrated similar photo-activity as salts containing [1.36]– and [1.38]–.170-174 The “linking” strategy of two anion motifs has been also applied for [1.52]–. This WCA has been studied as co-catalyst in combination with a zirconium metallocene for propene polymerization. The catalyst system revealed lower catalytic activity than the aluminate analog [1.44]–.136-138      23   Another modification of boron-based WCAs is the carborane anion. The effort to distribute the charge over a large number of atoms has led to the development of polyhedral carboranes. The cesium carborane salt of [1.53]– was first synthesized by Knoth in 1967.175,176 However, the weakly coordinating ability of [1.53]– was not studied until the mid-1980s as the anion is prone to oxidation.177,178 In order to overcome this limitation, partial halogenated derivatives were intensively studied that are less coordinating, chemically robust towards oxidation and acid cleavage, and thermally stable.179-181 Particularly intriguing are the hexa-halogenated carborane anions [CB11R6X6]– (R = H, Me; X = Cl, Br), [1.54]– and [1.55]–, reported by Reed and Ozerov. These WCAs delocalize the negative charge and stabilize highly electrophilic silylium cations [R3Si]+ (e.g. [iPr3Si]+, [Et3Si]+ and [Mes3Si]+).182-186    24  Carborane anion, [1.54]– (X = F, Cl, Br, I) and fully halogenated derivatives have been pioneered by Reed and co–workers and are considered “the least coordinating anions” and stabilize several highly reactive cations (e.g. [HC60]+, C60+, [C6H7]+, H+, [H5O2]+, [H(CO2)2]+, [H(OEt2)2]+, [Ph3C]+).187-195   Carborane anions have been utilized as ionic liquids196 and have been incorporated into transition metal frameworks as catalysts for olefin polymerization.197 For instance, Exxon disclosed zirconocene complexes of [1.53]– as catalyst for ethylene polymerization.111,198 Manners and Reed reported the trialkylsilylium salts of carborane anions [1.54]– and [1.55]– (X = Br) for the ring opening polymerization of cyclic chlorophosphazene, [Cl2P=N]3.199 Further, Reed reported the complex [Et2Al][1.54] (X = Cl, Br) as catalyst for ethane and cyclohexene oxide polymerization.200 The complex Li[1.56] catalyzes the radical polymerization of terminal alkenes.201 Despite their application as WCAs, their widespread use is hindered due to the extensive synthetic procedure.  Other p-block elements such as the triflate anion analogues [1.58]–, [1.59]– and [1.60]– have been applied as WCAs.202-206 These anions are described as highly charge delocalized.207,208 The incorporation of sulfonyl groups enables the development of larger anions, [1.58]–, [1.59]– and [1.60]–, and facilitates the delocalization of the negative charge over the sulfonyl groups. The triflimidate anion, [1.58]–, was first reported in 1984209 and reveals great WCA properties and has been employed as an electrolyte in batteries.210,211 Salts containing [1.58]– have been used as ionic liquids for the copolymerization of styrene and CO.212 The Brønsted acid H[1.58] is a highly efficient initiator for the group transfer polymerization of methyl methacrylate and a co-catalyst for the polymerization of N,N–dimethylacrylamide.213,214 Although the Brønsted acid H[1.59] was first reported by Seppelt and co-workers in 1988, the application of the anion  25  [1.59]– as a WCA is limited to electrolytes in lithium ion batteries due to the challenging synthesis.215-217 The intriguing anion [1.60]– has recently been reported as an allylic C–H acid, in which the negative charge is delocalized over four trifyl groups. The WCA [1.60]– reveals high catalytic activity in Friedel-Crafts acylation reactions.218    Larger derivatives of the “classical” anions of [EF6]– (E = As, Sb), namely [1.61]–, [1.62]– and [1.63]– were characterized in 1966 and have since been employed as WCAs.219-234 However, the application of these anions has not received attention in catalysis. The anion [1.64]– that is based on pentafluoroorthotellurate groups exhibits weakly coordinating character.235 The WCA [1.64]– (E = Al) has been recently reported in 2017 to promote the stabilization of reactive cations (e.g. H+, [Ph3C]+, [Ph4P]+, [C6H7]+, [C9H13]+).236 Among the class of hexacoordinate teflate-based anion [1.65]–,237-243 the anion [Sb(OTeF5)6]–241 is the most promising WCA to facilitate the stabilization of reactive cations (e.g. [XeOTeF5]+, [Ag(S8)2]+, [Ag2(Se6)(SO2)2]+).156,244,245 Catalytic application of the hexacoordinate anion [1.65]– has not been demonstrated yet.     26    A key take-home message from this section is that there are relatively few single component initiator systems that have been developed for cationic polymerization. Namely, the only systems that have been used are H(OEt2)2[Al{OC(CF3)3}4], H(OEt2)2[B(C6F5)4], Na(H2O)[B{3,5-(CF3)2C6H3}4], and H[B(C2O4)2] for the cationic ring-opening polymerization of oxaolines, and cationic polymerization of isobutene, isobutyl vinyl ether, and styrene.33,64-66 The potential advantages of these Brønsted acids are accurate control over monomer to initiator ratios during polymerization and polymerizations performed at higher temperatures than those typically used (i.e. –100 °C).246  1.5 Group 15 Element Based WCAs  The main goal of this dissertation is the isolation of solid weighable Brønsted acids as single-component initiator systems for the cationic polymerization of olefin monomers. The initiator system requires a WCA that stabilizes the reactive carbocation during polymerization. Substantial studies have been performed in the development of WCAs based on group 13 elements that are dominated by tetracoordinate boron and aluminum anion analogues. In comparison, WCAs containing group 15 elements are less common. The investigation of hexacoordinate phosphorus compounds is of fundamental interest. Anionic species of the form [PX6]–, such as [PF6]– and [PCl6]–, have been employed as WCAs.247 Larger derivatives of the [PF6]– anion are promising. The hexacoordinate phosphorus(V) anion facilitates the design of  27  larger WCAs that are thought to be more charge delocalized. In particular, the protic acid of the tris(oxalato)phosphate anion, [1.66]–, catalyzes Friedel-Crafts type alkylation reactions.248 The early work of Allcock and Hellwinkel has pioneered the development of hexacoordinate phosphorus(V) anions. The anion [1.67]– (R = H) was accidentally discovered by Allcock in 1963 as a potential WCA.249-252 At the same time Hellwinkel isolated a hexacoordinate phosphorus(V) anion with three bidentate biphenylidene ligands, [1.68]–.253-256 Since the 1970s a library of stable and more complex phosphorus(V) anions has been generated.257-260 An established example is the chiral tris(tetrachlorobenzenediolato)phosphate anion (TRISPHAT), [1.67]– (R = Cl), that was first reported by Schmutzler in 1992.261 Lacour and co-workers shed light on [1.67]– (R = Cl) by resolving the anion into enantiomerically pure [1.67]– (R = Cl) and unveiled its numerous application.260,262-265 The trityl salt of [1.67]– (R = Cl), in combination with a co-initiator, is an efficient initiator system for the polymerization of butyrolactone and methacrylate.266     28  1.6 Outline of Thesis  The Gates group has demonstrated the weakly coordinating ability of the non-chlorinated derivative of [1.67]– to stabilize alkali metal complexes as halide abstraction agent.267 Advances have led to the syntheses of Brønsted acids, H(L)2[1.67] (L = DMF, DMSO; R = H), for the protonolysis of late transition metal-carbon bonds.268 Building on this prior work, we successfully isolated the strong Brønsted acid H(OEt2)2[1.67] (R = Cl) as a single-component initiator for the cationic polymerization of different vinyl monomers including n-butyl vinyl ether, styrene, -methylstyrene and isoprene.269 To further explore the reactivity of single-component initiators containing the anion [1.67]– (R = Cl), we pursued the design of new Brønsted acids. Chapter 2 describes the isolation and characterization of strong Brønsted acids, H(L)2[1.67] (L = DMF, THF, CH3CN; R = Cl), and their application as solid and weighable single component initiators for the cationic polymerization of n-butyl vinyl ether and                 p-methoxystyrene. Although alkali metal salts of [1.68]– are known,253,254 we sought an alternative to the WCA [1.67]–. Chapter 3 discusses the synthesis, isolation and characterization of a chiral P–C-containing spiro–compound, [P(C12H8)(C24H16)][1.68], and the characterization of the pentavalent phosphorane P(C12H8)2(C12H9). Chapter 4 focuses on the weakly coordinating ability of the anion [1.69]–. In particular, the isolation and characterization of several ammonium  salts and an alkali metal salt of [1.69]– are reported. Chapter 5 describes the development of two transition metal-containing WCAs and the syntheses of strong Brønsted acids for the cationic polymerization of olefin monomers. Chapter 6 gives a summary of the research findings contained within this thesis and considerations for future work are postulated.  29      30  Chapter 2:  [HL2][P(1,2-O2C6Cl4)3] (L = THF, DMF): Brønsted Acid Initiators for the Polymerization of n-Butyl Vinyl Ether and p-Methoxystyrene*  2.1 Introduction The carbocationic polymerization of olefins is a challenging reaction with significantly higher propagation rate constants and more termination/chain transfer pathways than related radical or anionic methods.17,37 Therefore, initiators must be carefully designed with a cation source (the simplest being a proton or carbenium ion) and a weakly coordinating anion (WCA) that balances the electrophilic propagating cation.26,27,68,71,270,271 The design and synthesis of large, charge delocalized and non-nucleophilic WCAs is an area of considerable current interest to generate and stabilize highly reactive cations for fundamental and applied                     studies.84,147,151,179,182,194,272,273 Despite these efforts, only a few such systems have been employed as cationic initiators for polymerization.  Most recent developments of cationic initiators have focused on two-component initiators composed of a Lewis acid (e.g. B(C6F5)3, o-C6F4[B(C6F5)2]2, Al(C6F5)3, [6-Ar2Ga]+) and a      co-initiator (e.g. protic acid, water, alcohol, or carbenium source).167,274-279 Even in the case of the commercial two-component systems (e.g. BF3 or AlCl3 with “adventitious” water) the exact structure of the initiating species and the mechanism of initiation is not easily studied.280 The very rapid rates of propagation and sensitivity of the cationic intermediates make it very difficult to systematically study cationic polymerizations, in general. Commensurate with the rapid improvement in WCA chemistry, single-component initiators are of growing interest with examples including: [Al(η5-C5H5)2][Al{OC(CF3)3}4],58 [Ga(C6H5F)2][Al{OC(CF3)3}4],60  * This chapter has previously been published: Hazin, K.; Serin, S.C.; Patrick, B. O.; Ezhova, M. B.; Gates, D. P. Dalton Trans. 2017, 46, 5901.  31  [EtZn(arene)2][Al{OC(CF3)3}4] (arene = toluene, mesitylene),61 [Cp*Ti(CH3)2][CH3B(C6F5)4],36 [Al(η5-C5H5)2][CH3B(C6F5)4],59 [Ph3C][B(C6F5)4],55-57,266 and [Ni(C12H19)][B{3,5-(CF3)2C6H3}4].63  Single-component initiator systems based on Brønsted acids are less common with examples being shown in Figure 2.1 (A,65 B,64,281 C,282 and D33,66). These are attractive since there is no question of the initiating species (H+) or the mechanism of propagation. One limitation to their widespread usage is the difficulty in synthesizing, purifying and handling highly reactive strong non-aqueous Brønsted acids with WCAs, which necessitate handling at low temperatures and/or in donor solvents.   Figure 2.1. Examples of isolable Brønsted acids that have successfully been employed as single-component initiator systems for olefins.   32  The well-known charge delocalized tris(tetrachlorobenzenediolato)phosphate {TRISPHAT, [2.1]–}263,265,283-293 exhibits ideal properties as a WCA and recently caught our attention as a potentially convenient WCA for protic acids. We have shown that the simple reaction of 1,2-C6Cl4(OH)2 (3 equiv) with PCl5 in CH2Cl2 and a weak base (Et2O, MeCN) permits the isolation of the Brønsted acids H(OEt2)2[2.1] and H(OEt2)(CH3CN)[2.1].269 Remarkably, these solid weighable compounds show modest stability at ambient temperature and are as effective as single-component initiators for the polymerization of n-butyl vinyl ether,      -methylstyrene, styrene and isoprene. They are rare examples of strong Brønsted acids containing P-based anions.248,268,269  Herein, the scope of this convenient route to Brønsted acids of [2.1]– is expanded to the synthesis and isolation of H(DMF)2[2.1], H(THF)(MeCN)[2.1] and H(THF)2[2.1] The latter is a rare example of a crystallographically characterized compound containing the [H(THF)2]+ cation. Both are effective initiators for the polymerization of n-butyl vinyl ether and p-methoxystyrene. Notably, high molecular weight poly(p-methoxystyrene) (Mn up to 649,000    g mol–1) in good yield (53–98%) is obtained with an unexpected branched structure.  2.2  Results and Discussion 2.2.1 Synthesis and Characterization of Initiators It has been reported by Lacour et al. that the treatment of phosphorus pentachloride (PCl5) with tetrachlorocatechol (3 equiv) in hot toluene, followed by addition of an amine affords the ammonium salt of [2.1]–.262 Building on this previous work, we aimed to develop H(DMF)2[2.1] and H(THF)2[2.1] as initiators for cationic olefin polymerization with the more acidic [H(DMF)2]+ cation (pKa = –1.2 ± 0.5)294 and [H(THF)2]+ cation (pKa = –2.05).295 Treating  33  PCl5 with tetrachlorocatechol (3 equiv) in hot dichloromethane resulted in 2.2 ( = –29 ppm). Subsequently, the weakly donating solvent (DMF or THF) was added to afford an  off-white precipitate of either H(DMF)2[2.1] or H(THF)2[2.1] (Scheme 2.1). It is important to keep the THF concentration low to prevent its polymerization (< 50 vol% in CH2Cl2). The crude products, H(DMF)2[2.1] or H(THF)2[2.1] were recrystallized as described in the experimental section to afford colorless crystals suitable for X-ray crystallography. The molecular structures of the moisture and air-sensitive Brønsted acids H(DMF)2[2.1] and H(THF)2[2.1] are shown in Figures 2.4 and 2.5, respectively (vide infra). Although it is preferable to store H(DMF)2[2.1] at low temperatures (ca. –30 °C), the solid may be handled for 1 week or more at ambient temperature in an inert atmosphere without decomposition. In contrast, H(THF)2[2.1] degrades in < 1 h at ambient temperature.    Scheme 2.1. Synthesis of Brønsted acid H(L)2[2.1] (L = DMF, THF). The 31P{1H} NMR spectra of H(L)2[2.1] (L = DMF, THF) in CD3CN each show a singlet resonance (L = DMF: δ = –81.8; L = THF: δ = –80.6) (see Appendix A, Figures A1 and A2), which is in the range expected for salts containing [2.1]– (δ = –80.1).261 In addition, the isolated Brønsted acids H(DMF)2[2.1] and H(THF)2[2.1] were characterized by 1H and 13C{1H} NMR  34  spectroscopy, X-ray crystallography and elemental analysis. At ambient temperature, the 1H NMR spectra of H(L)2[2.1] (L = THF, DMF) in CD2Cl2 revealed signals assigned to the two coordinated DMF molecules (δ = 8.07, 1H, O=CH; 3.10, 3H, NCH3; 2.97, 3H, NCH3) or two coordinated THF moieties (δ = 4.08, 4H, OCH2; 2.04, 4H, CH2), respectively. In addition, a broad downfield signal was observed that is assigned to the acidic proton of HL2[2.1] (L = DMF: δ = 16.6, 1H, fwhm = 565 Hz; L = THF: δ = 13.4, 1H, fwhm = 532 Hz). For comparison, related salts containing the [H(DMF)2]+ cation show similar downfield chemical shifts in             H2(DMF)4[TeBr6]: δ = 16.8, CD3CN; H(DMF)2[CF3SO3]: δ = 16.9, CD3CN;296 H(DMF)2[P(1,2–O2C6H4)3]: δ = 15.3 CD3CN;268 H(DMF)2[CF3CO2]: δ = 15.1, (CD3)2SO].297 The salt H(THF)2[CHB11R5X6] displayed a similar downfield shift for the acidic proton (δ = 14.8 ppm)195 to that of H(THF)2[2.1] whilst [H(THF)2][Al{OC(CF3)3}4] is quite different (δ = ~ 8 ppm).298  At low temperature, the 1H NMR spectra of H(THF)2[2.1] (Figure 2.2) display much sharper signals for the acidic proton and are shifted downfield with respect to the ambient temperature spectra (T = –85 °C, CD2Cl2: L = DMF: δ = 19.2, fwhm = 102 Hz; L = THF: δ = 16.9, fwhm = 15 Hz). To our knowledge, these are the furthest downfield signals detected for the acidic protons of [H(DMF)2]+ and [H(THF)2]+ cation containing salts and are comparable to that of H[CHB11Cl11] (1H = 20.4 in SO2 at –65 °C).182 Importantly, the integrated ratio of the signals assigned to the acidic proton and the coordinating solvent are consistent with the 2:1 ratio within the [HL2]+ cation.   35   Figure 2.2.1H NMR (400 MHz, CD2Cl2, –85 °C) spectrum of (a) H(THF)2[2.1] and (b) H(DMF)2[2.1]. * indicates residual CHDCl2. † unassigned signal. To further investigate the integrity of [HL2]+ (L = DMF; L = THF) moiety in solution, low temperature 1H–1H COSY NMR experiments were performed. Given that no correlation was observed between the acidic proton and the THF OCH2 protons, the 1H–1H NOESY NMR  36  spectrum was recorded in CD2Cl2 at –85 °C. The spectrum of H(THF)2[2.1] clearly showed an NOE between the acidic proton and the THF methylene protons, as revealed by the cross-peaks between the corresponding resonances (at 4.1 and 16.9 ppm, respectively) (Figure 2.3). These 2D NOESY NMR findings for H(THF)2[2.1] were reproducible confirming the stability of the molecule. The low temperature 2D NOESY NMR spectrum of H(DMF)2[2.1] (see Appendix A, Figure A5) revealed negative NOE between the acidic proton and the HC=O formyl proton as well as between the HC=O and methyl proton. This was surprising considering that H(THF)2[2.1], which is similar in size, shows positive NOE at –85 °C. To confirm that negative NOE was observed in this experiment and exclude exchange, 2D ROESY data was collected for H(DMF)2[2.1] in CD2Cl2 at –85 °C (see Appendix A, Figure A6). These data confirmed the NOE between the HC=O and methyl proton. No through space interactions have been observed for the acidic proton and formyl proton in the 2D ROESY experiment. Similarly, the 2D ROESY NMR spectrum of H(THF)2[2.1] (see Appendix A, Figure A7) showed no interaction between the acidic proton and the THF OCH2 protons and revealed positive NOE between CH2 and OCH2 protons. In general, the tumbling rate of a molecule is responsible for the sign of NOE and is dependent on size of the molecule and solution conditions such as temperature and viscosity.299 Since both H(DMF)2[2.1] and H(THF)2[2.1] have a similar molecular weight and both experiments were conducted under identical conditions, we tentatively attribute the difference in sign to a difference in viscosity of the solutions. Overall, these data confirmed that the [H(THF)2]+ and [H(DMF)2]+ cations are retained in CD2Cl2 solution at –85 °C.   37   Figure 2.3. 2D 1H–NOESY(400 MHz, CD2Cl2, –85 °C) experiment of H(THF)2[2.1]. A mixing time of 0.59 s was used.* indicates residual CHDCl2.         38   Scheme 2.2. Synthesis of Brønsted acid H(THF)(MeCN)[2.1]. We have previously shown that dissolution of H(OEt2)2[2.1] in acetonitrile results in the precipitation of single crystals of H(OEt2)(MeCN)[2.1], containing the rare [OEt2–H–NCMe]+ cation. Similarly, dissolution of H(THF)2[2.1] in CD3CN affords single crystals of H(THF)(MeCN) as determined by X-ray crystallography (Figure 2.6). The 31P{1H} NMR spectrum of H(THF)(MeCN)[2.1] in CD3CN recorded at 25 °C revealed a singlet resonance (= –80.1 ppm) suggesting that the integrity of the [TRISPHAT]– anion was preserved in solution. The 1H NMR spectrum at 25 °C showed signals that were consistent with the presence of THF but the signal for the H+ proton was not observed, presumably due to its breadth. Low temperature analysis in CD2Cl2 was not possible due to the compound’s limited stability in dichloromethane.  2.2.2 Metrical Parameters Determined by X-ray Crystallography Single-crystal X-ray structures were obtained for H(DMF)2[2.1], H(THF)2[2.1] and H(THF)(MeCN)[2.1]. The molecular structures along with important metrical parameters are given in Figures 2.4, 2.5 and 2.6, respectively. Additional details are found in the supporting information. The structure of H(DMF)2[2.1] shows five crystallographically independent  39  complexes per asymmetric unit. For clarity, only one molecule is displayed in Figure 2.4. Compound H(THF)2[2.1] (Figure 2.5) crystallizes with one tetrachlorocatechol and one THF molecule whilst H(THF)(MeCN)[2.1] (Figure 2.6) crystallizes with large area of disordered MeCN and THF as solvate. H(THF)2[2.1] displays close solvate interaction between an oxygen of the anion [2.1]– and a hydrogen of free tetrachlorocatechol [O(5)···H(9) = 2.28(5) Å] and between an oxygen of THF solvate and a hydrogen of the unbound tetrachlorocatechol [O(11)···H(10) = 1.932(6) Å]. Solvate interactions in H(THF)(MeCN)[2.1] occur between an oxygen of the anion [2.1]– and a methyl group of the acetonitrile solvate [O(1)···H(20a) = 2.656(2) Å; O(3)···H(24c) = 2.634(3) Å].   The closest cation-anion contacts in H(DMF)2[2.1] occur between an oxygen atom of the anion [2.1]– and a methyl group of DMF [O–H range: 2.379(4)–2.717(5) Å] and are within the sum of the van der Waals radii for oxygen and hydrogen [rvdw = 2.72 Å]. Similarly, the closest cation-anion contacts in H(THF)2[2.1] are between an oxygen atom of the anion [2.1]– and a methylene group of THF [O–H range: 2.620(4)–2.755(4) Å]. In contrast, H(THF)(MeCN)[2.1] displays close contacts between an oxygen of the anion [2.1]– and a methyl group of the          H+–coordinated acetonitrile [O(2)···H(22c) = 2.62(18) Å; O(5)···H(22b) = 2.619(2) Å] and between a chlorine of the anion [2.1]– and a methyl group of the acetonitrile solvate [Cl(5)···H(24b) = 2.780(13)]. The phosphorus(V) anion, [2.1]–, shows only minor perturbation from regular octahedral symmetry displaying metrical parameters similar to those previously reported. The average P–O bond lengths in HLL'[2.1] [L = L' = DMF:  avg. = 1.71(3) Å; L = L' = THF: avg. = 1.715(9) Å;  L = THF, L' = MeCN: avg. = 1.712(4) Å] are similar to those found in [NEt2H2][2.1],261  40  [Et3NH][2.1],250 H(OEt2)2[2.1]269 and [tris(4-dimethylaminobenzene)carbenium][2.1]300 (avg. = 1.713(8), 1.715(6), 1.715(1), 1.75(2) Å, respectively].    Figure 2.4. Molecular structure of H(DMF)2–rac–[2.1]·0.2 CH2Cl2 (Δ isomer is shown; molecule 1 of 5 unique molecules). Ellipsoids are drawn at the 50% probability level. Solvents of crystallization (0.2 x CH2Cl2) and hydrogen atoms are omitted for clarity. Selected bond lengths [Å]: P(1)–O(1) = 1.719(5); P(1)–O(2) = 1.72(5); P(1)–O(3) = 1.716(5); P(1)–O(4) = 1.721(5); P(1)–O(5) = 1.709(5); P(1)–O(6) = 1.704(5); C(6)–O(2) = 1.356(8); C(94)–O(31) = 1.259(10); C(91) –O(32) = 1.261(10); C(94)–N(1) = 1.291(9); C(91)–N(2) = 1.309(10); O(31)–O(32) = 2.41(7). Selected bond angles []: O(1)–P(1)–O(2) = 90.8(2); O(3)–P(1)– O(4) = 91.3(3); O(5)–P(1)–O(6) = 91.1(2); C(94)–N(1)–C(96) = 121.9(7).    41    Figure 2.5. Molecular structure of H(THF)2–rac–[2.1]·C6H2O2Cl4·THF (Λ isomer is shown). Ellipsoids are drawn at the 50% probability level. Solvents of crystallization (1  THF), unbound tetrachlorocatechol (1  C6H2O2Cl4) and hydrogen atoms are omitted for clarity, except for H(1). Selected bond lengths [Å]: P(1)–O(1) = 1.707(3); P(1)–O(2) = 1.718(4); P(1)–O(3) = 1.714(4); P(1)–O(4) = 1.704(4); P(1)–O(5) = 1.733(3); P(1)–O(6) = 1.719(4); O(7)–H(1) = 1.35(7); O(8)–H(1) = 1.05(7); C(19)–O(7) = 1.408(16); C(22)–O(7) = 1.500(9); C(23)–O(8) = 1.465(5); C(26)–O(8) = 1.34(5); O(7)–O(8) = 2.394(5). Selected bond angles []: O(2)–P(1)–O(1) = 91.1(2); O(3)–P(1)–O(4) = 91.2(2); O(5)–P(1)–O(6) = 90.2(2).        42   In contrast to the anion, the metrical parameters for the cation moiety provide valuable insight into the bonding within each compound. For H(THF)2[2.1] the acidic proton was located in the difference electron density map, whereas the acidic proton was not found for H(DMF)2[2.1] and H(THF)(MeCN)[2.1]. The acidic proton of H(THF)2[2.1] was refined isotropically and is coordinated asymmetrically through the oxygen atom of two THF molecules [O(7)–H(1) = 1.35(7) Å; O(8)–H(1) = 1.05(7) Å]. Asymmetric binding has been reported for related H(OEt2)2[2.1],269 H(OEt2)2[Al{OC(CF3)3}4]298 and H(OEt2)2[B(C6F5)4],301 however, it has not been noted for the more rare [H(THF)2]+ cation. Since the determination of the position of the central proton is generally unreliable, the more precisely determined C–O and C–C bond lengths are often used to evaluate the symmetry within the [H(OEt2)2]+ cation.298 These data are given in Figure 2.7 along with the previously reported H(THF)2[CHB11H5Br6],195 H(THF)2[MnCl4(THF)2],302 H(THF)2[TeCl5],303 and H(THF)2[Al{OC(CF3)3}4].298 A shortening of the C–O and C–C bonds is observed for THFB of the [THFA–H–THFB]+ cation in H(THF)2[2.1]. This may reflect asymmetric binding within the cation. For comparison, a similar bonding situation has been observed for H(THF)2[Al{OC(CF3)3}4] whilst the binding within H(THF)2[CHBr11H5Br6] and H(THF)2[MnCl4(THF)2] appears to be more symmetric.  The C–C and C–N bonds within the acetonitrile moiety within the cation of H(THF)(MeCN)[2.1] [1.443(7) and 1.136(7) Å, respectively] are similar in length to those of acetonitrile (1.44 and 1.13, respectively)304 and to the cation of H(OEt2)(CH3CN)[2.1] (1.45 and 1.14 Å, respectively).269 The C–O distance in the coordinated THF molecule [C(25)–O(8a) = 1.422(18) Å; C(28a)–O(8a) = 1.42(3) Å] displays a slight lengthening from the C–O bond lengths found in THF lattice solvate [1.41(1) Å].305    43    Figure 2.6. Molecular structure of H(THF)(MeCN)–rac–[2.1]·3.35 MeCN·1.52 THF (Δ isomer is shown). Ellipsoids are drawn at the 50% probability level. Solvents of crystallization and hydrogen atoms are omitted for clarity. Selected bond lengths [Å]: P(1)–O(1) = 1.714(2); P12)–O(2) = 1.711(2); P(1)–O(3) = 1.707(2); P(1)–O(4) = 1.707(2); P(1)–O(5) = 1.714(2); P(1)–O(6) = 1.722(2); C(25)–O(8a) = 1.422(18); C(28a)–O(8a) = 1.42(3); O(8a)–N(2) = 3.15(2); C(21)–N(2) = 1.136(7). Selected bond angles []: O(1)–P(1)–O(2) = 91.1(10); O(5)–P(1)–O(4) = 92.9(10); O(5)–P(1)–O(6) = 90.7(10).  The extent of hydrogen bonding within the cation of H(DMF)2[2.1] and H(THF)2[2.1] may be evaluated by considering the O···O distances. The O···O distance within the [H(DMF)2]+ cation [O···Oavg. = 2.41(2); range: 2.410(7)–2.431(9)] and the [H(THF)2]+ cation [O(7)···O(8) = 2.394(5) Å] are significantly shorter than the sum of the van der Waals radii [rvdw = 3.04Å].306 For comparison, these data are similar to the O···O distances for known compounds containing the [H(DMF)2]+ cation [O···Oavg. = 2.42(3) Å]268,296,307-309 or [H(THF)2]+ cation [O···Oavg. =  44  2.40(4) Å].195,298,302,303 The O···N distance within the rare [H(THF)(CH3CN)]+ cation [O(8a)···N(2) = 3.15(2) Å] is significantly longer than the O···N distance found in  [H(OEt2)(NCMe)]+ [O(13)···N(1) = 2.536(3) Å], each with the [2.1]– anion, and slightly larger than the sum of van der Waals radii for oxygen and nitrogen [rvdw=3.07 Å].306   Figure 2.7. Comparison of C–O and C–C bond length of [H(THF)2]+ in H(THF)2[2.1], H(THF)2[CHB11H5Br6], H(THF)2[Al{OC(CF3)3}4] and H(THF)2[MnCl4(THF)2].   2.2.3 H(DMF)2[2.1] and H(THF)2[2.1]-initiated Cationic Polymerization  The complexes H(DMF)2[2.1] and H(THF)2[2.1] were investigated as initiators for the cationic polymerization of n-butyl vinyl ether and p-methoxystyrene (p-MeOSt) in dichloromethane at various temperatures. The results are shown in Tables 2.1 and 2.2 and each data point is representative of between two and eight repeat runs. Each polymerization was  45  performed utilizing freshly distilled solvent and monomers. n-Butyl vinyl ether was successfully polymerized by H(DMF)2[2.1] and H(THF)2[2.1] under a variety of temperatures. At ambient temperature, poly(n-butyl vinyl ether) was isolated as a brown viscous oil in moderate yield (47%, Table 2.1, entry 1) using H(DMF)2[2.1] as initiator. Although polymer is obtained in modest yield and reasonable molecular weight (Mn = 16,400 g mol–1, Đ = 1.46) at ambient temperature, the coloration suggests that terminal conjugated polyene moieties are present. Presumably, these ene functions are formed from proton elimination followed by dealcoholation.310-313 Chain-transfer processes in cationic polymerizations are suppressed at lower temperatures, therefore resulting in polymers of higher molecular weight.26,27,314 As the temperature was lowered, the brown color obtained at 18°C, was not present in polymer prepared at –50 °C using H(DMF)2[2.1] as initiator.   Scheme 2.3. H(L)2[2.1] (L = DMF, THF) initiated cationic polymerization of n-butyl vinyl ether.  The 1H NMR spectrum of the brown poly(n-butyl vinyl ether) produced at 18 °C (Figure 2.8 a) displayed signals in the vinyl region (5.0–6.0 ppm) that were not present in the colorless polymer produced at –50 °C (Figure 2.8 c). Although, H(DMF)2[2.1] was a competent initiator down to –50 °C, the yields averaged ca. 50% with the molecular weights (Mn ≈ 10,000–15,000   g mol–1) being much lower than those expected from the monomer-to-initiator ratio [Mn (calcd) = 45,100 g mol–1] (Table 2.1, entry 1–5). In contrast to the H(DMF)2[2.1] initiator, the more acidic H(THF)2[2.1] generally afforded higher yields of polymer at all temperatures with higher molecular weights (Mn ≈ 17,000–41,000 g mol–1) and moderate dispersity being observed. As   46    Figure 2.8. 1H NMR (400 MHz, CDCl3, 25 °C) spectra of poly(n-butyl vinyl ether) polymerized using (a) H(DMF)2[2.1] at 18 °C, (b) H(THF)2[2.1] at 18 °C and (c) H(DMF)2[2.1] at –50 °C. * indicates residual CHDCl2. † indicates residual CH2Cl2 solvent.  47  the polymerization temperature was lowered to –84 °C, a colorless poly(n-butyl vinyl ether) was produced. The observed Mn (41,400 g mol–1) was consistent with the expected                           Mn (45,100 g mol–1). The GPC trace (differential refractive index) of the resultant              poly(n-butyl vinyl ether) polymerized by H(DMF)2[2.1] at –50 °C was narrow and symmetrical (Figure 2.9 for Table 2.1, entry 5), whereas the differential refractive index trace of the resultant poly(n-butyl vinyl ether) polymerized using H(THF)2[2.1] as initiator at –84 °C exhibited low molecular weight tailing (Figure 2.9 for Table 2.1, entry 14). In general, the new initiators, H(DMF)2[2.1] and H(THF)2[2.1], performed quite differently than the previously reported H(OEt2)2[2.1], which showed characteristics of a living system for n-butyl vinyl ether.269    Figure 2.9. Refractive index traces of poly(n-butyl vinyl ether) initiated by H(DMF)2[2.1] (Table 2.1, entry 5) and H(THF)2[2.1] (Table 2.1, entry 14).       48  Table 2-1. Cationic polymerization of n-butyl vinyl ether using H(DMF)2[2.1] and H(THF)2[2.1] as initiator. Initiator entry T (°C) t (min) [M]:[I]a Yield (%) Mnb (g mol–1) Đc H(DMF)2[2.1] 1 18 15 450 47 16,400 1.46  2 0 15 450 67 12,250 1.51  3 –15 15 450 59   9,300 1.33  4 –38 15 450 42 13,400 1.06  5 –50 15 450 53 15,000 1.05  6 –78 15 450 0 n.d. d n.d. d  7 –84 15 450 0 n.d. d n.d. d         H(THF)2[2.1]   8 18 15 450 73 17,200 1.55  9 0 15 450 86 21,000 1.49  10 –15 15 450 79 21,000 1.60  11 –38 15 450 72 21,800 1.84  12 –50 15 450 72 25,600 1.66  13 –78 15 450 82 21,000 2.07  14 –84 15 450 37 41,400 1.64 The polymerization was carried out in 2 mL CH2Cl2 solvent using 0.011 mmol of Brønsted acid as initiator. a [Monomer]/[Initiator] ratio. b Absolute molecular weights were determined using laser light scattering gel permeation chromatography (GPC–LLS); differential refractive index (dn/dc) of poly(n-butyl vinyl ether) (dn/dc = 0.068 mL g–1) in THF was calculated by assuming 100% mass recovery. c Dispersity (Đ = Mw/Mn), where Mw is the weight–average molar mass and Mn is the number–average molar mass. d Not determined.   Scheme 2.4. H(L)2[2.1] (L = DMF, THF) initiated cationic polymerization of p-methoxystyrene. p-Methoxystyrene was successfully polymerized using either H(DMF)2[2.1] or H(THF)2[2.1] as the initiator over a range of temperatures (18 °C to –84 °C) with an [M]:[I] ratio of 400:1. Employing these single-component initiators produced high molecular weight poly(p-methoxystyrene) in good to high isolated yield (Table 2.2). In general, the polymer obtained  49  from H(DMF)2[2.1] initiation gave higher yield but lower molecular weight than that gained for H(THF)2[2.1]. At ambient temperature, the molecular weight obtained using H(THF)2[2.1] (Mn = 382,000 g mol–1) was much higher than that observed using H(DMF)2[2.1] (Mn = 74,900             g mol–1) and both were considerably higher than that expected from the monomer-to-initiator ratio [Mn (calcd) = 40,800 g mol–1]. For comparison, the single component initiator [Ph3C][SbCl6] produces poly(p-methoxystyrene) (Mn = 92,500 g mol–1) when polymerizations are performed in CH2Cl2 solution (T = –15 to + 25 °C).315 In contrast, a number of binary initiator systems have been reported to give living cationic polymerization [e.g. HI/ZnI2 in toluene at –15 to 25 °C;54,316 and HI/I2 and HI/ZnI2 in the presence of nBu4NX (X = Cl, Br, I) in CH2Cl2].53,317   At lower temperatures, high molecular weights (>140,000 g mol–1) of                      poly(p-methoxystyrene) were obtained using either H(DMF)2[2.1] or H(THF)2[2.1] as initiators (Table 2.2). Although the H(DMF)2[2.1] initiator presented a decrease in dispersity as the polymerization temperature was lowered, the H(THF)2[2.1] did not show a significant change in dispersity as a function of polymerization temperature. Quantitative yields were observed for H(DMF)2[2.1] down to –50 °C. Remarkably, below this temperature, this initiator demonstrated no activity for p-MeOSt polymerization. In contrast, the H(THF)2[2.1] initiator afforded moderate (ca. 50–60%) yields of polymer regardless of temperature. Perhaps most noteworthy are the high molecular weight values observed, which are at the upper limits of the separation capability for our GPC-MALS columns (ca. 500,000 g mol–1), so may even be underestimates. Clearly, there is a considerable difference in the molecular weights observed when using H(DMF)2[2.1] relative to H(THF)2[2.1], which can only be due to the difference in the nature of  50  the propagating species in the presence of either DMF or THF. Further studies are needed to gain insight into this interesting observation.  Table 2-2. Cationic polymerization of p-methoxystyrene using H(DMF)2[2.1] and H(THF)2[2.1] as initiator. Initiator entry T (°C) t (min) [M]:[I]a yield (%) Mnb (g mol–1) Đc H(DMF)2[2.1] 1 18 15 400 96   74,900 2.00  2 0 15 400 98 140,000 1.77  3 –15 15 400 96 291,000 1.71  4 –38 15 400 96 351,000 1.42  5 –50 15 400 96 289,800 1.28  6 –78 15 400 0 n.d. d n.d. d  7 –84 15 400 0 n.d. d n.d. d         H(THF)2[2.1] 8 18 15 400 58 382,000 1.42  9 0 15 400 62 145,200 1.58  10 –15 15 400 61 315,000 3.54  11 –38 15 400 58 375,700 2.28  12 –50 15 400 56 221,500 3.21  13 –78 15 400 56 342,800 3.16  14 –84 15 400 53 649,000 1.88 The polymerization was carried out in 2 mL CH2Cl2 solvent using 0.011 mmol of Brønsted acid as initiator. a [Monomer]/[Initiator] ratio. b Absolute molecular weights were determined using laser light scattering gel permeation chromatography (GPC–LLS); differential refractive index (dn/dc) of poly(p-methoxystyrene) used is 0.174 mL g–1. c Dispersity (Đ = Mw/Mn), where Mw is the weight–average molar mass and Mn is the number–average molar mass. d Not determined.  The cationic polymerization of p-MeOSt rarely affords polymer in high yield and with a higher molecular weight than that predicted from the [M]:[I] ratio. A single example has been reported with a hexafluoroisopropanol-based initiator (Yield = 95%, Mn = 295,000 g mol–1, PDI = 3.82),318 however, this work has not been elaborated upon. Rare examples also occur with styrene using stannic chloride as initiator at 0 °C (up to 97 %, Mw up to 149,000 g mol–1).42-44,319  51  To account for the latter results, the authors postulated several methods of chain transfer that can lead to a branched polymer. Evidence for branching in the present study was gained by comparing the intrinsic viscosity of the sample to that of linear polystyrene. Since an authentic sample of linear poly(p-methoxystyrene) was unavailable, we analyzed the H(THF)2[2.1]-initiated p-MeOSt polymer against a linear polystyrene standard. For samples with identical molecular weight (Mw = 106 g mol–1), a significantly lower intrinsic viscosity was observed for the p-methoxystyrene when compared to linear polystyrene ([]w = 136 mL g–1 vs. 250 mL g–1), which is consistent with a branched polymer. The hydrodynamic radius (Rh) determined from dynamic light scattering was significantly lower for the p-methoxystyrene sample when compared to linear polystyrene [(Rh)z = 25 nm vs 34 nm], again suggesting a branched polymer. The final evidence for a branched polymer was obtained from the 1H NMR spectrum of the poly(p-methoxystyrene) samples. Figure 2.10 shows a representative spectrum (Table 2.2, entry 1). Importantly, small signals were obtained in the range of 4.0 – 6.4 ppm that have previously been attributed to vinylic protons that result from branching caused by Friedel-Crafts alkylation/arylation and hydride transfer reactions during living cationic polymerization.320,321 A recent study has accounted for branched structures in methoxystyrene polymers by invoking a simultaneous chain- and step-growth mechanism.322       52   Figure 2.10. 1H NMR (400 MHz, CDCl3, 25 °C) spectrum of poly(p-methoxystyrene) prepared using H(DMF)2[2.1] at 18°C. * indicates residual CHDCl2. † indicates residual CH2Cl2 solvent.  2.3 Summary We have synthesized and fully characterized three new Brønsted acids containing the weakly coordinating phosphorus(V)-based [TRISPHAT]– anion. H(DMF)2[2.1], H(THF)2[2.1] and H(THF)(CH3CN)[2.1] are isolable and weighable proton sources. H(DMF)2[2.1] and H(THF)2[2.1] have proven to be good single-component initiators for the cationic polymerization of n–butyl vinyl ether and p-methoxystyrene. The polymerization of the olefin monomers was investigated at a variety of temperatures ranging from ambient to low temperatures keeping the monomer/initiator ratio constant. Remarkably, H(THF)2[2.1] afforded high molecular weight poly(p-methoxystyrene) with Mn up to 649,000 g mol–1 in good isolated yield. This unique  53  combination of high molecular weight and high yield is unusual for cationic polymerization and we postulate it arises from branching of the poly(p-methoxystyrene) through either Friedel-Crafts alkylation/arylation or hydride transfer.   2.4 Experimental 2.4.1  General Procedures  All experiments were performed using standard Schlenk or glove box techniques under nitrogen atmosphere. CH2Cl2 (Sigma Aldrich) and Et2O (Fisher Scientific) were deoxygenated with nitrogen and dried by passing the solvent through a column containing activated, basic alumina. Subsequently, the CH2Cl2 and Et2O were dried over CaH2, freshly distilled, and freeze-pump-thaw (x3) degassed. Acetonitrile (Sigma Aldrich), dimethylformamide (DMF) (Fisher Scientific), p-methoxystyrene (TCI America) and n-butyl vinyl ether (Sigma Aldrich) were dried over calcium hydride, distilled and freeze-pump-thaw (x3) degassed prior to use. CH2Cl2, Et2O, acetonitrile, and DMF were stored over 3 Å molecular sieves. Tetrahydrofuran (THF) (Fisher Scientific) was dried and distilled over sodium/benzophenone ketyl immediately prior to use. Phosphorus pentachloride (Aldrich) was sublimed prior to use. Tetrachlorocatechol323 was prepared following literature procedure, azeotropically distilled and recrystallized from hot toluene prior to use.   Elemental analyses, mass spectrometry and NMR spectra were performed in the Department of Chemistry Facilities. 1H, 13C{1H} and 31P{1H} NMR spectra were recorded on Bruker Avance 300 or 400 MHz spectrometers at room temperature unless noted. H3PO4 (85 %) was used as external standard for 31P NMR spectra with δ = 0.0. 1H NMR and 13C{1H} NMR spectra were referenced to deuterated solvents. 1D and 2D 1H–1H NOESY and ROESY NMR  54  spectra were recorded on Bruker Avance 400 MHz spectrometer at –85 C. 2D NOESY spectra of complex H(THF)2[2.1] were recorded by using a mixing time of 0.59 s. T1 measurements were conducted according to Bruker T1 measurement guide as a series of 1D experiments (pulse program t1ir1d) by varying d7 (inversion recovery delay). D1 (relaxation delay) was chosen to be at least 7 times longer than T1. T1 was calculated according to the formula T1=d7/ln2 with d7 (inversion recovery delay) at which magnetization goes through null. The 2D ROESY spectra of H(DMF)2[2.1] and H(THF)2[2.1] (see Appendix A, Figures A6 and A7) were acquired using standard Bruker pulse program roesyetgp.2 with a continuous spin-lock during mixing (200 ms), a relaxation delay of 1.5 s and 16 scans/FID. For H(DMF)2[2.1] 2D ROESY spectrum was obtained with 128 increments (9.19 kHz spectral width) and for H(THF)2[2.1] with 154 increments (8 kHz spectral width).   Molecular weights were determined by triple detection gel permeation chromatography (GPC-LLS) utilizing an Agilent 1260 Series standard auto sampler, an Agilent 1260 series isocractic pump, Phenomenex Phenogel 5 μm narrowbore columns (4.6 x 300 mm) 104 Å (5000-500,000), 500 Å (1,000-15,000), and 103 Å (1,000-75,000), Wyatt Optilab rEx differential refractometer ( = 658 nm, 25 C), as well as a Wyatt Tristar miniDAWN (laser light scattering detector:  = 690 nm) and a Wyatt ViscoStar viscometer. Samples were dissolved in THF (ca. 2 mg mL–1) and a flow rate of 0.5 mL min–1 was applied. The differential refractive index (dn/dc) of poly(n-butyl vinyl ether) (dn/dc = 0.068 mL g–1) in THF was calculated by using Wyatt ASTRA software 6.1 assuming 100 % mass recovery. The differential refractive index (dn/dc) of poly(p-methoxystyrene) (dn/dc = 0.174 mL g–1)324 has been reported. The hydrodynamic radius Rh was measured using a DynaPro-99-E50 dynamic light scattering module with a GaAs laser  55  (658 nm) at 25 C with a temperature-controlled microsampler (MSXTC 12). The sample concentration was the same as that of the GPC samples in THF (1mg/1 mL).   2.4.2 Synthesis of H(DMF)2[2.1] PCl5 (0.11 g, 5.30 mmol) and tetrachlorocatechol (0.36 g, 15.8 mmol) were stirred in CH2Cl2 (6 mL). The dark green suspension was slowly heated to reflux. After 2 h a colorless precipitate formed and was cooled to ambient temperature. Upon addition of DMF (1.5 mL) a clear solution was obtained. The solution was cooled in an ice bath to afford a white precipitate. The solid was collected by filtration and dried in vacuo. A concentrated solution of the crude product in CH2Cl2 afforded colorless crystals (ambient temperature, ca. 7 d). A crystal was removed for X-ray crystallographic analysis without drying. Yield = 0.27 g, 56%. 31P{1H} NMR (162 MHz, CD3CN, 25 C): δ = –81.76; 1H NMR (400 MHz, CD2Cl2, 25 C): δ = 16.66 (s, 1H, H(DMF)2), 8.16 (s, 2H, O=CH), 3.23 (s, 6H, NCH3), 3.03 (s, 6H, NCH3); 1H NMR (400 MHz, CD2Cl2,        –85 C): δ = 19.24 (s, 1H, H(DMF)2), 8.09 (s, 2H, O=CH), 3.17 (s, 6H, NCH3), 2.95 (s, 6H, NCH3); 13C{1H} NMR (101 MHz, CD2Cl2, 25 C): δ = 164.3 (s, O=CH), 141.6 (d, JCP = 6.6 Hz,  Ar–C), 122.8 (s, Ar–C), 113.8 (d, JCP = 20 Hz, Ar–C), 39.2 (s, NCH3), 33.5 (s, NCH3); elem. anal. calcd for C24H15Cl12N2O8P: C, 31.48; H,1.65; N, 3.06; found: C, 31.68; H, 1.83; N, 3.26. LRMS (ESI, negative mode) m/z = 768.5 ([M]–).  2.4.3 Synthesis of H(THF)2[2.1] PCl5 (0.06 g, 3.20 mmol) and tetrachlorocatechol (0.25 g, 10.1 mmol) were stirred in CH2Cl2      (4 mL). The dark blue suspension was slowly heated to reflux. After 2 h a colorless precipitate formed and was cooled to ambient temperature. Upon addition of THF (1.4 mL) a clear solution  56  was obtained. The solution was cooled at 0 C to afford a white precipitate. The solid was collected by filtration, washed with CH2Cl2 (4 mL) and dried in vacuo. A concentrated solution of the crude product in CH2Cl2:THF (6:1) afforded colorless crystals (–30 C, ca. 3 d). A single crystal was removed for X-ray crystallographic analysis without drying. Yield = 0.13 g, 44%. 31P{1H} NMR (162 MHz, CD3CN, 25 C): δ = –80.6; 1H NMR (400 MHz, CD3CN, 25 C): δ = 13.42 (s, 1H, H(THF)2), 4.08 (s, 8H, OCH2), 2.04 (s, 8H, CH2); 1H NMR (400 MHz, CD2Cl2,  –85 C): δ = 16.92 (s, 1H, H(THF)2), 4.17 (s, 8H, OCH2), 2.13 (s, 8H, CH2); 13C{1H} NMR (101 MHz, CD3CN, 25 C): δ = 141.6 (d, JCP = 6.6 Hz, Ar–C), 122.7 (s, Ar-C), 113.8 (d, JCP = 19 Hz, Ar–C), 70.9 (s, CH2O), 25.0 (s, CH2); elem. anal. calcd for C26H17Cl12O8P: C, 34.17; H,1.88; found: C, 34.31; H, 2.02; LRMS (ESI, negative mode) m/z = 768.5 ([M]–).  2.4.4 Synthesis of (CH3CN)(THF)[2.1] H(THF)2[2.1] (0.036 g) was dissolved in CD3CN (0.5 mL) in an NMR tube. Within 7 days colorless crystals were obtained upon standing at ambient temperature. A crystal was removed for X-ray crystallographic analysis. 31P{1H} NMR (162 MHz, CD3CN, 25 C): δ = –80.1.  2.4.5 Representative H(DMF)2[2.1]-initiated Polymerization of n-Butyl Vinyl Ether In a glovebox, freshly distilled, degassed CH2Cl2 (2 mL) was added to H(DMF)2[2.1] (0.010 g, 0.011 mmol) in a 10 mL Schlenk flask. The flask was removed from the glovebox and cooled to 0 C. Freshly distilled, n-butyl vinyl ether (0.49 g, 4.92 mmol) was prepared in a syringe, removed from the glovebox and added rapidly to the initiator solution. After 15 min, the  57  polymerization was quenched with a solution of NH4OH in MeOH (0.2 mL, 10 vol%), and all volatiles were removed in vacuo. The crude product was dissolved in CH2Cl2 (2 mL) and added one drop at a time to stirred MeOH (40 mL) to precipitate a yellow oily residue. The polymer was collected by centrifugation and dried in vacuo. Yield = 0.32 g, 65%. 1H NMR spectroscopy (300 MHz, CDCl3, 25 C): δ = 3.51-3.40 (br, CH2CH), 1.84-1.36 (br, CH2CH2CH2), 0.91 (t, CH3); GPC–LLS (THF): Mn = 12,250 g mol–1, Đ = 1.51.   2.4.6 Representative H(DMF)2[2.1]-initiated Polymerization of p-Methoxystyrene  In a glovebox, freshly distilled, degassed CH2Cl2 (2 mL) was added to H(DMF)2[2.1] (0.010 g, 0.011 mmol) in a 10 mL Schlenk flask. The flask was removed from the glovebox and cooled to 0 C. Freshly distilled, p-methoxystyrene (0.59 g, 4.37 mmol) was prepared in a syringe, removed from the glovebox and added rapidly to the initiator solution. After 15 min, the polymerization was quenched with a solution of NH4OH in MeOH (0.2 mL, 10 vol%) and all volatiles were removed in vacuo. The crude product was dissolved in CH2Cl2 (2 mL) and added one drop at a time to stirred MeOH (40 mL) to precipitate a white solid. The polymer was collected by filtration and dried in vacuo. Yield = 0.57 g, 98%.  1H NMR spectroscopy (400 MHz, CDCl3, 25 C): δ = 6.59-6.32 (br, Ar–H), 3.76 (br, OCH3), 2.02-1.37 (br, CH2CH(Ar-OCH3)CH2) and GPC–LLS (THF): Mn = 140,000 g mol–1, Đ =1.77 .   2.4.7 X-ray Structure Determination  X-ray crystallography data were collected on a Bruker X8 APEX II diffractometer with graphite-monochromated Mo K radiation. A single crystal was immersed in oil and mounted on a glass fiber. Data were collected and integrated using the Bruker SAINT325 software package  58  and corrected for absorption effect using SADABS.326 All structures were solved by direct methods and subsequent Fourier difference techniques. The PLATON/SQUEEZE327 program was used for H(THF)(NCMe)[2.1] to generate a data set free of solvent in the regions with disordered solvent. Unless noted, all non-hydrogen atoms were refined anisotropically, whereas all hydrogen atoms were included in calculated positions but not refined. All data sets were corrected for Lorentz and polarization effects. All refinements were performed using the SHELXL-2014328 via the Olex2 interface.329  H(THF)2[2.1] co-crystallizes with one free tetrachlorocatechol molecule and one THF solvate molecule. H(1) is bound by two molecules of THF and was located using the difference map and refined isotropically. H(THF)(NCMe)[2.1] crystallizes with both CH3CN and THF in the lattice. CH3CN occupies four sites, two fully occupied and two partially occupied while THF occupies two sites, each only partially occupied.  Restraints and constraints were employed to maintain reasonable bond lengths and angles as well as reasonable ADPs, in the case of disordered solvents.  In the case of the THF molecule containing O8, the molecule resides on an inversion center.  Its occupancy, as well as that of the adjacent disordered CH3CN molecules were refined such that the sum of their occupancies was 1. H(DMF)2[2.1] crystallizes with five crystallographically independent complexes per asymmetric unit and one CH2Cl2 solvate molecule. A hydrogen atom is located between two adjacent oxygens in the DMF molecule; however the hydrogen atom could not be located or accurately modelled. Crystal data and refinement parameters are listed in Table 2.3. CIF files containing supplementary crystallographic data for the structures reported in this chapter are available from The Cambridge Crystallographic Data Centre (CCDC 1520146–1520148).   59  Table 2-3. X-ray crystallographic data and refinement details for compounds H(DMF)2[2.1], H(THF)2[2.1] and H(THF)(CH3CN)[2.1]. a R1 = Σ||Fo| - |Fc||/Σ|Fo|. b wR2(F2[all data]) = {Σ[w(Fo2 - Fc2)2]/Σ[w(Fo2)2]}1/2.  5{H(DMF)2[2.1]}· 0.2 CH2Cl2 H(THF)2[2.1]·THF C6H2O2Cl4 H(THF)(CH3CN)[2.1]· 3.35 MeCN·1.52 THF. formula C121H77Cl62N10O40P5 C36H27Cl16O11P C29.3H19.23Cl12N3.35O7.14P Fw 4658.64 1233.74 988.96 Cryst. syst.  monoclinic   triclinic    Triclinic space group Cc  P-1    P-1   a (Å)  40.2932(19)  11.5738(12)  11.823(3)    b (Å) 26.2969(12) 12.1413(13) 12.984(3) c (Å) 16.7720(8) 17.4244(18)  14.193(3)  α (deg)   90(2)    96.359(6)   66.919(5) β (deg) 104.450(2) 100.305(5) 83.382(6) γ (deg)    90(2)   106.108(5) 84.392(5) V (Å3) 17209.2(14) 2280.9(4) 1987.8(7) T (K) 100(2) 100(2) 90(2) Z 20 2 2 μ (MoKα) (mm-1) 1.093 1.056  0.925   crystal size (mm3) 0.46×0.27×0.11 0.2×0.13×0.05 0.25×0.15×0.14 ρcalcd. (g cm-3) 1.800 1.796 1.652 2θ(max) (°) 55.9 46.5 60.31 F(000)  9288.0    1236.0   989.0 No. of total reflns. 132635 20385 40254 No.of unique reflns. 40536 6470 11707 R(int) 0.0570 0.0371 0.0337 Refln./param. Ratio 18.73 9.98 20.87 R1 [I > 2σ(I)]a 0.0539 0.0449 0.0546 wR2 [all data]b 0.1339 0.1032 0.1460 GOF 1.050  1.020    1.041    60  Chapter 3:  A Twist on Hellwinkel′s Salt, [P(2,2'-biphenyl)2]+[P(2,2'-biphenyl)3]– *  3.1 Introduction  The development of WCAs is of particular interest as it plays a critical role in the generation and stabilization of highly reactive cations.68,69,84,147,151,187,330 Many of the major advances in this area have involved the elaboration of classical group 13-element-based anions such as [BF4]– and [AlCl4]–. Particularly noteworthy are the fluorinated anions [A]–,64,98,121,128,266,331-337 [B]–,119,281,338-347 and            [C]–60,61,65,147,167,348,349 illustrated in Figure 3.1. These anions are large and charge-delocalized and possess low nucleophilicity with electron withdrawing groups, which are ideal properties for WCAs. Each of these WCAs has been isolated as Brønsted acids and must be stored at low temperatures.   Figure 3.1. Selected examples of boron(III)–, aluminum(III)– and phosphorus(V)–containing WCAs.    We were inspired by the evolution of [BF4]– and [AlCl4]– to more complex and less donating anions (e.g. [A]––[C]–). Less common are WCAs of group 15 elements. As a result, we have been exploring the WCA properties of larger derivatives of the classical WCA, [PF6]–. In particular, the WCA  properties of the  fascinating tris(tetrachlorobenzenediolato)phosphate (Figure 3.1, [D]–) are of  * This chapter has previously been published: Hazin, K.; Gates, D.P. Can. J. Chem. 2018, 96, 526.  61    interest.350 Hexacoordinate phosphorus(V) anions, such as [D]– and its derivatives, are large and charge  delocalized. The ability of [D]– to stabilize highly reactive cations has been described in Chapter 2 and  has led to the synthesis of Brønsted acids HL2[D] (L = Et2O, THF, CH3CN, DMF) that can be isolated as solids and used as initiators for the cationic polymerization of olefins.269,351 These systems compare to the established Brønsted acid H(OEt2)2[A] and initiator system H(OEt2)2[C]. Attractive features of HL2[D] include: its ease of synthesis [prepared by the direct reaction of PCl5 and C6Cl4(OH)2], its moderate stability at ambient temperature, and its ability to initiate polymerization at higher temperatures than are required of typical cationic initiators.246 A potential concern with using [D]– in cationic polymerization applications is the lability of the P–O bonds and the donor properties of the oxygen atoms within the anion.  Figure 3.2. Hellwinkel’s spiro-compound [3.1][3.2]. In order to eliminate these concerns, we sought anions featuring P–C rather than P–O bonds, analogues of the tetraarylborates. The salt [3.1][3.2] (Figure 3.2) featuring the P–C-containing anion [3.2]– was appealing. This compound, along with Li[3.2], was first reported in 1965 and was resolved into optically active enantiomers.253,254,352 Derivatives of [3.2]– with a 4–methyl–biphenyl chelate have also been synthesized.255 An ammonium salt, [PhNMe2H][P(C12F8)3], has been claimed as a protic activator for metallocene catalysts for ethylene polymerization.353 It should be noted that limited  62  synthetic and characterization details for this compound were provided. Therefore, we set out to explore the synthesis of parent [3.1][3.2] with the ultimate goal of accessing new Brønsted acids for the cationic polymerization of olefin monomers. Herein, the efforts to synthesize and isolate Hellwinkel’s salt [3.1][3.2] and the unexpected discovery of the byproducts [3.1'][3.2] and 3.3 are reported. Both [3.1'][3.2] and 3.3 were structurally characterized by X-ray crystallography.  3.2 Results and Discussion  It has been shown previously that the direct metallation of biphenyl with n-BuLi in the presence of N,N,N′,N′–tetramethylethylenediamine (TMEDA) leads to 2,2'–dilithiobiphenyl.354,355 In order to prepare Hellwinkel’s salt, biphenyl was directly lithiated with n-BuLi (2.4 equiv) in TMEDA (2.4 equiv) at ambient temperature (Scheme 3.1, Route A). In the present work, the dilithiation was confirmed by slowly quenching a small aliquot removed from the reaction mixture with Me3SiCl [1H NMR (THF-d8:  = 0.43, 6H, Si(CH3)3; 7.24–7.89, 8H, Ar-H)]. Subsequently, a solution of PCl5 in THF/Et2O (40 mL/ 6 mL) was slowly added to 2,2'–dilithiobiphenyl to afford Hellwinkel′s salt [3.1][3.2] as the major product as estimated by 31P{1H} NMR spectroscopy [Figure 3.3 (a):  = 25.8 [3.1]+ and –184.7 ppm [3.2]–]. Surprisingly, the 31P{1H} NMR spectrum of the reaction mixture suggested that at least two additional products were present as evidenced by the presence of a singlet resonance at 30.6 ppm and another singlet resonance at –86.2 ppm.    63   Scheme 3.1. Synthesis of [3.1][3.2] via route A–C.  Attempts to isolate [3.1][3.2] from the aforementioned mixture were unsuccessful given the poor solubility of the products in typical organic solvents (e.g. CHCl3, CH2Cl2, Et2O, THF, acetone, toluene).  Analysis of the crude material by electrospray mass spectrometry (ESI-MS, see Appendix B, Figures B1 and B2) was particularly informative. In the negative mode, a single ion was observed that was assigned to [3.2]– (m/z = 487.1). Unexpectedly, analysis in the positive mode revealed two ions, one of which was assigned to [3.1]+ of Hellwinkel′s salt (m/z = 335.2). The other cation (m/z = 487.2) had the same mass as the anion [3.2]–, suggesting that this cation had the formulation [P(C12H8)3]+.   64   Figure 3.3. 31P{1H} NMR (162 MHz, 25 °C) spectra of: (a) the reaction mixture obtained by reacting PCl5 with 2,2'–lithiobiphenyl [obtained from biphenyl, n-BuLi and TMEDA] in THF/Et2O – Route A in Scheme 3.1; (b) the reaction mixture obtained by reacting a portion of isolated reaction mixture from Route A (above) with 2,2'-dilithiobiphenyl in Et2O; (c) crystals of isolated [3.1'][3.2] dissolved in THF/Et2O solution; and (d) crystals of isolated 3.3 dissolved in THF/Et2O.  65  This was perplexing since the bond connectivity necessary to generate a P–centered cation with this molecular formula was not immediately obvious.  It has previously been reported that treating [3.1][3.2] with dilithiated biphenyl (1.0 equiv) affords Li[3.2].253 In an effort to simplify this unexpected product mixture, a portion of the isolated reaction mixture from above (Route A) was suspended in THF and treated with C12H8Li2 (1 equiv) in Et2O. The 2,2'–dilithiobiphenyl was prepared from C12H8Br2 and n-BuLi (2.0 equiv). Analysis of an aliquot of the soluble portion of the reaction mixture by 31P{1H} NMR spectroscopy revealed that the major signals were at 35.2 and –183.3 ppm {see Figure 3.3 (b): major signals assigned to [3.1'][3.2]} and a very small signal {<10% of the intensity of [3.1']+} at 27.2 ppm (assigned to [3.1]+ of [3.1][3.2]). The aforementioned signal at –86.2 ppm, observed in the product mixture for Route A, was no longer observed. The reaction mixture was filtered to remove poorly soluble residual salts (e.g. [3.1][3.2], Li[3.2], LiBr, etc.). The filtrate was collected and the soluble product was isolated as a solid after solvent removal. Crystals suitable for X-ray diffraction were obtained by cooling (–30 °C) a solution of  the crude product in a mixture of THF and Et2O (1:1) (Figure 3.5).  The molecular structure of the isolated compound, [3.1'][3.2], is displayed in Figure 3.5, along with selected metrical parameters. Importantly, the structure confirms the formulation obtained from mass spectrometric analysis, [P(C12H8)3][P(C12H8)3], yet the bond connectivity was totally unexpected. Particularly striking, is the structure of the cation [3.1']+, which contains the twisted                           2,2'–bis(phenyl)biphenyl ligand (Figure 3.4). Although the neutral compound 2,2'–bis(phenyl)biphenyl is known and has been structurally characterized,356-362 to our knowledge there are only three examples of complexes featuring the 2,2'–bis(phenyl)biphenyl dianionic ligand.363-365 It should be noted that in the early reports of Hellwinkel, the possible coupling of the biphenyl moieties to form a byproduct was considered on the basis of IR spectra and melting point data.253,366 In the present case, the structurally  66  characterized product [3.1'][3.2] was further characterized by 31P NMR spectroscopy and ESI-MS (see Appendix B, Figures B1 and B2). The 1H and 31C{1H} NMR spectra as well as the 1H–31P HMBC NMR spectrum were not particularly informative with many overlapping signals.  The salt [3.1'][3.2] co-crystallizes with THF and diethyl ether solvent in the lattice. There are weak interactions between the cation and the anion in [3.1'][3.2] (see Appendix B, Figure B3) with weak C···H, C···C and H···H contacts [closest contacts: C(21)···H(38) = 2.677(1) Å; C(15)···C(69) = 3.281(2) Å; H(21) ···H(38) = 2.361(2) Å]. In addition, there are moderate to strong interactions between the oxygen in the THF solvent and hydrogen atoms of the [3.1']+ cation [O(1)···H(29) = 2.531(2) Å; O(2b)···H(28) = 2.553(5)]. There is also a close contact between the oxygen of THF and a methyl group of diethyl ether solvate [H(84C)···O(2B) = 1.639(4) Å]. For comparison, the sum of the van der Waals radii for oxygen and hydrogen is 2.72 Å, that for carbon and hydrogen is 2.90 Å367 and a typical O–H bond length is 0.96 Å in water.368   The unprecedented cation [3.1']+ adopts a highly distorted tetrahedral geometry at phosphorus. Specifically, the C(1)–P(1)–C(12) angle of the chelated 2,2'–biphenyl ligand [94.0(1)°] is significantly more acute than the C(7)–P(1)–C(36) angle of the 2,2'–bis(phenyl)biphenyl ligand [121.5(5)°]. In contrast, the bond lengths in the cation moiety show only minor perturbations from those expected. For example, the average P–C bond lengths [1.80(3) Å] are longer than the average P–C bond length in the previously reported [3.1]+ [1.777(4) Å].369 The C–C bond lengths connecting the four phenylene moieties of the twisted 2,2'–bis(phenyl)biphenyl ligand in [3.1']+ [avg. 1.493(3) Å] are slightly longer than that between the phenylene of the biphenyl in [3.1']+ [C(6)–C(7) = 1.475(2) Å]. This lengthening presumably reflects the decreased π-conjugation that accompanies the twisting in [3.1']+. For example, angles between the mean planes of the phenylene moieties in the 2,2'–bis(phenyl)biphenyl ligand   67   Figure 3.4. Spiro–compound [P(C12H8)(C24H16)][P(C12H8)3] ([3.1'][3.2]).    Figure 3.5.Molecular structure of the salt (S)–[3.1']–Δ–[3.2]·1.73 THF·0.27·Et2O. For clarity, one enantiomer of the cation [3.1']+ and one enantiomer of the anion [3.2]– are shown. Solvents of crystallization (1.73 x THF and 0.27 x Et2O) and hydrogen atoms are omitted for clarity. Ellipsoids are drawn at the 50 % probability level. Selected bond lengths [Å]: P(1)–C(1) = 1.795(1); P(1)–C(12) = 1.795(1); P(1)–C(36) = 1.807(1); P(1)–C(13) = 1.797(1); P(2)–C(49) = 1.925(1); P(2)–C(61) = 1.933(1); P(2)–C(72) = 1.926(1). Selected bond angles []: C(1)–P(1)–C(12) = 94.0(1); C(36)–P(1)–C(13) = 121.1(5); C(12)–P(1)–C(36) = 109.6(6); C(49)–P(2)–C(72) = 178.2(5); C(60)–P(2)–C(61) = 89.7(5).   68  [(C13–C18)–(C19–C24) = 80.0(4); (C19–C24)—(C25–C30) = 81.9(4); (C25–C30)–(C31–C36) =73.9(4)] are significantly greater than that for the chelated 2,2'–biphenyl [(C1–C6)–(C7–C12) = 3.4(5)]. In comparison, the angle between the mean planes of the aryl moieties in the uncomplexed 2,2'–(biphenyl)biphenyl are shorter [ = 47.3, 50.9, 43.0].357  In contrast to the cation [3.1']+, the phosphorus(V) center in [3.2]– elucidates only minor perturbation from regular octahedral geometry displaying metrical parameters similar to those found in the previously reported salt [3.1][3.2].369 For example, the average P–C bond length in the anion of [P(2,2'–biphenyl)2][3.2] [dP–C = 1.932(2) Å] is similar to the average P–C bond length observed in [3.1'][3.2] (dP–C = 1.929(4) Å]. The P(2)–C(48) bond length 1.944(1) Å is slightly elongated with respect to the other P–C bonds in the anion of [3.1'][3.2]. The C–C bond lengths between the biphenyl moieties in the anion of [3.1'][3.2] [avg. 1.478(3) Å] are shorter than the C–C bond length in biphenyl itself [1.506(17) Å].370,371 Within the biphenyl ligands of [3.2]–, the angle between the mean planes of the aryl moieties show only minor deviations from planarity [i.e. (C49–C54)–(C55–60) = 4.4(4), (C37–C42)–(C43–C48) = 7.2(4) and (C61–C66)–(C67–C72) = 5.6(5)]. These angles are similar to those between the mean planes of the aryl moieties in the salt [3.1][3.2] [  = 3.0(6), 5.1(5), 6.3(5)].369  With the identity of [3.1'][3.2] confirmed, it remained to identify the species responsible for the signal at –86.2 ppm in the 31P NMR spectrum of the reaction mixture from Route A [see Figure 3.3 (a)]. Thus, a second portion of the isolated crude reaction mixture from Route A was suspended in n-butanol and gravity filtered. Upon standing of the filtrate at ambient temperature in air atmosphere for three weeks, crystals suitable for X-ray crystallographic analysis were isolated. The 31P{1H} NMR spectrum of the crystals of 3.3 in THF/Et2O [see Figure 3.3 (d)] displayed a singlet resonance assigned to the product ( = –86.2) and a small signal attributed to an unidentified species ( = 37.4). The molecular  69  structure of the pentacoordinate phosphorane 3.3 is shown in Figure 3.7. The phosphorus(V) center in 3.3 adopts a distorted trigonal bipyramidal geometry with one carbon of each of the chelating  Figure 3.6. Pentacoordinate phosphorane 3.3, [P(C12H8)2(C12H9)].  Figure 3.7. Molecular structure of 3.3. Ellipsoids are drawn at the 50 % probability level. Hydrogen atoms are omitted for clarity. Selected bond lengths [Å]: P(1)–C(1) = 1.868(4); P(1)–C(12) = 1.925(4); P(1)–C(13) = 1.861(4); P(1)–C(24) = 1.909(4); P(1)–C(25) = 1.874(4). Selected bond angles []: C(1)–P(1)–C(12) = 86.1(2); C(1)–P(1)–C(13) = 108.7(1); C(13)–P(1)–C(24) = 86.7(1); C(13)–P(1)–C(25) = 130.6(1); C(25)–P(2)–C(24) = 90.(1).  70  biphenyl ligands in the axial positions [i.e. C(12) and C(24)], leaving the second carbon of each of the two chelating ligands along with the carbon of the monodentate biphenyl in the equatorial plane [i.e. C(1), C(13)  and C(25)]. As expected, the equatorial P–C bonds [avg. 1.868(7) Å] are shorter than the axial P–C bonds [avg. 1.917(6) Å].  The Cax–P–Ceq bond angles [avg. 90.0(4)] are in the range expected for a trigonal bipyramid with the maximum deviations being C(24)–P(1)–C(1) [94.5(2)] and C(12)–P(1)–C(1) [86.1(2)]. The C–C bond length connecting the two phenylene moieties of the monodentate biphenyl [C(31)–C(30) = 1.491(6) Å] is slightly elongated compared to the other two chelating biphenyl ligands in 3.3 [C(6)–C(7) = 1.475(7) Å; C(18)–C(19) = 1.474(5) Å]. This lengthening is most likely due to disruption of             π–conjugation within the twisted monodentate biphenyl ligand. Specifically, the angle between the mean planes of the phenylene moieties in the monodentate 2–biphenyl ligand [(C25–C30)–(C31–C36) = 51.5(2)] are significantly greater than that for the two chelated 2,2'–biphenyl ligands [(C1–C6)–(C7–C12) = 4.9(2); (C13–C18)—(C19–C24) = 2.3(2)].  Unfortunately, the poor solubility and limited quantity of 3.3 obtained thwarted additional characterization of this product. It should be noted that Hellwinkel previously observed 3.3 and its        4–methyl–biphenyl derivative as characterized by IR spectroscopy, elemental analysis and optical rotation studies.253,255,352  Although Hellwinkel′s earlier reports mentioned the possibility that [3.1'][3.2] was a byproduct in the formation of [3.1][3.2] from 2,2'–diiodobiphenyl,253 this was not shown explicitly. Thus, we followed his procedure exactly (Scheme 3.1, Route B), albeit on a smaller scale. 2,2'–Dilithiobiphenyl was prepared by treating 2,2'–diiodobenzene with n-BuLi (2.4 equiv) in diethyl ether at 0 °C. To this mixture was added PCl5 in diethyl ether at –78 °C and the “product” was isolated according to the  71  reported procedure. The crude reaction mixture was dissolved in THF/Et2O and the 31P{1H} NMR spectrum is shown in Figure 3.8(a). Remarkably, the major product we observed was assigned as [3.1'][3.2] (δ = 29.8 and –183.8) with the minor product being [3.1][3.2] (δ = 26.8 and –183.8). The intensity of the signal for [3.2]– was very small compared to that of [3.1']+ or [3.1]+, suggesting that there may be significant quantities of the Cl– or I– counterion present. These results were in contrast to those of Hellwinkel who reported only the signals attributed to [3.1][3.2] ( = 26.5 and      –186.5 ppm in DMF-d7) [the 31P{1H} NMR spectrum of the reaction mixture we obtained in DMF-d7 revealed signals at  = 31.9, 27.0 and –183.4 ppm]. In our hands, it appeared that the insertion product   Figure 3.8. 31P{1H} NMR (162 MHz, 25 °C) spectrum of [3.1][3.2] and [3.1'][3.2] via (a) dilithiated 2,2'–diiodobiphenyl recorded in THF/Et2O solution (Route B); (b) dilithiated 2,2'–dibromobiphenyl recorded in THF/Et2O solution (Route C).  72  [3.1']+, was the major product. Given the 3:1 stoichiometric ratio of the 2,2'–diiodobiphenyl ligand to phosphorus pentachloride, there was insufficient 2,2'–diiodobiphenyl to afford both [3.1']+ and [3.2]– stoichiometrically. It was for this reason we surmise that the main products were [3.1']X and [3.1]X (X = Cl or Br) with minimal amounts of [3.1'][3.2] and [3.1][3.2] being formed.   Given the above results, we became interested to see whether the ratio of [3.1]+ to [3.1']+ could be influenced by starting with 2,2'–dibromobiphenyl instead of 2,2'–diiodobiphenyl. In this case (Scheme 3.1, Route C), 2,2'–dilithiobiphenyl was prepared by treating 2,2'–dibromobenzene with          n-BuLi (2.2 equiv) in diethyl ether at 0 °C. To this mixture was added PCl5 in diethyl ether at –78 °C. The crude product mixture isolated from the reaction mixture was dissolved in THF/Et2O and analyzed by 31P{1H} NMR spectroscopy. The spectrum, shown in Figure 3.8 (b), revealed that the major product contained the cation [3.1]+ with the minor product containing [3.1']+. Although the relative intensity of the signal ascribed to [3.2]– was greater than that for the iodo-precursor, the spectrum still suggested that a significant quantity of halide salt was formed.  Before closing, a comment on the mechanism of formation for [3.1'][3.2] is warranted. It is remarkable that the coupling of biphenyl is observed following all three routes. First, the coupling arylene moieties during the lithiation of aryl halides [i.e. Ar–X + Ar–Li  Ar–Ar + LiX (X = Br or I)] is well precedented.372,373 In fact, the reaction of 1,2–diiodobenzene or 1,2–dibromobenzene with         n-BuLi (2.4 equiv) followed by carboxylation afforded low yields of 2,2'–C12H8(COOH)2 (up to 17%).374-376 Thus, it may be inferred that the presumptive intermediate, 1–halo–2–lithiobenzene is readily coupled to itself or to 1,2–dihalobenzene to afford 2–halo, 2'–lithiobiphenyl and                     2,2'–dihalobiphenyl, respectively. These products may be further lithiated and/or coupled to the corresponding tetraphenyl derivatives. Thus, the observed formation of [3.1']+ when starting with         2,2'–dihalobiphenyl derivatives (i.e. Routes B or C) can be rationalized.  73   It is considerably more difficult to explain the observed coupling of biphenyl to give [3.1']+, which was observed following Route A. In this case, nucleophilic aromatic substitution was not possible and only an oxidative coupling of Ar–Li moieties is plausible. However, the possible oxidizing agents were limited to the phosphorus(V) of PCl5, adventitious oxygen or perhaps solvent. Since the reactions were performed under rigorously anaerobic conditions and the results are entirely reproducible, we consider that the most likely oxidant is PCl5. That said, we did not observe any evidence by 31P NMR spectroscopy of the reactions solutions for the reduced products although it is possible these species are insoluble. The coupling reaction of phosphorus(V) compounds with lithiated aryl or Grignard reagents (PhMgBr) is favoured. For example, the reaction of EtP(=O)(OEt)2 with 2PhMgBr in THF at 68 °C gives substituted phosphonates [Ph2P(=O)OEt, PhP(=O)(OEt)2, (EtO)2P(=O)OEt, EtP(=O)(OEt)2, and (EtO)3P(=O)]377 as well as the coupling of ((C6H5)O)POCl2 with PhMgBr to afford (C6H5)3P=O.378 In another instance, (biphenyl)(Ph)P(=N–Ts) reacts with 2,2'–dilithiated biphenyl to give P(biphenyl)2(Ph).363 The spirophosphorane (Ph(C(CF3)2O)2)P–H reacts with RLi (R= Me, n-Bu, t–Bu, aryl) to yield (Ph(C(CF3)2O)2)P–R.379  3.3 Summary We have explored three potential routes to afford Hellwinkel′s salt [3.1][3.2]. In addition to the desired compound, we have isolated a novel complex cation incorporating an alternative cation [3.1']+ with the formulation [P(C12H8)3]+ that is formally derived from the insertion of an additional biphenyl unit into [3.1]+ and the phosphorus(V) containing WCA [3.2]–. The insertion product was observed by direct lithiation of biphenyl (Route A), 2,2'–diidobiohenyl (Route B) and 2,2'–dibromobiphenyl (Route C). This new “twist” on Hellwinkel’s salt was characterized by means of mass spectrometry, 31P{1H} NMR  74  spectroscopy and X-ray crystallography. Additionally, we were able to isolate and characterize the neutral species 3.3 by X-ray crystallography and 31P{1H} NMR spectroscopy.   3.4 Experimental  3.4.1 General Procedures  All experiments were performed using standard Schlenk or glove box techniques under nitrogen atmosphere. Diethyl ether (Et2O) (Fisher Scientific) was deoxygenated with nitrogen and dried by passing the solvent through a column containing activated, basic alumina. Subsequently, the Et2O was dried over calcium hydride, freshly distilled, and freeze-pump-thaw (x3) degassed and stored over 3 Å molecular sieves prior to use. Tetrahydrofuran (THF) (Fisher Scientific) was dried and distilled over sodium/benzophenone ketyl prior to use. Phosphorus pentachloride (Sigma Aldrich) was sublimed prior to use. 2,2'–Dibromobiphenyl380 was prepared following literature procedure. 2,2'–Diiodobiphenyl was prepared following the analogous 2,2'–dibromobiphenyl procedure. Mass spectrometry and NMR spectra were performed in the Department of Chemistry Facilities. Low resolution electrospray ionization mass spectra {LRMS (ESI)} were recorded on Bruker Esquire LC. High resolution electrospray ionization mass spectra {HRMS (ESI)} were recorded on Micromass LCT time of flight (TOF) mass spectrometer. 1H and 31P{1H} NMR spectra were recorded on Bruker Avance 400 MHz spectrometers at ambient temperature. H3PO4 (85 %) was used as external standard for 31P NMR spectra with δ = 0.0. 1H NMR NMR spectra were referenced to deuterated solvents.    75  3.4.2 Synthesis of [P(C12H8)(C24H16)]+ ([3.1']+), [P(C12H8)2]+ ([3.1]+), [P(C12H8)3]– ([3.2]–) and P(C12H8)2(C12H9) (3.3)  Route A. To a solution of biphenyl (4.73 g, 30.7 mmol) in TMEDA (11.0 mL, 8.60 g, 74.0 mmol) was added n-BuLi (46.0 mL, 74.0 mmol, 1.6 M in n-hexane). The bright orange solution was stirred at ambient temperature under N2 atmosphere for 3 d. The reaction mixture was cooled to –20 °C to obtain yellow crystals. The supernatant was removed by cannula filtration and the residue washed with THF (20 mL). Subsequently a solution of PCl5 (2.51 g, 12.0 mmol) in THF/Et2O (40 mL/ 6 mL) was slowly added at –78 °C. Upon addition, a light brown precipitate was obtained and the mixture stirred overnight. The supernatant was removed via cannula filtration and the precipitate was washed with diethyl ether (30 mL), filtered and dried in vacuo. A beige powder was isolated (2.41 g), which was later shown to contain [3.1][3.2], [3.1'][3.2] and 3.3.  31P{1H} NMR (162 MHz, THF/Et2O, 25 °C): δ = 30.6, 25.8, –184.7; HRMS (ESI/TOF, positive mode) m/z = [M]+ calcd for C24H16P1 335.0990; found 335.0987 and [M]+ calcd for C36H24P1 487.1616; found 487.1620; LRMS (ESI, negative mode) m/z = 487.1 ([M]–).  Route B. To a solution of 2,2'–diiodobiphenyl (1.01 g, 2.50 mol) in Et2O (20 mL) was added n-BuLi (3.42 mL, 5.25 mol, 1.53 M in n-hexane) at 0 °C. The reaction mixture was stirred for 4 h at 0 °C and cooled down to –78 °C for an additional 1 hour followed by the addition of a PCl5 (0.17 g, 0.83 mmol) solution in Et2O (17 mL) at –78 °C to afford a light brown precipitate. The reaction mixture was allowed to warm up to ambient temperature overnight and extracted with degassed H2O (7 mL). The precipitate was cannula filtered, washed with Et2O and dried in vacuo. A beige powder was isolated (0.66 g), which contains [3.1][3.2] and [3.1'][3.2].  31P{1H} NMR (162 MHz, THF/Et2O, 25 °C): δ = 29.8, 26.8, –183.8; (CD3)2NCOD δ = 31.9, 27.0,         –183.4; 1H NMR (400 MHz, (CD3)2NCOD, 25 °C): δ = 8.69 (m, 1H, Ar–H), 8.22 (m, 1H, Ar–H), 7.99  76  (m, 2H, Ar–H), 7.88 (m, 1H, Ar–H), 7.81 (m, 1H, Ar–H), 7.74 (m, 1H, Ar–H), 7.66 (m, 1H, Ar–H), 7.57 (m, 2H, Ar–H), 7.37 (m, 1H, Ar–H), 7.21 (m, 2H, Ar–H), 7.01 (m, 1H, Ar–H), 6.82 (m, 1H,      Ar–H), 6.70 (m, 1H, Ar–H). Route C. 2,2'–dibromobiphenyl (0.73 g, 2.35 mol) was dissolved in 11 mL anhydrous Et2O. The colorless mixture was cooled at 0 °C followed by the slow addition of n-BuLi (2.90 mL, 4.70 mol, 1.6 M in n-hexane). The reaction mixture was stirred for 4 hours at 0 °C. PCl5 (0.12 g, 0.59 mol) was added at –78 °C and stirred overnight to afford a light brown precipitate. The precipitate was extracted with H2O (20 mL), cannula filtered and dried in vacuo. A beige powder was isolated (0.64 g), which contains [3.1][3.2] and [3.1'][3.2].  31P{1H} NMR (162 MHz, THF/Et2O, 25 °C): δ = 32.6, 24.4, –183.8.  3.4.3 Synthesis of [P(C12H8)(C24H16)][3.2] To a stirred solution of 2,2'–dibromobiphenyl (0.57 g, 1.83 mol) in diethyl ether (20 mL) at 0 °C was slowly added n-BuLi (2.30 mL, 3.70 mol, 1.6 M in n-hexane). The pale yellow solution was stirred for  4 h at 0 °C. To the reaction mixture was added a suspension of the solid from Route A described above (1.00 g, 0.56 mol) in THF (20 mL). Upon addition, an off yellow precipitate was obtained. The reaction mixture was stirred overnight at ambient temperature. The supernatant was collected by cannula filtration and dried in vacuo. A beige powder was isolated (0.45 g), which contains [3.1'][3.2] and minor [3.1][3.2]. A concentrated solution of the crude product in THF/Et2O afforded colorless crystals of [3.1'][3.2] (–30 °C, ca. 7 days). A crystal was removed for X-ray crystallographic analysis without drying.   77  31P{1H} NMR (162 MHz, THF/Et2O, 25 °C): δ = 35.2, –184.4; HRMS (ESI/TOF, positive mode) m/z = [M]+ calcd for C36H24P1 487.1616; found 487.1615 and LRMS (ESI, negative mode) m/z = 487.1      ([M]–).   3.4.4 Synthesis of 3.3 A portion of the mixture from Route A described above (0.177 g) was dissolved in n–butanol (2.5 mL) and subsequently filtered to remove insoluble material. Within 3 weeks colorless crystals were obtained upon standing at ambient temperature. A crystal was removed for X-ray crystallographic analysis. 31P{1H} NMR (162 MHz, THF/Et2O, 25 C): δ = –86.2.  3.4.5 X-ray Structure Determination  X-ray crystallography data were collected on a Bruker X8 APEX II diffractometer with graphite-monochromated Mo K radiation. A single crystal was immersed in oil and mounted on a glass fiber. Data were collected and integrated using the Bruker SAINT325 software package and corrected for absorption effect using SADABS.326 All structures were solved by direct methods and subsequent Fourier difference techniques. Unless noted, all non-hydrogen atoms were refined anisotropically, whereas all hydrogen atoms were included in calculated positions but not refined. All data sets were corrected for Lorentz and polarization effects. All refinements were performed using the SHELXL–2015328 via the Olex2 interface.329 [3.1'][3.2] co–crystallizes with 0.27 diethyl ether and 1.73 THF solvate molecules. Crystal data and refinement parameters are listed in Table 3.1. CIF files containing supplementary crystallographic data for the structures reported in this chapter are available from The Cambridge Crystallographic Data Centre (CCDC–1573488 and CCDC–173489).   78  Table 3-1. X-ray crystallographic data for [3.1'][3.2] and 3.3.                   a R1 = Σ||Fo| - |Fc||/Σ|Fo|. b wR2(F2[all data]) = {Σ[w(Fo2 - Fc2)2]/Σ[w(Fo2)2]}1/2.   [3.1'][3.2]·1.73 THF·0.27·Et2O 3.3 Formula C80H64.54O2P2 C36H25P Fw 1119.80 488.53 Cryst. syst. Triclinic Trigonal space group P –1 P 31 Color Green Colorless a (Å) 13.5082(17) 9.2847(5) b (Å) 14.9299(19) 9.2847(5) c (Å) 15.662(2) 24.6168(17) α (deg) 90.349(3) 90 β (deg) 104.088(3) 90 γ (deg) 106.054(3) 120 V (Å3) 2935.0(6) 1837.8(2) T (K) 90(2) 90(2) Z 2 3 μ(MoKα) (mm-1) 0.126 0.137 crystal size (mm3) 0.26 × 0.25 × 0.25 0.15 × 0.13 × 0.07 ρcalcd. (g cm-3) 1.267 1.327 2θ(max) (°) 60.2 55.8 F(000) 1181 768 No. of total reflns. 64238 13205 No.of unique reflns. 17187 5784 R(int) 0.028 0.042 Refln./param. Ratio 20.24 17.32 R1 [I > 2σ(I)]a 0.0450 0.052 wR2 [all data]b 0.1251 0.1044 GOF 1.033 1.059  79  Chapter 4: Ammonium and Potassium Salts of a Hexacoordinate Phosphorus(V) Anion Featuring P–O and P–C Bonds  4.1 Introduction  Phosphorus displays a tremendous diversity of coordination numbers in its compounds with the two extremes of one-coordinate (e.g. phosphaalkyne, phosphinidene) and hexacoordinate (e.g. phosphate) systems being the rarest. Despite the fact that the simple anions [PF6]– and [PCl6]– are ubiquitous in inorganic chemistry, hexacoordinate phosphorus(V) anions featuring organic substituents are rare. Selected examples are shown in Figure 4.1 ([A]–,264,287,381-384 [B]–,250,252,350,351,385-390 [C]–,248 [D]– 253,255,352). The first example of a hexacoordinate organophosphate was isolated in 1963 as a triethylammonium salt of [P(1,2-(C6O2H4)3]– ([B]–).249,250,252 Ideal properties for WCAs are large charge delocalized anions (e.g. [B]– and its derivatives) that possess low nucleophilicity. The well–known large chiral tris(tetrachlorobenzenediolato)phosphate [B]– (R = Cl) has been widely employed as a WCA in the stabilization of unsaturated cations, as chiral solvate and resolving agent.350 Chapter 2 described the isolation of Brønsted acids of HL2[B] (L = THF, CH3CN, DMF) as initiators for the cationic polymerization of olefins.351 An advantage of HL2[B] includes the convenient one–pot reaction of PCl5 and C6Cl4(OH)2. However, a potential concern with employing [B]– as a WCA  is the donor properties of the oxygen atoms within the anion. P–O bonds are prone to protonation and ring opening reactions. We therefore targeted P–C containing WCAs such as the famous anion [D]–. The compounds Li[D] and [P(C12H8)2][D] have been previously reported.253 Chapter 3 described the isolation of a salt containing the anion [D]– with the rare cation [P(C12H8)(C24H16)]+ by reacting PCl5 with C12H8Li2 (generated from either C12H10, C12H8Br2 or C12H8I2).391  * A version of this chapter will be submitted for publication. Hazin, K. and Gates, D.P.  80   Figure 4.1. Examples of hexacoordinate phosphorus(V) weakly coordinating anions.  Noteworthy, less common are hybrid anions with mixed P–O and P–C bonds (e.g. mer–[4.1]–). Triethylammonium and diethylammonium salts of mer–[4.1]–392 and their reactivity studies were reported by Holmes and inspired us to target the development of complexes featuring a potential WCA containing strong O–P–C bonds with the ultimate goal to isolate Brønsted acids containing the anion mer–[4.1]–.  Herein, we report the synthesis and crystallographic characterization of ammonium [NbaseH] salts featuring the anion mer–[4.1]–. The convenient preparation involves treating phosphorane P(C6H4CO2)2(C6H4COOH), 4.2, with various amines [Nbase = PhNMe2, PhNH2, pyridine (py), isoquinoline, (–)-brucine, N(n-C8H17)3]. In addition, the synthesis and crystallographic characterization of K–rac–mer–[4.1] are discussed.  81  4.2 Results and Discussion 4.2.1 Synthesis and Characterization of Ammonium Salts of mer–[4.1]–  Inspired by the single report of [Et2NH2]+ and [Et3NH]+ salts of anion mer–[4.1]–,392 we prepared several ammonium salts as a starting point to explore the WCA potential of mer–[4.1]– (Scheme 4.1). We noted that an ammonium salt, [PhNMe2H][D],353 has been reported in a patent as a protic activator for metallocene catalysts for ethylene polymerization. Although very limited characterization details were provided, we were inspired to explore the synthesis of [PhNMe2H][4.1] and [PhNH3][4.1] to evaluate the prospective WCA properties of mer–[4.1]–. An acetone solution of acid P(C6H4CO2)2(C6H4COOH) (4.2) was treated with dimethylaniline (PhNMe2) or aniline (PhNH2) to afford [NPhMe2H]–rac–mer–[4.1] or [PhNH3]–rac–mer–[4.1], respectively (vide infra). Based on these positive results, other bases were also explored [i.e. pyridine (py), isoquinoline, (–)-brucine and        N(n-C8H17)3].    Scheme 4.1. General synthetic route of [NbaseH][4.1] with Nbase = PhNMe2, PhNH2, py, isoquinoline, (–)-brucine and N(n-C8H17)3. 4.2 is phosphorane P(C6H4CO2)2(C6H4COOH).  Each crude product was recrystallized as described in the experimental section and colorless crystals suitable for X-ray crystallographic analysis were obtained for [PhNMe2H]–rac–mer–[4.1],       [pyH]–rac–mer–[4.1], [isoquinolineH]–rac–mer–[4.1], and [(–)-brucineH]–Λ–mer–[4.1]. The molecular structures of each ammonium salt are shown in Figure 4.3 and the metrical parameters will be  82  discussed in detail below. Crystallization of [(–)-brucineH]–rac–mer–[4.1] from CD2Cl2 afforded enantiomerically pure [(–)-brucineH]–Λ–mer–[4.1]. Spectroscopic analysis of the isolated complexes was performed in either acetone-d6 or DMSO-d6 due to their solubility. The 31P{1H} NMR spectra (see Appendix C, Figures C1 and C2) revealed signals characteristic of preservation of mer–[4.1]– upon dissolution (range: –104.7 to –135.2 ppm, see Table 4.1). These signals were in the range reported for known salts containing mer–[4.1]– {[Et2NH2][P(C6H4CO2)3]: δ = –135.5 and [Et3NH][P(C6H4CO2)3]: δ = –135.7 in DMF-d7}.392 In the case of [PhNH3]–rac–mer–[4.1], the 31P{1H} NMR spectrum in DMSO-d6 was accompanied by a second signal at –55.7 ppm (ca. 5%). The downfield signal is attributed to the formation of a small amount of P(C6H4CO2)2(C6H4COOH), 4.2, from the solution protonation of     mer–[4.1]–. Spectroscopic analysis of the other salts in acetone-d6 or DMSO-d6 solutions showed only the signal attributed to mer–[4.1]–, even after several weeks at ambient temperature. Whilst the 31P{1H} NMR spectrum of [(–)-brucineH]–rac–mer–[4.1] recorded in DMSO-d6 showed only a singlet resonance ( = –135.2), that recorded in CD2Cl2 displayed two resonances (δ = –114.3 and –114.6), see Figure 4.2. We speculate that these observations suggest that there is ion-pairing in the solvent of lower polarity (i.e. CD2Cl2) to afford the distinct diastereomers [(–)-brucineH]–Δ–mer–[4.1] and [(–)-brucineH)–Λ–mer–[4.1]), which have slightly different chemical shifts.          83                        Table 4-1. 31P{1H} and 1H-NMR chemical shifts of [NbaseH]–rac–mer–[4.1]. Compound [NbaseH]+–rac–mer–[4.1]–  δ31P δ1H [NPhMe2H]–rac–mer–[4.1] –107.7(a) 9.31(a) [PhNH3]–rac–mer–[4.1] –133.6(b) 6.56(b) [pyH]–rac–mer–[4.1] –126.8(a) 16.37(c) [isoquinolineH]–rac–mer–[4.1] –104.7(a) 16.34(c) [(–)-brucineH]–rac–mer–[4.1] –135.2(b) 10.60(b) [(–)-brucineH]–rac–mer–[4.1] –114.3, –114.6(c) 12.63(c) [(n-C8H17)3NH]–rac–mer–[4.1] –128.9(a) 10.40(c) [NEt2H2][P(C6H4CO2)3] –135.5 (d) 392 NA [NEt3H][P(C6H4CO2)3] –135.7 (d) 392 NA                                     (a) in (CH3)2CO-d6; (b) in (CH3)2SO-d6; (c) CH2Cl2-d2; (d) in C3H7NO-d7.    Figure 4.2. 31P{1H} NMR (162 MHz, 25 °C) spectra of a) [(–)-brucineH]–rac–mer–[4.1] recorded in (CD3)2SO and  b) [(–)-brucineH]–rac–mer–[4.1] recorded in CD2Cl2 solvent.  84   The new ammonium salts were also characterized by 1H NMR spectroscopy and the spectra were consistent with the assigned formulation [NbaseH]–mer–[4.1] (see Appendix C). The acidic protons, [NbaseH]–mer–[4.1], were detected with a wide range of chemical shifts. For instance, the signal assigned to the NbaseH protons in the related isoquinolinium and pyridinium salts were observed at 16.34 and 16.37 ppm, respectively, in CD2Cl2 solution. For comparison, the same proton of the pyridinium salt, [pyH][As(N3)6], resonates slightly upfield [δ = 13.6 (in CD2Cl2 )].393 Although slightly upfield from the pyridinium salt, the chemical shifts of acidic protons in the tertiary ammonium salts were quite similar [PhNMe2H]–rac–mer–[4.1]: δ = 9.31 (in acetone-d6); [(n-C8H17)3NH]–rac–mer–[4.1]: δ = 9.76 (in acetone-d6), 10.40 (in CD2Cl2); [(–)-brucineH]–rac–mer–[4.1]: δ = 10.60 (in DMSO-d6); [(–)-brucineH]–Λ–mer–[4.1]: δ = 12.63 (in CD2Cl2). The related salt featuring the weakly coordinating fluoroarylborate anion, [PhNMe2H][HB(C6F5)3], exhibits a very similar chemical shift [δ = 8.88 ppm (in CD2Cl2)].394 Slightly different was the anilinium salt, [PhNH3]–rac–mer–[4.1], wherein a much higher field shift was observed [δ = 6.56 (in DMSO-d6)]. However, this behavior is quite similar to that observed for [PhNH3][BF4] [δ = 8.20 (in CD3CN)].395    Additional insight into the solution behavior of the new salts was gained from their 13C{1H} NMR spectroscopic analysis. Although the spectra (see Appendix C) displayed signals consistent with the assigned formulations, the fact that the carboxylate ligands within mer–[4.1]– were inequivalent is noteworthy. For instance, three signals were observed that were assigned to the C=O moieties (range:  = 163.9–170.7), whilst eighteen signals were observed that were assigned to the aromatic carbons. In the case of [(–)-brucineH]–rac–mer–[4.1], the 13C NMR spectrum revealed that most signals assigned to the anion were broadened or split when compared to those of enantiomerically pure                                    [(–)-brucineH]–Λ–mer–[4.1]. This is most likely attributable to diastereotopism, which results from weak cation–anion interactions that differentiate [(–)-brucineH]––mer–[4.1] and [(–)-brucineH]–– 85  mer–[4.1]. A similar phenomenon was discussed above for the 31P NMR analysis of this compound. Overall, the 13C{1H} NMR spectroscopic data suggested significant asymmetry within anion mer–[4.1]– in solution that has not previously been observed with salts featuring the TRISPHAT anion, [P(O2C6Cl4)3]–.265,396 The asymmetry within mer–[4.1]– will be discussed further in the next section as this is also observed in the solid state.  4.2.2 Metrical Parameters Determined by X-ray Crystallography  Fortuitously, several of the new salts featuring [4.1]– afforded single-crystals suitable for X–ray crystallographic analysis. Each complex crystallizes as the mer–[4.1]– isomer and has been also observed by Holmes and co–workers392,434 and each mer–[4.1]– isomer has solvent molecules of crystallization. The molecular structures of [PhNMe2H]–rac–mer–[4.1]·Me2C=O, [pyH]–rac–mer–[4.1]·0.5 Me2C=O, [isoquinolineH]–rac–mer–[4.1]·isoquinoline, and enantiomerically pure                 [(–)-brucineH]–Λ–mer–[4.1]·2 CH2Cl2 are displayed in Figure 4.3. The assignment of the                   Λ–configuration of [4.1]– in the latter structure is supported by the Flack parameter of 0.05(8).   In each salt, the closest cation-anion contact is a hydrogen-bonding interaction between the acidic N–H proton and the oxygen in the C=O moiety of anion mer–[4.1]–. Specifically, the O···H distances are similar in [PhNMe2H]–rac–mer–[4.1] [O(2)···H(1) = 1.67(3) Å], [pyH]–rac–mer–[4.1] [O(2)···H(1) = 1.92(4) Å], [(–)-brucineH]–Λ–mer–[4.1] [O(2)···H(1) = 1.88(1) Å]. In each case, these contacts are well within the sum of the van der Waals radii for oxygen and hydrogen [rvdw = 2.72 Å].306 In contrast, the analogous O···H distance in [isoquinolineH]–rac–mer–[4.1] is 3.13(9) Å [O(6)···H(1)] suggesting little to no significant cation–anion interaction. This may be a consequence of the presence   86    Figure 4.3. Molecular structures of (a) [PhNMe2H]–rac–mer–[4.1]·Me2C=O (Λ isomer is shown); (b) [pyH]–rac–mer–[4.1]·0.5 Me2C=O (Δ isomer is shown); (c) [isoquinolineH]–rac–mer–[4.1]·(C9H7N) (Δ isomer is shown); (d) [(–)-brucineH]–Λ–mer–[4.1]·2.02 CH2Cl2. Ellipsoids are drawn at the 50% probability level. Solvents of crystallization and hydrogen atoms are omitted for clarity, except for H(1). Only one enantiomer is shown in 5(a)-(c), whereas 5(d) is enantiomerically pure.   87  of a second hydrogen bonding interaction involving the isoquinoline solvent molecule [N(2)···H(1) = 1.76(8) Å, cf. rvdw = 2.75 Å].306 Similar H-bonding interactions have been reported for [isoquinolineH]4 [isoquinoline]2[Mo8O26] [N(3)···H(1A) = 1.84(1) Å].397 No such interactions between the acidic N–H proton and solvent are present in the other salts.  The ammonium salts show N–H distances within the cation that are typical of those found in related salts, especially given the difficulty determining H-positions. For instance, the                     N,N’–dimethylanilinium salt has an N–H distance of 1.04(3) Å [N(1)–H(1)], which is at the long end of the typical range [range: 0.84(5)–1.083(2) Å].398-407 The pyridinium salt features a slightly shorter N–H distance of 0.85(4) Å [N(1)–H(1)] that is within the range found in related salts featuring [pyH]+ [range: 0.77(6)–0.88(2) Å].408-413 The analogous distance within [isoquinolineH]–rac–mer–[4.1] is 0.94(7) Å   [N(1)–H(1)], which fits in the middle of the normal range [range: 0.848(8)–1.13(3) Å].397,414-417 Likewise, the N–H distance in [(–)-brucineH]–Λ–mer–[4.1] [N(2)–H(1) = 0.88(9) Å] is also in the typical range [range: 0.80(3)–0.96(5) Å].418-425 As mentioned earlier, there is significant asymmetry within the phosphorus(V) anion, mer–[4.1]–, as concluded from solution-state NMR spectroscopic studies. In the solid state, the asymmetry is immediately apparent on consideration of the P–O bond lengths. In each case, the P–O bond of the carboxylate moiety that is H-bonded to the ammonium cation is significantly longer than the uncoordinated carboxylate moiety (see Appendix C, Table C1). For example, the P(1)–O(1) bond length in [PhNMe2H]–rac–mer–[4.1] of 1.92(1) Å is significantly elongated relative to P(1)–O(3) and P(1)–O(5) [1.778(1) and 1.774(1) Å], respectively. For comparison, the P(V)–O bond lengths found in related anions are slightly shorter than in mer–[4.1]– {e.g. 1.72 Å in [P(O2C6H4)3]–, 1.71 Å in [P(O2C6Cl4)3]–, 1.69 Å in [P(C2O4)3]–}.248,250,252,396 Virtually identical metrical parameters to those described above are observed in the molecular structures of [pyH]–rac–mer–[4.1] and [(–)-brucineH]–Λ–mer–[4.1]. Likewise, analogous observations were made with the previously  88  characterized [NEt2H2][4.1] and [Et3NH][4.1] [avg.P(V)–O: 1.853(3) Å and 1.856(8) Å, respectively] with asymmetry within mer–[4.1]–.392  4.2.3 Placement of mer–[4.1]– on IR Scale for WCAs  Based on the above results that suggest significant coordinating properties for mer–[4.1]–, we analyzed mer–[4.1]– in the context of the simple infrared scale proposed by Reed and co-workers to assess WCA properties.426 Since there is no absolute scale to compare the WCA properties of specific anions, this analysis provides a rough idea of the donor properties of mer–[4.1]–. Specifically, the method involves comparing the N–H stretching frequencies of tri(n-octyl)ammonium salts in the solid-state and in solution. Solution spectra are recorded in carbon tetrachloride, where (n-C8H17)3N+–H···A– contact ion pairs are typically formed to varying extents dependent upon the anion. The results for mer–[4.1]– and for selected anions are presented in Table 4.2. The stretching frequency for [(n-C8H17)3NH]–mer–[4.1] in CCl4 (N–H = 3069 cm–1, 0.01 M) was close to those of classical WCAs such as [ClO4]– (N–H = 3050, 2801 cm–1) and [N(SO2CF3)2]– (N–H = 3086 cm–1). For comparison, very weakly donating [B(C6F5)4]– and [CMeB11F11]– rank much higher (N–H = 3233 and 3219 cm–1, respectively), whereas the strongly donating Cl– ranks much lower (N–H = 2330 cm–1). The results in the solid state also suggest that the WCA properties of mer–[4.1]– are comparable to perchlorate and triflamide according to this IR scale and are consistent with the moderate cation-anion interactions described for mer–[4.1]– in solution and in the solid-state.      89   Table 4-2. N–H frequencies for [(n-C8H17)3NH]+[Anion]– salts in CCl4 and solid state. [Anion]– N–H  in CCl4 solution N–H  solid or wax Reference [B(C6F5)4]– 3233 3241 426 [PF6]– 3191 3219 426 [BF4]– 3133 3156 426 [N(SO2CF3)2]– 3086 – 426 [4.1]– 3069 3064 This work [ClO4]– 3050, 2801 3098 426 [CF3SO3]– 3031, 2801 3056, 2815 426 [NO3]– 2451 2571 426 [Cl]– 2330 2452 426   4.2.4 Preparation of K+ and H+ Salts of mer–[4.1]–  With several ammonium salts in hand and a preliminary ranking of mer–[4.1]– as a WCA, we have explored the potential synthesis of alkali metal-based salts and stronger Brønsted acids. Treating a THF solution of [NEt3H][4.1] with KH (1.5 equiv) (Scheme 4.2) resulted in the immediate evolution of a gaseous species (presumably H2). Over 2 h, a colorless precipitate was observed that was separated and dried. The solid was dissolved in methanol-d4 and the solution was analyzed by 31P{1H} NMR spectroscopy. A singlet resonance was observed at –127.6 ppm, consistent with the preservation of the anion mer–[4.1]–. Additional characterization by 1H and 13C{1H} NMR spectroscopy as well as mass spectrometry {ESI (negative mode): m/z = 391.0, mer–[4.1]–} supported the formulation of the product as K–rac–mer–[4.1].     90   Scheme 4.2. Synthetic route of K–rac–mer–[4.1].  Confirmation of this tentative assignment was obtained by X-ray crystallographic analysis of crystals obtained from the methanol-d4 solution. The molecular structure is shown in Figure 4.4 and reveals that K–rac–mer–[4.1] is a coordination polymer with K+ ions bridging the anion centers. There are two crystallographically unique mer–[4.1]– anions and three unique K+ cations. Interestingly, K(2) is bound by two short and two long contacts to four different mer–[4.1]– anions [K(2)···O(6) = 2.660(2) Å, K(2)···O(8) = 2.668(2) Å, K(2)···O(12) = 2.926(2) Å, K(2)···O(2) = 3.019(2) Å] and by three methanol molecules [K···Oavg = 2.762(5) Å]. In stark contrast, K(1) and K(3) both sit on special positions and are bound by eight oxygen atoms. In each case, there are two short and two long K···O=C contacts [avg. = 2.727(3) and 3.038(3) Å], two K···O–P contacts [avg. 3.028(3) Å] and two K···OMe contacts [avg. = 2.787(5) Å]. The longer contacts involve binding of K+ by two chelating CO2 moieties of anion       mer–[4.1]– (i.e. four K···O interactions), which are related by inversion symmetry around K+. For comparison, a survey of the Cambridge Crystallographic Database revealed K···O=C contacts [between 2.678(2)–3.135(3) Å]427-431 and K···OMe contacts of methanol [2.750(2)–3.369(3) Å].432,433 Thus, the two short K···O=C contacts to anion mer–[4.1]– and the contacts to either two or three methanol molecules are at the short end of this range. The remaining contacts are at the long end of this range.    91   Figure 4.4. Extended structure showing the coordination polymer formed by K–rac–mer–[4.1]·3 CH3OH (K–Δ,Δ–mer–[4.1] is shown). Ellipsoids are drawn at the 50% probability level. Hydrogen atoms are omitted for clarity. O(13), O(14), O(15) are methanol solvate oxygen atoms. Oxygen atoms O(2), O(5), O(6), O(7), O(8), and O(12) are associated with anion mer–[4.1]– related by inversion symmetry around K+ with O(13)* (1-x, 1-y, 1-z), O(13) (-1+x, y, z), O(7)* (1-x, 1-y, 1-z), O(8)* (1-x, 1-y, 1-z), O(2)* (-x, 1-y, 1-z), O(5)* (2-x, 1-y, 1-z), O(6)* (2-x, 1-y, 1-z), O(14)* (2-x, 1-y, 1-z), O(12)* (3-x, 1-y, 1-z), O(14) (1+x, y, z), O(6) (1+x, y, z), O(5) (1+x, y, z), O(12)* (2-x, 1-y, 1-z), and O(2)* (1-x, 1-y, 1-z).   Analogous to the aforementioned ammonium salts, the phosphorus(V) anion, mer–[4.1]–, displays significant asymmetry. For instance, the P(1)–O(1) bond length [1.906(2) Å] is significantly longer than the P(1)–O(3) and P(1)–O(5) bonds [1.765(2) and 1.786(2) Å]. The situation is identical for P(2) with one long bond [P(2)–O(11) = 1.902(3) Å] and two short bonds [P(2)–O(7) = 1.785(2),     P(2)–O(9) = 1.767(2) Å]. The elongated P–O bond in mer–[4.1]– is not involved in binding to K+ in    K–rac–mer–[4.1], whereas for [PhNMe2H]–rac–mer–[4.1], [pyH]–rac–mer–[4.1] and [(–)-brucineH]–Λ–mer–[4.1] the elongated P–O moiety of mer–[4.1]– is the one that is involved in hydrogen bonding to the cation. In all cases, the P–C bond lengths in mer–[4.1]– do not show significant differences.   92   We finally explored the potential synthesis of strong Brønsted acids of mer–[4.1]– by dissolving phosphorane 4.2 in weakly basic solvents such as DMF (Scheme 4.3). Heating the reaction mixture to 120 °C and monitoring the reaction progress by 31P{1H} NMR spectroscopy suggested the quantitative formation of mer–[4.1]– after one month. Namely, the signal assigned to phosphorane 4.2 ( = –55.9) was replaced by two sharp singlet resonances at –134.6 and –138.9 ppm (ca. 9:1 ratio) (see Figure 4.5). The chemical shift of these anions is consistent with that previously observed for anion mer–[4.1]– (Table 4.1) and the presence of two signals may suggest both mer–and fac–isomers or strong ion-pairing as observed for [(–)-brucineH]–mer–[4.1].    Scheme 4.3. Proposed route to H(DMF)n–mer–[4.1] (n ≥ 1).  Although attempts to isolate or crystallize this product were not successful, the major signal in the negative mode in the electrospray mass spectrum (ESI–MS) was consistent with the formulation of mer–[4.1]– (m/z = 390.9; calcd mass of mer–[4.1]– = 391.0). The positive mode ESI-MS showed a signal that may be consistent with the cation [H(DMF)]+ (m/z = 74.4, DMF calcd m/z = 73.09). We hope that more definitive information about the formula of this exciting new compound can be provided in a future report.  93   Figure 4.5. 31P{1H} NMR (162 MHz, 25 °C) spectra of a) reaction mixture of H(DMF)n–mer–[4.1] recorded after 2 days and b) reaction mixture of H(DMF)n–mer–[4.1] recorded after ca. 4 weeks.  4.2 is phosphorane P(C6H4CO2)2(C6H4COOH).  4.3 Summary The synthesis, isolation and characterization of a series of salts incorporating the hexacoordinate phosphorus(V) anion mer–[4.1]– has been reported.. These compounds were conveniently obtained by treating phosphorane P(C6H4CO2)2(C6H4COOH) with an N-containing base or KH. The complexes [PhNMe2H]–rac–mer–[4.1], [pyH]–rac–mer–[4.1], [isoquinolineH]–rac–mer–[4.1], [(–)-brucineH]–Λ–mer–[4.1], and K–rac–mer–[4.1] were fully characterized by spectroscopic means and X-ray crystallography. [PhNH3]–rac–mer–[4.1] and [(n-C8H17)3NH]–rac–mer–[4.1] were characterized by NMR spectroscopy. The 31P{1H} NMR spectrum of [(–)-brucineH]–rac–mer–[4.1] recorded in CD2Cl2 solution revealed signals for one pair of diastereomers. The solid state structure elucidated enantiomerically pure [(–)-brucineH]–Λ–mer–[4.1] obtained from a CH2Cl2 solution. The solid state structure of K]–rac–mer–[4.1] revealed a coordination polymer with K+ ions bridging the anion centers. A preliminary assessment of the basicity of the mer–[4.1]– was conducted and revealed that the         94  tri(n-octyl)ammonium salt has a similar N–H frequency to the salts of [ClO4]– and [N(SO2CF3)2]–. Finally, preliminary evidence for the potential synthesis of the Brønsted acid H(DMF)n–mer–[4.1] has been obtained. Future work will explore the potential isolation of these novel protic species and the possible applications of the mer–[4.1]– ion as a novel WCA for application in catalysis and polymerization. . 4.4 Experimental 4.4.1 General Procedures  All experiments were performed using standard Schlenk or glove box techniques under nitrogen atmosphere. CH2Cl2 (Sigma Aldrich) was deoxygenated with nitrogen and dried by passing through a column containing activated alumina. CH2Cl2 (Sigma Aldrich) was deoxygenated with nitrogen and dried by passing the solvent through a column containing activated, basic alumina. Subsequently, CH2Cl2 was dried over CaH2, freshly distilled, and freeze-pump-thaw (x3) degassed. Acetonitrile (Sigma Aldrich) and DMF (Fisher Scientific) were dried over calcium hydride, freshly distilled, and freeze-pump-thaw (x3) degassed. Acetone (Fisher Scientific) was dried over calcium sulfate and freshly distilled. For extended periods of storage (1 day to 2 weeks), anhydrous solvents were stored over 3 Å molecular sieves. THF (Fisher Scientific) was freshly distilled from sodium/benzophenone ketyl immediately prior to use. (C6H4CO2)2P(C6H4CO2H)434 and [NEt3H][P(C6H4CO2)3]392 were prepared following literature procedure. Potassium hydride (30 wt% dispersion in mineral oil) was purchased from Sigma Aldrich, washed with hexanes and dried in vacuo prior to use. (–)-Brucine (Sigma Aldrich) was dried under vacuum at 40 oC prior use. Aniline (Sigma Aldrich) and N,N’-dimethylaniline (Sigma Aldrich) were dried over CaH2 and freshly distilled under partial vacuum at 40 °C. Pyridine (Fisher Scientific), trimethylamine (Fisher Scientific), and isoquinoline (Sigma Aldrich) were distilled under  95  partial vacuum at 30–50 °C. Tri(n-octyl)amine, N(n-C8H17)3 (Sigma Aldrich) was degassed with N2 gas prior to use. Elemental analyses, mass spectrometry and NMR spectra were performed in the Chemistry Department Facilities. 1H, 13C{1H} and 31P{1H} NMR spectra were recorded on Bruker Avance 400 MHz spectrometers at ambient temperature unless noted. H3PO4 (85 %) was used as external standard for 31P NMR spectra with δ = 0.0. 1H NMR and 13C{1H} NMR spectra were referenced to deuterated solvents. Low resolution electrospray ionization mass spectra, ESI-LRMS, were recorded on Bruker Esquire LC mass spectrometer. High resolution electrospray ionization mass spectra, ESI-HRMS, were recorded on Micromass LCT time of flight (TOF) mass spectrometer. Infrared spectra were recorded either in powder form or in CCl4 solution {0.01 M for [(n-C8H17)3NH][4.1]}.on a PerkinElmer FT-IR Frontier spectrometer.  4.4.2 X-ray Structure Determination  X-ray crystallography data were collected on a Bruker X8 APEX II diffractometer with graphite-monochromated Mo K radiation. A single crystal was immersed in oil and mounted on a glass fiber. Data were collected and integrated using the Bruker SAINT software package325 and corrected for absorption effect using SADABS.326 All structures were solved by direct methods and subsequent Fourier difference techniques. All non-hydrogen atoms were refined anisotropically. The hydrogen atom of N–H was located in a difference map and refined isotropically. All other hydrogen atoms were placed in calculated positions. All data sets were corrected for Lorentz and polarization effects. All refinements were performed using the SHELXT-2015328 via the Olex2 interface.329  [PhNMe2H]–rac–mer–[4.1] crystallizes with one molecule of solvent acetone in the asymmetric unit. [pyH]–rac–mer–[4.1] was solved using non-overlapped data from a major twin component.  Subsequent refinements were carried out using a data set containing complete data from component one  96  and any overlaps from component two. [pyH]–rac–mer–[4.1] crystallizes with one half-molecule of acetone in the asymmetric unit. Additionally, one coordinated benzoic acid ligand is disordered and is modelled in two orientations. [isoquinolineH]–rac–mer–[4.1] crystallizes as a twin, with a ~9:1 ratio between the major and minor twin components. [(–)-brucineH]–Λ–mer–[4.1] crystallizes with two molecules of solvent methylene chloride in the asymmetric unit.  One of these solvent molecules is disordered and was modeled in three orientations, such that their combined site occupancies summed to one. K–rac–mer–[4.1] crystallizes with three MeOH molecules coordinated to the potassium cation.  Additionally, K–rac–mer–[4.1] crystallizes with disordered free MeOH in the lattice. The disorder could not be reasonably modelled; therefore the PLATON/SQUEEZE435 program was used to generate a data set free of disordered solvent. O—H hydrogen atoms were located in difference maps and refined isotropically. All other hydrogen atoms were placed in calculated positions.  4.4.3 Synthesis of [PhNMe2H]–mer–[4.1] P(C6H4CO2)2(C6H4COOH) (0.11 g, 0.28 mmol) was dissolved in anhydrous acetone (3 mL). To the clear solution was added anhydrous N,N’-dimethylaniline (0.16 mL, 0.15 g, 1.23 mmol). The solution was stirred overnight and concentrated in vacuo to give a colorless precipitate. The crude product was washed with minimal amount of acetone and dried in vacuo. Single crystals suitable for X-ray diffraction analysis were obtained by cooling a concentrated solution of the crude product in anhydrous acetone (–30 °C, ca. 2 weeks). Yield = 0.23 (includes acetone). 31P{1H} NMR (162 MHz, (CD3)2CO, 25 oC): δ –107.7; 1H NMR (400 MHz, (CD3)2CO, 25 oC): δ 9.31 (br s, 1H, N(CH3)2C6H5H), 8.14–8.04 (m, 5H, Ar–H), 7.89–7.81 (m, 4H, Ar–H), 7.63–7.55 (m, 2H,   Ar–H), 7.34–7.29 (m, 1H, Ar–H), 7.28–7.24 (m, 2H, N(CH3)2C6H5H), 6.95–6.91 (m, 2H, N(CH3)2C6H5H), 6.84–6.80 (tt, JHH = 7.3 Hz, 1H, N(CH3)2C6H5H); 2.97(s, 6H, N(CH3)2C6H5H);  97  13C{1H} NMR (101 MHz, (CD3)2CO, 25 oC): δ 168.2 (s, C=O), 168.1 (s, C=O), 165.2 (s, C=O), 149.4 (s, N(CH3)2C6H5H), 141.2 (s, Ar–C), 140.8 (s, Ar–C), 139.7 (s, Ar–C), 138.8 (s, Ar–C), 135.1 (s, Ar–C), 134.9 (s, Ar–C), 134.3 (s, Ar–C), 134.1 (s, Ar–C), 133.6 (d, JCP = 3.7 Hz, Ar–C), 132.5 (s, Ar–C), 132.3 (d, JCP = 5.1 Hz,  Ar–C), 132.2 (s, Ar–C), 130.4 (s, Ar–C), 130.3 (s, Ar–C), 130.1 (d, JCP = 5.1 Hz, Ar–C), 129.3 (s, Ar–C), 129.1 (s, N(CH3)2C6H5H), 129.0 (s, Ar–C), 128.9 (s, Ar–C), 126.7 (s, N(CH3)2C6H5H), 126. 5 (s, N(CH3)2C6H5H), 118.1 (s, N(CH3)2C6H5H), 114.0 (s, N(CH3)2C6H5H), 40.9 (s, N(CH3)2C6H5H); IR (neat) : 3405 (vw), 3055 (vw), 3035 (vw), 2966 (vw), 2670 (vw), 1700 (s), 1644 (m), 1633 (sh, m), 1592 (m), 1574 (m), 1511 (m), 1495 (m), 1452 (m), 1353 (m), 1299 (vw), 1277 (s), 1241 (s), 1195 (w), 1159 (w), 1125 (s), 1110 (s), 1061(s), 1024 (w), 994 (w), 904 (m), 852 (s), 769 (m), 748 (s), 728 (sh), 700 (s), 684 (s) cm–1; LRMS (ESI, positive mode) m/z = 122.3 [M]+; HRMS (ESI/TOF, negative mode) m/z = [M]– calcd for C21H12O6P1 391.0372; found 391.0373.  4.4.4 Synthesis of [PhNH3]–mer–[4.1] P(C6H4CO2)2(C6H4COOH) (0.15 g, 0.38 mmol) was dissolved in anhydrous N,N’-dimethylformamide          (4 mL). The white suspension was stirred at ambient temperature for 40 min until fully dissolved. Upon addition of anhydrous aniline (2.00 mL, 2.05 g, 22.0 mmol) a colorless solution was obtained, which was concentrated in vacuo to give a colorless oil. The oily residue was washed with anhydrous        N,N’-dimethylformamide. Yield = 0.28 g (includes N,N’-dimethylformamide). A ~5 mg sample was prepared for elemental analysis by drying in vacuo for ca. 1 day at 40 °C. 31P{1H} NMR (162 MHz, (CD3)2SO, 25 oC): δ –133.6; 1H NMR (400 MHz, (CD3)2SO, 25 oC): δ     7.84–7.22 (m, 11H, Ar–H), 7.17–6.78 (m, 5H, PhNH3–Ar–H), 6.56 (br s, 3H, PhNH3), 6.10 (dd, JHH = 7.4 Hz, 1H, Ar–H); 13C{1H} NMR (101 MHz, (CD3)2SO, 25 oC): δ 168.6 (s, C=O), 167.2 (s, C=O), 167.1 (s, C=O), 156.9 (s, Ar–C), 154.0 (s, Ar–C), 145.0 (s, PhNH3, Ar–C), 142.3 (s, Ar–C), 133.6 (s,  98  Ar–C), 133.4 (s, Ar–C), 132.7 (s, Ar–C), 132.4 (s, Ar–C), 131.6 (s, Ar–C), 131.4 (s, Ar–C), 129.9 (s, Ar–C), 129.5 (s, PhNH3, Ar–C), 129.4 (d, JCP = 6.1 Hz, Ar–C), 129.1 (d, JCP = 3.3 Hz, Ar–C), 126.7 (s, Ar–C), 126.3 (d, JCP = 14.4 Hz, Ar–C), 125.0 (s, Ar–C), 124.8 (s, Ar–C), 121.2 (s, Ar–C), 119.7 (s,     Ar–C), 119.2 (s, PhNH3, Ar–C), 116.6 (s, PhNH3, Ar–C); IR (neat) : 3354 (vw), 3081 (vw), 3021 (vw), 2935 (vw), 2864 (vw), 1721 (m), 1754 (s), 1653 (s), 1594 (m), 1498 (w), 1483 (w), 1458 (s), 1397 (w), 1338 (m), 1292, (s), 1276 (s), 1253 (m), 1242 (s), 1123 (s), 1108 (s), 1063 (s), 1023 (w), 967 (w), 855 (s), 816 (m), 745 (s), 729 (m), 698 (s), 687 (s) cm–1; elem. anal. calcd for C27H20N1O6P1.0.15 C3H7N1O1: C, 66.42; H, 4.27; N, 3.27; found: C, 66.57; H, 4.07; N, 3.51.  4.4.5 Synthesis of [pyH]–mer–[4.1] To a solution of P(C6H4CO2)2(C6H4COOH) (0.36 g, 0.92 mmol) in anhydrous acetone (7 mL) was added pyridine (0.10 mL, 0.10 g, 1.26 mmol) and the colorless reaction mixture was stirred for two hours at ambient temperature to afford a colorless precipitate. The precipitate was filtered, washed with cold acetone (1.2 mL), and dried in vacuo. Yield = 0.26 g, 60%. Single crystals suitable for X-ray crystallography were isolated by cooling a saturated solution of the crude product in CH2Cl2/hexane (1:1) to –30 °C. 31P{1H} NMR (162 MHz, (CD3)2CO, 25 oC): δ –126.8; 31P{1H} NMR (162 MHz, CD2Cl2, 25 oC):         δ –118.1; 1H NMR (400 MHz, CD2Cl2, 25 oC): δ 16.37 (s, 1H, C5H5NH), 8.45 (d, JHH = 7.3 Hz, 2H,   Ar–H), 8.11–8.02 (m, 5H, Ar–H), 7.73–7.69 (m, 4H, Ar–H), 7.54–7.48 (m, 3H, C5H5NH), 7.46–7.41(m, 1H, C5H5NH), 7.11 (d, JHH = 6.4 Hz, 1H, C5H5NH), 7.06 (d, JHH = 7.3 Hz, 1H, Ar–H); 1H NMR (400 MHz, (CD3)2CO, 25 oC): δ 15.18 (br s, 1H, N–H); 13C{1H} NMR (101 MHz CD2Cl2, 25 oC): δ 170.2 (s, C=O), 170.1 (s, C=O), 166.0 (s, C=O), 146.2 (s, C5H5NH), 141.2 (s, Ar–C), 140.1 (s, Ar–C), 139.8 (s, C5H5NH), 138.1 (s, Ar–C), 134.9 (s, Ar–C), 134.7 (s, Ar–C), 134. 1 (s, Ar–C), 133.9 (s, Ar–C), 133.2 (d,  99  JCP = 2.9 Hz, Ar–C), 132.4 (d, JCP = 2.9 Hz, Ar–C), 132.1 (s, Ar–C), 131.9 (s, Ar–C), 131.2 (s, Ar–C), 131.1 (s, Ar–C), 130.1 (d, JCP = 3.7 Hz, Ar–C), 129.3 (s, Ar–C), 129.2 (s, Ar–C), 129.0 (s, Ar–C), 128.9 (s, Ar–C), 126.8 (s, C5H5NH); 126.7 (s, C5H5NH); 125.0 (s, C5H5NH); IR (neat) : 3187 (vw), 3132 (vw), 3101 (w), 3068 (vw), 2141 (vw), 1721 (m), 1699 (s), 1638 (m), 1613 (sh, m), 1593 (sh, m), 1574 (w), 1548 (m), 1482 (m), 1455 (m), 1399 (vw), 1352 (m), 1309 (w), 1274 (s), 1239 (s), 1159 (m), 1127 (m), 1112 (s), 1065 (m), 1059 (m), 1025 (w), 1001 (w), 881 (vw), 854 (s), 819 (w), 759 (s), 730 (m), 669 (s), 661 (s) cm–1; elem. anal. calcd for C26H18NO6P1·0.2 CH2Cl2: C, 64.87; H, 3.81; N, 2.89; found: C, 64.96; H, 4.06; N, 2.80.  4.4.6 Synthesis of [isoquinolineH]–mer–[4.1] To a solution of P(C6H4CO2)2(C6H4COOH) (0.21 g, 0.54 mmol) in anhydrous acetone (9 mL) was added isoquinoline (0.11 mL, 0.12 g, 0.93 mmol) via syringe. The reaction mixture was stirred for         2 days at ambient temperature and the solvent was removed in vacuo. The residue was dissolved in CH2Cl2/hexane (4mL/3mL) and stored at –30 oC to give a colorless precipitate. The precipitate was filtered, washed with minimal amount of CH2Cl2, and dried in vacuo. Yield = 0.19 g, 68 %. The aforementioned filtrate was cooled (–30 °C) to afford single crystals suitable for X-ray crystallography. 31P{1H} NMR (162 MHz, (CD3)2CO, 25 oC): δ –104.7; 1H NMR (400 MHz, CD2Cl2, 25 oC): δ 16.34 (s, 1H, NH), 9.19 (s, 1H, isoquinoline–Ar–H), 8.29 (d, 1H, isoquinoline–Ar–H), 8.09–8.04 (m, 5H, isoquinoline–Ar–H), 8.02–7.41 (m, 11H, Ar–H), 6.99(dd, JHH = 7.8 Hz, 1H, Ar–H); 13C{1H} NMR (101 MHz, (CD2Cl2, 25 oC): δ 170.7 (s, C=O), 170.6 (s, C=O), 166.8 (s, C=O), 148.9 (s, isoquinolineH,    Ar–C), 145.0 (s, Ar–C), 144.12 (s, Ar–C), 143.44 (s, Ar–C), 142.1 (s, Ar–C), 137.4 (s, isoquinolineH, Ar–C), 136.1 (s, isoquinolineH,  Ar–C), 134.0 (s, Ar–C), 133.9 (d, JCP = 2.2 Hz, Ar–C), 133.7 (s, Ar–C), 132.2 (d, JCP = 2.9 Hz, Ar–C), 132.0 (s, Ar–C), 131.0 (s, Ar–C), 130.9 (s, Ar–C), 130.8 (s, Ar–C), 129.7  100  (d, JCP = 3.7 Hz, Ar–C), 129.3 (s, isoquinolineH, Ar–C), 129.1 (s, isoquinolineH, Ar–C), 128.3 (s,      Ar–C), 128.1 (s, Ar–C), 127.9 (s, Ar–C), 127.8 (s, Ar–C), 127.6 (s, Ar–C), 126.9 (s, isoquinolineH,   Ar–C), 126.8 (s, isoquinolineH, Ar–C), 126.6 (s, isoquinolineH, Ar–C), 123.1 (s, isoquinolineH, Ar–C); IR (neat) : 3417 (vw), 3132 (vw), 3067 (w), 3009 (vw), 2998 (vw), 2930 (vw), 2112 (vw), 1975 (vw), 1709 (s), 1651 (s), 1616 (m), 1593 (w), 1575 (w), 1494 (w), 1452 (m), 1397 (w), 1341 (m), 1278 (s), 1242 (s), 1154 (m), 1128 (s), 1114 (s), 1065 (s), 1029 (vw), 976 (w), 951 (w), 853 (s), 824 (m), 802 (m), 746 (s), 731 (s), 717 (m), 700 (s), 696 (s), 685 (s) cm–1; HRMS (ESI/TOF, positive mode) m/z = [M]+ calcd for C9H8N1 130.0657; found 130.0658; HRMS (ESI/TOF, negative mode) m/z = [M]– calcd for C21H12O6P1 391.0372; found 391.0376.  4.4.7 Synthesis of [(–)-brucineH]–mer–[4.1] To a solution of P(C6H4CO2)2(C6H4COOH) (0.19 g, 0.48 mmol) in anhydrous acetone (6.5 mL) was added slowly a solution of (–)-brucine (0.22 g, 0.56 mmol) in anhydrous acetone (4mL). The reaction mixture was stirred for an hour to afford a colorless precipitate. The precipitate was filtered, washed with minimal amount of anhydrous acetone, and dried in vacuo. Crude yield = 0.30 g, 79 %. Cooling a concentrated solution of the crude product (80 mg) in CH2Cl2 (5 mL) afforded colorless crystals (–30 oC, ca. 5 d). Yield = 38 mg, 48 %. A crystal was selected for X-ray crystallographic analysis without drying. In addition, a concentrated solution of the crude product was dissolved in (CH3)2SO-d6 solvent. Single crystals suitable for X-ray diffraction analysis were obtained upon standing for 20 min at ambient temperature.  31P{1H} NMR (162 MHz, (CD3)2SO, 25 oC): δ –135.2; δ (CD2Cl2) –114.3, –114.6; 1H NMR (300 MHz, CD2Cl2, 25 oC): δ 12.63 (s, 1H, NH), 8.01–7.94 (m, 3H, Ar–H), 7.79 (s, 1H, (–)-brucinium, Ar–H), 7.75–7.35 (m, 8H, Ar–H), 6.77 (s, 1H, (–)-brucinium, Ar–H), 6.45 (dd, JHH = 7.4 Hz, 1H, Ar–H), 6.18 (t,  101  JHH = 6.2 Hz, 1H, (–)-brucinium, CH), 4.35–4.32 (m, 1H, (–)-brucinium, O–CH), 4.27–4.21 (m, 2H,    (–)-brucinium, OCH2), 4.10 (dd, JHH = 8.8 Hz, 1H, (–)-brucinium, CH), 3.93 (s, 1H, (–)-brucinium, –N–CH–C–), 3.91 (s, 3H, (–)-brucinium, OCH3), 3.88 (s, 3H, (–)-brucinium, OCH3), 3.82 (d, JHH = 13.7 Hz, 1H, (–)-brucinium, –N–CH2–), 3.63–3.59 (m, 1H, brucinium, CH2), 3.14 (s, 1H, (–)-brucinium, CH), 3.09 (t, JHH = 8.8 Hz, 1H, (–)-brucinium, CH2), 3.02–2.94 (m, 1H, (–)-brucinium, CH), 2.87 (d, JHH = 14.7 Hz, 1H, (–)-brucinium, CH), 2.67 (dd, JHH = 3.9 Hz, 1H, (–)-brucinium, CH), 2.00–1.86 (m, 3H,  (–)-brucinium, 3xCH), 1.47 (d, JHH = 14.7 Hz, 1H, (–)-brucinium, CH), 1.33 (dt, JHH = 10.8Hz, 1H,     (–)-brucinium, CH); 1H NMR (400 MHz, (CD3)2SO, 25 oC): δ 10.60 (br s, 1H, N–H); 13C{1H} NMR (101 MHz, CD2Cl2, 25 oC): δ 172.5 (s, (–)-brucinium, C=O), 172.2 (s, C=O), 168.3 (s, C=O), 168.1 (s, C=O), 150.5 (s, Ar–C), 148.9 (s, Ar–C), 146.9 (s, Ar–C), 136.0 (s, Ar–C), 135.5 (s, Ar–C), 133.4 (s,   Ar–C), 133.2 (s, Ar–C), 133.0 (s, (–)-brucinium, Ar–C), 132.8 (s, (–)-brucinium, Ar–C), 132.5 (s,      Ar–C), 132.3 (s, Ar–C), 131.7 (s, Ar–C), 131.5 (s, Ar–C), 129.9 (s, (–)-brucinium), 129.1 (s,                 (–)-brucinium), 127.2 (s, (–)-brucinium), 127.0 (s, Ar–C), 126.5 (s, Ar–C), 126.3 (s, Ar–C), 125.9 (s,    Ar–C), 125.7 (s, Ar–C), 125.1 (s, Ar–C), 124.9 (s, Ar–C), 118.8 (s, (–)-brucinium), 105.6 (s,                 (–)-brucinium), 101.0 (s, (–)-brucinium), 77.3 (s, (–)-brucinium), 64.0 (s, (–)-brucinium), 61.2 (s,           (–)-brucinium), 59.2 (s, (–)-brucinium), 56.6 (s, (–)-brucinium), 56.1 (s, (–)-brucinium), 52.1 (s,            (–)-brucinium), 52.0 (s, (–)-brucinium), 50.2 (s, (–)-brucinium), 46.9 (s, (–)-brucinium), 42.0 (s,           (–)-brucinium), 40.5 (s, (–)-brucinium), 30.4 (s, (–)-brucinium), 24.7(s, (–)-brucinium); IR (neat) : 3494 (vw), 3061 (vw), 3056 (vw), 2997 (vw), 2959 (vw), 2872 (vw), 2829 (vw), 1708 (sh, m), 1668 (s), 1648 (sh, s), 1594 (m), 1577 (w), 1502 (m), 1451 (m), 1414 (m), 1362 (w),1331 (w), 1283 (s), 1245 (m), 1220 (m), 1198 (m), 1176 (w), 1111(s), 1088 (w), 1071(m), 1065 (w), 1027 (m), 1012 (w), 986 (m), 964 (w), 938 (vw), 885 (vw), 849 (s), 817 (sh, w), 790 (w), 762 (sh, w), 728 (s), 719 (m), 701 (s), 684 (m)  102  cm–1; elem. anal. calcd for C45H41N2O10P. 0.7 CH2Cl2. 0.9 C3H6O: C, 63.71; H, 5.30; N, 3.06; found: C, 63.81; H, 5.40; N, 3.10.  4.4.8 Synthesis of [(n-C8H17)3NH]–mer–[4.1] To a suspension of P(C6H4CO2)2(C6H4COOH) (0.23 g, 0.58 mmol) in anhydrous acetone (6 mL) was added degassed tri(n-octyl)amine, N(n-C8H17)3 (0.50 mL, 0.40 g, 1.13 mmol). Within seconds, the reaction dissolved and was stirred overnight. Subsequently, the solvent was removed in vacuo to afford a pale yellow oil. The oily residue was washed with n-hexane, filtered and heated in vacuo at 140 oC for 4 h to remove residual solvent. Yield = 0.31 g, 73 %.  31P{1H} NMR (162 MHz, (CD3)2CO, 25 oC): δ –128.9; δ (CD2Cl2) –125.6; 1H NMR (400 MHz, (CD3)2CO, 25 oC): δ 9.76 (br s, 1H, (CH3(CH2)5CH2CH2)3NH), 8.50–7.20 (m, 11H, Ar–H), 6.29 (dd, JHH = 7.3 Hz, 1H, Ar–H), 3.04 (t, JHH = 8.3 Hz, 6H, (CH3(CH2)5CH2CH2)3NH), 1.69 (m, 6H, (CH3(CH2)5CH2CH2)3NH), 1.31 (br s, 30H, (CH3(CH2)5CH2CH2)3NH), 0.89 (t, JHH = 6.9 Hz, 9H, (CH3(CH2)5CH2CH2)3NH); 1H NMR (400 MHz, CD2Cl2, 25 oC): δ 10.40 (s, 1H, (CH3(CH2)5CH2CH2)3NH); 13C{1H} NMR (101 MHz, (CD3)2CO, 25 oC): δ 169.4 (s, C=O), 169.3 (s, C=O), 163.9 (s, C=O), 156.5 (s, Ar–C), 154.3 (s, Ar–C), 135.8 (s, Ar–C), 135.7 (s, Ar–C), 134.9 (s,  Ar–C), 134.8 (s, Ar–C), 132.3 (s, Ar–C), 132.1 (s, Ar–C), 131.7 (s, Ar–C), 131.5 (s, Ar–C), 130.7 (d, JCP = 3.7 Hz, Ar–C), 130.6 (s, Ar–C ), 130.4 (s, Ar–C), 128.5 (d, JCP = 4.4 Hz, Ar–C), 127.2 (s, Ar–C), 127.0 (s, Ar–C), 124.8 (d, JCP = 2.2 Hz, Ar–C), 124.7 (s, Ar–C), 52.5 (s, (CH3(CH2)5CH2CH2)3NH), 31.6 (s, (CH3(CH2)5CH2CH2)3NH), 29.0 (s, (CH3(CH2)5CH2CH2)3NH), 28.9 (s, (CH3(CH2)5CH2CH2)3NH), 26.4 (s, (CH3(CH2)5CH2CH2)3NH), 23.3 (s, (CH3(CH2)5CH2CH2)3NH), 22.4 (s, (CH3(CH2)5CH2CH2)3NH), 13.5 (s, (CH3(CH2)5CH2CH2)3NH); IR (CCl4) : 3069 (vw), 2955 (m), 2927 (m), 2879 (w), 2857 (m), 1709 (s), 1653 (m), 1596 (m), 1579 (w), 1454 (m), 1378 (vw), 1280 (s),  103  1242 (s), 1127 (s), 1112(m), 1071 (m), 1061(s), 1023 (w), 984 (m), 856 (s), 809 (w), 784 (s), 757 (s), 731 (sh, m), 700(m), 686 (w); IR (neat) : 3064 (vw), 3021 (vw) 2954 (m), 2925 (m), 2870 (w), 2856 (m), 1707 (s), 1653 (m), 1595 (m), 1579 (w), 1453 (m), 1378 (vw), 1277 (s), 1240 (s), 1125 (s), 1113 (s), 1071 (m), 1061(s), 1022 (w), 984 (m), 855 (s), 809 (w), 784 (s), 757 (s), 731 (sh, m), 699 (s), 686 (m) cm–1.  4.4.9 Synthesis of K–mer–[4.1] To a colorless solution of [NEt3H][P(C6H4CO2)3] (0.17 g, 0.34 mmol) in anhydrous THF (12 mL) was added slowly a suspension of potassium hydride (0.02g, 0.52 mmol) in anhydrous THF (6 mL) at ambient temperature. The immediate evolution of gas (i.e. H2) was observed and the reaction mixture was stirred for 2h at ambient temperature to afford a colorless precipitate. The precipitate was filtered and washed with minimal amount of anhydrous THF and dried in vacuo. Crude yield = 0.12 g, 82 %. Single crystals suitable for X-ray diffraction were obtained by cooling a concentrated solution of the crude product (44 mg) in MeOH-d4 (1.5 mL) (–30 oC, ca. 9 days). 31P{1H} NMR (162 MHz, CD3OD, 25 oC): δ –127.6, δ ((CD3)2CO) –136.4; 1H NMR (400 MHz, CD3OD, 25 oC): δ 7.94–7.28 (m, 11H, Ar–H), 6.26 (dd, JHH = 7.6 Hz, 1H, Ar–H); 13C{1H} NMR (101 MHz, CD3OD, 25 oC): δ 170.7 (s, C=O), 169.9 (s, C=O), 169.8 (s, C=O), 155.4 (s, Ar–C), 154.3 (s,   Ar–C), 153.2 (s, Ar–C), 133.3 (s, Ar–C), 133.1 (s, Ar–C), 132.3 (s, Ar–C), 132.1 (d, JCP = 2.9 Hz,      Ar–C), 130.2 (s, Ar–C), 130.1 (s, Ar–C), 129.0 (d, JCP = 2.9 Hz, Ar–C), 128.9 (s, Ar–C), 128.7 (d, JCP = 3.7 Hz, Ar–C), 128.6 (s, Ar–C), 126.0 (s, Ar–C), 125.9 (s, Ar–C), 125.8 (s, Ar–C), 124.7 (s, Ar–C), 124.5 (s, Ar–C); IR (neat) : 2962 (vw), 1689 (s), 1632 (sh, w), 1595 (m), 1580 (w), 1453 (m), 1391 (w), 1332 (w), 1282 (s), 1244 (s), 1120 (s), 1071 (m), 1062 (m), 1025 (w), 855 (s), 813 (w), 745 (s), 729 (s), 718 (w), 697 (s), 684 (m) cm–1; LRMS (ESI, negative mode) m/z = 391.0 [M]–.  104  4.4.10 Attempted Synthesis of H(DMF)n[4.1] To P(C6H4CO2)2(C6H4COOH) (0.20 g, 0.57 mmol) was added anhydrous N,N’-dimethylformamide (5 mL). The initially cloudy solution cleared within a few seconds and was subsequently stirred for ca. 16 h. Despite heating to 120 °C over ca. 4 weeks, no additional changes were observed in the 31P{1H} NMR spectrum of the reaction mixture. An aliquot was removed from the reaction mixture for mass spectrometric analysis. 31P{1H} NMR (162 MHz, N(CH3)2COH, 25 oC): δ –55.9,–134.6; –138.9; LRMS (ESI, negative mode) m/z = 391.0 [M]–.      105  Table 4-3. X-ray crystallographic data for [PhNMe2H]–rac–mer–[4.1], [pyH]–rac–mer–[4.1], [isoquinolineH]–rac–mer–[4.1], [(–)-(brucineH]–Λ–mer–[4.1], and K–rac–mer–[4.1].  [PhNMe2H]–rac–mer–[1]· Me2C=O [pyH]–rac–mer–[1]· 0.5 Me2C=O [isoquinolineH]–rac–mer–[1]· (C9H7N) [(–)-brucineH]–Λ–mer–[1]· 2.02 CH2Cl2 K–rac–mer–[1]· 3 CH3OH Formula C32H30NO7P C27.5H21NO6.5P C39H27N2O6P C46.01H43.03Cl4.03N2O10P C45H36K2O15P2 FW 650.59 500.42 650.59 957.87 956.88 Cryst. syst. Monoclinic monoclinic Monoclinic Orthorhombic monoclinic space group P21/n C2/c P21/n P212121 P21/n a (Å) 13.7182(6) 33.995(4) 8.3942(8) 14.000(2) 13.4404(4) b (Å) 9.6463(4) 7.8804(8) 12.9178(12) 14.214(3) 18.8521(5) c (Å) 21.0016(8) 18.711(2) 28.434(3) 22.114(4) 18.8164(5) α (deg) 90 90 90 90 90 β (deg) 95.7130(10) 109.712(3) 97.682(3) 90 93.2000(10) γ (deg) 90 90 90 90 90 V (Å3) 2765.3(2) 4718.7(9) 3055.6(5) 4400.4(13) 4760.3(2) T (K) 90(2) 90(2) 90(2) 90(2) 100(2) Z 4 8 4 4 4 μ (MoKα) (mm-1) 0.151 0.164 0.145 0.369 0.332 crystal size (mm3) 0.20×0.11×0.10 0.30×0.1×0.1 0.18×0.15×0.08 0.10×0.04×0.04 0.13×0.12×0.08 ρcalcd. (g cm-3) 1.373 1.409 1.414 1.446 1.335 2θ(max) (°) 60.06 60.23 53.11 44.9 54.00 F(000) 1200.0 2080.0 1352.0 1987.0 1976.0 No. total reflns. 32422 7158 38996 11777 37894 No. unique reflns. 8097 399 6467 5484 10359 R(int) 0.0496 0.036 0.0572 0.0766 0.036 Refln./param. Ratio 14.7 17.9 14.7 9.00 17.5 R1 [I > 2σ(I)]a 0.0470 0.0654 0.0774 0.0658 0.0613 wR2 [all data]b 0.1181 0.1594 0.2349 0.1471 0.1782 GOF 1.011 1.137 1.054 1.011 1.036 a R1 = Σ||Fo| - |Fc||/Σ|Fo|. b wR2(F2[all data]) = {Σ[w(Fo2 - Fc2)2]/Σ[w(Fo2)2]} 1/2  106  Chapter 5: Brønsted Acids with Hexacoordinate Tantalum(V) Weakly Coordinating Anions as Highly Effective Initiators for the Cationic Polymerization of Vinyl Monomers   5.1 Introduction  The cationic polymerization of olefins is a challenging reaction due to its very fast rate of propagation and the many possible chain transfer and termination processes.17,37 The polymerization necessitates initiators comprised of a cation source (a proton or carbenium ion) and a WCA that stabilizes the electrophilic propagating cation.27,68,271 The nature of the coordinating anion is critical, as it affects the degree of ion-pairing and therefore has an influence over initiation, propagation, chain transfer and termination. A strong interaction between the cation and anion leads to termination, whereas a weak interaction evokes side reactions such as chain transfer. Ideally, WCAs will be able to delocalize the negative charge over a large number of atoms and will be non-nucleophilic. WCAs composed of group 13 elements, such as boron, aluminum and gallium are of particular interest and have been ubiquitously designed to stabilize highly reactive cations.33,65,66,69,74,84,119,137,138,147,148,153,155,171,174,182,186,195,298,331,436,437 Only a few of these systems have been studied as potential initiators for cationic polymerization. Two-component systems comprised of a Lewis acid (e.g. AlCl3 and BF3) in combination with a co-initiator (e.g. traces of water or alcohol) have been established as initiators for cationic polymerization; however, the initiating species is not well understood. Recent developments of solid and weighable single-component initiators based on Brønsted acids are of growing interest  since they allow for better control over the monomer-to-initiator ratio.  * A version of this chapter will be submitted for publication. Hazin, K. and Gates, D.P.  107  To date, they are limited to H(OEt2)2[Al{O(CF3)3}4], H(OEt2)2[B(C6F5)4], H[B(C2O4)4], Na(H2O)2[B{3,5-C(CF3)2C6H3}4], and H(L)2[P(1,2-O2C6Cl4)3] (L= OEt2, THF, DMF) due to the challenges in the synthesis and isolation of strong Brønsted acids.33,64-66,269,282,351 For instance, the aforementioned systems must be stored and handled at low temperatures (e.g. below –30 °C). In Chapter 2 it was shown that the large charge-delocalized tris(tetrachlorocatecholato)phosphate anion can facilitate the isolation of Brønsted acids with stabilized protons such as: [H(DMF)2]+, [H(THF)2]+, and [H(THF)(CH3CN)]+. Building on this previous work, we pursued the design of group 5 transition metal containing WCAs for the stabilization of protic acids.  We hypothesized that tantalum(V)–containing WCAs would possess ideal properties to isolate Brønsted acids due to the large coordination numbers possible for tantalum, which would permit the incorporation of large, charge-delocalizing ligands. The delocalization of the negative charge over a large number of atoms minimizes the potential reaction with the counter cation.  Selected examples of compounds containing tantalum(V) WCAs are illustrated in Figure 5.1. Tantalum(V)-containing WCAs with chelating oxygen ligands are limited and only a few such systems (A–C)438-442 have been structurally characterized. Of particular importance, tantalum(V)-containing Brønsted acids are restricted to Li(H2O)[Ta{O(CF3)3}6] (D),443 where the proton is part of the water molecule. To our knowledge, [Ph3C][TaF6] (E)444 is the only system containing a tantalum(V) WCA that has been studied as a single-component initiator. In contrast, binary initiators containing tantalum(V) anions and a co-initiator have been established in the following systems: [Ph3C][Ta(OC6F5)6] (F),149,150 L[TaX6] (X = Cl, Br, I; L = [TaX4(THF){O(CH2)4O(CH2)3CH2)}] with X = F, Cl),445 TaCl5/Bu4NCl/isobutyl vinyl        ether–HCl,446 and TaF5.447   108   Figure 5.1. Examples of characterized tantalum(V)-containing complexes.   In this chapter, the synthesis and characterization of novel Brønsted acids H(OEt2)2[5.1] and H(OEt2)2[5.2] are reported. Both are highly effective single–component initiators for the cationic polymerization of olefin monomers, including n-butyl vinyl ether, -methylstyrene, styrene and isoprene. Remarkably, high molecular weight poly(-methylstyrene) and polystyrene (Mn  200,000 g mol–1) are obtained with moderate to narrow dispersity at temperatures above –100 °C. To our knowledge, H(OEt2)2[5.1] and H(OEt2)2[5.2] are the only examples of hexacoordinate Ta(V)–bidentate oxo–complexes that have successfully been used in the cationic polymerization of olefins.  109   Figure 5.2. Brønsted acids H(OEt2)2[5.1] and H(OEt2)2[5.2].   5.2 Results and Discussion 5.2.1 Synthesis and Characterization of Initiators  Our group previously reported the convenient reaction of 1,2-C6Cl4(OH)2 with PCl5 in CH2Cl2 and Et2O that permitted the isolation of solid Brønsted acid                      H(OEt2)2[P(1,2–O2C6Cl4)3].269 Remarkably, this solid and weighable compound is a highly effective single-component initiator for the polymerization of n-butyl vinyl ether,                       -methylstyrene, styrene and isoprene. Based on these results, it was speculated that if TaCl5 was employed in place of PCl5, a strong Brønsted acid with a hexacoordinate tantalum(V) anion could be isolated that may be an effective cationic initiator for olefin polymerization.   Scheme 5.1. Synthesis of Brønsted acid H(OEt2)2[5.1].   110   Thus, a warm solution containing an excess tetrachlorocatechol (4 equiv) in CH2Cl2 was added to TaCl5 in CH2Cl2 that was heated to reflux. Subsequently, excess Et2O was added at ambient temperature, to give an off-white product that was presumed to be          H(OEt2)2[Ta(1,2-O2C6Cl4)3]. The isolated product was characterized by 1H and 13C{1H} NMR spectroscopy, and elemental analysis.   At ambient temperature, the 1H NMR spectrum of H(OEt2)2[5.1] in CD2Cl2 exhibited signals assigned to the two coordinated ether molecules (δ = 4.00, 8H, OCH2CH3; 1.40, 12H, CH2CH3). Surprisingly, the 1H NMR spectrum displayed a broad undefined signal at 9.37 ppm. At low temperature, this signal became much sharper (T = –85 °C, CD2Cl2: δ = 9.40). In order to investigate the identity of H(OEt2)2[5.1], a 1H–13C HMBC-NMR experiment was conducted at  –85 °C that illustrated correlation between the resonance at 9.40 ppm and two aryl carbon atoms at 118.6 and 145.3 ppm (see Appendix D, Figure D1). It was assumed that the resonance at 9.40 ppm was presumably assignable to a hydroxyl proton of a tetrachlorocatechol moiety that was coordinated in a monodentate fashion. However, the identity of the compound H(OEt2)2[5.1] was not immediately obvious. A sharp signal assigned to the acidic proton in H(OEt2)2[5.1] was observed at δ = 16.73 in the low temperature spectrum (Figure 5.3) that is similar to the acidic proton in our previously reported H(OEt2)2[P(1,2-O2C6Cl4)3] (T = –85 °C, CD2Cl2: δ = 16.70, H).269 For comparison, related salts containing the [H(OEt2)2]+ cation show similar downfield chemical shifts in H(OEt2)2[B(C6F5)4] (δ = 15.5, CD2Cl2 at 25 °C),331 H(OEt2)2[B(CF3)4] (δ = 16.3, CD2Cl2 at 25 °C),448 H(OEt2)2[(C3H3N2){B(C6F5)3}2] (δ = 16.3, CD2Cl2),449 H(OEt2)2[H2N{B(C6F5)3}] (δ =16.6, CD2Cl2),124 H(OEt2)2[C6F4–1,2–{B(C6F5)2}2(–OCH3)] (δ = 16.4, CD2Cl2),450 H(OEt2)2[P(C2O4)3] (δ = 15.5, CDCl3).248 The salts H(OEt2)2[B{3,5-(CF3)2C6H3}4] (δ =11.1, CD2Cl2),119 H(OEt2)2[CHB11Me5X6] (X = Cl, δ = 13.8; X = Br, δ = 11.7  111  ppm, C6D6),195 and H(OEt2)2[Al{OC(CF3)3}4] (δ = 14.7, C6D6)298 show a slight difference in downfield shift for the acidic proton to that of H(OEt2)2[5.1]. Importantly, the integrated ratio of the signals assigned to the acidic proton and the coordinating solvent are consistent with the 2:1 ratio within the [HL2]+ cation (L = OEt2).   The 13C{1H} NMR spectrum provided additional insight into the structural elucidation of H(OEt2)2[5.1]. Two resonances were assigned to the coordinated diethyl ether molecule (δ = 70.3, OCH2CH3; 13.3, OCH2CH3). In addition, nine resonances were observed for the aromatic carbon atoms in H(OEt2)2[5.1] that are consistent with three resonances for the bidentate tetrachlorocatechol aryl carbon atoms and six signals for the monodentate C6Cl4O2H moieties. (see Appendix D, Figure D2).  Figure 5.3. 1H NMR (400 MHz, CD2Cl2, –85 °C) spectrum of H(OEt2)2[5.1]. * indicates residual CHDCl2, indicates free diethyl ether solvent. ‡ unassigned signal.  Crystallization from a concentrated CD2Cl2 solution afforded a single crystal suitable for X-ray crystallography. Analysis of the crystal determined by X-ray diffraction elucidated a  112  product, namely H(OEt2)(H2O)[Ta(1,2–O2C6Cl4)2(1,2–(OH)OC6Cl4)2], H(OEt2)(H2O)[5.1]. The molecular structure of the moisture and air-sensitive Brønsted acid H(OEt2)(H2O)[5.1] and important metrical parameters are presented in Figure 5.4 and will be discussed in detail below (vide infra).   Figure 5.4. Molecular structure of H(OEt2)(H2O)–cis–[5.1]·OEt2·0.17 CH2Cl2. Ellipsoids are drawn at the 50% probability level. Solvents of crystallization (0.17 x CH2Cl2) and hydrogen atoms are omitted for clarity, except for H(4), H(8), H(10), H(11a) and H(11b). Selected bond lengths [Å]: Ta(1)–O(1) = 2.011(18); Ta(1)–O(2) = 2.027(17); Ta(1)–O(3) = 1.879(18); Ta(1)–O(5) = 1.967(19); Ta(1)–O(6) = 2.074(18); Ta(1)–O(7) = 1.932(18); C(8)–O(4) = 1.360(3); C(13)–O(5) = 1.31(3); C(24)–O(8) = 1.340(3); C(26)–O(9) = 1.41(3); C(30)–O(10) = 1.49(5); O(9)–O(11) = 2.43(3); O(10)–O(11) = 2.46(3); O(4)–H(4) = 0.84(2); O(10)–H(10) = 1.10(4); O(11)–H(11a) = 0.87(2). Selected bond angles []: O(1)–Ta(1)–O(2) = 77.1(7); O(3)–Ta(1)–O(6) = 83.5(8); O(2)–Ta(1)–O(7) = 82.2(7); O(2)–Ta(1)–O(6) = 163.4(7); O(3)–Ta(1)–O(5)= 159.4(7); C(31)–O(10)–C(32) = 107.0(3).  113   Although it is preferable to store H(OEt2)2[5.1] at low temperatures (ca. –30 °C), the integrity of the [H(OEt2)2]+ moiety in solution was investigated. A concentrated sample of H(OEt2)2[5.1] in CD2Cl2 was stored at ambient temperature under an inert atmosphere. The stability of the complex in solution was monitored by recording low temperature 1H–NMR spectra at –85 °C over a period of 15 days (see Appendix D, Figure D3). The spectra showed no change for a period of ca. one week. After one week an additional signal was observed at around 13.1 ppm suggestive of degradation. Elemental analysis of the crude product was consistent with the assigned formulation of H(OEt2)2[5.1] with CH2Cl2 (1.4 equiv) solvate of reaction.   Inspired by the successful synthesis and isolation of H(OEt2)2[5.1], we set out to isolate a Brønsted acid containing a hexacoordinate tantalum(V) anion with three chelated       tetrachlorocatechol moieties. The reaction of TaCl5 and tetrachlorocatechol (3 equiv) in CH2Cl2 afforded the Brønsted acid H(OEt2)2[5.2] in moderate yield (Scheme 5.2).  Scheme 5.2. Synthesis of Brønsted acid H(OEt2)2[5.2].  H(OEt2)2[5.2] was characterized by 1H and 13C{1H} NMR spectroscopy, elemental analysis and mass spectrometry. At ambient temperature, the 1H NMR spectrum of H(OEt2)2[5.2] in CD2Cl2 exhibited signals assigned to the two coordinated diethyl ether molecules (δ = 4.00,  114  8H, OCH2CH3; 1.40, 12H, OCH2CH3). At low temperature, the 1H NMR spectrum of H(OEt2)2[5.2] (Figure 5.5) displayed a much sharper signal for the acidic proton in H(OEt2)2[5.2] (δ = 16.74). This chemical shift is similar to that observed for the acidic proton in our previously reported H(OEt2)2[P(1,2-O2C6Cl4)3] (T = –85 °C, CD2Cl2: δ = 16.70, H).269 The 1H NMR spectrum did not reveal a signal in the range 9.0 to 10.0 ppm, attributable to a hydroxyl group of a tetrachlorocatechol moiety in H(OEt2)2[5.2]. The 13C{1H} NMR spectrum (Figure 5.6) exhibited only three aromatic resonances confirming the symmetry and equivalence of the three chelated tetrachlorocatechol moieties. In addition, elemental analysis and mass spectrometry were consistent with a tris(tetrachlorobenzenediolato)tantalate(V) anion species.  Figure 5.5. 1H NMR (400 MHz, CD2Cl2, –85 °C) spectrum of H(OEt2)2[5.2].  * indicates residual CHDCl2, indicates free diethyl ether solvent. ‡ grease.  115   Figure 5.6. 13C{1H} NMR (400 MHz, CD2Cl2, 25 °C) spectrum of H(OEt2)2[5.2].  * indicates residual NMR solvent.  5.2.2 Metrical Parameters Determined by X-ray Crystallography   The crude Brønsted acid H(OEt2)2[5.1] was crystallized from a concentrated solution of the crude product in CD2Cl2 at –30 °C under inert atmosphere to afford colorless crystals within ca. 3 days. The solid state structure exhibits one water molecule and one diethyl ether molecule within the cation moiety in [H(OEt2)(H2O)]+. Presumably, adventitious water in the solvent for crystallization led to the unexpected growth of a single crystal of [H(OEt2)(H2O)][5.1]·OEt2·0.17 CH2Cl2.  116   Particularly intriguing is the structure of the anion with two chelated tetrachlorocatechol moieties [Ta(1)–O(1) and Ta(1)–O(2); Ta(1)–O(5) and Ta(1)–O(6)] and two monodentate tetrachlorocatechol ligands coordinated in the cis position. The molecular structure of H(OEt2)(H2O)[5.1] displays close interaction between an oxygen of the bidentate tetrachlorocatechol of the anion [5.1]– and a hydrogen of the hydroxyl group of the monodentate tetrachlorocatechol of the anion [5.1]– [O(6)···H(4) = 1.91(2) Å; O(2)···H(8) =  2.23(2) Å].   The closest cation–anion contact in H(OEt2)(H2O)[5.1] occurs between an oxygen atom of the anion [5.1]– and a hydrogen atom of H2O solvate [O(4)···H(11a) = 2.00(2) Å] and is within the sum of the van der Waals radii for oxygen and hydrogen [rvdw = 2.72 Å].306 Notably striking is the coordination environment around the Ta(V) center. Specifically, the hydroxyl groups of the two monodentate C6Cl4O(OH)–ligand moieties are bent toward the oxygen atoms of the chelated tetrachlorocatechol ligands. The tantalum(V) center in the anion [5.1]– exhibits a distorted octahedral geometry. The two monodentate coordinated tetrachlorocatechol moieties are cis disposed and demonstrate a deviation from octahedral angles for the anion in H(OEt2)(H2O)[5.1] [O(3)–Ta(1)–O(7) = 93.0(8)°; O(1)–Ta(1)–O(3) = 95.4(8)°; O(2)–Ta(1)–O(7) = 82.2(7)°; O(5)–Ta(1)–O(7) = 86.7(8)°; O(3)–Ta(1)–O(6) = 86.6(7)°], likely due to steric repulsion or short intermolecular contacts. The chelated tetrachlorocatechol ligands occupy positions through the oxygen atoms [Ta(1)–O(2) and Ta(1)–O(6); Ta(1)–O(1) and Ta(1)–O(5)] and display perturbation from regular octahedral angles [O(2)–Ta(1)–O(6) = 163.4(7)°;       O(3)–Ta(1)–O(5) = 159.4(7)°]. In comparison, a pseudo–octahedral geometry around the tantalum(V) center has been observed in [NEt2H2][Ta–(O2C20H10{SiMe3}2–3,3')2Cl2] with two binaphthoxide ligands bound to the metal center in a bidentate fashion and two chlorine atoms bound in a cis-arrangement [O–Ta–O, 92.7°; Cl–Ta–Cl, 84.6°].438 Furthermore, a pseudo– 117  octahedral geometry around each metal center has been reported in [Ta(OCH3)4{(Me)3CCOCH2CO(Me)3}] [O–Ta–O range from 79.3(2)° to 92.7(3)°] and [Ta(OCH3)4{(CH3C(O)CH2C(O)CH3}] [O–Ta–O range from 78.9(2)° to 92.5(5)°].451  The Ta–O bond distances in H(OEt2)(H2O)[5.1] range from 1.879(12) Å to 2.074(16) Å. The average Ta–O bond lengths in H(OEt2)(H2O)[5.1] [avg. Ta–O 2.019(34) Å and 1.906(21) Å] is at the shorter end of the typical range found in [Ta(C6H4O2)3py] [avg. 2.025(12) Å],452 [Ph3C][Ta(OC6F5)6] [avg. 1.952(3) Å],150 and other tantalum-oxygen containing bidentate and mono-dentate systems [avg. range: 2.032(2)–2.16(1) and 1.863(3)–1.976(1)].441,451,453-457   In addition to the anion, the metrical parameters for the cation moiety provide valuable  insight into the bonding within the compound. The [H(OEt2)(H2O)]+ moiety in H(OEt2)(H2O)[5.1] crystallizes out with one H2O molecule. The acidic proton in [H(OEt2)(H2O)]+ was located in the difference electron density map and refined isotropically. It appears that the acidic proton is coordinated asymmetrically through the oxygen atom of one diethyl ether molecule and an oxygen atom of the H2O group [O(10)–H(10) = 1.10(4) Å;     O(11)–H(10) = 1.50(4) Å] (Figure 5.7). Further, a close contact is observed in the cation moiety in [H(OEt2)(H2O)]+ between an oxygen atom of diethyl ether solvate molecule and a hydrogen of the H2O molecule [O(9)–H(11b) = 1.57(2) Å] and is within the sum of the van der Waals radii for oxygen and hydrogen [rvdw =2.72 Å].306  Figure 5.7. Metrical parameters [Å] for the cation in H(OEt2)(H2O)[5.1]·OEt2·0.17 CH2Cl2.  118   Asymmetric binding has been reported for related systems containing the cation moiety [H(OEt2)2]+ in H(OEt2)2[P(1,2-O2C6Cl4)3] [1.09(4) Å and 1.34(4) Å],269 H(OEt2)2[Al{OC(CF3)3}4] [0.75(5) Å and 1.76(5) Å]298, H(OEt2)2[B(C6F5)4] [0.93(1) Å and 1.52(1) Å],331 H(OEt2)2[CHB11Me5Cl6] [1.08(3) Å and 1.59(3) Å; 0.80(3) Å and 1.45(3) Å]195 and H(OEt2)2[(C3H3N2){B(C6F5)3}2] [1.11(1) Å and 1.34(9) Å].449 Though, it has not been extensively noted for the more rare [H(OEt2)(H2O)]+ cation. Reed and co-workers reported the mixed [H(OEt2)(H2O)]+ cation and concluded that the position of the acidic proton is located closer to the ether molecule.195 In addition, theoretical calculations of the gas-phase structure of [H(MeOH)(H2O)]+ suggest an asymmetric binding of H+–O–H in protonated methanol.458 Since the determination of the position of the central proton is generally unreliable, the more precisely determined C–O and C–C bond lengths are often used to evaluate the symmetry within the [H(OEt2)(H2O)]+ cation. The C–O distances in the coordinated ether molecules [C(30)–O(10) = 1.49(5) Å and C(31)–O(10) = 1.44(4) Å; C(26)–O(9) = 1.41(3) Å and       C(27)–O(9) = 1.48(4) Å] display a slight lengthening from the C–O bond lengths found in ether lattice solvate [1.416 Å].459 This may reflect asymmetric binding within the [H(OEt2)(H2O)]+ cation. For comparison, a similar bonding situation has been observed for H(OEt2)(H2O)[CHB11H5Cl6] [avg. 1.445(9) Å and 1.471(1) Å],195 H(OEt2)2[B(C6F5)4] [1.443(14) Å and 1.429(13) Å; 1.542(12) Å and 1.466(15) Å],331 H(OEt2)2[Al{OC(CF3)3}4] [1.440(6) Å and 1.508(5) Å; 1.412(5) Å and 1.470(6) Å],298 as well as H(OEt2)2[(C3H3N2){B(C6F5)3}2] [1.44(1(12) Å and 1.52(2) Å; 1.456(9) Å and 1.448(10) Å].449   The extent of hydrogen bonding within the cation of [H(OEt2)2(H2O)][5.1] may be evaluated by considering the O···O distances. The O···O distance within the [H(OEt2)2(H2O)]+ cation between one diethyl ether molecule and water [O(9)···O(11) = 2.43(3) Å; O(10)···O(11)  119  = 2.46(3) Å] is significantly shorter than the sum of the van der Waals radii [rvdw = 3.04 Å].306 For comparison, this data is similar to the O···O distances for the known compounds containing the [H(OEt2)2]+ cation in H(OEt2)(H2O)[CHB11H5Cl6] [avg. 2.441(6) Å] and H(OEt2)2[CHB11Me5Cl6] [avg. 2.40(1) Å],195 H(OEt2)2[B(C6F5)4] [2.446(9) Å],331 H(OEt2)2[P(1,2-O2C6Cl4)3] [2.429(2) Å],269 H(OEt2)2[Zn2Cl6] [2.396(4) Å],460 H(OEt2)2[Al{OC(CF3)3}4] [2.424(5) Å],298 whilst the O···O distances in H(OEt2)2[(C3H3N2){B(C6F5)3}2] [2.395(8) Å],449 and H(OEt2)2[P(C2O4)3] [avg. 2.37(3) Å]248 are slightly shorter.  5.2.3 H(OEt2)2[5.1] and H(OEt2)2[5.2]-initiated Cationic Polymerization   The complexes H(OEt2)2[5.1] and H(OEt2)2[5.2] were investigated as initiators for the cationic polymerization of olefins at a variety of temperatures (between 18 °C to –78 °C). Chain transfer processes are suppressed in cationic polymerization by applying low temperatures resulting in higher molecular weight polymers.26,27,314 The results of the polymerization studies are given in Tables 5.1 and 5.2 and each data point is representative of two or more repeat runs. Each polymerization was performed utilizing freshly distilled solvents and monomers. The polymerization results demonstrated that the Brønsted acids H(OEt2)2[5.1] and H(OEt2)2[5.2] were effective initiators for the carbocationic polymerization of n-butyl vinyl ether (Scheme 5.3) and -methylstyrene (Scheme 5.4). H(OEt2)2[5.1] was investigated as a single–component initiator for the cationic polymerization of styrene (Scheme 5.5) and isoprene (Scheme 5.6).   120   Scheme 5.3. H(OEt2)2[5.1] and H(OEt2)2[5.2]-initiated cationic polymerization of n-butyl vinyl ether.  Vinyl ethers are ideal monomers for cationic polymerization studies since they form more stable carbocations during polymerization than many other monomers. This is due to the ether group that effectively stabilizes the propagating carbocation with strong electron donating ability. n-Butyl vinyl ether was successfully polymerized by H(OEt2)2[5.1] and H(OEt2)2[5.2]. The ambient temperature polymerization resulted in poly(n-butyl vinyl ether) as a brown viscous oil in moderate yield and reasonable molecular weight (yield: 38%, Mn = 19,800 g mol–1, Đ = 1.69, Table 5.1, entry 1; yield: 33%, Mn = 16,300 g mol–1, Đ = 1.54, Table 5.2, entry 1). For comparison, other binary initiator systems [e.g. EtAlCl2/H3C(CH2)3(O)CH(CH2)COOCH3 (Mn = 19,500 g mol–1, Đ = 1.14, T = 20 °C)] afford poly(n-butyl vinyl ether) with comparable moderate molecular weight.461 Although the polymers obtained at 18 °C and 19.3 °C were colored, the polymerizations at lower temperatures gave colorless poly(n-butyl vinyl ether). The brown color of the isolated poly(n-butyl vinyl ether) suggested that terminal conjugated polyene moieties were present. It has previously been reported that these ene functionalities were formed from proton elimination followed by dealcoholation.310-313 The 1H NMR spectra of poly(n-butyl vinyl ether) with a brown coloration produced at 18 °C and 19.3 °C using initiators H(OEt2)2[5.1] and H(OEt2)2[5.2], respectively, displayed signals in the vinyl region (5.0–6.0 ppm) that were not present in the colorless polymer produced at –84 °C (Figure 5.8).     121   At lower temperatures, the isolated yields and molecular weights of poly(n-butyl vinyl ether) each increased when similar monomer-to-initiator ratios were employed (yield: 65–71%, Mn = 25,300–39,100 g mol–1, Đ = 2.07–1.12, Table 5.1, entries 3–7; yield: 31–77%, Mn = 19,400–53,100 g mol–1, Đ = 1.69–1.14 Table 5.2, entries 2–5). Remarkably, the initiators, H(OEt2)2[5.1] and H(OEt2)2[5.2], were able to initiate n-butyl vinyl ether at temperatures as low as –84 °C and gave similar results producing poly(n-butyl vinyl ether) with moderate isolated yield, high molecular weight and narrow dispersity (Mn = 39,100 g mol–1, Đ = 1.12 and Mn = 53,100 g mol–1, Đ = 1.14, respectively). It should be noted that the molecular weights observed  were close to that predicted from the monomer-to-initiator ratio [Mn = 40,100 g mol–1 and Mn = 40,900 g mol–1, respectively] and may indicate characteristics of a living polymerization for      n-butyl vinyl ether, similar to our findings with the previously reported single–component initiator H(OEt2)2[P(1,2-O2C6Cl4)3] (–78 °C: 88%; Mn = 41,600 g mol–1, Đ = 1.11).269 Confirming the living character of n-butyl vinyl ether polymerization is beyond the scope of the present study. Living cationic polymerization of vinyl ethers has been investigated with binary initiator systems (e.g. HCl/ZnCl2 in toluene at –30 °C; HCl/ZnCl2 in CH2Cl2 at –15 °C; C9H12N6Cl6/ZnCl2 in CH2Cl2 at –45 °C).177,462,463 In contrast, the cationic polymerization of isobutyl vinyl ether and tert-butyl vinyl ether with two-component systems comprised of Lewis acids (e.g. ZnCl2, TiCl4, SnCl4, EtAlCl2) and a proton donor (e.g. CF3COOH, HCl) give low to moderate molecular weight poly(vinyl ethers) at –78 °C.464,465 Notably, these initiators afford polymers with lower molecular weights and broader dispersity than those obtained using H(OEt2)2[5.1] as initiator.    122   Figure 5.8. 1H NMR (400 MHz, CDCl3, 25 °C) spectrum of poly(n-butyl vinyl ether); polymerization performed (a) with initiator H(OEt2)2[5.1] at 18 °C, (b) with initiator H(OEt2)2[5.2] at 19.3 °C, (c) with initiator H(OEt2)2[5.1] at –84 °C.  * indicates residual CHCl3. indicates H2O residue.  123  Table 5-1. Temperature dependencies of H(OEt2)2[5.1]-initiated cationic polymerizations of n-butyl vinyl ether, -methylstyrene, styrene, and isoprene in CH2Cl2. The results shown are representative of multiple repeat runs. Entry monomer T  (°C) t  (min) [M]:[I]a yield  (%) Mnb  (g mol–1) Đ c 1 n-butyl vinyl ether 18 15 492 38  19,800 1.69 2 n-butyl vinyl ether 0 15 492 40  17,000 1.21 3 n-butyl vinyl ether –15 15 492 65  25,300 1.89 4 n-butyl vinyl ether –38 15 492 62  30,600 1.96 5 n-butyl vinyl ether –50 15 492 68  29,400 2.07 6 n-butyl vinyl ether –78 15 492 71  32,200 1.58 7 n-butyl vinyl ether –84 15 492 57  39,100 1.12         8 styrene 18 15 492 67   6,100 2.16 9 styrene 0 15 492 82   9,500 2.94 10 styrene –15 15 492 85  12,800 3.51 11 styrene –38 15 492 72 131,500 1.34 12 styrene –50 15 492 78 147,100 1.43 13 styrene –78 15 492  5 205,600 1.29         14 -methylstyrene 19 15 400  0  n.d.d n.d.d 15 -methylstyrene 0 15 400  3   5,100 1.63 16 -methylstyrene –15 15 400 45   4,800 2.37 17 -methylstyrene –38 15 400 63  10,100 1.87 18 -methylstyrene –50 15 400 84  66,400 1.81 19 -methylstyrene –78 15 400 75 279,500 1.21         20 isoprene 18 15 400 70    3,000 2.13 21 isoprene 0 15 400 52    3,200 4.84 22 isoprene –15 15 400 65    2,100 5.01 23 isoprene –38 15 400 55    2,900 1.52 24 isoprene –50 15 400 40    2,600 1.73 25 isoprene –78 15 400 4   n.d. d  n.d. d The polymerization was carried out in 2 mL CH2Cl2 solvent using 0.0075 mmol of Brønsted acid as initiator.                                  a [Monomer]/[Initiator] ratio. bAbsolute molecular weights were determined using laser light scattering gel permeation chromatography (GPC–LLS); differential refractive index (dn/dc) of poly(n-butyl vinyl ether) (dn/dc = 0.068 mL g–1.) in THF was calculated by assuming 100% mass recovery; (dn/dc) of poly(-methylstyrene) used is 0.174 mL g–1; (dn/dc) of polystyrene used is 0.185 mL g–1 and (dn/dc) of polyisoprene used is 0.129 mL g–1. c Dispersity (Đ = Mw/Mn), where Mw is the weight–average molar mass and Mn is the number–average molar mass. d Not determined.    124  Table 5-2.Temperature dependencies of H(OEt2)2[5.2]-initiated cationic polymerizations of n-butyl vinyl ether and -methylstyrene in CH2Cl2. Entry monomer T  (°C) t  (min) [M]:[I]a yield  (%) Mnb  (g mol–1) Đ c 1 n-butyl vinyl ether 19.3 15 400 33 16,300 1.54 2 n-butyl vinyl ether 0 15 400 31 19,400 1.69 3 n-butyl vinyl ether –50 15 400 61 18,200 1.57 4 n-butyl vinyl ether –78 15 400 72 34,100 1.45 5 n-butyl vinyl ether –84 15 400 77 53,100 1.14         6 -methylstyrene 19 15 400  0   n.d.d n.d.d 7 -methylstyrene 0 15 400 38    3,500 1.67 8 -methylstyrene –38 15 400 75  10,100 1.86 9 -methylstyrene –50 15 400 65  17,000 1.59 10 -methylstyrene –78 15 400 53       205,000 1.28 The polymerization was carried out in 2 mL CH2Cl2 solvent using 0.010 mmol of Brønsted acid as initiator.                                    a [Monomer]/[Initiator] ratio. b Absolute molecular weights were determined using laser light scattering gel permeation chromatography (GPC–LLS); differential refractive index (dn/dc) of poly(n-butyl vinyl ether) (dn/dc = 0.068 mL g–1.) in THF was calculated by assuming 100% mass recovery; (dn/dc) of poly(-methylstyrene) used is 0.174 mL g–1. c Dispersity (Đ = Mw/Mn), where Mw is the weight–average molar mass and Mn is the number–average molar mass. d Not determined.            125   Scheme 5.4. H(OEt2)2[5.1] and H(OEt2)2[5.2]-initiated cationic polymerization of -methylstyrene.  -Methylstyrene was successfully polymerized by using either H(OEt2)2[5.1] or H(OEt2)2[5.2] as the initiator over a range of temperatures (0 °C to –78 °C; Table 5.1, entries  15–19; Table 5.2, entries 7–10). The ceiling temperature (Tc) of -methylstyrene is around ambient temperature at which the rate of polymerization and depolymerization are equal.466,467 Thus, the ambient temperature polymerization of -methylstyrene initiated by H(OEt2)2[5.1] and H(OEt2)2[5.2] gave no polymer. This effect has also been observed using H(OEt2)2[P(1,2–O2C6Cl4)3] as initiating system269 and other binary initiators.466, 467 In particular, lowering the polymerization temperature ranging from 0 °C to –50 °C resulted in moderate to high molecular weight poly(-methylstyrene) (Mn = 5,100–66,400 g mol–1, Table 5.1, entry 15–18; Mn = 3,500–17,000 g mol–1, Table 5.2, entry 6–8) in low to good yield. The low molecular weight of poly(-methylstyrene) obtained using H(OEt2)2[5.1] and H(OEt2)2[5.2] at temperatures ranging from     0 °C to –38 °C were indicative of chain transfer and/or termination reactions. Above all, lowering the polymerization temperature to –78 °C afforded very high molecular weight polymer (Mn = 279,500 g mol–1, Đ = 1.21, yield: 75%, Table 5.1, entry 19; Mn = 205,000 g mol–1, Đ =  1.28, yield: 53%, Table 5.2, entry 10) with narrow dispersity in a moderate to good yield.   Integration of the triad signal (rr) of the 1H NMR spectra of the poly(-methylstyrene) produced at –78 °C using either H(OEt2)2[5.1] or H(OEt2)2[5.2] as initiator (Figure 5.9 and Appendix D, Figure D4) suggested a predominantly syndiotactic rich polymer (%rr = 90 and  126  %rr = 86, respectively). Similarly, syndiotactic rich poly(-methylstyrene) has been isolated with single-component initiators (e.g. H(OEt2)2[P(1,2-O2C6Cl4)3] (%rr = 87); [Ph3C][BF4] %rr = 86 and [Ph3C][SnCl6] %rr = 87)269,468 and binary initiator systems (e.g FeCl3/[nBu4NBr] %rr = 84; BI3/{(CH3)3C}2C5H3N %rr = 90; C8H17Cl/TiCl4/Et3N %rr = 94; BCl3/{(CH3)3C}2C5H3N %rr = 87).41,469-472   The cationic polymerization of -methylstyrene initiated by either H(OEt2)2[5.1] or H(OEt2)2[5.2] afforded polymer with a higher molecular weight compared to the calculated [M]:[I] ratio that suggested the presence of side reactions during polymerization. The 1H NMR spectra of poly(-methylstyrene) (Figure 5.9 and Appendix D4) displayed small signals in the vinyl region in the range between 4.0 to 6.0 ppm. These signals have previously been ascribed to vinylic protons that may result from branching caused by Friedel-Crafts alkylation/arylation and hydride transfer reactions during living cationic polymerization of styrene.320,321 In order to investigate branching in the high molecular weight polymer obtained by either H(OEt2)2[5.1] or H(OEt2)2[5.2] as initiator, the intrinsic viscosity of the samples were compared to that of a linear polystyrene standard with identical molecular weight (Mw = 105g mol–1), as a bona fide sample of linear poly(-methylstyrene) was unavailable. The intrinsic viscosity for poly(–methylstyrene) was lower than that for linear polystyrene ([]w = 67 mL g–1 vs. 76 mL g–1) that may indicate branching in the polymer. Branched polymers possess unique physical properties including viscosity and elasticity, when compared to linear polymers. The physical property of the branched polymer was not studied further.  127   Figure 5.9. 1H NMR (400 MHz, CDCl3, 25 °C) spectrum of syndiotactic-rich poly(-methylstyrene) (rr = 90%); polymerization performed with initiator H(OEt2)2[5.1] at –78 °C. * indicates residual CHCl3.   Scheme 5.5. H(OEt2)2[5.1]-initiated cationic polymerization of styrene.  Controlled cationic polymerization of styrene is challenging due to chain transfer reaction and termination.37 Unlike vinyl ethers, styrene forms a relatively unstable growing carbocation during polymerization due to weaker electron donating properties of the aryl substituent.473 Uncontrolled polymerization with broad dispersity and low molecular weight polymer has been observed with binary cationic initiators [e.g. AlCl3/CH2Cl2 (Mn = 4,400 g mol–1, Đ = 3.6, T =       128  0 °C); C6H5(C2H4)Cl/SnCl4 CH2Cl2 (Mn = 5,000 g mol–1, Đ = 3.6, T = 20 °C)].66,474 Styrene was successfully polymerized by H(OEt2)2[5.1] over a range of temperatures (18 °C to –78 °C; Table 5.1, entries 8–13). The ambient temperature polymerization afforded an off-white polymer in moderate yield with low molecular weight (18 °C: 67%; Mn = 6,100 g mol–1, Đ = 2.16; Table 5.2, entry 8). These data are typical of styrene polymers obtained when prepared at higher temperatures. Notably, at lower temperatures (–38 °C to –50 °C) high molecular weight polystyrene was obtained (Mn = 131,500–147,100 g mol–1, Đ = 1.34–1.43; Table 5.1, entries   11–12) as a colorless solid in high yield (ca. 72–78%). The single-component system H(OEt2)2[P(1,2-O2C6Cl4)3] afforded polystyrene with lower molecular weight (Mn = 37,800         g mol–1, Đ = 1.88, [M]:[I] = 493)269 opposed to H(OEt2)2[5.1] at –50 °C with the same monomer-to-initiator ratio.   The 1H NMR spectrum of polystyrene produced at –50 °C displayed small signals in the vinyl region between 4.0–6.2 ppm (Figure 5.10). These signals have previously been attributed to vinylic protons that may result from branching caused by Friedel-Crafts alkylation/arylation and hydride transfer reactions during living cationic polymerization of styrene.320, 321 Branching due to chain transfer in polystyrene has been reported when using stannic chloride as the initiator at 0 °C and higher molecular weights were obtained than that calculated from the [M]:[I] ratio (Mw up to 149,000 g mol–1).42-44,319 A lower intrinsic viscosity was obtained for polystyrene afforded by H(OEt2)2[5.1] compared to that of a linear polystyrene standard ([]w = 63 mL g–1 vs. 76 mL g–1) that may indicate branching in the polymer. It should be noted that samples with the same molecular weight (Mw = 105 g mol–1) were used. The tacticity of polystyrene produced at –50 °C was investigated by 13C{1H} NMR spectroscopy. The analysis of the resonances for the aromatic and methylene carbon regions was consistent with that of atactic polystyrene.  129  Remarkably, the polymerization at –78 °C afforded the highest molecular weight polymer with a narrow dispersity (Mn = 205,600 g mol–1, Đ = 1.29, Table 5.1, entry 13), albeit in low yield (5%). At this temperature, the initiator, H(OEt2)2[5.1], shows limited capability to polymerize styrene. Similarly, this effect has been noticed with the single component initiator H(OEt2)2[P(1,2–O2C6Cl4)3].269 Lower molecular weight polystyrene in higher dispersity has been observed with other cationic initiators at –80 °C (e.g. (C6H5C(CH3)3OH/AlCl3OBu2/Py, Mn = 82,000 g mol–1,  Đ = 1.80; yield: ca. 35%). However, the polymer revealed a broader dispersity compared to the H(OEt2)2[5.1]-initiated polystyrene.475   Figure 5.10. 1H NMR (400 MHz, CDCl3, 25 °C) spectrum of polystyrene; polymerization performed with initiator H(OEt2)2[5.1] at –50 °C. * indicates residual CHCl3 and CH2Cl2.  indicates H2O residue.     130   Scheme 5.6. H(OEt2)2[5.1]–initiated cationic polymerization of isoprene.  The cationic polymerization of isoprene is a challenging reaction and the polymerization mechanism has not been fully elucidated. Controlled or living cationic polymerization of isoprene is demanding due to side reactions, including chain transfer, cyclization, and cross–linking reactions.476,477 Low molecular weight polyisoprene or oligomeric polymer have been observed with the single-component initiator H(OEt2)2[P(1,2–O2C6Cl4)3] (Mn = 5,500 g mol–1)269 and other binary systems (e.g. BF3OEt2/CCl3COOH, TiCl4/CCl3COOH, ZnBr/CCl3COOH, B(C6F5)3/CH3OC6H4CH2CH2OH, B(C6F5)3/C6H10CHCH2OH, B(C6F5)3/CH2Cl2 with Mn = 680 to 8,800 g mol–1).275,478,479 Similarly, the polymerization of isoprene initiated by H(OEt2)2[5.1] at  18 °C afforded low molecular weight polyisoprene as a pale yellow solid with broad dispersity (Mn = 3,000 g mol–1, Đ = 2.13, Table 5.1, entry 20). It should be noted that a small fraction of the polymer sample was soluble in THF solution and only the soluble fraction was utilized for GPC analysis.  At lower temperatures (–38 °C to –50 °C), side reactions were reduced and resulted in polymer with narrower dispersity. However, chain transfer processes were not fully suppressed, thereby compromising molecular weight and yield of oligoisoprene. Only traces of polymer were isolated when the polymerization was performed at –78 °C (Table 5.1, entry 25), likely a consequence of the limited initiation capability of H(OEt2)2[5.1]. For comparison, the        single–component initiator H(OEt2)2[P(1,2-O2C6Cl4)3] gave polyisoprene of moderate molecular weight and yield at –38 °C (Mn = 11,600 to g mol–1; yield 56%). At lower polymerization temperatures the initiator was not active.269 In contrast, other binary initiators (e.g. TiCl4/tBuCl  131  and TiCl4/CCl3COOH) afford low to moderate molecular weight polyisoprene at –78 °C, albeit with broader dispersity (Mn = 6,400–16,200 g mol–1, Đ = 3.6 to 21.5; yield: 35 to 37%).480,481  Analysis of the H(OEt2)2[5.1]–initiated oligoisoprene at –50 °C by 1H-NMR spectroscopy revealed signals associated with 1,4–unit [δ (CH) = 5.0–5.1; δ (CH2) = 2.1–2.2;       δ (CH3) = 1.6], 3,4–unit [δ (CH2) = 4.6–4.8] and 1,2–unit [δ (CH2) = 4.8–5.0]. In addition, a broad signal detected between 0.7 and 0.9 ppm was presumably assignable to cyclized or branched units that have been commonly observed for cationic polymerized polyisoprene.275,482-485 Analysis of the 13C{1H} NMR spectrum (Figure 5.11) elucidated methyl carbon atom signals attributed to predominantly trans–1,4 unit (δ = 15.6) and minor signals were detected for the cis–1,4 unit (δ = 23.4), 3,4–unit (δ = 18.3) and 1,2–unit (δ = 22.2). A signal was observed at 13.6 ppm that has also been detected in polyisoprene obtained from two–component systems and is associated with the signal for the methyl group of the cyclic or branched structure.483  H(OEt2)2[5.1]-initiated cationic polymerization at varying monomer-to-initiator ratios:  The effect of monomer-to-initiator ratio on the performance of the initiator H(OEt2)2[5.1] was investigated. The cationic polymerizations of n-butyl vinyl ether and styrene were conducted at temperatures that gave the highest molecular weight polymer. Increasing the monomer-to- initiator ratio remarkably afforded poly(n-butyl vinyl ether) with increased molecular weight and low dispersity (Table 5.3, entries 1–3). The refractive index traces displayed unimodal distribution. In contrast, increasing the monomer-to-initiator ratio for the polymerization of styrene at –50 °C did not result in an increase in molecular weight and may indicate a chain transfer to monomer process.    132   Figure 5.11. 13C{1H} NMR (101 MHz, CDCl3, 45 °C) spectrum of oligoisoprene; polymerization performed with initiator H(OEt2)2[5.1] at 18 °C.  Methyl group of cyclic or branched structure.        133  Table 5-3. H(OEt2)2[5.1]-initiated cationic polymerizations of n-butyl vinyl ether and styrene in CH2Cl2 with varying monomer-to-initiator ratio.  entry Monomer T  (°C) t  (min) [M]:[I]a yield  (%) Mnb  (g mol–1) Đ c 1 n-butyl vinyl ether –84 15 200 29  34,200 1.24 2 n-butyl vinyl ether –84 15 492 57  39,100 1.12 3 n-butyl vinyl ether –84 15 800 44  73,300 1.13         4 Styrene  –50 15 200 72 147,100 1.37 5 Styrene –50 15 492 78 147,100 1.43 6 Styrene –50 15 800 72 106,000 1.76 The polymerization was carried out in 2 mL CH2Cl2 solvent using 0.0075 mmol of Brønsted acid as initiator. a [Monomer]/[Initiator] ratio. b Absolute molecular weights were determined using laser light scattering gel permeation chromatography (GPC–LLS); differential refractive index (dn/dc) of poly(n-butyl vinyl ether) (dn/dc = 0.068 mL g–1) in THF was calculated by assuming 100% mass recovery; (dn/dc) of polystyrene used is 0.185 mL g–1. c Dispersity (Đ = Mw/Mn), where Mw is the weight–average molar mass and Mn is the number–average molar mass.   Effect of H2O addition on the H(OEt2)2[5.1]-initiated cationic polymerization of styrene:  The stability of the single component initiator H(OEt2)2[5.1] during the cationic polymerization of styrene was investigated under the influence of traces of water. Various amounts of distilled H2O were added to a CH2Cl2 solution containing the initiator H(OEt2)2[5.1] at –50 °C. The results are demonstrated in Table 5.4 (entries 1–5). As the amount of added H2O was increased, the molecular weight and yield of polystyrene were significantly reduced and an increase in the dispersity was observed. The nature and stability of the initiator is highly influenced by the amount of H2O and has a significant effect on the cationic polymerization of styrene, leading to chain transfer and termination process. Therefore, it is of utmost importance to carry out the cationic polymerization of olefin monomers, initiated by single-component systems, under an inert atmosphere with dry solvent.   134  Table 5-4. H(OEt2)2[5.1]-initiated cationic polymerizations of styrene in CH2Cl2 with varying amounts of added H2O (L). Entry monomer T  (°C) H2O (L) [M]:[I]a yield  (%) Mnb  (g mol–1) Đ 1 styrene –50 0 492 78 145,000 1.43 2 styrene –50 1 492 1.6   54,800 1.42 3 styrene –50 5 492 0.9   67,700 1.58 4 styrene –50 10 492 0.8   59,900 1.62 5 styrene –50 100 492 0.6   47,110 1.84 The polymerization was carried out in 2 mL CH2Cl2 solvent using 0.0075 mmol of Brønsted acid as initiator. a [Monomer]/[Initiator] ratio. b Absolute molecular weights were determined using laser light scattering gel permeation chromatography (GPC–LLS); differential refractive index (dn/dc) of polystyrene used is 0.185 mL g–1. c Dispersity (Đ = Mw/Mn), where Mw is the weight–average molar mass and Mn is the number–average molar mass.   5.3 Summary In this chapter, the synthesis and characterization of unprecedented solid and weighable Brønsted acids, H(OEt2)2[5.1] and H(OEt2)2[5.2], comprised of weakly coordinating Ta(V)–containing anions were presented. Particularly intriguing is the reaction of TaCl5 with tetrachlorocatechol (4 equiv) that resulted in the product H(OEt2)2[5.1]. X-ray crystallographic analysis, however, elucidated the formation of H(OEt2)(H2O)[5.1]. The compound H(OEt2)2[5.2] was isolated by treating TaCl5 with tetrachlorocatechol (3 equiv). The complexes H(OEt2)2[5.1] and H(OEt2)2[5.2] were characterized by NMR spectroscopy and elemental analysis. The Brønsted acids have proven to be highly effective single–component initiators for the cationic polymerization of vinyl monomers at various temperatures. The H(OEt2)2[5.1] and H(OEt2)2[5.2]-initiated polymerization of n-butyl vinyl ether at low temperatures revealed moderate molecular weight poly(n-butyl vinyl ether) with low dispersity that is close to the calculated molecular weight. The polymerization of -methylstyrene initiated by H(OEt2)2[5.1] and H(OEt2)2[5.2] gave high molecular weight syndiotactic rich poly(-methylstyrene) in good  135  yield. The Brønsted acid H(OEt2)2[5.1] is an effective single-component initiator for the polymerization of styrene to give polystyrene of high molecular weight at –50 °C with moderate yield and dispersity. Remarkably, the same initiator, H(OEt2)2[5.1], was able to polymerize isoprene at various temperatures and generated oligoisoprene in moderate yield.  5.4 Experimental 5.4.1 General Procedures  All experiments were performed using standard Schlenk or glove box techniques under nitrogen atmosphere. CH2Cl2 (Sigma Aldrich) and Et2O (Fisher Scientific) were deoxygenated with nitrogen and dried by passing the solvents through a column containing activated, basic alumina. Subsequently, CH2Cl2 and Et2O were dried over CaH2, freshly distilled, and freeze-pump-thaw (x3) degassed. For extended periods of storage (1 day to 2 weeks), anhydrous solvents were stored over 3 Å molecular sieves. THF (Fisher Scientific) was freshly distilled from sodium/benzophenone ketyl immediately prior to use. Styrene (Sigma Aldrich) and n-butyl vinyl ether (Sigma Aldrich) were dried over calcium hydride, distilled and freeze-pump-thaw (x3) degassed prior to use. Tantalum pentachloride (Sigma Aldrich) was used without further purification. Tetrachlorocatechol was prepared following a literature procedure486 and azeotropically distilled and recrystallized from hot toluene prior to use.   Mass spectrometry, NMR spectra, X-ray crystallography, elemental analysis and GPC analysis were performed in the Chemistry Department Facilities. 1H and 13C{1H} NMR spectra were recorded on Bruker Avance 400 MHz spectrometers at ambient temperature unless noted. 1H NMR and 13C{1H} NMR spectra were referenced to deuterated solvents. Molecular weight of poly(n-butyl vinyl ether) was determined by triple detection gel permeation chromatography  136  (GPC-LLS) utilizing an Agilent 1260 Series standard auto sampler, an Agilent 1260 series isocractic pump, Phenomenex Phenogel 5 μm narrowbore columns (4.6 x 300 mm) 104 Å (5000-500,000), 500 Å (1,000-15,000), and 103 Å (1,000-75,000), Wyatt Optilab rEx differential refractometer (λ = 658 nm, 25 °C), as well as Wyatt tristar miniDAWN (laser light scattering detector (λ = 690 nm)) and a Wyatt ViscoStar viscometer. Samples were dissolved in THF (ca. 2 mg mL–1) and a flow rate of 0.5 mL min–1 was applied. The differential refractive index (dn/dc) of poly(n-butyl vinyl ether) (dn/dc = 0.068 mL g–1) in THF was calculated by using Wyatt ASTRA software 6.1 assuming 100 % mass recovery. The differential refractive indices (dn/dc) of polystyrene (dn/dc = 0.185 mL g–1), poly(-methylstyrene) (dn/dc = 0.204 mL g–1)487 and of polyisoprene (dn/dc = 0.129 mL g–1)488 have been reported.  5.4.2 Synthesis of H(OEt2)2[5.1] TaCl5 (0.53 g, 1.48 mmol) was stirred in anhydrous CH2Cl2 (10 mL) and the white suspension was slowly heated to reflux under N2 atmosphere. In another Schlenk flask, tetrachlorocatechol (1.48 g, 5.99 mmol) was prepared in warm anhydrous CH2Cl2 (14 mL) and the bright orange-red solution was added via cannula to the refluxing TaCl5 solution at 90 °C to afford a dark green reaction mixture. After 10 min, a faint green precipitate was obtained. The reaction mixture was refluxed for 80 min and cooled to ambient temperature. Upon addition of Et2O (25 mL), a green clear solution formed. The solution was cooled in an ice bath to afford a colorless precipitate within 15 min. The solid was collected by filtration, washed with CH2Cl2 (5 mL) and dried in vacuo. Yield = 1.13 g, 0.85 mmol, 57 % based on TaCl5. A concentrated solution of the crude product in CH2Cl2 afforded colorless crystals of H(OEt2)2(H2O)[Ta(1,2-O2C6Cl4)2(1,2– 137  O(OH)C6Cl4)2] (–30 °C, ca. 3 d). A crystal was removed for X-ray crystallographic analysis without drying. 1H NMR (400 MHz, CD2Cl2, 25 C): δ = 9.37 (br, OH), 4.00 (q, 3JHH= 7.1 Hz, 8H, OCH2CH3), 1.40 ppm (t, 3JHH=7.1 Hz, 12H, OCH2CH3); 1H NMR (400 MHz, CD2Cl2, –85 C): δ = 16.73 (s, 1H, H(OEt2)2), 9.40 (s, 1H, OH), 4.03 (q, 3JHH= 7.0 Hz, 8H, OCH2CH3), 1.38 (t, 3JHH= 7.1 Hz, 12H, OCH2CH3); 13C{1H} NMR (75 MHz, CD2Cl2, –85 C): δ = 149.9 (s, Ar–C), 145.3 (s,      Ar–C) , 144.3 (s, Ar–C), 139.8 (s, Ar–C), 124.9 (s, Ar–C), 121.6 (s, Ar–C), 121.1 (s, Ar–C), 118.6 (s, Ar–C), 116.7 (s, Ar–C), 70.3 (s, OCH2CH3), 13.3 (s, OCH2CH3) ppm; elem. anal. calcd for C33H26Cl16O10Ta·1.4 CH2Cl2: C, 28.50; H, 2.00; found: C, 28.30; H, 1.80.  5.4.3 Synthesis of H(OEt2)2[5.2] TaCl5 (0.48 g, 13.4 mmol) was stirred in anhydrous CH2Cl2 (6 mL) and the white suspension was slowly heated to reflux under N2 atmosphere. In another Schlenk flask, tetrachlorocatechol (1.00 g, 40.3 mmol) was prepared in warm anhydrous CH2Cl2 (6 mL) and the bright orange-red solution was added via cannula to the refluxing TaCl5 solution at 90 °C to afford a dark green reaction mixture. After 10 min, a faint green precipitate was obtained. The reaction mixture was refluxed for 100 min and cooled to ambient temperature. Upon addition of Et2O (22 mL), a green clear solution formed. The solution was cooled in an ice bath to afford a colorless precipitate within 20 min. The solid was collected by filtration, washed with CH2Cl2 (3 mL) and dried in vacuo. Yield = 1.28 g, 11.9 mmol, 89 % based on TaCl5.  1H NMR (400 MHz, CD2Cl2, 25 C): δ = 7.54 (br, 1H, H(OEt2)2), 4.00 (br, 8H, OCH2CH3), 1.40 ppm (br, 12H, OCH2CH3); 1H NMR (400 MHz, CD2Cl2, –85 C): δ = 16.74 (s, 1H, H(OEt2)2),  138  4.04 (br, 8H, OCH2CH3), 1.38 (br, 12H, OCH2CH3); 13C{1H} NMR (75 MHz, CD2Cl2, 25 C): δ = 140.4 (s, Ar–C), 123.4 (s, Ar–C), 118.9 (s, Ar–C), 67.9 (s, OCH2CH3), 14.2 (s, OCH2CH3) ppm; elem. anal. calcd for C26H21Cl12O8Ta·1.35 CH2Cl2: C, 27.78; H, 2.02; found: C, 27.51; H, 1.74.; MALDI–TOF MS (355 nm) m/z = 918.6 [M]–.  5.4.4 Representative H(OEt2)2[5.1]-initiated Polymerization of n-Butyl Vinyl Ether In a glovebox, freshly distilled, degassed CH2Cl2 (2 mL) was added to H(OEt2)2[5.1] (0.010 g, 0.008 mmol) in a 10 mL Schlenk flask. The flask was removed from the glovebox and cooled to –78 C. Freshly distilled, n-butyl vinyl ether (0.37 g, 3.70 mmol, 0.49 mL) was prepared in a syringe, removed from the glovebox and added rapidly to the initiator solution. After 15 min, the polymerization was quenched with a solution of NH4OH in MeOH (0.2 mL, 10 vol%) and all volatiles were removed in vacuo. The crude product was dissolved in CH2Cl2 (2 mL) and added one drop at a time to stirred MeOH (40 mL) to precipitate a yellow oily residue. The polymer was collected by centrifugation and dried in vacuo. Yield = 0.27 g, 71 %. The isolated material was analyzed by 1H NMR spectroscopy (400 MHz, CDCl3, 25 C): δ = 3.52–3.36 (br, CH2CH(O(CH2)3CH3)CH2), 1.86–1.39 (br, OCH2CH2CH2), 0.93 (t, CH3). GPC–MALS (THF): Mn = 32,200 g mol–1, Đ = 1.58.  5.4.5 Representative H(OEt2)2[5.1]-initiated Polymerization of Styrene  In a glovebox, freshly distilled, degassed CH2Cl2 (2 mL) was added to H(OEt2)2[5.1] (0.010 g, 0.008 mmol) in a 10 mL Schlenk flask. The flask was removed from the glovebox and cooled to –15 C. Freshly distilled styrene (0.38 g, 3.70 mmol, 0.34 mL) was prepared in a syringe, removed from the glovebox and added rapidly to the initiator solution. After 15 min, the  139  polymerization was quenched with a solution of NH4OH in MeOH (0.2 mL, 10 vol%) and all volatiles were removed in vacuo. The crude product was dissolved in CH2Cl2 (2 mL) and added one drop at a time to stirred MeOH (40 mL) to precipitate a colorless residue. The polymer was collected by centrifugation and dried in vacuo. Yield = 0.33 g, 85 %. The isolated material was analyzed by 1H NMR spectroscopy (400 MHz, CDCl3, 25 C): δ = 7.11–6.39 (br, Ar-H), 2.22–1.46 (br, CH2CH(Ar-H)CH2CH2). GPC–MALS (THF): Mn = 12,800 g mol–1, Đ = 3.51.  5.4.6 Representative H(OEt2)2[5.1]-initiated Polymerization of -Methylstyrene  In a glovebox, freshly distilled, degassed CH2Cl2 (2 mL) was added to H(OEt2)2[5.1] (0.010 g, 0.008 mmol) in a 10 mL Schlenk flask. The flask was removed from the glovebox and cooled to –50 C. Freshly distilled, -methylstyrene (0.35 g, 3.00 mmol, 0.39 mL) was prepared in a syringe, removed from the glovebox and added rapidly to the initiator solution. After 15 min, the polymerization was quenched with a solution of NH4OH in MeOH (0.2 mL, 10 vol%), and all volatiles were removed in vacuo. The crude product was dissolved in CH2Cl2 (2 mL) and added one drop at a time to stirred MeOH (40 mL) to precipitate a colorless residue. The polymer was collected by centrifugation and dried in vacuo. Yield = 0.30 g, 84%. The isolated material was analyzed by 1H NMR spectroscopy (400 MHz, CDCl3, 25 C): δ = 7.15–6.69 (br, Ar–H), 1.56–1.53 (br, CH2CH2CH(Ar–H)CH3), 0.91 (t, CH3CH(Ar-H)CH2CH2). GPC–MALS (THF): Mn = 66,400 g mol–1, Đ = 1.81.   5.4.7 Representative H(OEt2)2[5.1]-initiated Polymerization of Isoprene In a glovebox, freshly distilled, degassed CH2Cl2 (2 mL) was added to H(OEt2)2[5.1] (0.010 g, 0.008 mmol) in a 10 mL Schlenk flask. The flask was removed from the glovebox and cooled to  140  0 C. Freshly distilled, isoprene (0.20 g, 3.00 mmol, 0.31 mL) was prepared in a syringe, removed from the glovebox and added rapidly to the initiator solution. After 15 min, the polymerization was quenched with a solution of NH4OH in MeOH (0.2 mL, 10 vol%), and all volatiles were removed in vacuo. The crude product was dissolved in CH2Cl2 (2 mL) and added one drop at a time to stirred MeOH (40 mL) to precipitate a light brown residue. The polymer was collected by centrifugation and dried in vacuo. Yield = 0.11 g, 52 %. The isolated material was analyzed by 1H NMR and 13C-NMR spectroscopy. The isolated material was analyzed by GPC-MALS (THF): Mn = 3,200 g mol–1, Đ = 4.84.  5.4.8 Representative H(OEt2)2[5.2]-initiated Polymerization of n-Butyl Vinyl Ether  In a glovebox, freshly distilled, degassed CH2Cl2 (2 mL) was added to H(OEt2)2[5.2] (0.011 g, 0.010 mmol) in a 10 mL Schlenk flask. The flask was removed from the glovebox and cooled to –78 C. Freshly distilled, n-butyl vinyl ether (0.41 g, 4.10 mmol, 0.54 mL) was prepared in a syringe, removed from the glovebox and added rapidly to the initiator solution. After 15 min, the polymerization was quenched with a solution of NH4OH in MeOH (0.2 mL, 10 vol%) and all volatiles were removed in vacuo. The crude product was dissolved in CH2Cl2 (2 mL) and added one drop at a time to stirred MeOH (40 mL) to precipitate a colorless oily residue. The polymer was collected by centrifugation and dried in vacuo. Yield = 0.29 g, 72 %. The isolated material was analyzed by 1H NMR spectroscopy (400 MHz, CDCl3, 25 C): δ = 3.53–3.37 (br, CH2CH(O(CH2)3CH3)CH2), 1.87–1.39 (br, OCH2CH2CH2), 0.93 (t, CH3). GPC–MALS (THF): Mn = 34,100 g mol–1, Đ = 1.45.   141  5.4.9 Representative H(OEt2)2[5.2]-initiated Polymerization of -Methylstyrene  In a glovebox, freshly distilled, degassed CH2Cl2 (2 mL) was added to H(OEt2)2[5.2] (0.011 g, 0.010 mmol) in a 10 mL Schlenk flask. The flask was removed from the glovebox and cooled to –78 C. Freshly distilled, -methylstyrene (0.48 g, 4.10 mmol, 0.54 mL) was prepared in a syringe, removed from the glovebox and added rapidly to the initiator solution. After 15 min, the polymerization was quenched with a solution of NH4OH in MeOH (0.2 mL, 10 vol%) and all volatiles were removed in vacuo. The crude product was dissolved in CH2Cl2 (2 mL) and added one drop at a time to stirred MeOH (40 mL) to precipitate a colorless residue. The polymer was collected by centrifugation and dried in vacuo. Yield = 0.26 g, 53%. The isolated material was analyzed by 1H NMR spectroscopy (400 MHz, CDCl3, 25 C): δ = 7.17–6.67 (br, Ar–H), 1.61–1.53 (br, CH2CH2CH(Ar–H)CH3), 0.07 (t, CH3CH(Ar–H)CH2CH2). GPC–MALS (THF): Mn = 205,000 g mol–1, Đ = 1.28.   5.4.10 X-ray Structure Determination of H(OEt2)2(H2O)[5.1]  X-ray crystallography data were collected on a Bruker X8 APEX II diffractometer with graphite-monochromated Mo K radiation. A single marginal crystal was immersed in oil and mounted on a glass fiber. Data were collected with 120 s exposure and integrated using the Bruker SAINT software package and corrected for absorption effect using SADABS.325,326 All structures were solved by direct methods and subsequent Fourier difference techniques. The material crystallizes with one molecule of water and two molecules of diethyl ether in the asymmetric unit. A hydrogen atom situated between a water molecule and an ether molecule was located in a difference map and refined isotropically. All other O—H hydrogen atoms were placed in calculated positions. All C—H hydrogen atoms were placed in calculated positions. All  142  non-hydrogen atoms were refined anisotropically. All refinements were performed using the SHELXL-2015328 via the Olex2 interface.329  Table 5-5. X-ray crystallographic parameters for H(OEt2)(H2O)[5.1].  H(OEt2)(H2O)[5.1]·OEt2·0.17 CH2Cl2 formula  C32H25O11Cl16Ta Fw  1333.67 crystal size (mm)  0.12 x 0.15 x 0.25 colour  Colorless cell setting  Monoclinic space group  P 21/c  a (Å)  10.3993(9) b (Å)  29.634(3) c (Å)  15.4817(14) α (°)  90  β (°)  108.100(2) γ (°)  90  V (Å3)  3708.8(10) Z  4 ρcalcd (g cm-3)  1.953 F(000)  2600.00  μ (MoKα) (mm-1)  34.21  2θ max (°)  45.6  total no. of reflns  32468  no. of unique reflns  6060  no. of reflns  15262  no. of variables  667  R1 (F, I > 2σ(I))  0.116  wR2 (F2, all data)  0.286 goodness of fit  1.24  a R1 = Σ||Fo| - |Fc||/Σ|Fo|. b wR2(F2[all data]) = {Σ[w(Fo2 - Fc2)2]/Σ[w(Fo2)2]}1/2.     143  Chapter 6: Conclusion and Future Work  6.1 Introduction  The main goal of this dissertation was the isolation of solid weighable Brønsted acids as single–component initiator systems for the cationic polymerization of olefin monomers. In addition, the aim was to obtain high molecular weight polymers at higher temperatures than        –100 C. The initiator system requires a WCA that stabilizes the reactive carbocation during cationic polymerization. Substantial studies have been performed in the development of WCAs based on group 13 elements, dominated by tetracoordinate boron and aluminum anion analogues.68-70,84,151 Therefore, it was postulated that hexacoordinate phosphorus(V) anions facilitate the design of large and more charge-delocalized anions and thus, sought to be weakly coordinating.   6.2 Hexacoordinate WCAs  Chapter 2 described the one–pot reaction of PCl5 with tetrachlorocatechol to afford the compound H(L)2[6.1] (L = DMF, THF, CH3CN) in the presence of weak donor solvents (Scheme 6.1). The Brønsted acids H(L)2[6.1] incorporated the weakly coordinating phosphorus(V)-based [TRISPHAT]– anion, [6.1]–. The integrity of the [H(L)2]+ moiety (L = DMF, THF) in solution was investigated. The low temperature 1H-1H-NOESY NMR spectrum elucidated positive NOE for H(THF)2[6.1] and negative NOE for H(DMF)2[6.1]. The compounds H(DMF)2[6.1], H(THF)2[6.1] and H(THF)(CH3CN)[6.1] are isolable and weighable Brønsted acids. In particular, H(DMF)2[6.1] and H(THF)2[6.1] were employed as effective single–component initiators for the cationic polymerization of n-butyl vinyl ether and                  144  p-methoxystyrene at various temperatures. Remarkably, H(THF)2[6.1] afforded high molecular weight poly(p-methoxystyrene) with Mn up to 649,000 g mol–1 at –78 °C. The unexpected high molecular weight might arise from branching of the poly(p-methoxystyrene) through either Friedel-Crafts alkylation/arylation or hydride transfer. The physical properties (for example Tg or Tm) of the branched polymer were not studied and are of interest and may be investigated further.     Scheme 6.1. Synthesis of Brønsted acid H(L)2[6.1] (L = DMF, THF).  The main objective of Chapter 3 was the search of an alternative for the WCA [6.1]– to ultimately access new Brønsted acids for the cationic polymerization of olefin monomers. Despite that Brønsted acids containing the anion [6.3]– were not isolated, intriguing research findings have been harvested in exploring the WCA potential of [6.3]–. Chapter 3 outlined three potential routes to afford Hellwinkel′s salt, [6.2][6.3], that features a P–C-containing anion. In addition to the desired compound, an unexpected complex cation was isolated incorporating an alternative cation [6.2']+, with a “twist”, that was formally derived from the insertion of an additional biphenyl unit into [6.2]+ and the phosphorus(V)-containing WCA [6.3]–. The insertion product was observed by direct lithiation of biphenyl, 2,2'–diidobiphenyl and                           145  2,2'–dibromobiphenyl. A pentavalent phosphorane P(C12H8)2(C24H9) was isolated and characterized.   The application of the WCA [6.3]– in the stabilization of highly reactive cations is of interest. In order to decrease the nucleophilicity of the anion [6.3]–, it may be possible to introduce halogenated biphenyls and investigate the development of halogenated P–C containing WCAs. The incorporation of electron withdrawing fluorinated aryl groups to afford anions of type [6.4]– with a charge-balancing [PhNMe2H]+ cation has been mentioned in a patent application and these systems have been employed as activators in metallocene-based coordination polymerization. Detailed characterization of the activator was not reported.353 As an extension to the work reported in this thesis, future work might be aimed at generating Brønsted acids of anion [6.4]– as outlined in Scheme 6.2.  Scheme 6.2. Proposed synthetic route of compound Li[6.4] and H(L)2[6.4] (L = DMF or Et2O).  146   Chapter 4 described the synthesis and characterization of [NbaseH]–mer–[6.5] (Nbase = PhNMe2, PhNH2, py, isoquinoline, (–)-brucine, N(n-C8H17)3) and K–rac–mer–[6.5] featuring the hexacoordinate phosphorus(V) anion mer–[6.5]–. The molecular structure of K–rac–mer–[6.5] elucidated a coordination polymer. The 31P{1H} NMR spectrum of [(–)-brucineH]–rac–mer–[6.5] recorded in CD2Cl2 solution revealed signals for one pair of diastereomers. Further, the development towards Brønsted acids containing the anion mer–[6.5]– have been alluded to in Chapter 4. The weakly coordinating character of mer–[6.5]– was investigated. The basicity of mer–[6.5]– was determined by comparing the N–H stretching vibration of [(n-C8H17)3NH]–mer–[6.5] in CCl4 solution with the N–H stretching frequency of tri(n-octyl)ammonium salts of several weakly basic anions utilizing IR spectroscopy. The basicity of the anion mer–[6.5]– in [(n-C8H17)3NH]–mer–[6.5] was found to be similar to the anions [ClO4]– and [N(SO2CF3)2]–, respectively.     A potential future direction in this area involves the incorporation of halogenated substituents to provide additional delocalization properties to the anion, thereby significantly lowering the donor ability of the halogenated version of [6.5]–.  Chapter 5 described the synthesis and characterization of solid and weighable Brønsted acids, H(OEt2)2[6.6] and H(OEt2)2[6.7], comprised of unprecedented weakly coordinating   Ta(V)–containing anions. Particularly intriguing was the reaction of TaCl5 with different  147  amounts of tetrachlorocatechol that resulted in the products H(OEt2)2[6.6] and H(OEt2)2[6.7], respectively, (Scheme 6.3). The Brønsted acids have proven to be highly effective               single–component initiators for the cationic polymerization of vinyl monomers at various temperatures. The H(OEt2)2[6.6] and H(OEt2)2[6.7]-initiated polymerization of n-butyl vinyl ether at low temperatures revealed moderate molecular weight poly(n-butyl vinyl ether) with narrow dispersity that is close to the calculated molecular weight. The living cationic polymerization was not explored further within the research contained in this thesis and might be of interest. The living cationic polymerization study of vinyl ethers might allow for the synthesis of block copolymers with intriguing physical properties.  Scheme 6.3. Synthesis of Brønsted acids H(OEt2)2[6.6] and H(OEt2)2[6.7].  The polymerization of -methylstyrene initiated by H(OEt2)2[6.6] and H(OEt2)2[6.7] gave high molecular weight syndiotactic rich poly(-methylstyrene) (Mn up to 279,000 g mol–1, rr up to 90%). The Brønsted acid H(OEt2)2[6.6] was an effective single-component initiator for the polymerization of styrene to give polystyrene of high molecular weight (Mn up to 147,000 g mol–1) at –50 °C. Remarkably, H(OEt2)2[6.6] was able to polymerize isoprene at various temperatures. In conclusion, the strong Brønsted acids H(OEt2)2[6.6] and H(OEt2)2[6.7] have provided access to high molecular weight polymers at higher temperatures than –100 C. The development of tantalum(V)-containing WCAs, [6.6]– and [6.7]–, has opened a new avenue in  148  exploring the design of large charge delocalized WCAs. The investigation of the basicity of the unprecedented anions [6.6]– and [6.7]– is of importance. Future work should consider the isolation of the salts [(n-C8H17)3NH][6.6] and [(n-C8H17)3NH][6.7] to determine the basicity of the anions [6.6]– and [6.7]– on the IR scale that can be compared to existing WCAs. The acidity of the Brønsted acids H(OEt2)2[6.6] and H(OEt2)2[6.7] could be determined by applying Krossing’s recently reported unified Brønsted acidity scale.489 Further, the reactivity of the Brønsted acids H(L)2[6.6] and H(L)2[6.7] as single-component initiators for the cationic polymerization of olefin monomers may be investigated with different ethers.  6.3 Concluding Remarks By this point, the reader will acknowledge that crafting an ideal WCA for the stabilization of reactive cations is challenging. The research work contained within this dissertation has made an impact in the development of WCAs.   149  References (1) Morton, M. Rubber Technology, 3rd ed.; Van Nostrand Reinhold: New York, 1987. (2) Mark, J. E.; Erman, B.; Eirich, F. R. Science and Technology of Rubber, 3rd ed.; Elsevier  Inc.: Boston, 2005. (3) Kush, A.; Goyvaerts, E.; Chye, M.-L.; Chua, N.-H. Proc. Natl. Acad. Sci. U.S.A. 1990,  87, 1787. (4) Van Beilen, J. B.; Poirier, Y. Plant J. 2008, 54, 684. 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(*) indicates CH3CN-d3 solvent.          170    Figure A.5. 1H–1H NOESY (400 MHz, CD2Cl2, –85 °C) spectrum of H(DMF)2[2.1].  * indicates residual CHDCl2 solvent.   171    Figure A.6. 1H–1H ROESY (400 MHz, CD2Cl2, –85 °C) spectrum of H(DMF)2[2.1]. * indicates residual CHDCl2 solvent.  172    Figure A.7. 1H–1H ROESY (400 MHz, CD2Cl2, –85 °C) spectrum of H(THF)2[2.1]. * indicates residual CHDCl2. † indicates residual toluene solvent.    173  Appendix B    B.1 Supplementary Spectra for Chapter 3   Figure B.1. LRMS (ESI; positive mode) mass spectrum of [3.1]+ and [3.1']+ via Route A.    174    Figure B.2. LRMS (ESI; negative mode) mass spectrum of [3.2]– via Route A .    175   Figure B.3. Crystal packing of the molecular structure of [3.1'][3.2] is shown with 2 unit cells along the b axis (x,y,z). Solvent molecules have been omitted for clarity. Ellipsoids are drawn at the 50 % probability level. Dashed bonds represent H-bond interactions (green = H···H interaction and black = C···H interaction). Black = carbon atom, red = phosphorus atom and white = hydrogen atom.             176  Appendix C   C.1 Supplementary Spectra for Chapter 4   Figure C.1. 31P{1H} NMR (162 MHz, (CD3)2CO, 25 °C) spectra of: a) [PhNMe2H]–mer–[4.1], b) [pyH]–mer–[4.1], c) [isoquinolineH]–mer–[4.1], and d) [(n-C8H17)3NH]–mer–[4.1].      177    Figure C.2. 31P{1H} NMR (162 MHz, (CD3)2SO, 25 °C) spectra of a) [PhNH3]–mer–[4.1] and b) [(–)-brucineH]–rac–mer–[4.1]. 4.2 is phosphorane P(C6H4CO2)2(C6H4COOH).    Figure C.3. 1H NMR (400 MHz, (CD3)2CO, 25 oC) spectrum of [PhNMe2H]–mer–[4.1].  * indicates residual (CHD2)(CD3)CO solvent.  178    Figure C.4. 13C{1H} NMR (101 MHz, (CD3)2CO, 25 oC) spectrum of [PhNMe2H]–mer–[4.1].  * indicates (CH3)2CO-d6 solvent.           179    Figure C.5. 1H NMR (400 MHz, (CD3)2SO, 25 oC) spectrum of [PhNH3]–mer–[4.1]. * indicates residual (CHD2)(CD3)SO solvent. † indicates residual dimethylformamide solvent.  Figure C.6. 13C{1H} NMR (101 MHz, (CD3)2SO, 25 oC) spectrum of [PhNH3]–mer–[4.1]. * indicates (CH3)2SO-d6 solvent. † indicates residual dimethylformamide solvent.  180    Figure C.7. 1H NMR (400 MHz, CD2Cl2, 25 oC) spectrum of [pyH]–mer–[4.1].  * indicates residual CHDCl2 solvent. † indicates residual acetone solvent.   181   Figure C.8. 13C{1H} NMR (101 MHz, CD2Cl2, 25 oC) spectrum of [pyH]–mer–[4.1].  * indicates CH2Cl2-d2 solvent. † indicates residual acetone solvent.              182    Figure C.9. 1H NMR (400 MHz, CD2Cl2, 25 oC) spectrum of [isoquinolineH]–mer–[4.1].  * indicates residual CHDCl2 solvent.  Figure C.10. 13C{1H} NMR (101 MHz, CD2Cl2, 25 oC) spectrum of [isoquinolineH]–mer–[4.1].  * indicates CH2Cl2-d2 solvent.  183     Figure C.11. 1H NMR (400 MHz, CD2Cl2, 25 oC) spectrum of [(–)-brucineH]–Λ–mer–[4.1].  * indicates residual CHDCl2 solvent. † indicates residual acetone solvent.   184   Figure C.12. 13C{1H} NMR (101 MHz, CD2Cl2, 25 oC) spectrum of [(–)-brucineH]–Λ–mer–[4.1].  * indicates CH2Cl2-d2 solvent. † indicates residual acetone solvent.             185    Figure C.13. 1H NMR (400 MHz, (CD3)2CO, 25 oC) spectrum of [(n-C8H17)3NH]–mer–[4.1]. * indicates residual (CHD2)(CD3)CO solvent. † indicates CH2Cl2 solvent.  186   Figure C.14. 13C{1H} NMR (101 MHz, (CD3)2CO, 25 oC) spectrum of [(n-C8H17)3NH]–mer–[4.1].  * indicates (CH3)2CO-d6 solvent. † indicates CH2Cl2 solvent.           187    Figure C.15. 1H NMR (400 MHz, CD3OD, 25 oC) spectrum of K–mer–[4.1].  * indicates residual CHD2OD solvent. † indicates residual CH2Cl2 solvent.  Figure C.16. 13C{1H} NMR (101 MHz, CD3OD, 25 oC) spectrum of K–mer–[4.1].  * indicates CH3OH-d3 solvent.  188  Table C-1. Selected bond lengths [Å] and bond angles [°] of [PhNMe2H]–rac–mer–[4.1], [pyH]–rac–mer–[4.1], [isoquinolineH]–rac–mer–[4.1], [(–)-brucineH]–Λ–mer–[4.1], and K–rac–mer–[4.1].   Bond distances [PhNMe2H]–rac–mer–[4.1] [pyH]–rac–mer–[4.1] [isoquinolineH]–rac–mer–[4.1] [(–)-brucineH]–Λ–mer–[4.1] K–rac–mer–[4.1] P1–O1 1.92(1) 1.926(2) 1.838(3) 1.908(6) 1.906(2) P1–O3 1.778(1) 1.774(2) 1.774(3) 1.776(7) 1.765(2) P1–O5 1.774(1) 1.769(2) 1.77(3) 1.765(8) 1.786(2) P1–C1 1.861(2) 1.854(2) 1.865(4) 1.85(1) 1.85(3) P1–C8 1.849(2) 1.87(2) 1.857(4) 1.85(1) 1.852(3) P1–C15 1.849(2) 1.842(2) 1.853(4) 1.856(9) 1.841(3) O1-C7 1.300(2) 1.303(3) 1.333(5) 1.30(1) 1.32(4) C7-O2 1.239(2) 1.235(3) 1.218(5) 1.24(1) 1.217(4) O3-C14  1.341(2) 1.38(2) 1.337(5) 1.33(1) 1.329(4) O4-C14 1.216(2) 1.24(2) 1.214(6) 1.23(1) 1.217(4) O5-C21 1.341(2) 1.339(3) 1.341(5) 1.35(1) 1.334(4) O6-C21 1.212(2) 1.208(3) 1.215(6) 1.21(1) 1.213(4) Bond angles      O1-P1-C15 83.2(6) 81.9(9) 85.7(2) 83.2(3) 89.9(1) O1-P1-O3 86.8(5) 84.8(9) 87.9(2) 86.5(3) 91.5(9) O3-P1-C8 88.3(6) 91.3(6) 88.5(2) 88.7(4) 87.5(1) C8-P1-O5 95.4(6) 92.9(6) 92.9(6) 95.7(4) 92.7(1) C8-P1-O3 92.6(6) 91.3(6) 91.3(6) 88.7(4) 87.5(1) C8-P1-C15 97.0(7) 94.2(1) 93.0(2) 95.2(4) 92.9(1) C15-P1-O5 87.7(6) 87.5(1) 87.9(2) 87.6(4) 87.9(1) C1-P1-O3 90.3(6) 91.2(1) 90.6(2) 90.0(4) 87.7(1) O5-P1-O3 176.3(5) 175.6(9) 178.0(2) 175.5(3) 175.6(1) C1-P1-C8 97.0(7) 100.5(1) 95.9(2) 97.8(4) 167.7(1) C8-P1-O1 174.9(6) 174.3(1) 176.1(2) 174.9(4) 84.5(1) C15-P1-C1 166.9(7) 164.4(1) 170.8(2) 166.7(4) 171.5(1) C7-O1-P1 115.8(1) 116.3(2) 116.6(3) 116.3(6) 115.9(2) C1-P1-O1 84.3(6) 83.8(1) 85.7(2) 84.1(3) 84.3(1) O1-C7-O2 123.8(2) 122.2(2) 122.2(2) 123.8(9) 122.5(3) O3-C14-O4 122.3(1) 119.1(3) 119.1(3) 121.8(9) 122.0(3) O5-C21-O6 122.8(2) 121.8(2) 121.8(2) 122.1(1) 121.0(3)  189  Appendix D   D.1 Supplementary Spectra for Chapter 5   Figure D.1. 1H–13C HMBC NMR (400 MHz for 1H, CD2Cl2, –85 °C) spectrum of H(OEt2)2[5.1].   190   Figure D.2. 13C{1H} NMR (400 MHz, CD2Cl2, –85 °C) spectrum of H(OEt2)2[5.1].  * indicates CH2Cl2-d2 solvent.  191   Figure D.3.1H NMR (400 MHz, CD2Cl2, –85 °C) spectrum of H(OEt2)2[5.1]: a) day 1; b) day 2; c) day 3; d) day 5; e) day 8 (addition of CD2Cl2 ca. 0.9 mL); f) day 12 and g) day 15. † indicates free Et2O.  192   Figure D.4.1H NMR (400 MHz, CDCl3, 25 °C) spectrum of syndiotactic-rich poly(-methylstyrene) (rr =  86 %); polymerization performed with initiator H(OEt2)2[5.2] at –78 °C. * indicates residual CHCl3 solvent. 

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