Science, Faculty of
Chemistry, Department of
DSpace
UBCV
Suen, Jeffrey Jun-Yan
Master of Science - MSc
University of British Columbia
This thesis outlines the synthesis, characterization, and catalytic use of phosphorus containing copolymers. The incorporation of phosphorus imparts unique functionalities that allow for the use of polymeric ligands in catalysis. In Chapter 2, the gold metallated phosphorus containing copolymer (PMP-r-PS)-Au-Cl was used as a hydroamination catalyst for the intermolecular hydroamination of phenyl acetylene with aniline. At 5 mol% catalyst loading (5 mol% Au centres), the total product conversion was 99.6% at room temperature and 98.6% at 110°C. The (PMP-r-PS)-Au-Cl catalyst was also selective in producing only the Markovnikov product. In Chapter 3, the free radical copolymerization of PMP-r-PBA was investigated. The linkages between phosphaalkene (PA) and n-butyl acrylate (BA) residues were fully characterized by edHSQC NMR spectroscopy and GPC. The reactivity ratios between PA and BA monomers were determined using the Fineman-Ross linear method and the Mayo-Lewis graphical method. The reactivity ratios were rPA = 18.1, rBA = 0.670 and rPA = 22.7, rBA = 0.784 from both methods, respectively. The reactivity ratios suggested that a propagating PAâ¢ radical has a strong preference for homo-propagation and a propagating BAâ¢ radical has a slight preference for cross-propagation. To conclude, these instigations have opened the doors to new possibilities in the synthesis of PMP copolymers as well as their uses as catalyst supports in gold catalysis
COPOLYMERS OF POLY(METHYLENEPHOSPHINE)S: CHARACTERIZATION AND APPLICATION IN POLYMER-SUPPORTED CATALYSIS by Jeffrey Jun-Yan Suen B.Sc., McMaster University, 2016 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE AND POSTDOCTORAL STUDIES (Chemistry) THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver) December 2021 © Jeffrey Jun-Yan Suen, 2021 ii The following individuals certify that they have read, and recommend to the Faculty of Graduate and Postdoctoral Studies for acceptance, a thesis entitled: Copolymers of Poly(methylenephosphine)s: Characterization and Application in Polymer-Supported Catalysis submitted by Jeffrey Jun-Yan Suen in partial fulfillment of the requirements for the degree of Master of Science in Chemistry Examining Committee: Dr. Derek P. Gates, Professor, Department of Chemistry, UBC Supervisor Dr. Zachary M. Hudson, Associate Professor, Department of Chemistry, UBC Supervisory Committee Member Dr. Eva M. Nichols, Assistant Professor, Department of Chemistry, UBC Supervisory Committee Member iii Abstract This thesis outlines the synthesis, characterization, and catalytic use of phosphorus containing copolymers. The incorporation of phosphorus imparts unique functionalities that allow for the use of polymeric ligands in catalysis. In Chapter 2, the gold metallated phosphorus containing copolymer (PMP-r-PS)-Au-Cl was used as a hydroamination catalyst for the intermolecular hydroamination of phenyl acetylene with aniline. At 5 mol% catalyst loading (5 mol% Au centres), the total product conversion was 99.6% at room temperature and 98.6% at 110°C. The (PMP-r-PS)-Au-Cl catalyst was also selective in producing only the Markovnikov product. In Chapter 3, the free radical copolymerization of PMP-r-PBA was investigated. The linkages between phosphaalkene (PA) and n-butyl acrylate (BA) residues were fully characterized by edHSQC NMR spectroscopy and GPC. The reactivity ratios between PA and BA monomers were determined using the Fineman-Ross linear method and the Mayo-Lewis graphical method. The reactivity ratios were rPA = 18.1, rBA = 0.670 and rPA = 22.7, rBA = 0.784 from both methods, respectively. The reactivity ratios suggested that a propagating PAâ¢ radical has a strong preference for homo-propagation and a propagating BAâ¢ radical has a slight preference for cross-propagation. To conclude, these instigations have opened the doors to new possibilities in the synthesis of PMP copolymers as well as their uses as catalyst supports in gold catalysis iv Lay Summary Catalysts have been widely used in research and industrial applications to increase the rate of reaction while not being consumed itself during the reaction. Many catalysts comprise of expensive transition metals. However, these catalysts are often lost during the purification step. If these metals are supported on a polymer, recovery of these metals are simplified to a precipitation in an insoluble solvent followed by a filtration. These purification steps not only minimize the need for considerable quantities of organic solvents during column chromatography, but the recovered catalyst can be further reused. The purpose of this thesis is to synthesize a novel gold-based catalyst supported by a phosphorus containing polymer for use as a catalyst in the activation of unsaturated hydrocarbons. Furthermore, other novel phosphorus copolymers with acrylates are also synthesized and characterized in this thesis as potential candidates for catalyst supports. v Preface This thesis is original, unpublished, independent work by the author Jeffrey Suen. None of the text of contained in this thesis is taken directly from previous published work. Each research chapter is designed to be published as a self-contained academic paper submitted to a peer-reviewed journal. This thesis was achieved with help from others. All synthetic work in Chapter 2 was performed by myself. The copolymerization procedure for PMP-r-PS in Section 2.2.4 was developed by Dr. Chi-Wing Tsang. All GPC measurements were run by Dr. Khatera Hazin and Henry Walsgrove. All catalysis experiments with the PMP-r-PS copolymer support are my original work. Additional hydroamination trials were performed by Mr. Nolton Woods confirming the repeatability of the results. In Chapter 3, all synthetic work was conducted by myself. NMR experiments in Section 3.2.1 and 3.2.2 were run with help from Dr. Maria Ezhova. All size exclusion chromatography experiments were performed on a column packed with reusable Bio-Rad Bio-Beads S-X1 borrowed from Prof. Dr. Zachary M. Hudson. The purification procedure for the isolation of the PMPO-r-PBA copoolymer was developed by myself. vi Table of Contents Abstract ......................................................................................................................................... iii Lay Summary ............................................................................................................................... iv Preface .............................................................................................................................................v Table of Contents ......................................................................................................................... vi List of Tables ..................................................................................................................................x List of Figures ............................................................................................................................... xi List of Schemes ........................................................................................................................... xvi List of Equations ..........................................................................................................................xx List of Abbreviations ................................................................................................................. xxi Acknowledgements .................................................................................................................. xxiv Dedication ...................................................................................................................................xxv Chapter 1: Introduction ................................................................................................................1 1.1 Brief History of Polymers ................................................................................................... 1 1.1.1 History of Organic Polymers ...................................................................................... 1 1.1.2 Common Main Group Polymers ................................................................................. 4 1.2 Phosphaalkene and their Polymers ..................................................................................... 5 1.2.1 Phosphaalkenes ........................................................................................................... 5 1.2.2 Applications of Poly(methylenephosphine)s ............................................................ 12 1.3 Polymer Supports for Catalysis......................................................................................... 19 1.3.1 Phosphorus Containing Supports for Catalysis......................................................... 19 1.3.2 Poly(methylenephosphine)s as Supports for Pd Cross-Coupling Reactions ............ 28 vii Chapter 2: Gold(I) Metallated Poly(methylenephosphine)s Copolymers as Catalyst Supports for Hydroamination .....................................................................................................................32 2.1 Introduction: Catalysis with Gold(I) ................................................................................. 32 2.1.1 Olefin and Alkyne Activation ................................................................................... 32 2.2 Results and Discussions .................................................................................................... 35 2.2.1 Experimental Design of Polymer-Supported Au(I) Catalysts .................................. 35 2.2.2 Hydroamination with Ph3P-Au-Cl as Precatalyst ..................................................... 36 2.2.3 Hydroamination with Au(I) Metallated Model Compound as Precatalyst ............... 39 2.2.4 Synthesis and Characterization of Au(I)-Metallated Poly[(methylenephosphine)-ran-styrene] ...................................................................................................................... 44 2.2.5 Hydroamination with (PMP-r-PS)-Au-Cl as Precatalyst .......................................... 49 2.2.6 Summary of Hydroamination Reactions ................................................................... 56 2.3 Summary ........................................................................................................................... 64 2.4 Experimental ..................................................................................................................... 65 2.4.1 Materials and General Procedures for the Synthesis and Characterization of the (PMP-r-PS)-Au-Cl Copolymer Precatalyst and its Hydroamination Reactions ................. 65 2.4.2 Preparation of Unmetallated Model Compound ....................................................... 66 2.4.3 Preparation of Gold-Metallated Model Compound .................................................. 67 2.4.4 Preparation of Poly[(methylenephosphine)-ran-styrene] Copolymer ...................... 67 2.4.5 Preparation of Gold-Metallated Poly[(methylenephosphine)-ran-styrene] Copolymer ................................................................................................................................... 68 2.4.6 Procedure for Hydroamination Reaction with Ph3AuCl at Room Temperature ....... 68 viii 2.4.7 Procedure for Hydroamination Reaction with Gold-Metallated Model Compound at Room Temperature ................................................................................................... 69 2.4.8 Procedure for Hydroamination Reaction with Gold-Metallated Model Compound at 110°C ........................................................................................................................ 69 2.4.9 Preparation of Hydroamination Reactions with (PMP-r-PS)-Au-Cl at Room Temperature .............................................................................................................. 70 2.4.10 Preparation of Hydroamination Reactions with (PMP-r-PS)-Au-Cl at 110°C ......... 70 Chapter 3: Radical Copolymerizations of MesP=CPH2 and Acrylates ..................................71 3.1 Introduction ....................................................................................................................... 71 3.2 Results and Discussion...................................................................................................... 72 3.2.1 Synthesis and Purification of Poly[(methylenephosphine)-ran-(n-butyl acrylate)] Copolymer................................................................................................................. 72 3.2.2 Evidence of Phosphaalkene-n-Butyl Acrylate Linkages .......................................... 76 3.2.3 Brief Introduction of Unique Phosphaalkene / n-Butyl Acrylate Reactivity Ratios . 86 3.2.4 Experimental Design of Reactivity Ratio Studies of MesP=CPh2 (rPA) and n-Butyl acrylate (rBA) in Copolymerizations ......................................................................... 90 3.2.5 Determination of Copolymerization Ratio by Inverse Gated 13C NMR Spectroscopy................................................................................................................................... 92 3.2.6 Determination of Reactivity Ratios rPA and rBA ....................................................... 94 3.2.7 Copolymerization of MesP=CPh2 and Methyl Methacrylate ................................... 99 3.3 Summary ......................................................................................................................... 102 3.4 Experimental ................................................................................................................... 103 ix 3.4.1 Materials and General Procedures for the Synthesis and Characterization of PMP Homopolymer, PMP-r-PBA Copolymer and PMP-r-PMMA Copolymer ............. 103 3.4.2 Preparation of Poly(methylenephosphine) Homopolymer ..................................... 104 3.4.3 Preparation of Poly(n-butyl acrylate) Homopolymer ............................................. 104 3.4.4 Preparation of Poly[(methylenephosphine)-ran-(n-butyl acrylate)]60:40 Copolymer................................................................................................................................. 105 3.4.5 Preparation of Poly[(methylenephosphine oxide)-ran-(n-butyl acrylate)] Copolymer at Low Conversion .................................................................................................. 106 3.4.6 Attempted Preparation of PMMA Poly[(methylenephosphin)-ran-(methyl methacrylate)] Copolymer ...................................................................................... 108 Chapter 4: Overall Conclusions and Future Work ................................................................109 4.1 Summary of Thesis Work ............................................................................................... 109 4.2 Future Work .................................................................................................................... 112 4.2.1 Polymer-Supported Catalysis.................................................................................. 112 4.2.2 PMP Copolymers .................................................................................................... 116 4.3 Closing Remarks ............................................................................................................. 118 References ...................................................................................................................................120 x List of Tables Table 2.1 Hydroamination product 2.5 conversion data for precatalyst Ph3PAuCl. ............. 38 Table 2.2 Hydroamination product 2.5 conversion data for the model compound precatalyst 2.9. ......................................................................................................................... 43 Table 2.3 Hydroamination product 2.5 conversion data for the polymeric precatalyst (PMP-r-PS)-Au-Cl 2.11. ..................................................................................................... 53 Table 2.4 Summary of conversion data for precatalysts Ph3PAuCl, model compound 2.9, and (PMP-r-PS)-Au-Cl 2.11 at room temperature and at 110°C. ................................ 58 Table 3.1 Summary of PA/BA copolymerization data with four different feed ratios. ........ 95 Table 3.2 Summary of reactivity ratios of rPA and rPB using the Fineman-Ross and Mayo-Lewis methods. ...................................................................................................... 98 xi List of Figures Figure 1.1 Common polymers produced on a large scale. ....................................................... 3 Figure 1.2 Four common classes of main group polymers: 1.7 polysiloxanes; 1.8 polyphosphazenes; 1.9 polysilanes; 1.10 poly(ferrocenylsilane)s. ......................... 4 Figure 1.3 Various examples of phosphaalkenes: 1.11 phosphacyanine; 1.12 phosphorine; and 1.13 localized phosphaalkene. ................................................................................. 6 Figure 1.4 PMP random copolymers synthesized by free radical polymerization: 1.24 poly[(methylenephosphine)-ran-styrene]; 1.25 poly[(methylenephosphine)-ran-(methyl methacrylate)]; 1.26 poly[(methylenephosphine)-ran-(2-ethylhexyl acrylate)]; and 1.27 poly[(methylenephosphine)-ran-(n-butyl acrylate)]. ............ 15 Figure 1.5 Illustration of: I heterogeneous catalysis, II homogenous, and III polymer-supported catalysis. ............................................................................................... 20 Figure 2.1 Dewar-Chatt-Duncanson model representation displaying interactions between Au+ and an alkyne ligand. ............................................................................................. 34 Figure 2.2 1H NMR (Tol-d8, 400 MHz) spectra stack plot of hydroamination reaction mixture at room temperature with Ph3PAuCl as precatalyst. * = residual toluene............. 37 Figure 2.3 1H NMR (Tol-d8, 400 MHz) spectrum of hydroamination reaction mixture with Ph3PAuCl as precatalyst. * = residual toluene. ..................................................... 38 Figure 2.4 Progress of gold(I) catalyzed hydroamination with Ph3PAuCl precatalyst. ......... 39 Figure 2.5 Structure of PMP model compound 2.7 and structure of PMP polymer 2.1. ........ 40 xii Figure 2.6 1H NMR (Tol-d8, 400 MHz) spectra stack plot of hydroamination reaction mixture at room temperature with the Au(I) metallated model compound 2.9 as the precatalyst. ............................................................................................................. 42 Figure 2.7 1H NMR (Tol-d8, 400 MHz) spectrum of hydroamination reaction mixture with the Au(I) metallated model compound 2.9 as the precatalyst. * = residual toluene. ... 43 Figure 2.8 Progress of gold catalyzed hydroamination with the Au(I) metallated model compound 2.9 as the precatalyst. ........................................................................... 44 Figure 2.9 Inverse gated proton 13C{1H} NMR (CDCl3, 101 MHz) spectrum of PMP-r-PS 2.10 copolymer. * = residual CHCl3. ............................................................................ 46 Figure 2.10 31P NMR (CDCl3, 162 MHz) spectrum of PMP-r-PS 2.10 and (PMP-r-PS)-Au-Cl 2.11. ....................................................................................................................... 48 Figure 2.11 GPC trace of unmetallated copolymer PMP-r-PS 2.10 (dashed blue trace) and the gold metallated copolymer (PMP-r-PS)-Au-Cl 2.11 (solid orange trace). ........... 49 Figure 2.12 1H NMR (Tol-d8, 400 MHz) spectra stack plot of hydroamination reaction mixture at room temperature with (PMP-r-PS)-Au-Cl 2.11 as the precatalyst. ................. 52 Figure 2.13 1H NMR (Tol-d8, 400 MHz) spectrum of hydroamination reaction mixture with (PMP-r-PS)-Au-Cl 2.11 as the precatalyst after 216 hours (9 days). * = residual toluene. .................................................................................................................. 53 Figure 2.14 Progress of gold catalyzed hydroamination with (PMP-r-PS)-Au-Cl 2.11 as the precatalyst. ............................................................................................................. 54 Figure 2.15 1H NMR (Tol-d8, 400 MHz) spectra of: I crude reaction mixture and II after reprecipitation, filtration and rotary evaporation for hydroamination with (PMP-r-xiii PS)-Au-Cl 2.11 at 110°C. Residual phenyl acetylene starting material is marked as â . * = residual toluene. .......................................................................................... 56 Figure 2.16 Summary histogram of conversion data for precatalysts Ph3PAuCl, model compound 2.9, and (PMP-r-PS)-Au-Cl 2.11 at room temperature and at 110°C. 58 Figure 2.17 Gold mirror formation on the surface of the NMR tube after hydroamination reaction with precatalyst (PMP-r-PS)-Au-Cl 2.11. Similar observations were also observed for all gold-catalyzed hydroamination reaction in this thesis. ............... 59 Figure 2.18 (I) 31P NMR (CDCl3, 162 MHz) of model compound precatalyst 2.9. (II) 31P NMR (Tol-d8, 162 MHz) spectra of the reaction mixture after treading model compound 2.9 with AgOTf (1 equiv) at the following times: (a) ca. 40 mins, (b) 2h, and (c) 22h. ........................................................................................................................ 61 Figure 2.19 Comparison of the cone angle of the active catalytic species of I Ph3P-Au+, II Au(I) metallated model compound MesMe(CH2Ph2)P-Au+, and III (PMP-r-PS)-Au+. 63 Figure 2.20 Comparison of total product reaction progress of gold catalyzed hydroamination with precatalysts Ph3PAuCl, model compound 2.9, and (PMP-r-PS)-Au-Cl 2.11 at room temperature. The independent data may be found in Figures 2.4, 2.8, and 2.14. ....................................................................................................................... 64 Figure 3.1 31P NMR (162 MHz) of PMP-r-PBA20:80 copolymer 3.2: I crude (neat), II after three reprecipitations in 80% v/v MeOH in water (CDCl3), and III after four reprecipitations in 80% v/v MeOH in water (CDCl3). .......................................... 73 Figure 3.2 31P NMR (CDCl3, 162 MHz) spectra of I) PMP-r-PBA60:40 3.2; and II) Homo-PMP NMR (referred to as 1.14 and/or 2.1 earlier in this thesis; (Mn = 6,200, PDI = 1.19). ............................................................................................................................... 77 xiv Figure 3.3 GPC trace of homopolymer PMP 2.1 (dotted blue line), homopolymer PBA (dashed orange line) and copolymer PMP-r-PBA60:40 3.2 (solid grey line). ...................... 78 Figure 3.4 1H NMR (CDCl3, 400 MHz) spectrum of PMP-r-PBA60:40 3.2. * = residual CHCl3. ............................................................................................................................... 79 Figure 3.5 Inverse gated 13C{1H} NMR (CDCl3, 101 MHz) spectrum of PMP-r-PBA60:40 3.2. * = residual CHCl3. ............................................................................................... 80 Figure 3.6 Depiction of a single phosphaalkene residue within a PMP copolymer. CHc and CH2d represent C-H environments most affected by neighbouring polymer residues. ............................................................................................................................... 80 Figure 3.7 1H-13C edHSQC NMR spectra (400 MHz for 1H, CDCl3, 298K) of I PMP homopolymer, II PBA homopolymer, and III PMP-r-PBA60:40. Green dashed circles in I and II denote the absent correlations only present in III. The multiplicity editing during the acquisition of the edHSQC spectra allowed for discrimination between CH3/CH3 (blue) and CH2 (red) moieties. * = residual CHCl3................. 84 Figure 3.8 The four possible environments for a given phosphaalkene residue (highlighted in grey) in a PMP-r-PBA copolymer 3.2. End group with either the PA or BA residue is not considered. ................................................................................................... 85 Figure 3.9 31P NMR (CDCl3, 162 MHz) spectrum of low conversion PMPO-r-PBA60:40 3.3. ............................................................................................................................... 86 Figure 3.10 Four different possible scenarios for the addition of a monomer in a propagating radical. ................................................................................................................... 87 Figure 3.11 Copolymerization plot of incremental polymer composition F as a function of monomer feed f for different reactivity ratios of common monomers.108-112 ........ 89 xv Figure 3.12 Outline for experimental design in determining reactivity ratios. ........................ 91 Figure 3.13 Inverse gated 13C{1H} NMR (CDCl3, 101 MHz) spectrum of PMPO-r-PBA20:80 3.3. * = residual CHCl3. â = residual BHT. ................................................................. 93 Figure 3.14 Inverse gated proton 13C{1H} NMR (CDCl3, 101 MHz) spectra of: I homopolymer PBA, II-V copolymer PMPO-r-PBAm:n, and VI homopolymer PMP 2.1. * = residual CHCl3. â = residual BHT. â¡ = CH3 of n-butyl group. ............................. 94 Figure 3.15 Equations to calculate nPA,BA, XPA,BA, and percentage yield adjusted for oxidation post-polymerization of PMP-r-PBA. .................................................................... 95 Figure 3.16 Fineman-Ross plot of G against H for the PA/BA copolymer system. ................. 96 Figure 3.17 Mayo-Lewis plot of rPA against rBA for the PA/BA copolymer system. ............... 97 Figure 3.18 Predicted copolymerization plot of the phosphaalkene/n-butylacrylate copolymer system using the predicted reactivity ratios by the Fineman-Ross and Mayo-Lewis methods. Experimental plots are overlaid with the trace. ..................................... 99 Figure 3.19 GPC traces of the crude after attempted PMP-r-PMMA copolymerization (Scheme 3.3) with various feed ratios overlaid with the PMP homopolymer 2.1 trace. .... 101 xvi List of Schemes Scheme 1.1 Synthesis of nitrocellulose 1.2 and cellulose acetate 1.3 by treatment of cellulose 1.1 with nitric acid and acetic anhydride, respectively. .......................................... 2 Scheme 1.2 General overview of reactions with phosphaalkenes analogous with olefins: A Diels-Alder [4+2] cycloaddition; B hydrogenation; C 1,2-addition reaction; D coordination chemistry; and E addition polymerization. ........................................ 7 Scheme 1.3 Various synthetic methods for phosphaalkenes. ..................................................... 8 Scheme 1.4 Three variants of the phospha-Peterson reaction for the synthesis of phosphaalkenes monomers. ............................................................................................................... 9 Scheme 1.5 Reaction of Au(I) metallated MesP=CPh2 with two equivalents of TEMPO results in C-H activation. .................................................................................................. 10 Scheme 1.6 Reaction of MesP=CPh2 with one equivalent of MeLi (anionic initiator) and quenched with trityl chloride results in C-H activation. ....................................... 11 Scheme 1.7 Structure of PMP after addition polymerization of MesP=CPh2. ......................... 11 Scheme 1.8 Chemical modification of poly(methylenephosphines). PMPs 1.15 can undergo oxidation reactions to produce 1.16 and 1.17 or coordination reactions to produce 1.18 and 1.19. ........................................................................................................ 13 Scheme 1.9 âTurn-onâ emissions of PMPs were observed with oxidation. ............................. 14 Scheme 1.10 Living anionic block copolymerization of: A PS-b-PMP and B PI-b-PMP. ........ 16 Scheme 1.11 Living anionic block copolymerization using the propagating anionic end of PMP to initiate acrylates. ............................................................................................... 17 Scheme 1.12 Synthesis of poly(1-phospha-1,3-butadiene). ........................................................ 18 xvii Scheme 1.13 Synthesis of poly(1-phosphaisosprene). ................................................................ 18 Scheme 1.14 A generic synthetic method to functionalize a polystyrene based polymer with a transition metal phosphine complex. ..................................................................... 22 Scheme 1.15 The synthesis of a Pd-based catalyst supported by a polystyrene resin for use as a catalyst in oligomerization reactions with 1,3-Butadiene. .................................... 23 Scheme 1.16 The synthesis of a polymer with a pendant bidentate-phosphine-palladium complex for use as a catalyst in Heck arylation. .................................................................. 24 Scheme 1.17 The synthesis of a Au-based catalyst supported by a polystyrene resin for use as a catalyst in cyclization reactions to produce a furan 1.45. ..................................... 25 Scheme 1.18 Synthesis of a porous organophosphorus support ................................................. 26 Scheme 1.19 Generation of the active catalytic species from polystyrene resin-based Au(I) precatalyst. ............................................................................................................. 26 Scheme 1.20 Alkyne hydration reactions catalyzed by catalyst 1.51. ........................................ 27 Scheme 1.21 Intermolecular hydroamination reaction catalyzed by catalyst 1.51. .................... 28 Scheme 1.22 Comparison of conventional catalysts immobilized onto pendant groups of polymers with that of catalysts immobilized onto the polymeric backbone of PMPs. ............................................................................................................................... 30 Scheme 1.23 Suzuki cross-coupling using homopolymer PMP 1.15 and copolymer PMP-r-PS 1.24 as catalyst supports for palladium. ................................................................ 31 Scheme 2.1 Metallation of PMP homopolymer with Au(I). ..................................................... 32 Scheme 2.2 General catalytic cycle of gold catalysis. .............................................................. 34 Scheme 2.3 Hydroamination of phenyl acetylene with aniline using Ph3P-Au-Cl as the precatalyst. ............................................................................................................. 37 xviii Scheme 2.4 Synthesis of PMP model compound precatalyst 2.9 from MesP=CPh2 monomer. ............................................................................................................................... 40 Scheme 2.5 Hydroamination of phenyl acetylene with aniline using the Au(I) metallated model compound 2.9 as the precatalyst. .......................................................................... 41 Scheme 2.6 Coordination of Au(I) to PMP-r-PS 2.10 to produce the precatalyst (PMP-r-PS)-Au-Cl 2.11. ............................................................................................................ 48 Scheme 2.7 Hydroamination of phenyl acetylene with aniline using the (PMP-r-PS)15:85-Au-Cl 2.11 as the precatalyst. .......................................................................................... 51 Scheme 2.8 Reaction of model compound catalyst 2.9 with one equivalent of AgOTf generating active Au+ species. ................................................................................................ 60 Scheme 3.1 Synthesis of PMP-r-PBA polymer. ....................................................................... 72 Scheme 3.2 Oxidation of PMP-r-PBA 3.2 to PMPO-r-PBA 3.3 with H2O2. ........................... 76 Scheme 3.3 Free radical polymerization of PMP-r-PMMA copolymer 3.3. .......................... 100 Scheme 4.1 Intramolecular cyclization of propargylic amides 4.1 to form oxazoline 4.2 moieties catalyzed by commercially available Ph3PAuNTf2 precatalyst. ......................... 113 Scheme 4.2 Intramolecular cyclization of propargylic amides to form oxazoline moieties catalyzed by proposed (PMP-r-PS)-Au-Cl polymeric precatalyst 2.11. ............. 114 Scheme 4.3 Synthesis of the (PMP-r-PS)-Au-NTf2 precatalyst 4.3 from (PMP-r-PS)-Au-Cl precatalyst 2.11. ................................................................................................... 115 Scheme 4.4 Intermolecular hydroamination and intramolecular cyclization of propargylic amides with the polymeric precatalyst (PMP-r-PS)-Au-NTf2 4.3. ..................... 115 Scheme 4.5 Reduction of a phosphine oxide 4.4 to a phosphine 4.5 using a mild reducing agent HBpin. ................................................................................................................. 117 xix Scheme 4.6 Reduction of PMPO-r-PBA 3.3 to PMP-r-PBA 3.2 using a mild reducing agent HBpin. ................................................................................................................. 117 Scheme 4.7 Proposed reduction of 1.20/1.22 to 1.21/1.23, respectively to regenerate the phosphine. ........................................................................................................... 118 xx List of Equations Equation 2.1 Equation to calculate product conversion of the Markovnikov product 2.5. ........ 38 Equation 2.2 Equation to determine copolymer composition FPA and FSty of PMP-r-PS 2.10. . 46 Equation 2.3 Equation to determine moles of phosphorus (nPA) for a given mass of polymer (mPolymer) for PMP-r-PS 2.10. ................................................................................ 46 Equation 2.4 Equation to determine moles of Au centers for given mass of Au metallated polymer (mPolymer) for (PMP-r-PS)-Au-Cl 2.11. .................................................................. 48 Equation 3.1 Copolymer equation also known as the Mayo-Lewis equation. ........................... 87 Equation 3.2 Equation to determine copolymer composition FPA and FSty of PMPO-r-PBA 3.3. ............................................................................................................................... 93 Equation 3.3 Fineman-Ross equation; linear form of the copolymer Equation 3.1. .................. 96 Equation 3.4 Rearranged Mayo-Lewis equation (Equation 3.1) such that rPA is a function of rBA. ............................................................................................................................... 97 Equation 3.5 Equations to determine the centroid of a triangle on a cartesian plane. ................ 97 Equation 3.6 Mayo-Lewis equation to predict the molar incorporation of FPA using feed ratios fPA,BA for the PMP-r-PBA 3.2 copolymer system. ................................................ 98 xxi List of Abbreviations AIBN Azobisisobutyronitrile AMP Anti-Markovnikov product BA n-Butyl acrylate BMA n-Butyl methacrylate Bn Benzyl °C Celsius C Concentration DCM Dichloromethane DFT Density functional theory dn/dc Refractive index increment DVB Divinylbenzene edHSQC Edited heteronuclear single quantum coherence spectroscopy EtOH Ethanol fPA Feed ratio of phosphaalkene (MesP=CPh2) fBA Feed ratio of n-Butyl acrylate FPA Mole fraction of phosphaalkene (MesP=CPh2) monomer in copolymer FBA Mole fraction of n-butyl acrylate monomer in copolymer g Gram(s) GPC Gel permeation chromatography HBpin Pinacolborane HCP Hyper-crosslinked polymer xxii HOMO Highest occupied molecular orbital HSQC Heteronuclear single quantum coherence spectroscopy Mes Mesityl; 2,4,6-trimethylbenzene Mes* 2,4,6-Tri-tert-butylphenyl MeOH Methanol MMA Methylmethacrylate mol Moles(s) MP Markovnikov product MW Molecular weight nBA n-Butylacrylate NHC N-Heterocyclic carbene NMR Nuclear Magnetic Resonance PA Phosphaalkene (MesP=CPh2) PAAuCl Gold metallated phosphaalkene residue in a phosphaalkene copolymer PBA Poly(n-butyl acrylate) PDI Polydiversity index Ph Phenyl PI Polyisoprene PMMA Poly(methyl methacrylate) PMP Poly(methylenephosphine) PMP-r-PBA Poly[(methylenephosphine)-ran-(n-butylacrylate)] PMP-r-PMMA Poly[(methylenephosphine)-ran-(methyl methacrylate)] PMPO-r-PBA Poly[(methylenephosphine oxide)-ran-(n-butylacrylate)] xxiii PMP-r-PS Poly[(methylenephosphine)-ran-styrene] (PMP-r-PS)-Au-Cl Poly[(methylenephosphine gold(I))-ran-polystyrene] (PMP-r-PS)15:85-Au-Cl Poly[(methylenephosphine gold(I))-ran-polystyrene] where ratio of PA:PS is 15:85 r.t. Room temperature rBA Reactivity ratio of n-butyl acrylate rPA Reactivity ratio of phosphaalkene RI Refractive Index SEC Size-exclusion chromatography Sty Styrene TEM Transmission Electron Microscopy TEMPO (2,2,6,6-Tetramethylpiperidin-1-yl)oxyl THF Tetrahydrofuran THT Tetrahydrothiophene TMS Trimethylsilane VAZO-88 1,1â-Azobis(cyanocyclohexane) xxiv Acknowledgements I offer my sincerest gratitude to faculty, students, and staff of the UBC Department of Chemistry. First and foremost, I would like to thank my supervisor Dr. Derek P. Gates for his guidance and offering an opportunity to gain insight into the world of phosphaalkenes. I would also like to acknowledge all the members of the Gates research group, past and present, who have helped me throughout this project. I would like to thank Dr. Benjamin Rawe for teaching me the synthesis of the phosphaalkene. I would especially like to thank Dr. Kerim Samedov for his assistance and troubleshooting skills for numerous experiments. I would also like to thank Khatera Hazin, Zeyu Han, and Henry Walsgrove for their help in providing feedback for my work. Lastly, I would like to thank the members of the Gates group Ann Bennett, Harvey Mackenzie, Leixing Chen, Chuantian Zhan, Tanvi Garg, Tian Zhang, Rebecca Yang, Nolton Woods, Paul Heine, Jessamine Palima, and Rodella Chowdhury for their support and being good company during pub nights and brew-offs. I would also like to acknowledge other members of the UBC Department of Chemistry. I would like to thank Dr. Zachary Hudson and his group for graciously allowing me to borrow their size-exclusion column for experiments in Chapter 3. I would also like to give a huge thanks to the NMR staff, in particular Dr. Maria Ezhova, for helping me acquire some of the most beautiful NMR spectra. Finally, I would like to thank my family, most notably my mother, for all their emotional support throughout this journey especially during the COVID-19 pandemic. xxv Dedication This thesis is dedicated to the people who were there to inspire and support me at the start of my educational journey. I dedicated this to my parents and Mrs. Irene Gomez, who always believed in me.1 Chapter 1: Introduction 1.1 Brief History of Polymers 1.1.1 History of Organic Polymers Polymers are a class of materials consisting of large molecules also known as macromolecules. These comprise of smaller repeating units known as monomers connected in a linear manner analogous to a string of pearls. The term âpolymerâ was first coined by Jöns Jakob Berzelius in 1833 deriving from the Greek prefix âpolyâ meaning âmanyâ and the suffix âmerâ meaning âpartsâ.1 One of the first examples of modern polymer science was the research in a natural polysaccharide cellulose 1.1 (Scheme 1.1). In 1839, a French chemist Anselme Payen treated wood with nitric acid and obtained a fibrous substance which he named cellulose. This natural polymer could be further modified post-extraction to produce various materials with different applications. In 1845, Christian Schönbein, a German/Swiss chemist, accidentally discovered nitrocellulose 1.2 (Scheme 1.1) at home while mixing cellulose and nitric acid.3 The result was an extremely flammable material that was also named âguncottonâ (Scheme 1.1). Nitrocellulose is still used today as a component of smokeless gunpowder. Another example of a cellulose-based material was cellulose acetate 1.3 (Scheme 1.1) which was synthesized by treating cellulose with acetic anhydride. Cellulose acetate was used for photographic film bases.4 2 Scheme 1.1 Synthesis of nitrocellulose 1.2 and cellulose acetate 1.3 by treatment of cellulose 1.1 with nitric acid and acetic anhydride, respectively. The first large scale production of a polymeric material was natural rubber 1.4 derived from a rubber tree (Hevea brasiliensis) (Figure 1.1). Due to its ability to ârubâ away pencil markings, the name ârubberâ was coined.5 In the 1830s, Charles Goodyear attempted to dry rubber with various drying agents and accidentally discovered that if heated with sulfur and lead monoxide, the stickiness was eliminated; however, the elasticity remained 1.5.5 This process of heating rubber with sulfur was known as vulcanization. The physical properties of rubber can be adjusted through the degree of vulcanization to fit the stiffness requirements for a variety of applications such tires, hockey pucks, and shoes. The demand for rubber production exploded in World War II due to its use as an essential war material.6 Despite these naturally derived polymers, production could not keep up with the growing demand for cheap materials. In 1907, Leo Baekeland synthesized a synthetic plastic known as Bakelite 1.6 (Figure 1.1) which was made from reacting the monomers phenol and formaldehyde. This was the first example of a widely used synthetic plastic. Bakelite was demonstrated to exhibit high thermal stability and high strength and found use in applications such as insulating materials, jewelry, telephone casings, and billiard balls. 3 Figure 1.1 Common polymers produced on a large scale. The objective of this dissertation includes the development and characterization of novel synthetic organophosphorus polymers. In particular, the goal is to synthesize a polymeric catalyst for use in organic reactions and study their efficiency and ease of recovery post-reaction. To understand these hybrid organic-inorganic polymers, one must understand the development of inorganic polymers and their unique properties. 4 1.1.2 Common Main Group Polymers The incorporation of main group elements into polymeric systems imparts unique functionalities and desirable physical/chemical properties compared to their organic counterparts. For example, in polysiloxanes 1.7 (Figure 1.2), the bending and torsional flexibility of the Si-O-Si bond provides structural flexibility in the main polymer chain and gives this class of materials remarkable elastomeric properties.8 These polysiloxanes, e.g., polydimethylsiloxane (PDMS), are widely used in contact lenses, sealants, and artificial breast implants. Another common class of inorganic polymers are polyphosphazenes 1.8 (Figure 1.2). They are identified by their P=N double bond in the polymer backbone. Polyphosphazenes may undergo hydrolytic degradation yielding non-toxic and pH neutral products giving these polymers biocompatible and biodegradable properties.9 Common applications of polyphosphazenes include biodegradable polymers, tissue engineering, and controlled drug delivery. Furthermore, polysilanes 1.9 (Figure 1.2), have shown optical and electrical properties.10 Lastly, poly(ferrocenylsilane)s 1.10 (Figure 1.2), only gained significance recently and is one of the most well-developed class of metal-containing polymers (metallopolymers). The metal centres allow for applications in high refractive index materials, redox responsive gels, and precursors to magnetic ceramic materials.11 These are the four dominant classes of inorganic polymers currently.12 Figure 1.2 Four common classes of main group polymers: 1.7 polysiloxanes; 1.8 polyphosphazenes; 1.9 polysilanes; 1.10 poly(ferrocenylsilane)s. 5 1.2 Phosphaalkene and their Polymers 1.2.1 Phosphaalkenes Phosphaalkenes are a unique class of phospha-organic compounds containing a phosphorus carbon double bond. The first evidence of a P=C double bond was described by Dimroth and Hoffman in 1964 in their synthesis of a mesomeric two-coordinate phosphorus in a phosphamethinecyanine cation 1.11 (Figure 1.3).13 That was followed by the synthesis of the first P=C bond in a phosphinine compound 2,4,6-triphenylphosphorine 1.12 (Figure 1.3) by Märkl in 1966 (these compounds are also known as phosphorines or phosphabenzenes).14 Further in 1976, the first localized phosphaalkene 1.13 (Figure 1.3) was synthesized by Becker.15 Since the discovery of phosphaalkenes, researchers have revealed striking parallels between the P=C double bond and the analogous C=C double bond. The HOMO of a phosphaalkene is calculated to be the (C2p-P3p)Ï-bond similar to the HOMO in alkenes calculated be the (C2p-C2p)Ï-bond. Moreover, density functional theory (DFT) studies on the model HP=CH2 have shown that the lone electron pair on phosphorus has a higher s character than p and does not reside in the HOMO.16,17 On the other hand, the lone electron pair of their imines congeners (N=C) does reside in the HOMO. As a result, phosphaalkene moieties are isolobal with alkenes and very often their reactivities are compared to each other rather than with imines. 6 Figure 1.3 Various examples of phosphaalkenes: 1.11 phosphacyanine; 1.12 phosphorine; and 1.13 localized phosphaalkene. Phosphaalkenes undergo many of the same reactions as their carbon analogues such as Diels-Alder [4+2] cycloadditions 1.2A,18,19,20 hydrogenations reactions 1.2B,21 1,2-additions of polar molecules 1.2C,18,22,23 and coordination to metals 1.2D24,25 (Scheme 1.2). It is worth mentioning that alkenes only undergo η2 coordination to metals while phosphaalkenes may coordinate in both the η1 or η2 manner. This is because of the access to the lone electron pair on the phosphorus atom. Due to the widely known parallels between olefins and phosphaalkenes, it was hypothesized that addition polymerization might be possible for phosphaalkenes. In 2003, the Gates group discovered the first evidence of the addition polymerization of phosphaalkenes to produce poly(methylenephosphine)s. Specifically, following the distillation of MesP=CPh2, a 31P NMR spectroscopic analysis of the remaining viscous brown residue showed a broad signal (-10 ppm) which was attributable to a polymeric phosphorus species.22 Further polymerization studies showed that MesP=CPh2 undergoes radical and anionic polymerizations methods 1.2E (Scheme 1.2).26 7 Scheme 1.2 General overview of reactions with phosphaalkenes analogous with olefins: A Diels-Alder [4+2] cycloaddition; B hydrogenation; C 1,2-addition reaction; D coordination chemistry; and E addition polymerization. Since the synthesis of the first localized phosphaalkene 1.13 (Figure 1.3), various synthetic methods were employed in the preparation of phosphaalkenes (Scheme 1.3): the Becker method of a condensation reaction followed by a 1,3-silatropic rearrangement 1.3A,16,27,28 thermally or base-promoted 1,2-elimination 1.3B,29,30,31 nucleophilic substitution followed by a 1,2-elimination 1.3C,32,33,34 reaction of aromatic phosphines with amide acetals 1.3D,34,35 phospha-Wittig reaction 1.3E,36,37,38 phospha-Wittig type reaction using a metal-complexed phosphinidene as the phosphorus ylide 1.3F,39,40 tautomerization 1.3G,41,42,43 and phospha-Peterson reaction 1.3H44,45,46. 8 Scheme 1.3 Various synthetic methods for phosphaalkenes. The Gates group has a particular interest in the phospha-Peterson synthesis of phosphaalkene monomers since this reaction can be used on multigram scales. In addition, this route benefits from the straightforward removal of volatile side products and simple filtration of trace amounts of solid catalyst.47 Analogous to the Peterson olefination,48 the phospha-Peterson reaction describes the reaction between an α-silyl phosphide with a ketone or aldehyde shown in Scheme 1.4C. This reaction is also modular, allowing for the aromatic side groups of P-aryl or C-aryl to be tuned with ease, creating many PMP variants including those with chiral groups.60,61 There are two additional variants of the phospha-Peterson reaction shown in Scheme 1.4. The base-catalyzed phospha-Peterson reaction involves the reaction of an arylbis(trimethylsilyl)phosphine directly with a ketone or aldehyde using catalytic NaOH or KOH 1.4A.44,46 The other variant is the Lewis-acid mediated phospha-Peterson reaction which employs 9 a Lewis-acid mediator such as AlCl3 or GaCl3 to facilitate the condensation of arylbis(trimethylsilyl)phosphine with a ketone or aldehyde 1.4B.49 The base-catalyzed phopha-Peterson reaction is by far the simplest method because lithiation of MesP(TMS)2 in situ is avoided and the volatile side product Me3SiOSiMe3 is easily removed in vacuo, negating extra purification steps.44,46,47 This method is used extensively in the preparation of the MesP=CPh2 monomer. On the other hand, the original phospha-Peterson reaction is a two-step reaction 1.4C (Scheme 1.4) and generates siloxides which need to be quenched and filtered of residual lithium salts.44,45,59,60 The Lewis-acid mediated phospha-Peterson reaction requires a time-consuming Et2O or CH2Cl2 extraction from an aqueous NaOH solution.49 Scheme 1.4 Three variants of the phospha-Peterson reaction for the synthesis of phosphaalkenes monomers. As shown in Scheme 1.2, hydrogenation 1.2B and 1,2-addition of polar compounds 1.2C occurs across the P=C double bond. Interestingly, the addition polymerization of the MesP=CPh2 monomer does not occur in the expected 1,2-addition manner (Scheme 1.7D), but rather follows an unprecedented addition isomerization mechanism (Scheme 1.7A, 1.7B, and 1.7C). A study of the mechanism of radical initiation/propagation of MesP=CPh2 with two equivalents of the radical mediator TEMPO showed that the second TEMPO radical adds to the ortho-methyl group of the 10 mesityl moiety instead of the methylene carbon at the preceding P=C bond as shown in Scheme 1.5.50 This evidence strongly suggests polymer propagation proceeds through C-H activation. A 1H-13C HSQC NMR study of a 13C labeled polymer revealed that the polymer exists primarily of monomer linkages through the C-H activation as shown in microstructure x of structure 1.15 with no spectroscopic evidence of microstructure y. However, addition across the P=C double bond (microstructure y) could not be ruled out based on these experiments. In the same study, it was shown that MesP=CPh2 may undergo nitroxide-mediated radical polymerization with alkoxy amine as the initiator/mediator (Scheme 1.7A). The resulting PMP structure is depicted in Scheme 1.5 and includes both isomers. It is believed that the polymeric structure of the first reported radical polymerization of MesP=CPh2 with the initiator VAZO-88 (Scheme 1.7B)26 maybe also be more accurately described as structure 1.15 (Scheme 1.7). Scheme 1.5 Reaction of Au(I) metallated MesP=CPh2 with two equivalents of TEMPO results in C-H activation. A second study on the mechanism of anionic propagation came to a similar conclusion. Monomer MesP=CPh2 was treated with one equivalent of MeLi to simulate initiation and was subsequently quenched with trityl chloride. Like the radical propagation study, the trityl group added to the ortho-methyl group of the mesityl moiety as shown in Scheme 1.6.51 However, smaller electrophiles such as protons, methyl cations, phosphenium moieties, and silylium moieties did add to the diphenyl position.98 The 1H-13C HSQC NMR spectrum of the PMP polymer closely 11 resembled that of the radically polymerized PMP with evidence of monomer linkages predominantly through C-H activation. However, the existence a P-C-P-C linkage as shown in microstructure y of 1.15 (Scheme 1.7) cannot be ruled out. Therefore, the anionically polymerized PMP may also be more accurately described as structure 1.15. The C-H activation during propagation was speculated to be a steric effect because of the bulky nature of phosphaalkene monomers. Scheme 1.6 Reaction of MesP=CPh2 with one equivalent of MeLi (anionic initiator) and quenched with trityl chloride results in C-H activation. Scheme 1.7 Structure of PMP after addition polymerization of MesP=CPh2. 12 PMPs are versatile polymers that can be easily modified post-polymerization due to the unique properties of phosphorus. Phosphorus has two stable oxidation states and the lone electron pair of a phosphine is easily accessible. The phosphorus centres of PMPs can be oxidized from phosphorus (III) to phosphorus (V) by treatment with elemental sulfur or H2O2 to form 1.16 and 1.17 (Scheme 1.8), respectively.26,52,55,60,61 On the other hand, PMPs can undergo coordination chemistry by treatment with a Lewis acid such as BH3â¢SMe353 or (tht)AuCl54 to from 1.18 and 1.19 (Scheme 1.8), respectively. These coordinated PMPs are air and moisture stable. 1.2.2 Applications of Poly(methylenephosphine)s The versatility of the phosphine functionality has led to many interesting applications of PMPs. Polymer 1.15 and its oxidized form 1.17 have been found to exhibit flame-retardant properties.55 Papers made from thermomechanical pulp and coated with solutions of 1.15 and 1.17 in CH2Cl2 were shown to promote char formation and inhibit burning. The major advantage of PMP based flame-retardants over the commercial flame-retardant monobasic ammonium phosphate is the resistance to water leaching. With the current push for sustainable materials, this development for cellulose-based products offers potential commercial applications in the wood and the pulp and paper industry. Previously flammable materials such as wood may now have an additional layer of safety in the construction industry. 13 Scheme 1.8 Chemical modification of poly(methylenephosphines). PMPs 1.15 can undergo oxidation reactions to produce 1.16 and 1.17 or coordination reactions to produce 1.18 and 1.19. PMPs also exhibit interesting photophysical properties. Phosphines with Ï-conjugated chromophores are widely used as fluorescent probes because they undergo a âturn-onâ emission upon oxidation or a coordination reaction.56-59 In 2014, Gates and co-workers observed a selective âturn-onâ emission upon the oxidation of the P moieties on PMPs with polyaromatic chromophores.60 When PMP 1.20 was oxidized to 1.21 using H2O2, a strong emission in THF solution was observed (λem = 342 nm) (Scheme 1.9). More fascinatingly, this âturn-onâ emission was selective only towards oxidation with oxygen and no emissions were observed by oxidation with sulfur or coordination with either borane or gold(I). The photophysical properties of PMP 14 1.20 was subsequently tuned to increasing the chromophore conjugation by replacing the 1-naphthyl moiety with 1-pyrene 1.23.61 Although 1.22 itself exhibited a low emission intensity, the oxidized 1.23 emission was much more intense. Again, the âturn-onâ emission in THF solution was observed. Three maxima were observed (λem = 379max, 389, and 400 nm) with a shoulder (λem = 423 nm) that tapers into the blue region (450-485 nm). The increased conjugation of the 1-pyrene compared to 1-naphthyl had red shifted the emission wavelength into the visible spectrum allowing for potential applications as oxygen sensors. Scheme 1.9 âTurn-onâ emissions of PMPs were observed with oxidation. Phosphaalkenes also undergo addition copolymerization with common commercial monomers. The first PMP copolymer was reported by Gates and co-workers in 2004.62 The phosphaalkene MesP=CPh2 1.14 was randomly copolymerized with styrene under free radical conditions with VAZO-88 as the radical initiator producing the polymer poly[(methylenephosphine)-ran-styrene] (PMP-r-PS) 1.24 (Figure 1.4). Since then, Gates and co-workers published a patent for three other random copolymers using the same procedure: poly[(methylenephosphine)-ran-(methyl methacrylate)] (PMP-r-PMMA) 1.25, poly[(methylenephosphine)-ran-(2-ethylhexyl acrylate)] 1.26, and poly[(methylenephosphine)-ran-(n-butyl acrylate)] (PMP-r-PBA) 1.27 (Figure 1.4).63 15 Figure 1.4 PMP random copolymers synthesized by free radical polymerization: 1.24 poly[(methylenephosphine)-ran-styrene]; 1.25 poly[(methylenephosphine)-ran-(methyl methacrylate)]; 1.26 poly[(methylenephosphine)-ran-(2-ethylhexyl acrylate)]; and 1.27 poly[(methylenephosphine)-ran-(n-butyl acrylate)]. In 2006, Gates and co-workers proved the first example of phosphaalkenes undergoing living anionic polymerization.64 In the same study, it was also shown that the living end of polystyrene may be used to initiate polymerization of MesP=CPh2 to afford a block copolymer poly[styrene-block-(methylenephosphine)] shown in Scheme 1.10A.64 The same procedure was also used to produce poly[isoprene-block-(methylenephosphine)] (PMP-b-PI) shown in Scheme 1.10B.65 PMP-b-PI was subsequently metallated with gold(I) to afford an amphiphilic PMP-b-PIâ¢AuCl with self-assembly behaviour.65 16 Scheme 1.10 Living anionic block copolymerization of: A PS-b-PMP and B PI-b-PMP. Further in 2018, Chen and co-workers reported the first example of utilizing the living -CPh2 anion end of a propagating PMP chain to initiate polymerization of acrylates to afford: poly[(methylenephosphine)-block-(methyl methacylate)] (1.28), poly[(methylene xylylphosphine)-block-(methyl methacylate)] (1.29), and poly[(methylenephosphine)-block-(tert-butyl acylate)] (1.30) (Scheme 1.11).66 17 Scheme 1.11 Living anionic block copolymerization using the propagating anionic end of PMP to initiate acrylates. Thus far, only phosphaalkenes with a single polymerizable moiety have been discussed. However, there are carbon-based monomers with two unsaturated function groups such as isoprene and butadiene. Both of which are extensively studied in the tire industry. In 1997, attempts were made to synthesize the phosphorus analogue of butadiene using a cross-coupling procedure affording P-Mes*-substituted 1-phospha-1,3-butadiene 1.31 shown in Scheme 1.12.67 However, 1-phospha-1,3-butadiene 1.31 was found to be unstable and speculated to auto-polymerize. This observation piqued the interested of further investigations by the Gates group. The 31P{1H} NMR spectroscopy of 1.32 revealed that polymerization primarily occurs through 3,4-addition.68 18 Scheme 1.12 Synthesis of poly(1-phospha-1,3-butadiene). In an attempt to synthesize an isolable monomer, the same cross-coupling procedure was employed to affording 1-phosphaisoprene 1.33 (phosphorus analogue of isoprene) (Scheme 1.13).68 Unlike 1-phospha-1,3-butadiene 1.31 , 1-phosphaisoprene may be isolated by purification within 24 hours to prevent auto-polymerization. The isolated 1-phosphaisoprene was subsequently treated with anionic initiator nBuLi to afford poly(1-phosphaisoprene) (1.34) (Scheme 1.13). Similar to 1.32, 31P{1H} NMR spectroscopy revealed that poly(1-phosphaisoprene) comprised primarily of the x microstructure leaving the P=C moiety intact. Due to the excellent Ï-acceptor properties of phosphaalkenes, these may provide a low valent phosphorus ligand for metals.69,70 Scheme 1.13 Synthesis of poly(1-phosphaisosprene). 19 1.3 Polymer Supports for Catalysis In the field of organometallic chemistry, phosphines have found widespread use as ligands in numerous metal-based catalysts.17 Therefore, it comes as no surprise that phosphine containing polymers would be also excellent ligands in the application of catalysis. Polymeric catalysts have several advantages over their molecular cousins and those will be discussed in this section. Furthermore, the use of phosphines in macromolecular supports will also be explored. 1.3.1 Phosphorus Containing Supports for Catalysis In recent years, the growing need for more environmentally friendly and sustainable processes in the chemical industry has led to the shift in research towards âGreen Chemistryâ.71 Green chemistry is defined as the design of chemical products and processes that reduce or eliminate the use or generation of hazardous substances. One of the fundamental pillars of green chemistry is catalysis.72,73 It is estimated that more than 85% of all chemical products are produced with the aid of catalysts.74 The approximate usage of catalysts by industry is 21% for polymer production, 22% for coal, oil and gas refinement, 27% for chemical manufacturing, and 30% for environmental applications.75 The demand for catalysts and the shift towards Green Chemistry has renewed interest in polymer-supported catalysts that often make use of metal-bound polymers. To understand the need for polymer-supported catalysis one must understand their advantages. Catalysts are often separated into two categories that describe the phase of the catalyst, namely heterogenous or homogeneous. A heterogenous catalyst acts in a different phase than the substrates as shown in Figure 1.5I. Some well-known examples of this are the palladium(0)-catalyzed hydrogenation of alkenes (solid palladium on carbon (Pd/C) as the catalyst with gaseous hydrogen and dissolved alkenes as the substrate)76 and the Haber-Bosch process (solid iron-based 20 catalyst with gaseous hydrogen and nitrogen substrates)77. A homogeneous catalyst acts in the same phase as the substrates as shown in Figure 1.5II. Examples of this are the Fischer-Speier esterification (dissolved acid catalyst with dissolved carboxylic acid and alcohol substrates)78 and the Monstanto process used in the industrial production of acetic acid (dissolved rhodium-based catalyst with dissolved MeOH and CO2 substrates).79 Figure 1.5 Illustration of: I heterogeneous catalysis, II homogenous, and III polymer-supported catalysis. Homogeneous catalysts usually have well defined active sites that are readily accessible by substrates in the same phase offering the advantage of high catalytic activity and efficiency. Furthermore, many metal complex catalysts allow for fine tuning of their steric and electronic properties through ligand design. This affords high selectivity, which is a requirement for many pharmaceutical applications. However, homogeneous catalysts do suffer from several drawbacks. The difficulty in catalyst separation from product could pose an obstacle for commercialization. Metals such as palladium and platinum are some of the most commonly used metals in the pharmaceutical industry. However, trace amounts of these heavy metals are toxic to the human body. In the United States, the Food and Drug Administration has outlined strict limits for heavy metals in pharmaceutical drugs. For example, palladium and platinum have been set at a maximum of 1.0 μg/g.80 Many conventional purification techniques, although effective at separating catalyst I II III Solid catalyst Dissolved Molecular Catalyst Polymer Supported Catalyst Dissolved Substrate 21 from product, causes the loss or destruction of the catalyst. For example, the common technique of column chromatography may result in the catalyst being adsorbed onto the silica rendering it irrecoverable. Other techniques such as distillation can destroy the catalyst. Many homogeneous catalysts are thermally sensitive and typically decompose at temperatures below 150°C.81 In order to improve the stability of homogeneous catalysts as well as the ease of recovery and reuse, several approaches have been employed. These include performing the reactions in ionic liquids or supercritical CO2 fluids or immobilization of homogeneous catalysts onto inert materials such as polymers.81 In polymer-supported catalysis, metal centres are bound to polymeric ligands as opposed to free ligands (Figure 1.5III). Depending on the solubility of these polymeric supports, they may serve as either heterogenous or homogenous catalysts. The former immobilizes the catalyst onto an insoluble polymeric support and can be used in a continuous flow microreactor. The latter makes use of a soluble polymeric support working in the same phase as the substrates. The catalyst may be easily separated by precipitation from a co-solvent or ultra-filtration. Due to the multitude of transition metal phosphine complexes, phosphines have been used extensively in transition metal catalysts. It is therefore not surprising that polymeric phosphines have gained much attention as candidates for polymer supports for catalysis. One of the common and straightforward methods to introduce a phosphine moiety into a polymer was a simple direct reaction between a halide functionalized polystyrene such as bromopolystyrene or poly[(styrene)-ran-(chloromethyl styrene)] copolymer (Merrifieldâs Resin) with a phosphine to produce 1.35 (Scheme 1.14). The subsequent attachment of the desired metal may be achieved through a ligand substitution with an organometallic precursor producing a polymeric metal phosphine complex 1.36 (Scheme 1.14).82 Polymeric phosphine ligands 1.35 and its variants have the capability to form metal phosphine complexes with a myriad of transition metals: Cr, Mn, Ru, Os, Co, Rh, Ir, 22 Ni, Pd, Pt, Cu, and Au.83-87,90,91 Therefore, the phosphine functionalized polystyrene is a common ligand candidate for polymer-supported catalysis. Scheme 1.14 A generic synthetic method to functionalize a polystyrene based polymer with a transition metal phosphine complex. The polystyrene resin with styrene supported triphenylphosphine moieties 1.37 gained significant interest due to its ability to form 1.38, which was analogous to the well-known Pd(PPh3)4. One of the earliest examples of 1.38 was synthesized in the 1970s by Pittman and co-workers, and Trost and co-workers by heating the polymeric resin 1.37 in a solution of Pd(PPh3)4 (Scheme 1.15).84,85 Through elemental analysis, it was determined that 1.38 contained 1.2 â 1.6% Pd.84,85 Pittman and co-workers demonstrated that 1.38 could be used as an oligomerization catalyst for 1,3-butadiene to produce oligobutadiene with 100% yield. Furthermore, the palladium(0) complex 1.38 could be recycled with simple filtration and a second reaction cycle resulted in 85% yield.84 Since then, 1.38 has found many applications in catalysis including the Suzuki-Miyaura cross-coupling reaction, which was discovered later in 1979.86 23 Scheme 1.15 The synthesis of a Pd-based catalyst supported by a polystyrene resin for use as a catalyst in oligomerization reactions with 1,3-Butadiene. Thus far, the discussion on phosphine functionalized polystyrene (Scheme 1.14/1.15) only touched on monodentate ligands. Interestingly, in 1994 Wang and co-workers reported one of the first bidentate ligands based on functionalizing a polystyrene polymer.87 A pendant bidentate-phosphine ligand 1.39 was installed onto poly(vinylbenzyl chloride) to create the polymer support 1.40 which was subsequently metallated with Pd(II) using (PhCN)2PdCl2 to produce an insoluble polymer-supported catalyst in organic solvents shown in Scheme 1.16. The catalytic ability of 1.41 was demonstrated using a Heck arylation reaction between iodobenzene and methyl acrylate with 1 mol% catalyst loading with acetonitrile as the solvent. Although yields were not discussed, figures showed yields over 80%. Recyclability studies showed easy recovery of the catalyst through simple filtration and yields decreased less than 10% after five cycles. 24 Scheme 1.16 The synthesis of a polymer with a pendant bidentate-phosphine-palladium complex for use as a catalyst in Heck arylation. As previously discussed, the modularity of polystyrene-based phosphine ligands 1.35/1.37 allows for metallation with a variety of metals. One such metal that is of particular interest in our research group is gold (Au) and will be further discussed in Chapter 2 of this thesis. Interestingly, metallic Au was considered inert and therefore catalytically inactive for a long time88 until 1973 when Bond and co-workers demonstrated the hydrogenation of olefins with a supported Au(I) catalyst.89 Due to the later entry of the field of gold catalysis compared to other transition metals such as Pd and Pt, research regarding polymer-supported gold catalysis has only gained attention as recently as the 2010s.90,91 In 2010, Egi reported the first synthesis of a recyclable and durable Au(I) polymeric catalyst based on the same polystyrene-based resin with phosphine ligands 1.35.90 Precatalyst 1.42 was generated by metallating 1.37 with (Me2S)AuCl shown in Scheme 1.17. This precatalyst 1.42 was structurally analogous to the triphenylphosphinegold(I) chloride (Ph3PAuCl) 25 precatalyst which is an extensively studied and commonly available precatalyst.93,96-99 The active catalytic species was generated by abstracting the chloride anion of 1.42 with a silver salt (AgOTf or AgNTf2) generating the Au+ catalytic site of 1.43 (Scheme 1.17). Intramolecular cyclization reactions were attempted on substrate 1.44 to produce the furan 1.45 with 0.5 mol% of Au(I) catalyst. After the first reaction, the yield was 98% and the catalyst 1.43 was recovered by decantation. After the 8th catalytic run, the yield was reduced to 94%. Furthermore, 1.43 could be implemented in a continuous flow reactor system where 2.5 mol% of Au(I) catalyst could cyclize 1.44 to produce 1.45 with a yield 92% at a flow rate of 1.0 mL min-1. This robust catalytic system was one of the inspirations for the current catalytic work in Chapter 2. Scheme 1.17 The synthesis of a Au-based catalyst supported by a polystyrene resin for use as a catalyst in cyclization reactions to produce a furan 1.45. By far, the most common method to introduce a phosphine onto a polystyrene support would be to functionalize the styrene residue after polymerization and crosslinking (Scheme 1.14-1.17). A unique alternative approach would be to install the phosphine prior to polymerization. In 2015, Cai and co-workers were able to treat monomer 4-bromostyrene 1.46 with PCl3 to produce a triarylphosphine 1.47 with three polymerizable moieties (Scheme 1.18).91 Through the radical polymerization of 1.47 with the radical initiator AIBN, a porous organophosphorus support 1.48 was fabricated (Scheme 1.18). To metallate this porous support, 1.48 was treated with (Me2S)AuCl 26 to produce 1.49 which was structurally analogous to Ph3PAuCl. The authors further coordinated a triazole ligand producing 1.50 (Scheme 1.19) to prevent the formation of AgCl salts that are typically formed after the abstraction of Cl- anion during the generation of the Au+ active catalytic species. Instead, the Au+ cation 1.51 would be generated through treatment with an acid such as HOTf (Scheme 1.19). Scheme 1.18 Synthesis of a porous organophosphorus support Scheme 1.19 Generation of the active catalytic species from polystyrene resin-based Au(I) precatalyst. The catalyst 1.51 was able to catalyze alkyne hydrations with a variety of substrates (Scheme 1.20). Reactions 1.20A, 1.20B, 1.20C, and 1.20D, were able to produce impressive yields of 93%, 91%, 90%, and 91%, respectively.91 The polymeric catalyst was also shown to be superior to the molecular analogue triphenylphosphine-Au-triazole which produced the yields 85%, 45%, 27 90%, and 89%, respectively. The higher yields were likely attributed to the increased stability of the gold cation from the porous scaffold. Furthermore, this catalyst could be regenerated by the addition of more HOTf after washing with MeOH. Regenerated 1.51 exhibited no significant loss in catalytic performance after seven reaction cycles with the exception of Scheme 1.20B due to the less reactive alkyne. Scheme 1.20 Alkyne hydration reactions catalyzed by catalyst 1.51. Gold catalysts are also known to activate alkynes for nucleophilic attacks. Cai and co-workers also demonstrated the ability for 1.51 to perform intermolecular hydroamination of phenylacetylene with p-anisidine producing 1.52 at a yield of 43% (Scheme 1.21).91 In comparison, the molecular analogue triphenylphosphine-Au-triazole produced a low yield of 30%. Once again, the increased stability of the polymer resin stabilized support proved beneficial. Due to the relatively inexpensive substrates phenyl acetylene and aniline, this reaction inspired the hydroamination studies for a polymer-supported Au(I) catalyst in Chapter 2. 28 Scheme 1.21 Intermolecular hydroamination reaction catalyzed by catalyst 1.51. 1.3.2 Poly(methylenephosphine)s as Supports for Pd Cross-Coupling Reactions Up to this point, all polymer/polymer resin supported catalysts discussed have been heterogeneous in nature. A soluble support would greatly increase the efficiency of catalysis. In addition, all polymers/materials have relied on pedant ligands which adds additional synthetic steps shown in Scheme 1.22A. The unique class of polymers, poly(methylenephosphine)s (PMPs), have offered solutions to these shortcomings. As previously discussed, Gates and co-workers have synthesized the PMP homopolymer and PMP-r-PS copolymer. In the same study, these polymers were proven to be excellent ligand supports for palladium.62 PMPs can be synthesized without the need for pendant attachments to monomers or the chemical modifications post-polymerization. The phosphorus ligand is part of the polymerizable moiety of the phosphaalkene monomer. After polymerization, the metal is simply immobilized onto the polymeric backbone shown in Scheme 1.22B. PMPs metallated with Pd0 and Au+ are soluble in common solvents such as DCM and THF. This allows for homogenous catalysis, which greatly improves catalytic efficiency. As described previously, PMP homopolymers 1.15 are prepared by the polymerization of the MesP=CPh2 phosphaalkene monomer 1.14 through radical or anionic polymerization. However, the random 29 copolymer PMP-r-PS 1.24 can only be prepared by radical copolymerization between phosphaalkene and styrene. In the catalysis portion of the study, Suzuki cross-coupling was performed by dissolving the PMP homopolymer or the PMP-r-PS copolymer in THF together with the substrates phenyl bromide and phenyl boronic acid, 3.3 equivalents of a weak base CsF, and 5 mol% of Pd2(dba)3 (Scheme 1.23). The exact structure of active catalytic species is not known because the Pd centres may coordinate to a phosphine from another polymer chain or could coordinate to a phosphine on the same polymer chain in a loop. Upon the completion of the reaction, the PMP-Pd or (PMP-r-PS)-Pd complex would be precipitated out of solution using hexanes and filtered leaving only the product behind. It was found that the biphenyl yields using PMP-r-PS copolymer supports were 2.7 times higher than that of using PMP homopolymer supports. The advantages of PMP-r-PS over PMP is threefold: 1) active metal centres are more spaced out allowing for less congested access for substrates; 2) Copolymers allow for a higher molecular weight with the same number of phosphorus centres making polymer separation through reprecipitation easier; 3) the higher molecular weights also make it is easier to weigh out catalytic amounts of phosphorus centres without the need for serial dilutions. Further optimization of reaction conditions, where the phosphorous ligand to Pd ratio was 2.8:1 and the temperature at 80°C, resulted in a 90% yield. Polymer-supported catalysis with PMP polymers bridge the gap between homogenous and heterogeneous catalysis by offering homogenous-like efficiencies and heterogeneous-like ease of product separation. 30 Scheme 1.22 Comparison of conventional catalysts immobilized onto pendant groups of polymers with that of catalysts immobilized onto the polymeric backbone of PMPs. 31 Scheme 1.23 Suzuki cross-coupling using homopolymer PMP 1.15 and copolymer PMP-r-PS 1.24 as catalyst supports for palladium. 32 Chapter 2: Gold(I) Metallated Poly(methylenephosphine)s Copolymers as Catalyst Supports for Hydroamination 2.1 Introduction: Catalysis with Gold(I) In 2008, Gates and co-workers reported the first example of a Au(I) metallated PMP by metallating PMP 2.1 with (tht)AuCl as shown in Scheme 2.1.54 Since PMPs have been used in the past as a polymeric support for palladium catalyzed Suzuki-Miyaura cross-coupling (Scheme 1.23)62, we wanted to investigate the possibility for catalysis with Au(I) metallated PMP. Scheme 2.1 Metallation of PMP homopolymer with Au(I). 2.1.1 Olefin and Alkyne Activation Unlike many late transition-metal catalysts such as Pd-based catalysts, which has two readily accessible oxidation states Pd(0) and Pd(II), Au-based catalysts do not readily cycle between the Au(I) and Au(III) oxidation states. Thus, Au-based catalysts are unable to undergo classic oxidative-addition and reductive-elimination cycles.92 However, Au(I) catalysts have unique electronic properties that make them desirable for the activation of Ï-systems. Au(I) complexes have a unique propensity for the formation Ï-complexes with the Ï-bonds of alkenes and alkynes. This behaviour can be explained by relativistic effects of gold which causes the 33 contraction of the valance 6s and 6p orbitals. In Au(I) complexes, the contraction results in a low-lying lowest unoccupied molecular orbital (LUMO) giving rise to its strong Lewis acidity. The other effect of the contraction of the 6s and 6p orbitals causes the 4f and 5d orbitals to be shielded thus expanding their size. These 5d electrons are too low in energy to participate in backbonding to the antibonding orbitals of alkenes and alkynes.92 The bonding interactions between Au+ and an alkyne can be described with the Dewar-Chatt-Duncanson model shown in Figure 2.1. A computational study of the [Au+(C2H2)] complex showed that the largest bond energy contribution is the Ï interaction between the dz2 and the Ïâ¥ bonding orbital (ca. 65%), followed by the weaker in-plane Ïâ¥ interaction between the dxy and the Ïâ¥* antibonding orbital (ca. 27%), following that, the orthogonal Ïâ¥ interactions between the dyz and the Ïâ¥ bonding orbital (ca. 7%) and lastly the δ interaction between the dxy and the Ïâ¥* antibonding orbital (ca. 1%), which are negligible.93 The strong bond energy contribution of the Ï interaction and the weak in-plane Ïâ¥ interaction concludes that alkyne ligands are good Ï donors and weak Ï acceptors towards Au+. In a [Au+(C2H2)] complex, the overall electron density in the alkyne ligand is reduced, increasing its electrophilicity and allowing for nucleophilic attack. Therefore, Au(I) complexes are commonly used as catalysts for reactions involving alkyne activations. 34 Figure 2.1 Dewar-Chatt-Duncanson model representation displaying interactions between Au+ and an alkyne ligand. A typical LnAuCl precatalyst (where L = neutral ligand) starts by the Cl- abstraction with a Ag+ salt generating the LnAu+ active catalytic species 2.2. The Ï-system of the neutral alkyne ligand will interact with the metal coordinating in a η2 manner initially 2.3 and will subsequently slip η2 â η1 2.4 as depicted in Scheme 2.2, thereby increasing alkyne electrophilicity and facilitating a nucleophilic attack.93,94 Finally, the product is released from the LnAu+ catalyst via protodemetallation (Scheme 2.2).95 Scheme 2.2 General catalytic cycle of gold catalysis. 35 2.2 Results and Discussions 2.2.1 Experimental Design of Polymer-Supported Au(I) Catalysts To assess the suitability for (PMP-r-PS)-Au-Cl to be a polymer-supported precatalyst, it was important to find a simple reaction that works with a common Au(I) catalyst analogue. The same reactions would then be applied to a model compound of (PMP-r-PS)-Au-Cl and then finally with the polymeric precatalyst itself. Ph3P-Au-Cl was chosen as the commercial catalyst analogue due its ease of synthesis and more importantly, its widely cited use in the literature.93,96-99 As described earlier, the Ï-acidic nature of Au(I) makes it ideal for activations of olefins and alkynes.93 As such, hydroamination was chosen as the model reaction. The substrates chosen were: aniline as the nucleophile, and phenylacetylene as the electrophile. Both substrates were readily available in the lab. The active catalytic species was a Au+ cation that was generated by the abstraction of the Cl- anion with Ag+. Tol-d8 was chosen as a non-coordinating solvent. The reaction was premixed in a vial and transferred into a J Young NMR tube in order to monitor the reaction progress via 1H NMR spectroscopy. The benchmark reaction with the Ph3PAuCl precatalyst is depicted in Scheme 2.3. After the successful hydroamination trials with Ph3P-Au-Cl as the precatalyst, the same reaction under the same conditions was attempted with the Au(I) metallated model compound precatalyst MesMeP-CHPh2 2.9 (Scheme 2.5) and finally with the polymeric precatalyst (PMP-r-PS)-Au-Cl 2.11 (Scheme 2.7). 36 2.2.2 Hydroamination with Ph3P-Au-Cl as Precatalyst Hydroamination between aniline and phenyl acetylene produces a major Markovnikov product 2.5 as well as a minor anti-Markovnikov product 2.6 after tautomerizing from an enamine into an imine (Scheme 2.3).99,100 As a benchmark test, the hydroamination reaction was performed using the substrates phenyl acetylene and aniline with 5 mol% of Ph3PAuCl precatalyst and 5 mol% AgOTf (Scheme 2.3). The reaction progress was monitored by 1H NMR spectroscopy and the stack plot is shown in Figure 2.2. After 411 hours at room temperature, the consumption of substrates aniline and phenyl acetylene were assigned to the decreasing signals at 3.21 ppm (broad singlet, NH2) and 2.75 ppm (singlet, â¡CH), respectively. Only the Markovnikov product 2.5 was observed by the signals attributed to 7.94 â 7.89 ppm (multiplet, ArH2) and 1.86 ppm (singlet, CH3), respectively, as shown in Figure 2.3. Conversely, the anti-Markovnikov product 2.6 was not observed due to the absence of methylene signals in the 3.5 ppm region. Furthermore, there was no evidence of the anti-Markovnikov enamine product prior to isomerization as there were no other broad signals in the 5 â 3 ppm region which are characteristic of aromatic amine signals. The diagnostic integrations at 2.75 and 1.86 ppm were used to determine product conversion using Equation 2.1. Table 2.1 shows the data for the conversion of product 2.5 over time, and the plot for the progress of conversion is shown in Figure 2.4. After 411 hours, the total conversion to product 2.5 was 53.1%. 37 Scheme 2.3 Hydroamination of phenyl acetylene with aniline using Ph3P-Au-Cl as the precatalyst. Figure 2.2 1H NMR (Tol-d8, 400 MHz) spectra stack plot of hydroamination reaction mixture at room temperature with Ph3PAuCl as precatalyst. * = residual toluene. * 38 Figure 2.3 1H NMR (Tol-d8, 400 MHz) spectrum of hydroamination reaction mixture with Ph3PAuCl as precatalyst. * = residual toluene. % ConversionMP =ð»MPð»MP + 3ð»PhAce Where: HPhAce represents the integration of the proton from the alkyne group of phenyl acetylene HMP represents the integration of the protons from the methyl group of the Markovnikov product Equation 2.1 Equation to calculate product conversion of the Markovnikov product 2.5. Table 2.1 Hydroamination product 2.5 conversion data for precatalyst Ph3PAuCl. Entry Elapsed time (h) Percentage conversion of product 2.5 determined by 1H NMR (%) 1 0 0.3 2 4 2.9 3 24 12.7 4 47 19.1 5 72 31.4 6 117 43.4 7 239 49.6 8 411 53.2 * 39 Figure 2.4 Progress of gold(I) catalyzed hydroamination with Ph3PAuCl precatalyst. 2.2.3 Hydroamination with Au(I) Metallated Model Compound as Precatalyst After successful trials of hydroamination using the Ph3PAuCl precatalyst, hydroamination was attempted on the metallated model compound precatalyst 2.9 (Scheme 2.4) of the polymer-supported catalyst (PMP-r-PS)-Au-Cl polymer 2.11 (Scheme 2.6). The unmetallated model compound 2.7, was previously synthesized as part of a mechanistic study of the initiation and termination steps of the anionic polymerization of the MesP=CPh2 phosphaalkene monomer 2.8 (Scheme 2.4).101 At that time, it was assumed that polymerization of MesP=CPh2 would undergo addition polymerization across the P=C double bond shown in microstructure y of 2.1 (Figure 2.5).26,62 However, as previously discussed in Section 1.2.1., it was established since 2013 that polymerization predominantly involves a C-H activation step as represented by microstructure x of 2.1 (Figure 2.5).50,51 Therefore, it is important that the chemical environment of the phosphorus centre in the model compound mimics that of the phosphorus centres on the polymer. In the model compound, the methyl group is adjacent to phosphorus atom similar to the methylene -CH2- on the 01020304050607080901000 50 100 150 200 250 300 350 400 450Percentage Conversion (%)Elapsed time (h)40 mesityl group of the polymer (microstructure x of 2.1) which is also adjacent to the phosphorus atom due to the C-H activation. Therefore, the model compound 2.7 is a reasonable representation of both microstructures x and y of the PMP polymer 2.1. Model compound 2.7 is easily synthesized by treating monomer 2.8 with MeLi followed by quenching with MeOH at -78°C shown in Scheme 2.4. Figure 2.5 Structure of PMP model compound 2.7 and structure of PMP polymer 2.1. Scheme 2.4 Synthesis of PMP model compound precatalyst 2.9 from MesP=CPh2 monomer. The precatalyst 2.9 was prepared by treating model compound 2.7 with (tht)AuCl (Scheme 2.4). Phenyl acetylene was hydroaminated with aniline using 5 mol% of precatalyst 2.9 and 5 mol% of AgOTf (Scheme 2.5). The reaction progress was monitored by 1H NMR spectroscopy and the stack plot is shown in Figure 2.6. After 167 hours at room temperature, the consumption of substrates aniline and phenylacetylene was confirmed by the consumption of signals at 2.97 ppm (broad singlet, NH2) and 2.72 ppm (singlet, â¡CH), respectively. The production of the Markovnikov product (MP) 2.5 was observed by the signals at 7.95 â 7.89 ppm (multiplet, ArH2) 41 and 1.86 ppm (singlet, CH3), respectively, as shown in Figure 2.7. Similar to using the Ph3P-Au-Cl precatalyst, no methylene signals from the anti-Markovnikov product 2.6 were observed in the 3.5 ppm region. The diagnostic integrations at 2.72 and 1.86 ppm were used to determine product conversion using Equation 2.1. For the hydroamination reaction at room temperature, Table 2.2 shows the data for the conversion of product 2.5 over time, and the plot for the progress of conversion is shown in Figure 2.8. After 167 hours (ca. 7 days) at room temperature, the total conversion to product 2.5 was 64.6%. The same reaction was repeated at a temperature of 110°C resulting in a similar result with a total conversion of 2.5 at 69.3%. The results are summarized in Table 2.4. It appears that the elevated temperature only accelerated the rate of reaction and did not affect catalyst decomposition. Scheme 2.5 Hydroamination of phenyl acetylene with aniline using the Au(I) metallated model compound 2.9 as the precatalyst. 42 Figure 2.6 1H NMR (Tol-d8, 400 MHz) spectra stack plot of hydroamination reaction mixture at room temperature with the Au(I) metallated model compound 2.9 as the precatalyst. 43 Figure 2.7 1H NMR (Tol-d8, 400 MHz) spectrum of hydroamination reaction mixture with the Au(I) metallated model compound 2.9 as the precatalyst. * = residual toluene. Table 2.2 Hydroamination product 2.5 conversion data for the model compound precatalyst 2.9. Entry Elapsed time (h) Percentage conversion of product 2.5 determined by 1H NMR (%) 1 0 1.4 2 2 4.5 3 20 24.2 4 47 40.7 5 72 48.1 6 101 56.1 7 123 58.3 8 142 63.7 9 167 64.6 * 44 Figure 2.8 Progress of gold catalyzed hydroamination with the Au(I) metallated model compound 2.9 as the precatalyst. 2.2.4 Synthesis and Characterization of Au(I)-Metallated Poly[(methylenephosphine)-ran-styrene] The PMP-r-PS copolymer was selected as the polymer support for the Au(I) precatalyst over the PMP homopolymer for two reasons. The first being the possibility of the steric congestion around the phosphorus centres causing difficulty for substrate access resulting in reduced catalytic activity.62 The second being the ease of accurately weighing out the catalyst, since the mass per gold centre is inflated by the styrene residues. PMP-r-PS was synthesized using radical copolymerization between the monomers MesP=CPh2 and styrene; based on the literature procedure shown in Scheme 1.7B and Figure 1.4.62,102 However, using a copolymer support comes with its difficulties. Due to the costs of Au(I), the phosphorus (III) centres should be metallated in a stochiometric fashion. In addition, the exact stoichiometric ratio of catalytic gold centres must be known for a catalytic reaction. Therefore, inverse gated proton decoupled 13C NMR 01020304050607080901000 50 100 150 200Percentage conversion (%)Elapsed time (h)45 spectroscopy was used to quantify the phosphorus content and to facilitate accurate Au:P stoichiometry.102 For the polymeric catalyst support, phosphaalkene MesP=CPh2 and styrene were copolymerized with a loading ratio of 20:80, respectively, and initiated with 1 mol% VAZO 88 radial initiator to afford PMP-r-PS 2.10. After the polymerization and purification of PMP-r-PS, 31P NMR spectrum (Figure 2.10I) was obtained and showed broad overlapping signals with maxima at 4.6, -4.9, -8.0, -10.3, and -18.9 ppm, indicating a successful polymerization. Inverse gated 13C spectrum was obtained and shown in Figure 2.9. The aromatic carbons Ar-C in the 150-120 ppm region can be distinguished from the methyl carbons Mes-CH3 and methylene carbons Mes-CH2 at 26-20 ppm from the mesityl group of the phosphaalkene residue. Equation 2.2 was used to determine the phosphaalkene composition (FPA) in the PMP-r-PS copolymer and Equation 2.3 was used to determine the stoichiometric ratio of phosphorus centres per mass of polymer. It was determined that the copolymer composition was FPA = 0.15 with 1.10 mmol of phosphorus per gram of PMP-r-PS polymer. GPC analysis determined the molecular weight (Mn) to be 6,200 g mol-1 with a PDI of Ä = 1.22. 46 Figure 2.9 Inverse gated proton 13C{1H} NMR (CDCl3, 101 MHz) spectrum of PMP-r-PS 2.10 copolymer. * = residual CHCl3. FPA =2ð¶Me(ð¶Arâ6ð¶Me)+2ð¶Me and FSty = 1 â FPA CMe represents the integration value of methyl and methylene carbons of the mesityl group CAr represents the integration value of aromatic carbons Equation 2.2 Equation to determine copolymer composition FPA and FSty of PMP-r-PS 2.10. ðPA =ðPolymerðPA + FStyðStyFPA and ðSty =ðPolymerðSty + FPAðPAFSty MPA represents the molar mass of a single phosphaalkene monomer MSty represents the molar mass of a single styrene monomer *Mass is conserved during polymerization as it is an addition polymerization. The mass of the monomer is the same as the mass of the residue in the polymer chain Equation 2.3 Equation to determine moles of phosphorus (nPA) for a given mass of polymer (mPolymer) for PMP-r-PS 2.10. Mes-CH2 Mes-CH3 Ar-C * 47 PMP-r-PS15:85 2.10 was metallated with (tht)AuCl to produce the precatalyst (PMP-r-PS)15:85-Au-Cl 2.11 with an adapted procedure from Gillon et al shown in Scheme 2.6.54 A downfield shift of the 31P NMR spectrum shown in Figure 2.10II can be observed upon the metallation of the phosphine centres showing broad overlapping signals with maxima at 41, 31.2, 21.3, and 18.0 ppm with no signals in the 4.6 â -18.9 ppm region indicating the successful Au(I) metallation of all phosphorus (III) centres. This downfield shift is expected due to the withdrawal of electron density of the lone pair on phosphorus to form a dative bond with Au. Furthermore, the GPC refractive index (RI) trace in Figure 2.11 shows the (PMP-r-PS)-Au-Cl 2.11 eluting at an earlier retention time compared to the unmetallated PMP-r-PS15:85 2.10 indicating an increase in molecular weight. The analysis of the RI trace confirmed an increase in molecular (Mn) from 6,200 g mol-1 to 7,700 g mol-1. Since the copolymer composition was FPA = 0.15 (PA:PS ratio is 15:85), there would be a single 31P atom for every 6.67 polymer residues where the 6.67 residues consisted of one PA residue (MPA = 316.4 g mol-1) and 5.67 PS residues (MPS = 104.15 g mol-1). In terms of molecular weight, there is one 31P atom for every 906.9 g mol-1 of PMP-r-PS15:85 polymer. After metallation with (tht)AuCl (Scheme 2.6), every 31P center would gain 139.6 g mol-1 for the coordination of both the Au and Cl atoms. Therefore, there would be a 139.6 g mol-1 increase for every 906.9 g mol-1 of unmetallated PMP-r-PS15:85. The theoretical molecular weight of (PMP-r-PS)15:85-Au-Cl should be 7,100 g mol-1 and is within the margin of error of the experimental 7,700 g mol-1. Equation 2.4 can then be applied to determine the stoichiometric amount of Au(I) for a given mass of polymer 2.11 which was determined to be 0.878 mmol of Au(I) per gram of (PMP-r-PS)15:85-Au-Cl copolymer. This ratio was necessary in determining the precise catalyst to substrate ratios. 48 Scheme 2.6 Coordination of Au(I) to PMP-r-PS 2.10 to produce the precatalyst (PMP-r-PS)-Au-Cl 2.11. Figure 2.10 31P NMR (CDCl3, 162 MHz) spectrum of PMP-r-PS 2.10 and (PMP-r-PS)-Au-Cl 2.11. ðPA =ðPolymerðPAAuCl+ðStyFStyFPA and ðSty =ðPolymerðPAAuClFPAFSty+ðSty MPAAuCl represents the molar mass of a single phosphaalkene monomer with the phosphine coordinated to Au-Cl. Equation 2.4 Equation to determine moles of Au centers for given mass of Au metallated polymer (mPolymer) for (PMP-r-PS)-Au-Cl 2.11. 4.6 ppm -4.9 ppm -8.0 ppm -10.3 ppm -18.9 ppm 41.0 ppm 31.2 ppm 21.3 ppm 18.0 ppm I. PMP-r-PS (2.10) II. (PMP-r-PS)-Au-Cl (2.11) 49 Figure 2.11 GPC trace of unmetallated copolymer PMP-r-PS 2.10 (dashed blue trace) and the gold metallated copolymer (PMP-r-PS)-Au-Cl 2.11 (solid orange trace). 2.2.5 Hydroamination with (PMP-r-PS)-Au-Cl as Precatalyst The promising results of hydroamination with the Au(I) metallated model compound 2.9 precatalyst prompted further investigations with the polymer-supported precatalyst (PMP-r-PS)15:85-Au-Cl 2.11 where the ratio of PA:PS residues in the polymer chain is 15:85. For the purposes of the catalytic studies in this thesis, all (PMP-r-PS)15:85-Au-Cl are denoted as (PMP-r-PS)-Au-Cl and represented by compound 2.11. Reaction conditions were kept consistent with both previous hydroamination studies using precatalysts Ph3PAuCl and model compound 2.9. Phenyl acetylene was hydroaminated with aniline using 5 mol% of Au(I) catalytic centers on (PMP-r-PS)-Au-Cl (Scheme 2.7). The reaction progress was monitored by 1H NMR spectroscopy and the stack plot is shown in Figure 2.12. After 216 hours (9 days) at room temperature, the consumption of substrates aniline and phenylacetylene can be seen by the decrease in signals at 2.88 ppm (broad singlet, NH2) and 2.69 ppm (singlet, â¡CH), respectively (Figure 2.13). The production of the Markovnikov product (MP) 2.5 can be seen by signals at 7.94 â 7.87 ppm (multiplet, ArH2) and 12 14 16 18 20 22 24Retention time (mins)PMP-r-PS(PMP-r-PS)-Au-Cl50 1.86 ppm (singlet, CH3), respectively, as shown in Figure 2.13. The diagnostic integrations at 2.69 and 1.86 ppm are used to determine product conversions with Equation 2.1. It is worth noting that the baseline does contain several broad peaks due to the signals from the polymer support. For the hydroamination reaction at room temperature, Table 2.3 shows the data for the conversion of product 2.5 over time, and the plot for the progress of conversion is shown in Figure 2.14. The plot for the progress of conversion is shown in Figure 2.14. After 1008 hours (42 days), the total conversion to product 2.5 was 99.6%. The same reaction was repeated at a temperature of 110°C, resulting in a similar result with a total conversion of 2.5 at 98.6% after 30 hours. Similar to the results using the Au(I) metallated model compound precatalyst 2.9, the elevated temperature did not affect catalyst decomposition of the (PMP-r-PS)-Au-Cl precatalyst. Residual phenylacetylene starting material can be seen in the baseline of Figure 2.15I at 2.70 ppmâ . The conversion data results are summarized in Table 2.4 and the performance differences between the precatalysts Ph3PAuCl, model compound 2.9, and (PMP-r-PS)-Au-Cl 2.11 are discussed in Section 2.2.6. 51 Scheme 2.7 Hydroamination of phenyl acetylene with aniline using the (PMP-r-PS)15:85-Au-Cl 2.11 as the precatalyst. 52 Figure 2.12 1H NMR (Tol-d8, 400 MHz) spectra stack plot of hydroamination reaction mixture at room temperature with (PMP-r-PS)-Au-Cl 2.11 as the precatalyst. 53 Figure 2.13 1H NMR (Tol-d8, 400 MHz) spectrum of hydroamination reaction mixture with (PMP-r-PS)-Au-Cl 2.11 as the precatalyst after 216 hours (9 days). * = residual toluene. Table 2.3 Hydroamination product 2.5 conversion data for the polymeric precatalyst (PMP-r-PS)-Au-Cl 2.11. Entry Elapsed time (h) Percentage conversion of product 2.4A determined by 1H NMR (%) 1 0 3.6 2 25 9.6 3 49 13.2 4 73 16.4 5 97 18.2 6 121 20.2 7 144 21.1 8 168 22.8 9 192 25.7 10 216 26.7 11 240 30.7 12 265 32.4 13 289 32.9 14 313 36.8 15 336 38.9 16 361 42.4 17 384 44.6 18 408 47.2 19 432 48.2 20 457 51.5 * 54 21 481 54.0 22 504 57.5 23 528 59.9 24 553 63.3 25 576 65.9 26 600 69.0 27 624 72.6 28 649 74.8 29 679 79.7 30 696 81.8 31 720 85.4 32 744 87.3 33 768 88.9 34 793 91.9 35 818 93.7 36 841 95.7 37 864 96.2 38 889 97.5 39 914 98.2 40 936 97.8 41 1008 99.6 Figure 2.14 Progress of gold catalyzed hydroamination with (PMP-r-PS)-Au-Cl 2.11 as the precatalyst. 01020304050607080901000 200 400 600 800 1000 1200Percentage conversion (%)Elapsed time (h)55 Upon completion of the hydroamination reaction (Scheme 2.7), the crude reaction mixture was first precipitated into hexanes which precipitated the polymer and AgCl out of solution. This was followed by filtration through a 0.22 μm pore-sized syringe filter. Finally, the volatiles of the filtered solution were removed in vacuo leaving only the solvent (toluene-d8) and the Markovnikov product 2.5. The 1H NMR spectra of the reaction mixture before and after workup are shown in Figures 2.15I and 2.15II, respectively. The broad peaks in the baseline of the crude spectrum were not observed in the spectrum after workup, indicating that precipitation and filtration were successful in removing the polymeric catalyst. It was also noted that the diagnostic peaks of the starting materials aniline and phenylacetylene (2.88 ppm and 2.69 ppm, respectively) present in crude spectrum (Figure 2.15I) were not visible in the spectrum of the isolated product (Figure 2.15II). It has been shown that the (PMP-r-PS)-Au-Cl 2.11 catalyst allows for easy workup by precipitation, simple filtration, and solvent removal in vacuo. 56 Figure 2.15 1H NMR (Tol-d8, 400 MHz) spectra of: I crude reaction mixture and II after reprecipitation, filtration and rotary evaporation for hydroamination with (PMP-r-PS)-Au-Cl 2.11 at 110°C. Residual phenyl acetylene starting material is marked as â . * = residual toluene. 2.2.6 Summary of Hydroamination Reactions It is important to note that all results in Chapter 2 are preliminary and are currently being repeated by Mr. Nolton Woods to support and expand upon the data reported in this chapter. In the present work many reactions were conducted until the 1H NMR spectral data suggested that no further conversion of reagents to products was occurring. Therefore, these reactions were run on â I. Crude II. After workup * * 57 different lengths of time as summarized in Table 2.4 and future work will obtain data on fixed time lengths. In addition, the present work did not incorporate an internal standard to aid in the accurate determination of substrate conversion and product yield. Total conversions were calculated by comparing the proton integrals assigned to the product with those assigned to the substrate with no internal standard, and thus may not be entirely accurate. Gratifyingly, preliminary efforts by Mr. Woods to use the methoxy proton signals of 1,3-dimethoxybenzene (ï¤ = 3.36) as an internal standard have been consistent with the conversion data reported herein obtained without an internal standard. For instance, the analogous catalytic hydroamination of phenylacetylene and aniline using 2.11 and AgOTf as catalyst, gave a 99% conversion (100°C, 24 h), whereas in the present work the conversion was 99.6 % under similar conditions (see Section 2.2.5 and Table 2.4).103 The overall results from the hydroamination reaction of phenyl acetylene with aniline in this study are summarized in Table 2.4 with the conversion data summarized in a histogram in Figure 2.16. For room temperature reactions with 5 mol% precatalyst, the commercial precatalyst Ph3PAuCl produced an overall product conversion of 53.1% followed by the Au(I) metallated model compound 2.9 with an overall product conversion of 64.6% and lastly the polymer-supported Au(I) catalyst (PMP-r-PS)-Au-Cl 2.11 with an overall conversion of 99.6%. It is worth noting that a gold mirror formation reaction was observed on the surface of the borosilicate NMR tubes of all gold-catalyzed hydroamination reactions in this thesis. The image of the NMR tube for the hydroamination reaction with precatalyst (PMP-r-PS)-Au-Cl is shown in Figure 2.17. This interesting observation may suggest that the concentration of catalytically active Au+ is present in small but near constant concentration relative to Au0 throughout the reaction. Alternatively, the catalytically active Au+ slowly reduces to elemental Au0 gradually over the course of the reaction. However, the latter is less likely since the catalytic activity would be expected to slow significantly 58 over time as the concentration of catalytically active Au+ decreases over time (see Figure 2.14). Moreover, we note that the Au0 is formed at the very outset of the catalytic reaction and does not seem to increase notably throughout. In contrast, the catalytic activity remains near constant throughout the reaction until very late stages where it slows slightly as expected due to the decrease in substrate concentrations. Table 2.4 Summary of conversion data for precatalysts Ph3PAuCl, model compound 2.9, and (PMP-r-PS)-Au-Cl 2.11 at room temperature and at 110°C. Precatalyst Time (h) Total conversion to 2.5 (%) PhâPAuCl (RT) 411 53.1 Model compound-Au-Cl (RT) 167 64.6 Model compound-Au-Cl (110°C) 30 69.3 (PMP-r-PS)15:75-Au-Cl (RT) 1008 99.6 (PMP-r-PS)15:75-Au-Cl (110°C) 24 98.6 Figure 2.16 Summary histogram of conversion data for precatalysts Ph3PAuCl, model compound 2.9, and (PMP-r-PS)-Au-Cl 2.11 at room temperature and at 110°C. 0102030405060708090100PhâPAuCl (RT) Modelcompound (RT)Modelcompound(110°C)(PMP-r-PS)-Au-Cl(RT)(PMP-r-PS)-Au-Cl(110°C)Percentage Conversion (%)3 59 Figure 2.17 Gold mirror formation on the surface of the NMR tube after hydroamination reaction with precatalyst (PMP-r-PS)-Au-Cl 2.11. Similar observations were also observed for all gold-catalyzed hydroamination reaction in this thesis. To gain more insight into the activation process, model complex 2.9 was treated with AgOTf (1 equiv) in Tol-d8 and the reaction scheme is shown in Scheme 2.8. A precipitate was observed immediately upon the addition of AgOTf, suggesting the formation of the insoluble salt AgCl. The reaction progress was followed by 31P NMR spectroscopy shown in Figure 2.18. For comparison, the spectrum of pure 2.9 in CDCl3 is shown in Figure 2.18I. Significantly, the signal due to model compound 2.9 (δP = 16.1 ppm) was immediately replaced by a singlet resonance at 15.0 ppm which was tentatively assigned to 2.12 (Figure 2.18IIa) along with additional smaller signals. The slight change in chemical shift may be due to solvent effects switching from CDCl3 to Tol-d8. However, the formation of the precipitate AgCl is a strong indication of the active Au+ species being generated. Over time, a significant increase in the integrated ratios of these smaller 60 singlet resonances at 72.7, 29.4, and 29.0 ppm were observed. At 22 h (Figure 2.18IIc), these smaller resonances had integrations of 3, 12, and 16%, respectively, relative to 2.12 (69%). A previous study on P-Au+ complexes by Widenhoefer and co-workers offered insight into the possible chemical structures of those smaller resonances observed in Figure 2.18IIc.104 The resonance at 29.4 ppm was possibly a chloride-bridged bis(gold) cation 2.13 and the resonance at 29.0 ppm was possibly the weak Ï complex 2.14 (Scheme 2.8). These resonances were comparable to the Widenhoefer study where Ph3PAuCl was treated with the chloride abstracting agents AgSbF6 or AgOTf, followed by a reaction with a Ï ligand. Over time, [((Ph3Au)2(μ-Cl)]+SbF6- and Ph3AuOTf were produced with resonances at δP = 30.7 ppm and δP = 30.6 ppm, respectively, in CD2Cl2.104 In our case, we speculate that such a complex process is involved in generating the active hydroamination catalyst. However, experiments in the presence of alkyne and amine substrates have not be conducted. Scheme 2.8 Reaction of model compound catalyst 2.9 with one equivalent of AgOTf generating active Au+ species. 61 Figure 2.18 (I) 31P NMR (CDCl3, 162 MHz) of model compound precatalyst 2.9. (II) 31P NMR (Tol-d8, 162 MHz) spectra of the reaction mixture after treading model compound 2.9 with AgOTf (1 equiv) at the following times: (a) ca. 40 mins, (b) 2h, and (c) 22h. Interestingly, the model compound-Au-Cl 2.9 outperformed the commercial precatalyst Ph3PAuCl with an improvement of 11.5% in overall conversion. The improvement in catalyst performance could be explained by the larger cone angle of active catalytic species of the model compound MesMe(CH2Ph2)P-Au+ 2.9 (Figure 2.19II) compared to Ph3P-Au+ (Figure 2.19I). Despite the decrease in steric bulk from the methyl group (Figure 2.19IIA), the introduction of the IIa. ~0h (ca. 40 mins) IIb. 2h IIc. 22h I. Model compound 2.9 15.0 ppm 72.7 ppm 29.0 ppm 29.4 ppm 15.0 ppm 2.12 2.13 2.14 62 methylene diphenyl (-CH2Ph2) 2.19IIB and mesitylene 2.19IIC group contributes greatly to the steric bulk, and therefore increasing the cone angle. Particularly, mesitylene significantly increases the cone angle of a phosphine ligand. This can be observed by comparing the cone angle of Ph3P (145°) to Mes3P (212°).105 The cone angle is further exaggerated in the case of the polymeric catalyst (PMP-r-PS)-Au+ 2.19III where the methylene group 2.19IIIA is attached to a mesitylene group. The increase in steric bulk around the phosphine ligand helps provide kinetic stability for the Au+ centre during catalysis, retarding catalyst decomposition. Furthermore, the random coil formation of a polymer in solution could also contribute to kinetic stability. However, this also decreases the rate of reaction using the polymeric catalyst 2.11 as shown in Figure 2.20. Reactions performed at 110°C resulted in similar overall product conversions with the precatalyst Au(I) metallated model compound at 64.6% (RT) â 69.3% (110°C) and (PMP-r-PS)-Au-Cl at 99.6% (RT) â 98.6% (110°C). It appears that the differences in overall product conversions between the room temperature reactions and the 110°C reactions were negligeable, implying the heat did not accelerate catalyst decomposition. It is also worth noting that the precatalyst (PMP-r-PS)-Au-Cl only produces the Markovnikov product, thus demonstrating high selectivity. This is consistent with other Au-based catalysts for the intermolecular hydroamination of aryl alkynes with primary amines.99,106 63 Figure 2.19 Comparison of the cone angle of the active catalytic species of I Ph3P-Au+, II Au(I) metallated model compound MesMe(CH2Ph2)P-Au+, and III (PMP-r-PS)-Au+. The reaction progress of all room temperature hydroamination reactions are summarized in the kinetic trace in Figure 2.20. The initial rates of overall product conversion for the precatalysts Ph3PAuCl and Au(I) metallated model compound 2.9 were much higher compared to the polymeric precatalyst (PMP-r-PS)-Au-Cl 2.11. This observation is to be expected since all active catalytic sites are evenly diffused in solution allowing for easy access of substrates. Polymers in solution, however, adopt a random coil conformation due to entropic effects. This causes many of the active catalytic centres to be buried within the hydrodynamic sphere. Substrates would take a longer amount of time to penetrate the hydrodynamic perimeter resulting in the slow rate of conversion for the (PMP-r-PS)-Au-Cl precatalyst. This is especially true for intermolecular 64 hydroamination since both phenyl acetylene and the aniline substrates must find an active Au+ catalytic site for a hydroamination reaction to occur. However, despite the slower rate of conversion, the (PMP-r-PS)-Au-Cl 2.11 precatalyst had the highest overall conversion compared to either the Ph3P-Au-Cl or the model compound 2.9. The higher overall conversion could be explained by the increased kinetic stability of the bulky mesityl and phenyl groups combined with the coil formation of a polymeric ligand slowing the rate of reduction of the active catalytic Au(I) species to Au0. Figure 2.20 Comparison of total product reaction progress of gold catalyzed hydroamination with precatalysts Ph3PAuCl, model compound 2.9, and (PMP-r-PS)-Au-Cl 2.11 at room temperature. The independent data may be found in Figures 2.4, 2.8, and 2.14. 2.3 Summary A polymer-supported gold(I) precatalyst (PMP-r-PS)-Au-Cl 2.11 (Scheme 2.6) was successfully synthesized and isolated. (PMP-r-PS)-Au-Cl was used as a hydroamination precatalyst to catalyze reactions between phenylacetylene and aniline (Scheme 2.7). The catalytic performance of (PMP-r-PS)-Au-Cl was compared with its gold(I) metallated model compound 2.9 01020304050607080901000 200 400 600 800 1000 1200Percent conversion (%)Elapsed time (h)PhâPAuClAu(I) Metallated ModelCompound(PMP-r-PS)-Au-Cl3 65 and the commercial precatalyst Ph3P-Au-Cl. The hydroamination reactions were monitored by 1H NMR spectroscopy. The catalytic performances were summarized in Table 2.4 and the total product conversions were summarized in a histogram in Figure 2.16. The polymeric precatalyst (PMP-r-PS)-Au-Cl outperformed both the commercial precatalyst Ph3P-Au-Cl and gold metallated model compound 2.9. (PMP-r-PS)-Au-Cl was also shown to allow for easy isolation of products with a simple reprecipitation, filtration, and solvent removal in vacuo. 2.4 Experimental 2.4.1 Materials and General Procedures for the Synthesis and Characterization of the (PMP-r-PS)-Au-Cl Copolymer Precatalyst and its Hydroamination Reactions All manipulations of air and/or water sensitive compounds were performed under a nitrogen atmosphere using Schlenk line techniques and/or in an Innovative Technology glovebox. Dichloromethane was dried over CaH2 overnight, distilled under a nitrogen atmosphere, degassed, and stored in activated 4 Ã molecular sieves in the glovebox. Diethyl ether (Sigma-Aldrich) was deoxygenated with nitrogen and dried by passing through an activated alumina column. Hexanes, mixture of isomers (Sigma-Aldrich, GR grade), was deoxygenated with nitrogen, and dried by passing through an activated alumina column. THF (Sigma-Aldrich) was dried over sodium/benzophenone ketyl, distilled under a nitrogen atmosphere, and then stored in activated 4 Ã molecular sieves. Methanol was deoxygenated by bubbling nitrogen through the solvent prior to use. CDCl3 was obtained from Cambridge Isotope Laboratories Inc. Silver triflate (â¥99%) was obtained from Sigma-Aldrich. Aniline (ACS, Sigma-Aldrich, â¥99.5%) was dried over CaH2 overnight, distilled under reduced pressure, and degassed prior to use. Phenyl acetylene (Sigma-66 Aldrich, GR grade) was dried over CaH2 overnight, distilled under reduced pressure, and degassed prior to use. Styrene (Sty, Sigma-Aldrich, 99%) was dried over CaH2 overnight, distilled under reduced pressure, and degassed prior to use. MesP=CPh2 (2.8) was prepared using a literature procedure.44 MeLi (1.6 M in diethyl ether, Sigma-Aldrich) was titrated with N-benzylbenzamide prior to use. Azobis(cyclohexanecarbonitrile) (VAZO 88, Sigma-Aldrich, 98%) was recrystallized twice from anhydrous ethanol (99%), dried under vacuum for 24 h, and stored in the glove box prior to use. 1H, 13C, and 31P NMR spectra were recorded on the Bruker Avance 400 MHz spectrometers. Chemical shifts are reported relative to CHCl3 [1H: δ = 7.24; 13C: δ = 77.0] and toluene [1H: δ = 7.09 (m), 7.00 (s), 6.98 (quint), 2.00 (quint)]. 85% H3PO4 in H2O was used in 31P NMR as the external standard δ = 0.00. Polymer molecular weights were analyzed by Gel Permeation Chromatography with triple detection (GPC-LLC) using an Agilent liquid chromatograph equipped with an Agilent 1200 series isocratic pump, Agilent 1200 series standard autosampler, Phenomenex Phenogel 5 mm narrow bore columns 515 (4.6 x 300 mm) 104 Ã (5000-500000 g mol-1), 500 Ã (1000-15000 g mol-1), and 103 Ã (1000-75000 g mol-1), Wyatt Optilab T-rEx differential refractometer (λ = 658 nm, 40°C), Wyatt TriStar miniDAWN laser light scattering detector λ = 690 nm), and a Wyatt ViscoStar viscometer. A flowrate of 0.5 mL min-1 was used, and samples were dissolved in THF (ca. 2 mg mL-1). 2.4.2 Preparation of Unmetallated Model Compound The procedure was a modified procedure adapted from Gillon, 2007.99 To a cooled (-78°C) yellow solution of MesP=CPh2 (2.06 g, 6.51 mmol) in THF (100 mL) was added MeLi in Et2O 67 (4.90 mL, 1.60 M, 7.84 mmol) in a dropwise fashion. An immediate colour change from pale yellow to a dark red was observed. The solution was stirred for one hour at -78°C. An aliquot was removed at one hour for 31P{1H} (THF) NMR spectroscopic analysis and showed a single signal at (δ = -43 ppm). The reaction was quenched with the dropwise addition of degassed methanol (0.50 mL, 12.4 mmol). Upon the addition, the solution changed from dark red to clear. The solution was warmed gradually to room temperature and stirred for one additional hour. The solvent was removed in vacuo leaving a pale-yellow oil. The oil was dissolved in hexanes (ca. 100 mL) and filtered through a fine frit. Hexanes were removed in vacuo leaving a colorless oil. The oil crystalized over several days affording colourless crystals. Yield = 0.18 g (63.8%). 31P NMR (162 MHz, Hexanes): δ -26.3 (s). 2.4.3 Preparation of Gold-Metallated Model Compound Procedure was adapted from Gillon, 2008.54 2.4.4 Preparation of Poly[(methylenephosphine)-ran-styrene] Copolymer Monomer MesP=CPh2 (1.000 g, 3.163 mmol) and VAZO 88 (0.039 g, 0.158 mmol) were dissolved in neat styrene (1.318 g, 12.653 mmol). The pale-yellow solution was charged into a sealable pyrex tube and flame sealed. The tube was heated at 140°C for 14 h in an oven equipped with a rocking tray. The tube was subsequently broken in an inert atmosphere. The polymer was purified by reprecipitating a viscous solution of 2.10 in CH2Cl2 into hexanes three times. The product, a white powder, was dried in a vacuum oven at 60°C for 24 h. Yield = 0.59 g (25.4%). 31P NMR (162 MHz, Tol-d8): δ 4.5 (br), 8.0 (br), 10.2 (br), 19.2 (br); 1H NMR (400 MHz, Tol-d8): δ 8.0 â 5.7 (br, Ar-H), 2.7 â 0.8 (br, CH3, CH2, CH); 13C NMR (101 68 MHz, CDCl3): δ 148 â 124 (br, Ar-C), 55 â 38 (br, CH, CH2), 24 â 20 (CH3) GPC-MALS (triple detection): Mn = 6,200 g mol-1; PDI = 1.22 ± 0.01; dn/dc = 0.19 (as determined by 100% mass recovery methods). 2.4.5 Preparation of Gold-Metallated Poly[(methylenephosphine)-ran-styrene] Copolymer A Schlenk flask was charged with 2.10 (0.214 g), (tht)AuCl (0.156 mg, 16.0 mmol), and CH2Cl2 (ca. 5 mL). The solution was stirred for one hour at room temperature. The solvent was removed in vacuo leaving a white residue. The metallated polymer was purified by reprecipitating a viscous solution of 2.11 in CH2Cl2 into hexanes. After filtration, 2.11 was dried in vacuo leaving a white powder. Yield = 0.18 g (84%). 31P NMR (162 MHz, Tol-d8): δ 41 (br), 31.3 (br), 21.7 (br) 1H NMR (400 MHz, CDCl3): δ 7.8 â 5.9 (br, Ar-H), 3.0 â 0.6 (br, CH3, CH2, CH) GPC-MALS (triple detection): Mn = 7,700 g mol-1; PDI = 1.185 ± 0.004; dn/dc = 0.18 (as determined by 100% mass recovery methods). 2.4.6 Procedure for Hydroamination Reaction with Ph3AuCl at Room Temperature To a scintillation vial was added aniline (47 mg, 0.505 mmol), phenylacetylene (46 mg, 0.450 mmol), Ph3AuCl (11 mg, 0.022 mmol), silver triflate (12 mg, 0.046 mmol), and deuterated toluene (ca. 1.5 mL). Upon stirring, a yellow precipitate was observed. The mixture was quickly transferred to an NMR tube, flame sealed, and left at room temperature for 411 days (ca. 17 days). The reaction progress was monitored through 1H NMR (400 MHz, Tol-d8). Total substrate conversion to Markovnikov product 2.5 = 53.1%. 69 2.4.7 Procedure for Hydroamination Reaction with Gold-Metallated Model Compound at Room Temperature To a scintillation vial was added aniline (47 mg, 0.505 mmol), phenylacetylene (46 mg, 0.450 mmol), 2.9 (12 mg, 0.021 mmol), silver triflate (6 mg, 0.023 mmol), and deuterated toluene (ca. 1.5 mL). Upon stirring, a yellow precipitate was observed. The mixture was quickly transferred to an NMR tube, flame sealed, and left at room temperature for 167 h (ca. 7 days). The reaction progress was monitored through 1H NMR (400 MHz, Tol-d8). Total substrate conversion = 64.6%. 2.4.8 Procedure for Hydroamination Reaction with Gold-Metallated Model Compound at 110°C To a scintillation vial was added aniline (47 mg, 0.505 mmol), phenylacetylene (46 mg, 0.450 mmol), 2.9 (13 mg, 0.023 mmol), silver triflate (16 mg, 0.023 mmol), and deuterated toluene (ca. 1.5 mL). Upon stirring, a yellow precipitate was observed. The mixture was quickly transferred to an NMR tube, flame sealed, and heated at 110°C for 29 h (overnight). The reaction progress was monitored through 1H NMR (400 MHz, Tol-d8). Total substrate conversion = 69.3%. 70 2.4.9 Preparation of Hydroamination Reactions with (PMP-r-PS)-Au-Cl at Room Temperature To a scintillation vial was added aniline (16 mg, 0.172 mmol), phenylacetylene (15.8 mg, 0.155 mmol), 2.11 (13 mg, 0.0079 mmol*), silver triflate (7 mg, 0.027 mmol), and deuterated toluene (ca. 1.5 mL). Upon stirring, a yellow precipitate was observed. The mixture was quickly transferred to a J Young NMR tube, sealed, and left at room temperature for 1008 h (42 days). The reaction progress was monitored daily through 1H NMR (400 MHz, Tol-d8). Total substrate conversion = 99.6%. *Number of moles of metallated gold centers on (PMP-r-PS)-Au-Cl 2.4.10 Preparation of Hydroamination Reactions with (PMP-r-PS)-Au-Cl at 110°C To a scintillation vial was added aniline (47 mg, 0.501 mmol), phenylacetylene (46 mg, 0.451 mmol), 2.11 (38 mg, 0.023 mmol*), silver triflate (6 mg, 0.023 mmol), and deuterated toluene (ca. 1.5 mL). Upon stirring, a yellow precipitate was observed. The mixture was quickly transferred to an NMR tube, flame sealed, and heated at 110°C for 24 h. The reaction progress was monitored through 1H NMR. Total substrate conversion = 98.6%. *Number of moles of metallated gold centers on (PMP-r-PS)-Au-Cl 71 Chapter 3: Radical Copolymerizations of MesP=CPH2 and Acrylates 3.1 Introduction It has been known that phosphaalkenes 3.1 (Scheme 3.1) form copolymers with commercial monomers through anionic and radical polymerization methods (Scheme 1.7).62-66 Through living anionic polymerization, Chen and co-workers showed it was possible to form phosphaalkene block copolymers with styrene, methyl methacrylate, and tert-butyl acrylate.66 On the other hand, free radical copolymerization was shown to form random copolymers with the commercial monomersâ styrene, methyl methacrylate, 2-ethylhexyl acrylate, and n-butyl acrylate (Figure 1.4).62,63 However, only the poly[(methylenephosphine)-ran-(styrene)] (PMP-r-PS) copolymer has been studied extensively.60,102 Preliminary polymerization studies with the PMP copolymers poly[(methylenephosphine)-ran-(methyl methacrylate)] (PMP-r-PMMA) 1.25/3.4 and poly[(methylenephosphine)-ran-(n-butyl acrylate)] (PMP-r-PBA) 3.2 showed unusual behaviors. PA and MMA monomers tend homopolymerize rather than copolymerize and PMP-r-PBA polymers tended to favor a high incorporation of phosphaalkene even at low feed ratios of phosphaalkenes. These two interesting observations prompted further investigations into PMP-r-PBA and PMP-r-PMMA copolymers. 72 3.2 Results and Discussion 3.2.1 Synthesis and Purification of Poly[(methylenephosphine)-ran-(n-butyl acrylate)] Copolymer In this study, PMP-r-PBA was synthesized through neat free radical polymerization between MesP=CPh2 and n-butyl acrylate monomers with 1 mol% VAZO 88 as the radical initiator shown in Scheme 3.1. After the polymerization of PMP-r-PBA with a feed ratio of fPA = 0.2, the 31P NMR spectrum of neat crude mixture (Figure 3.1I) showed a broad resonance at δP = 9.0 to -22.5 ppm that belonged to the PMP-r-PBA copolymer and three sharp signals at δP = -25.6, -29.2, and -32.3 ppm that likely belonged to oligomers. Approximate integrations of these two regions suggested a large ratio of oligomeric impurities to product. The 31P NMR spectrum also indicated that the phosphaalkene starting material (δP = 233) has been fully consumed, suggesting complete conversion into oligomeric/polymeric structures. Scheme 3.1 Synthesis of PMP-r-PBA polymer. 73 Figure 3.1 31P NMR (162 MHz) of PMP-r-PBA20:80 copolymer 3.2: I crude (neat), II after three reprecipitations in 80% v/v MeOH in water (CDCl3), and III after four reprecipitations in 80% v/v MeOH in water (CDCl3). Despite the successful synthesis of PMP-r-PBA 3.2 and the preliminary reports of its syntheses,63 it was a challenge to isolate. PMP-r-PBA copolymers could not be purified by reprecipitation, a technique used for other all other PMP homopolymers and copolymers.26,53-55,60-66,68 The concept of reprecipitation involves dropping a solution of the polymer into a solvent in which it is insoluble while unreacted monomers and other impurities remain dissolved in solution. Previously, reprecipitation using hexanes was successful in isolating the PMP-r-PS copolymer No phosphaalkene monomer OligomersPolymers Oxidized I. Crude (neat) II. After three reprecipitations III. After four reprecipitations 74 (FPA = 0.15) with high purity and a modest yield of 48%. However, the same methodology could not be applied to PMP-r-PBA copolymers. Although hexanes is a good solvent to dissolve the residual unreacted monomers of phosphaalkene and n-butyl acrylate, it also dissolves the copolymer due to the presence of highly soluble n-butyl groups on the acrylate residues. Using reprecipitation from hexanes to purify a PMP-r-PBA copolymer with a phosphaalkene feed ratio of fPA = 0.2 resulted in a yield that was too low to quantify (< 0.1 mg), where most of the polymer sample remains dissolved due to the high incorporation of n-butylacrylate residues. The miniscule amount of material isolated most likely resulted from polymers of very high molecular weight and consequently not representative of the entire copolymer sample. Reprecipitation was also attempted with 80% v/v MeOH in water and 80% v/v EtOH in water resulting in the precipitation of both polymer and impurities (phophaalkene and n-butyl acrylate oligomers). The 31P NMR of the PMP-r-PBA20:80 copolymer sample after three and four reprecipitations are shown in Figure 3.1I and 3.1II, respectively. The two spectra clearly show that 80% v/v MeOH in water is ineffective at removing oligomeric impurities. However, PMP-r-PBA copolymers with a phophaalkene feed ratio of fPA > 0.6 such as PMP-r-PBA60:40 could be purified by reprecipitation in degassed hexanes. Due to the unusually high incorporation of phosphaalkene in PMP-r-PBA60:40 (FPA = 0.88), the solubility was similar to the PMP homopolymer. It is important to note that reprecipitation with MeOH in water was successful in isolating block copolymers of phosphaalkene and acrylates, synthesized by anionic polymerization.66 Due to the clean reaction and 100% consumption of monomers during living anionic polymerization, the only impurity produced would be the lithium alkoxide salts after quenching. 75 After multiple unsuccessful attempts to reprecipitate the PMP-r-PBA copolymer, size-exclusion chromatography (SEC) was attempted as a method of purification. SEC works on the same principle as a GPC where molecules are separated by size. Polymers with the highest MWs will elude first followed by lower MWs. Samples are then collected in fractions of well-defined MW ranges. A major advantage of SEC is the 100% recovery of the entire sample, which can be useful in analyzing the quantities of polymers and oligomers in every MW range. This is especially useful in isolating polymers from low yielding polymerization reactions such as the case in the free radial polymerization of PMP-r-PBA. SEC is especially useful in the reactivity ratio studies outlined in Section 3.2.4., where polymerizations were prematurely halted to aim for low monomer conversion. Unfortunately, SEC purification comes with its disadvantages as well. It is impractical to keep the column free of air and moisture. While an air-free SEC column is theoretically possible, it would be very labor intensive to degas copious quantities of solvent. The phosphine centres of PMP-r-PBA are susceptible to oxidation with oxygen during separation. For the reactivity ratio study in Section 3.2.5, it was important to oxidize all phosphorus centres to keep the molecular weight of the phosphaalkene residues in the polymer chain consistent. Prior to separation via SEC column, all phosphorus centers of PMP-r-PBA were oxidized with hydrogen peroxide as shown in Scheme 3.2. Where the reprecipitation method was not possible, the SEC method was able to isolate PMP-r-PBA copolymers with an n-butyl acrylate loading ratio fBA > 0.4 in its oxidized form poly[(methylenephosphine oxide)-ran-(n-butyl acrylate)] (PMPO-r-PBA) 3.3. 76 Scheme 3.2 Oxidation of PMP-r-PBA 3.2 to PMPO-r-PBA 3.3 with H2O2. 3.2.2 Evidence of Phosphaalkene-n-Butyl Acrylate Linkages The 2010 patent by the Gates group showed limited evidence of linkages between phosphaalkene and n-butyl acrylate resides.63 Therefore, the present study was important to gain evidence of a true PMP-r-PBA copolymer rather than a mixture of two homopolymers. As previously discussed, PMP-r-PBA with a phosphaalkene feed ratio of fPA > 0.60 was purifiable by reprecipitation in degassed hexanes. As a result, PMP-r-PBA60:40 was chosen for this study to provide evidence for linkages between phosphaalkene and n-butyl acrylate residues in the polymer backbone. PMP-r-PBA60:40 3.2 was synthesized by free radical polymerization by heating MesP=CPh2 (fPA = 0.6), n-butyl acrylate (fBA = 0.4), and VAZO 88 (1 mol%) in a sealed glass tube 77 at 140°C overnight. Purification was accomplished by a series of reprecipitations in degassed hexanes yielding an off-white powder. The 31P NMR spectrum (Figure 3.2I) showed a broad signal at approximately δP = -9.5 ppm, which was consistent with the desired phosphorus containing polymer (cf. PMP Homopolymer 1.15/2.1: δP = â10 ppm).26,50 Figure 3.2 31P NMR (CDCl3, 162 MHz) spectra of I) PMP-r-PBA60:40 3.2; and II) Homo-PMP NMR (referred to as 1.14 and/or 2.1 earlier in this thesis; (Mn = 6,200, PDI = 1.19). The first piece of evidence of PA-BA linkages was obtained from the analysis of the GPC trace of PMP-r-PBA60:40 (Figure 3.3, solid grey line) showing a nicely gaussian monomodal molecular weight distribution. A blend of two homopolymers would likely result in a bimodal weight distribution unless coincidentally they had same MW and PDI, which would be highly unlikely. Therefore, we concluded that the isolated polymer was either homo-PBA, homo-PMP, or the copolymer PMP-r-PBA but not a mixture of homopolymers. The modest molecular weight of PMP-r-PBA60:40 (Mn) of 4,000 g mol-1 and a low PDI of 1.109 indicated a narrow Mn range and -9.5 ppm I. PMP-r-PBA60:40 Copolymer II. PMP Homopolymer 78 suggested that only a single type of polymer (in this case copolymer) was present. This was compared to the GPC traces of homopolymers PMP (dotted blue trace) and PBA (dashed orange trace) (Figure 3.3), which were synthesized under the same conditions as PMP-r-PBA60:40. Due to the high incorporation of PA residues FPA = 0.88, the GPC trace of PMP-r-PBA60:40 was very similar to the PMP homopolymer (FPA was determined by 13C NMR which will be discussed in Section 3.2.3). Figure 3.3 GPC trace of homopolymer PMP 2.1 (dotted blue line), homopolymer PBA (dashed orange line) and copolymer PMP-r-PBA60:40 3.2 (solid grey line). The monomodal weight distribution of PMP-r-PBA60:40 (Figure 3.3), although highly indicative of a copolymer, alone was not sufficient to prove that it was a copolymer rather than two homopolymers of identical molecular weight distribution. Therefore, additional evidence for the formulation of the product as copolymer PMP-r-PBA was gained by multinuclear NMR spectroscopy. The 31P NMR of PMP-r-PBA60:40 (Figure 3.2I) displayed peaks with slightly different chemical shifts compared to the homopolymer (Figure 3.2II), suggesting that the phosphorus chemical environments in PMP-r-PBA were unique from the homopolymer. 5 10 15 20 25Time (mins)PMPPBAPMP-r-PBA79 Examination of the 1H and 13C NMR spectra of PMP-r-PBA60:40 provided additional support of the existence of BA residues from the CH3 signals of the n-butyl moiety in the regions of δH = 1.0 and δC = 13.8 ppm, respectively, as shown in Figure 3.4 and 3.5; both of which were absent in the PMP homopolymer. Furthermore, the inverse gated 13C{1H} NMR of the isolated oxidized PMPO-r-PBA 3.3 (Figure 3.14) used in the reactivity ratio studies in Section 3.2.6, showed an increase in the integration of the methyl carbons (δC = 13.7 ppm, marked as â¡) of the n-butyl moiety as the feed ratio of n-butyl acrylate (fBA) increased (stack plot shown in Figure 3.14). This strongly suggests that the n-butyl acrylate residues are integrated into the copolymer chain. Figure 3.4 1H NMR (CDCl3, 400 MHz) spectrum of PMP-r-PBA60:40 3.2. * = residual CHCl3. 1.0 ppm nBu-CH3 * 80 Figure 3.5 Inverse gated 13C{1H} NMR (CDCl3, 101 MHz) spectrum of PMP-r-PBA60:40 3.2. * = residual CHCl3. Another approach to determine the existence of a true copolymer would be to examine the polymer linkages itself, through spectroscopic techniques. The C-H bonds from CHc and CH2d of the phosphaalkene residues highlighted in grey of Figure 3.6, were the closest to neighboring polymer residues. Therefore, any changes to their neighboring residues would cause the most significant change to the chemical environment of those C-H correlations. It is important to note that any complexity as a result of tacticity is not considered. Figure 3.6 Depiction of a single phosphaalkene residue within a PMP copolymer. CHc and CH2d represent C-H environments most affected by neighbouring polymer residues. nBu-CH3 13.8 ppm * Ar-C 81 One of the most effective spectroscopic techniques at probing these C-H correlations would be two-dimensional 1H-13C edited HSQC (edHSQC) NMR spectroscopy. Previously, Serin and co-workers showed evidence of styrene-phosphaalkene linkages in the copolymer of a chiral oxazoline-based phosphaalkene and styrene using edHSQC NMR spectroscopy.107 NMR experiments with edHSQC were collected with multiplicity editing, allowing for the 13C signals to be differentiated between CH/CH3 and CH2 moieties. The positive phase signals were denoted with the color blue for CH/CH3 moieties and the negative phase signals were denoted with the color red for CH2 moieties. Notably, edHSQC would be valuable in revealing the chemical environments of the diagnostic C-H correlations of the CHc and CH2d moieties (highlighted in grey in Figure 3.6). In the present work, the edHSQC NMR spectra of homopolymers PMP and poly(n-butyl acrylate) are shown in Figure 3.7I and 3.7II, respectively. Strikingly, the edHSQC NMR spectrum of PMP-r-PBA60:40 (Figure 3.7III) showed two C-H correlations at [13C: δ = 49.9; 1H: δ = 3.7] and [13C: δ = 27.4; 1H: δ = 2.2] which were not observed in the spectra of either homopolymer (Figure 3.7I and 3.7II). These new signals are denoted by the dashed green circles in Figure 3.7III and their absence is indicated by dashed green circles in Figure 3.7I and 3.7II. These C-H signals that are only present in the copolymer, are attributable to a new C-H chemical environment possibly influenced by the formation of new bonds between PA and BA residues as will be discussed below. The first new C-H correlation in the PMP-r-PBA copolymer spectrum [13C: δ = 49.9; 1H: δ = 3.7 in Figure 3.7III (left dashed green circle)] was tentatively assigned to the PMP CHcâ² moiety in either microstructure B or D (Figure 3.8) since it was observed in close proximity to the CHc moiety [13C: δ = 52.0; 1H: δ = 4.8], which was attributed to the microstructure A or C (Figure 3.8), both of which are closely related to that of the signals in the PMP homopolymer. 82 The second new C-H correlation in the PMP-r-PBA copolymer spectrum [13C: δ = 27.4; 1H: δ = 2.2 in Figure 3.7III (right dashed green circle)] was tentatively assigned to the PMP CH2dâ² moiety in either microstructure C or D (Figure 3.8) since it was observed in close proximity to the CH2d moiety [13C: δ = 52.0; 1H: δ = 4.8], which was attributed to the microstructure A or B (Figure 3.8), both of which are both closely related to that of the homopolymer PMP signals. The chemical shift from CH2d to CH2dâ² was probably also due to influence from the adjacent BA (right residue, right of the ortho-methylene group) shown in scenario C and D (Figure 3.8). The 1H upfield chemical shift change δH = 3.6 â 2.2 was due to the replacement of a phosphorous heteroatom directly adjacent to CH2d with an aliphatic methylene group of the polymer backbone directly adjacent to CH2dâ². The chemical shift change at CH2d was more significant compared to CHc because CH2d was directly adjacent to the neighboring monomer residue compared to CHc which would be two atoms away. Furthermore, the replacement of a phosphine with an aliphatic group would be more significant compared to the replacement of an aliphatic group with another aliphatic group, as in the case of CHc. The intensities of the new C-H correlations CHcâ² and CH2dâ² were much weaker compared to CHc and CH2d, respectively. This could be explained by the high incorporation of phosphaalkene FPA = 0.88, which resulted in scenario A (Figure 3.8) being the most common and therefore their C-H correlations would be the most comparable to that of the PMP homopolymer. Furthermore, the CHcâ² correlation was more intense compared to CH2dâ². This could be explained by the unusual reactivity ratio where rPA >> rBA. Reactivity ratios will be discussed extensively in the next Section 3.2.3. It was found that rPA >> 1 meaning the growing end of a PAâ¢ radical had a far greater probability to add to another PA monomer (homo-propagate) rather than to a BA monomer (cross-propagate). On the other hand, rBA < 1, implied that the growing end of a BAâ¢ 83 radical had a slight preference for cross-propagation. Therefore, the number of BA-PA linkages should be statistically higher than the number of PA-BA linkages causing scenario B (Figure 3.8) to be the second most common in a PMP-r-PBA copolymer followed by scenario C, which explains the higher intensity of CHcâ² compared to CH2dâ² (Figure 3.7). Finally, scenario D would be the least likely. 84 Figure 3.7 1H-13C edHSQC NMR spectra (400 MHz for 1H, CDCl3, 298K) of I PMP homopolymer, II PBA homopolymer, and III PMP-r-PBA60:40. Green dashed circles in I and II denote the absent correlations only present in III. The multiplicity editing during the acquisition of the edHSQC spectra allowed for discrimination between CH3/CH3 (blue) and CH2 (red) moieties. * = residual CHCl3. CH2d CHc CHc Cd/Cdâ /Cz I II III Ha/Hb Hd Hc Hu Hv * * * Cu Cv Cw Cx Cy Cz Hy Hx Hw/Hz Hz Cb Ca Cd Cc Cu Cv Cb Ca Hc Hcâ/Hd Hu Ha/Hb/Hw/Hy/Hz Cw Cc Cy Cx Hdâ CH2d CHcâ CH2dâ 85 Figure 3.8 The four possible environments for a given phosphaalkene residue (highlighted in grey) in a PMP-r-PBA copolymer 3.2. End group with either the PA or BA residue is not considered. The last piece of evidence suggesting PA-BA linkages were the distinct signals in the 31P NMR spectrum of the low conversion oxidized PMPO-r-PBA 3.3 copolymer shown in Figure 3.9. Due to the miniscule yield from the low conversion study, a SEC column separation method was applied for complete sample recovery. PMP-r-PBA was oxidized prior to separation to keep molecular weights of PA residues consistent as discussed in Section 3.2.1. The five broad but distinct signals may have arisen from the four possible distinct phosphorus environments shown in Figure 3.8. Unfortunately, these environments cannot be assigned as attempts to synthesize PA-BA dimers resulted in a mixture of unreacted monomers, dimers, and oligomers. In addition, there were also separate environments for phosphaalkene monomers undergoing a P=C activation as opposed to the more common C-H activation. However, these environments have neither been observed nor ruled out.50,51 86 Figure 3.9 31P NMR (CDCl3, 162 MHz) spectrum of low conversion PMPO-r-PBA60:40 3.3. 3.2.3 Brief Introduction of Unique Phosphaalkene / n-Butyl Acrylate Reactivity Ratios Preliminary experiments of bulk copolymerizations between n-butyl acrylate and MesP=CPh2 showed an unusual reactivity pattern. With feed ratios of fPA = 0.6, the molar incorporation ratio in the copolymer was FPA = 0.96. This was indicative of a reactivity ratio of rPA << 1 and rBA >> 1. The extreme difference in reactivity ratios caused FPA to be unpredictable. Therefore, it was crucial that the reactivity ratios be determined in order to predict FPA and FBA when synthesizing polymers of different monomer incorporations. The Mayo-Lewis equation, also known as the copolymer equation, shown in Equation 3.1, describes the polymer composition (F) as a function of feed ratio (f) and reactivity ratios (r) of the two monomers. By determining the precise rPA and rBA, one can reliably predict the polymer composition for any given monomer feed ratio using the copolymer equation. 43.1 ppm 39.9 ppm 45.6 ppm 47.2 ppm 48.6 ppm 87 FPA =ðPAfPA2 + fPAfBAðPAfPA2 +2fPAfBA + ðBAfBA2 Where: fPA represents the feed ratio of MesP=CPh2; fBA represents the feed ratio of n-butyl acrylate; FPA represents the mole fraction of phosphaalkene in the PMP-r-PBA copolymer; FBA represents the mole fraction of n-butyl acrylate in the PMP-r-PBA copolymer Equation 3.1 Copolymer equation also known as the Mayo-Lewis equation. For any propagating chain in a copolymerization, the radical residue at the growing end has the ability to either homo-propagate or cross-propagate, as shown in Figure 3.10. There are a total of four propagation scenarios each with a rate constant k. In the case of PA, the reactivity ratio rPA describes the ratio of the rate constant of homo-propagation kPP to the rate constant of cross-propagation kPB, and vice versa, for rBA, as shown in Figure 3.10. A reactivity ratio of r > 1 indicates a propagating species that tends to homo-propagate, while r < 1 indicates a species that tends to cross-propagate, and lastly r â 1 indicates no preference for either homo- or cross-propagation. ðPA =ðPPðPB ðBA =ðBBðBP Figure 3.10 Four different possible scenarios for the addition of a monomer in a propagating radical. Figure 3.11 shows a copolymerization plot of incremental polymer composition F as a function of monomer feed f for different reactivity ratios of common monomers. In case I of the ethylene/vinyl acetate copolymerization, where r1 â r2 â 1, both propagating monomers have no preference for either homo- or cross-propagation, where the feed ratio fethylene reflects the mole fraction in the polymer Fethylene.108 In case II of the styrene/methyl methacrylate copolymerization, 88 where r1 and r2 are between 0-1.0, the copolymerization plot exhibits an azeotropic crossover point.109 This case is a common scenario for most copolymerizations and was also the scenario for the copolymerization of phosphaalkene 3.1 and styrene (PMP-r-PS 1.24/2.10), where rPA = 0.11±0.01 and rPS = 0.24±0.12.103 In the other extreme case III of styrene/maleic anhydride, where both r1 â r2 â 0, both propagating monomers have a strong preference to cross-propagate and the resulting copolymer contains alternating monomer residues. Therefore, the molar incorporation is F1 â F2 â 0.5 throughout most of the feed ratio range f â 0.1-0.9.110 Finally, in cases IV and V of methyl methacrylate/vinyl chloride and styrene/vinyl acetate, respectively, where r1 >> 1.0 and r2 << 1.0, the more reactive monomer 1 is incorporated to a greater extent throughout the entire feed ratio range.111,112 89 Monomer 1 Monomer 2 r1 r2 I Ethylene Vinyl acetate 1.08 1.07 108 II Styrene Methyl methacrylate 0.501 0.472 109 III Styrene Maleic anhydride 0.121 0.009 110 IV Methyl methacrylate Vinyl chloride 12.5 0.06 111 V Styrene Vinyl acetate 55 0.01 112 Figure 3.11 Copolymerization plot of incremental polymer composition F as a function of monomer feed f for different reactivity ratios of common monomers.108-112 In the case of copolymerizing phosphaalkene and n-butyl acrylate, a feed ratio of fPA = 0.6 gave a mole fraction of FPA = 0.96 in the copolymer. This suggested a case in between case IV and V in Figure 3.11, where rPA >> 1 and rBA << 1. In these extreme cases, small variations in the feed ratio range between fPA = 0-0.2 can result in drastic changes to the monomer incorporation in the polymer (FPA). Determining rPA and rBA would be crucial to predicting the copolymer compositions FPA and FBA. 00.20.40.60.810.0 0.2 0.4 0.6 0.8 1.0Feed ratio of M1 (F 1)Mole fraction of M1 incroporated in polymer (f1)IIIIIIIVV90 3.2.4 Experimental Design of Reactivity Ratio Studies of MesP=CPh2 (rPA) and n-Butyl acrylate (rBA) in Copolymerizations In order to determine the reactivity ratios, the copolymerization must be performed to a low monomer conversion of X < 10% to prevent monomer drift, also known as composition drift. Monomer drift is the result of variations in the instantaneous feed ratio as monomer is being consumed during polymerization. Once the conditions are found for a monomer conversion of X < 10%, the same conditions are repeated for experiments with varying feed ratios from 0-1.0. The polymers are then isolated and analyzed for their monomer incorporations using spectroscopic techniques. The data for both fPA,BA and FPA,BA are then used in the Fineman-Ross and Mayo-Lewis methods to determine their reactivity ratios rPA and rBA. Finally, the rPA and rBA from the two methods will be compared. The experimental design is outlined in Figure 3.12. 91 Figure 3.12 Outline for experimental design in determining reactivity ratios. In the case of PA and BA, a loading ratio of fPA = 0.6 was first used to determine the reactions conditions. It was determined that copolymerization at 100°C for 2 hours gave a low monomer conversion of X = 4.0%. The same conditions were then applied to feed ratios fPA = 0.1, Determine conditions to copolymerize polymers to low monomer conversion Repeat polymerizations with various feed ratios using same conditions Polymer purification Determine the mol% incorporation of each monomer (FPA and FBA) Use Mayo-Lewis method Use Fineman-Ross Method Compare rPA and rBA and get an average 92 0.2, and 0.4. Since SEC was used for purification, PMP-r-PBA 3.2 was oxidized to PMPO-r-PBA 3.3 with hydrogen peroxide before purification in order to keep all PA residues a consistent molecular weight. It was determined that oxidation with H2O2 does not degrade the polymer. GPC analysis after oxidation of homopolymer PMP 1.15 to 1.17 with H2O2 showed the expected molecular weight increase from the phosphine oxide moiety.26 Similarly, GPC analysis of a control study treating homopolymer PBA with H2O2 revealed no change in molecular weight. 3.2.5 Determination of Copolymerization Ratio by Inverse Gated 13C NMR Spectroscopy To analyze the mol% incorporation of phosphaalkene FPA, quantitative inverse gated proton decoupled 13C NMR was used. This method was chosen because the overlapping diagnostic signals and the poor baseline resolution in the 1H NMR spectrum prevented accurate integration of the methyl protons of n-butyl acrylate which were used to discriminate against the aromatic protons of PA residues. Inverse gated proton decoupled 13C NMR spectroscopy, however, was able to distinguish the methyl carbons (14.2 â 13.0 ppm) of the n-butyl acrylate residues from the aromatic carbons of the phosphaalkene residues (147 â 120 ppm) as shown by the example of PMPO-r-PBA20:80 3.3 in Figure 3.13. The inverse gated pulse sequence also allows for quantitative integration of carbon signals. Since the decoupler is only turned on during the acquisition period, carbon signals are not artificially enhanced by protons from the nuclear Overhauser effect. To calculate the phosphaalkene incorporation, the integration values of the aromatic carbons and the methyl carbons were used according to Equation 3.2. 93 Figure 3.13 Inverse gated 13C{1H} NMR (CDCl3, 101 MHz) spectrum of PMPO-r-PBA20:80 3.3. * = residual CHCl3. â = residual BHT. FPA =ð¶Arð¶Ar+18ð¶BuâMe and FBA = 1 â FPA CAr represents the integration value of aromatic carbons; CBu-Me represents the integration value of methyl carbons of the n-butyl group Equation 3.2 Equation to determine copolymer composition FPA and FSty of PMPO-r-PBA 3.3. * Ar-C nBu-CH3 â â â â â â 94 Figure 3.14 Inverse gated proton 13C{1H} NMR (CDCl3, 101 MHz) spectra of: I homopolymer PBA, II-V copolymer PMPO-r-PBAm:n, and VI homopolymer PMP 2.1. * = residual CHCl3. â = residual BHT. â¡ = CH3 of n-butyl group. 3.2.6 Determination of Reactivity Ratios rPA and rBA Data for the reactivity ratio calculations were obtained by conducting four copolymerizations with feed ratios fPA = 0.1, 0.2, 0.4, and 0.6. The data for these four experiments are summarized in Table 3.1. Due to the oxidation of PMP-r-PBA 3.2, any calculations involving the molecular weight of the new methylene phosphine oxide residue would need to be adjusted to compensate for the addition oxygen atom on the phosphaalkene residue in PMPO-r-PBA 3.3. The I. PBA II. PMPO-r-PBA10:90 (3.3a) VI. PMPO (2.1) III. PMPO-r-PBA20:80 (3.3b) V. PMPO-r-PBA60:40 (3.3d) * IV. PMPO-r-PBA40:60 (3.3b) â â â â â â â¡ 95 equations used to calculate moles of conversion (nPA,BA), monomer conversion (XPA,BA), and percentage yield are shown in Figure 3.15. Table 3.1 Summary of PA/BA copolymerization data with four different feed ratios. Feed ratio Mole fraction in polymer Monomer conversion GPC Yield fPA fBA FPA FBA XPA (%) XBA (%) Mn (g mol-1) Ä % 3.3a 0.1 0.9 0.27 0.73 1.3 3.5 4,200 1.163 4.9% 3.3b 0.2 0.8 0.58 0.42 1.8 1.3 5,700 1.264 3.8% 3.3c 0.4 0.6 0.89 0.11 1.1 0.13 - - 1.8% 3.3d 0.6 0.4 0.95 0.05 3.8 0.2 12,100 1.277 5.1% ðPA =ðYieldðPA=O+ðBAFBAFPA ðBA =ðYieldðBA+ðPA=OFBAFPA ðPA =ðPAðTotal ðBA =ðBAðTotal %Yield =ðYieldðPA=O (ðSMâPAðPA) + ðSMâBA Where: nPA represents the number of moles of monomer conversion of MesP=CPh2; nBA represents the number of moles of monomer conversion of n-butyl acrylate; nTotal represents the number of moles of total monomer conversion; mSM-PA represents the mass of MesP=CPH2 starting material; mSM-BA represents the mass of n-butyl acrylate starting material; mYield represents the mass of the total yield of isolated polymer; MPA=O represents the molar mass of an oxidized MesP=CPh2 residue structure x in Figure 3.3; MPA represents the molar mass of MesP=CPh2; MBA represents the molar mass of a n-butyl acrylate residue structure n in Figure 3.3; FPA represents the mole fraction of phosphaalkene in the PMP-r-PBA copolymer; FBA represents the mole fraction of n-butyl acrylate in the PMP-r-PBA copolymer; XPA represents the monomer conversion of polymerization of MesP=CPh2; XPA represents the monomer conversion of polymerization of n-butyl acrylate Figure 3.15 Equations to calculate nPA,BA, XPA,BA, and percentage yield adjusted for oxidation post-polymerization of PMP-r-PBA. The first method to determine the reactivity ratios makes use of the Fineman-Ross method. This method takes the copolymer equation (Equation 3.1) and rearranges it into a linear form known as the Fineman-Ross Equation 3.3. A plot of H versus G will yield a straight line where the slope is rPA and the y-intercept is rBA. The Fineman-Ross plot for the four PA/BA 96 copolymerizations is shown in Figure 3.16. The linear equation was determined to be G = 18.118H + 0.6702 with a coefficient of determination of r² = 0.9392 and the reactivity ratios were rPA = 18.1±0.04 and rBA = 0.67±0.03. The coefficient of determination was comparable to a previous reactivity ratio study between PA and styrene where r² = 0.9172.102 ðº = ð»ðPA + ðBA Where: ðº =fPA(FBAâFPA)fBA+FPA and ð» = âFBAfPA2FPAfBA2 Equation 3.3 Fineman-Ross equation; linear form of the copolymer Equation 3.1. Figure 3.16 Fineman-Ross plot of G against H for the PA/BA copolymer system. The second method is the Mayo-Lewis graphical method which rearranges the copolymer equation 3.1 such that rPA is a function of rBA as shown in Equation 3.4. A series of linear equations are formed by from the data obtained from each monomer composition. Lines are then plotted using the equations as shown in Figure 3.17. The intersection of these lines will be the solution for the reactivity ratios rPA and rBA. Experimentally, these lines do not intersect exactly at one point but rather an area. The centroid of the intersectional area, shown as the black cross in the grey highlighted area in Figure 3.17, would be the solution for rPA and rBA. Since the intersectional area y = 18.118x + 0.6702R² = 0.9392-1.6-1.4-1.2-1-0.8-0.6-0.4-0.200.20.4-0.14 -0.12 -0.1 -0.08 -0.06 -0.04 -0.02 0GHrPA = 18.1 rBA = 0.670 97 was determined to be a triangle, the centroid was determined by taking the intersecting cartesian coordinates of the triangle vertices and applying Equation 3.5. Using the Mayo-Lewis method, the reactivity ratios were rPA = 22.7±11 and rBA = 0.78±0.63. ðPA =fPAfBA[FBAFPA(1 +fPAðPAfBA) â 1] Equation 3.4 Rearranged Mayo-Lewis equation (Equation 3.1) such that rPA is a function of rBA. Figure 3.17 Mayo-Lewis plot of rPA against rBA for the PA/BA copolymer system. ðPAâCentroid =ðPAâVertex A + ðPAâVertex B + ðPAâVertex C 3 ðBAâCentroid =ðBAâVertex A + ðBAâVertex B + ðBAâVertex C 3 Equation 3.5 Equations to determine the centroid of a triangle on a cartesian plane. The reactivity ratios obtained from both the Fineman-Ross and Mayo-Lewis methods are summarized in Table 3.2. Both methods gave similar values of reactivity ratios. The average of both methods gave a reactivity ratio estimate of rPA = 20.4 and rBA = 0.88. The Mayo-Lewis 00.20.40.60.811.21.40 5 10 15 20 25 30 35 40r BArPA fBA = 0.1 fBA = 0.2 fBA = 0.4 fBA = 0.6CentroidBA = 0.1BA = 0.2BA = 0.4BA = 0.6(22.7 , 0.78)98 equation to predict the molar incorporation of PA monomers FPA as a function of feed ratios fPA,BA is given in Equation 3.6. The predicted traces using the Fineman-Ross, Mayo-Lewis, and the average of both methods were plotted in the copolymerization plot in Figure 3.18. Unfortunately, the Mayo-Lewis method produced a large error due to the nature of graphical methods. Nevertheless, both methods produced traces that compared closely to experimental values. For the PMP-r-PBA copolymer system, it was found that a propagating PAâ¢ radical has a strong preference to homo-propagate and a propagating BAâ¢ radical has a slight preference to cross-propagate. Table 3.2 Summary of reactivity ratios of rPA and rPB using the Fineman-Ross and Mayo-Lewis methods. Method rPA rBA Fineman-Ross 18.1±0.04 0.670±0.03 Mayo-Lewis 22.7±11 0.784±0.63 Average 20.4 0.727 FPA =20.4fPA2 + fPAfBA20.4fPA2 +2fPAfBA + 0.727fBA2 Equation 3.6 Mayo-Lewis equation to predict the molar incorporation of FPA using feed ratios fPA,BA for the PMP-r-PBA 3.2 copolymer system. 99 Figure 3.18 Predicted copolymerization plot of the phosphaalkene/n-butylacrylate copolymer system using the predicted reactivity ratios by the Fineman-Ross and Mayo-Lewis methods. Experimental plots are overlaid with the trace. 3.2.7 Copolymerization of MesP=CPh2 and Methyl Methacrylate The positive results from the random free radical copolymerizations between phosphaalkene MesP=CPh2 3.1 and n-butyl acrylate prompted investigations into copolymerizations with other acrylates such as methyl methacrylate. Preliminary GPC analysis showed an interesting bimodal trace that led us to attempt the copolymerization at various feed ratios. Reaction conditions were kept consistent with the copolymerizations of PMP-r-PS 1.24/2.10 and PMP-r-PBA 1.27/3.2 (Figure 1.4) as shown in Scheme 3.3. PMP-r-PMMA copolymers 3.4 were attempted with PA feed ratios of: fPA = 0.2, 0.4, and 0.6; and purified by reprecipitation in MeOH. The GPC trace of all three products revealed bimodal distributions of 00.20.40.60.810.0 0.2 0.4 0.6 0.8 1.0Mole fraction of phosphaalkene in polymer (F PA)Feed ratio of phosphaalkene (fPA)Fineman-RossMayo-LewisAverageExperimental100 molecular weights regardless of feed ratio (fPA), as shown in Figure 3.19; with a higher MW peak at 11-16 mins and a lower MW peak at 16-22 mins. Interestingly, the intensity of the lower MW peak at 16-22 mins increased as the feed ratio of PA (fPA) increased. Furthermore, the GPC trace overlay of the PMP homopolymer showed a monomodal peak at the same approximate retention time of 16-22 mins as shown by the solid orange trace in figure 3.19. This led to the conclusion that the lower MW peak at 16-22 mins was likely the PMP homopolymer 2.1, while the higher MW peak at 11-16 mins was likely the PMMA homopolymer. However, the existence of a copolymer with minute incorporations of MMA monomer cannot be ruled out since other PMP copolymers such PMP-r-PS 1.24/2.10 and PMP-r-PBA 1.27/3.2 also elute in that region. Scheme 3.3 Free radical polymerization of PMP-r-PMMA copolymer 3.3. 101 Figure 3.19 GPC traces of the crude after attempted PMP-r-PMMA copolymerization (Scheme 3.3) with various feed ratios overlaid with the PMP homopolymer 2.1 trace. Despite nBA and MMA being both acrylates, the inability for MMA to copolymerize with PA could be explained by the differences in their reactivities. A reactivity ratio study of a copolymerization between nBA and MMA shows large differences in reactivities between themselves where rBA = 0.3735 and rMMA = 1.8484 at 100°C with a propagating MMAâ¢ radical having a strong preference of homo-propagation.113 Furthermore, copolymerizations between n-butyl acrylate and n-butyl methacrylate (BMA) showed reactivity ratios of rBA = 0.460 and rBMA = 2.008 at 80°C.114 The additional methyl group next to the polymerizable olefin, has a large influence on the reactivity of methacrylates compared to acrylates. Further studies are needed to explain the inability for MMA to form copolymers with PA through free radical polymerization. 5 10 15 20 25Retention time (mins)PMP-r-PMMA 20:80PMP-r-PMMA 40:60PMP-r-PMMA 60:40PMP 100A : MMA (20:8 )A : MMA (40:6 )A : MMA (60:4 )100102 3.3 Summary A novel phosphorus containing copolymer poly[(methylenephosphine)-ran-(n-butylacrylate)] (PMP-r-PBA) 3.2 was successfully synthesized through free radical polymerization and characterized. It was discovered that PMP-r-PBA with feed ratios of fPA < 0.6 cannot be purified by reprecipitation in hexanes due to the high solubility of the n-butyl groups. Size-exclusion chromatography (SEC) was adopted as the purification method. Since the SEC purification method can only be performed practically in air, PMP-r-PBA was oxidized to PMPO-r-PBA 3.3 prior to purification. PMP-r-PBA was discovered to have an unusual reactivity ratio where a feed ratio of fPA = 0.6 produced a molar incorporation of FPA = 0.96, causing FPA to be difficult to predict. Reactivity ratios rPA and rBA were examined. PA and BA were copolymerized with the VAZO 88 initiator to a low monomer conversion of X < 10% by heating the reaction at 100°C for two hours preventing monomer drift. PMP-r-PBA copolymers were polymerized at feed ratios of fPA = 0.1, 0.2, 0.4, and 0.6. Inverse gated proton decoupled 13C NMR spectroscopy was used to quantify the molar incorporation (FPA,BA). Data for fPA,BA and FPA,BA were summarized in Table 3.1. The Fineman-Ross and Mayo-Lewis methods were applied giving a reactivity ratio average of rPA = 20.4 and rBA = 0.727, summarized in Table 3.2. It was found that a propagating PAâ¢ radical has a strong preference to homo-propagate and a propagating BAâ¢ radical has a slight preference to cross-propagate. Attempts to copolymerize PA with another acrylate MMA was unsuccessful leading to the homopolymerization of both monomers. 103 3.4 Experimental 3.4.1 Materials and General Procedures for the Synthesis and Characterization of PMP Homopolymer, PMP-r-PBA Copolymer and PMP-r-PMMA Copolymer All manipulations of air and/or water sensitive compounds were performed under a nitrogen atmosphere using Schlenk line techniques and/or in an Innovative Technology glovebox. All purification by size-exclusion chromatography (SEC) was performed on a column packed with reusable Bio-Rad Bio-Beads S-X1 (600â14,000 g mol-1 exclusion range) supports in THF. Dichloromethane was dried over CaH2 overnight, distilled under a nitrogen atmosphere, degassed, and stored in activated 4 Ã molecular sieves in the glovebox. Hexanes, mixture of isomers (Sigma-Aldrich, GR grade), was deoxygenated with nitrogen, and dried by passing through an activated alumina column. THF (Sigma-Aldrich) was dried over sodium/benzophenone ketyl, distilled under a nitrogen atmosphere, and stored in activated 4 Ã molecular sieves. Methanol was deoxygenated by bubbling of nitrogen through solvent prior to use. CDCl3 was obtained from Cambridge Isotope Laboratories Inc. n-Butyl acrylate (BA, Sigma-Aldrich, 99%) was dried over CaH2 overnight, distilled under reduced pressure, and degassed prior to use. Methyl methacrylate (MMA, Sigma-Aldrich, 99%) was dried over CaH2 overnight, distilled under reduced pressure, and degassed prior to use. MesP=CPh2 (3.1) was prepared using a literature procedure.44 1,1â²-Azobis(cyclohexanecarbonitrile) (VAZO 88, Sigma-Aldrich, 98%) was recrystallized twice from anhydrous ethanol (99%), dried under vacuum for 24 h, and stored in the glove box prior to use. 1H, 13C, and 31P NMR spectra were recorded on the Bruker Avance 400 MHz spectrometers. Chemical shifts are reported relative to CHCl3 [1H: δ = 7.24; 13C: δ = 77.0]. 85% H3PO4 in H2O was used in 31P NMR as the external standard δ = 0.00. 104 Polymer molecular weights were analyzed by Gel Permeation Chromatography with triple detection (GPC-LLC) using an Agilent liquid chromatograph equipped with an Agilent 1200 series isocratic pump, Agilent 1200 series standard autosampler, Phenomenex Phenogel 5 mm narrow bore columns 515 (4.6 x 300 mm) 104 Ã (5000-500000 g mol-1), 500 Ã (1000-15000 g mol-1), and 103 Ã (1000-75000 g mol-1), Wyatt Optilab T-rEx differential refractometer (λ = 658 nm, 40°C), Wyatt TriStar miniDAWN laser light scattering detector λ = 690 nm), and a Wyatt ViscoStar viscometer. A flowrate of 0.5 mL min-1 was used, and samples were dissolved in THF (ca. 2 mg mL-1). 3.4.2 Preparation of Poly(methylenephosphine) Homopolymer Procedure was adapted from Chun, 2009.102 3.4.3 Preparation of Poly(n-butyl acrylate) Homopolymer In an inert environment, pre-distilled and degassed monomer n-butyl acrylate (2.028 g, 15.8 mmol) and VAZO 88 (0.039 g, 0.158 mmol) were charged into a sealable pyrex carius tube and flame sealed. The tube was heated at 140°C for 14 h in an oven equipped with a rocking tray. The tube was subsequently broken, and the crude was dissolved with degassed CH2Cl2. Crude solution was then concentrated in vacuo into a viscous solution (ca. 3 mL), followed by precipitation into 80% v/v MeOH:H2O (3 x 125 mL). The product, a viscous colourless liquid, was dried in a vacuum oven at 60°C for 24 h. Yield = 1.402 g (64.1%). 1H NMR (400 MHz, CDCl3): δ 4.10 â 3.86 (br, C-H2), 2.43 â 2.08 (br, C-H), 1.96 â 1.24 (br, CH2, CH2, CH2), 0.96 â 0.83 (br, CH3); 13C NMR (101 MHz, CDCl3): δ 176 â 171 (br, O=C), 66 â 62 (br, O-CH2), 43 â 33 (br, CH2, CH), 33 â 28 (br, CH2), 21 â 17 (br, CH2), 105 15 â 12 (br, CH3). GPC-MALS (triple detection) (vs. polystyrene, THF): Mn = 3.220 x 105 g mol-1; PDI = 1.98. 3.4.4 Preparation of Poly[(methylenephosphine)-ran-(n-butyl acrylate)]60:40 Copolymer In an inert environment, MesP=CPh2 3.1 (3.508 g, 11.1 mmol), pre-distilled and degassed monomer n-butyl acrylate (0.946 g, 7.38 mmol), and VAZO 88 (0.045 g, 0.184 mmol) were charged into a sealable pyrex carius tube and flame sealed. The tube was placed in a preheated oven with a rocking tray and heated at 140°C for 14 h. The tube was subsequently broken in an inert atmosphere and the crude was dissolved with degassed CH2Cl2 into a Schlenk flask. Crude polymer solution was reduced in vacuo to ca. 3 mL. The crude solution was precipitated into a centrifuge tube with (3 x 45 mL) of degassed hexanes. The suspension was centrifuged and decanted, leaving the pellet to be dried in a vacuum oven at 60°C overnight, affording an off-white powder. Yield = 0.800 g (17.8%). 31P NMR (162 MHz, CDCl3): δ 9.3 â -22.7 (br); 13C NMR (101 MHz, CDCl3): δ 172.7 (br, O=C), 146.7 (br, Mes-C), 142.7 (br, Mes-C), 138.3 (br, Mes-C), 132.2 â 124.0 (br, m, Ar-C), 64.2 (br, O-C), 52.0 (br, P-C), 42.0 (br, O=CâCH), 40.6 â 27.8 (br, m, Ph2-CH2, CH2), 30.5 (br, n-Bu CH2), 23.1 (br, o-CH3), 20.9 (br, p-CH3), 19.1 (br, n-Bu CH2), 13.8 (br, n-Bu CH). GPC-MALS (triple detection) (THF): Mn = 4,200 g mol-1; PDI = 1.27; dn/dc = 0.21 (as determined by 100% mass recovery methods). 106 3.4.5 Preparation of Poly[(methylenephosphine oxide)-ran-(n-butyl acrylate)] Copolymer at Low Conversion In an inert environment, MesP=CPh2 3.1, pre-distilled and degassed monomer n-butyl acrylate, and VAZO 88 were charged into a sealable pyrex carius tube and flame sealed. The tube was placed in a preheated oven with a rocking tray and heated at 100°C for exactly two hours. The tube was subsequently broken in ambient atmosphere and the crude was dissolved in CH2Cl2. The crude solution was transferred into a round bottom flask and was then charged with hydrogen peroxide solution (30% aqueous w/w). The reaction mixture was stirred overnight at room temperature. All solvent was removed in vacuo and the crude polymer was dried in a vacuum oven at 60°C overnight. A sample was obtained for GPC analysis. The remaining crude was dissolved in minimal THF (ca. 3 â 5 mL). The viscous solution of crude polymer was purified by size-exclusion chromatography on a column packed with reusable Bio-Rad Bio-Beads S-X1 (600â14,000 g mol-1 exclusion range) supports in THF. Fractions were obtained in ca. 10 mL portions. GPC analysis was performed on first five fractions containing polymer. All fractions containing polymer were combined, removed of solvent in vacuo, and dried in a vacuum oven at 60°C overnight, affording an off-white powder. 31P NMR (162 MHz, CDCl3): δ 51.7-36.5 (br); 13C NMR (101 MHz, CDCl3): δ 174.6 (br s, O=C), 145.5 â 136.5 (br, m, Mes-C), 134.1 â 121.5 (br, m, Ar-C), 64.3 (br, O-C), 55.5 (br, P-C), 41.4 (br, O=CâCH), 38.0 â 32.4 (br, m, Ph2-CH2, CH2), 30.3 (br, n-Bu CH2), 25.6 â 22.1 (br, o-CH3), 22.0 â 19.8 (br, p-CH3), 19.1 (br, n-Bu CH2), 13.7 (br, n-Bu CH). 107 PMPO-r-PBA10:90 3.3a: MesP=CPh2 3.1 (0.498 g, 1.57 mmol), n-butyl acrylate (1.823 g, 14.2 mmol), VAZO 88 (0.039 g, 0.160 mmol), peroxide solution (30% aqueous w/w) (0.4 mL, 3 mmol). Yield = 0.115 g (4.9%). Mn = 4,200 g mol-1; PDI = 1.16; dn/dc = 0.11 (as determined by 100% mass recovery methods). PMPO-r-PBA20:80 3.3b: MesP=CPh2 3.1 (1.004 g, 3.17 mmol), n-butyl acrylate (1.623 g, 12.7 mmol), VAZO 88 (0.038 g, 0.156 mmol), peroxide solution (30% aqueous w/w) (ca. 0.8 mL, 6 mmol). Yield = 0.102 g (3.8%). Mn = 5,700 g mol-1; PDI = 1.26; dn/dc = 0.13 (as determined by 100% mass recovery methods). PMPO-r-PBA40:60 3.3c: MesP=CPh2 3.1 (2.010 g, 6.35 mmol), n-butyl acrylate (1.210 g, 9.44 mmol), VAZO 88 (0.040 g, 0.164 mmol), peroxide solution (30% aqueous w/w) (ca. 1.4 mL, 12 mmol). Yield = 0.0593 g (1.8%). PMPO-r-PBA60:40 3.3c: MesP=CPh2 3.1 (2.500 g, 7.90 mmol), n-butyl acrylate (0.671 g, 5.24 mmol), VAZO 88 (0.032 g, 0.131 mmol), peroxide solution (30% aqueous w/w) (ca. 1.8 mL, 26 mmol). Yield = 0.166 g (5.1%). Mn = 12,000 g mol-1; PDI = 1.28; dn/dc = 0.16 (as determined by 100% mass recovery methods). 108 3.4.6 Attempted Preparation of PMMA Poly[(methylenephosphin)-ran-(methyl methacrylate)] Copolymer In an inert environment, MesP=CPh2 3.1, pre-distilled and degassed monomer methyl methacrylate, and VAZO 88 were charged into a sealable pyrex carius tube and flame sealed. The tube was heated at 140°C for 15 h in an oven equipped with a rocking tray. The tube was subsequently broken, and the crude was dissolved with degassed CH2Cl2. Crude solution was then concentrated in vacuo into a viscous solution (ca. 3 mL), followed by precipitation into MeOH (15 x 45 mL). The suspension was centrifuged and decanted leaving the pellet to be dried in a vacuum oven at 60°C overnight, affording a white powder. The product was analyzed by GPC-MALS (triple detection): PMP-r-PMMA20:80 3.4a: MesP=CPh2 3.1 (0.994 g, 3.14 mmol), methyl methacrylate (1.266 g, 12.6 mmol), VAZO 88 (0.038 g, 0.156 mmol). Yield* = 0.716 g (31.1%). PMP-r-PMMA40:60 3.4b: MesP=CPh2 3.1 (2.002 g, 6.33 mmol), methyl methacrylate (0.952 g, 9.51 mmol), VAZO 88 (0.038 g, 0.164 mmol). Yield* = 0.440 g (14.9%). PMP-r-PMMA60:40 3.4c: MesP=CPh2 3.1 (2.996 g, 9.48 mmol), methyl methacrylate (0.636 g, 6.35 mmol), VAZO 88 (0.039 g, 0.160 mmol). Yield* = 0.314 g (8.6%). *Yield is the total recovered mass of polymer after purification. 109 Chapter 4: Overall Conclusions and Future Work 4.1 Summary of Thesis Work In Chapter 2, a new polymeric precatalyst (PMP-r-PS)-Au-Cl was synthesized and successfully used as an intermolecular hydroamination catalyst between aniline and phenyl acetylene, as shown in Scheme 2.7. The performance of (PMP-r-PS)-Au-Cl 2.11 was compared to its model compound 2.9 and the commercially available Ph3P-Au-Cl precatalyst. (PMP-r-PS)-Au-Cl was found to be superior to both the 2.9 and Ph3P-Au-Cl precatalysts. At room temperature, the catalyst 2.11 afforded a total conversion of 99.6% of the Markovnikov product 2.5 and at 110°C, the total conversion was 98.6% of the Markovnikov product 2.5. In comparison, the model compound 2.9 only afforded an overall 2.5 conversions of 64.6% (r.t.), and 69.3% (110°C); and the commercial catalyst Ph3P-Au-Cl afforded a conversion of 53.1% (r.t.). It was found that the precatalyst 2.11 exhibited high selectivity, yielding only the Markovnikov product. Overall conversion data was summarized in Table 2.4 and the histogram in Figure 2.16. Finally, catalyst 2.11 demonstrated an ease of separation post-catalysis by precipitation in hexanes, simple filtration, and solvent removal in vacuo. 110 Scheme 2.7 Hydroamination of phenyl acetylene with aniline using the (PMP-r-PS)15:85-Au-Cl 2.11 as the precatalyst. In Chapter 3, the random copolymer PMP-r-PBA was synthesized via free radical polymerization with the conditions outlined in Scheme 3.1. It was found that PMP-r-PBA 3.2 with a feed ratio greater than fPA > 0.6 could be purified by reprecipitation in degassed hexanes. PMP-r-PBA60:40,where fPA = 0.6, resulted in an unusually high molar incorporation of fPA = 0.96. PMP-r-PBA60:40 was characterized by GPC and two-dimensional 1H-13C edited HSQC NMR spectroscopy, suggesting linkages between PA and BA monomer residues. The reactivity ratios of the PA/BA copolymer system were investigated. As the PMP-r-PBA copolymers were unable to be isolated by reprecipitation, a new method of separating a PMP copolymer was adopted. PMP-r-PBA was purified via size-exclusion chromatography (SEC). Since SEC methods cannot be kept oxygen free, PMP-r-PBA 3.2 was oxidized to PMPO-r-PBA 3.3 prior to separation to keep the molecular weights of the PA residues consistent. PMPO-r-PBA 111 was copolymerized with feed ratios of fPA = 0.1, 0.2, 0.4, and 0.6. The molar incorporation data of FPA,BA are summarized in Table 3.1. Through the Fineman-Ross and Mayo-Lewis methods, it was determined that the reactivity ratios were rPA = 20.4 and rBA = 0.727. The predicted reactivity ratios are summarized in Table 3.2. The copolymerization equation for the PA/BA system is shown in Equation 3.6, with the copolymerization plot shown in Figure 3.18. It was found that a propagating PAâ¢ radical has a strong preference to homo-propagate and a propagating BAâ¢ radical has a slight preference to cross-propagate. Attempts to copolymerize PMP-r-PMMA 3.4 (Scheme 3.3) were unsuccessful resulting in the homopolymerization forming PMP 2.1 and poly(methyl methacrylate) PMMA. Scheme 3.1 Synthesis of PMP-r-PBA polymer. FPA =20.4fPA2 + fPAfBA20.4fPA2 +2fPAfBA + 0.727fBA2 Equation 3.6 Mayo-Lewis equation to predict the molar incorporation of FPA using feed ratios fPA,BA for the PMP-r-PBA 3.2 copolymer system. 112 Figure 3.18 Predicted copolymerization plot of the phosphaalkene/n-butylacrylate copolymer system using the predicted reactivity ratios by the Fineman-Ross and Mayo-Lewis methods. Experimental plots are overlaid with the trace. 4.2 Future Work 4.2.1 Polymer-Supported Catalysis While our studies have shown that (PMP-r-PS)-Au-Cl 2.11 was a viable catalyst for hydroamination that also provides for easy product isolation, further studies would be required to ascertain the recyclability of the catalyst. A method would need to be developed to fully recover the catalyst and to account for the reduction of Au(I) to Au0. Previously, our group demonstrated the ability of an isoprene-phosphaalkene block copolymer to self-assemble with gold nanoparticles.65 Au(I) metallated block copolymers could potentially serve as a hydroamination 00.20.40.60.810.0 0.2 0.4 0.6 0.8 1.0Mole fraction of phosphaalkene in polymer (F PA)Feed ratio of phosphaalkene (fPA)Fineman-RossMayo-LewisAverageExperimental113 catalyst with the possibility of stabilizing Au(I) centres that have reduced to Au0 as observed in Figure 2.17. Not only would the PMP copolymer act as the ligand, but it would also stabilize gold nanoparticles after reduction, extending the catalytic ability of this gold metallated block copolymer system. The hydroamination studies in this report are intermolecular, requiring two substrates aniline and phenylacetylene. While the substrates are simple and easy to obtain, the rates of reaction are significantly slower because both substrates must collide with an active catalytic center for a hydroamination event to occur. A common benchmark reaction for a Au+ catalyst is the intramolecular cyclization of propargylic amides 4.1 to form oxazoline moieties 4.2 (Scheme 4.1). The intramolecular reaction occurs by the nucleophilic attack of the carbonyl group onto a Au+ activated alkyne electrophile. This reaction was chosen in many studies to be a benchmark reaction due to its reliability and well-understood mechanism.115-118 Since propargylic amides 4.1 are soluble in toluene119, this intramolecular cyclization reaction can be performed in the same reaction conditions as all the intermolecular hydroamination reactions in this thesis, including with the use of the polymeric precatalyst (PMP-r-PS)-Au-Cl 2.11. The proposed catalytic reaction is shown in Scheme 4.2. Scheme 4.1 Intramolecular cyclization of propargylic amides 4.1 to form oxazoline 4.2 moieties catalyzed by commercially available Ph3PAuNTf2 precatalyst. 114 Scheme 4.2 Intramolecular cyclization of propargylic amides to form oxazoline moieties catalyzed by proposed (PMP-r-PS)-Au-Cl polymeric precatalyst 2.11. The (PMP-r-PS)-Au-Cl precatalyst requires a chloride abstracting agent such as AgOTf to generate the Au+ catalytic center. Adding silver salts adds an extra step of complexity and also prevents the catalyst from being recycled, since naked Au+ centres are prone to decomposition. A commonly available single component gold catalyst is the Ph3PAuNTf2, where the -NTf2 is a weakly coordinating anion. Au-NTf2 moieties are known to be isolable and air-stable.120 It is proposed that the (PMP-r-PS)-Au-NTf2 4.3 polymeric catalyst could be generated by treating (PMP-r-PS)-Au-Cl 2.11 with the silver salt AgNTf2, then isolated via reprecipitation in hexanes as shown in Scheme 4.3. (PMP-r-PS)-Au-NTf2 may then be used as a single component catalyst for both intermolecular hydroamination and intramolecular cyclization of propargylic amides as shown in Scheme 4.4. Since products 2.5, 2.6, and 4.2116 are all soluble in hexanes, product isolation will occur via a simple reprecipitation and filtration. (PMP-r-PS)-Au-NTf2 4.3 should also be simpler to recycle compared to (PMP-r-PS)-Au-Cl 2.11, given that the Au+ catalytic centre would be stabilized by the weakly coordinating anion -NTf2. (PMP-r-PS)-Au-NTf2 4.3 would be recovered by the removal of solvent in vacuo of the filtered solid residue. 115 Scheme 4.3 Synthesis of the (PMP-r-PS)-Au-NTf2 precatalyst 4.3 from (PMP-r-PS)-Au-Cl precatalyst 2.11. Scheme 4.4 Intermolecular hydroamination and intramolecular cyclization of propargylic amides with the polymeric precatalyst (PMP-r-PS)-Au-NTf2 4.3. 116 4.2.2 PMP Copolymers Thus far, PMP-r-PBA copolymers have been synthesized and characterized. However, the further functionalization of their phosphine moieties has not been discussed. Due to the difficulty of isolating PMP-r-PBA with phosphaalkene feed ratios greater than fPA > 0.6 and a mole fraction of phosphaalkene greater that FPA > 0.95, size-exclusion chromatography (SEC) was used as the purification method. Nevertheless, the SEC method is not air-free and will inadvertently cause the oxidation of phosphine moieties, since PMPs are especially susceptible to oxidation in solution. Development of a mild method to reduce phosphine oxides in a PMP copolymer would not only be valuable in the synthesis of unoxidized PMP-r-PBA with various feed ratios, but will also be a tool to reverse the oxidation of PMPs such as 1.20 and 1.22, which have potential applications as oxygen sensors (Scheme 1.9/4.7).60,61 Both 1.20 and 1.22 exhibit âturn-onâ emission properties upon oxidation. However, the reverse âturn-offâ emission upon reduction has not been studied. Furthermore, having access to the lone pair on phosphorus will also enable the copolymer to be functionalized with coordinations to BH3, Au, or Pd. While there are numerous ways to reduce a phosphine oxide, a mild reducing agent is needed such that only the phosphine oxide of the phosphaalkene residue is reduced, while leaving the n-butyl acrylate residues intact. Unfortunately, many reducing agents are also strong bases that will cleave the sensitive ester moieties of the n-butyl acrylate residues. Pinacolborane (HBpin) has been shown to be a mild reducing agent for reduction of diphenyl phosphine oxide 4.4 to diphenyl phosphine 4.5 at room temperature as shown in Scheme 4.5.121 The reduction was performed in toluene (90% conversion after 20 hours) and acetonitrile (100% conversion after two hours). HBpin alone without a catalyst was also mild enough to prevent the reduction of ester moieties.122 It would be possible to reduce PMPO-r-PBA 3.3 to PMP-r-PBA 3.2 with HBpin as shown in 117 Scheme 4.6. However, the solubilities in acetonitrile would have to be tested. Isolable PMP-r-PBA 3.2 would allow for the comparison of the physical properties such as the glass transition temperature of PMP-r-PBA 3.3 to the block copolymer PMP-b-PBA. Scheme 4.5 Reduction of a phosphine oxide 4.4 to a phosphine 4.5 using a mild reducing agent HBpin. Scheme 4.6 Reduction of PMPO-r-PBA 3.3 to PMP-r-PBA 3.2 using a mild reducing agent HBpin. 118 Scheme 4.7 Proposed reduction of 1.20/1.22 to 1.21/1.23, respectively to regenerate the phosphine. 4.3 Closing Remarks The research work outlined in this thesis expands the possibilities for the use of PMP copolymers in polymer-based catalysis. Thus far, PMPs have shown to be good ligands for Pd and Au. In particular, we have shown that a Au(I) metallated PMP copolymer is successful in activating unsaturated moieties. With the versatility of phosphines in ligand design, the possibilities for PMP-based polymeric catalysts are endless. 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Thesis/Dissertation
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Chemistry
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Gates, Derek P.
Copolymers of poly(methylenephosphine)s : characterization and application in polymer-supported catalysis
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