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Poly(methylenephosphine)s : homo- and copolymers bearing conjugated substituents Chun, Cindy Patricia 2009

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POLY(METHYLENEPHOSPHINE)S: HOMO- AND COPOLYMERS BEARING CONJUGATED SUBSTITUENTS by Cindy Patricia Chun Hon. B.Sc., The University of Toronto, 2006 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE STUDIES (Chemistry) THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver) March 2009 © Cindy Patricia Chun, 2009 11 Abstract New P-Mes (Mes = 2,4,6-trimethyiphenyl) phosphaalkenes bearing conjugated C substituents have been prepared: MesP=C(Naph)(Ph) (Naph = 1-naphthyl) (la), MesP=C(Phen)(Ph) (Phen = 9-phenanthrenyl) (ib), and MesP=C(C4H3S)(Ph)(C4H3S= 2- thienyl) (lc). Compounds la and ic were prepared by the base-catalyzed phospha-Peterson reaction, whereas lb was prepared via the standard phospha-Peterson route. Anionic polymerization of la and lb afforded [MesP—C(Naph)(Ph)] (2a) and [MesP—C(Phen)(Ph)] (2b), respectively. The anionic polymerization of ic was attempted, but there was no polymer formation. Poly(methylenephosphine)s 2a and 2b were chemically functionalized at the phosphorus centres by oxidation and coordination to BH3 moeities. The electronic properties of la, ib, 2a, 2b, and the functionalized polymers were investigated by UV/Vis and fluorescence spectroscopy. The results showed that naphthyl-derivatized phosphaalkene la and poly(methylenephosphine) 2a were non-emissive, whereas the functionalized naphthyl derivatized polymers emitted in the UV region when excited at 288 nm. Similarly, for the phenanthrenyl-derivatized species, phosphaalkene lb and phosphine polymer 2b were observed to be weakly fluorescent in comparison to the more emissive functionalized polymers. These results are consistent with the sensory behavior exhibited by “turn-on” chemical sensors. The phosphaalkene monomer, MesP=CPh2(3) was copolymerized with styrene (Sty) using radical initiator 1,1 ‘-azobis(cyclohexanecarbonitrile) over a range of monomer feed ratios to afford poly(methylenephosphine)-co-polystyrene (PMP-co-PS) copolymers. The compositions of these copolymers were evaluated using inverse gated proton decoupled 13C NMR spectroscopy. An adaptation of the Tidwell-Mortimer experimental approach was 111 employed to calculate reactivity ratios for the PMP-co-PS system. The first step of the approach involved a preliminary estimation of the reactivity ratios by the Fineman-Ross linearization and the Mayo-Lewis intersection method. Using the preliminary estimates, the Tidwell-Mortimer heuristic rules were applied to determine optimal feed compositions for further experimentation. Lastly, a nonlinear least squares regression was performed to provide the best estimates of the reactivity ratios (rpA = 0.11 and rs = 0.24). Based on these r values, Q-e reactivity parameters of phosphaalkene 3 were computed and the microstructure of PMP-co-PS was examined which revealed an alternating pattern of phosphaalkene and styrene units in the copolymer backbone. iv Table of Contents Abstract.ii Table of Contents iv List of Tables viii List of Figures ix List of Charts xi List of Abbreviations xii Acknowledgements xviii Dedication xix Statement of Co-authorship xx Chapter One Introduction 1 1.1 Phosphorus-Containing Polymers 1 1.1.1 Polyphosphazenes and Derivatives 2 1.1.2 Polymers with Phosphorus and Other Inorganic Elements in the Backbone 4 1.1.3 n-Conjugated Polymers containing Phosphorus in the Main Chain 6 1.1.3.1 Phosphole-Based n-Conjugated Polymers 6 1.1.3.2 Poly(arylphosphine)s 11 1.1.3.3 Phosphorus Analogues of PPV 12 1.1.4 Unconjugated Phosphorus-Carbon Polymers 16 1.2 Brief History of Poly(methylenephosphine)s 17 1.3 Research Objectives 21 1.4 Contributions by Other Researchers to This Work 23 V1.5 References .24 Chapter Two Synthesis and Polymerization Studies of New Phosphaalkenes Bearing Conjugated Substituents 29 2.1 Introduction 29 2.2 Results and discussion 31 2.2.1 Synthesis of Phosphaalkene 2.1 31 2.2.2 Synthesis of Phosphaalkene 2.2 34 2.2.3 Synthesis of Phosphaalkene 2.3 36 2.2.4 X-ray Crystallographic Analysis of Phasphaalkenes 2.1 —2.3 38 2.2.5 Polymerization Studies of Phosphaalkene Monomers 2.1 — 2.3 46 2.3 Summary 53 2.4 Experimental Section 53 2.4.1 Preparation of MesPC(Naph)(Ph) (2.1) 54 2.4.2 Preparation of MesP=C(C4H3S)(Ph) (2.2) 55 2.4.3 Preparation of MesP=C(Phen)(Ph) (2.3) 55 2.4.4 Preparation of [MesP—C(Naph)(Ph)] (2.4) 56 2.4.5 Attempted preparation of [MesP—C(C4H3S)( h)] 57 2.4.6 Preparation of [MesP—C(Phen)(Ph)] (2.5) 57 2.4.7 X-ray crystallography 58 2.5 References 59 Chapter Three Chemical Modification of Poly(methylenephosphine)s with Conjugated Substituents Accompanied by Changes in Electronic Properties 62 3.1 Introduction 62 vi 3.2 Results and discussion .64 3.2.1 Oxidation of 3.2a and 3.2b 64 3.2.2 Boronation of 3.2a and 3.2b 67 3.2.3 UV/Vis and Fluorescence Measurements of 3.la — 3.4a 69 3.2.4 UV/Vis and Fluorescence Measurements of 3.lb — 3.4b 74 3.3 Summary 78 3.4 Experimental section 79 3.4.1 Characterization of MesPC(Naph)(Ph) (3.la) 80 3.4.2 Characterization of MesPC(Phen)(Ph) (3.lb) 80 3.4.3 Characterization of [MesP—C(Naph)(Ph)J (3.2a) 80 3.4.4 Characterization of [MesP—C(Phen)(Ph)] (3.2b) 80 3.4.5 Preparation of [MesP(O)—C(Naph)(Ph)] (3.3a) 81 3.4.6 Preparation of [MesP(O)—C(Phen)(Ph)] (3.3b) 81 3.4.7 Preparation of [MesP(BH3)—C(Naph)(Ph)J1(3.4a) 82 3.4.8 Preparation of {MesP(BH)—C(Phen)(Ph)] (3.4b) 82 3.4.9 General procedure for preparing solution samples for UV/Vis and fluorescence measurements 83 3.5 References 84 Chapter Four Radical Copolymerization of P=C and C=C Bonds: Reactivity Ratios of Phosphaalkene-Styrene Copolymers 86 4.1 Introduction 86 4.2 Results and discussion 89 vii 4.2.1 Analysis of Copolymer Composition by Inverse Gated Proton Decoupled ‘3C NMR Spectroscopy 89 4.2.2 Experimental Design and Preliminary Estimation of rPA and 92 4.2.3 Application of Heuristic Rules 96 4.2.4 Determination of and by Nonlinear Least Squares Regression 98 4.2.5 Q-e values of PA and the Microstructure of PMP-co-PS 99 4.3 Summary 102 4.4 Experimental section 102 4.4.1 General procedure for synthesis of PMP-co-PS 104 4.4.2 General procedure for processing ‘3C NMR spectra and determining copolymer composition 104 4.5 References 106 Chapter Five Overall Conclusions and Future Work 109 5.1 Summary of Thesis Work 109 5.2 Future Work 113 5.2.1 Towards Poly(methylenephosphine)-Based Chemical Sensors 113 5.2.2 Copolymerization of Phosphaalkenes 113 5.3 Closing Remarks 114 5.4 References 115 viii List of Tables Table 1.1 Summary of selected characterization data for 1.5, 1.7a-c, 1.10— 1.13 7 Table 1.2 Summary of selected characterization data for 1.16a-d and 1.17 14 Table 2.1 X-ray crystallographic data for E-2.1, 2.2 (E/Z mixture), and Z-2.3 42 Table 2.2 Important metrical parameters for E-2.1, E-2.2, Z-2.2, Z-2.3, and MesPCPh2 43 Table 3.1 Summary of UV/Vis absorption bands and assignments of 3.la — 3.4a 69 Table 3.2 Summary of emission measurements on 3.la — 3.4a 72 Table 3.3 Summary of UV/Vis absorption bands and assignments of 3.lb —3.4b 75 Table 3.4 Summary of emission measurements on 3.lb — 3.4b 77 Table 4.1 Comparison of copolymer compositions measured by inverse gated proton decoupled ‘3C NMR spectroscopy and elemental analyses 91 Table 4.2 Summary of copolymerization experimental data 93 Table 4.3 Approximation of rpA and 95 Table 4.4 Summary of experimental data from copolymerizations according to optimal conditions 97 Table 4.5 Average sequence length of monomers units (lmonomer) and run number (R) of PMP-co-PS copolymers 101 ix List of Figures Figure 2.1 31P NMR spectrum (THF, 122 MHz) of 2.1 (E/Zmixture) formed after 2 weeks 32 Figure 2.2 ‘H NMR spectrum (CDC13,400 MHz) of E-2.1 33 Figure 2.3 3’P NMR spectra (THF, 122 MHz) of 2.2 (E/Zmixture) after 5 d 35 Figure 2.4 ‘H NMR spectrum (C6D,400 MHz) of 2.2 (E/Z mixture) 35 Figure 2.5 31P NMR spectrum (THF, 122 MHz) of 2.3 (E/Z mixture) formed 10 minutes after the addition of ketone to silyl phosphide 37 Figure 2.6 ‘H NMR spectrum (C6D,400 MHz) of 2.3 38 Figure 2.7 Molecular structure E-MesPC(Naph)(Ph) (E-2.1) 39 Figure 2.8 Molecular structure ofMesPC(C4H3S)( h) (2.2) 40 Figure 2.9 Molecular structure Z-MesPC(Phen)(Ph) (Z-2.3) 41 Figure 2.10 The crystal packing of Z-2.3 45 Figure 2.11 31P NMR spectrum (THF, 122 MHz) of isolated polymer 2.4 47 Figure 2.12 GPC trace of 2.4 48 Figure 2.13 31P NMR spectrum (THF, 122 MHz) of isolated polymer 2.5 49 Figure 2.14 GPC trace of 2.5 50 Figure 2.15 NMR spectra (THF, 122 MHz) of aliquots removed from the reaction between 2.3 and one equivalent of MeLi 52 Figure 3.1 3’P NMR spectra (THF, 122 MHz) of 3.3a 65 Figure 3.2 3’P NMR spectra (THF, 122 MHz) of 3.3b 66 Figure 3.3 3’P NMR spectra (THF, 122 MHz) of 3.4a 68 Figure 3.4 31P NMR spectra (THF, 122 MHz) of 3.4b 68 xFigure 3.5 UV/Vis spectra (THF) of 3.la — 3.4a .70 Figure 3.6 Emission spectra (THF) of 3.la — 3.4a 72 Figure 3.7 Orbital energy diagram illustrating the process of the photoinduced electron transport mechanism and the resulting effect on fluorescence of a fluorophore 73 Figure 3.8 UV/Vis spectra (THF) of 3.lb — 3.4b 74 Figure 3.9 Emission spectra (THF) of 3.lb — 3.4b 76 Figure 4.1 Inverse gated proton decoupled ‘3C NMR spectrum (CDC13,101 MHz) of a PMP-co-PS 90 Figure 4.2 Monomer conversions of copolymerization experiments carried through different t 92 Figure 4.3 Fineman-Ross plot of G versus F for PA/Sty copolymerization experiments 94 Figure 4.4 PA/Sty copolymerization data plotted according to the Mayo-Lewis intersection method 96 Figure 4.5 Nonlinear least squares curving fitting of copolymerization data 98 xi List of Charts Chart 4.1 Flowchart illustrating the Tidwell—Mortimer approach to determining reactivity ratios 89 xii List of Abbreviations Anal. analysis aq. aqueous Ar aryl a.u. arbitrary units A Wp atomic mass of phosphorus br broad (spectra) Bu butyl n-Bu n-butyl i-Bu iso-butyl sec-Bu sec-butyl C Celsius ca. circa Calcd calculated CAr integration value of the chemical shift assigned to aryl carbons cat. catalytic CD circular dichroism CMe integration value of the chemical shift assigned to methyl carbons COD 1 ,5-cyclooctadiene Cp cyclopentadienyl d day doublet (spectra) dba dibenzylideneacetone xlii dn/dc refractive index increment DP degree of polymerization DSC differential scanning calorimetry DVDS divinyltetramethyldisiloxane e polarity parameter according to Aifrey-Price Q-e scheme E electrophile energy E entgegen (configuration) EA elemental analysis e.g. for example El electron impact epA polarity parameter of mesityldiphenylphosphaalkene according to Aifrey-Price Q e scheme eq equation equiv equivalent(s) e5, polarity parameter of styrene according to Alfrey-Price Q-e scheme Et ethyl et al. and others exp exponential function FW formula weight FWPA formula weight (or molar mass) of phosphaalkene FWs1 formula weight (or molar mass) of styrene GOF goodness of fit (crystallography) xiv GPC gel permeation chromatography h hour HOMO highest occupied molecular orbital HPLC high-performance liquid chromatography I ipso i.e. that is ‘PL intensity of photoluminescence JR infrared k rate constant K kelvin wavelength A2 red shift 2em wavelength of emission ex wavelength of excitation umax absorption maximum ‘PA average sequence length of consecutive phosphaalkene units ‘sty average sequence length of consecutive styrene units LLS laser light scattering LUMO lowest unoccupied molecular orbital m multiplet (spectra) M molecular ion Me methyl Mes mesityl; 2,4,6-trimethylphenyl xv MHz megahertz mm minute number average molecular weight mol mole mpA mole fraction of phosphaalkene in the copolymer composition MPA mole fraction of phosphaalkene in the monomer feed MS mass spectrometry m53, mole fraction of styrene in the copolymer composition Ms mole fraction of styrene in the monomer feed weight average molecular weight m/z mass-to-charge ratio Naph 1 -naphthyl NMR nuclear magnetic resonance o ortho OTf trifluoromethanesulfonate; CF3503 OLED organic light emitting diode PPL quantum yield of photoluminescence p para PA mesityldiphenylphosphaalkene PDI polydispersity index %FEA percent of phosphorus detected by elemental analysis Ph phenyl Phen 9-phenanthrenyl xvi PLED polymer-based light emitting diode PMP poly(methylenephosphine) PMP-co-PS poly(methylenephosphine)-co-polystyrene ppm parts per million PPV poly(p-phenylenevinylene) PS polystyrene Q reactivity parameter from Aifrey-Price Q-e scheme QPA reactivity parameter of mesityldiphenylphosphaalkene from Aifrey-Price Q-e scheme Qsty reactivity parameter of styrene from Aifrey-Price Q-e scheme r reactivity ratio R average number of sequences per 100 units, also known as run number R or R’ side group ref. reference RMSE root mean squared error ROP ring-opening polymerization rpA monomer reactivity ratio of mesityldiphenylphosphaalkene monomer reactivity ratio of styrene RT room temperature s second singlet (spectra) sh shoulder Sty styrene xvii t time T1 spin lattice relaxation Temp temperature Tg glass transition THF tetrahydrofuran TMEDA N, N, N N’-tetramethylethylenediamine UV ultraviolet UV/Vis ultraviolet/visible VAZO 88 1,1 ‘-azobis(cyclohexanecarbonitrile) vs. versus X monomer conversion XPA monomer conversion of mesityldiphenylphosphaalkene Xs monomer conversion of styrene Z zusammen (configuration) xviii Acknowledgements Professor Derek P. Gates For advice (scientific and non-scientific), patience, encouragement, and reference letters Dr. Mandy Yam, Dr. Bronwyn Gillon, Dr. Kevin Noonan, Dr. Vittorio Cappello, Josh Bates, Julien Dugal-Tessier, Paul Siu, Line Christiansen, and former and present undergrads For help in the lab and good times Mario Ulises Delgado Jaime, Matt Roberts, Tim Kelly, Derrick Lee, and Fergus Chung For assistance with certain components of this work (MATLAB, instrumentation, statistics, and collaboration) Professor Mark MacLachlan and Professor Ed Grant For reference letters Staff in Department of Chemistry (UBC) For their assistance, and technical and administrative support NSERC, UBC, and Department of Chemistry (UBC) For financial support Steph Lee, Insun Yu, Joseph Hui, and my karaoke buddies For fun times, yummy food, tvb soaps, and for passing the mic Mommy, Dad, , and For unconditional love and support Michael, Lily, Andrew, and Sarah For being a good brother/sister Neal Yonson For assistance, support, encouragement, patience, and love xix Dedication To my mother xx Statement of Co-authorship The results presented in Chapters 2 and 3 will be submitted for publication in due course. A version of Chapter 4 has been prepared as a manuscript to be submitted for publication shortly. A detailed account of contributions by other researchers is stated below and included in Section 1.4 (Page 23). Some of the work in this thesis was achieved in collaboration with other researchers. For Chapter 2, all of the synthetic work was done by myself with the exception of the synthesis and recrystallization of MesP=C(C4H3S)(Ph) (C4H3S= 2-thienyl), which was a collaborative effort between myself and Fergus Chung. Fergus was an undergraduate researcher under my supervision. All crystallographic data were obtained primarily by Josh Bates with some assistance from Paul Siu using the departmental X-ray diffractometer. The solution and refinement of the molecular structures of MesP=C(Naph)(Ph) (Naph = 1 -naphthyl) and MesP=C(C4H3S)(Ph) were completed by Josh. The solution and refinement of the molecular structure of MesP=C(Phen)(Ph) (Phen = 9-phenanthrenyl) were performed by Paul. All of the work presented in Chapters 3 and 4 was completed by myself. 1Chapter One Introduction 1.1 Phosphorus-Containing Polymers Since the discovery of “inorganic rubber” by Stokes in the 1 89Os,1 history has witnessed an exciting evolution of inorganic polymers with phosphorus atoms in the main chain.59 “Inorganic rubber”, which is actually a crosslinked form of poly(dichlorophosphazene), was first prepared by the thermal ring-opening polymerization (ROP) of hexachiorocyclotriphosphazene (Scheme 1.1, Route A). The resulting material was insoluble and hydrolytically unstable. Due to its intractability, “inorganic rubber” remained a chemical curiosity until the 1 960s. That was when Allcock and Kugel showed that the carefully controlled ROP of sublimed hexachlorocyclotriphosphazene afforded uncrosslinked poly(dichlorophosphazene) (1.1 a) which was soluble in organic solvents (Scheme 1.1, Route Nearly half a century after this discovery, research on polyphosphazene-based materials continues to grow.”2 Route A Route B heat sublime 250 °C CI “inorganic rubber” ci Cl 60-65 °C in vacuo [ , 1.la Scheme 1.1 The discovery of polyphosphazenes has also inspired the development of other polymers with phosphorus atoms in the main chain.59”The synthesis of phosphorus-containing polymers, like that of other inorganic macromolecules, is challenging but offers the potential of accessing new materials with useful and interesting properties.’3This introduction will feature some References begin on page 24 Chapter One 2 examples of phosphorus-containing polymers to demonstrate their uniqueness and highlight the strategies employed to overcome synthetic obstacles. 1.1.1 Polyphosphazenes and Derivatives Polyphosphazenes comprise the most heavily studied class of main group polymers.”2 As mentioned in the introduction, the preparation of poly(dichlorophosphazene) (1.la) via thermal ROP of pure hexachiorocyclotriphosphazene affords a material that is soluble in organic solvents. However, 1.la is unstable due to its hydrolytically sensitive P—Cl bonds. This reactive polymeric species can be treated with nucleophiles in a macromolecular substitution approach, allowing replacement of the chlorine groups by alkoxide, aryloxide, or amino groups to afford a wide range of hydrolytically stable polyphosphazenes (1.lb) (Scheme l.2).b0h114 Macromolecular Polycondensation substitution 91 1 2 NaR or HR 1 heat -I-P=N--I- -1—P=N± Me3S1NP-OCH2CF[ — 2 NaCI or HCI [ j — SiMe3OCH2CF 1 ia R = alkoxide, aryloxide, 1.lb-cNHR or NR’R” b: R = alkoxide, aryloxide, NHR’ or NR’R” C: R = alkyl or aryl Scheme 1.2 There are other methods to prepare polyphosphazenes. A polycondensation method was developed in the mid-1980s by Neilson and Wisian-Neilson and their co-workers to afford 1.lc, which has alkyl or aryl side groups (Scheme 1.2). 15,16 The number average molecular weight (Ma) of these polymers ranged between 29,000 g moi’ and 94,500 g mol’, and the polydispersity index (PDI) of 1.lc ranged between 1.7 and 2.2. References begin on page 24 Chapter One 3 In 1995, Honeyman et al. reported an ambient temperature route using PCi5 (Scheme 1 3),17 affording poly(dicholorophosphazene) 1.la of controllable molecular weights and low polydispersity (PDI = 1.04), a feat that was unprecedented for polyphosphazenes. While the original polymer prepared by Alicock and Kugel contained about 370 PN units in the backbone,’° the average number of PN units in the poly(dicholorophosphazene) prepared by Honeyman et al. was 55 units. There are many other methods reported for the preparation of polyphosphazenes,” however it is beyond the scope of this introduction to describe each one. r CI3P=NSiMe —f-P=N [ci 1.la Scheme 1.3 With over 300 known examples,” the wide structural diversity of polyphosphazenes gives rise to materials with unique properties including: flame-resistance, hydrophilicity or hydrophobicity, amorphous or microcrystalline structure, or with nonlinear optical, liquid crystalline or photochromic properties. Important applications of polyphosphazenes include dental liners, fuel liners, and flame-retardant materials.11”2 Similar to polyphosphazenes are poly(thionylphosphazene)s (1.2), which have phosphorus, nitrogen and sulfur atoms in the backbone.’82’Polymers of 1.2 containing [(9) ‘ tN=N [R R’ 1.2 hydrolytically sensitive sulfur(IV)—nitrogen bonds were first reported by Allcock and co-workers in 1990.18 In 1991, Liang and Manners reported the preparation of the more stable sulfur(VI) analogue by ROP of a cyclic thionyiphosphazene at 165 oC.19 Both groups had prepared 1.2 References begin on page 24 Chapter One 4 bearing chlorine substituents (i.e R = R’ = Cl), which could be replaced by aryloxy or amino groups via macromolecular substitution. Turner and co-workers extended the work on poly(thionylphosphazene)s by synthesizing polymers in which the substituents are alkyl groups.20 Remarkable properties of poly(aminothionylphosphazene)s, derivatives of 1.2 (R = R’ = amino groups), include high free volume in the material, as demonstrated by studies of gas permeability, high solubility and processability.22Some of these polymers have glass transitions, Tg’s, below —10 °C, an important characteristic that allows for large-scale conformational motions for effective gas diffusion.23’4Block copolymers, poly(aminothionylphosphazene)-b poly(tetrahydrofuran) have found application as matrices for fluorescent dyes which are very effective as photoluminescent oxygen sensors for pressure-sensing composite technology.22’56 1.1.2 Polymers with Phosphorus and Other Inorganic Elements in the Backbone A rare example of a phosphorus-containing polymer is poly(ferrocenylphosphine) (1.3) because the backbone includes not only phosphorus atoms but also the transition metal iron.2729 These polymers were first prepared by Seyferth and co-workers in 1982 by a condensation polymerization involving dilithioferrocene, N, N, NN’-tetramethylethylenediamine (TMEDA) and PhPC12 (Scheme 1.4, Route A).27 In 1996, Manners and co-workers discovered that phosphorus-bridged ferrocenophanes could undergo thermal ROP to afford 1.3.28 Shortly thereafter, they reported that the ROP could also proceed in a living fashion by an anionic method at room temperature provided that the starting monomers were of high purity (Scheme 1.4, Route B).29 References begin on page 24 Chapter One 5 Me Ph —Li N 2 Route A i4 Fe ) + PhPCI2 Fe Fe P—Ph N j 2) H20 1.3 Scheme 1.4 The living route allowed access to well-defined architectures such as block copolymers of poly(ferrocenylphenylphosphine)-b-poly(dimethylsiloxane) and poly(ferrocenylphenylphosphine)-b-poly(ferrocenyldimethylsilane) 29 In addition to opening the door to the construction of specially designed macromolecular architectures, living polymerization in general allows one to access polymers of narrow polydispersities and to control their molecular weights by varying the monomer:initiator ratio. Another interesting class of phosphorus-containing polymers is polyphosphinoboranes (1.4), which are composed alternating four-coordinate boron and phosphorus atoms in the skeleton chain.30’Cyclic phosphinoboranes have been known since the 1950s.32 There is limited documentation of polyphosphinoboranes from that time, and product characterization was only partially reported or not reported at all.33’4 In 2000, the preparation of polyphosphinoboranes 1.4 was reported by Manners and co-workers which involved a rhodium- catalyzed dehydrocoupling ofRPH2B3(Scheme l.5).° Interestingly, 1.4 is air and water stable in the solid state, but has low thermal stability. [Rh] ER 100-120°C I I RPH2•B3 — -j-P—BH2 H2 [H n 1.4 R = Ph, i-Bu, p-n-BuC6H or p-dodecylC6H4 Scheme 1.5 References begin on page 24 Chapter One 6 1.1.3 it-Conjugated Polymers containing Phosphorus in the Main Chain 1.1.3.1 Phosphole-Based it-Conjugated Polymers Inorganic materials based on polypyrrole and polythiophene architectures are widely known and have been extensively studied with regard to their synthesis, conductivity, and photochemical properties. Phosphole, the phosphorus analogue of pyrrole and thiophene, has also recently been investigated for incorporation into extended it-conjugated structures.6’835 Phosphole-containing it-conjugated polymers are interesting candidates for applications involving organic or polymer-based light emitting diodes (OLED5/PLED5) and chemical sensors.3638 Due to the versatile reactivity of trivalent three-coordinate phosphorus (i.e. complexation to Lewis acids or transition metals, oxidation),39’4°electronic tuning of phosphole containing it-conjugated materials should be feasible, giving a diversity of properties and functions.6’7354Table 1.1 summarizes the key physical and electronic properties of the phosphole-based polymers which will be discussed in this section. The first report of phospholes being integrated into it-conjugated systems occurred in 1990 when Mathey and co-workers reported their work on oligomers containing two phosphole and four thiophene units.42 In 1997, Mao and Tilley synthesized the first it-conjugated polymer containing phosphole moieties in the backbone.43The synthesis of the biphenyl-bridged phosphole polymer (1.5) was achieved using a zirconocene-coupling method (Scheme 1.6). The different regiochemistry in 1.5 originated from its precursor and was confirmed by 111 ‘3C, and 31P NMR spectroscopy. Interestingly, 1.5 exhibited photoluminescence in the visible blue-green region = 470 nm). Its Stokes shift of 157 nm is large in comparison to the range of Stokes shifts reported for other phosphole-containing it-conjugated polymers (Table 1.1). Analysis of 1.5 by gel permeation chromatography (GPC) suggested that it exhibited an M value of 6,200 g References begin on page 24 Chapter One 7 Table 1.1 Summary of selected characterization data for 1.5, 1.7a-c, 1.10 — 1.13. polymer ‘rnax Ar ?‘.em / [X] Stokes shift 4PL M11 (g moE’) / PDI ref. (nm) (nm) (nm) (nm) [DP] 1.5 308 62 470 / [313] 157 0.092 6,200 / [17] 2.58 43 1.7a 410 56 490/[410] 80 0.09 10,200/[15] 1.5 45 1.7b 414 60 487/[410] 77 0.14 10,000/{121 1.4 45 1.7c 382 28 435 / [390] 45 0.08 6,800 / [7] 1.3 45 1.10 378 21 460/[378] 82 0.562 8,000/[15] 3.1 46 1.11 353 (sh), 10 459 / [393] 66 0.566 10,000 / [20] 3.2 46 393 1.12 456 (sh), 123 555 / [502] 53 - - - 37 502 1.13 345, 485 109 509, 540 / 24 0.47 5,800 / [9] 1.7 47 [485] a 2max of polymer compared to the 2max of model compounds (i.e. red shift). b = quantum yield of photoluminescence. LN:J Cp2ZrCI,2 n Cp2Zr R O.8n —2n PhPCI RR \ Ph /A O.8n “O.2n_ 1.5 Scheme 1.6 A = (CH2)4C3 References begin on page 24 Chapter One 8 mol’, which translates to approximately 17 repeat units. While this number of repeat units seems rather low, it is similar to the degree of polymerization (DP) for other phosphole-based polymers listed in Table 1.1. A common synthetic challenge shared by researchers in this field is increasing the DP values. Another convenient method to access phosphole-containing n-conjugated polymers was reported by the Réau group which involved the electropolymerization of a protected 2,5-bis(2- thienyl)phosphole followed by deprotection (Scheme 1 7)38.44 This resulted in a material that was insoluble in common organic solvents, and thus no GPC data were reported. Remarkably, the phosphorus centres in 1.6 were strongly coupled to the conjugated system along the backbone, and could act as receptor sites for elemental chalcogenides in chemical sensing experiments.38The sensor properties were evaluated by using optical and electrochemical responses measured by UV/Vis spectroscopy and cyclic voltammetry. In the presence of Sg or Se, bathochromic shifts were observed in the UV/Vis spectra and positive shifts of the oxidation current offset were observed in the cyclic voltammograms. AucI Ogfl AucI PPh Scheme 1.7 More phosphole-containing n-conjugated polymers (1.7a-c) were prepared by Chujo and co-workers via the Heck-Sonogashira reaction.45 The palladium-catalyzed coupling of bis(p bromophenyl)phosphole with diethynylarenes (Scheme 1.8) afforded 1.7a-c, which have extended n-conjugation. The extension of the n-conjugation was supported by UV/Vis data: the absorption bands of the polymers were red-shifted compared to the absorption band of the References begin on page 24 Chapter One 9 Heck-Sonagashira coupling + Ar 0C6H13 0C12H25 C12H250 0C12H25 -Ar- = _1çj.[. or C6H130 C12H250 a b c Scheme 1.8 phosphole compound, 1.8. Interestingly, 1.7a (M 10,200 g mol’; PDI = 1.5) and 1.7b (M = 10,000 g mol’; PDI = 1.4) were green emitters when irradiated at 410 nm, and 1.7c (M11 = 6,800 g mol’; PDI = 1.3) emitted blue light when excited at 390 nm (see Table 1.1). In this sense, electronic properties of 1.7 can be tuned by varying the conjugated spacer in the main chain. There are also polymers based on dithienophosphole (1.9), originating from the research group of Baumgartner.37’46The advantage offered by the annelated ring system is maximization of the it-overlap by forcing a coplanar geometry. Ph 1.9 Ph 1.7a-c References begin on page 24 Chapter One 10 Using PtDVDS (DVDS = divinyltetramethyl disiloxane), Baumgartner and co-worker synthesized polymers 1.10 and 1.11 (Scheme 1.9) with M values up to 8000 g mof’ and 10,000 g mol’, respectively.46Compared to other phosphole-containing polymers, 1.10 and 1.11 have relatively high PDI values (Table 1.1). The absorption and emission properties of 1.10 and 1.11 are very similar to those of their respective model compounds, suggesting a nearly localized it system. This is not surprising since it is expected that the —SiMe2moieties would inhibit it delocalization from one dithienophosphole unit to the next. HMe2SiSiMe Ph’O n Scheme 1.9 Dithienophosphole-based it-conjugated polymers, 1.12 and 1.13, were obtained via a Stille coupling and Suzuki-Miyaura coupling, respectively (Scheme The absorption and emission properties of 1.12 and 1.13 were strongly red-shifted compared to those of the corresponding monomers (A?.1.i2= 123 nm; A?.4.13 = 109 nm; see Table 1.1). These data suggest significant iu-delocalization along the conjugated backbone. Both polymers fluoresce in the yellow-green region of the visible spectrum. Despite having long alkoxy chains, 1.12 exhibits poor solubility in THF, and thus the investigators have been unable to analyze 1.12 by GPC. The Stokes shift reported for 1.13 is small compared to those of other phosphole-based polymers (see 1.10 1.11 References begin on page 24 Chapter One 11 R Stille A + 1*1 coupling 1.12 A = 0C8H17 + (HO)2B—-B(oH) Ph Me C6H13 C6H13 Ph’ Me C6H13 C6H13 1.13 Scheme 1.10 Table 1.1), which was attributed to rigidity in the main chain. In addition to the extended t conjugation, the ionic nature of 1.13 makes this material a promising candidate for conjugated polyelectrolyte applications.47 1.1.3.2 Poly(arylphosphine)s Poly(arylphosphine)s (1.14) comprise a class of polymers developed by Lucht and co workers.485°In 2000, Lucht and St. Onge reported the synthesis of poly(p-phenylenephosphine)s (1.14a) by a palladium-catalyzed carbon-phosphorus bond formation (Scheme 1.1 1).48 The M11 of 1.14a varied between 1,300 g mol’ and 3,100 g mo[1, depending on the R substituent (isobutyl, phenyl or 2,4,4-trimethylpentyl) on the phosphorus centre. The number of repeat units ranged between 7 to 14 units. The intriguing feature of 1.14a was the spectroscopic evidence for electronic delocalization along the backbone which must formally pass through the phosphorus atoms. The extended ar-conjugation was supported by red shifted optical absorptions (Az. 30 nm for 1.14a R Ph) and lower oxidation potentials of the polymers compared to model References begin on page 24 Chapter One 12 compounds. These results are puzzling because the type and degree of overlap between the lone pair on phosphorus and the adjacent aromatic groups are unclear. Pd(PPh3)4 F 1 Ni(COD)2 — I — I—Ar—I + RPH2 —--Ar_P-j- ‘ Br—---P—-(—Br 1 .14a-b a: —Ar— = —--——- , R = i-Bu, Ph, or 2,4,4-trimethylpentyl b: —Ar— = , R = 2,4,4-trimethylpentyl Scheme 1.11 In 2002, Lucht and Jin reported an extension of their work that employed palladium and nickel mediated coupling, as shown in Scheme 1.11, to prepare poly(arylphosphine)s in which the aryl group was biphenyl.49The M value of 1.14b was 3,100 g mol’, which suggested approximately 10 repeat units. The low molecular weights and low number of repeat units in 1.14a and 1.14b were attributed to poor solubility, consequently precipitating out of the reaction mixture before higher molecular weight polymers could be attained. In 2005, Lucht and Jin prepared poly(p-phenylenephosphine)-co-polyaniline.5°Like 1.14a, characterization of the copolymer obtained by UV/Vis spectroscopy and cyclic voltammetry provided the spectroscopic evidence for extended n-conjugation through the copolymer backbone, which must formally pass through the trivalent phosphorus centres. More interestingly, oxidation of the phosphorus centres to phosphine oxides inhibited the electronic delocalization, suggesting participation from the phosphorus lone pair in the conjugated system when phosphorus was in the trivalent state. 1.1.3.3. Phosphorus Analogues of PPV Poly(p-phenylenephosphaalkene)s5155 comprise a very interesting class of conjugated References begin on page 24 Chapter One 13 phosphorus-containing polymers because they represent the phosphorus analogues of poiy(p phenylenevinylene) (PPV), a luminescent organic macromolecule. The first example, 1.15a, was reported in 2002 by Wright and Gates and was achieved by thermolysis of tetramethylterephthaloyl chloride and (SiMe3)2P-C6H4-P(SiMe,eliminating SiMe3Cl (Scheme 1.12).’ I? 85°C(SiMe3)2P—Ar—P(SiMe + C—Ar—C ci bi — 2 SIMe3CI a: —Ar— = —;::D---- and —Ar’— = b: —Ar— = and —Ar’— = Scheme 1.12 31P NMR spectroscopic analysis of 1.15a suggested that the polymer was comprised of E and Z-P=C units (i.e. a mixture of cis and trans arylene moieties). The M11 value of 1.15a was estimated to be 10,500 g mol’ using end group analysis, while a degree of polymerization equal to 21 was considered to be moderate and not unusual for a step-growth reaction. Polymer 1.15a was studied by UV/Vis spectroscopy, which showed a broad absorption (?.rnax = 338 1UTL) slightly red shifted compared to the absorption band of the model compound for 1.15a. The red shift is small (ca. 28 nm) in comparison to the red shift exhibited by organic counterparts (Ca. 125 nm for trans-PPV vs. trans-stilbene), and is possibly due to the mixture of isomers present (E and 2) in 1.15a. 1.15a—b References begin on page 24 Chapter One 14 A very similar derivative, 1.15b, was reported in 2006 (Scheme 1.1 2).52 In contrast to the mixture of E- and Z-P=C units along the backbone of 1.15a, the main chain of 1.15b consisted of solely Z-P=C moieties (i.e. trans arylene moieties). This polymer was isolated as a brittle solid that was insoluble in common organic solvents, thus the molecular weight of 1.15b could not be obtained. The absorption maximum exhibited by 1.15b (?max = 338 nm) is red shifted compared to that of a mono(phosphaalkene) model compound (A3.= 70 nm), giving strong evidence of t conjugation along the main chain. The Protasiewicz group found that poly(p-phenylenephosphaalkene)s could also be prepared by a phospha-Wittig reaction provided that substituents were bulky enough to protect the P=C bond (Scheme 1.1 3)5354 Using the phospha-Wittig methodology, they obtained (E) poly(p-phenylenephosphaalkene)s (1.16a-d). Polymer 1.16a was moderately fluorescent, with fluorescence intensity per P=C unit measured to be about 8% that of E-stilbene.53 On the other hand, fluorescence intensities of 1.16b-d were approximately equal to that of E-stilbene (see Table 1 The molecular weights (Me) of 1.16a-d ranged between 5,000 g mol’ to 7,300 g mol’, and each polymer chain consisted of approximately 4 to 6 repeat units. Although these numbers seem low, the total number of aromatic units in the chains ranges from 18 to 26 units, resulting in an extended ir-delocalized system. Table 1.2 Summary of selected characterization data for 1.16a-d and 1.17. polymer ?max (fliT’) 2.em (rim) ‘PL (%)a M (g mol’) / [DPI PDI ref. 1.16a 445 545 8 6,500/[6] N/A 53 1.16b 435 481 80 5,000/[4] 2.3 54 1.16c 427 486 130 7,200 / [6] 2.2 54 1.16d 416,473(sh) 481 110 7,300/[6] 1.9 54 1.17 435,481 none 0 5,900/[6] 2.1 54 ‘PL = intensity of photoluminescence compared to E-stilbene References begin on page 24 Chapter One 15 ,,PMe3 ,P—Ar—P Me3P’ + 0 0 I, H H HO—Arstir overnight P—Ar—F” —2 Me3P=0 1.16a—d —Ar—for a—Ar— = 0C6H13 a: —Ar — = 06H13 forb—d C: —Ar— = d: —Ar— = b: —Ar— = -—c-- Scheme 1.13 The Protasiewicz group also synthesized a diphosphene analogue of PPV.54 Polymer 1.17 was prepared by thermolysis or photolysis ofMe3P=P—Ar—P=PMe,eliminating two equivalents of PMe3 (Scheme 1.14). Remarkably, 1.17 (M = 5,900 g mo11;DP = 6; PDI = 2.1) is the first polymer with multiple bonds between two heavier main group elements in the main chain. Although structurally interesting, 1.17 does not exhibit fluorescence, which may be due to quenching by the phosphorus lone pairs. /,PMe3 heat or hv F p-i- —Ar— = P-Ar—P I // Me3P” —2 PMe3 TArP in 1.17 Scheme 1.14 References begin on page 24 Chapter One 16 A common strategy used by the research groups of Gates and Protasiewicz is the employment of bulky groups to protect the heavy-element multiple bond (i.e. P=C or P=P) and prevent dimerization and/or cyclooligomerization. This strategy is in fact commonly used to stabilize exotic multiply bonded inorganic molecules and monomers for polymerization.13’5659 1.1.4 Unconjugated Phosphorus-Carbon Polymers Recently, a new class of phosphorus-containing polymers was developed by Vanderark et al. via the anionic ring-opening polymerization of a strained phosphirene (Scheme 1.1 5)60 This synthetic route led to polyvinylenephosphine (1.18). High molecular weight 1.18 (M11 = 18,000 g mol’; DP = 111; PDI = 1.23) was obtained. However, properties and potential applications of 1.18 have not been reported. Ph Ph MeMe 7800 25°C 14 h MMe065:3 1 1 8 Scheme 1.15 In 2007, Chujo and co-workers reported the synthesis of polymers containing chiral phosphorus atoms in the backbone (1.19).61 This was achieved by using chiral biphosphine borane adducts and a,a’-dibromoxylene as building blocks (Scheme 1.16). Polymers 1.19 were studied by circular dichroism (CD) spectroscopy and differential scanning calorimetry (DSC) experiments. The results from CD spectroscopy suggested that the polymers derived from meta xylene and para-xylene exhibited optically active higher-ordered structures, such as helical References begin on page 24 Chapter One chains. On the other hand, the polymer derived from ortho-xylene displayed an unresponsive CD spectrum, suggesting the absence of a higher-ordered structure. Potential applications for 1.19 include heavy-metal sensors and transition-metal catalysts for asymmetric reactions, however no studies have been reported thus far to demonstrate this possibility. 1) 2 equiv sec-BuLi, (-)-sparteine BH3 BH3 2) BrJ/Br Me t-Bu Scheme 1.16 Poly(methylenephosphine)s are polymers composed of alternating phosphorus and carbon atoms in the main chain.62 Since the work on these polymers was conducted by the Gates group and builds the foundation for virtually all of the work presented in this thesis, a brief history of poly(methylenephosphine)s demands a section of its own. 1.2 Brief History of PoIy(methylenephosphine)s In 2003, Chi-Wing Tsang and Mandy Yam of the Gates group discovered the first addition polymerization of a phosphaalkene (1.20) to afford poly(methylenephosphine) (1.21).62 The discovery of 1.21 occurred after the purification of 1.20 by vacuum distillation at 150 °C. Through GPC and NMR spectroscopic analysis, Tsang and Yam showed that the gummy, pale- brown residue that remained after distillation contained poly(methylenephosphine) (M = 11,500 g moi’; DP = 36; PDI = 1.25). It was slightly surprising that the polymerization occuned so readily with just heat alone. Subsequently, it was shown that the polymerization could be achieved using a radical initiator such as 1,1 ‘-azobis(cyclohexanecarbonitrile) (VAZO 88), or 1.19 References begin on page 24 Chapter One 18 using an anionic initiator such as MeLi or n-BuLi (Scheme 1.17). These methods afforded 1.21 with M values ranging between 5,400 g mol’ and 6,600 g mol’ (DP = 17 to 21) and PDI values between 1.10 and 1.55.62 10% VAZO 88 Ph _—00°-.. E Phi Mes= Mes’Ph 24h,150°C 5% MeLi or 5% n-BuLi 1 21 Scheme 1.17 The development by Tsang and Yam is an incredible feat for two reasons. Firstly, their development introduced a new method to access inorganic polymers. Although addition polymerization is well-established for olefins,63 prior to Tsang and Yam’s development addition polymerization had not been generalized to heavy-element multiple bonds. Most synthetic methods to access inorganic polymers involve a ROP process, polycondensation or a coupling strategy, all of which were shown as examples in section 1.1. Secondly, it has been observed that phosphaalkenes share some of the same reactivities as olefins, such as 1,2-addition of polar molecules (i.e. HX), the Diels-Alder reaction, epoxidation, metal complexation and hydrogenation (Scheme 1.1 8).39566465 Tsang and Yam’s development is significant because it expands the analogy between P=C and C=C bonds to polymer science.55 References begin on page 24 Chapter One 19 1,2 Addition XH HX I I I —P—C— or —P—C— I Compxation /P=C\ Diels-Alder Hydrogenation —P—C— P—C” EpoxidationI initiator - Addition Polymerization Scheme 1.18 In 2004, the Gates group reported their work on the radical copolymerization of phosphaalkene 1.20 and styrene to afford random copolymers (1.22) (Scheme 1.19).66 Ph H H 1%VAZO P=C + CzC Mes’ Ph H’ Ph 100 C 1.20 Scheme 1.19 The new hybrid inorganic-organic macromolecule, 1.22, was tested as a ligand for the Suzuki cross-coupling of bromobenzene and phenylboronic acid to form biphenyl. Results showed that in the presence [Pd2(dba)3](dba = dibenzylideneacetone), CsF, and copolymer 1.22, the cross-coupling proceeded and biphenyl was isolated in 90% yield. However, when the cross- coupling reaction was attempted using [Pd2(dba)3],CsF and homopolymer 1.21, the yield was 1.22 References begin on page 24 Chapter One 20 the same as that in the absence of any ligand (yield = 25%). Thus, the study provided evidence for the potential of copolymer 1.22 for use in polymer-supported catalysis. In 2006, Kevin Noonan of the Gates group showed that the anionic polymerization of phosphaalkene 1.20 could proceed at ambient temperature and in a living fashion using substoichiometric quantities of n-BuLi.67 This allowed for control over the molecular weight of the poly(methylenephosphine) with M values up to 29,600 g mof’ (DP = 94) and polymers of low polydispersities (PDI = 1.0 — 1.1). Furthermore, the living polymerization of 1.20 permitted the preparation of block copolymers, such as polystyrene-b-poly(methylenephosphine) (1.23) (Scheme 1.20).67 1)1 mol% n-BuLi, toluene 2) m 1.20, glyme F H H Ph 1H 3)MeOH I I I I CC PC H’ Ph II I I I[H Ph MesPh m 1.23 Scheme 1.20 The chemical functionality of poly(methylenephosphine) 1.21 has also been investigated. Like most three-coordinate trivalent phosphines, the phosphine moieties in 1.21 can be oxidized using 02, H20 or S8 (Scheme 1.21).62 Similar to phosphine ligands, the phosphine moieties can also be coordinated to transition metals.68 Additionally, 1.21 can be chemically modified by coordinating the phosphorus atoms to BR3 moieties to form phosphine-borane adducts along the backbone, or by reacting with MeOTf to afford methylphosphonium ionomers.69 References begin on page 24 Chapter One 21 S Phi I Ii I -t--% [Mes Ph S4 _L0PhJ. 02orH202 LPhJ Cs-AucI,, L-1_ [MS h] [MS hJ [MS Phj 1.21 MeO,y E I Mes Ph L In Scheme 1.21 Although there have been more studies on poly(methylenephosphine) 1.21 and derivatives thereof,7074 brevity limits me and I have discussed the founding developments that lead to my research objectives. 1.3 Research Objectives It is clear that the polymerization of phosphaalkenes is a convenient method to prepare polymers with alternating phosphorus and carbon atoms in the main chain.62’7 It has also been shown by previous members in the Gates group that the chemical functionalization of phosphorus centres in poly(methylenephosphine) 1.21 can be easily achieved via oxidation reactions, or complexation to transition metals or Lewis acids.62’89When I joined the Gates group, my first goal was to prepare poly(methylenephosphine)s bearing fluorescent side groups, and my second objective was to study the changes in electronic properties upon chemical x=50% y=50% References begin on page 24 Chapter One 22 modification. The synthetic work will be discussed in Chapter 2, whereas the chemical functionalization of the new polymers and the concomitant changes in electronic properties will be covered in Chapter 3. The long-term goal behind the work presented in Chapters 2 and 3 is to develop a chemical sensor based on poly(methylenephosphine). This would require further studies, such as experiments examining their selectivity and sensitivity, which have not been conducted to this date. Thus, the results included in Chapters 2 and 3 represent the ground work towards the long-term goal of poly(methlyenephosphine)-based chemosensors. While Chapters 2 and 3 focus on homopolymers, sensory behaviors may also be realized by random copolymers derived from phosphaalkenes since it may not be necessary to have phosphorus at every other atomic site in the backbone. As mentioned in section 1.2, some promising work had been achieved on the radical copolymerization of phosphaalkene 1.20 and styrene, affording poly(methylenephosphine)-co-polystyrene 1.22 66 However, little information was known about the microstructure of 1.22, such as the monomer distribution along the copolymer chain. To model the microstructure of a random copolymer formed by radical copolymerization, one would need to calculate the associated reactivity ratios.75 In addition to modeling the microstructure of 1.22, the reactivity ratios of phosphaalkene 1.20 and styrene would also be key synthetic parameters for future designs of tailored copolymers using phosphaalkenes and other monomers,76such as copolymers for chemical sensory applications. Thus my third goal was to calculate the reactivity ratios of phosphaalkene 1.20 and styrene. More information about reactivity ratios and the experiments conducted to achieve my third goal will be included in Chapter 4. Lastly, Chapter 5 summarizes the findings of this thesis and proposes some future directions for this work. This thesis has been written following the style of References begin on page 24 Chapter One 23 a manuscript-based thesis. Each chapter is essentially self-contained with its own introduction, results and discussion, summary, experimental section and references. 1.4 Contributions by Other Researchers to This Work Some of the work in this thesis was achieved in collaboration with other researchers. For Chapter 2, all of the synthetic work was done by myself with the exception of the synthesis and recrystallization of MesP=C(C4H3S)(Ph)(C4H3S= 2-thienyl), which was a collaborative effort between myself and Fergus Chung. Fergus was an undergraduate researcher under my supervision. All crystallographic data were obtained primarily by Josh Bates with some assistance from Paul Siu using the departmental X-ray diffractometer. The solution and refinement of the molecular structures of MesPC(Naph)(Ph) (Naph = 1 -naphthyl) and MesPC(C4H3S)( h) were completed by Josh. The solution and refinement of the molecular structure of MesP=C(Phen)(Ph) (Phen 9-phenanthrenyl) were performed by Paul. All of the work presented in Chapters 3 and 4 was completed by myself. References begin on page 24 Chapter One 24 1.5 References (1) Stokes, H. N. Am. Chem. 1 1895, 17, 275-290. (2) Stokes, H. N. Am. Chem. 1 1896, 18, 629-663. (3) Stokes, H. N. Am. Chem. 1 1897, 19, 782-796. (4) Stokes, H. N. Am. Chem. 1 1898, 20, 740-760. (5) McWilliams, A. R.; Dorn, H.; Manners, I. Top. Curr. Chem. 2002, 220, 141-167. (6) Baumgartner, T.; Réau, R. Chem. Rev. 2006, 106, 4681-4727. (7) Hissler, M.; Dyer, P. W.; Réau, R. Coord. Chem. Rev. 2003, 244, 1-44. (8) Crassous, J.; Réau, R. Dalton Trans. 2008, 6865-6876. (9) Noonan, K. J. T.; Gates, D. P. Annu. Rep. Frog. Chem., Sect. A: Inorg. Chem. 2008, 104, 394-4 13. (10) Alicock, H. R.; Kugel, R. 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Ed. 2006, 45, 6152-6155. (39) Mathey, F.; Nixon, J. F.; Dillon, K. B. Phosphorus: The Carbon Copy; Wiley-VCH: Weinheim, 1997. (40) Mathey, F. Phosphorus-Carbon Heterocyclic Chemistry: The Rise ofa New Domain; Elsevier Science: Oxford, 2001. (41) Hissler, M.; Dyer, P. W.; Réau, R. Top. Curr. Chem. 2005, 250, 127-163. (42) Bevierre, M. 0.; Mercier, F.; Ricard, L.; Mathey, F. Angew. Chem., mt. Ed. Engi. 1990, 29, 655-657. (43) Mao, S. S. H.; Tilley, T. D. Macromolecules 1997, 30, 5566-5569. References begin on page 24 Chapter One 27 (44) Hay, C.; Fischmeister, C.; Hissler, M.; Toupet, L.; Réau, R. Angew. Chem., mt. Ed. 2000, 39, 1812-1815. (45) Morisaki, Y.; Aiki, Y.; Chujo, Y. Macromolecules 2003, 36, 2594-2597. (46) Baumgartner, T.; Wilk, W. Org. Lett. 2006, 8, 503-506. (47) Durben, S.; Dienes, Y.; Baumgartner, T. Org. Lett. 2006, 8, 5893-5896. (48) Lucht, B. L.; St. Onge, N. 0. Chem. Commun. 2000, 2097-2098. (49) Jin, Z.; Lucht, B. L. J Organomet. Chem. 2002, 653, 167-176. (50) Jin, Z.; Lucht, B. L. J Am. Chem. Soc. 2005, 127, 5586-5595. (51) Wright, V. A.; Gates, D. P. Angew. Chem., mt. Ed 2002, 4], 2389-2392. (52) Wright, V. A.; Patrick, B. 0.; Schneider, C.; Gates, D. P. 1 Am. Chem. Soc. 2006, 128, 8836-8844. (53) Smith, R. C.; Chen, X. F.; Protasiewicz, J. D. Inorg. Chem. 2003, 42, 5468-5470. (54) Smith, R. C.; Protasiewicz, J. D. I Am. Chem. Soc. 2004, 126, 2268-2269. (55) Gates, D. P. Top. Curr. Chem. 2005, 250, 107-126. (56) Regitz, M.; Scherer, 0. J. Multiple Bonds and Low Coordination in Phosphorus Chemistry; Thieme: New York, 1990. (57) Romanenko, V. D.; Sanchez, M. Coord Chem. Rev. 1997, 158, 275-324. (58) Niecke, B.; Gudat, D. Angew. Chem., mt. Ed. Engi. 1991, 30, 2 17-237. (59) Rivard, E.; Power, P. P. Inorg. Chem. 2007, 46, 10047-10064. (60) Vanderark, L. A.; Clark, T. J.; Rivard, B.; Manners, I.; Slootweg, J. C.; Lammertsma, K. Chem. Commun. 2006, 3332-3333. (61) Morisaki, Y.; Ouchi, Y.; Tsurui, K.; Chujo, Y. I Polym. Sci., Part A: Polym. Chem. 2007, 45, 866-872. References begin on page 24 Chapter One 28 (62) Tsang, C. W.; Yam, M.; Gates, D. P. J Am. Chem. Soc. 2003, 125, 1480-148 1. (63) Odian, G. Principles ofPolymerization; 3rd ed.; Wiley-Interscience: New York, 1991. (64) Mathey, F. Acc. Chem. Res. 1992, 25, 90-96. (65) Mathey, F. Angew. Chem., mt. Ed. 2003, 42, 1578-1604. (66) Tsang, C. W.; Baharloo, B.; Riendi, D.; Yam, M.; Gates, D. P. Angew. Chem., mt. Ed. 2004, 43, 5682-5685. (67) Noonan, K. J. T.; Gates, D. P. Angew. Chem., mt. Ed. 2006, 45, 727 1-7274. (68) Gillon, B. H.; Patrick, B. 0.; Gates, D. P. Chem. Commun. 2008, 2161-2163. (69) Noonan, K. J. T.; Feldscher, B.; Bates, J. I.; Kingsley, J. J.; Yam, M.; Gates, D. P. Dalton Trans. 2008, 445 1-4457. (70) Gillon, B. H.; Gates, D. P. Chem. Commun. 2004, 1868-1869. (71) Noonan, K. J. T.; Patrick, B. 0.; Gates, D. P. Chem. Commun. 2007, 3658-3660. (72) Gillon, B. H.; Noonan, K. J. T.; Feldscher, B.; Wissenz, J. M.; Kam, Z. M.; Hsieh, T.; Kingsley, J. J.; Bates, J. I.; Gates, D. P. Can. J. Chem. 2007, 85, 1045-1052. (73) Noonan, K. J. T.; Gillon, B. H.; Cappello, V.; Gates, D. P. 1 Am. Chem. Soc. 2008, 130, 12876-12877. (74) Noonan, K. J. T.; Gates, D. P. Macromolecules 2008, 41, 196 1-1965. (75) Tidwell, P. W.; Mortimer, G. A. I Polym. Sd., Part A: Gen. Pap. 1965, 3, 369-387. (76) Aifrey, T.; Bobrer, J. J.; Mark, H. Copolymerization; Interscience Publishers, Inc.: New York, 1952. References begin on page 24 29 Chapter Two Synthesis and Polymerization Studies of New Phosphaalkenes Bearing Conjugated Substituents* 2.1 Introduction As mentioned in Chapter 1, the first goal of this thesis work is to synthesize poly(methylenephosphine)s bearing conjugated substituents. The motivation behind this work is to develop poly(methylenephosphine)-based chemical sensors. Thus far, the field of phosphorus- containing macromolecular chemosensors is dominated by phosphole-based polymers.16The changes in electronic properties upon chemical modification of poly(methylenephosphine)s with conjugated substituents are of interest and expected to give a sensor-like behavior. Chemical modification of these new polymers should be feasible given the demonstrated functionalization of phosphorus centres in [MesP—CPh2]1by oxidation and coordination to electrophiles (e.g. transition metals and boranes).79The purpose of the conjugated groups is to facilitate the detection of changes in electronic responses upon functionalization at phosphorus. Although the long-term goal of this project is to develop a polymeric chemosensor, this thesis discusses only the synthesis and functionalization of these polymers and the concomitant changes in their electronic properties. This chapter relates to the synthetic work involved in preparing the new poly(methylenephosphine)s for the project described above. To access these polymers, it is necessary to first synthesize phosphaalkene monomers 2.1 — 2.3 (Scheme 2.1). *A version of this chapter will be submitted for publication. Chun, C. P., Chung, F. and Gates, D. P. Synthesis and Polymerization of New Phosphaalkenes Bearing Conjugated Substituents. Chapter Two 30 R FR pd polymerization Mes Ph LMes Ph 2.1 R = EIEIJ Mes = 1 -naphthyl (Naph) mesityl 2.2 R = 2-thienyl (C4H3S) 2.3 R = 9-phenanthrenyl (Phen) Scheme 2.1 A convenient method that has been commonly used to prepare P-mesityl phosphaalkenes is the phospha-Peterson reaction,’°’8a phosphorus analogue of the Peterson olefination reaction.’9This synthetic route involves the reaction between a silyl phosphide and a ketone or an aldehyde to yield a phosphaalkene provided that sufficiently bulky substituents are employed to protect the P=C bond (Scheme 2.2). RC(O)R’SiMe Li R / MeLi / SiMe3CIMes-F Mes-P PC SiMe3 heat SiMe3 - LiCI Mes’ R’ - (SiMe3)20 Scheme 2.2 Similar to the phospha-Peterson reaction is the base-catalyzed phospha-Peterson reaction.20’In this analogous reaction, a bis(trimethylsilyl)phosphine is mixed with one equivalent of a ketone and a catalytic amount (0.5 mol%) of anhydrous base (i.e. KOH or NaOH) to afford P-mesityl phosphaalkenes with a variety of aromatic C-substituents (Scheme 2.3).22 References begin on page 59 Chapter Two 31 Presumably, a catalytic amount of base facilitates the in situ generation of the [MesP(SiMe3)f anion. The byproduct, hexamethyldisiloxane, is a volatile nonpolar liquid that can be easily removed in vacuo. In short, the base-catalyzed phospha-Peterson reaction is attractive because it is a simple one-step method to access P-mesityl phosphaalkenes bearing aromatic C-substituents. Both the standard phospha-Peterson reaction and the base-catalyzed phospha-Peterson approach were employed to prepare the target phosphaalkenes 2.1 — 2.3. SiMe3 R KOH or NaOH (cat.) ,R Mes-P + o=c . PC “SiMe3 R’ - (SIMe3)20 Me R’ Scheme 2.3 As discussed in Chapter 1, the polymerization of phosphaalkenes can be achieved using a radical initiator such as 1,1 ‘-azobis(cyclohexanecarbonitrile) (VAZO 88) or using an anionic initiator such as n-BuLi.7’23The anionic method was chosen for the work presented in this chapter as it is less laborious. Herein, the syntheses and structures of phosphaalkenes 2.1 — 2.3 are reported, followed by a discussion on the polymerization studies of these phosphaalkene monomers. 2.2 Results and Discussion 2.2.1 Synthesis of Phosphaalkene 2.1 Given the simplicity of the base-catalyzed phospha-Peterson reaction,20’this method was employed to prepare MesPC(Naph)(Ph) (2.1) (Naph = 1-naphthyl). The precursors to 2.1, MesP(SiMe3)2°and 1 -benzoylnaphthalene,24were prepared following modified literature procedures. To prepare compound 2.1, MesP(SiMe3)was mixed with one equivalent of 1- benzoylnaphthalene in the presence of a catalytic quantity of KOH (Scheme 2.4). The reaction mixture turned yellow within five minutes of being stirred. References begin on page 59 Chapter Two 32 Si Me3 Mes-Fç SiMe3 Naph KOH (cat.) + 0=0 Ph 55°C,THF - (SiMe3)20 ,Naph P =G\ Met Ph 2.1 Scheme 2.4 The reaction progress was rather slow and was monitored over 2 weeks by 31P NMR spectroscopy (Figure 2.1). The spectra revealed that the signal assigned to MesP(SiMe3)2(3p = —16 1; Figure 2.la) was gradually depleted and replaced by signals assigned to phosphaalkene 2.1 (&lp = 251 and 239, E/Z mixture; Figure 2.lb). There were two unidentifiable impurities in the reaction mixture, labeled A and B on the 31P NMR spectrum in Figure 2. lb. The minor impurity labeled C is MesPH2,5 and the signal labeled D is residual MesP(SiMe3)2. -161 ppm 251 ppm 239 ppm — ppm50 200 10 100 50 0 -50 -100 -150 Figure 2.1. 31P NMR spectra (THF, 122 MHz) of(a) MesP(SiMe32and (b) 2.1 (E/Zmixture) formed after 2 weeks. Minor impurities are labeled A — C. The identities of A and B are unknown, and C is MesPH2.The signal labeled D is residual MesP(SiMe3)2 The product, C-naphthyl-.substituted phosphaalkene 2.1, was purified by vacuum distillation followed by multiple recrystallizations from hexanes, and isolated as yellow crystals (a) (b) References begin on page 59 Chapter Two 33 in 25% yield. X-ray diffraction analysis of the yellow crystals showed 2.1 in the E configuration.* The 31P NMR spectrum of the yellow crystals showed one signal at 239 ppm, hence this chemical shift was assigned to E-2.1. However, over time (i.e. 24 h), 31P NMR spectroscopic analysis of the same sample showed two signals at 251 ppm and 239 ppm, suggesting the occurrence of E/Z isomerization in solution. The isomerization of phosphaalkenes has been studied before.”2’26 8 This process can occur in as short as 30 mm when irradiated with UV light, 24 h when exposed to sunlight, and 48 h in the absence of light.22 The ‘H NMR spectrum of E-2.1 in CDC13 (Figure 2.2) exhibits the characteristic upfield signal assigned to the ortho-CH3that has double the intensity of the signal assigned to the para 9-CH3 H3C><P01) o-CH3 C H H 30 E-2.1 C26H3P p-CH3 14 Ar-H Figure 2.2. ‘H NMR spectrum (CDCI3,400 MHz) of E-2.1. Residual CHC13 (*) Silicone grease (t). * The molecular structure and X-ray crystallographic analysis of E-2. 1 will be presented in section 2.2.4. References begin on page 59 Chapter Two 34 CH3 of the mesityl ring. Integration of the ‘H NMR spectrum accounts for 9 methyl hydrogens (‘H = 2.4 and 2.3 ppm) and 14 aromatic hydrogens (1H = 7.9 — 6.8 ppm). Compound 2.1 was also characterized by ‘3C { ‘H }NMR spectroscopy (see Experimental). 2.2.2 Synthesis of Phosphaalkene 2.2 Similar to the preparation of 2.1, the synthesis ofMesP=C(C4H35)(Ph) (2.2) (C4H3S= 2- thienyl) was achieved via the base-catalyzed phospha-Peterson route (Scheme 2.5). The ketone precursor to 2.2, 2-benzoylthiophene, was prepared via a Friedel-Crafts acylation following an adapted literature procedure.29The reaction between 2-benzoylthiophene and MesP(SiMe3)2(31p = —161) in THF with a catalytic amount of KOH afforded 2.2 as a mixture of E- and Z- isomers (3ip 227 and 220) over 5 days (Figure 2.3). SiMe3 KOH (cat.)Mes—R + O=C P=C\ SiMe3 Ph THE Met Ph - (SiMe3)20 2.2 Scheme 2.5 The C-thienyl-substituted phosphaalkene, 2.2, was purified by vacuum distillation, resulting in a yellow viscous oil (yield = 60%). Recrystallization of 2.2 in hexanes afforded bright yellow crystalline needles. The 3’P NMR spectrum of the needles showed the same two signals (&ip 227, 58%; ip = 220, 42%) as observed during the course of the reaction. The ‘H NMR spectrum of 2.2 dissolved in C6D is displayed in Figure 2.4. There are four signals in the upfield region due to the presence of two isomers. Based on integration, the more intense signal of the pair of chemicals shifts assigned to the ortho-CH3and the more intense signal of chemical shifts assigned to the para-CH3were attributed to the same isomer. The remaining two signals References begin on page 59 Chapter Two 35 (b) ppm 200 150 100 50 0 -50 -ibo -io Figure 2.3. 31P NMR spectra (THF, 122 MHz) of(a) MesP(SiMe32and (b) 2.2 (E/Z mixture) (after 5 d). were assigned to the other isomer. The ratio of isomers (5 8:42) based on integration of the 31P NMR spectrum agrees with that based on integration of the methyl protons in the ‘H NMR spectrum. Integration of the benzylic region relative to the aromatic region gives 9 methyl hydrogens and 10 aromatic hydrogens. Compound 2.2 was also characterized by‘3C{’H} NMR spectroscopy (see Experimental). -161 ppm (a) 227 ppm 220 ppm H3 10 Ar-H CH3 9-CH3 Ph o-CH3- -- N 2.2 C2QH19PS Figure 2.4. ‘H NMR spectrum (C6D,400 MHz) of 2.2 (E/Z mixture). Residual C6D5H (*)• References begin on page 59 Chapter Two 36 2.2.3 Synthesis of Phosphaalkene 2.3 The synthesis of MesPC(Phen)(Ph) (2.3) (Phen = 9-phenanthrenyl) via the base- catalyzed phospha-Peterson reaction was attempted. The ketone precursor, 9- benzoylphenanthrene, was prepared from benzoyl chloride and 9-bromophenanthrene according to modified literature procedures following a copper(I) coupling and using LiC1 as an additive.24’30Unfortunately, the preparation of 2.3 via the base-catalyzed route required extremely long reaction times (over 1 month), even at elevated temperatures (i.e. 50 °C), and afforded a mixture of products. For these reasons, the preparation of 2.3 was attempted via the standard phospha-Peterson reaction described in the introduction of this chapter. By this method, one equivalent of a silyl phosphide (prepared in situ, 31p = —187, Figure 2.5 a) was treated with 9-benzoylphenanthrene in THF at —78 °C (Scheme 2.6). 1) PhenC(O)Ph, -78 c 10 mm MesP’ MeLi MesP” 2) SIMe3CI, -78 00 ,Phen THF,65°C IC” I ‘)IIvIe3 overni ht ,Iivie3 - Mes Ph - (S1Me3)20 2.3 Scheme 2.6 An aliquot was removed from the dark green reaction mixture and analyzed by 31P NMR spectroscopy. As shown in Figure 2.5b, the 31P NMR spectroscopic analysis suggested a quantitative conversion of Li[MesP(SiMe3)]to the desired product 2.3 (31p = 252 and 238; E/Z mixture). Upon quenching of the presumed byproduct LiOSiMe3with Me3SiCl, the reaction mixture instantaneously turned red. A red oil remained after the removal of solvent in vacuo, and was admixed with hexanes. Insoluble salts were removed by filtering the mixture through Celite. Phosphaalkene 2.3 was isolated as yellow crystals from recrystallization in hexanes. References begin on page 59 Chapter Two 37 -187 ppm (a) 238 ppm (b)_ I I I I I I I Ippm250 200 150 100 50 0 -50 -100 -150 Figure 2.5. 31P NMR spectra (THF, 122 MHz) of(a) Li[MesP(SiMe3](generated in situ) and (b) 2.3 (E/Z mixture) formed 10 minutes after the addition of ketone to silyl phosphide. The 31P NMR spectrum of the yellow crystals dissolved in C6D showed one signal at 252 ppm. The X-ray diffraction analysis of the yellow crystals showed 2.3 in the Z stereochemistry, hence the 31P NMR signal at 252 ppm was assigned to Z2.3.t The ‘H NMR spectrum of 2.3 dissolved in C6D,shown in Figure 2.6, exhibits broad resonances in the aromatic region (ölH 6.5 and 6.0) and the allylic region (ólH = 2.5 and 2.0). The multiple broad signals are likely to be due to restricted rotation of the mesityl ring. As indicated on the ‘H NMR spectrum in Figure 2.6, the broad resonances at 6.5 ppm and 6.0 ppm are assigned to Mes-H, while the broad resonances at 2.5 ppm and 2.0 ppm are assigned to the ortho-CH3.Integration of the spectrum agrees with this assignment and accounts for the remaining hydrogens in the molecule. A variable-temperature NMR experiment showed that the two pairs of broad signals (1H = 6.5 and 6.0; 1H = 2.5 and 2.0) eventually coalesced upon heating at 45 °C, giving one broad signal at 6.3 ppm and one broad signal at 2.3 ppm. The molecular structure and X-ray crystallographic analysis of Z-2.3 will be presented in section 2.2.4. 252 ppm References begin on page 59 Chapter Two 38 * 3p-CH 14 Ar-H 2 Mes-H 6 opH3 I III ii lilA I I t LJJLJ ___ ppm8765 43210 Figure 2.6. ‘H NMR spectrum (C6D,400 MHz) of 2.3. The multiple broad signals are likely to be due to restricted rotation of the mesityl ring. Residual C6D5H (*)• Silicon grease (t). 2.2.4 X-ray Crystallographic Analysis of Phosphaalkenes 2.1 —2.3 In all three cases, crystals suitable for X-ray diffraction were successfully grown from concentrated hexanes solutions at room temperature. Under these conditions, 2.1 crystallizes as the E isomer, 2.2 crystallizes as a mixture of E/Z isomers, and 2.3 surprisingly crystallizes as the Z-isomer, as opposed to the expected E configuration based on sterics. This surprising result may be due to a conjugation or crystal packing effect, both discussed towards the end of this section. The molecular structures of E-2.1, 2.2, and Z-2.3 are displayed in Figures 2.7, 2.8, and 2.9, respectively. The solution and refinement of these molecular structures were completed by Josh Bates and Paul Siu. Z-2.3 C30H25P References begin on page 59 Chapter Two 39 C17 P1 ClO cli Cl Figure 2.7. Molecular structure E-MesPC(Naph)(Ph) (E-2.1). Ellipsoids are drawn at 50% probability level, hydrogen atoms are omitted for clarity. Selected bond lengths (A) and angles (°): P(1)—C(1) 1.8307(16), P(1)—C(10) 1.6876(14), C(10)—C(l 1)1.4821(18), C(10)—C(17) 1.4933(19), C(1)—P(1)—C(10) 108.36(7), P(1)—C(10)—C(1 1)129.23(10), P(l)—C(10)—C(17) 114.15(10), C(17)—C(10)—C(11) 116.56(12). References begin on page 59 Chapter Two 40 Figure 2.8. Molecular structure ofMesP=C(C4H3S)(Ph) (2.2). Ellipsoids are drawn at 50% probability, hydrogens are omitted for clarity, and overlapping atoms are omitted in respective isomers. Selected bond lengths (A) and angles (°): P(1)—C(1) 1.827(3), P(1)—C(l0) 1.687(3), C(10)—C(l la) 1.484(10), C(l0)—C(15a) 1.458(8), C(l0)—C(1 ib) 1.49(2), C(10)—C(15b) 1.44(2), C(l)—P(l)—C(10) 107.39(12), P(l)—C(l0)—C(l la) 116.2(4), P(l)—C(l0)—C(15a) 127.5(3), C(l la)—C(10)—C(15a) 116.3(5), P(1)—.C(10)—C(15b) 115.2(10), P(1)—C(10)—C(1 ib) 129.9(9), C(1 lb)—C(10)—C(15b) 114.8(13). A summary of cell constants and refinement parameters is displayed in Table 2.1. Important metrical parameters of phosphaalkenes 2.1 —2.3 are presented in Table 2.2, and for comparison, metrical parameters of MesP=CPh2,reported by the Bickeihaupt and Becker groups independently,31’2are also included. Before proceeding to a discussion of the metrical parameters of the new phosphaalkenes, the evident disorder in the refined structure of 2.2 (Figure 2.8) demands an explanation. The elongated and enlarged ellipsoids of a few atoms are attributed to disorder in the C-substituents. Disorder in the aromatic C-substituents of asymmetric phosphaalkenes has been observed in previous work in our lab. The solution and refinement process of the molecular structures of 2.2 Sla Cl E-2.2 Z-2.2 References begin on page 59 Chapter Two 41 Figure 2.9. Molecular structure Z-MesP=C(Phen)(Ph) (Z-2.3). Ellipsoids are drawn at 50% probability level, hydrogen atoms are omitted for clarity. Selected bond lengths (A) and angles (°): P(l)—C(l) 1.8273(18), P(1)—C(10) 1.6926(16), C(10)—C(1 1)1.483(2), C(10)—C(17) 1.483(2), C(1)—P(1)—C(lO) 105.76(8), P(1)—C(10)—C(1 1)117.74(12), P(1)—C(10)—C(l7) 123.89(12), C(17)—C(10)—C(11) 118.14(13). proved to be challenging due to the overlapping electron densities from both isomers. Considering the challenge and difficulties in modeling the molecular structure of 2.2, the hard work in accomplishing this task is credited to Josh Bates despite the disorder. To overcome this challenge during the solution and refinement process, the metrical parameters of the phenyl and thienyl rings of the dominant isomer (i.e. E-2.2) were used to give relative positions of atoms in the rings of the other isomer. The reason why there is an elongated ellipsoid for C(20a) is due to the influence of the electron density from the sulfur atom in the other isomer (i.e. S( 1 b)). Other enlarged or elongated ellipsoids observed in the molecular structure of 2.2 can be similarly explained by the influence of overlapping electron densities. Due to this disorder, only the P1 ClO 11 References begin on page 59 Chapter Two 42 metrical parameters that do not involve the phenyl and thienyl rings in 2.2 can be discussed with confidence, whereas the metrical parameters involving these rings are reported for completion and must be taken with caution. Table 2.1. X-ray crystallographic data for E-2.1, 2.2 (E/Z mixture), and Z-2.3 compound E-2.1 2.2 (E/Z mixture) Z-2.3 Formula C26H3P C20H19PS C30H25P FW 366.41 322.38 416.47 crystal system monoclinic monoclinic monoclinic space group P 2/n P 21/c C 2/c color yellow yellow yellow a(A) 12.0535(4) 11.4651(14) 19.514(2) b(A) 9.2978(3) 6.1645(9) 13.3010(14) c(A) 18.7237(6) 24.1496(28) 20.028(2) a (°) 90.0 90.0 90.0 /3(0) 99.3480(10) 90.952(6) 119.5190(10) y(°) 90.0 90.0 90.0 Z 4 4 8 Temp (K) 173 173 173 R1 [I>2a(I)] 0.0412 0.0620 0.0433 wR2(alldata) 0.1043 0.1948 0.1372 GOF 1.009 1.016 1.054 References begin on page 59 Chapter Two 43 Table 2.2. Important metrical parameters for E-2.1, E-2.2, Z-2.2, Z-2.3, and MesP=CPh2. Angles between planes (o)b Ar,rans 59.3 34 43 20.6 36.6 21.4 41.8 44 51 63.2 42.9 59.2 Mes 64.8 737a 737a 85.3 71 72.2 Reference This work This work This work This work 31 32 a The bond lengths reported for the P=C bond of E-2.2 and Z-2.2 are actually measured between the same atoms (i.e. P(1) and C(10)), and thus explains why the values are exactly the same. Analogous arguments explains the cases for the PCMeS bond, the LCMesP=C angle, and the angle between best planes of the Mes ring and the PC bond. b The angle between the mean plane of the atoms that comprise the aromatic substituent and the mean plane defined by CipsoPC(Cgrans)(Ccjs) atoms. Now that the disorder in 2.2 has been discussed, the discussion on the metrical parameters of 2.1 — 2.3 shall begin here, starting with the P=C bond lengths. The P( 1 )—C( 10) E-2.1 E-2.2 Z-2.2 Z-2.3 MesP=CPh2 MesPCPh2compound Bond lengths (A) PC 1.6876(14) 1.687(3)a 1.687(3)a 1.6926(16) 1.692(3) 1.693(2) PCMes 1.8307(16) I.827(3)a 1.827(3)a 1.8273(18) 1.828(3) 1.830(2) CCtrans 1.4933(19) 1.484(10) 1.44(2) 1.483(2) 1.491(5) 1.491(5) C—Cm, 1.4821(18) 1.458(8) 1.49(2) 1.483(2) 1.487(4) 1.489(2) Bond Angles (°) LCMesPC 108.36(7) 107.39(12)a 107.39(12)a 105.76(8) 107.5(2) 107.6(2) LP=C—C, 114.15(10) 116.2(4) 115.2(10) 117.74(12) 116.2(2) 118.0(2) LPCCcic 129.23(10) 127.5(3) 129.9(9) 123.89(12) 127.2(2) 124.8(2) LCtrancCCciv 116.56(12) 116.3(5) 114.8(13) 118.14(13) 116.6(2) 1 17.1(3) References begin on page 59 Chapter Two 44 bond lengths in E-2.1, 2.2, and Z-2.3 (Ca. 1.69 A) are indicative of phosphorus-carbon double bonds. They are clearly shorter than the typical P—C single bond (1.83 A — 1.90 A)33 and are in the range of P=C bond lengths of related C-substituted phosphaalkenes (1.61 A— 1.71 A).34 The P=C bond lengths exhibited by E-2.1, 2.2, and Z-2.3 are in the long end of this range, which is characteristic of P-mesityl phosphaalkenes with aromatic C-substituents, such as MesP=CPh2.2’31The P—CMeS bond lengths exhibited by 2.1 —2.3 (Ca. 1.83 A) are consistent with the average PCAr bond length (1.836 A).33 The CCgrans and C—C1bond lengths in E-2.1 and Z-2.3 (ca. 1.48 A — 1.49 A) are shorter than the average C—C single bond length (1.54 A),33 but agree with the typical CSp2Ar bond lengths (1.483 A).33 It is noticeable in Table 2.2 that the CCirans bond length of Z-2.2 and the C—C1bond length of E-2.2 appear to be comparatively short (ca. 1.44 A — 1.45 A). These are the bonds between C(10) and the ipso carbon of the thienyl substituent. The molecular structure of 2-benzoylthiophene shows a similar shortening effect of the analogous bond.35 The bond length between the carbonyl carbon and the ipso carbon of the thienyl substituent measures 1.459 A, and the bond length between the carbonyl carbon and the ipso carbon of the phenyl group is 1.482 A. The geometry of the carbon atom in the Pr=C bond is essentially planar (sum of angles 360°) in 2.1 — 2.3. All of the LPC—C1angles in E-2.1, E-2.2, Z-2.2, and Z-2.3 are greater than the LPCCtrans angles ( 1230 — 129° vs. —1 140 — 117°) implying that the Ar rings are bent further away from the P=C bond than the Arirans rings. This is most likely an impact of steric repulsion between the Ar1and the mesityl rings. However, it is interesting that the angles LCMesPC and LP=C—C1in Z-2.3 are smaller than the analogous angles in the other phosphaalkenes reported in Table 2.2, indicating that the mesityl and the phenanthrenyl rings surprisingly bend closer towards each other. This may be an effect of the crystal packing of Z References begin on page 59 Chapter Two 45 2.3. As shown in Figure 2.10, the crystal packing of Z-2.3 exhibits Jt—3t interactions (3.4 A) between the carbons along the edges of the phenanthrenyl moieties of adjacent phosphaalkene molecules. These interactions are very similar to the Jt—3t interactions in the crystal packing of phenanthrene molecules reported by Professor Trotter of this department in 1963.36 The phenanthrene rings in Trotter’s report were oriented in the same fashion, respective to each other, as shown in Figure 2.10. And remarkably, the t—t interactions existed between the same carbons of the phenanthrenyl ring. Figure 2.10. The crystal packing of Z-2.3. Green dotted lines represent the 3t-3t interactions (3.4 A). The angle between the best planes of the P=C bond and the aromatic P- and C substituents in the phosphaalkenes can indicate the degree of n-conjugation present in the References begin on page 59 Chapter Two 46 molecule. A larger angle would suggest minimal it-conjugation, whereas a smaller angle would suggest a larger degree of it-conjugation between the P=C bond and the respective aromatic moiety. In the molecular structure of Z-2.3, the angle between the best planes of the mesityl ring and the P=C bond is 85.3°, indicating little or no conjugation between these moieties. On the other hand, the angle between the P=C bond and the best plane of the phenyl ring is 20.6°, suggesting that the P=C bond is more likely to be conjugated with the phenyl ring than the mesityl ring. In E-2.1, the angle between planes of the naphthyl ring and the P=C bond is 59.3°, and the angle between planes of the phenyl ring and the PC bond is 41.8°. The data suggest that the existence of it-conjugation among the naphthyl ring, phenyl ring, and the P=C bond in E-2.1 is unlikely. 2.2.5 Polymerization Studies of Phosphaaikene Monomers 2.1 — 2.3 We aimed to polymerize phosphaalkenes 2.1 — 2.3 by anionic polymerization. The polymerization of 2.1 and 2.3 was successfully achieved by treating a THF solution of the monomer with n-BuLi (2 mol%) at room temperature (Scheme 2.7). The polymerization of 2.2 was attempted, but no evidence of polymer formation was observed. This observation will be discussed later in this section. 2moI%n-BuLi F 1 p=c n-Bu+-P—C-+H Met Ph THF, RT [Mes Phj 2.1 R = Naph 2.4 R = Naph 2.3 R = Phen 2.5 R = Phen Scheme 2.7 The addition of the anionic initiator n-BuLi (2 mol%) to a yellow solution of 2.1 resulted in an instantaneous color change to dark green. The progress of the anionic polymerization was References begin on page 59 Chapter Two 47 monitored by 31P NMR spectroscopy. As the polymerization advanced, the 31P NMR signals of 2.1 (631p = 251 and 239, E/Z mixtures) gradually decreased in relative intensity and were replaced by a broad signal (631p = —9 ppm). This broad signal was assigned to [MesP— C(Naph)(Ph)] 2.4 and is similar to the broad ‘3P NMR chemical shift of [MesP—CPh2](831p = —10 ppm).7 After 14 days, the color of the reaction mixture was brown-green. Analysis of the 31P NMR spectrum of an aliquot removed from the reaction mixture suggested very little advancement in the polymerization. Integration of the 31P NMR spectrum showed 73% conversion of monomer 2.1 to polymer 2.4 (Figure 2.11 a). Since there was little advancement in the polymerization thereafter, 2.4 was isolated by addition of methanol to quench any remaining lithiates, followed by repeated precipitations using hexanes (yield = 40%). A 31P NMR spectrum of the isolated polymer is shown in Figure 2.llb. 251 ppm 239 ppm -9ppm (br) (a) (b) flfla I I • I I I I ppm 200 100 0 -100 -200 Figure 2.11. 31P NMR spectra (THF, 122 MHz) of (a) an aliquot removed from polymerization of phosphaalkene 2.1 to form polymer 2.4 (after 14 d); (b) isolated polymer 2.4. References begin on page 59 Chapter Two 48 Analysis of 2.4 by triple detection gel permeation chromatography (GPC) showed that the polymer had an absolute number average molecular weight (Me) of 40,100 g mol’ and a polydispersity index (PDI) of 1.42. GPC traces of 2.4 from the laser light scattering signal and the refractive index signal are presented in Figure 2.12. The anticipated molecular weight of the polymer based on the monomer feed and initiator feed is 18,300 g mo11.Although the goal of this project was to simply prepare poly(methylenephosphine) bearing the specified substituents, an explanation is required for the difference between the anticipated molecular weight and M measured by GPC. 40 time (mm) Figure 2.12. GPC trace of 2.4; M 40,100 g moP1,PDI = 1.42. (Red trace — laser light scattering signal, blue trace — refractive index signal.) The higher than anticipated M value is mostly likely due to a fair amount of quenching of reactive chain ends during the polymerization by minor impurities, and there is evidence of impurities in the ‘H NMR spectrum of 2.1 (Figure 2.2). The quenching would result in shorter chains of the quenched species and higher molecular weights for the remaining polymer chains. Most of the shorter chains were probably removed from the isolated product during the work-up, U(a, 1.2 0.8 0.4 0 -0.4 0 10 20 30 References begin on page 59 Chapter Two 49 explaining why the measured M of the isolated polymer was so much higher than the anticipated molecular weight. The polymerization of 2.1 was repeated a number of times and gave similar results. Similar to the polymerization of 2.1, the same color change from yellow to dark green was observed when a solution of C-phenantbrenyl-substituted phosphaalkene 2.3 was treated with n-BuLi (2 mol%). As the polymerization moved forward, the conversion of monomer 2.3 (531p = 252 and 238, E/Zmixtures) to polymer 2.5 (631p —10, broad) was monitored by 31P NMR spectroscopy (Figure 2.1 3a). After 8 days, the conversion of monomer to polymer was 60%, and the reaction mixture was brown-green in color. At this point, there was very little progress in the polymerization, and thus methanol was added to the reaction mixture to quench any remaining lithiates. Polymer 2.5 was isolated in the same manner as described for the isolation of 2.4 with a 32% yield. The 31P NMR spectrum of 2.5 is shown in Figure 2.13b. 252 ppm 238 ppm -10 ppm (br) (a) — — .— . j-.a—’’””.ernv. -.——tr-_jJln,kIrsw- .J—JAaPt-_--V- -: L.a ppm 200 100 0 -100 -200 Figure 2.13. 31P NMR spectra (TFIF, 122 MHz) of(a) an aliquot removed from the reaction mixture of the polymerization of phosphaalkene 2.3 to form polymer 2.5 (after 8 d); (b) isolated polymer 2.5. References begin on page 59 Chapter Two 50 40 time (mm) Figure 2.14. GPC trace of 2.5; M = 27,100 g moF1,PDI = 1.39. (Red trace — laser light scattering signal, blue trace — refractive index signal.) As mentioned earlier in this section, the polymerization of C-thienyl-substituted phosphaalkene 2.2 was attempted, but there was no polymer formation. The polymerization was first attempted using 2 mol% n-BuLi at room temperature. Upon the addition of the anionic initiator to a THF solution of 2.2, a change of coloration from yellow to dark red was observed. The polymerization was monitored over 7 days by removing aliquots from the reaction mixture, then analyzing the aliquots by 31P NMR spectroscopy. No change was observed in the 31P NMR According to the data analysis of 2.5 by triple detection GPC, the polymer had an M of 27,100 g mo11 and a PDI of 1.39. The GPC traces of 2.5 are displayed in Figure 2.14. The analyzed M is greater than the anticipated molecular weight (20,900 g mol’). This difference alludes to the event of quenching by impurities in solution during the polymerization progress, which was previously discussed. It is puzzling and unclear why the elemental analysis of polymers 2.4 and 2.5 showed a lower carbon content than expected; this may be a sign of inorganic impurities or fragmentation of—C(R)(Ph) chain ends (R = Naph or Phen). 1.2 0.8 a -0.4 0 10 20 30 References begin on page 59 Chapter Two 51 spectra of the aliquots. More specifically, only signals assigned to phosphaalkene 2.2 (31p = 227 and 220, E/Z mixture) were observed and there was no broad signal that would be characteristic of phosphine moieties in poly(methylenephosphine). The polymerization of 2.2 was further attempted with a higher initiator loading (up to 5 mol%) and at elevated temperatures (45 °C). Again, reactions were monitored by 31P NMR spectroscopy and there was no evidence of polymer growth. There are several possible reasons to account for the absence of polymerization activity: 1. The initiated species, Li[Mes(n-Bu)P—C(C4H3S)(Ph)], did not form. However, reactivity was observed in an NMR-scale experiment in which 2.2 was treated with one equivalent of MeLi at —78 °C in THF. 31P NMR analysis of the red reaction mixture showed two signals at —32 ppm and —44 ppm (Figure 2.15a). It was speculated that both signals are representative of the lithiated species, whereby one was assigned to Li[Mes(Me)P— C(C4H3S)(Ph)], and the other signal was assigned to Mes(Me)PCH(Ph)(C4H2SLi (lithium at the ct-position of the thienyl ring). As a reference, Li[Mes(Me)P—CPh2]has a 31P chemical shift of—42 ppm in THF.37 When the reaction mixture was quenched with MeOH, there was one singlet at —18 ppm in the 31P NMR spectrum of the quenched reaction mixture, suggesting the formation of Mes(Me)P—CH(C4HS)( h) (Figure 2.15b). For comparison, the phosphine, Mes(Me)P—CHPh2has a 31P chemical shift of—24 ppm.37 The species at —18 ppm was not isolated as this was a test reaction at NMR-scale. 2. Assuming that the formation of the initiated species was successful, then it is possible that the initiated species did not attack any monomers in solution to initiate the propagation step for forming a growing chain. The lack of propagation could be due to the stability of the carbanion, thereby not being reactive enough to attack a monomer. In References begin on page 59 Chapter Two 52 (a) (b) -44 ppm ppm 120 100 80 60 40 20 0 -20 -40 -60 -80 -100 -120 -140 Figure 2.15. 31P NMR spectra (THF, 122 MHz) of aliquots removed from the reaction between 2.3 and one equivalent of MeLi. (a) 31P NMR spectrum of an aliquot removed from reaction mixture after lithiation; (b) 31P NMR spectrum of reaction mixture after quenching with MeOH. order for propagation to occur, the carbanion must be relatively unstable thereby giving a driving force for the addition to a monomer. 3. It has been shown the anionic polymerization of phosphaalkenes requires conditions of high purity.23 It is possible that the samples of 2.2 used in the polymerization experiments were not pure enough as there is evidence of minor impurities in the ‘H NMR spectrum of 2.2 (Figure 2.4). Initiated species could be quenched by impurities present in solution. I speculate that the absence of polymerization is likely due to a lack of propagation. The NMR-scale experiment suggests that a lithiated species can form. However, it is possible that this species does not actually add to another monomer to propagate chain growth. Likewise, the lithiated species could be quenched by impurities in solution, consequently inhibiting polymer formation. -32 -18 ppm References begin on page 59 Chapter Two 53 2.3 Summary New phosphaalkenes 2.1 and 2.2 were successfully prepared via the base-catalyzed phospha-Peterson reaction, whereas the synthesis of 2.3 was achieved via the standard phospha Peterson route. The molecular structures of these new phosphaalkenes were studied by X-ray diffraction analysis. Anionic polymerization of 2.1 and 2.3 afforded new polymers, 2.4 and 2.5. Attempted polymerization of 2.2 resulted in no polymer formation. The electronic properties of phosphaalkenes 2.1 and 2.3 and polymers 2.4 and 2.5, as well as the chemical functionalization of these polymers, will be discussed in Chapter 3. 2.4 Experimental section General procedures. All manipulations of air and/or water sensitive compounds were performed under a nitrogen atmosphere using standard Schlenk techniques or in a glovebox. Hexanes and dichloromethane were deoxygenated with nitrogen and dried by passing through a column containing activated alumina. THF was freshly distilled from sodium/benzophenone ketyl. KOH and NaOH were made anhydrous by following a literature procedure (recrystallization from EtOH and subsequent heating in vacuo).38 CDC13 and C6D were dried over molecular sieves prior to use. MesP(SiMe3)2,5 l-benzoylnaphthalene,242- benzoylthiophene,29and 9-benzoylphenantbrene24’3°were prepared following modified literature procedures. n-BuLi (1.6 M in hexanes) and MeLi (1.6 M in diethyl ether) were purchased from Aldrich and were titrated prior to use to determine the concentration.39 Equipment. ‘H, 31P, and‘3C{’H} NMR spectra were recorded on Bruker Avance 300 MHz or 400 MI-Iz spectrometers. Chemical shifts are reported relative to: residual CHC13 (5 = 7.26 for ‘H); C6D5H (5 = 7.15 for ‘H); 85% H3P04as an external standard (.5 = 0.0 for 31P); CDC13(.5= References begin on page 59 Chapter Two 54 77.16 for ‘3C { ‘H}). Molecular weights were estimated by triple detection gel permeation chromatography (GPC-LLS) using a Waters liquid chromatograph equipped with a Waters 515 HPLC pump, Waters 717 plus autosampler, Waters Styragel columns (4.6 x 300 mm) HR2, HR4, and HR5E, and a Waters 2410 differential refractometer (refractive index detector A. = 940 nm), Wyatt tristar miniDAWN (laser light scattering detector operating at A. 690 nm) and a Wyatt ViscoStar viscometer. A flow rate of 0.5 mL min1 was used, and samples were dissolved in THF (ca. 2 mg mL1). The dn/dc for each sample was determined using the software. Elemental analyses were performed in the UBC-.chemistry Microanalysis Facility. Mass Spectra were recorded on a Kratos MS 50 instrument in El mode (70 eV). 2.4.1 Preparation of MesP=C(Naph)(Ph) (2.1). MesP(SiMe32(8.6 g, 0.029 mol) dissolved in THF (15 mL) was treated with 1-benzoylnaphthalene (6.7 g, 0.029 mol) dissolved in minimal THF and a catalytic amount of KOH (4 mg, 0.07 mmol). The yellow mixture was stirred and the reaction progress was monitored by 31P NMR spectroscopy. After being stirred for 2 weeks at 55 °C, 80% of MesP(SiMe3)2had converted to the desired product (31p = 251, 239; E/Z mixture), and the solvent was removed in vacuo. The crude product was purified by vacuum distillation at 210 °C (0.01 mmHg). Recrystallization of the distillate in hexanes at room temperature afforded yellow crystals suitable for X-ray diffraction. Yield: 2.56 g (25%). 31P NMR (CDC13,162 MHz): 251 (Z-isomer), 239 (E-isomer); 1H NMR (CDC13,400 MHz) (E-isomer): ó 7.9—6.8 (m, 14H, Ar), 2.4 (s, 6H, o-CH3), 2.3 (s, 3H,p-CH);‘3C{1H} NMR (CDcl3, 101 MHz): ö 191.1 (d, ‘Jcp = 44Hz, PC), 143.3 (d, Jcp = 15 Hz), 141.7 (d, Jcp = 27 Hz), 140.5 (d, Jp = 7 Hz), 138.9 (s), 136.7 (d, 1Jcp = 40 Hz, i-Mes), 134.1 (s), 132.0 (d, Jcp 9 Hz), 129.4— 124.8 (m), 22.2 (d, 3Jcp = 9 Hz, o-CI-13), 21.3 (s,p-CH);MS (El, 70eV): m/z [%] References begin on page 59 Chapter Two 55 368,367,366 [2,21,91;Mj;365 [100;M—H];246 [21;M—H—Mes]; 119[8;M—H—Mes — Naph]. 2.4.2 Preparation of MesP=C(C4H3S)(Ph) (2.2). MesP(SiMe3(7.89 g, 0.027 mol), 2- benzoylthiophene (5.01 g, 0.027 mol), and anhydrous KOH (4 mg, 0.07 mmol) were mixed and dissolved in THF (15 mL). The reaction mixture was stirred, and the reaction progress was monitored by 31P NMR spectroscopy. After 5 days, MesPC(C4H3S)( h) was formed quantitatively (&ip = 227, 220; E/Z mixture). The solvent was removed in vacuo, resulting in a dark amber oil. The crude product was purified by vacuum distillation at 195 °C (0.01 mmHg). Yellow crystals suitable for X-ray diffraction were obtained from slow evaporation of a hexanes solution. Yield = 5.19 g (60 %). 31P NMR (CDC13,162 MHz) (E/Zmixture): 227, 220. ‘H NMR (C6D,400 MHz) (E/Z mixture): 7.6—6.4 (m, 1OH, Ar), 2.39, 2.27 (s, 6H, o-CH3), 2.14, 1.94 (s, 3H,p-CH).‘3C{’H} NMR (CDC13, 101 MHz) (E/Zmixture): 184.8 (d, 1Jcp = 40 Hz, P=C), 181.3 (d, Jcp = 45 Hz, PC), 149.5 (d, Jcp 28 Hz), 146.2 (d, Jcp = 20 Hz), 144.4 (d, Jcp 26 Hz), 142.5 (d, Jcp = 13 Hz), 141.2 (d, Jcp = 7 Hz), 140.7 (d, Jcp = 7 Hz), 136.2 (d, ‘Jcp = 46 Hz, i-Mes), 135.5 (d, ‘Jcp 40Hz, i-Mes), 129.4— 127.7 (m), 127.5 (s), 126.6— 126.1 (m), 22.5 (d,3Jcp= 9Hz, o-CH3), 21.9 (d, 3Jcp 8 Hz, o-CH3), 21.4 (s,p-CH3),21.2 (s,p-CH3).MS (El, 70eV): m/z [%] 324, 323, 322 [6, 24, 100; Mj; 321 [15; M— H]; 244 [29; M — H — Ph]; 238 [73; M— H —C4H3S]; 202 [5; M— H — Mes]; 161 [8; M— H — C4H3S— Ph]; 119 [8; M— H — C4H3S — Mes]. 2.4.3 Preparation of MesPC(Phen)(Ph) (2.3). A stirred solution of MesP(SiMe3)2(2.38 g, 8 mmol) in THF was treated with MeLi in Et20 (5.35 mL, 1.5 M, 8 mmol) at 25 °C. After heating References begin on page 59 Chapter Two 56 the reaction mixture at 65 °C for 12 h, analysis of an aliquot removed from the reaction by 31P NMR spectroscopy suggested the complete lithiation of the starting material to MesP(SiMe3)Li (31p = —187). To this reaction mixture was added 9-benzoylphenanthrene (2.27 g, 8 mmol) dissolved in THF at —78 °C. After the reaction mixture was stirred for 10 mm at —78 °C, 31P NMR spectroscopic analysis of an aliquot removed from the reaction mixture suggested quantitative formation of 2.3 (ö3ip = 252, 238; E/Zmixture). The reaction mixture was then treated with Me3SiC1 (1.0 mL, 8 mmol) to quench LiOSiMe3.After the removal of solvent, the crude oil was extracted with hexanes (3 x 40 mL) and filtered through Celite. The solvent was removed in vacuo leaving a red oil. Yellow crystals suitable for X-ray diffraction were obtained from slow evaporation of a hexanes solution. Yield: 0.50 g (15%). 31P NMR (CDC13, 162 MHz): 252 (Z-isomer), 238 (E-isomer); ‘H NMR (C6D,400 MHz) (Z isomer): 8.3 —7.0 (m, 14H, Ar-fl), 6.7—5.8 (br, 2H, Mes-fl), 2.8 — 1.8 (br, 6H, o-CH3), 1.6 (s, 3H,p-CH);‘3C{’H} NMR (CDC13, 101 MHz) (E!Zmixture): 193.7 (d, 1Jcp 44Hz, P=C), 191.0 (d, 1Jcp = 44 Hz, P=C), 144.2 (d, Jp = 24 Hz), 142.7 (d, Jcp = 15 Hz), 140.5 (d, Jcp = 6 Hz), 140.1 (d, Jp = 28 Hz), 138.9 (s), 138.1 (s), 138.0 (s), 136.6 (d, Jcp = 7 Hz), 140.7 (d, Jcp = 7 Hz), 136.6 (d, 1Jcp = 40 Hz, i-Mes), 135.9 (d, 1Jcp = 41 Hz, i-Mes), 131.6 — 122.5 (m), 22.6 (br, o-CH3), 22.6 (d, 3Jcp 9 Hz, o-Cl-13), 21.3 (s,p-CH),21.0 (s,p-CH3).MS (El, 70eV): m/z [%] 418, 417, 416 [3, 29, 98; Mj; 415 [100; M—H]; 296 [29; M— H— Mes]; 220 [5; M— Mes — Phen]; 119 [13; M— H —Mes — Phen]. Anal. Calcd forC30H25P: C, 86.51; H, 6.05. Found: C, 86.15; H, 6.09. 2.4.4 Preparation of [MesP—C(Naph)(Ph)] (2.4). The polymerization of 2.1 was carried out inside a glovebox. To a stirred solution of 2.1 (0.84 g, 2.3 mmol) dissolved in THF (6 mL) was References begin on page 59 Chapter Two 57 added n-BuLi (1.2 M, 38 iL, 0.05 mmol). The reaction mixture was stirred at room temperature and monitored by 31 NMR spectroscopy, which showed an increase in intensity of a broad signal over 2 weeks. Thereafter, the reaction mixture was removed from the glovebox and quenched using methanol (3 drops). After the removal of solvent in vacuo, the polymer was isolated via hexanes precipitation (3 x 100 mL), then dried in a vacuum oven at 65 °C for 24 h. Yield 327 mg (40%). 31P NMR (CDC13,122 MHz): ö —9 (br). ‘H NMR (CDC13,300 MHz): 9 — 5 (br, Ar-H), 3.5 — 0.5 (br, CH3). GPC-LLS (THF): M = 40,100, PDI = 1.42. Anal. Calcd for (C26H3P): C, 85.22; H, 6.33. Found: C, 83.38; H, 6.45. 2.4.5 Attempted preparation of IMesP—C(C4H3S)( h)] . The polymerization of 2.2 was attempted a number of times using different monomer:initiator ratios and different temperatures inside a glovebox. The following procedure describes an attempt using 2 mol% initiator at room temperature: To a stirred solution of 2.2 (0.47 g, 1.5 mmol) dissolved in THF (3 mL) was added n-BuLi (1.2 M, 24.6 L, 0.03 mmol). The reaction mixture was stirred at room temperature and monitored by 3’P NMR spectroscopy for 7 days by removing aliquots from the reaction mixture. The 3’P NMR spectra of the aliquots showed two signals that were assigned to 2.2 (31p = 227, 220); there was no broad signal that would be characteristic of polymer formation. 2.4.6 Preparation of [MesP—C(Phen)(Ph)] (2.5). The polymerization of 2.3 was performed inside a glovebox. A stirred solution of 2.3 (0.39 g, 1.3 mmol) dissolved in THF (3 mL) was treated with n-BuLi (1.2 M, 16 tL, 0.02 mmol). The reaction mixture was stirred at room temperature and monitored by 31P NMR spectroscopy, which showed the gradual increase in intensity of a broad signal over 8 days. The reaction mixture was subsequently removed from References begin on page 59 Chapter Two 58 the glovebox and quenched with methanol (3 drops). The solvent was removed in vacuo, leaving an orange oil. The polymer was isolated by hexanes precipitation (3 x 100 mL), then dried in a vacuum oven at 65 °C for 24 h. Yield = 124 mg (32%). 31P NMR (CDC13,122 MHz): —10 (br). ‘H NMR (CDC13,300 MHz): 9 — 5 (br, Ar), 3.5 — 0.5 (br, CH3). GPC-LLS (THF): M11 = 27,100, PDI 1.39. Anal. Calcd for (C3oH25P): C, 86.51; H, 6.05. Found: C, 85.12; H, 6.06. 2.4.7 X-ray crystallography. All single crystals were immersed in oil and were mounted on a glass fiber. Data were collected on a Bruker X8 APEX II diffractometer with graphite Mo Ka radiation. All structures were solved by direct methods and subsequent Fourier difference techniques and refined anisotropically for all non-hydrogen atoms. All data sets were corrected for Lorentz and polarization effects. 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(11) Yoshifuji, M.; Toyota, K.; Inamoto, N. Tetrahedron Lett. 1985, 26, 1727-1730. (12) Van der Does, T.; Bickelhaupt, F. Phosphorus, Sulfur Silicon Relat. Elem. 1987, 30, 515- 518. (13) Jouaiti, A.; Geoffroy, M.; Bernardinelli, G. Tetrahedron Lett. 1992, 33, 507 1-5074. (14) Jouaiti, A.; Geoffroy, M.; Bernardinelli, G. Tetrahedron Lett. 1993, 34, 3413-3416. (15) Jouaiti, A.; Geoffroy, M.; Bernardinelli, G. Chem. Commun. 1996, 437-438. (16) Kawanami, H.; Toyota, K.; Yoshifuji, M. I Organomet. Chem. 1997, 535, 1-5. (17) lonkin, A. S.; Marshall, W. J. Heteroat. Chem. 2002, 13, 662-666. (18) Termaten, A.; van der Sluis, M.; Bickeihaupt, F. Eur. I. Org. Chem. 2003, 2049-2055. (19) van Staden, L. F.; Gravestock, D.; Ager, D. J. Chem. Soc. Rev. 2002, 3], 195-200. References begin on page 59 Chapter Two 60 (20) Becker, G.; Uhi, W.; Wessely, H. J. Z. Anorg. Aug. Chem. 1981, 479, 4 1-56. (21) Becker, G.; Becker, W.; Mundt, 0. Phosphorus, Sulfur Silicon Relat. Elem. 1983, 14, 267-283. 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(32) Mundt, 0.; Becker, G.; Uhi, W.; Massa, W.; Birkhahn, M. Z. Anorg. Aug. Chem. 1986, 541, 319-335. (33) CRC Handbook of Chemistry and Physics; 84 ed.; CRC Press: Boca Raton, Florida, 2003. References begin on page 59 Chapter Two 61 (34) Regitz, M.; Scherer, 0. J. Multiple Bonds and Low Coordination in Phosphorus Chemistry; Thieme: New York, 1990. (35) Bai, C.; Fu, H.; Zhang, M. Huaxue Tongbao 1983,3, 14-15. (36) Trotter, J. Acta Crystallogr. 1963, 16, 605-609. (37) Gillon, B. H.; Noonan, K. J. T.; Feldscher, B.; Wissenz, J. M.; Kam, Z. M.; Hsieh, T.; Kingsley, J. J.; Bates, J. I.; Gates, D. P. Can. J. Chem. 2007, 85, 1045-1052. (38) Armarego, W. L. F.; Perrin, D. D. Purflcation ofLaboratory Chemicals; 4th ed.; Butterworth Heinemann Press: Oxford, 1998. (39) Burchat, A. F.; Chong, J. M.; Nielsen, N. J Organomet. Chem. 1997, 542, 28 1-283. (40) SHELXTL Version 5.1. Bruker AXS Inc., Madison, Wisconsin, USA, 1997. References begin on page 59 62 Chapter Three Chemical Modification of Poly(methylenephosphine)s with Conjugated Substituents Accompanied by Changes in Electronic Properties* 3.1 Introduction As discussed in Chapter 2, new poly(methylenephosphine)s bearing naphthyl and phenanthrenyl substituents were successfully prepared by anionic polymerization of phosphaalkenes. The chemical equation for the reaction is shown in Scheme 3.1. 2 mol% n-BuLl F 1 - P=c n-Bu-f---P—C----I-H Mes = Met Ph THF, RT [MS Phj - mesityl 3.la R = Naph 3.2a R = Naph 3.lb R = Phen 3.2b A = Phen Naph= — — 1 -naphthyl Phen = 9-phenanthrenyl Scheme 3.1 Due to the Lewis basicity and unique reactivity of phosphorus (III) (e.g. oxidation and coordination),”2the chemical modification of the phosphine centres in [MesP—C(Naph)(Ph)J (3.2a) and [MesP—C(Phen)(Ph)] (3.2b) should be feasible. In this sense, the phosphorus atoms may act as receptor sites for analytes, possibly leading to a change in the electronic structure to give a sensor-like behavior. Following the preparation of macromolecules 3.2a and 3.2b, the *A version of this chapter will be submitted for publication. Chun, C. P. and Gates, D. P. Chemical Modification of Poly(methylenephosphine)s Bearing Conjugated Substituents Accompanied By Changes in Electronic Properties. Chapter Three 63 next goal was to chemically modify the polymers and examine the concomitant changes in the electronic properties. Based on literature precedent,3’4we expect that the presence of the phosphorus lone pair in 3.2a and 3.2b would lead to a fluorescence quenching effect on the polymer, resulting in weaker fluorescence intensity or no fluorescence at all. The lone pair on phosphaalkenes, 3.la and 3.lb, is expected to invoke a similar quenching effect. We hypothesize that coordination of the phosphorus lone pairs in poly(methylenephosphine)s 3.2a and 3.2b to an electrophilic analyte (E) will eliminate the quenching effect and allow fluorescence to occur (Scheme 3.2). nBuf_H E nBuf_H Mes Ph MesPh Weak fluorescence or Coordination of lone pair no fluorescence due to to E allows fluorescence lone pair quenching effect to occur Scheme 3.2 This chapter describes experiments undertaken to test the hypothesis that chemical functionalization of phosphine polymers 3.2a and 3.2b would lead to fluorescence. More specifically, this discussion entails the post-polymerization functionalization of 3.2a and 3.2b via oxidation and coordination to borane moieties. In addition, this chapter includes preliminary results from the investigation of the electronic properties of phosphaalkenes 3.1 a and 3. ib, poly(methlyenephosphine)s 3.2a and 3.2b, and the new chemically functionalized polymers. References begin on page 84 Chapter Three 64 3.2 Results and Discussion 3.2.1 Oxidation of 3.2a and 3.2b Previous work in the Gates lab showed that [MesP—CPh2]1can be easily oxidized using 11202 or by exposing a solution of the polymer to air for four days.5 In this thesis work, the oxidation of poly(methylenephosphine)s 3.2a and 3.2b was investigated. According to 31P NMR spectroscopic analysis, a solution of naphthyl-derivatized polymer 3.2a did not show any evidence of oxidation after being exposed to air for one week, suggesting that 3.2a was quite air stable. Nonetheless, the oxidation of 3.2a was achieved by treating a CH21 solution of 3.2a with aqueous 30% H20 (Scheme 3.3). The oxidation progress was monitored by 31P NMR spectroscopy. The complete oxidation of 3.2a required an excess ofH20 (2.6 equiv) and the reaction mixture was stirred overnight. The 31P NMR spectrum of the oxidized polymer [MesP(0)—C(Naph)(Ph)] (3.3a) is shown in Figure 3.1, and for comparison the 31P NMR spectrum of 3.2a is also included. The 31P chemical shift of 3.3a (47 ppm) is the same as that of [MesP(0)—CPh2].5 F Naphi F 0 Naphi n-Bu-I—P—C—j-H 30% H20 (aq.) LMes Ph CH2CI2 [MS Ph 3.2a 3.3a Scheme 3.3 References begin on page 84 Chapter Three 65 E Naph n-Bu fe—c —FH -9 ppm [Mes PhJ (a)4/ E ONaPh] -Bu ----P — C —t H 47 ppm [Mes Ph (b’ ppm 150 100 50 0 -50 -100 -150 Figure 3.1. 31P NMR spectra (THF, 122 MHz) of(a) 3.2a and (b) 3.3a. In contrast to the naphthyl-derivatized phosphine polymer 3.2a, the phenanthrenyl derivatized poly(methylenephosphine) 3.2b oxidizes more readily in air when dissolved in THF (Scheme 3.4). After 3 hours of exposure to air, the 31P NMR spectrum of a THF solution of 3.2b showed the appearance of a new broad signal at 49 ppm (Figure 3 .2b). The broad resonance at 10 ppm is assigned to unoxidized phosphorus centres in the polymer, which is consistent with the 31P NMR chemical shift of 3.2b (Figure 3.2a). After 1 week, 3.2b was completely oxidized to give [MesP(O)—C(Phen)(Ph)] (3.3b) (&lp = 49) (Figure 3.2c). r Pheni r Pheni n-Bu-l---P—C—j-H air n-Bu-l——C--4H [MS Ph j THE [MS Ph 1 week 3.2b 3.3b Scheme 3.4 Oxidized polymers 3.3a and 3.3b were isolated as white solids after the removal of solvent in vacuo. Analysis of 3.3a and 3.3b by triple detection gel permeation chromatography (GPC) showed that 3.3a exhibited an absolute number average molecular weight (Ma) of 43,500 References begin on page 84 Chapter Three 66 (a) 10 ppm F Pheni n-Bu -f-- P — C —f H [Mes Ph 49ppm lOppm F 0 Pheni n-Bu-j—-P—C—-I-H 49 ppm [Mes Phi (C)4 ppm io 100 50 -50 -100 -150 Figure 3.2. 31P NMR spectra (THF, 122 MHz) of(a) 3.2b; (b) an aliquot from the THF solution of 3.2b exposed to air for 3 h; (c) an aliquot from the same solution exposed to air for 7 d to form 3.3b. g mol’ and 3.3b exhibited an M value of 31,300 g mof’. Both oxidized macromolecules have slightly higher M values than their parent unoxidized polymers (3.2a: M = 42,160 g mol’; 3.2b: M = 27,000 g moij, which is expected. According to the GPC analysis, the polydispersity index (PDI) of 3.3a is 1.16, while that of 3.3b is 1.46. Oddly, the two oxidized macromolecules 3.3a and 3.3b have narrower PDI values than their parent unoxidized polymers (3.2a: PDI = 1.40; 3.2b: PDI 1.49). This may be due to interaction of the phosphine moieties in the unfunctionalized poly(methylenephosphine)s with the GPC columns, which has been reported for phosphine polymers in the past.6’7For example, the PDI of [MesP(BH3)—CPh2](M = 4.13 x i0 g moF1)was reported to be 1.26, slightly lower than that of the parent unfunctionalized [MesP—CPh2](M = 3.89 x i04 g mol’; PDI = 1.34). 3.2b References begin on page 84 Chapter Three 67 3.2.2 Boronation of 3.2a and 3.2b Chemical functionalization of poly(methylenephosphine)s 3.2a and 3.2b can also be accomplished by using BH3 moieties to form phosphine-borane adducts along the main chain. This was achieved by treating the polymers dissolved in THF with BHySMe2(1.3 equiv) at —78 °C, then allowing the reaction mixtures to warm slowly to room temperature. Reaction progress was monitored by 31P NMR spectroscopy, which suggested that the phosphine moieties in 3.2a and 3.2b were only partially complexed with borane moieties after the first addition of BH3SMe2(1.3 equiv). Hence, additional BH3SMe2(1.3 equiv) was added to each reaction mixture at —78 °C. 31P NMR spectroscopic analysis suggested that 70% of the phosphorus atoms in naphthyl-derivatized polymer 3.2a were functionalized with borane moieties, giving a partially functionalized phosphine-borane polymer (3.4a) (Scheme 3.5). On the other hand, 31P NMR analysis revealed that 3.2b was completely functionalized to give [MesP(BH3)— C(Phen)(Ph)] (3.4b) (Scheme 3.6). Surprisingly, it appears that phenanthrenyl-derivatized poly(methylenephosphine) 3.2b is more reactive than naphthyl-derivatized polymer 3.2a. This may be due to an effect whereby the phenanthrenyl side groups are oriented in such a way that allows easier access to the phosphorus centres and the naphthyl substituents are oriented in such a way that hinders access. F Naphi [7 BHNaph\ /7 Naph\ n-Bu--I—P—C-4H BH3’SMe2(excess), —78 C n-Bu-I-(—P-——C /-(—-—c H LMes Ph warm slowly to RT, 12 h [\Ms PhJ07/ \Mes Ph103 3.2a 3.4a Scheme 3.5 F Pheni F BH3Phenl n-Buf_9_-[H BH3SMe2(excess), 7800 n-Bu-—P-—C-----H LMes Ph j THE [Mes Ph] warmslowlytoRT, 12h 3.2b 3.4b Scheme 3.6 References begin on page 84 Chapter Three 68 Figures 3.3 and 3.4 show 31P NMR spectra of new borane-phosphine adduct polymers 3.4a and 3.4b, and for comparison, 31P NMR spectra of the unfunctionalized macromolecules are also included. The 31P chemical shift of 3.4b (31p = 28) and the downfield 31P chemical shift of 3.4a (31p = 27) are similar to the 31P chemical shift of [MesP(BH3)—CPh1(31p = 26.8). E Naph n-Bu -I— p — C—i-H -9 ppm [MS Phi (a) [4 BHNaph\ /1/f Naph\\ 27 ppm nBu.f[Iç_f__9 ) /19 ) H (b) 0.3n n ppm 150 100 50 0 -50 -100 -150 Figure 3.3. 31P NMR spectra (THF, 122 MHz) of(a) 3.2a and (b) 3.4a. 10 ppm (a) E BH3Phenf n-B u-f—P-—c —f-H [Mes Ph] (b) ppm’ 100 ‘ so ‘ -so ‘ -100 Figure 3.4. 31P NMR spectra (THF, 122 MHz) of(a) 3.2b and (b) 3.4b. E Phen n-Bu -f—P—C—-f-H [Mes Ph 3.2b 3.4 b -150 References begin on page 84 Chapter Three 69 Boronated polymers 3.4a and 3.4b were isolated as off-white solids after removal of solvent in vacuo, and were analyzed by triple detection GPC. According to the analysis, the M11 values of 3.4a and 3.4b were 24,700 g mol’ and 27,900 g mol’, respectively. These values are slightly higher than the M values of their parent unfunctionalized polymers (3.2a: M = 22,900 g mol’; 3.2b: M = 27,000 g mol’). Similar to the case observed for the oxidized polymers, the PDI values of 3.4a (PDI 1.33) and 3.4b (PDI = 1.32) are lower than the PDI values of their parent poly(methylenephosphine) (3.2a: PDI = 1.39; 3.2b: PDI = 1.49). This effect may be attributed to interaction of the phosphine moieties in 3.2a and 3.2b with the GPC columns, as discussed previously. 3.2.3 UV/Vis and Fluorescence Measurements of 3.la — 3.4a The UV/Vis spectra of the naphthyl-derivatized phosphaalkene 3.la, the unfunctionalized naphthyl-derivatized poly(methylenephosphine) 3.2a, and the functionalized naphthyl derivatized polymers 3.3a and 3.4a are shown in Figure 3.5. THF was used as a solvent for all absorption spectra. A summary of the absorption bands and their assignments is tabulated in Table 3.1. Table 3.1. Summary of UV/Vis absorption bands and assignments of 3.la — 3.4a. ?max (nm) (M’cm’) assignment 3.la 296 1.6x 10 tit*(Naph) 316 (shoulder) 1.5 x 1 0 — * (P=C) 3.2a 290 1.5x 10 rt_t*(Naph) 3.3a 272 4.4 x i03 — 3t* (Naph) 288 7.6x 10 3.4a 288 1.Ox 10 3t_n*(Naph) References begin on page 84 Chapter Three 70 0 300 350 400 450 Wavelength (nm) Figure 3.5. UV/Vis spectra (THF) of 3.la (3.1 x 105M), 3.2a (3.1 x 105M), 3.3a (4.3 x 105M), and 3.4a (4.2 x i0 M). A common absorption band shared by the naphthyl-derivatized monomer and polymers 3.la — 3.4a occurs around 290 nm. Since these absorption bands around 290 nm nearly align with the band assigned to one of the 2t — 3t* transitions of naphthalene (?max = 286 nm),8 these absorptions around 290 nm are assigned to it — transitions of the naphthyl substituent. References begin on page 84 Chapter Three 71 Naphthalene exhibits three absorptions in the UV region assigned to t — transitions which include transitions that are symmetry-allowed and spin-forbidden but occur due to vibronic coupling.9The oxidized polymer, 3.3a, shows an additional shoulder at 272 nm. Since the wavelength of this absorption is very similar to another band of naphthalene assigned to a n — transition Qrnax = 276 nm),8 the shoulder is assigned to a t — it transition of the naphthyl substituent. A shoulder is also observed in the spectrum of phosphaalkene monomer 3.la at 316 nm. This shoulder is assigned to the n — transition of the P=C bond, and is similar to that observed for MesP=CPh2(?max = 324 nm).’° After obtaining the ?max values of 3.la — 3.4a by UV/Vis spectroscopy, the emissive properties of 3.la — 3.4a were examined. Dilute solutions of 3.la — 3.4a in THF (ca. i0 M) were excited at their 2’max values. The wavelength and intensity of their emissions were recorded and these spectra are displayed in Figure 3.6. As illustrated in the spectra, naphthyl-derivatized phosphaalkene 3.1 a and unfunctionalized poly(methylenephosphine) 3.2a showed no fluorescence when excited at 296 nm and 290 nm, respectively. However, oxidized polymer 3.3a and boronated polymer 3.4a were fluorescent when irradiated at 288 nm. The wavelengths of their emission bands were 329 nm and 312 nm, respectively, both in the UV region. A summary of these fluorescence measurements is presented in Table 3.2, including the values of the Stokes shifts. The Stokes shifts exhibited by 3.3a and 3.4a are 41 nm and 24 nm, respectively. The small Stokes shift exhibited by 3.4a, in comparison to the range of Stokes shifts reported in the literature, can be a sign of rigidity in the main chain. References begin on page 84 Chapter Three 72 z C 0 U) U) E UI 300 450 Wavelength (nm) Figure 3.6. Emission spectra (THF) of 3.la (3.1 x i0M), 3.2a (3.1 x 105M), 3.3a (4.3 x i0 M), and 3.4a (4.2 x i0 M). Table 3.2. Summary of emission measurements on 3.la — 3.4a. ?ex (iuti) ?em (nm) Stokes shift (nm) 3.la 296 none — 3.2a 290 none — 3.3a 288 329 41 3.4a 288 312 24 We have shown that the complexation of the phosphorus lone pairs in non-emissive poly(methylenephosphine) 3.2a resulted in fluorescence in the UV region. The lack of fluorescence in the 3.2a is consistent with our expectation that the unfunctionalized phosphine polymer would be non-emissive or weakly emissive, as discussed in the introduction of this chapter. The fact that 3.2a is non-emissive is likely due to a quenching effect from the lone pair electrons on phosphorus, while coordination of these lone pair electrons leads to emission. A possible mechanism to account for these observations is the photoinduced electron transport 350 400 References begin on page 84 Chapter Three 73 process, a mechanism that is commonly reported for “turn-on” chemosensors.’126In this process, there exists a relatively high-energy nonbonding electron pair that quenches the fluorescence of the fluorophore in the absence of an analyte (Figure 37) 11,21,24,25 The quenching occurs by a rapid intramolecular electron transfer from the lone pair orbital to the HOMO of the fluorophore. However, coordination of the electron pair to another functionality lowers the energy of the lone pair, thus allowing fluorescence to occur from the excited fluorophore. Figure 3.7 shows a simplified depiction of the electronic processes involved in relaxation to ground state. In addition to fluorescence, relaxation to the ground state also includes internal conversion and vibrational relaxation. In the absence of analyte: Upon coordination of lone pair to another functionality: F F LUMO LUMO HOMO 1 HOMO 1 ‘pI Fluorophore Nonbonding Fluorophore Coordinated Lone Pair Lone Pair Non-emissive or Fluorescent weakly fluorescent Figure 3.7. Orbital energy diagram illustrating the process of the photoinduced electron transport mechanism and the resulting effect on fluorescence of a fluorophore.”21’45This orbital diagram carries a simplified depiction of the electronic processes involved in the relaxation to the ground state. In reality, relaxation includes internal conversion, vibrational relaxation, and fluorescence. References begin on page 84 Chapter Three 74 3.2.4 UVIVis and Fluorescence Measurements of 3.lb — 3.4b The UV/Vis spectra of the phenanthrenyl-derivatized phosphaalkene monomer and polymers, 3.lb — 3.4b, dissolved in THF, are shown in Figure 3.8. A summary of the absorption bands and their assignments is presented in Table 3.3. U C 0 .0 Wavelength (nm) Figure 3.8. UV/Vis spectra (THF) of 3.lb (3.8 x 105M), 3.2b (3.3 x 105M), 3.3b (3.7 x l0 M), and 3.4b (3.0 x 105M). References begin on page 84 Chapter Three 75 Table 3.3. Summary of UV/Vis absorption bands and assignments of 3.lb — 3.4b. 2max (nm) (M’cm’) assignment 3.lb 252 (strong) 5.9 x i04 — u’ (Phen) 300 (weak) 2.3 x i04 — * (Phen and P=C) 3.2b 254 (strong) 4.4 x i0 — t (Phen) 301 (weak) 9.5 x — it (Phen) 3.3b 256 (strong) 3.7 x i0 — (Phen) 301 (weak) 8.0 x — rt (Phen) 3.4b 254 (strong) 2.4 x — rt (Phen) 288 (weak) 5.5 x iü t—t (Phen) 301 (weak) 5.1 x 1 ü — * (Phen) The strong absorption bands that are observed in the spectra of the phenanthrenyl derivatized monomer and polymers, 3.lb — 3.4b, near 250 nm are assigned to rt — 3t* transitions of the phenanthrenyl moieties because the wavelength and strength of these bands are very similar to the t — transition of phenanthrene at 252 nm.8’27 Like naphthalene, phenanthrene exhibits a number of ‘r — n’ transitions in the UV region, some of which are symmetry-allowed and some of which are spin-forbidden but made possible due to vibronic coupling.9The UV/Vis spectra of 3.lb — 3.4b also show weak absorption bands around 300 nm. These bands are also assigned to 3t — it transitions of the phenanthrenyl substitent, and are similar to the weak band observed in the UV/Vis spectrum of phenanthrene (?qnax = 293 nm).8’27 The UV/Vis spectrum of boronated phenanthrenyl-derivatized polymer 3.4b exhibits an additional band at 288 nm that is similar to a side band observed in the UVIVis spectrum of phenanthrene (?‘max = 283 nm). Hence the band at 288 nm is tentatively assigned to a t — it’ transition of the phenanthrenyl moiety. Unlike the UV/Vis spectrum of naphthyl-derivatized phosphaalkene 3.la, the UV/Vis spectrum of phenanthrenyl-derivatized phosphaalkene 3.lb does not show a separate shoulder attributed to the t — it transition of the PC bond. This transition may be completely obscured by the bands already present in the spectrum. On the other hand, its absence may suggest that the References begin on page 84 Chapter Three 76 PC bond is more delocalized with the aromatic C-substituents in phenanthrenyl-derivatized phosphaalkene 3.lb than in naphthyl-derivatized phosphaalkene 3.la. Support for the latter can be obtained by comparing the angles between the best planes of the aromatic C-substituents and the P=C bond (discussed in section 2.2.4, Chapter 2). The molecular structure of 3.la shows that the phenyl and naphthyl rings are twisted out of the plane of the P=C bond by 400 and 60°, respectively. The molecular structure of 3.lb shows that the phenanthrenyl ring is twisted out of plane of the P=C bond by 60°, but the phenyl ring is twisted only by 20°. These data suggest that there is a greater degree oft-conjugation present in 3.lb than 3.la, at least in the solid state. Following the UV/Vis measurements discussed above, the emissive properties of phenanthrenyl-derivatized monomer and polymers 3.lb — 3.4b were investigated. Dilute solutions of 3.lb — 3.4b in THF (ca. i0 M) were excited at the wavelengths of their values. Maximum emission was observed when 3.lb was excited at 300 nni, and when 3.2b — 3.4b were excited at 301 mm The emission spectra of 3.lb — 3.4b are presented in Figure 3.9 and a summary of the data is tabulated in Table 3.4. C 0 E Ui 325 350 375 400 425 450 Wavelength (nm) Figure 3.9. Emission spectra (THF) of 3.lb (3.8 x 103M), 3.2b (3.3 x 105M), 3.3b (3.7 x i0 M), and 3.4b (3.0 x i0 M). References begin on page 84 Chapter Three 77 Table 3.4. Summary of emission measurements on 3.lb — 3.4b. ex (nm) ?ern (nm) Stokes shift (nm) 3.lb 300 367 67 3.2b 301 357 56 374 73 3.3b 301 367 66 3.4b 301 367 66 In contrast to naphthyl-derivatized phosphaalkene 3.la and poly(methylenephosphine) 3.2a which are non-emissive, the spectra of 3.lb and 3.2b show that the phenanthrenyl derivatized phosphaalkene and poly(methylenephosphine) are emissive. The difference in emissive properties between the analogous species is probably due to the extra conjugation in the phenanthrenyl substituent. As shown in Figure 3.9, phenanthrenyl-derivatized phosphaalkene 3.lb, oxidized polymer 3.3b, and boronated polymer 3.4b exhibit maximum emission at 367 nm, which is the same wavelength reported for the maximum emission of phenanthrene (em = 367 )27 Phenanthrene also exhibits emission bands of lower intensity at 345 nm and 385 nm, and interestingly, the emission spectrum of phenanthrenyl-derivatized poly(methylenephosphine) 3.2b shows two bands at 357 nm and 374 nm, close to those of phenanthrene. The Stokes shifts exhibited by 3.lb — 3.4b range between 56 nm and 73 nm (Table 3.4) and are within normal range compared to Stokes shifts reported in the literature. Comparison between the spectra in Figure 3.9 shows that the fluorescence intensities of phosphaalkene monomer 3.lb and unfunctionalized poly(methylenephosphine) 3.2b are weaker than the fluorescence intensities of the functionalized polymers 3.3b and 3.4b. This observation is consistent with our hypothesis that the phosphalkenes and unfunctionalized poly(methylenephosphine)s would be non-emissive or weakly emissive while the functionalized References begin on page 84 Chapter Three 78 polymers would be more emissive. The weaker fluorescence intensities of phosphaalkene monomer 3.lb and unfunctionalized poly(methylenephosphine) 3.2b are most likely due to a quenching effect from the phosphorus lone pairs. Due to the structural similarity between naphthyl-derivatized polymers 3.2a — 3.4a and phenanthrenyl-derivatized polymers 3.2b — 3.4b, the photoinduced electron transport 1212425 (discussed in the section 3.2.3) can again be invoked to account for the emissive behaviors of 3.2b — 3.4b. To confirm the relative strengths of the fluorescence emissions, the quantum yields of 3.lb — 3.4b must be determined. This is considered as future work. 3.3 Summary Poly(methylenephosphine)s 3.2a and 3.2b were chemically functionalized by oxidation and boronation of the phosphorus centres to afford oxidized macromolecules 3.3a and 3.3b, and boronated polymers 3.4a and 3.4b, respectively. The electronic properties of the unfunctionalized and functionalized polymers, as well as those of phosphaalkenes 3.la and 3db, were investigated by UV/Vis and fluorescence spectroscopy. For the naphthyl-derivatized species, the results showed that phosphaalkene 3.la and unfunctionalized poly(methylenephosphine) 3.2a were non-emissive while oxidized polymer 3.3a and boronated polymer 3.4a exhibited emissions in the UV region when irradiated at 288 rim. Similarly, for the phenanthrenyl-derivatized species, the emission intensities of phosphaalkene 3. lb and unfunctionalized poly(methylenephosphine) 3.2b were observed to be lower than those of oxidized polymer 3.3b and boronated polymer 3.4b. These results are consistent with our hypothesis that the chemical functionalization of the phosphorus lone pair in naphthyl-derivatized poly(methylenephosphine) 3.2a and phenanthrenyl References begin on page 84 Chapter Three 79 derivatized poly(methylenephosphine) 3.2b would prevent quenching of the fluorophore by the lone pair electrons and therefore allow fluorescence to occur. However, further studies are required using other phosphine polymers and different chemical modifications, in addition to measurements of quantum yields, to further generalize and test the hypothesis. Based on the preliminary results presented in this chapter, 3.2a appears to be a better candidate as a sensor than 3.2b because 3.2a is non-emissive whereas 3.2b demonstrates an emissive behavior. It is only upon complexation of the phosphorus lone pairs in 3.2a that fluorescence occurs from this polymer. Consequently, using non-emissive 3.2a instead of 3.2b as a sensor should give a lower probability of false positive results. 3.4 Experimental section General procedures. All manipulations of air and/or water sensitive compounds were performed under a nitrogen atmosphere using standard Schlenk techniques or in a glovebox. Dichloromethane was deoxygenated with nitrogen and dried by passing through a column containing activated alumina. THF was freshly distilled from sodium/benzophenone ketyl. CDC13 was dried over molecular sieves prior to use. H20 and BH3SMe2were purchased from Aldrich and used as received. Equipment. ‘H, 31P, and‘3C{’H} NMR spectra were recorded at room temperature on Bruker Avance 300 MHz or 400 MHz spectrometers. Chemical shifts are reported relative to: residual CHC13(ô= 7.26 for ‘H); 85%H3PO4asan external standard (5= 0.0 for 3’P); CDCI3(5= 77.16 for‘3C{’H}). Molecular weights were estimated by triple detection gel permeation chromatography (GPC-LLS) using a Waters liquid chromatograph equipped with a Waters 515 HPLC pump, Waters 717 plus autosampler, Waters Styragel columns (4.6 x 300 mm) HR2, References begin on page 84 Chapter Three 80 HR4, and HR5E, and a Waters 2410 differential refractometer (refractive index detector ?. = 940 nm), Wyatt tristar miniDAWN (laser light scattering detector operating at ? = 690 nm) and a Wyatt ViscoStar viscometer. A flow rate of 0.5 mL min’ was used, and samples were dissolved in THF (Ca. 2 mg mL’). The dn/dc for each sample was determined using the software. Solution absorption spectra were obtained in THF on a Varian Cary 5000 UV-vis-near-IR spectrophotometer using a 1 cm quartz cuvette. Fluorescence spectra were obtained in THF on a Photon Technology International QuantaMaster fluorimeter using a 1 cm quartz cuvette. 3.4.1 Characterization of MesP=C(Naph)(Ph) (3.la) Experimental procedures, yield, and spectroscopic data were reported in Chapter Two (Section 2.4.1, Page 54). UV/Vis (THF): Xmax/nm (E/M’ cm’) 296 (1.6 x 10), 216 (1.5 x 10k). 3.4.2 Characterization of MesP=C(Phen)(Ph) (3.lb) Experimental procedures, yield, and spectroscopic data were reported in Chapter Two (Section 2.4.3, Page 55). UV/Vis (THF): ?max/nm (E/M’ cm’) = 252 (5.9 x 10), 300 (2.3 x 10). 3.4.3 Characterization of [MesP—C(Naph)(Ph)] (3.2a) Experimental procedures, yield, spectroscopic data, and GPC data were reported in Chapter Two (Section 2.4.4, Page 56). UV/Vis (THF): Xmax/nm (E/M’ cm’) = 290 (1.5 x 10). 3.4.4 Characterization of jMesP—C(Phen)(Ph)] (3.2b) Experimental procedures, yield, spectroscopic data, and GPC data were reported in Chapter Two (Section 2.4.5, Page 57). UV/Vis (THF): ?‘max/nm (E/M’ cm’) = 254 (4.4 x 10), 301 (9.5 x 10). References begin on page 84 Chapter Three 81 3.4.5 Preparation of [MesP(O)—C(Naph)(Ph)]11(3.3a) To a solution of polymer 3.2a (0.075g, 0.20 mmol, M = 42,160 g moF’) in CH2I (5 mL) was added 30% H20 in water (1.5 mL). The reaction mixture was stirred vigorously for 3 h. NMR spectroscopic analysis of an aliquot of the reaction mixture showed a partially oxidized polymer (&ip = 47, 40%; &,p = —9, 60%). The reaction mixture was treated with another 1.5 mL of 30% H20in water. The reaction mixture was stirred overnight. Analysis of the reaction mixture by 31P NMR spectroscopy suggested complete oxidation of the polymer (31p = 47). The layers were separated and aqueous layer was extracted with CH21 (2 x 3 mL). The organic layers were combined and washed with H20 (3 x 5 mL). The organic layer was dried over MgSO4.After evaporation of the solvent in vacuo, a white solid was obtained then dried in a vacuum oven at 65 °C. Yield = 24 mg (3 2%). 31P NMR (CDCI3, 162 MHz): 47 (br); ‘H NMR (CDCI3,400 MHz): 9.0—5.0 (br, Ar-H), 3.3— 0.5 (br, —CH3);‘3C NMR (CDC13, 101 MHz): 148—123 (br, Ar-C), 30—17 (br, CH3), GPC-LLS (THF): M = 43,500 g mol1,PDI = 1.16. UV/Vis (THF): ?‘max/nm (E/M’ cm’) = 272 (4.4 x 10), 288 (7.6 x 10). 3.4.6 Preparation of [MesP(O)—C(Phen)(Ph)] (3.3b) A THF (2 mL) solution of 3.2b (0.05 g, 0.12 mmol, M = 27,000 g mol’) was left in air for oxidation of the phosphorus atoms. The oxidation progress was monitored by 31P NMR spectroscopy, and THF was added when there was significant solvent evaporation. After 1 week, a 31P NMR spectrum of the solution showed a broad signal at 49 ppm. The solvent was allowed to evaporate in air. An off-white solid remained and was dried in a vacuum oven at 65 °C for 12 hours. Yield = 0.04 g (82 %). References begin on page 84 Chapter Three 82 31P NMR (CDCI3, 162 MHz): 49 (br); ‘H NMR (CDC13,400 MHz): 8.5—65 (br, Ar-H), 3.0— 1.5 (br, CH3); GPC-LLS (THF): M 31,300 g mo[’, PDI = 1.46. UV/Vis (THF): max/nm (E/M cm’) = 256 (3.7 x 10), 301 (8.0 x 10). 3.4.7 Preparation of jMesP(BH3)—C(Naph)(Ph)] (3.4a) To a THF solution of 3.2a (0.30 g, 0.82 mmol, M = 22,900 g mol’) was added BHySMe2(0.55 mL, 2 M, 1.17 mmol) at — 78 °C. The reaction mixture was allowed to warm slowly to room temperature. 31P NMR spectrum of the reaction mixture showed the presence of a new broad signal (&Ip = 27, 50%) in addition to the broad chemical shift of the starting material (b3lp= — 9, 50%). The reaction mixture was treated with more BH3SMe2(0.55 mL, 2 M, 1.17 mmol) at — 78°C and allowed to warm slowly to room temperature and stir overnight. After removal of solvent in vacuo, a white solid was obtained. Yield 0.26 g (83%). 31P NMR (CDCI3, 162 MHz): 27 (br), -9 (br); 1H NMR (CDCL3,400 MHz): ó 9.0—6.0 (br, Ar if), 3.0—0.5 (br, CH3,BH3); ‘3C NMR (CDC13, 101 MHz): 137—122 (br, Ar-C), 28—18 (br, CH3), GPC-LLS (THF): M = 24,700 g mol’, PDI = 1.33. UV/Vis (THF): ?max/nm (E/M’ cm1) =288 (1.Ox 10). 3.4.8 Preparation of [MesP(BH3)—C(Phen)(Ph)] (3.4b) A THF solution of 3.2b (0.04 g, 0.09 mmol, M = 27,000 g mo[’) was treated with BH3SMe2(0.06 mL, 2 M, 0.12 mmol) at — 78 °C. The reaction mixture was allowed to warm slowly to room temperature. An aliquot was removed from the reaction mixture and analyzed by 31P NMR spectroscopy. The spectrum showed the presence of a new broad signal (&ip = 28) in addition to the broad chemical shift of the starting material (ö3ip= —10). The reaction mixture was treated with more BH3SMe2(0.06 mL, 2 M, 0.12 References begin on page 84 Chapter Three 83 mmol) at — 78 °C and was allowed to warm slowly to room temperature and stir overnight. After removal of solvent in vacuo, a white solid was obtained. Yield = 0.03 g (78 %). 31p NMR (CDC13, 122 MHz): S 28 (br); ‘H NMR (CDCI3,400 MHz): 9.0—6.5 (br, Ar-H), 3.0— 1.0 (br, CH3 BH3); GPC-LLS (THF): M = 27,900 g mol’, PDI = 1.32. UV/Vis (THF): ?max/nm (E/M’ cm’) = 254 (2.4 x l0), 288 (5.5 x 10), 301 (5.1 x 10). 3.4.9 General procedure for preparing solution samples for UV/Vis and fluorescence measurements Solution samples were prepared inside a glovebox, except for 3.3a, 3.3b, 3.4a, and 3.4b. The procedure for preparing a solution sample of 3.la is described in the following as an example: THF was added to 3.la (7 mg, 0.02 mmol) in a 25.0 mL volumetric flask and diluted to the mark. The volumetric flask was inverted 20 times to ensure proper mixing. Using a volumetric pipette, 1.00 mL of this solution was transferred to another 25.0 mL volumetric flask, and THF was added to dilute to the mark. Again the volumetric flask was inverted 20 times before transferring a small amount of the solution to a 1 cm quartz cuvette. References begin on page 84 Chapter Three 84 3.5 References (1) Mathey, F.; Nixon, J. F.; Dillon, K. B. Phosphorus: The Carbon Copy; Wiley-VCH: Weinheim, 1997. (2) Mathey, F. Phosphorus-Carbon Heterocyclic Chemistry. The Rise ofa New Domain; Elsevier Science: Oxford, 2001. (3) Smith, R. C.; Protasiewicz, J. D. J. Am. Chem. Soc. 2004, 126, 2268-2269. (4) Wright, V. A.; Patrick, B. 0.; Schneider, C.; Gates, D. P. J Am. Chem. Soc. 2006, 128, 8836-8844. (5) Tsang, C. W.; Yam, M.; Gates, D. P. J Am. Chem. Soc. 2003, 125, 1480-1481. (6) Honeyman, C. H.; Foucher, D. A.; Dahmen, F. Y.; Rulkens, R.; Lough, A. J.; Manners, I. Organometallics 1995, 14, 5503-55 12. (7) Noonan, K. J. T.; Feldscher, B.; Bates, J. I.; Kingsley, J. J.; Yam, M.; Gates, D. P. Dalton Trans. 2008, 445 1-4457. (8) Friedel, R. A.; Orchin, M. Ultraviolet Spectra ofAromatic Compounds; John Wiley and Sons, mc: New York, 1951. (9) Sathyanarayana, D. N. Electronic Absorption Spectroscopy and Related Techniques; University Press: India, 2001. Page 363. (10) Kiebach, T. C.; Lourens, R.; Bickeihaupt, F. J Am. Chem. Soc. 1978, 100, 4886-4888. (11) Bissell, R. A.; Desilva, A. P.; Gunaratne, H. Q. N.; Lynch, P. L. M.; Maguire, G. E. M.; McCoy, C. P.; Sandanayake, K. Top. Curr. Chem. 1993, 168, 223-264. (12) James, T. D.; Sandanayake, K.; Iguchi, R.; Shinkai, S. J Am. Chem. Soc. 1995, 117, 8982-8987. References begin on page 84 Chapter Three 85 (13) Kijima, H.; Takeuchi, M.; Robertson, A.; Shinkai, S.; Cooper, C.; James, T. D. Chem. Commun. 1999, 2011-2012. (14) McQuade, D. T.; Hegedus, A. H.; Swager, T. M. J Am. Chem. Soc. 2000, 122, 12389- 12390. (15) Gunnlaugsson, T.; Davis, A. P.; Glynn, M. Chem. Commun. 2001, 2556-2557. (16) Gunnlaugsson, T.; Bichell, B.; Nolan, C. Tetrahedron Lett. 2002, 43, 4989-4992. (17) Gunnlaugsson, T.; Lee, T. C.; Parkesh, R. Org. Biomol. Chem. 2003, 1, 3265-3267. (18) He, H. R.; Mortellaro, M. A.; Leiner, M. J. P.; Young, S. T.; Fraatz, R. J.; Tusa, J. K. Anal. Chem. 2003, 75, 549-555. (19) Nolan, E. M.; Lippard, S. J. J Am. Chem. Soc. 2003, 125, 14270-14271. (20) Gunnlaugsson, T.; Au, H. D. P.; Glynn, M.; Kruger, P. E.; Hussey, G. M.; Pfeffer, F. M.; dos Santos, C. M. G.; Tierney, J. J. Fluoresc. 2005, 15, 287-299. (21) Fan, L. J.; Zhang, Y.; Jones, W. E. Macromolecules 2005, 38, 2844-2849. (22) Tal, S.; Sahman, H.; Abraham, Y.; Botoshansky, M.; Eichen, Y. Chem.—Eur. J. 2006, 12, 4858-4864. (23) Kulatilleke, C. P.; de Silva, S. A.; Eliav, Y. Polyhedron 2006, 25, 2593-2596. (24) Fan, L. J.; Jones, W. E. J Am. Chem. Soc. 2006, 128, 6784-6785. (25) Fan, L. J.; Jones, W. E. J Phys. Chem. B 2006, 110, 7777-7782. (26) Schwarze, T.; Muller, H.; Dosche, C.; Klamroth, T.; Mickler, W.; Kelling, A.; Lohmannsroben, H. G.; Saalfrank, P.; Holdt, H. J. Angew. Chem., mt. Ed. 2007, 46, 1671-1674. (27) Skoog, D. A.; Holler, F. J.; Nieman, T. A. Principles ofinstrumentalAnalysis; 5th ed.; Saunders College Publishing: Orlando, 1998. Page 365. References begin on page 84 86 Chapter Four Radical Copolymerization of P=C and CC Bonds: Reactivity Ratios of Phosphaalkene-Styrene Copolymers* 4.1 Introduction Although synthetically challenging, the incorporation of inorganic functionalities into macromolecules is attractive because it often leads to materials with unique properties that cannot be attained using organic counterparts.”2Lately, the incorporation of phosphorus atoms into polymers has captured considerable attention and resulted in materials with interesting properties and important potential applications, such as chemosensors, polymer-based light emitting diodes (PLED5), and flame-retardant materials.3’In 2003, the Gates group reported the addition polymerization of a phosphaalkene, MesP=CPh2(PA) (Mes 2,4,6-trimethyiphenyl) to afford poly(methylenephosphine).’4This is the first addition polymerization of a heavy-element multiple bond and represents an important step forward in the field of inorganic polymers. Previously, addition polymerization had primarily been limited to olefins.15 Our group subsequently reported the copolymerization of PA with styrene (Sty) to afford new hybrid inorganic-organic copolymers.’6”7The copolymerization can be achieved via a radical method using the radical initiator 1,1 ‘-azobis(cyclohexanecarbonitrile) (VAZO 88) to yield a random copolymer poly(methylenephosphine)-co-polystyrene (PMP-co-PS),’6or the reaction can proceed via an anionic route using n-BuLi to give block copolymers.’7The focus of this chapter will be on the random copolymer PMP-co-PS. This hybrid inorganic-organic macromolecule is particularly attractive for its potential application in polymer-supported catalysis.16 Our group *A version of this chapter will be submitted for publication. Chun, C. P. and Gates, D. P. Radical Copolymerization of P=C and C=C Bonds: Reactivity Ratios of Phosphaalkene-Styrene Copolymers. Chapter Four 87 showed that PMP-co-PS could be used as a ligand in the presence of [Pd2(dba)3](dba = dibenzylideneacetone) and CsF to execute a Suzuki cross-coupling of bromobenzene and phenylboronic acid to form biphenyl with 90% yield.’6On the other hand, when the cross- coupling reaction was attempted using [Pd2(dba)3],CsF and a homopolymer of PA, the yield was the same as that in the reaction using only [Pd2(dba)3]and CsF (yield = 25%). To better understand the microstructure of PMP-co-PS, which has not been reported, we decided to further examine the PA/Sty copolymerization system at 100 °C using VAZO 88 as the radical initiator (Scheme 4.1). The elucidation of the PMP-co-PS microstructure would require the determination of the reactivity ratios of PA (rpA) and of Sty (rs). Reactivity ratios describe the relative tendency of the growing chain to add to a particular monomer. More specifically, reactivity ratios are defined as a ratio of rate constants as shown in Scheme 4.2 using rpA and rs as examples. Starting in the 1 940s, reactivity ratios have played an important role for the copolymerization of olefins to develop commercial products.’8They are crucial synthetic parameters in predicting predilections of a specific monomer to copolymerize with certain other monomers.19’20To that end, we believe that rpA and r5, may have a long term impact to the sensing work discussed in Chapters 2 and 3 if chemosensors could be realized by random copolymers derived from phosphaalkenes. It may be possible that a sensory behavior does not necessitate phosphorus at every other atomic position in the main chain. ,Ph VAZO88 \ / / MePh + Ph/t 100C PA Sty PMP-co-PS Scheme 4.1 References begin on page 106 Chapter Four 88 “PA + PA kpp ‘‘PA-PA + Sty kss ““Sty-Sty u111PA. + Sty kp “PA-Sty “Sty + PA ksp ““Sty-PA k5 rpA= rSty= kp5 sp Scheme 4.2 Herein we describe our investigation on the reactivity ratios of PA and of Sty in the PMP co-PS copolymerization system by following an adaptation of the Tidwell-Mortimer experimental approach,2’illustrated in Chart 4.1. The first step requires data, such as copolymer compositions, from several copolymerization experiments over a broad range of monomer feed ratios. These data are necessary for the preliminary estimation of the r values by one or more linear methods. The Fineman-Ross linearization22and the Mayo-Lewis intersection method23 were used in this study. The second step of the experimental approach requires the input of the preliminary r values for the application of the heuristic rules introduced by Tidwell and Mortimer. These rules approximate the optimal feed compositions for further copolymerization experiments. Lastly, further experiments are performed at the optimal feed compositions, and the data are fitted to the copolymer composition equation (eq I) by nonlinear least squares regression to provide the best estimates of the reactivity ratios. = rMPA + MpAMs (I) + MPAMSIY where: mmonomer represents the molar fraction of PA or Sty in the copolymer; Mmonomer represents the molar fraction of PA or Sty in the monomer feed. Based on the best estimates of rpA and the microstructure of PMP-co-PS was examined and Q-e reactivity parameters of PA were computed. References begin on page 106 Chapter Four 89 Chart 4.1. Flowchart illustrating the Tidwell-Mortimer approach to determining reactivity ratios. data from copolymerization experiments Step I Preliminary estimation of rvalues by linear methods - Fineman-Ross Linearization - Mayo-Lewis Intersection Method preliminary rvalues Step 2 Application of Tidwell and Mortimers heuristic rules using preliminary rvalues to determine optimal feed compositions for further copolymerization experiments optimal feed compositions copolymerization experiments based on optimal feed V compositions and obtain data Step 3 Determination of rvalues by nonlinear least squares fitting of data to the copolymer composition equation * best estimates of rvalues 4.2 Results and Discussion 4.2.1 Analysis of Copolymer Composition by Inverse Gated Proton Decoupled ‘3C NMR Spectroscopy Since our investigation of reactivity ratios required analysis of many copolymer samples, a simple and rapid method to analyze copolymer compositions was desired. NMR spectroscopy is commonly used for the analysis of copolymer compositions.243’Unfortunately, ‘H NMR References begin on page 106 Chapter Four 90 spectroscopy was not a feasible option in our investigation because the technique could not differentiate changes in the copolymer composition of PMP-co-PS. Thus, we considered using another technique, ‘3C NMR spectroscopy, which is a common method for the analysis of copolymer compositions and microstructures.2527’930Since T,s for macromolecules are usually very short (10-s to is),33 inverse gated proton decoupled ‘3C NMR spectroscopy may be a viable method to measure compositions of PMP-co-PS in a quantitative fashion. In this method, the decoupler is off during the relaxation delay and on during acquisition, thereby eliminating the Nuclear Overhauser Effect from the protons, resulting in more quantitative integrations than the typical ‘3C{H} experiment. To further ensure that the ‘3C NMR experiment yields results as quantitative as possible, a 90° pulse can be used. A ‘3C NMR spectrum of a sample of PMP-co PS, obtained via the method described above, is shown in Figure 4.1. The signals for the aromatic carbons resonate between 155 ppm and 120 ppm, whereas the signals for the methyl carbons resonate around 25 ppm. To evaluate the accuracy of inverse gated proton decoupled ‘3C NMR spectroscopy as a method to analyze PMP-co-PS samples, compositions of four different samples of PMP-co-PS, / Ph\ /H H I I i/i I I I P—c I/I c—c I I 1/ I I\ MesPh/ \H Phx Y backbone Cs \ -CH3 PPm18O 160• 140120 100 80 60 20 0 Figure 4.1. Inverse gated proton decoupled ‘3C NMR spectrum (CDc13, 101 MHz) of a PMP-co PS. CDC13 (*) Ar-C * References begin on page 106 Chapter Four 91 prepared under conditions specified in Table 4.1, were estimated using the ‘3C NMR spectroscopic technique described above. These estimations were compared to compositions analyzed by elemental analysis (EA) which include phosphorus analysis, which is a service available only outside of our department (see Table 4.1). The copolymer compositions, determined by both methods, agreed within 0.05. The estimations by 31C NMR and EA for entry 3 differed by only 0.01. The maximum difference was observed in entry 2 in which the estimations differed by 0.05. Encouraged by these results and the convenience of the ‘3C NMR spectroscopic technique to deliver results rapidly, 13C NMR spectroscopy with inverse gated proton decoupling was chosen as the method for determining PMP-co-PS compositions. Table 4.1. Comparison of copolymer compositions measured by inverse gated proton decoupled 1 3C NMR spectroscopy and elemental analyses. monomer feed copolymer composition GPC EAC entry t (h) MPA Msty mpA ms mpA m5 (10 g moi’) PDI 1 2 0.2 0.8 0.55 0.45 0.57 0.43 14.7 1.17 2 10 0.4 0.6 0.36 0.64 0.41 0.59 9.6 1.20 3 16 0.4 0.6 0.44 0.56 0.43 0.57 8.8 1.29 4 24 0.4 0.6 0.35 0.65 0.38 0.62 10.4 1.25 a The duration of each copolymerization experiment conducted at 100 °C is represented by t. b See Experimental section. (FWSY )(EA )(0.0 1) m = and m8 = 1—PA 100xAW —(FWPA —FWStY)(%PEA) ly where: FW51 is the molar mass of styrene; %PEA is the percent of phosphorus detected by elemental analysis; A Wp is the atomic mass of phosphorus; FWPA is the molar mass of phosphaalkene PA. References begin on page 106 Chapter Four 92 4.2.2 Experimental Design and Preliminary Estimation of rpA and r5 All copolymerization experiments were performed by heating PA and Sty in a vacuum- sealed glass tube at 100 °C. It is critical to minimize monomer drift in studies of reactivity ratios, thus we aimed to carry all experiments to low monomer conversion (X 10%). To determine the number of hours of heating at 100 °C (t) that would minimize X, several copolymerization experiments were performed with variable t. In these experiments, we used a monomer feed ratio of MPA= 0.40 and M51 = 0.60. Figure 4.2 plots the conversion of each copolymerization. Monomer conversion (X) was calculated based on the number of moles of each monomer in the copolymer divided by the number of moles of each monomer in the monomer feed. As illustrated in the plot, longer heating durations led to higher monomer conversions. Allowing a copolymerization experiment to proceed at 100 °C for 2 h resulted in XPA = 3% and X5 = 2%.* According to Figure 4.2, t equal to 4 h also resulted in monomer conversions below 10%. However, t of 2 h was chosen to keep monomer conversion to a minimum in order to reach more reliable results in our later calculations of rpA and rg. 50 45 40 35 30 X (%) 25 20 15 ______ PA 10 •Sty 5 U U 0 2 4 6 8 10 12 14 16 18 20 22 24 t (h) Figure 4.2. Monomer conversions of copolymerization experiments carried through different t. MPA = 0.40; = 0.60. Conversion was calculated by Xmonomer = (moles of monomer in the copolymer)/(moles of monomer in the monomer feed). * Heating a reaction mixture at 100°C for 1 hour (i.e. t = 1 h) led to very little copolymer formation thereby rendering product isolation and analysis difficult. References begin on page 106 Chapter Four 93 To obtain data for the first step in calculating reactivity ratios (Chart 4.1), eight different copolymerization experiments, with heating for 2 h, over a range of monomer feed ratios were conducted. Table 4.2 summarizes the data from the eight experiments. According to the data, as the monomer feed of PA (i.e. MPA) increased, the mole fraction of PA in the isolated copolymer (i.e. mpA) increased. This is logical and the same pattern is observed for Sty. The copolymers in Table 4.2 have M values ranging from 7,700 g mol’ to 16,200 g mol’. In general, copolymers with higher M values were found to have more PA in their compositions; this makes sense since the molecular weight of PA is greater than that of Sty. The GPC traces of the copolymer samples were unimodal, which gave support to the presence of PMP-co-PS, and not a polyblend of homopolymers and copolymers. The PDI values of the copolymers range between 1.11 and 1.20. Table 4.2. Summary of copolymerization experimental data. monomer feed PMP-co-PS monomer GPC composition (1 conversion v a v a -“PA -“Sty 1V1 entry MPA mpA msty (%) (%) g moF’) PDI 1 0.20 0.80 0.36 0.64 5 2 8.0 1.11 2 0.20 0.80 0.39 0.61 3 1 7.7 1.17 3 0.40 0.60 0.44 0.56 4 3 10.5 1.13 4 0.40 0.60 0.44 0.56 2 2 11.6 1.15 5 0.60 0.40 0.46 0.54 4 8 14.1 1.16 6 0.60 0.40 0.52 0.48 4 6 11.4 1.18 7 0.80 0.20 0.55 0.45 3 10 14.7 1.17 8 0.80 0.20 0.56 0.44 3 10 16.2 1.20 a Conversion is calculated by Xmonomer (moles of monomer in the copolymer)/(moles of monomer in the monomer feed). References begin on page 106 Chapter Four 94 Following the first step in the Tidwell-Mortimer approach (Chart 4.l),21 the Fineman Ross linearization22was employed to obtain preliminary estimates of rpA and r5. In this method, the copolymer composition equation (eq I) is rearranged to a linear form (eq II): G = FrPA + r1 (II) MPA(mSIY —mPA) where: G= M1mp4 F — mYMPA mPA ‘SIy Hence by plotting G versus F, the line of best fit has a slope represented by rpA and a y-intercept represented by rs. Figure 4.3 shows the Fineman-Ross plot generated from the data presented in Table 4.2. From the equation of the regression line (R-squared = 0.9 172), the reactivity ratio values obtained are rpA = 0.07±0.02 and rs = O.2l±O.l2. The results of the Fineman-Ross linearization are tabulated in Table 4.3, which summarizes the r values calculated in this study. 0.4 0.2 0.0 -0.2 G -0.4 -0.6 -0.8 -1.0 -15 -13 -11 -9 -7 -5 -3 -1 1 F Figure 4.3. Fineman-Ross plot of G versus F for PA/Sty copolymerization experiments. The linear least-squares function (G = 0.07F — 0.21) has an R-squared value of 0.9 172. The errors reported are the 95% confidence intervals that were calculated based on the standard deviation of the slope and y-intercept of the regression function shown in the Fineman-Ross plot. rPA r, G = 0.07F - 0.21 References begin on page 106 Chapter Four 95 Table 4.3. Approximation of rpA and Method Fineman-Ross Linearizationa Mayo-Lewis Intersection Methodb Average of Preliminary Estimates Nonlinear Least-Squares Regressiona 0.11±0.01 a Errors are the 95% confidence intervals associated with the respective r value. b Errors are determined the dividing the difference between the maximum and minimum values of the intersection by two. For comparison, we also estimated the r values by the Mayo-Lewis intersection method.23 In this method, the copolymer composition equation (eq I) is rearranged to eq III: rpA 0.07±0.02 0.21±0.12 0.06±0.18 0.17±0.04 0.065 0.19 0.24±0. 12 1= MPA rPA = SrSI}, + I (III) Each copolymerization experiment is represented by a straight line with a slope and y-intercept defined by S and J, respectively, on ar5, rpA plane. This is shown in Figure 4.4 using the data summarized in Table 4.2. There are eight straight lines, one for each copolymerization experiment. Lines representing entries 3 and 4 overlap. The r values, obtained by the intersection method, are the coordinates of the centroid in the area of common intersection shown in the plot. Therefore by this method, rpA = 0.06±0.18 and r5 = 0.17±0.04 (Table 4.3). The error in rpA is quite large, which is typical of r values calculated by this method. The errors are determined by dividing the difference between the maximum and minimum values of the intersection area by two. where: = m]AMS,Y mS(YMPA References begin on page 106 Chapter Four 96 1.0 0.8 0.6 0.4 0.2 rPA 0.0 -0.2 -0.4 -0.6 -0 8 -1.0 0 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 Figure 4.4. PA/Sty copolymerization data plotted according to the Mayo-Lewis intersection method. (rs, rpA) = (0.17, 0.06) are the coordinates of the centroid in the area of common intersection among all the lines. The averages of the reactivity ratios calculated from both methods (i.e. Fineman-Ross linearization and Mayo-Lewis intersection method) were taken as the preliminary estimates, giving rpA = 0.065 and r5 = 0.19 (Table 4.3). These r values were used in the second step of the Tidwell-Mortimer approach (see Chart 4.1) which is described in the next section. 4.2.3 Application of Heuristic Rules It has been shown and recognized that not all experimental conditions serve equally well in the determination of reactivity ratios and there are some conditions that reveal more information about the r values.’9’2For this reason, Tidwell and Mortimer developed heuristic rules (eq IV and eq V) that approximate the two sets of monomer feed conditions, referred to as the optimal monomer feed compositions, that lead to more accurate estimates of r values.2’ References begin on page 106 Chapter Four 97 2 2+ rPA where: MPA’ is the optimal monomer feed of PA for the first experiment; MPA” is the optimal monomer feed of PA for the second experiment; and rpA are the preliminary estimates obtained by linear approximations Given the preliminary estimates (rpA 0.065 and rs 0.19), the second step of the experimental approach involved the application of heuristic rules (eq IV and eq V). This resulted in the following set of conditions for further work in our study: 1) MPA 0.09, Ms = 0.91; and 2) MPA 0.97, Ms 0.03. Two additional runs were conducted at each of these conditions and their data are summarized in Table 4.4. Table 4.4. Summary of experimental data from copolymerizations according to optimal monomer feed compositions. monomer feed entry MPA M5 mpA m5 1 0.09 0.91 0.24 0.76 2 0.09 0.91 0.20 0.80 3 0.97 0.03 0.82 0.18 4 0.97 0.03 0.85 0.15 a Conversion is calculated by Xmonomer = (moles monomer in the monomer feed). monomer GPC conversion v a v- a -“PA -‘i-Sty JVI (%) (%) (10 gmol’) PDI 10 3 7.8 1.07 9 3 7.0 1.08 2 10 13.4 1.16 2 10 16.7 1.17 of monomer in the copolymer)/(moles of M ‘ (IV)PA + (V) PMP-co-PS composition References begin on page 106 Chapter Four 98 4.2.4 Determination of rpA and rsty by Nonlinear Least Squares Regression To provide the best estimates of rpA and rst3, and minimize the error associated with the solutions, nonlinear least squares regression (Step 3, Chart 4.1) was performed on both sets of data: the data presented in Table 4.2 and the data found in Table 4.4. A substitution was made to simplify the curve-fitting procedure. Since M5 = 1 — MPA, the right hand side of the copolymer composition equation (eq I) was expressed in terms of one variable as shown in eq VI: 1PA = rPAMPA + MPA(l — MPA) (VI) r(Y(lMPA) +MPA(l—MPA) Using the data specified, a plot of mpA/ms versus MPA was constructed (Figure 4.5). A line of best fit, following the form of the eq VI, was obtained by using a nonlinear least squares curve- fitting tool in the MATLAB software. This function correlates well with the data points (RMSE = 0.1358). The plot shows that when MPA is greater than 0.8, there is a drastic increase of PA in the copolymer composition. From the equation of this line (shown in Figure 4.5), the best estimates of the reactivity ratios are rpA = 0.11±0.01 andr8,= 0.24±0.12 (Table 4.3). 6 rPA — + Mp4(1 — MPA) MPA Figure 4.5. Nonlinear least squares curving fitting of copolymerization data. RMSE 0.1353. § The errors are the 95% confidence intervals associated with the respective r value. References begin on page 106 Chapter Four 99 4.2.5 Q-e values of PA and the Microstructure of PMP-co-PS To compare the reactivity of PA to the reactivity of other monomers, it would be helpful to first assign reactivity parameters to PA following the well-known Aifrey-Price Q-e scheme.34 According to this framework, the Q value describes the specific reactivity of the monomer, and the e value represents the polarity of the radical adduct. Styrene was chosen as a universal standard for this scheme and hence was arbitrarily assigned the Q value of 1.0 and an e value of —0.8. To determine the Q and e values of PA, we used the Alfrey-Price formulas: rPArstY = exp[—(en,ononeri — enlonomer2)l (VII) r — monomerl ex e 1e VIIImonomer I — PL monomerl ‘ monomerl emoflomer2 monomer 2 Using eq VII, eq VIII, and the Q-e values of styrene, we arrived to QPA 0.9 and epA = 1.1. The QPA value being less than the Qsty value is consistent with our observations of a lower reactivity of PA when compared to the reactivity of Sty during polymerization. The lower reactivity of the PA monomer can be attributed to a higher degree of conjugation in PA compared to Sty thus allowing for greater radical stabilization of the PA radical adduct. It has been demonstrated that monomers with e values of opposite signs, which signifies opposite polarities, have a tendency to alternate upon copolymerization.’9’356Price rationalized this behavior by explaining that a radical species with a negative character exhibits a preference for a monomer with a positively charged double bond and vice versa.35’6 The fact that PA and Sty have e values of opposite signs (es = —0.8; epA = 1.1) suggests that the PAJSty system would exhibit an alternating behavior upon copolymerization. This suggestion coincides with our expectation based on the r values. Referring back to the definition of rpA and r5 (Scheme 4.2), rpA = = 0.11 indicates that the radical of a growing chain with a terminal PA unit is more likely to attack a Sty monomer. Similarly, = = 0.24 suggests that the radical on a References begin on page 106 Chapter Four 100 growing chain with a terminal Sty unit is more likely to add to a PA monomer. As a result, this should give rise to alternating PA and Sty monomers along the copolymer chain. In addition to being important in kinetic aspects of copolymerization and in the determination of Q-e reactivity parameters, reactivity ratios are also key parameters to revealing monomer distribution and heterogeneity in the main chain. The microstructure of a copolymer can be deduced by formulas that are well-known and found in general polymer science textbooks.’9’2°The average sequence length (1) of PA or Sty units linked consecutively is defined by eq IX:20 1 — 1 + r Mmonomeri ixmonomerl — monomerl lvi monomer 2 Using eq IX, we computed the mean sequence length of consecutive PA and Sty monomers in PMP-co-PS samples synthesized from various monomer feed ratios in this study (see Table 4.5). In entries 3—5 of Table 4.5, the copolymers have ‘PA and ‘sty values slightly greater than one unit, therefore these copolymers most likely consist of alternating PA and Sty units. In the case of entry 2, the average sequence length of consecutive PA units is about 1 unit, and that of Sty is about 2 units. This would render a copolymer with a backbone of mostly repeating PA-Sty-Sty triads. In copolymers prepared from a large excess of one monomer in the monomer feed (i.e. entries 1 and 6), there is a tendency to form blocks of the monomer in excess. Inevitably, the number of monomers in a sequence is related to the number of sequences in a given length of a copolymer chain. For example, longer sequences results in fewer sequences in a given chain length. The average number of sequences per 100 units, also known as the run number (R), can be obtained via eq X:20 R= 200 (X) ‘PA + ‘Sty References begin on page 106 Chapter Four 101 Table 4.5. Average sequence length of monomers units (imonomer) and run number (R) of PMP co-PS copolymers prepared from various monomer feed ratios in this study. t = 2 h. entry MPA ‘PA 1Sty R 1 0.09 0.91 1.01 3.43 45.07 2 0.20 0.80 1.03 1.96 66.95 3 0.40 0.60 1.07 1.36 82.19 4 0.60 0.40 1.17 1.16 86.02 5 0.80 0.20 1.44 1.06 80.00 6 0.97 0.03 4.56 1.01 35.94 Not surprisingly, copolymers of PMP-co-PS prepared from a large excess of one monomer have fewer sequences in a given chain length, which appears to be the case for entries 1 (R 45.07) and 6 (R = 35.94) in Table 4.5. In other instances, PMP-co-PS contains about 67 to 86 sequences per 100 units, suggesting a large degree of heterogeneity along the copolymer backbone. From our study, it is apparent that PMP-co-PS generally has a highly alternating PA I Sty microstructure unless prepared under monomer feed conditions of greater than 8:2. An alternating pattern leads to more open space around the phosphorus atoms in comparison to the phosphorus atoms in a homopolymer of PA. This is because phosphorus atoms in the copolymer would be preceded by CHPh moieties whereas the phosphorus atoms in the latter case would be preceded by CPh2 moieties. Returning to the observations from previously reported Suzuki cross-coupling reactions using PMP-co-PS,’6the open space probably facilitated the coordination of phosphorus atoms in PMP-co-PS to Pd thereby promoting coupling activity. References begin on page 106 Chapter Four 102 4.3 Summary In conclusion, we calculated the reactivity ratios of PA and Sty via nonlinear least squares regression and the values obtained are rpA = 0.11±0.01 and rs = 0.24±0.12. These r values led us to assign Q-e reactivity parameters to PA, which will enable reactivity comparison of PA to other monomers, and also evaluate their compatibility for copolymerization. The PMP co-PS microstructure analysis revealed that under feed compositions of less than 8:2 an alternating pattern predominates along the copolymer chain, which allows for more open space around the phosphorus atoms in comparison to the more hindered spatial environments around the phosphorus centres in poly(methylenephosphine). This insight provides an explanation to our previously reported success of Suzuki cross-coupling reactions using PMP-co-PS.’6We have demonstrated the utility of reactivity ratios in modeling compositional heterogeneity and monomer sequence distribution along the backbone of PMP-co-PS. The architectures of PMP co-PS ultimately influence the behavior and physical attributes of the resulting material, which will be investigated in future studies. Results from this study, particularly the Q-e values of PA, will undoubtedly play a crucial role in the future design of copolymers composed of PA and in the evaluation of the specific applications for these tailored materials. 4.4 Experimental Section General procedures. All manipulations of air and/or water sensitive compounds were performed under a nitrogen atmosphere using standard Schlenk techniques or in an Innovative Technology Inc. glovebox. Hexanes and dichloromethane were deoxygenated with nitrogen and dried by passing through a column containing activated alumina. THF was distilled from sodium/benzophenone ketyl. Styrene (Aldrich) was stirred with CaR2 for 24 h, distilled twice References begin on page 106 Chapter Four 103 under partial vacuum and used immediately after distillation. 1,1’- azobis(cyclohexanecarbonitrile) (VAZO 88) (Aldrich) was recrystallized twice from ethanol (99%) and dried for at least 24 h under vacuum. Monomer MesPz=CPh2was prepared following previously reported procedures.37 Equipment. 1H, 31P NMR and ‘3C spectra were recorded at 298 K on Bruker Avance 300 MHz or 400 MHz spectrometers. Chemical shifts are reported relative to 85% H3P04as an external standard (5= 0.0 for 31P) and residual CHC13(5= 7.26 for ‘H and 77.16 for ‘3C). Samples for ‘3C NMR spectroscopy were prepared by dissolving 40 mg of PMP-co-PS samples in 0.4 mL CDC13. For ‘3C experiments with inverse gated proton decoupling, pulse program zgig was used. The relaxation delay (dl) was set to 3 s, and approximately 2048 scans were used for each experiment.** Molecular weights were determined by triple detection GPC using a Waters liquid chromatograph equipped with a Waters 515 HPLC pump, Waters 717 plus autosampler, Waters Styragel columns (4.6x300mm), HR2 x 2 and HR4, Waters 2410 differential refractometer (refractive index detector, ? 940 urn), Wyatt tristar miniDAWN (laser light scattering detector, = 690 nm) and a Wyatt ViscoStar viscometer. A flow rate of 0.5 mL min1 was used and samples were dissolved in THF (ca. 2 mg/mL). The dn/dc for each sample was determined using the software. Elemental analyses were performed by the Canadian Microanalytical Service Ltd. Calculations and plots for preliminary estimates of the reactivity ratios were obtained using Microsoft Excel. Nonlinear least squares regression was performed using MATLAB V.7.0.4 R14. ** Increasing the relaxation delay to 1 Os and/or the number of scans does not change the relative integration of signals in the spectra, and therefore did not affect the estimations of copolymer compositions. References begin on page 106 Chapter Four 104 4.4.1 General procedure for synthesis of PMP-co-PS. The experimental procedure for PMP co-PS (entry 1, Table 4.2) is described in the following as an example: A pyrex tube was charged with phosphaalkene (1.14 g, 3.6 mmol), VAZO 88 (0.044 g, 0.18 mmol) and styrene (1.55 g, 14.4 mmol). The tube was flame sealed in vacuo, then heated at 100 °C in an oven equipped with a rocking tray. After 2 hours of being heated, the tube was broken. Precipitation of the copolymer was achieved by adding hexanes (100 mL) to a viscous solution of the tube’s contents dissolved in THF or CH21.Precipitation was repeated three times. The product, a white powder, was redissolved in THF (3 mL), then filtered through glass wool into a small vial. The solvent was allowed to evaporate, leaving the copolymer as a white solid, which was then dried in a vacuum oven at 60 °C for 24 hours. Yield = 0.08 g (3%). 31P NMR (CDC13,162 MHz): ô = 4, —9 (br). ‘H NMR (CDC13,400 MHz): ô 7.5 — 6.3 (br, Ar II), 2.5 — 1.0 (CH3,CH2,Cl]). ‘3C NMR (CDC13,101 MHz): 5 155— 120 (br, Ar-C), 50,35 (br, CR, CR2), 25 (br, CH3). GPC-LLS (THF): M = 8.0 x iü g moF’, PDI = 1.11. 4.4.2 General procedure for processing 13C NMR spectra and determining copolymer composition. The raw data, obtained via the inverse gated proton decoupled ‘3C NMR technique described above, were processed using the Bruker software, XWINNMR. A line-broadening setting of 25 was used, the spectrum was manually phased in zero-order and first-order, and a baseline correction was applied. The broad signals for the aromatic carbons and the methyl carbons were integrated. Each integral was phased and their values were used to calculate the copolymer composition according to the following equations: References begin on page 106 Chapter Four 105 600C mPA = Me and m =1—rn 3 — 12CM PA where: CMe represent integration value of the chemical shift assigned to methyl carbons; CAr represent integration value of the chemical shift assigned to aryl carbons References begin on page 106 Chapter Four 106 4.5 References (1) Mark, J. E.; Alicock, H. R.; West, R. Inorganic Polymers; 2nd ed.; Oxford University Press, 2005. (2) Manners, I. J Polym. Sci., Part A: Polym Chem. 2002, 40, 179-191. (3) McWilliams, A. R.; Dorn, H.; Manners, I. Top. Curr. Chem. 2002, 220, 141-167. (4) Hay, C.; Fischmeister, C.; Hissler, M.; Toupet, L.; Réau, R. Angew. Chem., mt. Ed. 2000, 39, 1812-1815. (5) Hissler, M.; Dyer, P. W.; Réau, R. Coord. Chem. Rev. 2003, 244, 1-44. (6) Hissler, M.; Dyer, P. W.; Réau, R. Top. Curr. Chem. 2005, 250, 127-163. (7) Sebastian, M.; Hissler, M.; Fave, C.; Rault-Berthelot, J.; Odin, C.; Réau, R. Angew. Chem., mt. Ed. 2006, 45, 6152-6155. (8) Baumgartner, T.; Réau, R. Chem. Rev. 2006, 106, 468 1-4727. (9) Hobbs, M. G.; Baumgartner, T. Eur. I Inorg. Chem. 2007, 3611-3628. (10) Durben, S.; Dienes, Y.; Baumgartner, T. Org. Lett. 2006, 8, 5893-5896. (11) Crassous, J.; Réau, R. Dalton Trans. 2008, 6865-6876. (12) Morisaki, Y.; Aiki, Y.; Chujo, Y. Macromolecules 2003, 36, 2594-2597. (13) Morisaki, Y.; Ouchi, Y.; Tsurui, K.; Chujo, Y. I Polym. Sci., Part A: Polym Chem. 2007, 45, 866-872. (14) Tsang, C. W.; Yam, M.; Gates, D. P. 1 Am. Chem. Soc. 2003, 125, 1480-1481. (15) Odian, G. Principles ofPolymerization; 3rd ed.; Wiley-Interscience: New York, 1991. (16) Tsang, C. W.; Baharloo, B.; Riendi, D.; Yam, M.; Gates, D. P. Angew. Chem., mt. Ed. 2004, 43, 5682-5685. (17) Noonan, K. J. T.; Gates, D. P. Angew. Chem., mt. Ed. 2006, 45, 7271-7274. References begin on page 106 Chapter Four 107 (18) Aifrey, T.; Bohrer, J. J.; Mark, H. Copolymerization; Interscience Publishers, Inc.: New York, 1952. Chapter 1. (19) Aifrey, T.; Bohrer, J. J.; Mark, H. Copolymerization; Interscience Publishers, Inc.: New York, 1952. (20) Alicock, H. R.; Lampe, F. W.; Mark, J. E. Contemporary Polymer Chemistry, 3rd ed.; Prentice Hall: New Jersey, 2003. (21) Tidwell, P. W.; Mortimer, G. A. I Polym. Sci., Part A. Gen. Pap. 1965, 3, 369-387. (22) Fineman, M.; Ross, S. D. I Polymer Sci. 1950, 5, 259-262. (23) Mayo, F. R.; Lewis, F. M. J. Am. Chem. Soc. 1944, 66, 1594-1601. (24) Brar, A. S.; Hooda, S.; Goyal, A. K. I Mol. Struct. 2007, 828, 25-37. (25) Brar, A. S.; Charan, S. I Appl. Polym. Sci. 1994, 51, 669-674. (26) Cheetham, P. F.; Huckerby, T. N.; Tabner, B. J. Eur. Polym. 1 1994, 30, 581-587. (27) Corno, C.; Roggero, A.; Salvatori, T.; Mazzei, A. Eur. Polym. I 1977, 13, 77-82. (28) Duc, S.; Petit, A. Polymer 1999, 40, 589-597. (29) Gan, L. M.; Lee, K. C.; Chew, C. H.; Ng, S. C.; Gan, L. H. Macromolecules 1994, 27, 6335-6340. (30) Pazhanisamy, P.; Sulochana, P.; Anwaruddin, Q.; Ariff, M. I Polym. Sci. Part A: Polym. Chem. 1997, 35, 193-195. (31) Shaaban, A. F.; Khalil, A. A.; Messiha, N. N. I Appi. Polym. Sci. 1989, 37, 205 1-2058. (32) Brar, A. S.; Dutta, K. Macromol. Chem. Phys. 1998, 199, 2005-20 15. (33) Abraham, R. J.; Loftus, P. Proton and Carbon-13 NMR Spectroscopy: An Integrated Approach; Heydon & Son Ltd: London, 1978. (34) Aifrey, T.; Price, C. C. I Polymer Sd. 1947, 2, 101-106. References begin on page 106 Chapter Four 108 (35) Price, C. C. J. Polymer Sci. 1946, 1, 83-89. (36) Price, C. C. J. Polymer Sci. 1948, 3, 772-775. (37) Becker, G.; Uhi, W.; Wessely, H. J. Z. Anorg. Aug. Chem. 1981, 479, 41-56. References begin on page 106 109 Chapter Five Overall Conclusions and Future Work 5.1 Summary of Thesis Work Before I joined the Gates lab, former members had discovered the first addition polymerization of a phosphaalkene (5.1) to afford poly(methylenephosphine) (5.2).’ This can be achieved via a radical route using 1,1’-azobis(cyclohexanecarbonitrile) (VAZO 88), or via an anionic approach using an anionic initiator such as n-BuLi or MeLi. (Scheme 5.1).12 10% VAZO 88 Ph f Phi Mes= MePh or2%nuLi 5.2 Scheme 5.1 It has also been demonstrated by previous members of the Gates group that the phosphine centres in 5.2 can be chemically modified via oxidation reactions,’ or coordination to Lewis acids3 or transition metals.4One of the major objectives in this thesis was to synthesize new poly(methylenephosphine)s that would manifest fluorescence upon chemical modification. We have now successfully prepared new phosphaalkenes MesPC(Naph)(Ph) (Naph = 1- naphthyl) (5.3a), MesP=C(Phen)(Ph) (Phen = 9-phenanthrenyl) (5.3b), and MesP=C(C4H3S)(Ph) (C4H3S= 2-thienyl) (5.3b). The syntheses of 5.3a and 5.3c were achieved by the base-catalyzed phospha-Peterson reaction (Scheme 5.2), whereas the synthesis of 5.3b was realized via the standard phospha-Peterson route (Scheme 5.3). Crystals suitable for X-ray diffraction analysis were obtained for 5.3a-c. References begin on page 113 Chapter Five 110 SiMe3 KOH (cat.) RMes-P + OC P=C SiMe3 Ph - (SiMe3)20 Me( Ph 5.3a R = Naph 5.3c R = C4H3S Scheme 5.2 1) PhenC(O)Ph,-78°C,lOmin ,SiMe3 MeLi ,Li 2” SiMe Cl -78 0 ,rhOfl Mes—P Mes—P / ‘\ \ SIMe3 ° -‘ S1Me3 - L1CI Mes Ph overnight - (SiMe3)20 5.3b Scheme 5.3 Anionic polymerization of 5.3a and 5.3b afforded new poly(methylenephosphine)s 5.4a and 5.4b, respectively (Scheme 5.4). The attempted polymerization of 5.3c did not yield any polymer, presumably due to an inhibition of chain propagation. All of the synthetic work described above is presented in Chapter 2. R 2 mol% n-BuLi F 1 p=c n-Bu-I---P—C-+H Me( Ph THE, RT [Mes Phj 5.3a R = Naph 5.4a R = Naph 5.3b R = Phen 5.4b R = Phen Scheme 5.4 Based on literature precedent,5’6we had expected that phosphaalkenes 5.3a and 5.3b and poly(methylenephosphine)s 5.4a and 5.4b would be either weakly fluorescent or non-emissive due to a quenching effect from the phosphorus lone pair. Thus, we hypothesized that the chemical functionalization of phosphine centres in polymers 5.4a and 5.4b would result in an increase in fluorescence. In Chapter 3, we discussed the chemical modification of 5.4a and 5.4b. This was achieved by oxidation of the phosphine centres and coordination to borane moieties to afford functionalized macromolecules 5.5a, 5.5b, 5.6a, and 5.6b (Scheme 5.5). We studied the electronic properties of 5.3a — 5.6a and 5.3b — 5.6b by UV/Vis and fluorescence spectroscopy. References begin on page 113 Chapter Five 111 30% H20 (aq.) F ¶j NPh1 n-Bu-f--P—C-—-f-H CH2I, 12 h [Mes Ph jr Naph] n-Bu-j---P—C—4H — 5.5a [Mes Ph] 5.4a BH3SMe2(excess), —78 °C Ft BH3Naph’\ /4 Naph\ THE n-Bufl—P——C ) /t’9 ) H warm slowly to RT, 12 h [\Mes Ph/07/ \Mes Ph/03 ,, 5.6a EoPhenl air I II I n-Bu-f—P—C---f-H THF,7d [MS Phi E Pheni I I 5.5b n-BufP—C—-fH — [Mes Ph 5.4b BH3SMe2(excess), —78 °c F H3Phen1 THE n-Bu-j—P——C---j-H [Mes Ph] warm slowly to RT, 12 h fl 5.6b Scheme 5.5 The results showed that the naphthyl-derivatized phosphaalkene 5.3a and poly(methylenephosphine) 5.4a were non-emissive, while functionalized polymers 5.5a and 5.6a fluoresced in the UV region when irradiated at 288 nm. Similarly, for the phenanthrenyl derivatized species, the emission intensities of phosphaalkene 5.3b and poly(methylenephosphine) 5.4b were observed to be lower than those of the functionalized macromolecules 5.5b and 5.6b. These results support our hypothesis that chemical functionalization of the phosphorus centres in poly(methylenephosphine)s 5.4a and 5.4b would prevent quenching from the phosphorus lone pair and give rise to fluorescent behaviors. The long-term goal behind the work presented in Chapters 2 and 3 is to develop a poly(methylenephosphine)-based chemical sensor. The results obtained thus far builds a foundation for further work towards this ultimate goal. References begin on page 113 Chapter Five 112 While Chapters 2 and 3 focus on homopolymers with conjugated substituents, it is possible to envision analogous copolymers designed for the same sensory purpose since it may not be necessary to have phosphorus at every other atomic position in the main chain. Former members of the Gates group had studied the radical copolymerization of phosphaalkene 5.1 and styrene (Sty) to form poly(methylenephosphine)-co-polystyrene (PMP-co-PS) (Scheme 5.6). ,Ph VAZO88 / Ph / / MePh + Ph” 100C 1esPiPhlJ 5.1 Sty PMP-co-PS Scheme 5.6 We wanted to know more about the microstructure of PMP-co-PS, thus another objective of my work was to calculate the reactivity ratios of phosphaalkene 5.1 (rpA) and of styrene (rs,) to model the microstructure of PMP-co-PS. Using data from a number of copolymerization experiments, we calculated rpA and rs by following the Tidwell-Mortimer approach.8According to a nonlinear least squares regression of the data, the best estimates of the reactivity ratios are rpA = 0.11 and = 0.24. Using these r values, we modeled the microstructure of PMP-co-PS and showed that an alternating pattern predominates in the backbone unless the copolymer was prepared from a monomer feed ratio of greater than 8:2. We also computed the reactivity parameters of phosphaalkene 5.1 according to the widely used Alfrey-Price Q-e scheme.9”°The reactivity parameters of 5.1 will enable us to predict compatibility of 5.1 (and other phosphaalkenes that are structurally and electronically similar) with other monomers for future copolymerization projects. References begin on page 113 Chapter Five 113 5.2 Future Work 5.2.1 Towards Poly(methylenephosphine)-Based Chemical Sensors While our studies have provided spectroscopic evidence to support our hypothesis that chemical functionalization of phosphorus atoms in poly(methylenephosphine)s 5.4a and 5.4b would lead to fluorescence, further studies are required to generalize and confirm this hypothesis for poly(methylenephosphine)s bearing other fluorescent groups. Future directions include: • Prepare poly(methylenephosphine)s with fluorescent groups other than naphthyl and phenanthrenyl, preferably moieties that would emit in the visible region to give fluorescent responses that are observable to the human eye. • Measure the quantum yield of fluorescent polymers to confirm strength of emission. As mentioned previously, a chemosensor based on poly(methylenephosphine) may not need phosphorus at every other atomic position in the main chain. In fact, sensing behaviors may be realized by random copolymers. To this end, future work includes: • Copolymerize phosphaalkenes bearing fluorescent groups with vinyl monomers. • Study the electronic properties of copolymers by UV/Vis and fluorescence spectroscopy. To evaluate the potential of new materials for sensing applications, one would need to: • Perform studies to test sensitivity and selectivity. 5.2.2 Copolymerization of Phosphaaikenes Using the Q-e reactivity parameters of phosphaalkene 5.1, we can predict the References begin on page 113 Chapter Five 114 predilections of 5.1 (and of structurally and electronically similar phosphaalkenes) to copolymerize with certain other monomers. It is possible to predict the microstructures prior to carrying out the copolymerization experiment. Copolymerization of phosphaalkenes with olefins offers the potential of adding new dimensions to materials available today. A few of the goals in our research include the development of water-soluble materials, macromolecular chemical sensors, and materials for polymer-supported asymmetric catalysis. Some of our targeted materials may be realized by copolymerization of phosphaalkenes with vinyl monomers. Future work involving copolymerization of 5.1 (and derivatives thereof) will be greatly aided by using the Q-e reactivity parameters of 5.1 to screen monomers for tailored applications. 5.3 Closing remarks The preparation and chemical functionalization of new poly(methylenephosphines)s bearing fluorescent substituents was accomplished. An investigation of the electronic properties showed that chemical functionalization of the phosphorus centres in the new poly(methylenephosphines)s resulted in enhanced fluorescent properties. We also modeled the microstructure of PMP-co-PS by calculating the reactivity ratios of phosphaalkene 5.1 and of styrene. The architecture of PMP-co-PS is important as it ultimately influences the behavior, physical attributes, and function of the material. The results obtained by these studies represent the foundation towards chemical sensors based on homo- or copolymers derived from phosphaalkenes. Future development of new materials from the (co)polymerization of phosphaalkenes is an exciting and expanding area of research, and thus the story of poly(methylenephosphine)s is to be continued. References begin on page 113 Chapter Five 115 5.4 References (1) Tsang, C. W.; Yam, M.; Gates, D. P. J Am. Chem. Soc. 2003, 125, 1480-1481. (2) Noonan, K. J. T.; Gates, D. P. Angew. Chem., mt. Ed. 2006, 45, 727 1-7274. (3) Noonan, K. J. T.; Feldscher, B.; Bates, J. I.; Kingsley, J. J.; Yam, M.; Gates, D. P. Dalton Trans. 2008, 445 1-4457. (4) Gillon, B. H.; Patrick, B. 0.; Gates, D. P. Chem. Commun. 2008, 2161-2163. (5) Smith, R. C.; Protasiewicz, J. D. J Am. Chem. Soc. 2004, 126, 2268-2269. (6) Wright, V. A.; Patrick, B. 0.; Schneider, C.; Gates, D. P. J Am. Chem. Soc. 2006, 128, 8836-8844. (7) Tsang, C. W.; Baharloo, B.; Riendi, D.; Yam, M.; Gates, D. P. Angew. Chem., mt. Ed. 2004, 43, 5682-5685. (8) Tidwell, P. W.; Mortimer, G. A. I Polym. Sci., Part A: Gen. Pap. 1965, 3, 369-387. (9) Aifrey, T.; Price, C. C. I Polymer Sci. 1947, 2, 101-106. (10) Aifrey, T.; Bohrer, J. J.; Mark, H. Copolymerization; Interscience Publishers, Inc.: New York, 1952. References begin on page 113

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