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Living anionic polymerization of phospaalkenes : controlled homopolymers and block copolymers with phosphorus… Noonan, Kevin Joseph Taaffe 2008

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LIVING ANIONIC POLYMERIZATION OF PHOSPHAALKENES. CONTROLLED ROUTES TO HOMOPOLYMERS AND BLOCK COPOLYMERS WITH PHOSPHORUS ATOMS IN THE POLYMER MAIN CHAIN by KEVIN JOSEPH TAAFFE NOONAN B.Sc. (Hon), Dalhousie University, 2003 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in THE FACULTY OF GRADUATE STUDIES (CHEMISTRY) THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver) August 2008 ©Kevin Joseph Taaffe Noonan, 2008 Abstract In this thesis, the living anionic polymerization of the phosphaalkene MesPCPh2is reported. The polymer backbone consists of alternating phosphorus and carbon atoms. Several experiments have been conducted to illustrate the living nature of P=C bond polymerization including: controlling the polymer chain length by varying the concentration of initiator, determining that molecular weight increases linearly with conversion and showing that the polymerization follows pseudo first order kinetics. Investigations into the mechanism of the n butyllithium initiated MesP=CPh2polymerization allowed for the experimental determination of the activation energy of propagation for the growing polymer chain, Ea = 14.0 ± 0.9 kcal mor1. -Several new block copolymer species have been prepared by sequential anionic polymerization including polystyrene-b/ock-poly(methylenephosphine) and polyisoprene-b/ock poly(methylenephosphine). The polyisoprene-b/ock-poly(methylenephosphine) was coordinated to AuCI and dissolved in n-heptane to prepare micellar Au(l) spherical and wormlike nanostructures visible by transmission electron microscopy. Further evidence for the chemical functionality of the poly(methylenephosphine) species is reported in this thesis. Poly(methylenephosphine) was treated with several main group electrophiles to form a polymeric BH3 coordination complex and a partially methylated phosphonium ionomer. Finally, several P=C compounds bearing functional groups (i.e,C10HFe, 4-Cl-C6H4- NEt2-C6H4)on the carbon substituent have been synthesized. Several of these systems have been investigated as monomers for the anionic polymerization P=C bonds. Not all of the monomers polymerize by anionic methods and studies to better understand this behavior are underway. Table of Contents Abstract Table of Contents iii List of Tables ix List of Figures xi List of Schemes xiv List of Abbreviations xviii Acknowledgements xxi Co-Authorship Statement xxii Chapter 1 1.1 Introduction 1 1.2 Determination of Polymer Molecular Weights 2 1.2.1 Research objectives for this thesis 6 1.3 Living Polymerization — Characteristics and Challenges 7 1.3.1 Blockcopolymers 9 1.3.2 Different techniques employed to prepare polymers in a controlled fashion 10 1.4 Living Inorganic Polymers - Introducing Chemical Functionality in a Controlled Fashion ..12 1.5 Inorganic Multiple Bonds 19 1.5.1 The analogy between P=C and C=C bonds 21 1.6 Previous Research into the Addition Polymerization of P=C Bonds 24 1.7 Outline of Thesis 26 1.8 Contributions by Other Researchers to This Work 27 1.9 References 28 III Chapter 2 2.1 Introduction 34 2.2 Results and Discussion 35 2.2.1 Polymerization of phosphaalkene 2.la in solution 35 2.2.2 Confirmation of the living nature of phosphaalkene polymerization using kinetic investigations and NMR studies 36 2.2.3 Further confirmation of living polymerization behavior — construction of a linear M vs conversion plot 38 2.2.4 Control of the polymer chain length by varying the concentration of initiator 39 2.2.5 Block copolymer synthesis preparation of polystyrene-block poly(methylenephosphine) 42 2.3 Conclusions 44 2.4 Experimental 45 2.4.1 Materials and General Procedures 45 2.4,2 Solution phase polymerization of phosphaalkene 2.la to prepare poly(methylenephosphine) 2.3a 46 2.4.3 Preparation of controlled molecular weight poly(methylenephosphine)s 2.3a and 2.3b 46 2.4.4 Preparation of poly(methylenephosphine) 2.3a for determination of k 47 2.4.5 Procedure to obtain molecular weight vs monomer conversion data 47 2.4.6 Preparation of polystyrene—block-poly(methylenephosphine) 2.6 47 2.5 References 48 Chapter 3 3.1 Introduction 50 3.2 Results and Discussion 53 iv 3.2.1 Procedure employed to conduct kinetic studies of MesP=CPh2phosphaalkene polymerization 53 3.2.2 Determination of rate constant of propagation (kr) at different temperatures for MesP=CPh2polymerization 54 3.2.3 Determination of activation energy (Ea) of propagation for P=C bond polymerization 56 3.2.4 Rate behavior changes observed above 50% conversion 57 3.3 Conclusions 59 3.4 Experimental 59 3.4.1 Materials and General Procedures 59 3.4.2 Purification of MesP=CPh2(3.1) 60 3.4.3 Anionic polymerization of MesP=CPh2for kinetic studies 60 3.4.4 General procedure for processing 31P NMR spectra 61 3.5 References 62 Chapter 4 4.1 Introduction 65 4.2 Results and Discussion 67 4.2.1 Preparation of PI—b—PMP block copolymers through successive anionic polymerization of isoprene and MesP=CPh2 67 4.2.2 Preparation of gold complexes of the polyisoprene-block-poly(methylenephosphine) 70 4.2.3 Formation of P1—b—PM PAuCI nanostructures 72 4.3 Conclusions 75 4.4 Experimental 75 4.4.1 Materials and General Procedures 75 4.4.2 Preparation ofP1404—b—PMP32 76 V 4.4.3 Preparation of Pl—b—PMP .77 4.4.4 Preparation ofPl1—b—PMP85 77 4.4.5 Preparation ofPl404—b—(PMPAu32) 78 4.4.6 Preparation of PI—b—(PMPAu) 78 4.4.7 Preparation ofP1164—b—(PMPAu)85 79 4.4.8 Preparation of micellar structurePlo—b—(PMPAu)32 79 4.4.9 Preparation of micellar structurePl222—b—(PMPAu) 79 4.4.10 Preparation of micellar structurePIi64—b—(PMPAu)5 80 4.5 References 81 Chapter 5 5.1 Introduction 84 5.2 Results and Discussion 86 5.2.1 Synthesis of molecular model compounds 86 5.2.2 X-ray crystallography 87 5.2.3 Chemical functionalization of poly(methylenephosphine) 90 5.3 Conclusions 94 5.4 Experimental 95 5.4.1 Materials and general procedures 96 5.4.2 Preparation of Mes(Me)P(BH3)—CHPh2(5.4a) 96 5.4.3 Reaction of 5.4a with Et2NH 97 5.4.4 Preparation of Mes(Me)P(BH3)—C hSi e(5.4b) 97 5.4.5 Preparation of [Mes(Me)2P—CPhH]OTf(5.5) 98 5.4.6 Preparation of n-Bu[MesP(BH3)—C h]H(5.6) 98 5.4.7 Reaction of 5.6 with amines 99 5.4.8 Preparation of Bu[MesP—CPh2J—/—[Me P(Me)—CPh)H(5.7) 99 5.4.9 X-ray crystallography 99 vi 5.5 References .101 Chapter 6 6.1 Introduction 103 6.2 Results and Discussion 104 6.2.1 Synthesis of MesPC(Ph)(Fc) 104 6.2.2 Attempted synthesis of MesP=CFc2and MesP=C(th)(Fc) 105 6.2.3 X-ray Crystallography 106 6.2.4 Polymerization of ferrocenyl phosphaalkene monomer 6.1 .107 6.3 Conclusions 111 6.4 Experimental 112 6.4.1 Materials and general procedures 112 6.4.2 Preparation of MesP=C(Ph)(Fc) 113 6.4.3 Attempted synthesis of MesP=CFc2 114 6.4.4 Attempted synthesis of MesPC(th)(Fc) 114 6.4.5 Synthesis of[P(Mes)C(Fc)(Ph)] 115 6.4.6 X-ray crystallography 115 6.5 References 116 Chapter 7 7.1 Introduction 119 7.2 Results and Discussion 121 7.2.1 Synthesis of several new MesP=C(Ph)(Ar) phosphaalkenes using the phospha Peterson methodology 121 7.2.2 X-ray crystallographic analysis of compounds 7.la, 7.lb and 7.lf 124 7.2.3 Preliminary investigations into the polymerization behavior of phosphaalkenes 7.la —7.le 128 VII 7.3 Conclusions .131 7.4 5xperimental 132 7.4.1 Materials and general procedures 132 7.4.2 Preparation of MesP=C(Ph)(4-NEt2-6H4)7.la 133 74.3 Preparation of MesP=C(Ph)(4-Cl-C 7.lb 134 7.4.4 Preparation of MesP=C(Ph)(4-Me-C6H4)7.ic 135 7.4.5 Preparation of MesP=C(Ph)(4-Pyr) 7.lf 135 7.4.6 Isolation of poly(methylenephosphine) 7.2 from the distillation residue 136 7.4.7 Attempted Polymerization of MesP=C(Ph)(4-NEt2-6H4 136 7.4.8 Attempted polymerization of MesP=C(Ph)(4-F-C) 137 7.4.9 Attempted polymerization of MesP=C(Ph)(2-Py) 137 74.10 Polymerization of MesP=C(Ph)(4-Cl-C6H4)to form 7.5 137 7.4.11 Polymerization of MesP=C(Ph)(4-Me-C to form 7.6 138 7.4.12 X-ray crystallography 138 7.5 References 139 Chapter 8 8.1 Summary 142 8.2 Future Work 145 8.3 References 150 ApperidixA 152 ApperidixB 154 VIII List of Tables Table 2.1 Synthesis of controlled molecular weight poly(methylenophosphine)s (23) 40 Table 3.1 Determination of k at different temperatures for MesP=CPh2 56 Table 4.1 Selected characterization data for polyisoprene.b/ock-poly(methylenephosphine)s (PlnbPMPm) prepared by the successive living anionic polymerization f isoprene and MesP=CPh2 68 Table 4.2 GPC data for polyisoprene-block-poly(methylenephosphine) upon coordination to AuCl 71 Table 5.1 X-ray crystallographic data of 5.4 and 5.5 95 Table 6.1 X-ray crystallographic data of 6.1 112 Table 7.1 Important metrical parameters for crystallographically characterized phosphaalkenes 7.la, 7.lb and 7.lf 124 Table 7.2 X-ray crystallographic data of 7.la, 7.lb, 7.lf 132 Table BI Monomer conversion data collected for the polymerization of 3.1 using 2% BuL as initiator at 296.3 K 154 Table B2 Monomer conversion data collected for the polymerization of 3.1 using 2% BuLi as initiator at 301.8 K 155 Table B3 Monomer conversion data collected for the polymerization of 3.1 using 2% BuLi as initiator at 307.4 K 156 Table B4 Monomer conversion data collected for the polymerization of 3.1 using 2% BuLi as initiator at 313 K 157 Table B5 Monomer conversion data collected for the polymerization of 3.1 using 2% BuLI as initiator at 318.6 K 157 Table B6 Monomer conversion data collected for the polymerization of 3.1 using 2% BuLi as initiator at 324.2 K 158 ix Table B7 Monomer conversion data collected for the polymerization of 3.1 using 4% BuLi as initiator at 296.3 K 158 x List of Figures Figure 1.1 Comparison of two polystyrene chains with different ;hain lengths 3 Figure 1.2 Schematic of accessible architectures using living polymerization techniques 8 Figure 1.3 Formation of AB block copolymers by sequential polymerization of two different monomers 9 Figure 1.4 Spherical micelles formed by solution self-assembly of AB block copolymers 10 Figure 1.5 A simplified representation of controlled radical polymerization 11 ,.:igure 1.6 Some of the recent achievements in heavier element main group multiple bonds . .19 Figure 1.7 A reaction coordinate diagram representing the effect of a sterically unencumbered substituent versus a sterically bulky group on the activation barrier ofR2E=ER molecules 21 Figure 2.1 Observed colour change from yellow to red upon addition of BuLi to MesP=CPh2to form living poly(methylenephosphine) 37 Figure 2.2 Selected 31P NMR spectra and first order kinetic plot (inset) showing the progress of the polymerization of 2.la in glyme using BuLi (2 mol %) 38 Figure 2.3 A graph of molecular weight (Mn) and polydispersity index (M/M) for 2.3a versus conversion of monomer 39 Figure 2.4 Graph of refractive index response vs. concentration of 2.3a in THF 41 Figure 2.5 Graph of refractive index response vs. concentration of 2.3b in THE 41 Figure 2.6 31P NMR (CDCI3)spectrum of block copolymer 2.6 with M = 20 900 g mor1 42 Figure 2.7 Monomodal GPC traces of H-terminated PS and block copolymer PS-PMP 43 Figure 2.8 13C{H} NMR spectrum of block copolymer 2.6 with M = 20 900 g mor1 44 Figure 3.1 Selected 31P NMR spectra (glyme; 296.3 K) of the BuLi initiated polymerization mixture showing the conversion of 3.1 to 3.3 over time 54 Figure 3.2 A graph showing In [M]01[M versus time (h) up to —50% conversion for the polymerization of 3.1 with 2% 11BuLi at approximately 5 K temperature intervals between 296 and 324 K 55 xi Figure 3.3 An Arrhenius Plot was constructed from the linear least squares fit of In k versus l/T (K1) 57 Fgure 3.4. A plot of In [M]0/[ vs. time (h) up to ‘-90% conversion for the polymerization o MesP=CPh2with 2% BuLi at ca. 5 K temperature intervals between 296 324 K ...58 Figure 41 Schematic representations of diblock and trihiock copolyrnerc 65 igure 4.2 GPC chromatograms (refractive index traces) collected for 4.1 b and 4.2b 69 Figure 4.3 31P NMR spectra for compounds 4.2b and 4.3b 71 9gure 4.4 TEM images at 500 nm and 100 nm resolution which were formed from stow evaporation of a dilute n-heptane solution containing polyisoprene-bIock poly(methylenephosphine-gold(I)) 74 Figure 5.1 Solid state molecular structure of 5.4a 88 Figure 5.2 Solid state molecular structure of 5.4b 89 Figure 5.3 Solid state molecular structure 5.5 90 Figure 5.4 Stack plot of 31P NMR spectra of 5.2 (a), 5.6 (b) and 5.7 (c) in THF 91 Figure 5.5 The possibilities for methylation of P chain. (a) alternating positive charge, (b) random distribution of positive charge 93 Figure 5.6 13C{H} Spectra of compound 5.5 (top) and compound 5.7 (bottom) 94 Figure 6.1 Solid State Molecular Structure of Z-6.1 107 Figure 6.2 UVN1s spectra of monomer 6.1 (top) and polymer 6.2 (bottom) 109 Figure 6.3 Cyclic Voltammogram of 6.2 in CH2I 110 Figure 6.4 TGA of the ferrocenyl phosphine polymer 6.2 111 Figure 7.1 tH NMR spectrum of compound 7.lf in CD2I 123 Figure 7.2 Solid State Molecular Structure of 7.la 126 Figure 7.3 Solid State Molecular Structure of 7.lb 127 Figure 7.4 Solid State Molecular Structure 7.lf 127 Figure 7.5 3’P NMR spectrum of compound 7.5 131 Figure Al Refractive index traces of 2.3a (Table 2.1 entries 1-4) with increasing M 152 xii Figure A2 Refractive index trace of 2.3b (Table 2.1 entries 5) 153 Figure A3 Refractive index traces of 2.3b (Table 2.1 entries 6) 154 Figure BI t1 inversion recovery sequence for MesP=CPh2 159 xl” List of Schemes Scheme 1.1 General polymerization routes to —[E—E]— polymers (F .: elerrient) 5 Scheme 1.2 Polymerization of ethylene using a generic initiator R* 5 Scheme 1 .3 Living polymerization of styrene upon combination with sodium naphthalide 8 Scheme 1.4 The living polymerization of hexamethylcyclotrisiloxane 13 Scheme 1.5 Living ROP of silicon-bridged [1]ferrocenophane 14 &heme 1.6 Living anionic polymerization of phosphorus bridged [iferroc;.enophane 15 Scheme 1.7 Living cationic polymerization ofCI3P=NSiMe using catalytic PCI5 16 Scheme 1.8 1,1-dimethylsilacyclobutane living polymerization 16 Scherno 1.9 Vinyl ferrocene living polymerization 17 Scheme 1.10 Anionic polymerization of masked disilenes and cyclic tetrasilanes using organolithium reagents 18 Scheme 1.11 The first cyclic and acyclic phosphaalkenes that were stable and isolable at room temperature 22 Scheme 1.12 Phosphaalkenes mimicking the reactivity of olefins 23 Scheme 1.13 Formation of epoxide analogs by reaction of a complexed P=C compound with m chloroperoxybenzoic acid 23 Scheme 1.14 Intramolecular C-H activation of Mes*P=CH2in the presence of the Lewis acidic GaCI3 species 24 Scheme 1.15 Preparation of the MesP=CPh2phosphaalkene from commercially available PCI3 25 Scheme 1.16 Preparation of the MesP=CPh2phosphaalkene from treatment of MesP(Cl)(CPh2H with 1 ,5-d iazabicyclo[5.4.0)undec-5-ene (DBU) 25 Scheme 1.17 Reaction of MesP=CPh2phosphaalkene with anionic MeLi and subsequent oxidation to afford a methyl mesityl phosphine oxide. Polymerization of MesP=CPh2 using radical or anionic initiators at high temperature (150 °C) 25 xiv Scheme 1.18 Polymerization of a Ge=C compound using tert-butyllithium as the anionic initiator to form polycarbogermanes 26 Scheme 2.1 Anionic polymerization of MesP=CPh2using methyllithium as the initiator 36 Scherrie 2.2 Living anionic polymerization of phosphaalkenes 36 Scheme 2.3 Preparation of polystyrene-b/ock-poly(methylenephosphine) 42 Scheme 3.1 Living polymerization of alkenes 51 Scheme 3.2 The addition polymerization of a phosphaalkene to obtain poly(methylenephosphine) 51 Scheme 3.3 Proposed initiation, propagation and termination steps in the living anionic polymerization of phosphaalkene MesP=CPh2using n-butylHthium as initiator 52 Scheme 4.1 Polymerization of isoprene in THF at room temperature using BuLI followed by addition of MesP=CPh2to the living polyisoprene forming polyisoprene-block poly(methylenephosphine) 69 Scheme 4.2 Treatment of polyisoprene-block-poly(methylenephosphine) with (tetrahydrothiophene)gold(l) chloride to form a polyisoprene-block poly(methylenephosphine) gold(l) coordination complex 70 Scheme 5.1 Functionalization of poly(methylenephosphine) using H20,S8 and AuCl 85 Scheme 5.2 Living polymerization of phosphaalkenes using n-butyllithium as initiator in glyme 86 Scheme 5.3 Model compound preparation from MesP=CPh2phosphaalkene. The three- coordinate phosphine (5.3) is coordinated reversibly to BH3 87 Scheme 5.4 Methyl phosphonium model compound preparation from the three-coordinate phosphine (compound 5.3a) 87 Scheme 5.5 Borane protection of poly(methylenephosphine) using BH3SMe2.The BH3 group can be removed by treatment of the polymer with borane 91 Scheme 5.6 Methylation of poly(methylenephosphine) 92 Scheme 6.1 Synthesis of poly(methylenephosphine) containing a ferrocenyl moiety 104 xv Scheme 6.2 Preparation of ferrocenyl phosphaalkene from the MesP(SiM3)2,methyllithium and benzoylferrocene 105 Scheme 6.3 Attempted synthesis of MesPCFc2and MesP(ih)(ic) using the phcspha•• Peterson reaction 106 Scheme 7.1 Living polymerization of phophaalkenes 119 Scheme 7,2 Standard phospha-Peterson procedures as a route to phosphelkenc monomers 120 Scheme 1.3 Synthesis of several substituted mesityl-phosphaalkens. using the base catalyzed (NaOH) phospha-Peterson reaction 122 Scheme 7.4 Preparation of 4-pyridyl phosphaalkene 7.lf using the phospha-i’eterson reaction 123 Scheme 7.5 Anionic polymerization of styrene versus 2-vinyl pyridine 129 Scheme 7.6 Synthesis of poly(methylenephosphines) 7.5 and 7.6 130 Scheme 8.1 Preparation of ABA triblock copolymers where the A block is poly(methylenephosphine) and the B block is polystyrene 146 Scheme 8.2 Living poly(methylenephosphine) should be a suitable initiator to polymerize methyl methacrylate and synthesize poly(methylenephosphine) -block-poly(methyl methacrylate) 147 Scheme 8.3 Reaction of MesP=CPh2with BuLi forms a doubly benzylic carhanion. Addition of BuLi across the MesP=C(H)(Bu) phosphaalkene will form a lessstabilized carbanion because the t-butyl and H groups do not provide any resonance stabilization 148 Scheme 8.4 Preparation of thiophene-containing phosphaalkene from the combination of Mes(SiMe3)2and benzoyl thiophene 148 Scheme 8.5 Polymerization of Mes*PCH2using n-butyl lithium as the initiator 149 xvi List of Abbreviations A preexponential factol sec-BuLi sec-butyilithium orCH3H(Li)CH2 BuLi n-butyflithium orCHLi tBULI t-butyllithium or (CH3)CLi tE tert-butyl CCD charge-coupled device CCDC Cambridge Crystallographic Data Centre m-CPBA m-chloroperoxybenzoic acid - - - Dcaic -density - hexarnethylcyclotrisiloxane DLS dynamic light scattering DMSO dimethyl sulfoxide or (CH3)2S0 DNA deoxyribonucleic acid dn/dc differential index of refraction E generic element Ea activation energy Et Ethyl or CH32— Fc ferroceneor(C5H4)F (C GPC gel permeation chromatography K Kelvin kcal kilcalories k apparent rate constant kV kilovolt LLS laser light scattering MeLi methyllithium or MeLi xvii MOH methanol Mes 2,4,6trimethylphenyi MHz megahertz monomer to initiator ratio number-average molecular weight weight-average molecular weight N principal quantum number N MR nuclear magnetic resonance PDI olydispersity index (MIM) Ph phenyl Pl-b-PMP polyisoprene-block-poly(methylenephosphine) P1 polyisoprene PMP poly(methylenephosphine) PS polystyrene PS-b-PMP polystyrene-block-poly(methylenephosphine) py pyridyl or C5HN R generic substituent ROP ring-opening polymerization TEM transmission electron microscopy Tq glass transition temperature TGA thermal gravimetric analysis THF tetrahydrofuran Tf triflate or —SO2CF3 Triple detection GPC gel permeation chromatography equipped with light scattering instrument, viscometer and differential refractometer th thiophene or C4HS XVIII chemical shift in parts per million (ppm) wavelength (nm) xix Acknowledgements :here are so many people to acknowledge in so little time. To my supervisor, Dr. Derek Gates, who has been evergenerous with his time and who has taught me so many lessons not only about science but about life. I am forever indebted for his guidance and his understanding Through many difficult times. Working with the Gates’ Group has been a privilege, would like to thank aN members, both past and present, for their willingness to help and !ir the lite-restoring good times. In particular, I would like to thank Josh, Paul, Cindy and Julien or help in reading this thesis and for giving me insightful advice. Additional thanks to Josh Bates for his efforts in the x-ray crystallography lab, I know it is a tough job and I so appreciate his selfless generosity when working tirelessly for others. Vince Wright has been a great friend with whom I could !“ounce ideas back and forth; he was an absolutely fantastic co-worker. I cannot thank Bronwyn Gillon enough for our good times together over the past few years. Few peopie are blessed with such a close friend whose support is completely unconditional. I will treasure her friendship forever. Thanks to Nick Burlinson and Brian James, for putting up with my kinetics questions and never being too busy to help a man in desperate need. To Marshall Lapawa, who is always helpful both in the mass spectrometry lab and in Grass 6’s volleyball leagues. I am grateful for the support of NSERC through four years of funding. I would like to thank my family; in particular, my parents who have provided love and support through this journey. They give true meaning to the phrase “you iever give up”. I appreciate everything they have done. I would also like to thank Clara Gomez, who has been an amazing friend, a great supporter and a wonderful companion. xx CoAuthorshi Statement A version of Chapter 2 has been published as a communication: Noortan, K. J. T.; Gates, 1P. Angew. Chem. mt. Ed. 2006, 45, 7271. am the primary author and conducted ail synthetic experiments under the supervision of Prof. Derek Gates. The written work was a collaborative effort between my supervisor and myself. - A version of Chapter 3 has been published as a full paper: Noonan, K. .J. T.:. sates, ).P. Macromolecules. 2008, 41, 1961. I am the primary author and conducted all synthetic )xperiments under the supervision of Prof. Derek Gates. The written work was a collaborative effort between my supervisor and myself. A version of Chapter 5 has been published as a full paper: Noonan, K. J. T.; Feldscher, B.; Rates, J. I.; Kingsley, J. J.; Yam, M.; Gates, D. P. Dalton Trans. 2008, 4451. ,iUStjfl Kiniey was an undergraduate student and did some preliminary investigations into methylation of the poly(methylenephosphine) polymer under the supeivision of Mandy Yam, a previous graduate student in the Gates’ lab. Joshua Bates analyzed the crystallographically characterized compounds. Both Bastian Feldscher and myself conducted synthetic experiments. Bastian was an exchange student from Germany and was under my direct supervision while at UBC. The written work was a collaborative effort between Prof. Derek Gates and myself. A version of Chapter 6 has been published as a communication: Noonan, K. J. T.; Gates, D.P.; Patrick, B. 0. Chem. Commun. 2007, 3658. I am the primary author and conducted all synthetic experiments under the supervision of Prof. Derek Gates. The written work was a collaborative effort between my supervisor and myself. Dr. Brian Patrick performed the x-ray crystallographic analysis. xxi 1Chapter 1 Applying Living Polymerization Techniques to Inorganic Polymers, a Route to Diversify Structure and Function of Macromolecules. 1.1 Introduction The advent of synthetic polymer chemistry has been of paramount importance in shaping our modern world. Hermann Staudinger first proposed that macromolecules were not colloids but actually consisted of large numbers of covalently bonded atoms linked together in a long chain.1 This was a controversial topic, as researchers did not believe that molecules of such high molecular weights could exist. Some support for Staudinger’s macromolecular theory was provided by Meyer and Mark who employed x-ray crystallographic analysis to elucidate the structures of several naturally occurring macromolecules: cellulose, chitin, and natural rubber.24 These discoveries, in conjunction with the pioneering work on polymerization by Carothers and co-workers, led to the general acceptance of the macromolecular theory.54 Stauclinger was awarded the Nobel prize for his contribution to the field of polymer chemistry in I 953•15 Since the 1930’s, both synthetic and naturally occurring polymeric materials have had a profound impact on our civilization and they are ever-present commodities in our society. Macromolecules are used in a variety of applications such as clothing, car tires, packaging, televisions, pharmaceuticals, medical devices and computers. In general, synthetic polymers are produced industrially for their mechanical properties, such as their tensile strength, flexibility, lightweight nature and photonic properties.16 In contrast to synthetic polymers, naturally occurring macromolecules not only exhibit desirable mechanical properties but they also boast chemical functionality with the ability to mediate chemical processes.17 For example, deoxyribonucleic acid (DNA) is a polymer composed of only four nucleotide subunits (cytosine, guanine, adenine, and thymine). These Chapter 1 2 nucleotides can be arranged in a limitless number of combinations on a sugar phosphate backbone with the resultant DNA macromolecule being responsible for the transmission and storage of genetic information in the human body. Another example of functional biological polymers are proteins, which consist of covalently linked amino acids. Proteins are essential for the human body to function, for instance, actin and tubulin form strong fibers which are essential components for cytoskeleton mobility.18 The question remains whether humans can potentially synthesize polymers that can mimic the chemical complexity that biological polymers have already achieved. When we consider how biological polymers are prepared, it begins with two monomers being connected to form a dimer, the dimer is then combined with another monomer to form a trimer and this monomer incorporation will continue until high molecular weight polymer is reached. Impeccable control over both the chain length and polymer microstructure are observed during this process.18 When polymers are prepared synthetically, not all of the macromolecules have the same chain length; in fact, they generally consist of many polymer molecules of varying lengths. 1.2 Determination of Polymer Molecular Weights The chain length of a polymer is directly related to its molecular weight. As the length of a polymer chain increases, more monomer units are being incorporated into the chain and, as a consequence, the molecular weight of the macromolecule increases. For example, a polystyrene chain which is 100 repeat units weighs approximately 10,406 g mor1 whereas a polystyrene chain with 200 repeat units has a molecular weight double that value (Figure 1.1). Throughout this thesis, the discussion of chain length and molecular weight will be, in many cases, used interchangeably. References start on page 28 Chapter 1 3 rHH1 rHH II II II -t-C-C-I- -fC-C I_.i Ij% 100 200 100 repeat units x 104.06 g/mol 200 repeat units x 104.06 g/mol =10,406 g/mol =20,812 g/mol Figure 1.1 Comparison of two polystyrene chains with different chain lengths. A doubling of the polymer chain length is consistent with a doubling in the polymer molecular weight. Since all polymer samples are comprised of many macromolecules with varying chain lengths, the characterization of polymers must involve an average or statistical distribution. Conventional macromolecular science deals mainly with two statistical measurements,16 number-average molecular weight (Ma) and weight-average molecular weight (Mw). The M term is simply a mean, the total weight of all the molecules divided by the total number of molecules in the sample (Equation 1.1). Weight-average molecular weight(M) however, is biased towards larger macromolecules since these contribute more to the overall weight of the sample (Equation 1.1).16 It is important to realize that high molecular weight macromolecules (Mw) are desired as this is a crucial characteristic of materials with useful physical properties.16 Finally, the distribution of molecular weights in a polymer sample is defined as the polydispersity index (PDI) and is equal to the weight-average molecular weight divided by the number-average molecular weight (PDI = M/M).16 Most biologically relevant macromolecules are monodisperse and have PDI’s equal to one (PDI = 1), since all of the polymer molecules have the same chain length. Polymer samples prepared using synthetic protocols often possess broad molecular weight distributions with PDI’s approximately equal to two (PDI -. 2).16 NxM. N.xM2 M = M = “ W N1xM Equation 1.1 Description of number average molecular weight M and weight average molecular weight M. N represents a polymer molecule and M1 represents the molecular weight of that polymer molecule. Each equation is described as a sum of the polymer molecules that make up a sample. References start on page 28 Chapter 1 4 Carothers was the first to classify synthetic polymers according to their mechanism of formation; he called the two synthetic routes addition and condensation polymerization.14However, these definitions are no longer sufficient to appropriately describe all known polymerization processes with so many advances in macromolecular science since the 1930’s. Currently, a polymerization is defined as either a step-growth or chain-growth process.19 Chain-growth polymerization requires a reactive species (radical, cationic or anionic initiator) that successfully adds many monomer molecules to itself (Scheme 1.1 Route A and B) forming a macromolecule (—[E—E]— where E = element). Chain-growth polymerization can proceed with either a vinylic monomer (addition polymerization) or a strained cyclic species (ROP — ring-opening polymerization).19In contrast, step-growth polymerization is a process by which monomers come together and repeatedly eliminate a small molecule (XY) to form a macromolecule.9Step-growth necessitates two species that possess different functional groups (Scheme 1.1 Route C). A self- condensation is also possible, where two different functional groups are present in one molecule and intermolecular elimination occurs forming the desired polymer (Scheme 1.1 Route D). The key difference between these polymerization mechanisms is that in a chain growth process, the intermediate formed during polymerization is much more reactive than the monomer and relatively high molecular weight polymers can be obtained even at low conversion. In step growth processes, the intermediates formed are equally as reactive as the monomeric species and the size of the polymer chain grows relatively slowly with a high degree of conversion being necessary to achieve high molecular weight. For the purposes of this thesis, step polymerization techniques will not be discussed further. References start on page 28 Chapter 1 5 RR IF IF A ‘E=E’ Y—E—E—Y + X—E—E—X C / S I I IR R ,RR RR initiator F’XY LR R initiato3/ RR RRR—E—E—R I I I Y—E—E—XR—E--E—R I I RR Scheme 1.1 General polymerization routes to —[E—E]— polymers (E = element). Chain-growth processes, require an initiator to polymerize either a multiple bond (A) or a strained cyclic species (B). Step growth polymerization involves loss of a small molecule XY to form the desired polymer (C and D). Addition polymerization of C=C bonds is an important synthetic route to industrially relevant polymers. The polymerization proceeds with an initiator (usually a radical, cationic or anionic species — denoted as R*) adding across the double bond of an olefin (Scheme I .2).19 The propagation step involves the initiated species (RCH2..C*) consuming many monomer units and forming a long chain until, a termination step destroys the active chain end (Scheme 1.2). The monomer depicted in Scheme 1 .2 is ethylene; however, using other monomers such as CH2=CH(Ph) (styrene), CH2=CH(Cl) (vinyl chloride) or CH2=CH(Me) (propylene) can impart different and potentially useful properties to the synthesized polymer. As stated earlier, high molecular weight macromolecules are desired from these polymerization processes as this is a crucial characteristic of materials with useful properties.16 H ,H * I;II;I c=c R_C_C* I \ I I H H HH HH - HHHH - fHH1HHI CH2-.CH I I I .,H2—CH I I I I IR_C_C* R_C_C_C_C* - RfC_C+C_C* I I I I I II ill I HH HHHH LHHJ,HH HH1HH HH1 Termination, R-I-C--C4-R1 L L Scheme 12 Polymerization of ethylene using a generic initiator R*. References start on page 28 Chapter 1 6 The termination step depends completely on the type of initiator used to induce polymerization.19When analyzing the synthesis of biological macromolecules such as proteins, one realizes that no unwanted termination step occurs Upon achievement of the desired molecular weight for the macromolecule, the polymerization is terminated. Thus, is it possible to conduct synthetic polymerization without an unwanted termination step? Moreover, is this possible not only for organic C=C bond polymerizations but also for inorganic multiply bonded species? 1.2.1 Research objectives for this thesis Recent work in the Gates group has focused on extending addition polymerization, an industrially important reaction for C=C bonds, to inorganic multiple bonds for the first time. In particular, the extension of addition polymerization to phosphaalkenes (MesP=CPh2where Mes = 2,4,6-trimethyiphenyl) was a recent synthetic achievement to prepare poly(methylenephosphine)s which have a backbone of alternating phosphorus and carbon atoms.2°The three coordinate phosphine moiety has been exploited to form metal containing polymers,21 and the oxidation of the polymeric phosphine with H20 or S8 to form P(V) polymers has also been reported.2°This thesis describes the application of living polymerization techniques to the MesP=CPh2phosphaalkene. Several block copolymers incorporating poly(methylenephosphine)s were prepared to illustrate how living polymerization can be used to prepare new macromolecules. Furthermore, several compounds containing P=C bonds were synthesized and polymerized to expand upon the generality of addition polymerization for phosphaalkenes. The next sections will outline the requirements of living polymerization and how they can lead to controlled architectures such as block copolymers. The upcoming sections will also detail why inorganic multiple bonds are interesting candidates for addition polymerization. I Living Polymerization - Characteristics and Challenges (Section 1 .3) References start on page 28 Chapter 1 7 2 Living Inorganic Polymers - Introducing Chemical Functionality in a Controlled Fashion (Section 1.4) 3 Inorganic Multiple Bonds (Section 1.5) 4 Previous Research into the Addition Polymerization of P=C Bonds (Section 1.6) 5 Outline of Thesis (Section 1.7) 1.3 Living Polymerization — Characteristics and Challenges Szwarc was the first to discover that the anionic polymerization of styrene initiated with sodium naphthalide can proceed without termination (Scheme I .3). 23 He described this behavior, as a “living” polymerization and this subject will be prevalent throughout the thesis. In Scheme 1.3, the polymer chain is equipped with a reactive species at the polymer chain end. This carban ion can be exploited to promote further chemistry and is the key feature of a living polymerization. This landmark discovery by Szwarc provided a unique avenue to more complex macromolecular architectures some of which are displayed in Figure 1.2.24 The reactive chain end can be replaced by a functional group, it can be used to initiate polymerization of a second monomer forming block copolymers (see Section 1.3.1) or multifunctional initiators can be employed to fabricate star polymers. These synthetic architectures illustrated in Figure 1.2 are not as complex as those observed with biological polymers but they are starting to further our advancement towards macromolecules with higher order structure and function, The following seven features are requirements of a living polymerization.24 1. Over the course of the polymerization the monomer is completely consumed. 2. The molecular weight increases linearly with conversion. 3. The reaction follows pseudo-first order kinetics. 4. Once the polymerization is complete and the monomer is entirely consumed, the addition of more monomer to the reaction will result in a molecular weight increase for the polymer. 5. The synthesis of two covalently linked polymer chains should be possible. References start on page 28 Chapter 1 8 6. Control of the polymer chain length can be employed by varying the concentration of initiator 7. Polydispersities should be very narrow(i.e, PDI = 1.00-1.10). H ,H sodium naphthalide nC=C I H Ph F Ill fc-c-[Na [H Ph] n Scheme 1.3 Living polymerization of styrene upon combination with sodium naphthalide. Functional Chain End Block Copolymers (AB) A Block B Block Triblock Copolymers (ABA) A Block B Block A Block Graft Polymers lTrrnT Star Polymers Figure 1.2 Schematic of accessible architectures using living polymerization techniques.24 References start on page 28 Chapter 1 9 1.3.1 Block copolymers This section will focus on the advantages and potential applications of block copolymers which are synthesized by sequential polymerization of two chemically different monomer units affording two polymer chains linked by a covalent bond (Figure 1.3). In contrast, random copolymers consist of a statistical mixture of two monomer units and polymer blends are physical mixtures of two homopolymers. Each of these different copolymers offer different physical properties but several unique physical features of block copolymers will be discussed briefly. Block copolymers normally exhibit two separate glass transition temperatures (7) based on the two chemically linked polymer chains. Glass transition temperature is known as the temperature at which the onset of conformational mobility occurs in a polymer sample. AB block copolymers also exhibit microphase separation in the bulk when the A and B segments are incompatible.25The degree of separation is limited by the covalent bond between them and this leads to block copolymers undergoing self-organization on the nanometer and micrometer scale. Li mit - A Block A Block B Block Figure 1.3 Formation of AB block copolymers by sequential polymerization of two different monomers. If a block copolymer has two segments which exhibit different solubility properties and the polymer is dissolved in a solvent selective for only one block, organized structures such as micelles, rods and vesicles can be obtained.26The most common form of solution separation behavior observed is the spherical micelle (Figure 1.4). The insoluble block forms the core of the spherical micelle and the soluble block forms the surrounding corona. However, depending on solubility conditions and the size of the block copolymers, a variety of organized structures may be observed.26Applications for polymers that form ordered assemblies include: surfactants, drug-delivery systems, and nanoreactors.27With these unique chemical properties, block References start on page 28 Chapter 1 copolymers have exploded into a major field of study and continue to attract a great deal of attention today.2729 10 — Soluble Block - Corona Insoluble Block - Core 1.3.2 Different techniques employed to prepare polymers in a controlled or living fashion The early advances in living polymerization were limited to anionic polymerizations of styrenic and butadiene type monomers.24 In the 1980’s, research detailing living cationic polymerization strategies for monomers such as vinyl ethers and isobutylene appeared.3°In 1995, the first controlled radical polymerization as a route to access polyolefins was reported.31 Since more monomers will polymerize by radical methods as compared to cationic and anionic strategies, this stunning development has led to a wealth of new polymer chemistry, particularly in the area of block copolymers.32’3This ability to access a wide variety of olefinic monomers such as methacrylates and acrylates has increased the potential to tune the properties of the resultant block copolymers and access unique macromolecules. Figure 1.4 Spherical micelles formed by solution self-assembly of AB block copolymers. Insoluble blocks form the core of the micelle and the soluble blocks form the corona on the periphery. References start on page 28 Chapter 1 11 Controlled radical polymerization involves a dormant species (R-X) such as an alkyl halide being activated by a metal complex (Figure 1 •5)32 The oxidized metal results in the formation of the desired radical species (R) which will consume monomer repeatedly until the equilibrium process results in reduction of the metal complex forming a dormant polymer chain. However, because this process is in equilibrium, the dormant polymer chain can reoxidize the metal and actively consume monomer once again. This process will continue until the monomer is quantitatively converted to polymer with fairly narrow polydispersities (-1 .2). kact R—X + M — R + X-M1 kdeact kt Monomer Termination Figure 1.5 A simplified representation of controlled radical polymerization. R represents an alkyl group, X represents a halide, and M represents a metallic species. When compared to conventional cationic, radical or anionic polymerization methodologies, coordination-insertion polymerization has always been the superior method to control the stereochemistry of synthetic polymers. Combining the excellent degree of stereochemical control of insertion polymerization with controlled molecular weights has become a growing field of interest.35 There are several reasons to research new living polymerization methodologies. There is the desire to control the structure and function of macromolecules such that the properties of new materials can be tailored. It is also of interest to prepare polymer systems that display chemical functionality and can mediate chemical processes. When preparing macromolecules in a controlled fashion, synthetic protocols have been limited to C=C bond polymerization, or ROP of strained cyclics (i.e, lactides, lactones).24The preparation of inorganic polymers has attracted attention for synthesizing materials with unique features imparted by p-block or d-block elements.364°Moreover, the application of living techniques to inorganic monomers could allow for the preparation of more complex macromolecular architectures incorporating inorganic elements. References start on page 28 Chapter 1 12 1.4 Living Inorganic Polymers — Introducing Chemical Functionality in a Controlled Fashion The development of controlled or living polymerization techniques for inorganic monomers remains in its infancy,40 but there have been several developments in this area which are outlined below. Some interesting structural features of the polymers will also be discussed. Ring-opening polymerization of the cyclic compound, hexamethylcyclotrisiloxane (D3 - 1.1)to form poly(dimethylsiloxane) was the first living polymerization of an inorganic molecule.41 Upon treatment of D3 with an organolithium reagent such as sec-BuLi in a coordinating solvent (i.e, THE), controlled molecular weight poly(dimethylsiloxane) 1.2 was obtained with narrow polydispersity. The living polymerization must be carried out in coordinating solvents because in non-coordinating media two competing mechanistic pathways are observed: cyclic oligomer formation and acyclic polymer formation. The strongly coordinating ligand will complex the Li counterion during the polymerization process, impeding cyclic oligomer formation. Compounds such as THE and cryptands have been shown to effectively coordinate the Li counterion in living poly(dimethylsiloxane) preparation, these solvents effectively inhibit the cyclic oligomerization process.41 Polysiloxanes, which consist of repeating Si—C linkages, are an extremely important class of inorganic polymer and have found a variety of commercial applications including oils, lubricants and synthetic skin.36 They have an exceptionally low Tg (— 123 °C) and high thermooxidative stability making them incredibly versatile macromolecules.4° References start on page 28 Chapter 1 13 MeMe r , r Si IMe I IMe o o sec-BuLi SBUSiOJLj MeOH sBu.LSi..O H Me-SL Sit-Me THE, RT L ] THF, RTMe Me e e D3 1.1 1.2 Scheme 1.4 The living polymerization of hexamethylcyclotrisiloxane using sec-BuLi in tetrahydrofuran. Another inorganic system which was found to polymerize in a living fashion was the silicon-bridged [1]ferrocenophane 1.3.42 The poly(ferrocenylsilane) (1.4) is of considerable interest because of its fascinating magnetic, optical and electrochemical properties (Scheme I .5).’ Treating a solution of [1]ferrocenophane 1.3 in THE with BuLi at room temperature affords poly(ferroceriylsilane)s with controlled molecular weights. Molecular weight control was confirmed by decreasing the initiator concentration (BuLi) which resulted in an increase of the polymer molecular weight (M).42 The living poly(ferrocenylsilane) species was also used to initiate D3 polymerization yielding the desired poly(ferrocenylsilane)-block poly(dimethylsiloxane). This remarkable achievement marked the first living polymerization of a macromolecule incorporating transition metal atoms in the polymer main chain.42 Recent developments involving monomer 1.3 include a photolytic living polymerization using weakly nucleophilic, functional group-tolerant initiators such as Na(C5H).43’4The living anionic polymerization of 1.3 has led to a variety of different block copolymers that have been investigated for their solution self assembly properties4552 and for their bulk state organization capabilities.5356 References start on page 28 Chapter 1 14 1 .“BuLi Me Mel Fe Me 2.MeOH i/SIbMe THF, 25 °C H Fe n 1.3 1.4 MeMe MeMe).>31Onm Hj° Na MeOH Scheme 1.5 Top — The n-butyllithium initiated Living ROP of silicon-bridged [1]ferrocenophane in tetrahydrofuran at ambient temperature. Bottom — Photolytic polymerization of silicon-bridged [1]ferrocenophane with UV light and NaC5Has the mild initiator. The polymerization procedure is carried out below room temperature. One recent highlight of poly(ferrocenylsilane) block copolymer studies was the solution self assembly of poly(ferrocenylsilane)-block-poly(dimethylsiloxane) and polyisoprene-block poly(ferrocenylsilane) both of which formed “wormlike” cylindrical micelles upon slow evaporation from non-polar solvents.52 In both cases, the core of the micellar structures was the poly(ferrocenylsilane) block and the corona surrounding the core was either the poly(dimethylsiloxane) or the polyisoprene. This past year, the formation of spherical micelles upon oxidation of the ferrocenyl moiety in polystyrene-block-poly(ferrocenylsilane)s was reported.57 The Fe2centre of the poly(ferrocenylsilane) is oxidized using the one electron oxidant, tris(4-bromophenyl) ammoniumyl, which results in spherical micelles. The core is composed of the poly(ferrocenylsilane) block and the corona is composed of polystyrene; the authors attribute the self assembly behavior to an induced polarity change in the poly(ferrocenylsilane) block. This micelle formation can be reversed by one electron reduction of the Fe3 using decamethylcobaltocene. Two years after the discovery of living poly(ferrocenylsilane)s, a significant achievement in the development of phosphorus containing polymers was realized with the living anionic polymerization of a phosphorus-bridged [1]ferrocenophane (1.5) to form References start on page 28 Chapter 1 15 poly(ferrocenylphosphine)s (1.6).58 This work was analogous to the polymerization chemistry of compound 1.3 and block copolymers containing poly(ferrocenylphosphine)s have been investigated in earnest59 Remarkably, poly(ferrocenylphosphine) oligomerization was first reported in 1982 with oligomers up to five repeat units (1.6 where n=5) being observed (mass spectrometry).6° 1.’BuLi r Ph 2. H20 I —F’ ‘7Bu THF 25°C Hf n 1.5 1.6 Scheme 1.6 Living anionic polymerization of phosphorus bridged [1]ferrocenophane at ambient temperature using n-butyllithium. An important development for living inorganic polymerization was reported in 1995 by Allcock, Manners and co-workers.61’2They reported the living cationic polymerization of phosphoranimine 1.7 to prepare controlled polyphosphazene (1.8) structures. Polyphosphazenes are a very important class of inorganic polymer and have been well studied,36 They consist of an alternating phosphorus nitrogen backbone as illustrated in Scheme 1.7, where the phosphorus atom has an oxidation state of five with two pendant chloro substituents. The versatility of this polyphosphazene system lies in the ability to chemically substitute the two chloro groups very easily. In Scheme 1.7, the poly(dichlorophosphazene) 1.8 is treated with NaOCH2CF3to yield macromolecule 1.9. A wide range of substitution reactions are known for reactive P—Cl bonds and therefore a broad range of different polymer properties can be accessed from macromolecule 1.8. Moreover, since this pioneering development describing living phosphoranimine polymerization, a wide range of block copolymer architectures have been synthesized.637°Investigations in the field of polyphosphazenes are ongoing and the potential to use polyphosphazenes as drug delivery systems, flame retardant materials and fuel cell membranes continues to attract attention.71 References start on page 28 Chapter 1 16 CH2F3 Cl—N—SiMe3 _:3Cl fNf. NaOCH2CF3 CH2F3 1.7 1.8 1.9 Scheme 1.7 Living cationic polymerization ofCI3P=NSiMe using catalytic PCI5 resulting in the elimination of SiMe3Cl. Another significant synthetic achievement for living inorganic polymer preparation occurred in 1995 when Matsumoto and Yamaoka discovered that 1,1-dimethylsilacyclobutane 1.10 could be polymerized in the presence of BuLi or PhLi to prepare polycarbosilane 1.11 with controlled chain lengths.73The use of THF-hexane solvent mixtures at low temperatures (— 48 °C) were employed for the polymerization of 1.10 in a living manner. This remarkable report has resulted in some limited block copolymer work,7274 and the use of silacyclobutanes as “carbanion pumps”.7576 This carbanion pump reaction involves using the cyclic ring system 1.10 to prepare block copolymers from two incompatible monomers. Normally, in order to covalently link AB block copolymers, the reactive chain end of living polymer A must be a better nucleophile than the living chain end formed for the B block. The silacyclobutane ring-opening reaction is thermodynamically driven by the release of ring strain and therefore, ring-opening can proceed with weak nucleophiles to afford the strong nucleophile RCH2Li (Scheme 1.8). < Me ‘1BuLi Bu-L SiMe THE! hexane —48 °C LMI’L 1.10 1.11 1.10 monomer B —Li ‘Si(CH2)3Li I A Block A Block A Block B Block Scheme 1.8 Top — 1,1-dimethylsilacyclobutane living polymerization was initiated using n butyllithium in THF/hexane mixtures. The polymerization was conducted at low temperatures. Bottom — The I ,1-dimethylsilacyclobutane being utilized as a carbanion pump for block copolymer preparation. References start on page 28 Chapter 1 17 Finally, in 1997, the living anionic polymerization of vinyl ferrocene (compound t12) was reported.77 Polymerization of ferrocene-containing monomers by radical polymerization has attracted a great deal of attention for many years. Arimoto and Haven were the first to describe the radical polymerization of vinyl ferrocene and, since their work, the incorporation of the ferrocenyl organometallic moiety into polymers has become a fascinating point of study.7879 Nuyken and co-workers followed this original work with the successful living anionic polymerization of vinyl ferrocene (Scheme 1 .9). Studies outlining the synthesis of block copolymers using vinyl ferrocene and isobutylene as monomers have appeared recently.8081 HH 1 c=C Bu-I——CH2—CH-— I-Li H’ ‘7BuL1 Fe THF —45°C F 1.12 Scheme 1.9 Vinyl ferrocene living polymerization conducted at low temperature, in THF and initiated using n-butyllithium. Masked disilenes 1.13 have been polymerized in a living fashion but,82 cyclic tetrasilanes 1.14 have not been polymerized with a sufficiently narrow polydispersity to be considered strictly living.8384 Both of these methods are significant improvements upon the commonly employed Wurtz coupling to prepare polysilanes. The Wurtz strategy involves R2SiCI being treated with Na metal but it does not result in high yields of polysilane nor does it afford control over the molecular weight of the macromolecule. The efficient, high yielding methods to polysilanes outlined in Scheme 1 .10 offer a degree of control and can be used to incorporate polysilanes into more complex macromolecular architectures. A significant development was reported on helical polysilanes, as chirality is important for molecular recognition. Polysilane-b/ock poly(triphenylmethyl methacrylate) was synthesized (1.15) where the poly(triphenylmethyl methacrylate) block was prepared in the presence of (—) sparteine as this is known to induce helicity in polymers.85 Interestingly, below —20 °C the helical methacrylate component induces chirality in the polysilane block. This behavior was cycled reversibly using temperature.85 References start on page 28 Chapter 1 18 To the best of my knowledge, no other living polymerizations of inorganic monomers have been reported. Thus far, research in the area of controlled inorganic polymer synthesis has been primarily focused on ROP (ring-opening polymerization) or condensation polymerization. The controlled addition polymerization of vinyl ferrocene was a significant advance and it begs the question, can addition polymerization be expanded to multiple bonds other than C=C bonds? A potential route to inorganic polymers which has yet to be significantly explored is the addition polymerization of heavier element multiple bonds of the typeR2EE’R where one of either element E or E’ has N 3 (N = principal quantum number). In order to utilize these molecules as monomers for macromolecular synthesis, an investigation into their structure and bonding must be employed. R1_. _R2 R3 fl’R4 1.RL1 r231Si 2.MeOH RfSi-Si+H low ternp Li R4j 1.13 Me le 1.’7BuLi rM1 Ph—Si—Si—Ph 2.MeOH Bu-J-Si4H Ph—Si—Si—Ph I Phi MeMe L J 1.14 Me Me Hex,Hex 1 .‘BuLi [e He [ Me 1 “Bu-I-Si--Si C-C—H-H “ / 2. HC=K e Hex H ‘CPh3 CPh3(—) sparteine 3. EtOH Scheme 1.10 Anionic polymerization of masked disilenes and cyclic tetrasilanes using organolithium reagents. Block copolymerization of a masked disilene with triphenyl methyl methacrylate in the presence of sparteine induces helicity in the polymethacrylate segment. References start on page 28 Chapter 1 19 1.5 Inorganic Multiple Bonds Species containing multiple bonds have been of longstanding interest in chemistry. However, the preparation of multiple bonds with inorganic elements (principal quantum number greater than two) have been more difficult to synthesize than their organic counterparts.86These compounds display different physical and chemical properties than multiply bonded species involving lighter elements. They also display new and different bonding motifs that further the understanding of chemical bonding and structure. Many of the stable species isolated in the past 30 years with multiple bonds between heavy main group elements were originally thought to be unattainable because of the classical double bond rule. This rule implies that heavier element multiple bonds are not isolable because the (p-p)t interactions for E=E bonds (E has N > 2) are too weak.87 However, many species containing inorganic multiple bonds have been synthesized in the last 30 years, Figure 1.6 illustrates a few recent examples.86 \. / //SIC\ ,GeGe / / //Si=Si\ /P=P ,SnSn / //SiSi PC_ /BB Figure 1.6 Some of the recent achievements in heavier element main group multiple bonds. Much of the recent work on heavier element multiple bonds centers around establishing parallels to the well-known chemistry of olefins. Our research group is interested in extending addition polymerization protocols, a common route to polyolefins, to heavier element multiple bonds. This is an attractive route to introduce inorganic functionalities into macromolecular structures with the potential to discover materials exhibiting unique properties. However, one of the main reasons that widespread interest in polymerization ofR2E=ER bonds has been lacking are the large bulky substituents (R groups) normally required to render these monomers isolable. The (p-p)t interactions of heavier element multiple bonds are generally fairly weak making them thermodynamically unstable. Consequently, to make heavier element multiply References start on page 28 Chapter 1 20 bonded species isolable, a sterically encumbering R group surrounding the 3t bond is necessary to provide kinetic stabilization (Figure 1.7). Thus, increasing the steric congestion around the (p p)t bond results in a higher activation barrier (Ea) for these metastable species and allows for the isolation ofR2EER.From a polymer perspective, using big bulky R groups to prepare isolable R2E=ER molecules is also problematic as the activation barrier could be increased to a point which partially or completely inhibits any further reactivity of these compounds. In order to tap this vast resource of new monomers, a delicate balance where the R group supplies sufficient steric congestion to render isolation of E=E bonds possible but does not impede further reactivity must be obtained. From this standpoint, the potential to explore phosphorus containing double bonds (i.e, phosphaalkenes) seemed attractive, as these compounds have already been thoroughly investigated and exhibit some similarities to the reactivity of olefins.91 So the potential to expand this P=C, C=C analogy to polymer science seemed an intriguing possibility. References start on page 28 Chapter 1 21 Ea is large / R is large ER2 Ea :rn:ll —(R2)E-E(R Reaction Coordinate Figure 1.7 A reaction coordinate diagram representing the effect of a sterically unencumbered substituent versus a sterically bulky group on the activation barrier ofR2E=ER molecules. 1.5.1 The analogy between PC and C=C bonds Köhler and Michaelis were the first to report their attempt at the isolation of phosphorus- containing multiple bonds. They described the isolation of PhP=PPh (phosphobenzene) in 1877 but this was later shown to be the cyclic oligomer (PhP)5 or 6.92 The first discovery of a stable P=C bond was 2,4,6-triphenylphosphabenzene (1.16), discovered by Markl in 1966. However, this compound was isolable based not only on kinetic stabilization but also on thermodynamic stability imparted by the 3t-delocalized ring structure. Becker and co-workers were the first to prepare a stable acyclic phosphaalkene in 1976 using silatropic migration as the driving force for the preparation of compound 1.17.’ Since this work, a number of different routes have been utilized to prepare a host of kinetically stabilized phosphaalkenes.998 References start on page 28 Chapter 1 22 Ph ,OSiMe3 PhPh 1.16 1.17 Scheme 1.11 The first cyclic and acyclic phosphaalkenes that were stable and isolable at room temperature. The isolation of stable phosphaalkenes has prompted investigation into their reactivity and it was discovered that the phosphaalkenes mimic the chemistry of olefins in many respects.9199 These similarities have led to phosphorus being dubbed “the carbon copy”.91 There are some limitations to this analogy which generally arise from interference of the lone pair located on the phosphorus atom or from the higher energy P=C 3t bond as compared to the CC t bond. However, coordination of the lone pair to metal fragments such as W(CO)5can circumvent some of these limitations. Several interesting examples where P=C bonds mimic the behavior of olefins are discussed below. A 1 ,2-addition reaction has been described where electrophiles such as HBr can be added across the P=C bond of compound 1.18 (Scheme 1.12 —Top).’°° Because P is slightly electropositive compared to C (P÷=C), the proton becomes attached to the C atom of the P=C bond and the Br is bound to the phosphine moiety, as expected. Another interesting parallel between P=C and C=C bonds is the Diels-Alder reaction. This [4+2] cycloaddition has been used to trap unstable phosphaalkenes generated in situ,101 for example, CIP=C(TMS)2(1.19) can be prepared and will go on to act as the dienophile in the cycloaddition with 1.20 forming the cyclic phosphine 1.21 (Scheme 1.12— Middle). The formation of these cyclic structures using phosphaalkenes is not limited to [4+2] reactions, and many other cyclizations have been reported.10°Another illustration of the P=C, CC parallel involves a 1,2 elimination to prepare phosphaalkynes. The treatment of compound 1.22 with hydroxide results in the elimination of hexamethyldisiloxane to prepare phosphaalkyne 1.23,.98 The tert-butyl phosphaalkyne displays fascinating parallels to the chemistry of alkynes but this is beyond the scope of this thesis and will not be discussed further.91 References start on page 28 Chapter 1 23 — Br HBr Br—P—CHBr2Mes* Br Mes* 1.18 p=c3 ‘‘—OS1Me3 Cl S1Me3 Cl- 1.19 1.20 OSiMe3 0HP=c’ PCLBu Me3SI Bu Me3SiOSIMe 1.22 1.23 Scheme 1.12 Phosphaalkenes mimicking the reactivity of olefins. Top — 1,2-addition of HBr across the P=C bond of the sterically hindered Mes*P=CBr2. iddle — Diels-Alder reaction to trap the unstable compound CIP=C(SiMe3)2resulting in the formation of a cyclic phosphine. Bottom — 1,2-elimination of theMSIP=C(OSiMeBu)phosphaalkene to form the tbutyl phosphaalkyne. Treatment of the four-coordinate phosphaalkene 1.24 with m-chloroperoxybenzoic acid (m-CPBA) will induce an epoxidation-type reaction forming the 3-membered cyclic ring structure 1.25.102 Interestingly, this reaction will not occur without the presence of the W(CO)5moiety to complex the lone pair of the phosphorus atom. All of the examples described in this section illustrate the close reactivity mimic which exists between P=C bonds and C=C bonds. Can this PCICC bond analogy be extended to polymer science? Proper selection of monomer would be crucial in the potential success of this research. (CO5)W ,CHMe2 (CO)5W 5. ,CHMe ,P=Cs P—C Mes H Mel ‘H 1.24 1.25 Scheme 1.13 Formation of epoxide analogs by reaction of a complexed P=C compound with m-chloroperoxybenzoic acid. ;iMe3 1.21 References start on page 28 Chapter 1 24 1.6 Previous Research into the Addition Polymerization of P=C Bonds Initially, efforts in the Gates’ group were focused on the cationic polymerization of Mes*P=CH2(1.26). This phosphaalkene (1.26) is synthesized by combining Mes*PH2and CH2I in the presence of KOH.103 Cationic initiators such as GaCI3 and HOTf were employed to prepare polymers but unfortunately, stoichiometric combination of Mes*P=CH2with GaCl3 resulted in C-H activation of a methyl group on Mes* and the formation of compound 1.27.104 105 The combination of phosphaalkene 1.26 with HOTf yielded positive results with oligomers up to six repeats units being observed, however, larger molecular weight materials could not be obtained. H HHtBU “‘ GCI LBu\ a \ $P-ce H GaCl \/ tBu LBU MeMe 1.26 1.27 Scheme 1.14 Intramolecular C-H activation of Mes*P=CH2in the presence of the Lewis acidic GaCl3 species. Given the tendency of compound 1.26 to C-H activate, we turned our attention to the MesP=CPh2(1.28) phosphaalkene. Compound 1.28 has been synthesized using two different synthetic routes: by a phospha-Peterson reaction and by a 1,2-elimination reaction.106 107 The base catalyzed phospha-Peterson reaction involves treatment of MesP(SiMe3)2with benzophenone in the presence of catalytic NaOH or KOH to form the desired 1.28.106108 The MesP(SiMe3)2compound is prepared from literature procedures starting from commercially available PCI3 (Scheme 1.1 5)109 110 The 1,2-elimination procedure outlined by Bickelhaupt and co-workers is illustrated in Scheme 1.16, where, compound 1.29 is treated with the basic 1,5- diazabicyclo[5.4.O]undec-5-ene (DBU) to afford phosphaalkene 1.28. Importantly, in the same paper, the attempted isolation of a P=C bond where the mesityl (2,4,6-trimethylphenyl) group was replaced by o-methylphenyl (o-C6H4Me) did not yield phosphaalkene but led to the isolation of polymeric material. This suggested that MesP=CPh2may be reactive enough to polymerize under appropriate conditions. References start on page 28 Chapter 1 25 1.MeLi PCI3 MesMgBr MesPCl2 LJA1H4 MesPH2 ..7: MesP(SiMe3) THE ether THE Ph2C=O Ph MesP(SiMe3)2 25°CTHF Mes Ph 1.28 Scheme 1.15 Preparation of the MesP=CPh2phosphaalkene from commercially available PCI3. The phospha-Peterson reaction is employed as the final step to prepare the desired MesP=CPh2phosphaalkene. Ph Ph MesPCI2 LiC(H)(Ph)2 Mes—P—C—Ph DBU CIH Mes Ph 1.29 1.28 Scheme 1.16 Preparation of the MesP=CPh2phosphaalkene from treatment of MesP(CI)(CPh2H with 1, 5-diazabicyclo[5.4.O]undec-5-ene (DBU). Further evidence to support the theory of P=C bond polymerization was provided when stoichiometric combination of compound 1.28 and MeLi followed by combination with MeOH and air oxidation afforded compound 1.30. These results suggest that nucleophilic attack is possible at the P=C bond of the phosphaalkene (Scheme 1.17).hhl Following this important study to prepare compound 1.30, treatment of 1.28 with substoichiometric amounts of either anionic or radical initiators resulted in the synthesis of the remarkable —[MesP—CPh2] macromolecule 1.31 with alternating phosphine and carbon moieties (Scheme 1.17).20 Ph 1. MeOH 0 Ph “‘‘ MeL1 I 2. H20 HPC Me-P—C—Li Me—P—C—H / ‘ I I IMes Ph MesPh MesPh 1.28 1.30 anionic or radical r Phinitiators I ‘ —hP-C 150°C [MesPh 1.31 Scheme 1.17 Reaction of MesP=CPh2phosphaalkene with anionic MeLi and subsequent oxidation to afford a methyl mesityl phosphine oxide. Polymerization of MesP=CPh2using radical or anionic initiators at high temperature (ca. 150 °C). References start on page 28 Chapter 1 26 The functional phosphine moiety of the poly(methylenephosphine) can be oxidized, sulfurized and it can be used as a ligand for metal-catalyzed Suzuki cross-coupling 20, 112 To polymerize phosphaalkene 1.28, high temperatures (up to 150 °C), long reaction times (ca. 24 h) and minimal solvent were employed. Under these conditions, low monomer conversions and several unidentified phosphorus byproducts were observed which resulted in poor isolated yields of the poly(methylenephosphirie). It was of interest for our group to expand upon this work and search for cleaner, milder routes to these phosphine polymers. Recently, addition polymerization of inorganic multiple bonds has seen a significant step forward with the polymerizarion of Ge=C bonds (1.32) using tBuLi to afford polycarbogermanes 1.33.113 The polymer was isolated as an air stable material, in reasonable yield (45 %), with modest molecular weight (M = 36,000 g/mor1,PDI =1.5). The potential to form a variety of new copolymers incorporating Ge atoms is an exciting synthetic target within this research. Mes H liBuLi EMes H 12.MeOH Me ‘CH2 [Ms CH2J tBU 1Bu 1.32 1.33 Scheme 1.18 Polymerization of a Ge=C compound using tert-butyllithium as the anionic initiator to form polycarbogermanes. 1.7 Outline of Thesis With the discovery of addition polymerization of P=C bonds by Gates and co-workers, the application of living polymerization techniques to these inorganic multiple bonds is a logical extension for expanding upon the class of copolymers which could be prepared incorporating functional phosphine units. The application of living techniques to control the preparation of poly(methylenephosphine)s is outlined in Chapter Two. To illustrate the potential of this powerful polymerization technique, the preparation of a block copolymer, polystyrene-block poly(methyleriephosphine) is also described in that same chapter. Chapter Three describes kinetic investigations into the living polymerization of P=C bonds. Apparent rate constants and an apparent activation energy of polymerization were extracted. Chapter Four details the References start on page 28 Chapter 1 27 synthesis and solution self-assembly properties of polyisoprene-block poly(methylenephosphine) copolymers which have been coordinated to a AuCI moiety. Chapter Five describes some of the developments surrounding poly(methylenephosphine)s and their chemistry with several isoelectronic main group electrophiles (CH3 and BH3). Chapter Six outlines the synthesis and polymerization of a ferrocene-containing phosphaalkene. Chapter Seven, details the preparation and polymerization of several new phosphaaalkenes in an attempt to expand upon the generality of P=C bond polymerization. Chapter Eight provides a synopsis of the thesis findings and describes some possible research directions in the future. 1.8 Contributions by Other Researchers to This Work Several projects in this thesis were done in collaboration with other researchers and these people are listed in the Statement of Co-Authorship (xxi). For Chapters Two, Three and Six all synthetic work was completed by myself. Chapter Four was a collaborative effort between myself, Bronwyn Gillon and Dr. Vittorio Cappello. Two of the copolymers were prepared solely by myself and one was prepared in collaboration with Dr. Cappello, the Au(l) coordination to the polymer was realized by Bronwyn and Dr. Cappello whilst the TEM images were a collective effort of all three researchers. 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W.; Baharloo, B.; Riendi, D.; Yam, M.; Gates, D. P. Angew. Chem. mt. Ed. 2004, 43, 5682. 113. Pavelka, L. C.; Holder, S. J.; Baines, K. M. Chem. Commun. 2008, 2346. References start on page 28 34-49 Chapter 2 Ambient-Temperature Living Anionic Polymerization of Phosphaalkenes: Homopolymers and Block Copolymers with Controlled Chain Lengths* The material pertaining to this Chapter has been removed due to copyright restrictions. The Chapter describes the extension of living anionic polymerization techniques to P=C bonds. Experiments performed to confirm the living polymerization behavior of MesP=CPh2include: kinetic investigations of P=C bond polymerization, molecular weight versus conversion plots to confirm that molecular weight increases linearly with conversion and control of the polymer chain length by controlling the concentration of initiator. This new methodology has been used to prepare unprecedented polystyrene-block-poly(methylenephosphine) copolymers with narrow polydispersities and controlled molecular weights. This material is available at http://www3.interscience.wiley.com *Aversion of this chapter has been published. Kevin J. T. Noonan and Derek P. Gates. Ambient temperature living anionic polymerization of phosphaalkenes: homopolymers and block copolymers with controlled chain lengths. Angew. Chem. Intl. Ed. 2006, 45, 7271. 50 Chapter 3 Studying a Slow Polymerization: A Kinetic Investigation of the Living Anionic Polymerization of P=C bonds* 3.1 Introduction In establishing the living nature of PC bond polymerization as described in Chapter 2,1 an apparent rate constant of polymerization at room temperature using 2 mol % initiator was determined. Further investigations to extract kinetic parameters of this slow polymerization are described in this Chapter. Some background information on C=C bond polymerization kinetics is also presented for comparison. Detailed kinetic investigations of living anionic olefin polymerization, particularly with styrene, have allowed for the determination of activation parameters for propagation.2’3The effects of solvent (coordinating and non-coordinating), counterion (i.e, Li, Nat, etc) and temperature on the rates of propagation of styrenic monomers have formed the basis for the textbook models of the mechanism of living anionic polymerization.41The living anionic polymerization of alkenes proceeds via a two-step mechanism.12The initiation step involves addition of a nucleophilic species, such as n-butyllithium, to the C=C bond of monomer A forming the propagating species B (Scheme 3.1). Compound B, which resembles n-butyllithium in terms of its nucleophilicity, then repeatedly adds to the C=C bond of another monomer A forming polymer C. In the absence of monomer, living polymer C will rest indefinitely but can be terminated by controlled addition of an electrophile (i.e. H). When the rate of initiation is much faster than the rate of propagation, the rate equation can be expressed as shown below (Equation I). Typically, this equation is followed when the polymerization experiment is conducted in polar solvents. The rate constant of propagation is represented by k, [living ends] *A version of this chapter has been published. Kevin J. T. Noonan and Derek P. Gates. Studying a Slow Polymerization: a Kinetic Investigation of the Living Anionic Polymerization of P=C bonds. Macromolecules. 2008, 41, 1961. Chapter 3 51 stands for the concentration of the propagating polymer species that remains constant throughout the polymerization, and [M] represents the concentration of monomer A. \ / n-i c=c r 1 ‘7BuLi ‘7Bu—C—C---Li / “ nBu—LC—C_LU / \ k Lii n A B C Scheme 3.1 Living polymerization of alkenes. —d[M] dt = k ‘[living ends]• [Ml The development of synthetic routes to main chain phosphorus polymers is a vibrant area of research due to the potential applications of phosphorus materials as sensors, catalyst- supports, ceramic precursors, and biomedical materials.’23The successful extension of addition polymerization to P=C bonds D 24 (Scheme 3.2) forming poly(methylenephosphine)s E and the subsequent ambient temperature living anionic polymerization of MesP=CPh2,’are new contributions to the growing research on phosphorus-containing polymers. The living anionic polymerization of P=C bonds necessitates further investigation as this tool will enable the preparation of new macromolecules incorporating phosphorus atoms. In order to further understand this living polymerization, kinetic experiments were conducted to analyze the propagation step of P=C bond polymerization. Initiator _p/ \ [Ii D E Scheme 3.2 The addition polymerization of a phosphaalkene to obtain poly(methylenephosphine). We propose that both the initiation and propagation steps in the anionic polymerization of P=C bonds involve nucleophilic addition of a lithium carbanion (i.e. GuLi or 3.2) to the P=C bond in a regioselective fashion (Scheme 3.3).’ 25 This postulate is supported by molecular model studies where addition of MeLi to compound 3.1 affords Mes(Me)P—CHPh2after References start on page 62 Chapter 3 52 quenching with MeOH. These observations agree with the calculated polarity of the P=C bond in normally polarized phosphaalkenes (P8+ C).27 Moreover, the active growing species (i.e. 3.2 and 3.3) are doubly-benzylic carbanions which offer substantial st-stabilization by delocalization onto the aryl substituents and onto the phosphorus atom. Initiation Ph Ph flDI I “Bu—P—C—Li Mel ‘Ph glyme, 25- 50 °C Mes Ph 3.1 3.2 Propagation Ph Ph fl 1 ,P=C F Phi I Mes Ph I 1 “Bu—P—C—Li “Buj—P—C--f Li I I I I MesPh [MesPh fl 3.2 3.3 n=25 or 50 Controlled Termination MeOH t1BuEP_&}HMes Ph Mes Ph n n 3.3 3.4 Scheme 3.3 Proposed initiation, propagation and termination steps in the living anionic polymerization of phosphaalkene MesP=CPh2using n-butyllithium as initiator. In this chapter, the first kinetic studies of the living anionic polymerization of PC bonds are described. Apparent rate constants of propagation are measured and estimated by following the consumption of [3.1] and formation of [3.3] using 31P NMR data collected over a 9 h period. Moreover, kinetic experiments were conducted at several temperatures to elucidate the activation energy for polymerization propagation. References start on page 62 Chapter 3 53 3.2 Results and Discussion 3.2.1 Procedure employed to conduct kinetic studies of MesPCPh2phösphaalkene polymerization To study the kinetics of the living anionic polymerization of C=C bonds, specialized capillary tube stop flow techniques are often employed to measure the rates of these rapid reactions.28 In contrast to olefin polymerizations, which have half lives of seconds to minutes, the half life of phosphaalkene polymerization is several hours. Consequently, the anionic polymerization of 3.1 can be conveniently monitored using 31P NMR spectroscopy. All kinetic experiments performed in this Chapter were conducted as follows: 1. Monomer 3.1 was dissolved in glyme in an inert atmosphere 2. BuLi was added to this solution and an immediate color change from yellow to red was observed upon initiation (50:1 monomer to initiator ratio). 3. The reaction mixture was transferred to an NMR tube and 31P NMR spectra were recorded at 15 mm intervals. The two acquisition parameters of the NMR spectrometer, (i) relaxation delay and (ii) tip angle, were set to ensure that the integration of the 31P NMR spectra were reliable (d1 = 2 sand 300 tip angle). The relaxation time (T1) of the phosphorus atom in the MesP=CPh2monomer was measured prior to conducting this kinetic analysis to ensure adequate delay time for complete relaxation between data acquisition (T1 = 1.33 s). This ensures that integrations are reliable. Relaxation times (T1) for polymer 3.3 is not a concern as macromolecules relax much faster on the NMR timescale than molecular compounds. Representative 31P NMR spectra from the BuLi polymerization of 3.1 at 296.3 K are shown in Figure 3.1. In each spectrum, the signals assigned to the monomer 3.1 (ô31p = 233) and the growing polymer 3.3 (ô31p —7 ) were integrated separately and, using the known initial concentration of 3.1, the percent conversion was calculated. Under otherwise identical conditions, 31P NMR experiments were performed at 296.3 K, 301.8 K, 307.4 K, 313 K, 318.6 K, 324.2 K. Upon completion of the polymerization as References start on page 62 Chapter 3 54 determined by 31P NMR spectroscopy, the polymer 3.3 was quenched with methanol (0.1 mL), precipitated with hexanes (2 x 40 mL), and analyzed by triple-detection GPC. The molecular weights, which are listed in Table 3.1, were used to confirm that the polymer chain length correlated closely with the initiator concentration. Each experiment was repeated at least twice to ensure reproducibility. Although there was some variation in the observed molecular weights, the propagation rate constants determined were reproducible, within error, at each temperature. 3.1 I 3.3 t=7h - t=6h - - t=5h — - - t4h — - t=3h ______________________________ t=2h 200 ido 6 -lao -200 ppm Figure 3.1 Selected 31P NMR spectra (glyme; 296.3 K) of the BuLi initiated polymerization mixture showing the conversion of 3.1 to 33 over time ([Monomer]:[lnitiator] = 50:1). [M0] = 0.394 mol L1. 3.2.2 Determination of rate constant of propagation (kr) at different temperatures for MesP=CPh2polymerization The living polymerization of C=C bonds follows pseudo first order reaction kinetics (equation I) with [living ends] remaining constant throughout the polymerization and [M] decreasing over time.12 Therefore, if the living anionic polymerization of 3.1 is analogous to that of CC bonds, a plot of In [M]0/[ vs. time should be linear. At all temperatures, the propagation data collected is linear up to Ca. 50% conversion (Figure 3.2). The rate constant of propagation (kr) was determined by least-squares fitting the data at each temperature and the results are given in Table 3.1. Remarkably, the k for 3.1 (k = 21.0 ± 2.5 L moM h’ at 296.3 K) is several References start on page 62 0 . . . . . 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 Time (h) Figure 3.2 A graph showing In [M]J[M] versus time (h) up to —50% conversion for the polymerization of 3.1 with 2% BuLi at approximately 5 K temperature intervals between 296 and 324 K. These plots of In [M]d[M] versus time (h) were fitted to a linear least squares function to determine rate constants illustrated in Table 3.1. Chapter 3 55 orders of magnitude smaller than that observed for the sodium naphthalide initiated polymerization of styrene in THF at room temperature (k = 1.4 x 106 — 2.2 x 106 L mol1 h_i).4 Since MesCH=CPh2has not been polymerized, the closest steric comparison for 3.1 that we have come across is vinylmesitylene. Importantly, the rate constant for polymerization of H2C=CHMes in THF using sodium naphthalide (k = 1.210 L moM h’) is several orders of magnitude slower than styrene,6 which is attributed to larger steric constraints imposed by a mesityl group as compared to a phenyl group. 0.9 0.8 0.7 0.6 0.5 0 & 0.4 0.3 0.2 0.1 x A • 296.3 K • 301.8 K 307.4 K x 313.0 K x 318.6 K 324.2 K References start on page 62 Chapter 3 56 Table 3.1 Determination of k at different temperatures for MesP=CPh2. Entry [M]:[l]a Temperature (K) (L moV1 1r) Mncculaedc M observ?dd PDI I 50:1 296.3 21.0±2.5 15900 13500 1.07 2 50:1 301.8 32.7±3.9 15900 15100 1.02 3 50:1 307.4 41.8±4.9 15900 13800 1.05 4 50:1 313.0 70.7±8.9 15900 14400 1.09 5 50:1 318.6 125± 15 15900 12300 1.07 6 50:1 324.2 150± 17 15900 13600 1.05 7 50:2 296.3 15.3 ± 1.9 8000 8800 1.09 2[MesP=CPh]:[BuLiJ. brate constant of propagation. cCalculated using the monomer to initiator ratio. dMolecular weights were determined using triple detection GPC. 3.2.3 Determination of activation energy (Ea) of propagation for P=C bond polymerization The rate constant data was used to prepare an Arrhenius plot (Arrhenius equation displayed below: Equation II) from which the apparent activation energy (Ea) of the polymerization was extracted (Figure 3.3), The Ea for the anionic polymerization of 3.1 in glyme was calculated to be 14.0 ± 0.9 kcal mor1 and the preexponential factor (A = 4.4 x 1011) was also obtained. Interestingly, this activation barrier is much larger than the Ea measured for styrene polymerization in THF with Na counterion (Ea = 5.9 kcal mor1).23°For comparison, bulky substituted olefins have higher activation barriers and, therefore, slower polymerization rates. For example, the sterically hindered monomer ct-methylstyrene (E2 = 7.2 kcal mor’’) has a higher activation energy than styrene.3The high activation barrier in the anionic polymerization of 3.1 is almost certainly a consequence of the high degree of steric bulk surrounding the PC bond and, in addition, the propagating polymer species 3.3 is highly resonance stabilized, lowering its nucleophilicity. k’” — A Ea IRTe (II) References start on page 62 Chapter 3 57 5.5 5 4.5 4 3.5 3 25 3.05 3.10 3.15 120 3.25 3.30 3.35 3.40 liT (Kjx 1O Figure 3.3 An Arrhenius Plot was constructed from the linear least squares fit of In k versus lIT (K1). Error bars are reported to 3a. The linear least squares function (y = -7051.5x + 26.811) had an R2 value of 0.9841. 3.2.4 Rate behavior changes observed above 50% conversion Although rate constant data may be extracted, the plots of In [M]J[M] vs. time in the anionic polymerization of 3.1 only exhibit pseudo first order kinetics up to Ca. 50% conversion. Thereafter, a deviation from linearity is observed (Figure 3.4). For comparison, the anionic polymerization of styrene and a-methylstyrene exhibit linear behavior up to 90% Although for styrene the conversion rate decreases as the monomer is consumed, the rate of propagation actually increases above 50% conversion for 3.1. Interestingly, at higher polymerization temperatures the expected behavior is observed and the rate of propagation for 3.1 slows above 50% conversion. Particularly striking is the experiment conducted at 324.2 K that appears almost linear up to —80 % conversion. To our knowledge, an increase in rate at high conversion has not been observed for the living anionic polymerization of C=C bonds and suggests a more complex mechanism for the P=C system.31 References start on page 62 Chapter 3 58 3.5 3 N 2.5 N * B A I 2 * A 1.5 N z 1 ‘“ ‘ •296.3K N .301.8K jAil A3074K Q5 Z es x313.OK X318.6K 324.2K 0 1 2 3 4 5 6 7 8 9 Time (h) Figure 3.4 A plot of In [M]01[M vs. time (h) up to —90% conversion for the polymerization of MesP=CPh2with 2% BuLi at ca. 5 K temperature intervals between 296 — 324 K. In the polymerization of olefins, the observed or apparent rate constant k in polar solvents is actually composed of two different rate constants (equation III).12 Due to solvation phenomena, the rate equation must be rewritten in terms of, the free-ion rate constant (kr) and the ion-pair rate constant (k°). Both rate constants are expected to contribute to the rate of propagation for unsaturated bonds, however this contribution is not equal, especially in polar solvents. Consequently, increasing the number of ions in solution (i.e. increasing [living ends]) will affect the ion-pair free-ion equilibrium (i.e. [free-ion chain ends] and [ion-pair chain ends]) and alter the apparent rate of propagation k. A preliminary experiment was conducted to test whether this applies to the polymerization of 3.1 in glyme. Under otherwise identical conditions, the anionic polymerization of 3.1 was conducted with double the concentration of BuLi ([M]:[l] = 50:2) than that used in all other experiments (Table 3.1, entry 7). If only equation I applied, the reaction rate should be identical for both experiments. However, as predicted by equation III, polymerizations with a higher concentration of living ends results in a lower propagation rate constant (k = 15.3 ± 1.9 L mol 1 h1) as compared to the experiment with 2% References start on page 62 Chapter 3 59 initiator (k = 21.0 ± 2.5 L mol 1 h1) at 296.3 K. Future work will focus on determining kr and by conducting polymerizations with excess counterion (Li). — ‘MI = k[free - ion chain ends] [M] + k’[ion - pair chain ends] [M] (Ill) 3.3 Conclusions In summary, a kinetic investigation of the n-butyllithium initiated living anionic polymerization of MesP=CPh2has been completed. Rate constants over a 25 K range were obtained and used to determine an activation energy for the anionic polymerization of MesP=CPh2(14.0 ± 0.9 kcal mor1). This activation energy is significantly higher than that of styrene (5.9 kcal moE1)and a-methylstyrene (7.2 kcal moE1). This large activation energy is most likely a product of the bulky substituents (Mes and Ph) surrounding the P=C bond and the doubly stabilized carbanion formed during polymer propagation. Future work will focus on collecting kinetic data for other P=C monomers which polymerize in a living fashion. 3.4 Experimental 3.4.1 Materials and General Procedures Hexanes was dried by passing through activated alumina columns.32 I ,2-Dimethoxyethane (glyme) was distilled from sodium/benzophenone and was degassed under vacuum at —196 °C prior to use.33 MeOH was degassed by passing nitrogen through the solvent for 1 h prior to use. BuLi (1.6 M in hexarie) was purchased from Aldrich and was titrated with n-benzylbenzamide prior to use.34 MesP=CPh2was prepared according to literature procedures.35Allmanipulations of air and/or water sensitive compounds were performed under pre-purified nitrogen (Praxair, 99.998%) using standard high vacuum or Schlenk techniques or in an Innovative Technology glovebox. 31P NMR (121.5 MHz) spectra were recorded at room temperature on a Bruker References start on page 62 Chapter 3 60 Avance 300 MHz spectrometer. Chemical shifts are reported relative to 85% H3P04as an external standard ô = 0.0 for 31P. The relaxation time (T1) for 3.1 is 1.33 s. To ensure accurate integrations, a relaxation delay of 2 s with a 300 tip angle was employed for all 31P NMR experiments. Temperature was calibrated for NMR experiments using standard Bruker samples: 4 % MeOH in MeOH-d4for the 194-283 K range and 80 % ethylene glycol in DMSO-d6for the 300-400 K range. 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) HR5E (2 000 —4 000 000), HR4 (5 000 — 500 000) and HR2 (500 — 20 000), Waters 2410 differential refractometer (. = 920 nm), Wyatt tristar miniDAWN (laser light scattering detector operating at = 690 nm), and a Wyatt ViscoStar viscometer. A flow rate of 0.5 mL m1n1was used and samples were dissolved in THE (ca. 2 mg mL1). The refractive index increment of poly(methylenephosphine) 3.4 (dn/dc = 0.223 mL g1) was determined by plotting the refractive index vs. concentration for six solutions of 3.4 in THF (1 — 6 mg mL1). Aqueous NaCI was used to calibrate the Waters 410 Differential Refractometer. 3.4.2 Purification of MesPCPh2(3.1) Crude 3.1 was transferred to a short path distillation apparatus and was heated under vacuum with an oil bath (190 °C, 0.01 mm Hg). The yellow liquid distilled between 150—160°C and the distillate was recrystallized from hexanes. The crystalline solid was ground up into a fine powder using a mortar and pestle and was subsequently dried in vacuo for 12 h at 60 °C. 1H NMR was used to confirm purity. 3.4.3 Anionic polymerization of MesP=CPh2for kinetic studies. A solution of BuLi (12 tL, 1.37 M, 0.016 mmol) in hexanes was added to a stirred solution of 3.1 (0.250 g, 0.790 mmol) in glyme (2 mL) in the glovebox. Immediately after mixing, an aliquot was removed from the reaction mixture and was transferred to an NMR tube. The sample was References start on page 62 Chapter 3 61 loaded into the spectrometer (T = 296.3 K) and 31P NMR spectra were recorded every 15 mm (72 scans) until the reaction was complete. At completion, the living polymer was terminated by the addition of one drop of degassed MeOH (0.1 mL) and the polymer was isolated by precipitation into hexanes (2 x 40 mL) under N2. The purified polymer was dried in vacuo (4 h at 100 °C). GPC (absolute): M = 13 500 g mor1, PDI = 1.07. Experiments were repeated at least two times at each temperature to ensure reproducibility. 3.4.4 General procedure for processing 31P NMR spectra. The raw NMR data, obtained as described above, were processed using line broadening settings of (LB = 10) and a baseline correction was applied. The sharp signal for 3.1 (ô31p = 233) and the broad signal for 3.2 and 3.3 (ô31p = —7) were integrated using approximate ranges between 250 and 210 ppm and between 30 and —75 ppm, respectively. The relative integrations, after phasing, were used to determine the percent conversion of monomer to polymer and, consequently, the average concentration of monomer [M] during the acquisition of each spectrum. In each case, the first NMR experiment was started 13.5 mm after initiation. Since the acquisition time for 72 scans requires 3 mm, the time (t) for the first data point is 15 mm (0.25 h). The delay time between NMR experiments was 12 mm which results in data points at t = 30, 45, 60 mm, etc. The data is tabulated in Appendix B. References start on page 62 Chapter 3 62 3.5 References 1. Noonan, K. J. T.; Gates, D. P. Angew. Chem. mt. Ed. 2006, 45, 7271. 2. Shimomura, T.; Tolle, K. J.; Smid, J.; Szwarc, M. J. Am. Chem. Soc. 1967, 89, 796. 3. Comyn, J.; Dainton, F. S.; Harpell, G. A.; Hui, K. M.; Ivin, K. J. J. Polym. Sd. Part B: Polym. Lett. 1967, 5, 965. 4. Bhattacharyya, D. N.; Lee, C. L.; Smid, J.; Szwarc, M. J. Phys. Chem. 1965, 69, 612. 5. Bhattacharyya, D. N.; Lee, C. L.; Smid, J.; Szwarc, M. Polymer 1964, 5, 54. 6. Shima, M.; Bhattacharyya, D. N.; Smid, J.; Szwarc, M. J. Am. Chem. Soc. 1963, 85, 1306. 7. Lee, C. L.; Smid, J.; Szwarc, M. J. Am. Chem. Soc. 1963, 85, 912. 8. Geacintov, C.; Smid, J.; Szwarc, M. J. Am. Chem. Soc. 1962, 84, 2508. 9. Geacintov, C.; Smid, J.; Szwarc, M. J. Am. Chem. Soc. 1961, 83, 1253. 10. Worsfold, D. J.; Bywater, S. Can. J. Chem. 1958, 36, 1141. 11. Worsfold, D. J.; Bywater, S. J. Polym. ScL 1957, 26, 299. 12. Muller, A.H.E. In Comprehensive Polymer Science Vol 3; Allen, G.; Bevington, J. C.; Eds.; Pergamon, Oxford, 1989, Vol 3. 13. Cho, S. Y.; Alicock, H. R. Macromolecules 2007, 40, 3115. 14. Clark, T. J.; Lee, K.; Manners, I. Chem. Eur. J. 2006, 12, 8634. 15. Durben, S.; Dienes, Y.; Baumgartner, T. Org. Lett. 2006, 8, 5893. 16. Baumgartner, T.; Reau, R. Chem. Rev. 2006, 106, 4681. 17. Sebastian, M.; Hissler, M.; Fave, C.; Rault-Berthelot, J.; Odin, C.; Reau, R. Angew. Chem. Int. Ed. 2006, 45, 6152. 18. Wright, V. A.; Patrick, B. 0.; Schneider, C.; Gates, D. P. J. Am. Chem. Soc. 2006, 128, 8836. 19. Carriedo, G. A.; Alonso, F. J. G.; Valenzuela, C. D.; Valenzuela, M. L. Macromolecules 2005, 38, 3255. 20. Jin, Z.; Lucht, B. L. J. Am. Chem. Soc. 2005, 127, 5586. References start on page 62 Chapter 3 63 21. Smith, R. C.; Protasiewicz, J. D. J. Am. Chem. Soc. 2004, 126, 2268. 22. Smith, R. C.; Urnezius, E.; Lam, K. C.; Rheingold, A. L.; Protasiewicz, J. D. lnorg. Chem. 2002, 41, 5296. 23. Wright, V. A.; Gates, D. P. Angew. Chem. mt. Ed. 2002, 41, 2389. 24. Tsang, C. W.; Yam, M.; Gates, D. P. J. Am. Chem. Soc. 2003, 125, 1480. 25. Gillon, B. H.; Gates, D. P. Chem. Commun. 2004, 1868. 26. 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. 27. Mathey, F. Angew. Chem. mt. Ed. 2003, 42, 1578. 28. Odian, G., Principles of Polymerization, 4th Edition. Wiley: New York, NY, 2004. 29. A report with the rate constant (k = 3.3 x 1 L moE1h1) for vinyl mesitylene has been reported. Bhattacharyya, D. N.; Smid, J.; Szwarc, M. J. Polym. Sci.: Part A: Polym. Chem. 1965, 3, 3099. 30. The activation energy reported was determined for free polystyryl anions in THE. Solvent has a significant affect on the activation energy as it affects the free-ion to ion- pair equilibrium discussed in the text. For example, in a solvent such as dioxane, the polymerization of styrene proceeds with a much lower rate constant (k 4 L mor1 _1) and has a higher activation energy (Ea = 9 kcal/mol). This slower rate is likely due to lower concentration of free-ions than in a polar solvent such as THE. Szwarc, M., Carbanions, Living Polymers, and Electron Transfer Processes. lnterscience: New York, 1968. 31. Upon careful examination of the 31P NMR spectra of the BuLi-initiated polymerization of 3.1 in glyme reveals two unassigned signals (5 = —29 and -102). By comparison to the chemical shift of the anion model Mes(Bu)P-CPh2Liwhich resonates at —31.1 ppm in THE,(ref 34) we speculate that the resonance observed at —29 ppm corresponds to species 3.3. The high field signal at —102 ppm is much more difficult to rationalize. However, based on the high field chemical shift observed, we tentatively assign this References start on page 62 Chapter 3 64 species to the phosphide moiety of Me[MesP—CPh2]C h—PMesLi which would result from that reverse addition of 3.3 to 3.1 during propagation. NOTE: This species is <<1% of total phosphorus. For comparison, Mes*P(H)Li has been previously prepared by Cowley and coworkers and resonates at -110 ppm (THF) in the 31P NMR spectrum (Cowley, A. H.; Kilduff, J. E.; Newman, T. H.; Pakulski, M. J. Am. Chem. Soc. 1982, 104, 5820). 32. Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.; Timmers, F. J. Organometallics 1996, 15,1518. 33. Armarego, W. L. F.; Perrin, D. D., Purification of Laboratory Chemicals, 4th Ed. Butterworth-Heinemann: Oxford, 1997. 34. Burchat, A. F.; Chong, J. M.; Nielsen, N. J. Organomet. Chem. 1997, 542, 281. 35. Becker, G.; UhI, W.; Wessely, H. J. Z. Anorg. Allg. Chem. 1981, 479, 41. References start on page 62 65 Chapter 4 Self-Assembly of Amphiphilic Block Copolymers Containing Phosphorus in the Main Chain: A Block Copolymer Approach to Defined Gold Nanostructures 4.1 Introduction Living polymerization offers the unique possibility to tailor the size and properties of macromolecules.13The most important feature of this synthetic tool is the preparation of controlled macromolecular architectures, such as block copolymers, which consist of two chemically different polymer chains linked by a covalent bond (see Section 1.3.1). These copolymers are prepared through sequential polymerization of two monomers (A and B in Figure 4.1) and they are attracting a great deal of attention as these materials display unique properties.1’4-15 Block Copolymers (AB) A Block B Block Triblock Copolymers (ABA) A Block B Block A Block Figure 4.1 Schematic representations of diblock and triblock copolymers. As discussed in Section 1.3.1, block copolymers can display phase separation in solution with appropriate solvent selection promoting aggregated structures such as micelles, rods and vesicles.16 The spherical micelle (Figure 1.4) is a commonly observed morphology but solubility conditions, block copolymer sizes and the chemical nature of the two different segments (A and B — Figure 4.1) can promote different organizational behavior.16 Many applications in nanoelectronics are being envisioned for block copolymers. The recent discovery of living Chapter 4 66 phosphaalkene polymerization offers the possibility of preparing block copolymer architectures with phosphine segments along the polymer backbone.17These phosphine units could be exploited for metal coordination. There has been fairly extensive work on using block copolymers to stabilize and organize pre-formed metal (CdSe, Au and Ag) nanoparticles.’3’26 There has also been investigation into main chain iron copolymers which form ordered architectures by solution self-assembly.527-36 However, to my knowledge, there have been no block copolymer systems used to stabilize Au(l) assemblies. The Au(l) moiety may be useful in catalysis, or it may be reduced in situ to form Au(O) structures templated by the poly(methylenephosphine). The polystyrene-block-poly(methylenephosphine) macromolecule discussed in Chapter 2 was not a suitable candidate for solution self assembly as the polystyrene and poly(methylenephosphine) homopolymers are both soluble in polar solvents (CH2I,glyme, THF) and insoluble in non-polar solvents (hexanes, pentane).17 In an effort to prepare amphiphilic block copolymer structures, selecting a monomer amenable to living anionic polymerization that also forms a polymer which is soluble in nonpolar media, was imperative. Isoprene was selected as a co-monomer for polymerization with MesP=CPh2since isoprene readily polymerizes in a living fashion. Moreover, polyisoprene is soluble in both polar and non polar solvents.3741 In this chapter, the preparation of polyisoprene-block poly(methylenephosphine) copolymers (Pl—b--PMP) and their coordination to Au(l) is described. The solution self-assembly properties of these Pl—b—PMP-Au copolymers was investigated using transmission electron microscopy (TEM) and dynamic light scattering (DLS). References start on page 81 Chapter 4 67 4.2 Results and Discussion 4.2.1 Preparation of Pl—b--PMP block copolymers through successive anionic polymerization of isoprene and MesP=CPh2 Three different copolymer samples of polyisoprene-block-poly(methylenephosphine) were prepared and these are labeled as entries a, b and c in Table 4.1. Throughout the Results and Discussion section in this Chapter, the discussion of a polymer sample i.e, 4.2 will be followed by an a,b or c to indicate the appropriate macromolecule. Each copolymer was synthesized from successive anionic polymerization of isoprene and MesP=CPh2(Scheme 4.1). Treatment of an isoprene solution in THE with substoichiometric BuLi resulted in a pale yellow solution. The reaction mixture was stirred for 0.75 h at room temperature after which, a drop of the living polyisoprene (4.1) solution was removed from the reaction vessel, precipitated from MeOH, and analyzed by triple-detection GPC. The molecular weight determination indicated isoprene polymerization had proceeded successfully (M = 27 500 g mor1 PDI = 1.05). Then a MesP=CPh2solution in THE was rapidly added to the reaction mixture producing an immediate color change from yellow to red. This color change is consistent with the previously reported living MesP=CPh2polymerization using Bu Li.17 Complete consumption of the MesP=CPh2monomer was confirmed using 31P NMR spectroscopy (o31p = 233). The reaction mixture was precipitated using methanol (2 x 100 mL) and the desired Pl—b--PMP polymer (4.2a) was isolated as a white solid. Removal of the volatiles in vacuo yielded the desired copolymer 4.2a (M = 38 500 g mor1 PDI = 1.12). A 31P NMR spectrum of the copolymer displays only one signal at —7 ppm which confirms the synthesis of the poly(methylenephosphine) block.42 A small amount of quenched polyisoprene was detected in the GPC trace of copolymer 4.2a. The microstructure of the P1 block is dependent on the polymerization solvent and previous studies have determined that P1 formation in THE produces the microstructure illustrated in Scheme Unfortunately, this could not be confirmed using References start on page 81 Chapter 4 68 1H NMR spectroscopy as the spectrum of copolymer 4.2a displays very broad overlapping signals for the P1 and PMP segments. Table 4.1 Selected characterization data for polyisoprene-block-poly(methylenephosphine)s (PInbPMPm) prepared by the successive living anionic polymerization of isoprene and MesP=CPh2. P1 PInbPMPm Entry M (g moM) PDI M (g moM) PDI (a) 27500 1.05 38500 1.12 404:32 (b) 15100 1.06 39400 1.06 222:77 (c) 11200 1.09 38200 1.24 164:85 8The estimated chain lengths for each block (n and m) are determined from the absolute M of each homo- and copolymer samples. Since molecular weight correlates directly to polymer chain length, we can use the molecular weights determined from triple-detection GPC analysis to estimate the chain length of each block copolymer segment. Sample 4.2a has a P1 block with a molecular weight of 27 500 g moM, if this is divided by the molecular weight of the repeating isoprene unit (68.12 g moM) then we can estimate that the block copolymer has a P1 segment with 404 repeat units. Copolymer 4.2a has a total molecular weight of 38 500 g moM which corresponds to a 10,000 g moM molecular weight for the PMP segment. If we divide this weight by the molecular weight of the repeating phosphine unit (316.38 g moM) then this leads to a chain length of approximately 32 repeat units. Two other copolymer samples 4.2b and 4.2c were prepared with different chain lengths for the P1 and PMP blocks (Table 4.1). Analysis of samples 4.2b and 4.2c by GPC chromatography revealed a small signal assigned to quenched polyisoprene homopolymer. The polyisoprene could be removed by washing each sample with hexanes. A stack plot of the GPC chromatograms for H-terminated 4.1 b and copolymer 4.2b is shown in Figure 4.2 to illustrate the observed increase in molecular weight from the polyisoprene homopolymer to the polyisoprene-block-poly(methylenephosphine). References start on page 81 Chapter 4 69 1.m MesP=CPh2 r 1 r Phi BuLi Bu’PILi 2.MeOH Bu+PlP—H RT, THF L i RT,THF I I Mes Ph]LJL m 4.1 4.2 [y1’ ‘h1H’ Scheme 4.1 Polymerization of isoprene in THF at room temperature using BuLi followed by addition of MesP=CPh2to the living polyisoprene forming polyisoprene-block poly(methylenephosphine). 10 12 14 16 18 20 22 Time (mm) Figure 4.2 GPC chromatograms (refractive index traces) collected for 4.lb and 4.2b. Red trace — macromolecule 4.lb. Blue trace macromolecule 4.2b. 60% 30% 10% References start on page 81 Chapter 4 70 4.2.2 Preparation of gold complexes of the Pl—b—PMP The self-assembly of block copolymer 4.2a should be possible using non-polar solvents because the polyisoprene is soluble in non-polar media whereas the poly(methylenephosphine) is not. In addition, the potential to exploit the three coordinate phosphine moiety in the polymer backbone for transition metal coordination is a potential route to self-assembled metal nanostructures. Using gold(l) was an attractive starting point to synthesize metallated phosphorus polymers because several phosphine-containing polymers in the literature have been shown to form coordination complexes with AuCI moieties.’45 The metallation of Bu [MesP-CPh2]Hwith AuCI has been reported previously, and a similar procedure was followed for the coordination of the block copolymer 4.2a to AuCl.45 Sample 4.2a was treated with a (tetrahydrothiophene)AuCl solution in CH2I under N2 atmosphere. The reaction mixture was stirred for several hours before removal of the volatiles in vacuo. Analysis of the sample using 31P NMR spectroscopy revealed only one resonance at 25 ppm, this has been assigned to the coordination compound PI—b—PMRAuCI (4.3a). The observed resonance in the 31P NMR spectrum for macromolecule 4.3a is in close agreement with the previously reported signal for the poly(methylenephosphine) Au(l) coordination complex (ôp 25). Cl Aur 1 r Phi SAuCl 1 [• t Ph I 8u P1 P—C H ‘1Bu P1 P—C HI 42 CH2CI2 I Scheme 4.2 Treatment of polyisoprene-block-poly(methylenephosphine) with (tetrahydrothiophene)gold(l) chloride to form a polyisoprene-block-poly(methylenephosphine) gold(l) coordination complex. References start on page 81 Chapter 4 71 The metallated copolymer 4.3a was also characterized by triple detection GPC-LLS and a significant increase in the molecular weight is observed (Table 4.2 - entry (a): M = 43 500 g mor1; PDI = 1.18) as compared to 4.2a (Table 4.1 entry (a): M = 38 500 g mor1; PDI = 1.12). This behavior is consistent with the addition of a heavy AuCI moiety to the polymer microstructure. Copolymers 4.3b and 4.3c were prepared following an analogous procedure to 4.3a (Table 4.2). Representative 31P NMR spectra are displayed in Figure 4.3 for compounds 4.2b and 4.3b to illustrate the observed shift upon coordination of copolymer 4.2b (ô31p — 7) to AuCI (4.3b: ô31P 25). Table 4.2 GPC data for polyisoprene-block-poly(methylenephosphine) coordinated to AuCI. PlnbPMPmAuCl Entry M (g mor1) PDI ça Rh (C7H16)b (a) 43500 1.18 5nm 82nm (b) 44800 1.10 5nm 75nm (c) 57900 1.15 5nm ca.l400nm (a) hydrodynamic radius was determined using viscometer data from the triple detection GPC analysis; (b) hydrodynamic radius was determined from dynamic light scattering (DLS) data on the solutions used to prepare TEM samples. 200 150 100 50 0 -50 -100 -150 ppm Figure 4.3 31P NMR spectra for compounds 4.2b and 4.3b. Top — macromolecule 4.3b and bottom — macromolecule 4.2b. References start on page 81 Chapter 4 72 42.3 Formation of Pl—b—PMPAuCl nanostructures To determine whether self-assembly was feasible, transmission electron microscopy (TEM) and dynamic light scattering (DLS) were employed. Good contrast for TEM requires the presence of large atoms in specific domains and the scattering power of the phosphine-gold moiety compared to the organic P1 block provided sufficient contrast for TEM imaging and thus no TEM staining was required. Suitable solvent conditions for the polymers to self-assemble into macromolecular structures were crucial. Both PMP and P1 are soluble in polar solvents but only P1 is soluble in aliphatic solvents. Dilute solutions of 4.3a (0.5 mg mL1) in n-heptane were dropcast onto a copper TEM grid coated with Formvar. The sample was loaded into the transmission electron microscope and analyzed. The formation of well-defined nanospheres (Figure 4.4a) are clearly visible in the TEM images, it seems the assemblies are small spherical structures with fairly uniform shape and size. From the 197 spheres on the TEM image (Figure 4.4a — 100 nm resolution), 20 were taken and measured; the diameter of the structures is on average 28 — 32 ±11 - 15 nm. To ensure that sphere formation was not simply an aggregation effect from solvent evaporation, dynamic light scattering of the dilute n-heptane solution was employed. The hydrodynamic radius (Rh) of copolymer 4.3a in THF is approximately 5 nm whereas in dilute n heptane, a 15-fold increase is observed (Rh = 82 nm), supporting the hypothesis that the copolymer sample is forming assemblies in solution. The potential to access morphologies other than spheres was of interest and the two block copolymers with longer PMP segments, 4.3b and 4.3c, were investigated. Both macromolecules 4.3b and 4.3c were not soluble in n-heptane. Polymer 4.3b was dissolved in a minimal amount of THF after which, n-heptane was added (10% THF: 90% heptane). The cloudy solution was dropcast onto a Formvar coated TEM grid and analyzed using transmission electron microscopy (Figure 4.3b). The shapes observed in this case were significantly different than 4.3a. The morphologies varied along the grid; some spherical species were present (diametes = 22 - 25 nm) and some cylindrical or “wormlike” structures were References start on page 81 Chapter 4 73 observed. The sizes of the cylinders vary in length from 60 to 250 nm and the thickness was in the range of 15 - 25 nm. The oblong structures were more difficult to measure as the lengths varied quite a bit and thus a range is reported rather than an average. The solution of 4.3b in THF:heptane was analyzed using DLS experiments and the hydrodynamic radius (Rh = 75 nm) was similar to that of 4.3a. Once again, the Rh of 43b in THF:heptane was siginificantly higher than the Rh of 4.3b in THF(4.3b: Rh = 5 nm). The increase in the poly(methylenephosphine) chain length while decreasing the length of the polyisoprene block results in a change from well defined nanospheres to “wormlike” structures. To confirm this hypothesis, analysis of macromolecule 4.3c was necessary. It has the shortest P1 length and longest PMP segment of the three block copolymer samples and the expected trend is that longer cylindrical structures will result from solution self-assembly. Macromolecule 4.3c was not completely soluble in n-heptane and was dissolved in a THF n-heptane mixture (20% THE: 80% heptane). Upon drop-casting the solution of 4.3c onto a TEM grid for analysis, ordered cylinders were observed. These structures are long connected networks on the order of hundred’s of nm but are extremely difficult to measure. DLS measurements revealed the large micelle size (ca. 1400 nm) to corroborate the TEM analysis. Importantly, the expected behavior was observed from 4.3b to 4.3c, that the decrease in Pt length coupled with the increase in the PMP segment resulted in a size increase for the self assembled nanostructures. References start on page 81 Chapter 4 - t(b) - -, C —A . i:, t- ) ? ( * -i . - 3 ----,. ..- - S_.i_ —.-., y>_. - C ç 4 — - )__ •N•’• 5i •%-_-_i_) ‘i> 500nm .--- -!. (a) -: ;-- ii;, -• ;;r’- --‘ - - 74 ..1 , I. -E ‘ 2 ‘ • ‘S ‘ ‘:,;-- — 4 : i) t1$ it .%t -1’.:’lOOnm Z.t . .. ‘:-.,‘ . ‘.. --:-.(c) —&41 (c) 1 è; m - -t— ;i __ — 9 - - ‘ lOOatn. :-. Figure t4 TEM images at 500 nm and 100 nm resolution which were formed from slow evaporation of a dilute n-heptane solution containing polyisoprene-block poly(methylenephosphine-gold(l)). (a) — 4.3a, (b) — 4.3b, (c) — 4.3c. References start on page 81 Chapter 4 75 4.3 Conclusions New polyisoprene-b/ock-poly(methylenephosphine) copolymers have been synthesized by sequential anionic polymerization of isoprene and MesP=CPh2using BuLi. As polyisoprene is soluble in non-polar solvents and poly(methylenephosphine) is not, I hypothesized that self- assembly would be feasible with these systems. Three copolymer samples were prepared with different polyisoprene and poly(methylenephosphine) chain lengths. Each block copolymer was combined with (tht)AuCl to form a phosphineAuCl coordination complex. These metal- containing copolymers were then dissolved in n-heptane and their solution self-assembly properties were analyzed by TEM and DLS. The TEM images indicated that morphology control is possible with nanospheres and cylinders both being accessible simply by altering the length of the polyisoprene and poly(methylenephosphine) chain lengths in the copolymer samples. Further work will focus on attempting different solvents for self-assembly, and trying to exert more control over the self-assembled structures. 4.4 Experimental 4.4.1 Materials and General Procedures All manipulations of air and/or water sensitive compounds were performed under pre purified nitrogen (Praxair, 99.998%) using standard high vacuum or Schlenk techniques or in an Innovative Technology Inc. glovebox. Hexanes, toluene and CH2I were deoxygenated with nitrogen and dried by passing through a column containing activated alumina. THE was freshly distilled from sodium/benzophenone ketyl. Methanol was degassed prior to use. CD2I was purchased from Cambridge Isotope Laboratories and dried over molecular sieves (3 A). BuLi (1.6 M in hexanes) and n-heptane (spectrophotometric grade) were purchased from Aldrich used as received. Alkyllithium reagents were titrated prior to use. Isoprene was purchased from Aldrich and distilled prior to use. MesP=CPh246and (tht)AuCl47were prepared following literature procedures. References start on page 81 Chapter 4 76 31P NMR spectra were recorded on Bruker AV300 or AV400 spectrometers at room temperature. Chemical shifts for 31P NMR spectra are reported relative to H3P04as an external standard (85% in H20, = 0). 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) HR5E (2000-4 000 000), HR4 (5000-500 000), and HR2 (500-20 000), Waters 2410 differential refractometer ( X= 940 nm, 40 °C), Wyatt tristar miniDAWN (laser light scattering detector operating at ? = 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 mLj. The dn/dc of polyisoprene has been previously reported (dn/dc = 0.129 mLg1).48 TEM images were collected at the UBC Biolmaging Facility on a Hitachi H7600 TEM (120 kV tungsten filament) equipped with a side mount AMT Advantage (1 mega-pixel) CCD camera (Hamamatsu ORCA). The sample solutions were deposited on a Formvar-coated TEM grid and evaporated to dryness. DLS experiments were performed with a Coulter N4 Plus DLS instrument equipped with a 10-mW helium-neon laser (A = 632.8 nm) and thermoelectric temperature controller. Measurements were taken at a 90° scattering angle in a 3 x 3-mm quartz cuvette on solutions that had been equilibrated at 25 °C. Particle sizes were estimated by SDP weight and intensity analyses. 4.4.2 Preparation ofPl404—b—PMP32 To a stirred solution of isoprene (2.0 g, 29 mmol) in THF (1.0 mL) was added 45 tL of BuLi (1.36 M, 0.061 mmol) in hexanes via 100 L syringe. The reaction mixture turned yellow immediately and was stirred for approximately 45 mm. A drop of the reaction mixture was removed and added to 50 mL of methanol. The polymer 4.la precipitated out of solution as a white solid. After isolation, H-terminated polyisoprene was dried in vacuo and analyzed using GPC-LLS (M = 27 500 g mor1, PDI = 1.05). To the reaction mixture containing the living References start on page 81 Chapter 4 77 polyisoprene, a solution of MesP=CPh2(0.430 g, 1.36 mmol) in a minimal amount of THF was added. The solution immediately turned red and was allowed to stir for several days at which point the reaction mixture was almost black in colour. The solution was added dropwise into methanol (2 x 100 mL) and filtered. Volatiles were removed in vacuo at 60 C for several hours. The product was isolated as a yellow powder. Yield = 1.69 g (70%). p(l2l.5 MHz; THF; H3P04)—7 ppm (brs). GPC-LLS (THE): M = 38500 g mor1, PDI = 1.12, dn/dc = 0.129. 4.4.3 Preparation ofP1222—b—PMP77 To a stirred solution of isoprene (0.68 g, 10 mmcl) in THE (0.5 mL) was added 20 1iL of BuLi (1.36 M, 0.027 mmol) in hexanes via 100 1L syringe. The reaction mixture turned yellow immediately and was stirred for approximately 45 mm. A drop of the reaction mixture was removed and added to 50 mL of methanol. The H-terminated polyisoprene precipitated out of the solution as a white solid and was analyzed using GPC-LLS (M = 15 100; PDI = 1.06). To the living polyisoprene was added a solution of MesP=CPh2(0.520 g, 1.6 mmcl) in a minimal amount of THE. The solution immediately turned red and was allowed to stir for 24 h at which point the reaction mixture was almost black in colour. The solution was added dropwise into methanol (2 x 100 mL) and filtered. Volatiles were removed in vacuo at 60 °C for several hours. The product was isolated as a yellow powder. Yield = 0.86 g (72%). op(l62 MHz; THF; H3P04) —7 ppm (br s). GPC-LLS (THE): M = 39400 g mor1, PDI 1.06, dn/dc = 0.157. 4.4.4 Preparation ofPl164—b—PMP85 To a stirred solution of isoprene (0.68 g, 10 mmol) in THE (0.5 mL) was added 35 1iL of BuLi (1.36 M, 0.048 mmcl) in hexanes via 100 tL syringe. The reaction mixture turned yellow immediately and was stirred for approximately 45 mm. A drop of the reaction mixture was removed and added to 50 mL of methanol. H-terminated polyisoprene precipitated out of the solution as a white solid and was analyzed using GPC-LLS (M = 11 200; PDI = 1.09). A solution of MesP=CPh2(1.29 g, 4.1 mmcl) in a minimal amount of THF was added to the living References start on page 81 Chapter 4 78 polyisoprene. The solution immediately turned red and was allowed to stir for 24 h after which, the mixture was added dropwise into methanol (2 x 100 mL) and filtered. Several washings of the polymer with hexanes (2 x 100 mL) removed quenched polyisoprene homopolymer. Volatiles were removed in vacuo at 60 °C for several hours. The product was isolated as a yellow powder. Yield = 0.99 g (51%). öp(l62 MHz; THF; H3P04)— 7 ppm (br s). GPC-LLS (THF): M = 38200 g mor1, PDI = 1.24, dn/dc = 0.190. 4.4.5 Preparation ofPI4—b—(PMPAuCI)32 A solution of (tht)AuCI (9 mg, 0.028 mmol) in CH2I (5 mL) was added to a solution of (P1404—b—PMP32)(50.0 mg, M = 38 500, PDI = 1.12) in CH2I (5 mL) and stirred for 1 h. The solvent was removed in vacuo resulting in a white solid. Toluene (2 x 3 mL) followed by hexanes (2 x 5 mL) were added to the product and subsequently removed in vacuo to ensure the removal of tht. The product was dried overnight in vacuo. Yield = 52 mg (93%). op(l21.5 MHz; THE; H3P04)25 (br s). GPC-LLS (THE): M = 43 500, PDI = 1.18. dn/dc = 0.129. 4.4.6 Preparation ofP1222—b—(PMPAuCI)77 To a stirringsolution of copolymerPl222—b—PMP77(50 mg, M = 39 400, PDI = 1.06) in CH2I (3 mL) was added (tht)AuCl (25 mg, 0.078 mmol) in CH2I (2 mL). After stirring for 1 h, the reaction was monitored by 31P NMR spectroscopy (ô = 25 br). The solvent was removed in vacuo resulting in a yellow solid. The product was dissolved in a minimal amount of CH2I and precipitated from hexanes. Toluene (2 x 3 mL) followed by hexanes (2 x 5 mL) were added to the product and subsequently removed in vacuo to ensure the removal of tht. The product was dried overnight in vacuo. Yield = 54mg (79 %). op(l2l.5 MHz; THE; H3P04)25 (br s). GPC-LLS (THF): M = 44800 g mor1, PDI = 1.10, dn/dc = 0.157. References start on page 81 Chapter 4 79 4.4.7 Preparation ofPl1—b—(PMPAuCl)35 To a stirring solution of copolymerPl164—b—PMP85(68 mg, M = 38 200, PDI = 1.24) in CH2I (5 mL) was added (tht)AuCl (51 mg, 0.16 mmol) in CH2I (5 mL). After stirring for I h, the reaction was monitored by 31P NMR spectroscopy (ô = 25 br). The solvent was removed in vacuo resulting in a yellow solid. Toluene (2 x 3 mL) followed by hexanes (2 x 5 mL) were added to the product and subsequently removed in vacuo to ensure the removal of tht. The product was dried overnight in vacuo. Yield 104 mg (99%). ôp(l21.5 MHz; THF; H3P04)25 (br s). GPC-LLS (THF): M = 57900 g mor1, PDI = 1.15, dn/dc = 0.190. 4.4.8 Preparation of spherical structure from Pl—b.-(PMP•AuCl)32 To polymer 4.3a (2.9 mg) was added n-heptane (4 mL). The solution was sonicated for approximately 10 mm to assure complete dissolution of the polymer sample. The solution was dropcast on a Formvar-coated TEM grid. Solution was filtered through 0.2 m filter before DLS analysis. DLS: Rh = 82 nm. 4.4.9 Preparation of wormlike structure fromPl222—b—(PMPAuCl)77 Macromolecule 4.3b (3.1 mg) was dissolved in THF (0.5 mL) and to this solution was added n-heptane (3.5 mL). The opaque solution was sonicated for approximately 10 mm to ensure complete dissolution of the polymer sample. The solution was dropcast on a Formvar coated TEM grid. Solution was filtered through 0.2 m filter before DLS analysis. DLS: Rh = 75 nm. References start on page 81 Chapter 4 80 4.4.10 Preparation of long cylindrical structure fromPl164—b—(PMPAuCl)35 Macromolecule 4.3c (2.9 mg) was dissolved in THF (2.0 mL) and to this solution was added n-heptane (6.0 mL). The opaque solution was sonicated for approximately 10 mm to ensure complete dissolution of the polymer sample. The solution was dropcast on a Formvar coated TEM grid. Solution was filtered through 0.2 tm filter before DLS analysis. There is potentially some aurophilic interactions which are partially responsible for the large value of Rh. DLS: R11 = ca. 600 nm. References start on page 81 Chapter 4 81 4.5 References 1. Hadjichristidis, N.; Pitsikalis, M.; Pispas, S.; Iatrou, H. Chem. Rev. 2001, 101, 3747. 2. Webster, 0. W. Science 1991, 251, 887. 3. Odian, G., Principles of Polymerization, 4th Edition. Wiley: New York, 2004. 4. Noshay, A.; McGrath, J. 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Sd. 1999,4,587. 16. Hamley, I. W., Block Copolymers in Solution. Wiley: 2005. 17. Noonan, K. J. T.; Gates, D. P. Angew. Chem. mt. Ed. 2006, 45, 7271. 18. Lopes, W. A.; Jaeger, H. M. Nature 2001, 414, 735. 19. Yan, Y.; Besseling, N. A. M.; de Keizer, A.; Marcelis, A. T. M.; Drechsler, M.; Stuart, M. A. C. Angew. Chem. Int. Ed. 2007, 46, 1807. 20. Kang, Y. J.; Taton, T. A. Angew. Chem. lnt. Ed. 2005, 44, 409. 21. Zhang, Q. L.; Gupta, S.; Emrick, T.; Russell, T. P. J. Am. Chem. Soc. 2006, 128, 3898. References start on page 81 Chapter 4 82 22. Bockstaller, M. R.; Lapetnikov, Y.; Margel, S.; Thomas, E. L. J. Am. Chem. Soc. 2003, 125, 5276. 23. Soo, P. L.; Sidorov, S. N.; Mui, J.; Bronstein, L. M.; Vali, H.; Eisenberg, A.; Maysinger, D. Langmuir 2007, 23, 4830. 24. Watanabe, S.; Fujiwara, R.; Hada, M.; Okazaki, Y.; lyoda, T. Angew. Chem. mt. Ed. 2007, 46, 1120. 25. Sakai, T.; Alexandridis, P. Langmuir 2004, 20, 8426. 26. Chiu, J. J.; Kim, B. J.; Kramer, E. J.; Pine, D. J. J. Am. Chem. Soc. 2005, 127, 5036. 27. Wang, H.; Lin, W. J.; Fritz, K. P.; Scholes, G. D.; Winnik, M. A.; Manners, I. J. Am. Chem. Soc. 2007, 129, 12924. 28. Wang, X. S.; Wang, H.; Frankowski, D. J.; Lam, P. G.; Welch, P. M.; Winnik, M. A.; Hartmann, J.; Manners, I.; Spontak, R. J. Adv. Mater. 2007, 19, 2279. 29. Wang, H.; Winnik, M. A.; Manners, I. Macromolecules 2007, 40, 3784. 30. Wang, X. S.; Liu, K.; Arsenault, A. C.; Rider, D. A.; Ozin, G. A.; Winnik, M. A.; Manners, I. J. Am. Chem. Soc. 2007, 129, 5630. 31. Gohy, J. F.; Lohmeijer, B. G. G.; Alexeev, A.; Wang, X. S.; Manners, I.; Winnik, M. A.; Schubert, U. S., Aqueous metallosupramolecular micelles with spherical or cylindrical morphology. In Metal-Containing And Metallosupramolecular Polymers And Materials, Vol 928, American Chemical Society: Washington, 2006. 32. Gohy, J. F.; Lohmeijer, B. G. G.; Alexeev, A.; Wang, X. S.; Manners, I.; Winnik, M. A.; Schubert, U. S. Chem.-Eur. J. 2004, 10, 4315. 33. Wang, X. S.; Winnik, M. A.; Manners, I. Angew. Chem. mt. Ed. 2004, 43, 3703. 34. Ni, Y. Z.; Rulkens, R.; Manners, I. J. Am. Chem. Soc. 1996, 118, 4102. 35. Wang, X. S.; Winnik, M. A.; Manners, I. Macromolecules 2002, 35, 9146. 36. Massey, J. A.; Temple, K.; Cao, L.; Rharbi, Y.; Raez, J.; Winnik, M. A.; Manners, I. J. Am. Chem. Soc. 2000, 122, 11577. References start on page 81 Chapter 4 83 37. Wang, X.-S.; Arsenault, A.; Ozin, G. A.; Winnik, M. A.; Manners, I. J. Am Chem. Soc. 2003, 125, 12686. 38. Dyball, C. J.; Worsfold, D. J.; Bywater, S. Macromolecules 1979, 12, 819. 39. Lachance, P.; Worsfold, D. J. J. Polym. Sd. Part A: Polym. Chem. 1973, 11, 2295. 40. Worsfold, D. J.; Bywater, S. Can. J. Chem. 1964, 42, 2884. 41. Cao, L.; Manners, I.; Winnik, M. A. Macromolecules 2002, 35, 8258. 42. Tsang, C. W.; Yam, M.; Gates, D. P. J. Am. Chem. Soc. 2003, 125, 1480. 43. Young, R. N.; Quirk, R. P.; Fetters, L. J. Adv. Polym. Sd. 1984, 56, 1. 44. Sebastian, M.; Hissler, M.; Fave, C.; Rault-Berthelot, J.; Odin, C.; Reau, R. Angew, Chem. Int. Ed. 2006, 45, 6152. 45. GiIon, B. H.; Patrick, B. 0.; Gates, D. P. Chem. Commun. 2008, 2161. 46. Becker, G.; Uhi, W.; Wess&y, H.-J. Z. Anorg. Aug. Chem. 1981, 479, 41. 47. Uson, R.; Laguna, A.; Laguna, M.; Briggs, D. A.; Murray, H. H.; Fackler, J. P. lnorg. Synth. 1989, 26, 85. 48. Jackson, C.; Chen, Y. J.; Mays, J. W. J. App!. Polym. Sd. 1996, 61, 865. References start on page 81 84 Chapter 5 Chemical Functionality of Poly(methylenephosphine): Phosphine-Borane Add ucts and Methyiphosphonium onomers* 5.1 Introduction Main-group-element-containing macromolecules have garnered considerable attention in recent years.’13 In the quest for polymers exhibiting unusual properties, the poly(methylenephosphine) is an attractive starting material. The phosphine segments of this hornopolymer, which are present at every second atom along the polymer backbone, could be exploited for facile polymer modification. There are several possibilities to functionalize the — [MesP—CPh2] polymer: either through coordination chemistry, or perhaps by an oxidation reaction of the three coordinate phosphine to afford phosphorus(V) polymers. Some previous work in this area has already been reported by our group; polymeric phosphine oxides and phosphine sulfides were synthesized by treatment of —[MesP—CPh2] with H20 and S8, respectively (Scheme 5.1).14 Although a well-defined metal complex was not isolated, Dr. Chi Wing Tsang illustrated that the poly(methylenephosphine) prepared from monomer 5.1 is an effective support for Pd-catalyzd Suzuki cross-coupling.15More recently, Bronwyn Gillon prepared well-defined phosphine gold coordination complexes of [MesP—CPh2]upon treatment of poly(methylenephosphine) with tetrahydrothiophene gold(l) chloride (Scheme 5.1 )16 *A version of this chapter has been published. Kevin J. T. Noonan, Bastian Feldscher, Joshua I. Bates, Justin J. Kingsley, Mandy Yam and Derek P. Gates. Chemical Functionality of Poly(methylenephosphine): Phosphine-borane Adducts and Methylphosphonium lonomers. Dalton Trans. 2008, 4451. Chapter 5 85 19 ii H2O ?? electrophile ___ (tht)AuC Scheme 5.1 Functionalization of poly(methylenephosphine) using H20,S8 and AuCI. What will occur if the poly(methylenephosphine) is treated with common electrophiles. Although macromolecules possessing trivalent phosphorus atoms in the main chain are common,67 10, 13, 17-19 polymer 5.2 is the only polymer with an alternating phosphorus carbon backbone. As described in Chapter 2, the living anionic polymerization of 5.1 provides a mild route to controlled molecular weight poly(methylenephosphine) 5.2 and the phosphine moieties in 5.2 can be treated with some simple main group electrophiles to access polymers possessing unique features. In particular, phosphine-borane adducts are of interest as potential protecting groups for the slightly air-sensitive phosphine environments in 5.2 and for their potential use as pre-ceramic materials.3In addition, alkylation of the phosphine moieties would provide a convenient route to novel phosphonium ionomers.2°lonomers or polymers with ionic groups, are of interest in applications ranging from drug delivery to fuel cell membranes.21’2The successful methylation of 5.2 would also provide access to polymers with a high ion density in the main chain due to the close proximity of phosphorus atoms. References start on page 101 Chapter 5 86 1 .‘BuLi (1 - 4 mol%) ,Ph 2.MeOH [ l’h PC ‘Buf—P—C H Mes’ Ph glyme Ms Ph n 5.1 5.2 Scheme 5.2 Living polymerization of phosphaalkenes using n-butyllithium as initiator in glyme. In this Chapter, work on the chemical functionalization of phosphine polymer 5.2 through boronation and methylation reactions is described. To simplify polymer characterization, the potential reactivity of the high molecular weight polymer is first assessed by comparison to molecular model systems. Although borane functionalities may be incorporated at every atom along the main chain in 5.2, only Ca. 50% of the phosphine units could be methylated by MeOTf. 5.2 Results and Discussions 5.2.1 Synthesis of molecular model compounds Phosphines 5.3a and 5.3b were prepared from 5.1 following the literature procedures.23 24 These molecular compounds function as useful models to evaluate the chemical functionality of polymer 5.2. In an attempt to form a phosphine-borane adduct, a pale yellow solution of 5.3a in THE was treated with BH3SMe2inEt20 at —78 °C. Analysis of the reaction mixture using 31P NMR spectroscopy revealed that the signal for free phosphine 5.3a ( = —24.0) was replaced by a new signal (ô = 18.3). Likewise, treating silyl-terminated 5.3b with BH3SMe2affords a single product as judged by its 31P NMR spectrum (ô = 24.8 cf. 5.3b: ô = —23.9). Crystals of each product were obtained directly from the reaction solutions. Analysis of the crystals by x-ray crystallography confirmed that phosphine-boranes 5.4a and 5.4b had been formed successfully (see Figures 5.1 and 5.2). Compounds 5.4a and 5.4b were further characterized using 1H and 13C NMR spectroscopy. Interestingly, the borane can conveniently be removed to regenerate 5.3 by treating either phosphine-borane with amines such as diethylamine. References start on page 101 Chapter 5 87 1. MeLi Ph 2. MeOH Ph DLI .LA H3B Phf’IO4,A Li I LII 13 LIIvIe2 4 I p= OiIivi2ri Me-P—C—R Me-P—C-R Me Ph THE MesPh HNR2 MesPh 5.1 5.3a (R = H) 5.4a (R H) 5.3b (R = S1Me2H) 5.4b (R = S1Me2H) Scheme 5.3 Model compound preparation from MesP=CPh2phosphaalkene. The three- coordinate phosphine (5.3) is coordinated reversibly to 8H3. We are also interested in the functionaliztion of poly(methylenephosphine) with GH3, which is isoelectronic to BH3. From a polymer perspective, this would provide access to novel rnethylphosphonium polyelectrolytes. We chose MeOTf as the methylating agent rather than milder agents due to the anticipated difficulty tully alkylating the closely spaced phosphorus atoms in 5.2. Thus, a solution of 5.3a in CH2b was treated with excess MeOTf to give compound 5.5 (ô31p = 29.8) Slow evaporation of the solvent afforded large colorless crystals of the air•stahle phosphonium salt 5.5. A single crystal of compound 5.5 was analyzed using x-ray diffraction (Figure 5.3). The analytically pure crystals were further characterized by 31P, 1H, 13C and ‘9F NMR spectroscopy. The 1H NMR spectrum for compound 5.5 (in DMSO-d6)is consistent with the proposed product, although it is not possible to assign the overlapping signals for the methyl protons (i.e. P—CH3,o—CH3 and p—CH3). In the 19F NMR spectrum, a sharp signal is observed at —77.5 ppm, which is typical of uncoordinated triflate. Ph MePh I MeOTf 1 Me-P—C—H —•-----Me-P—C—H OTf MesPh CH2I MesPh 5.3a 5,5 Scheme 5.4 Methyl phosphonium model compound preparation trom the three-coordinate phosphine (compound 5.3a) 5.2.2 X-ray crystallography Compounds 5.4a, 5.4b and 5.5 were characterized crystallographically and the molecular structures are shown in Figures 5.1, 5.2 and 5.3, respectively. Important metrical parameters are found in the figure captions and details of the structure solution and refinement are found in Table 5.1. Interestingly, the P(1)—B(1) bond [1 .831(6) A] in 5.4a is shorter than the References start on page 101 Chapter 5 88 analogous bond in 5.4b [1.977(2) A]. For comparison, the typical range for P-B bonds is 1.90 to 1.95 A25 and the bond length in Ph3—BH [1.917 A].26 We speculate that the apparent shortening of the P—B bond in 5.4a results from difficulty modelling the disorder in the crystal rather than providing chemical insight into the bonding in 5.4a (see Experimental Section for details). C15 C16 C14 BI C13 C17 do C12 P1 cii C18 C23 Cl C22 c19 C8 C2 C20 C21 C7 C4 C5 C6 Figure 5.1 Solid state molecular structure of 5.4a (ORTEP). Thermal ellipsoids at 50% probability; hydrogen atoms are omitted for clarity. Selected bond lengths (A) and angles (°). P(1)—C(1) 1.814(4), P(1)—C(10) = 1.795(5), P(1)—C(11) = 1.837(4), P(1)—B(1) = 1.831(6); C(1)—P(1)—C(11) = 105.0(2) C(2)—C(1)—P(1) = 120.4(4), C(8)—C(1)—P(1) = 121.0(3), C(12)— C(1 1) ..—P(1) = 111 .6(3), C(1 8)—C(1 1 )—P(1) = 112.0(3), C(1 0)—P(1 )—B(1) = 102.6(3), B(1 )—P(1 )— C(11) = 115.1(3), C(1)—P(1)—B(1) = 121.1(3). The P—C bonds in 5.4a [avg. 1.815(8) A] and 5.4b [avg. 1.853(3) A] are in the range typical for P—C bonds (1 .85 — 1.90 A).25 For comparison, the analogous bonds in 5.3a [avg. 1.858(2)] and 5.3b [avg. 1.853(3) A] are similar in length to those in 5.4a and 5.4b. Interestingly, the longest P—C bond is the P—CPh2Rbond [5.4a: P(1)—C(11) = 1.837(4) A, 5.4b: P(1)—C(11) = 1.894(1) A]. These P—CPh2Rbonds in 5.4a and 5.4b are shorter than in the free phosphines [5.3a: 1 .882(1) A, 5.3b: 1.902(1) A].24 The shortening is less significant between 5.3b and 5.4b References start on page 101 Chapter 5 89 than between 5.3a and 5.4a. Presumably, this reflects the increased steric conjestion in the former [—CPh2(SiMeH)vs —CPh2(H)]. Similarly, in methylphosphonium 5.5 the P—Me bonds (avg. 1.794(3) A] and P—Mes [P(1)—C(l) = 1.809(2) A] bonds are significantly shorter than the P—CPh2H[P(1)—C(12) = 1.854(2) A]. The P-C bonds in 5.5 are all shortened considerably with respect to the analogous bonds in 5.3a [P—Me: z(P-C) = 0.046(3); P—Mes: A(P-C) = 0.043(2); P—CPh2H: A(P-C) = 0.030(2) A]. For the most part, the bond angles in compounds 5.4a, 5.4b and 5.5 are unremarkable with the exception of the Mes—P—CPh2Rangles. In particular, this angle expands significantly upon coordination. For example, Mes—P—CPh2Rangle is between 105 and 108° in 5.4a, 5.4b and 5.5 whereas the analogous angle in 5.3a is just 100°. This is likely a consequence of increased s-character in the phosphorus bonds upon quaternization of the phosphorus lone pair. C22 C21 C23 4 C20 Bi C19018 C25 P1 Cli C17 C24 C16 C12 Sil Cl C9 C3 013 08 C2 C15 C14 C7 C4 C5 C6 Figure 5.2 Solid state molecular structure of 5.4b (ORTEP). Thermal ellipsoids at 50% probability; hydrogen atoms are omitted for clarity. Selected bond lengths (A) and angles (°). P(1)—C(1) = 1.846(2), P(1)—C(10) = 1.819(2), P(1)—C(11) = 1.894(2), P(1)—B(1) = 1.977(2), C(11)—Si(1) 1.941(2), C(24)—Si(1) = 1.857(2); C(1)—P(1)—C(11) = 107.8(1), C(2)—C(1)—P(1) = 117.6(1), C(8)—.C(1) —P(1) = 124.1(1), C(1 2)—C(1 I )—P(1) = 106.6(1), C(1 8)—C(1 I )—P(1) = 112.0(1), C(1 0)—P(1 )—B(1) = 100.7(1), C(1 I ).—P(1 )—B(1) = 122.9(1), C(1 )—P(1 )—B(1) = 110.6(1). References start on page 101 Chapter 5 90 C6 Figure 5.3 Solid state molecular structure 5.5 (ORTEP). Thermal ellipsoids at 50% probability; hydrogen atoms are omitted for clarity. Selected bond lengths (A) and angles (°). P(1)—C(1) = 1.809(2), P(1)—C(10) = 1.797(2), P(1)—C(11) = 1.790(2), P(1)—C(12) = 1.854(2); C(1)—P(1 )—C(1 2) = 107.2(1), C(2)—C(1 ).—P(1) = 124.1(2), C(8)—C(1) —P(1) = 116.5(2), C(12)— P(1)—C(11) = 109.0(1), C(12)—P(1)—C(10) = 110.6(1). 5.2.3 Chemical functionalization of poly(methylenephosphine) Following the synthesis and characterization of the model compounds, the preparation of phosphine-borane and methyl phosphonium polymers was attempted. The anionic polymerization of 5.1 in glyme using BuLi as the initiator afforded poly(methylenephosphine) 5.2 (M of 3.89 x I g mor1; PDI = I •34)27 The polymerization was not conducted using the rigorous standards required for a living polymerization and, consequently, the molecular weight distribution (P Dl) is greater than 1.1. In an attempt to prepare poly(methylenephosphine borane) 5.6, the phosphine polymer 5.2 was treated with BH3SMe2(1.4 equiv). Polymer 5.6 was isolated as a colorless solid after the volatiles were removed in vacuo. The 31P NMR spectrum References start on page 101 Chapter 5 91 of 5.6 is shown in Figure 5.4(b) and the chemical shift for the borane polymer is similar to models 5.4a and 5.4b (ô = 18.3 and 24.8, respectively). The spectrum shows no evidence for the presence of uncoordinated phosphine moieties [cf. Figure 5.4(a)]. [ Phi BH3SMe2 3B Phi n-BuHP—C-f H _______ n-BuP—C-j-H [Mshl NR3 LMesiJ n 5.2 5.6 Scheme 5.5 Borane protection of poly(methylenephosphine) using BH3SMe2.The BH3 group can be removed by treatment of the polymer with amine. Interestingly, the signals observed for 5.6 are much sharper and are better resolved than those observed for 5.2. For example, the 31P NMR spectrum of phosphine-borane polymer 5.6 exhibits two signals at 32.4 ppm (minor) and 26.8 ppm (major). In addition, a small shoulder is observed on the high field end of the signal at 26.8 ppm. In contrast, uncomplexed poly(methylenephosphine) 5.2 shows broad unresolved signals that likely encompass the different environments which are resolved in 5.6. We speculate that the observation of multiple signals in the 31P NMR spectrum of macromolecule 5.6 may be an indication of the tacticity in poly(methylenephosphine)s. Unfortunately, this hypothesis cannot be confirmed until control over the tacticity can be obtained (i.e. isotactic or syndiotactic). (a) (c) FT 140 120 100 80 60 40 20 0 -20 -40 -60 -80 ppm Figure 5.4 Stack plot of 31P NMR spectra of (a) poly(methylenephosphine) 5.2 in THE, (b) poly(methylenephosphine borane) 5.6, (c) and poly(methylene phosphonium triflate) 5.7. (b) References start on page 101 Chapter 5 92 The absolute number average molecular weight (Ma) of 5.6 was determined using triple detection GPC (M = 4.13 x 1 g mor1; PDI = 1.26), very similar to that of 5.2 (M = 3.89 x I 4 g mor1; PDI = 1.34). The molecular weight data of 5.2 and 5.6 confirms that no backbone degradation occurs during the BH3 protection. Notably, the molecular weight distribution is much narrower for 5.6 than for 5.2. This is surprising since the polydispersity indices should not change upon complexation. We postulate that the larger PDI for 5.2 is due to some interaction of the phosphine moieties in the main chain with the GPC columns. Problems with separation of phosphine polymers using GPC has been observed previously for phosphine polymers.28 This is an important consideration for the entire thesis and it may be more appropriate to run the polymers as oxidized samples. The reaction of polymer 5.6 with excess amine such as NEt3 resufts in the clean deprotection of the BH3 group to form poly(methylenephosphine) 5.2. The reformation of 5.2 was confirmed by 31P NMR spectroscopy and GPC analysis (M = 3.71 x I g mor1; PDI = 1.36). Thus, borane may be a useful protecting group for the mildly air sensitive polymer. Ph Ph MePh n.BuPIH j nBuEP f/[tI_H ( OTf)y Scheme 5.6 Methylation of poly(methylenephosphine). The synthesis of poly(methylenephosphonium triflate) proved to be more difficult than the borane polymer. A solution of 5.2 in CH2I was treated with MeOTf (excess) and was heated to 50 °C. The reaction mixture was monitored by 31P NMR spectroscopy and signals for free phosphine were still observed even after several days. The 31P NMR spectrum of the product after precipitation is shown in Figure 5.4(c). Importantly, a signal is observed at 31 ppm which is consistent with methyiphosphonium moieties by comparison to the chemical shift of 5.5 (ô31p = 29.8). Integrating the signals for the methylated (ô31p = 31) and unmethylated (ô31p 7) phosphorus atoms in 5.7 suggests that approximately 50 % of the phosphorus atoms are methylated. This experiment was repeated several times and, even after several days of heating References start on page 101 Chapter 5 93 5.2 with excess MeOTf, the degree of methylation never exceeded 50 %. Complete methylation would require a formal positive charge at every second atom in the polymer backbone. We speculate that phosphorus atoms are methylated in a roughly alternating fashion rather than in a completely random fashion as shown in Figure 5.5. For both steric and electronic reasons the alternating addition would be favourable and would lead to Ca. 50 % methylation. — p_p_pL_p_pL_p vs + + ÷ + —P—p —P—P—P—P—P——P— Figure 5.5 The possibilities for methylation of P chain. (a) alternating positive charge, (b) random distribution of positive charge. Polymer 5.7 was characterized by 1H, 31P, 19F and 13C NMR spectroscopy. The 13C NMR spectrum of poly(methylenephosphonium triflate) 5.7 in DMSO-d6 is shown in Figure 5.6 (bottom) and, although the signals are broadened significantly, the spectrum shows signals in the same regions with that for model compound 5.5 [Figure 5.6 (top)]. Of note, are the signals assigned to P-CH3 (&c = 13.2) and O3SCF (ói3 = 120.7, q, JCF = 322 Hz). Macromolecule 5.7 is soluble in DMSO and, consequently GPC analysis in THF could not be obtained. Static light scattering experiments were attempted with this ionic polymer but reliable molecular weight data could not be attained. References start on page 101 Chapter 5 94 5.3 Conclusions In closing, we have investigated the chemical functionality of poly(methylenephosphine) 5.2 through phosphine coordination to main group Lewis acids. The chemical functionality of 5.2 was examined by reacting Mes(Me)P—CPh2R[R = H (5.3a) or S1Me2H (5.3b)], molecular model compounds for the polymer, with BH3SMe2or MeOTf. Three new functionalized model systems were prepared and characterized crystallographically; namely, Mes(Me)P(BH3)—C h2H(5.4a), Mes(Me)P(BH3)—C h2Si eH(5.4b) and [Mes(Me)2P—CPhH]OTf - (5.5). The analogous reactions were successful when polymer 5.2 was used. Specifically, we report a new * Figure 5.6 DMSO-d6. 140 130 120 110 160 90 80 70 60 50 40 30 20 10 ppm 13C{H} NMR spectra of compound 5.5 (top) and macromolecule 5.7 (bottom). * References start on page 101 Chapter 5 95 phosphine-borane polymer n-Bu[MesP(BH3)—C h2]H(5.6) and a methylphosphonium polymer n-Bu[MesP—CPh2]—/— esP(Me)—CPhWOTr(5.7: x:y = ca. 1:1). These new polymers were fully characterized spectroscopically and absolute molecular weights were determined for 5.6. Future work will focus on studying the properties of the phosphine-borane and methylphosphonium polymers reported herein. The prospect of preparing water soluble phosphorus homo- or copolymers by post polymerization modification of 5.2 is an exciting synthetic target. 5.4 Experimental Table 5.1 X-ray crystallographic data of 5.4 and 5.5 Crystal 5.4a 5.4b 5.5 Formula C23H8PB C25HPBSi C25H8PS03F Formula Weight 346.23 404.39 496.50 Crystal System monoclinic triclinic monoclinic Space Group P21/n PT P21/n Color colourless colourless colourless a(A) 8.342(5) 10.128(5) 10.118(5) b (A) 13.896(5) 10.750(5) 17.583(5) c (A) 16.931 (5) 12.890(5 13.314(5) a(°) 90.000(5) 108.324(5) 90.000(5) 99.909(5) 93.499(5) 98.116(5) y(°) 90.000(5) 117.089(5) 90.000(5) V(A3) 1933.4(15) 1151.0(9) 2344.6(16) Z 4 2 4 T(K) 173(2) 173(2) 173(2) (Mo Ka) (cm1 1.45 1.80 2.56 Crystal Size (mm) 0.20x0.60x0.90 0.40x0.20x0. 10 0.45x0.40x0.20 Dcaic. (g cm3) 1.189 1.167 1.407 20 (max) (°) 47.3 56.0 55.8 No. of Reflections 26106 23770 40481 No, of uniquedata 2889 5485 5623 0.077 0.029 0.055 Reflections/parameters 12.45 14.10 18.56 ratio R1, wR2[l > 2(l)r 0.073; 0.190 0.036; 0.091 0.044; 0.094 R1, wR2 (all data)a 0.110; 0.222 0.045; 0.097 0.075; 0.108 GOF 1.10 1.04 1.00 a R1 = 11F0 - IFII I 1F0. wR2 = [ S ( w (F02 — F2) )I S w(F02)]112 References start on page 101 Chapter 5 96 5.4.1 Materials and general procedures All manipulations of air and/or water sensitive compounds were performed under pre purified nitrogen (Praxair, 99.998%) using standard high vacuum or Schlenk techniques or in an Innovative Technology glovebox. Hexanes, and dichioromethane were deoxygenated with nitrogen and dried by passing through a column containing activated alumina. THF was freshly distilled from sodium/benzophenone ketyl, CDCI3was distilled from P205 and degassed. CD2I and DMSO—d6were purchased from Cambridge Isotope Laboratories and were used as received. Methanol was degassed prior to use. NEt3, HNEt2,DBU, MeLi (1.6 M in Et20) BuLi (1.6 M in hexanes), BH3SMe2 (2 M in Et20) and MeOTf were purchased from Aldrich and used as received. Alkyllithium reagents were titrated prior to use. MesP=CPh2(5.1), Me(Mes)P CPh2(H) (5.3a) and Me(Mes)P-CPh2(SiMeH)(5.3b) were prepared using literature methods.23 24 Polymer 5.2 was prepared according to literature procedure.27 1H, 13C, 19F and 31P NMR spectra were recorded on a Bruker Avance 300 MHz spectrometer. Chemical shifts are reported relative to residual CHCI3 (ö = 7.26 for 1H and and 77.23 for 13C), CHDCI2 (ô = 5.32 for 1H and and 54.00 for 13C) and DMSQ-d5(ô = 2.50 for 1H and 39.51 for 13C). CFCI3was used as an external standard = 0.0 for 19F. 85% H3P04was used as an external standard ô = 0.0 for 31P. Molecular weights were determined by triple detection gel permeation chromatography (GPC — LLS) using a Waters liquid chromatograph equipped with a Waters 515 HPLC pump, Waters 717 pIus autosampler, Waters Styragel columns (4.6 x 300 mm; HR5E, HR4 and HR2), Waters 2410 differential refractometer, 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 mL1). Elemental analysis was conducted at the University of British Columbia. 5.4.2 Preparation of Mes(Me)P(BH3)—CHPh2(5.4a) An ethereal solution of BH3SMe2(1.4 mL, 2 M, 2.8 mmol) was added dropwise by syringe to a cooled solution (—78 °C) of compound 5.3a (0.94 g, 2.8 mmol) in THF (40 mL). The References start on page 101 Chapter 5 97 reaction mixture was allowed to warm slowly to room temperature and an aliquot was removed for analysis by 31P NMR spectroscopy (ö = 18.3, br). After removal of the volatiles in vacua, an oil was obtained which crystallized slowly over a period of 10 h. Yield: 0.729, 74%. op(l2l.5 MHz; CDCI3H3P04)18.3(1 P, brs). ÔH(300.l MHz, CDCI3;SiMe4)7.69 —7.17 (10 H, m, aryl H), 6.86 (2 H, s, rn—H of Mes), 4.86 (1 H, d, 2JpH = 17 Hz, CHPh2), 2.40 (6 H, s, o—CH3), 2.27 (3 H, s, p—CH3), 2 — 0.5 (3H, br q, BH3), 1.69 (3 H, d, 2JPH = 9 Hz, PCH3). ôc(75.5MHz; CDCI3;SiMe4)unassigned) 143.9 (d, Jpc = 9 Hz), 140.9 (d, Jpc = 2 Hz) 137.2 (d, Jpc = 3 Hz), 131.1 (d, Jpc = 9 Hz), 129.9 (d, Jpc = 5 Hz), 129.4 (d, Jpc = 5 Hz), 128.6, 128.1 (d, Jp = 2 Hz), 127.4 (d, Jp = 2 Hz), 127.1 (d, Jpc = 3 Hz), 123.4 (d, Jpc = 46 Hz), 51.8 (d, Jpc = 26 Hz), 24.4 (d, Jpc 4Hz), 20.8, 15.7 (d, Jpc39 Hz). 5.4.3 Reaction of 5.4a with Et2NH A solution of compound 5.4a (0.72 g, 2.1 mmol) in THF (5 mL) was combined with Et2NH (7 mL). The reaction mixture was stirred for 4 h and an aliquot was removed for analysis by 31P NMR spectroscopy. Complete conversion to 5.3a (—24 ppm) was observed and the solvent was removed in vacua. The resultant oil was dissolved in CH2I and washed with water. The aqueous phase was then extracted with CH2I (3 x 20 mL). The collected extracts were combined and dried over MgSO4. Filtration of the CH2I solution and removal of the solvent in vacua afforded 5.3a as an oil. Yield: 0.22 g, 31%. 5.4.4 Preparation of Mes(Me)P(BH3)—C h2Si eH(5.4b) An ethereal solution of BH3SMe2(0.6 mL, 2 M, 1.2 mmol) was added dropwise to a cooled solution (—78 °C) of phosphine 5.3b (0.47 g, 1.2 mmol) in THF (20 mL). The reaction mixture was slowly warmed to room temperature. After evaporation of the solvent in vacua a white solid was obtained. The solid was recrystallized by slow evaporation in an inert atmosphere from a concentrated THE solution. Yield: 0.11 g, 22%. op(l2l.5 MHz; CDCI3 H3P04)24.8 (1 P, br s). ÔH(300.l MHz, CDCI3; SiMe4)7.55—7.19 (10 H, m, aryl H), 6.69 (2 H, br References start on page 101 Chapter 5 98 s, m-Mes), 4.77 (1 H, m, Si-H), 2.5-0.5 (3H, br q, BH3), 2.37 (6 H, br, o-CH3), 2.22 (3 H, s, p CH3), 1.88 (3 H, d, 2Jp = 8 Hz, PCH3), 0.12 (3 H, d, J = 3 Hz, SiCH3), 0.0 (3 H, d, J = 3 Hz, S1CH3).ôc(75.5MHz, CD2I:SiMe4)145.2, 140.4 (d, Jpc = 2 Hz), 139.0 (d, Jpc = 4 Hz), 138.4 (d, Jpc = 4 Hz), 131.9, 131.8, 131.1 (d, Jpc = 9 Hz), 127.8, 127.5, 126.7, 125.7 (47 Hz), 48.4, 25.4 (br), 20.8, 16.8 (d, Jpc = 39 Hz), —3.5, —3.6. 5.4.5 Preparation of [Mes(Me)2P—CPhH]OTf(5.5) To a solution of compound 5.1 (2.00 g, 6.3 mmol) in THF (20 ml), was added MeLi (5.4 mL., 1.4 M, 7.6 mmol). The reaction mixture was stirred for I h and then solvent was removed in vacuo. Extraction of the reaction mixture with hexanes (3 x 10 mL) provided compound 5.3a as an oil. This yellow oil was dissolved in CH2I and added to MeOTF (2 eq.) in the glovebox. The reaction mixture was placed in a vial and slow evaporation afforded the crystalline salt. The crystals were dried for 72 h. Yield: 0.60 g, 19%. óp(l2l.5MHz; DMSO-d6H3P04)29.8(1 P, s). ÔH(300.l MHz, DMSO-d6;SiMe4)7.57— 7.39 (10 H, m, aryl H), 7.06 (2 H, s, rn—H of Mes), 5.68 (1 H, d, 2JpH 18Hz, CHPh2)2.33-2.27 (15 H, m, o—CH3p—CH3, P—CH3).ôc(75.5 MHz; DMSO d6;SiMe4)(unassigned) 144.0 (d, Jc = 3 Hz), 143.6 (d, Jp = 10 Hz), 133.4 (d, Jpc = 4 Hz), 131.8 (d, Jc = 12 Hz), 129.7 (d, Jpc = 6 Hz), 129.2 (d, Jpc = 2 Hz), 128.6 (d, Jpc = 2 Hz), 120.7 (q, 1JFC = 322 Hz), 114.7 (d, Jpc = 77 Hz), 49.1 (d, Jpc = 43 Hz), 23.7(d, Jpc = 4 Hz), 20.4, 13.2 (d, Jp = 52 Hz): ÔF(282.4MHz; DMSO-d6;CFCI3)—77.5 (s, CF3). Anal. Calcd. forC25H8PS03F: C, 60.47; H, 5.68. Found: C, 60.41; H, 5.66. 5.4.6 Preparation of n-Bu[MesP(BH3)—C h2]H(5.6) Poly(methylenephosphine) 5.2 (0.35 g, 1 .1 mmol) (M = 3.89 x 1 g/mol, PDI = 1.34) was dissolved in THF (20 ml) and BH3SMe2(0.75 ml, 2 M, 1.5 mmol) was added dropwise via syringe at — 78 °C. The reaction mixture was allowed to slowly warm up to room temperature. After evaporation of the volatiles in vacuo a solid was obtained. Yield: 0.25 g, 68%. M = 4.13 x g/mol, PDI = 1.26. ôp(l2l.5 MHz; CDCI3H3P04) 32.4(1 P, brs), 26.8(1 P, brs). References start on page 101 Chapter 5 99 5.4.7 Reaction of 5.6 with amines A solution of the poly(methylenephosphine-borane) 5.6 (0.25 g) in THF was treated with excess amine (DBU, NEt3, NEt2H). The reaction was stirred for 12 h and an aliquot of the reaction was removed and analyzed using 31P NMR spectroscopy (31P = —7). Upon removal of the solvent in vacuo, the polymer was dissolved in CH2I (15 ml) and washed with degassed water (2 x 5 ml). The organic layer was dried over MgSO4 and solvent was removed in vacuo, affording 5.2. Yield: 0.22 g, 91 %. M = 3.71 x g/mol, PDI = 1.36. 5.4.8 Preparation of n-Bu[MesP—CPh]—I— esP(Me)—CPhH(5.7) To a solution of polymer 5.2 (0.40 g, 1.3 mmol) in CH2I (10 ml) was added excess methyl triflate (10 eq.). The reaction mixture was stirred overnight. Analysis of the mixture by 31P NMR spectroscopy exhibited two broad singlets with one signal at 31 ppm and the other at —7 ppm. Integration of the two signals revealed an approximate 1:1 ratio of the two signals. The polymer was isolated by precipitating a concentrated CH2I solution (ca. I mL) with hexanes (20 mL) (x3). The yellow solid was dried in vacuo at 80°C overnight. Yield: 0.23 g, 46 %. op(12l .5 MHz; DMSO-d6H3P04)31 (1 P, br s), —7 (1 P, br s). ÔH(300.l MHz, DMSO-d6;SIMe4) 7.2 (12 H, br, m-Mes-H, Ph-H), 2.2 (15H, o,p-CH3 P-CH3); ô(75.5 MHz; DMSO-d;SiMe4) (unassigned), 145, 140, 133, 129, 120.7 (q, 1JCF = 320 Hz), 114, 49, 23, 20, 12; ÔF(282.4MHz; DMSO-d6;CFCI3)—78.7 (s, CE3). 5.4.9 X-ray crystallography Crystal Data and refinement parameters are listed in Table 5.1. All single crystal were immersed in oil and mounted on a glass fiber. Data were collected at 173 ± 0.1K on a Bruker X8 APEX 2 diffractometer with graphite-monochromated Mo Ka radiation. Data was collected and integrated using the Bruker SAINT29 software package. All structures were solved by direct methods3°and subsequent Fourier difference techniques and refined anisotropically for all non References start on page 101 Chapter 5 100 hydrogen atoms using the SHELXTL31 crystallographic software package from Bruker-AXS. All data sets were corrected for Lorentz and polarization effects. Compounds 5.4b and 5.5 did not exhibit any crystallographic complexity. Data collection for compound 5.4a was attempted to 20 = 56°, however, due to poor quality crystals, no significant reflections were observed beyond 20 = 40°. We attribute this lack of long-range reflections to disorder in the crystal lattice. Although efforts to model the disorder have been thus far unsuccessful, we hypothesize the incorporation of non-boronated phosphine into the crystal lattice is responsible. The consequence of this lattice defect would be increased electron density near the phosphows atom from the lone pair. Our efforts to model the location of the boron atom are thus complicated as software compensates for the electron density by shortening the P-B distance to the observed bond length. CCDC reference numbers 668085 — 668087 References start on page 101 Chapter 5 101 5.5 References 1. Mark, J. E.; Ailcock, H. R.; West, R., Inorganic Polymers. Oxford University Press: New York, 2005. 2. Naka, K.; Umeyama, T.; Chujo, Y. J. Am. Chem. Soc. 2002, 124, 6600. 3. Dorn, H.; Rodezno, J. M.; Brunnhofer, B.; Rivard, E.; Massey, J. A.; Manners, I. Macromolecules 2003, 36, 291. 4. Smith, R. C.; Protasiewicz, J. D. J. Am. Chem. Soc. 2004, 126, 2268. 5. Baumgartner, T.; Bergmans, W.; Karpati, T.; Neumann, T.; Nieger, M.; Nyulaszi, L. Chem. Eur. J. 2005, 11, 4687. 6. Jin, Z.; Lucht, B. L. J. Am. Chem. Soc. 2005, 127, 5586. 7. Baumgartner, T.; Reau, R. Chem. Rev. 2006, 106, 4681. 8. Baumgartner, T.; Wilk, W. Org. Lett. 2006, 8, 503. 9. Sebastian, M.; Hissler, M.; Fave, C.; Rault-Berthelot, J.; Odin, C.; Reau, R. Angew. Chem. mt. Ed. 2006, 45, 6152. 10. Vanderark, L. A.; Clark, T. J.; Rivard, E.; Manners, I.; Slootweg, J. C.; Lammertsma, K. Chem. Commun. 2006, 3332. 11. Wright, V. A.; Patrick, B. 0.; Schneider, C.; Gates, D. P. J. Am. Chem. Soc. 2006, 128, 8836. 12. Na, H. S.; Morisaki, Y.; Aiki, Y.; Chujo, Y. J. Polym. Sd. Po!. Chem. 2007, 45, 2867. 13. Naka, K.; Umeyama, T.; Nakahashi, A.; Chujo, Y. Macromolecules 2007, 40, 4854. 14. Tsang, C. W.; Yam, M.; Gates, D. P. J. Am. Chem. Soc. 2003, 125, 1480. 15. Tsang, C. W.; Baharloo, B.; Riendi, D.; Yam, M.; Gates, D. P. Angew. Chem. lnt. Ed. 2004, 43, 5682. 16. B. H. Gillon, D. P. Gates, B.C. Patrick. Chem Commun. 2008, 2161. 17. Honeyman, C. H.; Peckham, T. J.; Massey, J. A.; Manners, I. Chem Commun. 1996, 2589. 18. Lucht, B. L.; St. Onge, N. L. Chem. Commun. 2000, 2097. References start on page 101 Chapter 5 102 19. Ouchi, Y.; Morisaki, Y.; Ogoshi, T.; Chujo, Y. Chem. Asian. J. 2007, 2, 397. 20. Recently, an example of a methylated phosphole ionomer has been reported. Durben, S.; Dienes, Y.; Baumgartner, T. Org. Left., 2006, 8, 5893. 21. Controlled Drug Delivery: Designing Technologies for the Future. Eds.; Park, K.; Mrsny R. J. Eds, ACS Symposium Series 752, American Chemical Society: Washington, DC 2000. 22. Hickner, M. A.; Ghassemi, H.; Kim, Y. S.; Einsla, B. R.; McGrath, J. E. Chem. Rev. 2004, 104, 4587. 23. Becker, G.; Uhl, W.; Wessely, H. J. Z. Anorg. Allg. Chem. 1981, 479, 41. 24. 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. 25. CRC Handbook of Chemistry and Physics. 84th edition. CRC Press, Boca Raton, Florida. 2003. 26. Huffman, J. C.; Skupinski, W. A.; Caulton, K. G. Cryst. Struct. Commun. 1982, 11, 1435. 27. Noonan, K. J. T.; Gates, D. P. Angew. Chem. mt. Ed. 2006, 45, 7271. 28. Honeyman, C. H.; Foucher, D. A.; Dahmen, F. Y.; Rulkens, R.; Lough, A. J.; Manners, I. Organometallics 1995, 14, 5503. 29. SAINT, Version 7.03A; BrukerAXS Inc.: Madison, Wisconsin, USA, 1997-2003. 30. A. Altomare, M. C. B., M. Camalli, G.L. Cascarano, C. Giacovazzo, A. Guagliardi, A.F.F. Moliterni, G. Polidori, R. Spagna, S1R97. J. App!. Cryst. 1999, 32, 115. 31. SHELXTL, Version 5.1; BrukerAXS Inc.: Madision, Wisconsin, USA, 1997. References start on page 101 103 Chapter 6 Redox-Active Iron-Containing Polymers: Synthesis and Anionic Polymerization of a C-Ferrocenyl Substituted Phosphaalkene * 6.1 Introduction Macromolecules containing transition metals are known to possess unique redox, magnetic, optical and electronic properties. These materials are attractive as potential ceramic precursors, catalyst supports and for specialty applications.13The ferrocenyl moiety has played an integral role in the growth of metal-containing polymer science; many polymers are known where ferrocene is incorporated into the main chain, side-chain and even into dendrimers.6 The earliest ferrocene-containing polymers were prepared from radical polymerization of vinyl ferrocene.7’6 The chemical functionality of the three-coordinate phosphine moiety in poly(methylenephosphine)s has already been demonstrated by utilizing these polymers as effective ligands for Pd-catalyzed Suzuki cross-coupling reactions.9The preparation of macromolecules composed of phosphines and ferrocenes is an attractive synthetic target with the prospect of accessing well-defined bimetallic polymers exhibiting interesting electronic, magnetic or catalytic properties. There are very few effective synthetic routes to phosphine ferrocene hybrid polymers, as of now, only a few examples have been reported.1012 In this Chapter, the synthesis and addition polymerization of C-ferrocenyl phosphaalkene 6.1 to afford a new redox-active, poly(methylenephosphine) (6.2) is described. *A version of this chapter has been published. Kevin J. T. Noonan, Derek P. Gates and Brian 0. Patrick. Redox-active iron-containing polymers: synthesis and anionic polymerization of a C-ferrocenyl substituted phosphaalkene. Chem Commun. 2007, 3658. Chapter 6 104 Ph 1 .‘7BuLI [ Fc = —--2.MeOH Bu1PC4H “ glymeRT I I IMes Fc IMes FcI L .Jfl 6.1 6.2 Scheme 6.1 Synthesis of poly(methylenephosphine) containing a ferrocenyl moiety by treatment of MesP=C(Ph)(Fc) with n-butyllithium in glyme. Although metalla-phosphaalkenes are quite common,115 the target monomers, ferrocenyl-substituted phosphaalkenes, are not widely available. Some Becker-type phosphaalkenes [i.e. RP=C(OSiMe3)R’] possessing C-Fe and P-Fe substituents are known;12° however, very few reported non-heteroatom-substituted P=C systems have been reported. A rare example,tBuP=CHFc, was detected in solution but cfimerized upon attempted isolation.2° For polymerization studies, monomers with no heteroatoms directly attached to the PC bond are desired to avoid possible side reactions during initiation. Consequently, methods to access new ferrocene-substituted phosphaalkenes are needed. The phospha-Peterson reaction is a general and convenient route to phosphaalkenes.2128This remarkable reaction involves the condensation of a silyl phosphide Li[RP(SiMe3)Jwith a ketone and affords phosphaalkenes with a variety of substituents. However, suitably bulky substituents must be employed to render the desired P=C compound isolable. 6.2 Results and Discussion 6.2.1 Synthesis of MesPC(Ph)(Fc) In order to prepare C-ferrocenyl phosphaalkene 6.1, benzoylferrocene was first synthesized according to a modified literature procedure and sublimed at 120 °C in vacuo.29 An ethereal solution of MeLi was added to the air-sensitive MesP(SiMe3)2in THF under N2 and this mixture was stirred for Ca. 1 h at 60 °C. Removal of an aliquot from the reaction mixture for analysis using 31P NMR spectroscopy revealed that MesP(SiMe3)2(ô31p = —162) had been completely consumed. A new signal was observed (ô31p = —187) which was assigned to Li[MesP(SiMe3)]. The reaction mixture was then treated with benzoylferrocene at 60 °C and References start on page 116 Chapter 6 105 stirred for approximately 30 mm. The deep red reaction mixture was analyzed using 31P NMR spectroscopy and two new signals at 218 and 211 ppm (70:30 ratio) had appeared and were consistent with the formation of E/Z-6.f. Noteably, the Li[MesP(SiMe)](631P = -i 87) had been completely consumed. Crystals suitable tor X-ray diffraction were obtained from the slow evaporation of a hexanes solution of EZ-6.1. The solid-state molecular structure of phosphaalkene 6.1 is shown in Figure 6.1 and, interestingly, the Fc substituent is cis to the bulky P-Mes substituent(i.e. Z-6.1). Dissolution of the crystals of Z-6.1 inCD,followed-by31P NMR analysis revealed signals consistent with both E-6.1 and Z-6.1 isomers in solution and is indicative of interconversion (ca. 85:15 ratio). Selective 1H NMR NOE experiments provided confirmation that the major isomer in solution is Z-6.1. Irradiating at the resonance frequency of the ortho CH3 groups on the mesityl ring (oH = 2.30) of the major isomer leads to enhancement of signals assigned to the ortho hydrogens of the substituted Cp ring (OH = 4.61), of the major isomer. This signal enhancement is consistent with the Mes and Fc substituents being cis configured and therefore the Z-6.1 isomer was concluded to be the major isomer (85 %) in solution. 0 M L FcPh Ph SIMe3CI Ph MesP(SiMe3)2 THF,60 : MesP(SiMe3)Li THF, 60 °C ,5Pz:C\ -LICIMes Fc Mes Fc -(SMe3)20 6.1 6.1 Scheme 6.2 Preparation of ferrocenyl phosphaalkene from the MesP(SiMe3)2,methyllithium and benzoyl ferrocene. 6.2.2 Attempted synthesis of MesP=CFc2(6.3) and MesP=C(th)(Fc) (6.4) Upon discovery that compound 6.1 was stable and isolable at room temperature, the synthesis of MesP=CFc2(6.3) and MesP=C(th)(Fc) (6.4) were attempted using the phospha Peterson reaction. 1,1-Diferrocenyl ketone and 1-[2-thiophenecarbonyl]ferrocene were prepared according to literature procedures.3°A solution of Li[MesP(SiMe3)]in THF was treated with diferrocenyl ketone. Unfortunately, upon analysis of the reaction mixture using 31P NMR spectroscopy, no signal was observed that could be assigned to P-Mes phosphaalkenes (oalp> References start on page 116 Chapter 6 106 200). Treatment of Li[MesP(SiMe3)]in THF with 1-[2-thiophenecarbonyl]ferrocene resulted in the formation of the desired phosphaalkerie (ó3lP = 221.8, 219.6 EIZ isomers in THF) along with several other unwanted side products. Neither recrystallization nor distillation could afford the pure product in appreciable quantities. MesP(SIMe3)Li ________ Fc Fc = Mes Fc Fe 6.3 C th s MesP(SMe3)Li 6O0Cjk = 6.4 Scheme 6.3 Attempted synthesis of MesP=CFc2and MesPC(th)(Fc) using the phospha Peterson reaction. 6.2.3 X-ray crystallography The molecular structure of Z-6.1 is shown in Figure 6.1 and the metrical parameters for this compound are displayed in Table 6.1. The P=C bond length in 6.1 (1.697(2) A) is fairly long compared to typical C-substituted phosphaalkenes (1 .61-1 .71 A);31 however, it is similar to the P=C bond length in MesP=CPh2(1.692(3) A).32 Interestingly, the cis-Fc substituent shows a larger angle to the P=C bond than the ideal sp2 angle (LPC—CFC = 130.7(1)0) and is significantly greater than the typical cis aryl substituent of P-mesityl phosphaalkenes (LP=C— = 125 — 1280).21 We speculate that this is a consequence of increased steric repulsion between the cis configured Fc and Mes moieties in Z-6.1. Remarkably, the angle between the best planes of the C5H4 moiety and the PC bond is just 13.2(1)°. For comparison, the analogous angle in the only other crystallographically characterized C-ferrocenyl phosphaalkene (Me3S1P=C(OSiMe)Fc)is 36.6019 whilst that in MesP=CPh2is 42.9°. This data suggests that significant m-conjugation is present between the Fc substituent and the P=C bond in Z-6.1. Additional support for ut-conjugation in Z-6.1 is provided by the shortening of C(1)—C(8) bond References start on page 116 Chapter 6 107 (1.468(2) A) with respect to the typical C—C single bond length (ca. 1.54 A) and by the intense red colour of 6.1 compared with pale yellow MesP=CPh2, C21 C5 C15 025 Figure 6.1 Solid state molecular structure of Z-6.l. Thermal ellipsoids at 50% probability; hydrogen atoms are omitted for clarity. Selected bond lengths (A) and angles (°). P1—Cl = 1.697(2), P(1)-C(18) 1.842(2), C(1)-C(2) = 1.512(2), C(1)-C(8) = 1.468(2); C(8)—C(1)—C(2) = 114.9(1), C(8)—C(1 )—P(1) = 130.7(1), C(2)—C(1 )—P(1) = 114.2(1), C(1 )—P(1 )—C(1 8) = 107.3(1). 6.2.4 Polymerization of ferrocenyl phosphaalkene monomer 6.1 To determine whether anionic initiation of the C-ferrocenyl phosphaalkene 6.1 was feasible, a stoichiometric combination of 6.1 with BuLi (1 equiv) in glyme (1 ,2-dimethoxyethane) was undertaken. The 31P NMR spectrum of the reaction mixture showed only a singlet at -18.7 ppm which is consistent with the quantitative formation of Li[Mes(Bu)PC(Fc)Ph]. Once the feasibility of anionic initiation had been demonstrated, a solution of monomer 6.1 in glyme was treated with BuLi (5 mcI %). The progress of the polymerization was monitored by 31P NMR C4 06 03 ClP1 C7 C26t 023 do C22 C14 C24 Cli C20 C17 C16 References start on page 116 Chapter 6 108 spectroscopy and, after seven days, 50 — 60 % of monomer 6.1 had been cleanly converted to polymer 6.2 ( —5 br). Quenching with methanol terminated the polymerization and polymer 6.2 was separated from 6.1 by precipitation from THF into methanol (x4). The golden coloured polymer was analyzed by triple detection GPC and an absolute number average molecular weight (Ma) was determined to be 9,500 with a polydispersity index (PDI) of 1 .21. The identical experiment was repeated and the same M was achieved with a PDI of 1.18. Further studies are underway to ascertain whether this polymerization may be conducted in a living fashion. In order to investigate the electronic properties of 6.1 and 6.2, both were analyzed by UV-Vis spectroscopy (Figure 6.2). Previous studies on phosphaalkenes have demonstrated that P=C bonds are capable of electronic communication through 3t conjugation.° The deep red solution of 6.1 exhibited two broad absorbances at = 512 nm and 331 nm which are assigned to the d-d transition of the ferrocenyl moiety and the t—it’ transition for the P=C bond, respectively. Interestingly, the absorbance maximum at 512 nm is significantly red-shifted when compared to that for vinylferrocene (max = 442 nm) and ferrocene (?max = 440 nm).8’41 The dramatic bathochromic shift is most likely attributed to some conjugation between the ferrocene group and the P=C bond. The second transition at 331 nm, assigned to the t—t transition of the P=C bond, is similar to that observed for MesP=CPh2(Xmax = 324 nm).42 In contrast, the gold coloured macromolecule 6.2 exhibits only a weak transition at 448 nm, which is very similar to the d—d transition for ferrocene (440 nm). References start on page 116 Chapter 6 109 0.5 0.4 0 CD 0(1) -o <C 0.2 0.1 300 400 500 600 700 800 Wavelength (nm) Figure 6.2 UV/Vis spectra of monomer 6.1 (top) and polymer 6.2 (bottom) (0.1 mM in toluene). The electrochemical properties of poly(methylenephosphine) 6.2 were analyzed by cyclic voltammetry (Figure 6.3). The observed quasi-reversible one electron oxidation of 6.2 is consistent with the expected ferrocene-ferrocenium couple. The detection of a single wave suggests that the Fc moieties are electronically isolated; analogous to the case of poly(vinylferrocene). The half-cell potential (vs SCE) for polymer 6.2 is (zE112 = 0.41 V) is slightly lower that for poly(vinylferrocene) (AE112 = 0.44 — 0.48 /). For comparison, FcCH2PPh a possible model compound for polymer 6.2, similarly exhibits a reversible oxidation slightly lower than that for ferrocene (zE = —0.04 V).44 References start on page 116 Chapter 6 110 2 !A. (A) Potential (V) vs SCE Figure 6.3 Cyclic Voltammogram of 6.2 in CH2I (scan rate I OOmV/s) containing 0.1 M [(n Bu)4N]PF6.Referenced to decamethyl ferrocene. Concentration of 6.2 = 2.4 mM Finally, compound 6.2 was analyzed by thermal gravimetric analysis (Figure 6.4). The onset polymer degradation temperature was found (Tonset = 290 °C) to be slightly higher than that of the —[MesP-CPh2] polymer (T05 = 265 °C). This is a consequence of increased thermal stability imparted by the ferrocene moiety. Moreover, the ceramic yield upon polymer degradation was found to be —21 % which is consistent with iron and phosphorus remaining. We suspect this polymer may be a useful precursor to iron-phosphide ceramic materials. -0.5 0.5 References start on page 116 Chapter 6 111 100 90 80 70 40 30 20 10 00 100 200 300 400 500 600 700 800 900 Temperature (°C) Figure 6.4 TGA of the ferrocenyl phosphine polymer 6.2. 6.3 Conclusions In summary, a phosphaalkene analogue of vinyl ferrocene has been prepared and polymerized anionically to afford new redox active polymers. This development could be used to synthesize bimetallic polymers possessing both Fc moieties and AuCI moities which may have interesting optoelectronic, magnetic and pre-ceramic properties. The potential to polymerize these monomers in a living fashion would also be of interest for preparing new macromolecules. References start on page 116 Chapter 6 112 6.4 Experimental Table 6.1 X-ray crystallographic data of 6.1. Crystal 6.1 Formula C26H5PFe Formula Weight 424.28 Crystal System triclinic Space Group p j Color red a(A) 8.0754(8) b (A) 8.4767(7) c(A) 16.382(2) a(°) 101.647(3) 96.033(4) y(°) 96.270(4) V(A3) 1082.4 (8) Z 2 T(K) 173(2) ! (Mo 1(a) (cm1 7.79 Crystal Size (mm) 0.25x0.20x0.10 DcaIcd. (g cm3) 1.302 20 (max) (°) 50.8 No. of Reflections 23402 No. of unique data 5083 0.032 Reflections/parameters 19 86 ratio R1, wR2[I > 20(l)]a 0.034; 0.091 R1, wR2 (all data)a 0.049; 0.095 GOF 1.07 aR = Z IIFI - IFII / Z 1F0. wR2 = [ (w (F02 — F2) )I w(F02)]112 6.4.1 Materials and general procedures All manipulations of air and/or water sensitive compounds were performed under pre purified nitrogen (Praxair, 99.998%) using standard high vacuum or Schlenk techniques or in an Innovative Technology glovebox. Hexanes and dichioromethane were deoxygenated with nitrogen and dried by passing through a column containing activated alumina. THF was freshly distilled from sodium/benzophenone ketyl. CD2I and C6D were purchased from Cambridge Isotope Laboratories and were used as received. Methanol was degassed prior to use. MeLi (1.5 M in Et20) BuLi (1 .6 M in hexanes), SiMe3Cl were purchased from Aldrich and used as References start on page 116 Chapter 6 113 received. Alkyllithium reagents were titrated prior to use. Benzoyl ferrocene was prepared according to literature procedures and sublimed in vacuo (120 oc)29 1,1-Diferrocenyl ketone and I -[2-thiophenecarbonyl]ferrocene were prepared according to literature procedures and sublimed in vacuo at 115 oC3 Air sensitive MesP(SiMe3)2was prepared from literature procedures and distilled at 110 °C in vacuo.45’6 1H, 13C, 19F and 31P NMR spectra were recorded on a Bruker Avance 300 MHz spectrometer. Chemical shifts are reported relative to CHDCI2 (ô = 5.32 for 1H, 54.00 for 13C) or C6HD5( = 7.16 for 1H). 85% H3P04was used as an external standard (ô = 0.0 for 31P). Molecular weights were determined 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; HR5E, HR4 and HR2), Waters 2410 differential refractometer, 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 mL1). Elemental analysis was conducted at the University of British Columbia. 6.4.2 Preparation of MesPC(Ph)(Fc) (6.1): To a stirred solution of MesP(SiMe3)2(5.03 g, 17 mmol) in THE was added MeLi in Et20 (12.2 mL, 1.4 M, 17 mmol) at 25 °C. The reaction mixture was heated to 60 °C for Ca. 1 h and analysis of an aliquot by 31P NMR spectroscopy suggested quantitative formation of MesP(SiMe3)Li(ô = —187). Subsequently, benzoylferrocene (4.94 g, 17 mmol) was added and the reaction mixture was stirred at 60 °C for ca. 30 mm. The 31P NMR spectrum showed signals at 218 and 211 ppm (70:30 ratio) assigned to Z—6.1 and E—6.1, respectively. To the solution was added Me3SiCI (2.15 mL, 17 mmol) to quench the L1OS1Me3.The volatiles were removed in vacuo, the residue was extracted into hexanes (3 x 50 mL), filtered through Celite, and the solvent removed in vacuo. Single crystals of 6.1 (4.16 g, 58%) were obtained from slow evaporation of a hexanes solution of the crude product. op(l21.5 MHz; C6D H3P04)218 (s, IP, References start on page 116 Chapter 6 114 Z- 85%), 211 (s, IP, E- 15%). ÔH(300.I MHz, CD2I;S1Me4)7.5 (m, 5H, E-o,m,p —Ph), 7.10 (m, 5H, Z-o,m,p —Ph), 6.98 (s, 2H, E-m-Mes), 6.69 (s, 2H, Z-m-Mes), 4.61 (t, 2H, 2JH-H = 1.2 Hz, Z-o-Fc), 4.45 (s, 2H, Z-m-Fc), 4.23 (m, 5H, Z-Cp-Fc, 2H, E-m-Fc), 4.10(s, 5H, E-Cp-Fc), 3.79 (s, 2H, E-o-Fc), 2.44 (s, 6H, E-o-CH3)2.37 (s, 3H, E-p-CH3), 2.30 (s, 6H, Z-o-CH3), 2,17 (s, 3H, Z p-CH3). ôc(7S.S MHz, CD2I;SiMe4)194.94 (d, 1Jpc 43 Hz, Z-PC) 190.23 (d, 1Jpc= 45.6 Hz, E-PC) 144.64(d,2Jpc= 27.5 Hz, E-i-Ph) 143.30(d,2Jpc= 14Hz, Z-i-Ph) 140.68(d, 2Jpc= 6.2 Hz, Z-o-Mes) 140.57 (d, 2Jpc= 6.5 Hz, E-o-Mes) 139.34 (s, E-p-Mes) 138.44 (s, Z-p-Mes) 137.76 (d, 1J-c= 48.4 Hz, E-i-Mes) 136.45 (d,1Jpc=40 Hz, Z-i-Mes) 129.93 (d, 3Jp.= 14Hz, E-o-Ph) 129.27 (s, E-m-Mes) 128.46 (s, Z-m-Mes) 128.03 (d, 3Jpc= 7.3 Hz, Z-o-Ph and E-m Ph)127.55 (s, Z-m-Ph) 127.13 (s, Z-p-Ph) 89.81 (d, 2Jpc= 31.2 Hz, Z-i-Fc) 87.28( d, 2Jpc 16.6 Hz, E-i-Fc) 70.87 (s, Z-Cp-Fc) 70.76 (s, E-Z-m-Fc) 70.44 (s, E-Cp-Fc) 69.13 (d, 3Jpc= 3.5 Hz, E-o-Fc) 67.79 (d, 3Jp.c= 17.1 Hz, Z-o-Fc) 22.99 (d, 3Jpc 8.7 Hz, Z-o-CH3)22.14 (d, 3Jpc 8.4 Hz, E-o-CH3)21.59 (s, E-p-CH3)21.31 (s, Z-p-CH3). MS (El, 70eV): 424 [8, 36; M]. UV/Vis (C7H9): ?.max () = 331 (4600), 512 (930). Anal. Calcd. ForC26H5PFe: C, 73.60; H, 5.94. Found: C, 73.30; H, 6.04. 6.4.3 Attempted synthesis of MesP=CFc2 (6.3): A solution of MesP(SiMe3)2(0.2 g, 0.67 mmol) in THF (5 mL) was treated with MeLi (0.45 mL, 1.5 M, 0.67 mmol). Removal of an aliquot from the reaction mixture for analysis by 31P NMR spectroscopy confirmed the formation of Li[MesP(SiMe3)](ô31p = — 187). To the reaction was added the 1,1 ‘-diferocenyl ketone but phosphaalkene formation was not observed. 6.4.4 Attempted synthesis of MesP=C(th)(Fc) (6.4): A solution of MesP(SiMe3)2(1.0 g, 3.37 mmol) in THE (5 mL) was treated with MeL1 (2.25 mL, 1.5 M, 3.4 mmol). Removal of an aliquot from the reaction mixture for analysis by 31P NMR spectroscopy confirmed the formation of Li[MesP(SiMe3)](ô31p = — 187). To the reaction was added the I -[2-thiophenecarbonyl]ferrocene and the mixture was stirred for ca. I h. Two References start on page 116 Chapter 6 115 signals attributed to the EIZ isomers of MesP=C(th)(Fc) 6.4 were observed in the 31P NMR spectrum of the reaction mixture (ô31p = 221.8, 219.6 EIZ isomers in THF). The EIZ mixture could not be isolated by recrytallization or distillation. 6.4.5 Synthesis of [P(Mes)C(Fc)(Ph)] (6.2): A typical polymerization procedure is described. To a stirred solution of MesP=CPh(Fc) (1.00 g, 2.3 mmol) at room temperature in glyme (7 mL) was added BuLi (1.5 M, 80 iL, 0.12 mmol). The reaction was stirred at room temperature and monitored by 31P NMR spectroscopy. The growth of a broad signal in the 31P NMR spectrum was observed over 7 days and, subsequently, the reaction mixture was removed from the glovebox, quenched and precipitated using methanol (3 x 100 mL). Residual solvent was removed in vacuo. Yield = 250 mg (25 %). ôp(l2l.5MHz; C8D6H3P04)—5 ppm(br, IP). ÔH(300.l MHz, C6D;SiMe4)8-6.5(br, 7H, Aryl-H), 4.5-3.5 (br, 9H, Fc-H), 3-1.5 (br, (H, Mes-H). GPC-LLS (THF): M = 9,500 PDI = 1.21 Rh = 1.5 nm. UVIV1s (C7H9): (s) = 448 (210). Anal. Calcd. forC26H5PFe: C, 73.60; H, 5.94. Found: C, 73.50; H, 6.29. 6.4.6 X-ray crystallography Crystal Data and refinement parameters are listed in Table 6.1 for compound Z-6.1. The single crystal was immersed in oil and mounted on a glass fiber. Data was collected at 173±0.1 K on a Bruker X8 APEX 2 diffractometer with graphite-monochromated Mo Ka radiation. Data collection and integration was completed using the Bruker SAINT47 software package. All structures were solved by direct methods and subsequent Fourier difference techniques and refined anisotropically for all non-hydrogen atoms using the SHELXT48crystallographic software package from Bruker-AXS. The data set was corrected for Lorentz and polarization effects. CCDC reference numbers 642679 References start on page 116 Chapter 6 116 6.5 References 1. Mark, J. E.; Ailcock, H. R.; West, R., Inorganic Polymers. Oxford University Press: Oxford, 2005. 2. Manners, I., Synthetic Metal Containing Polymers. Wiley-VCH: Weinheim, 2004. 3. Abd-El-Aziz, A. S.; CarraherJr., C. E.; Pittman Jr., C. U.; Sheats, J. E.; Zeldin, M., Macromolecules Containing Metal and Metal-like Elements. Wiley: Weinheim, 2003- 2006. 4. Abd-El-Aziz, A. S.; Manners, I. J. lnorg. Organomet. Polym. Mater. 2005, 15, 157. 5. Nguyen, P.; GOmez-Elipe, P.; Manners, I. Chem. Rev. 1999, 99, 1515. 6. D. Astruc, J.-C. Blais, E. Cloutet, L. Djakovitch, S. Rigaut, V. Sartor, C. Valerlo, Top. Curr. Chem., 2000, 210, 229. 7. Pittman, C. U. J. lnorg. Organomet. Polym. 2005, 15, 33. 8. Arimoto, F. S.; Haven Jr., A. C. J. Am. Chem. Soc. 1955, 77, 6295. 9. Tsang, C. W.; Baharloo, B.; RiencU, D.; Yam, M.; Gates, D. P. Angew. Chem. tnt. Ed. 2004, 43, 5682. 10. Withers, H. P.; Seyferth, D. Fellmann, J. D.; Garrou, P. D.; Martin, S. Organometallics 1982, 1, 1283. 11. Honeyman, C. H.; Peckham, T. J.; Massey, J. A.; Manners, I. Chem. Commun. 1996, 2589. 12. Smith, R. C.; Chen, X.; Protasiewicz, J. D. lnorg. Chem. 2003, 42, 5468. 13. Weber, L. Coord. Chem. Rev. 2005, 249, 741. 14. Weber, L. Angew. Chem. tnt. Ed. EngI. 1996, 35, 271. 15. Nixon, J. F. Chem. Rev. 1988, 88, 1327. 16. Pietschriig, R.; Niecke, E.; Nieger, M.; Airola, K. J. Organomet. Chem. 1997, 529, 127. 17. Pietschnig, R.; Nieger, M.; Niecke, E.; Airola, K. J. Organomet. Chem. 1997, 541, 237. 18. Moser, C.; Orthaber, A.; Nieger, M.; Belaj, F.; Pietschnig, R. Dalton Trans. 2006, 3879. References start on page 116 Chapter 6 117 19. Grunhagen, A.; Pieper, U.; Kottke, T.; Roesky, H. W. Z. Anorg. Aug. Chem. 1994, 620, 716. 20. Cummins, C. C.; Schrock, R. R.; Davis, W. M. Angew. Chem. mt. Ed. EngI. 1993, 32, 756. 21. Yam, M.; Chong, J. H.; Tsang, C. W.; Patrick, B. 0.; Lam, A. E.; Gates, D. P. lnorg. Chem. 2006, 45, 5225. 22. Kawanami, H.; Toyota, K.; Yoshifuji, M. J. Organomet. Chem. 1997, 535, 1. 23. Jouaiti, A.; Geoffroy, M.; Bernardinelli, G. Chem. Commun. 1996, 437. 24. Jouaiti, A.; Geoffroy, M.; Bernardinelli, G. Tetrahedron Lett. 1993, 34, 3413. 25. Jouaiti, A.; Geoffroy, M.; Bernardinelli, G. Tetrahedron Lett. 1992, 33, 5071. 26. Daugulis, 0.; Brookhart, M.; White, P. S. Organometaiics 2002, 21, 5935. 27. Termaten, A.; van der Sluis, M.; Bickelhaupt, F. Eur. J. Org, Chem. 2003, 2049. 28. lonkin, A. S.; Marshall, W. J. Heteroatom Chem. 2002, 13, 662. 29. Tappe, K.; Knochel, P. Tetrahedron: Asymmetty 2004, 15, 91. 30. Sarhan, A. E. W.; Nouchi, Y.; Izumi, T. Tetrahedron 2003, 59, 6353. 31. Appel, R., In Multiple Bonds and Low Coordination in Phosphorus Chemistiy, ed.; Regitz, M.; Scherer, 0. J., eds. Thieme: Stuttgart, 1990. 32. Van der Knaap, T. A.: Klebach, T. C.; Visser, F.; Bickeihaupt, F.; Ros, P.; Baerends, E. J.; Stam, C. H.; Konijn, M. Tetrahedron 1984, 40, 765. 33. Mundt, 0.; Becker, G.; UhI, W. Z. Anorg. Aug. Chem. 1986, 540/541, 319. 34. Wright, V. A.; Gates, D. P. Angew. Chem. mt. Ed. 2002, 41, 2389. 35. Wright, V. A.; Patrick, B. 0.; Schneider, C.; Gates, D. P. J. Am. Chem. Soc. 2006, 128, 8836. 36. Smith, R. C.; Protasiewicz, J. D. Eur. J. lnorg. Chem. 2004, 998. 37. Badri, A.; Jouaiti, A.; Geoffroy, M. Magn. Reson. Chem. 1999, 37, 735. 38. Jouaiti, A.; Geoffroy, M.; Terron, G.; Bernardinelli, G. J. Am. Chem. Soc. 1995, 117, 2251. References start on page 116 Chapter 6 118 39. Jouaiti, A.; Geoffroy, M.; Terron, G.; Bemardinelli, G. J. Chem. Soc. Chem. Commun. 1992, 155. 40. Kawanami, H.; Toyota, K.; Yoshifuji, M. Chem. Lett. 1996, 533. 41. Pittman, C. U.; Lai, J. C.; Vanderpool, D. P.; Good, M.; Prado, R. Macromolecules 1970, 3, 746. 42. Klebach, C,; Lourens, R.; Bickeihaupt, F. J. Am. Chem. Soc 1978, 100, 4886. 43. Flanagan, J. B.; Margel, S.; Bard, A. J.; Anson, F. C. J. Am. Chem. Soc. 1978, 100, 4248. 44. Downard, A. J.; Goodwin, N. J.; Henderson, W. J. Organomet. Chem. 2003, 676, 62. 45. Becker, G.; Mundt, 0.; Rössler, M.; Schneider, E. Z. Anorg. Aug. Chem. 1978, 443, 42. 46. Lidde, S. T.; Izod, K. Organometallics 2004, 23, 5550. 47. SAINT, Version 6.02. BrukerAXS Inc., Madison, Wisconsin, USA, 1999. 48. SHELXTL Version 5.1, Bruker AXS Inc.: Madision, Wisconsin, USA, 1997. References start on page 116 119 Chapter 7 Polymerization of MesP=CPh2Derivatives, Functionalized Poly(methylenephosphine)s 7.1 Introduction Most work in the broad field of polymer chemistry has focused on synthesizing materials composed primarily of organic elements such as C, N and Q.’ However, there is growing interest in the preparation of macromolecules containing inorganic elements because of the potential to access materials with unique properties.216 The recent discovery of living anionic P=C bond polymerization afforded the first macromolecule with alternating phosphorus and carbon atoms in the main chain (Scheme 7j)•17 18 The incorporation of different functional groups offers a means to tailor the polymer properties. For example, the incorporation of metal centers into poly(methylenephosphine)s described in Chapter Six of this thesis yielded a material with redox capabilities. In an attempt to expand on this work, the preparation of polymeric phosphines with different pendant functional groups is currently under investigation.19 21 1.’BuLi(1 -4mol%) r i Ph 2.MeOH PC Buj—P—C1H Mes’ Ph glyme Mshj n Scheme 7.1 Living polymerization of phosphaalkenes. In order to expand upon the polymerization of MesP=CPh2,several P=C containing monomers bearing electron donating and electron withdrawing groups have been synthesized and polymerized. The inspiration to modify the substituents surrounding the P=C bond is derived from olefins (i.e, styrene).22The living anionic polymerization of styrenic monomers bearing functional groups has been investigated; however, the functional moiety can have Chapter 7 120 undesirable effects on the polymerization reactivity of the olefinic species.22’3 Many functionalized styrenic monomers display different initiation and propagation behavior than styrene itself, which limits the generality of anionic polymerization.22 In an effort to expand upon anionic P=C polymerization, an investigation into MesP=CPh2derivatives is presented in this chapter. The versatile phospha-Peterson reaction was selected as a suitable route to prepare a series of phosphaalkenes.2433There are two reactions that are both classified as phospha-Peterson condensations. One reaction, which is analogous to the Peterson olefination reaction,34 involves the in situ formation of a RP(Li)S1Me3 and subsequent treatment with a sterically hindered ketone to render the desired phosphaalkene (Scheme 7.2 — Route A). The base catalyzed phospha-Peterson reaction proceeds by combination of a bis(silyl) phosphine [of the type RP(SiMe3)2]and a ketone in the presence of catalytic base (i.e, KOH or NaOH) to form the desired phosphaalkene along with the easily removable Me3SiOSiMe (Scheme 7.2 — Route B).35 Utilizing this well-known methodology for synthesizing new phosphaalkenes bearing electron donating or electron withdrawing groups at the periphery of the P=C bond seemed attractive. In this Chapter the synthesis and of four new phosphaalkenes (7.la, 7.lb, 7.lc and 7.lf) is described and preliminary polymerization experiments for monomers 7.la-7.le have been conducted. Several of these newly prepared polymers offer the intriguing possibility of post- polymerization modification as the pyridyl moiety in 7.2 could be used to coordinate metal atoms or the chloro substituent of 7.5 could undergo substitution reactions to alter the polymer microstructure. Li R’ R’ SiMe3 R’ R—F( + -L’OSM Base (cat) R—P + SiMe3 R” ° R’ R” SiMe3 R” Route A Route B Scheme 7.2 Standard phospha-Peterson procedures as a route to phosphaatkene monomers. References start on page 139 Chapter 7 121 7.2 Results and Discussion 7.2.1 Synthesis of several new MesP=C(Ph)(Ar) phosphaalkenes using the phospha Peterson methodology Compounds 7.la — 7.le were all synthesized using the base catalyzed phospha Peterson reaction (Scheme 7•3)•36 Only two of these compounds, 7.ld and 7.le, have been synthesized previously.33All five molecules were purified by distillation at approximately 200 °C followed by recrystallization from either hexanes ortoluene. The isolated yields for 7.la-7.le varied between —20 and 40 %. These molecules all exhibit characteristic 31P NMR shifts for P Mes phosphaalkenes (downfield atô3p> 200). Compound Z—7.la was obtained as a crystalline material from a concentrated hexanes solution. Upon dissolution of the Z—7.la crystals in CD2I for analysis by 31P and 1H NMR spectroscopy, signals corresponding to both the E and the Zisomers were observed (31P =211.0 and 209.8: E/Z—7.la), suggesting facile EIZ isomerization in solution. A concentrated hexanes solution of EIZ—7.1 b afforded crystalline E— 7.lb in modest yield (Yield = 32%). NMR analysis of the crystals dissolved in CD2Idid not reveal any E/Zisomerizatiori (ô31P = 238.1: E-7.lb). Phosphaalkene 7.lc has only been obtained as a viscous yellow oil and solution phase NMR studies revealed the presence of two signals assigned to both the E and Z isomers (ô31 229.9 and 229.2 ppm). Cisltrans isomerization of phosphaalkenes has been investigated previously,25 3739 and UV light was deemed necessary for interconversion between the two species in solution. Interestingly, studies in our laboratory have revealed that cis/trans isomerization for certain phosphaalkenes can occur even in the absence of light.33 Further investigations are currently underway to determine the mechanism of isomerization for compounds 7.la and 7.lc. Inducing isomerization of compound 7.lb is also under investigation. References start on page 139 Chapter 7 122 SiMe3 Ph Ph “P—Mes + cat. NaOH P=C’ SiMe( ‘r-Me3SiOSiMe Mes 7.la R = NEt2 7.lb R = Cl 7.lc R = Me 7.ld R = F SIMe3 Ph Ph P—Mes + ca. a SiMe( -Me3SiOSiMe Mess 7.1 e Scheme 7.3 Synthesis of several substituted mesityl phosphaalkenes using the base catalyzed (NaOH) phospha-Peterson reaction. Varying the electronic properties of the P=C bond by altering the surrounding side groups. Attempts to prepare the 4-pyridyl phosphaalkene 7.lf using the base catalyzed phospha-Peterson reaction were undertaken. Though phosphaalkene formation was confirmed by analysis of the reaction mixture using 31P NMR spectroscopy (7.lf: ôp = 255 and 246 in THF), several unidentified byproducts were observed in the region typical of trivalent phosphorus (ô31P = —20). Unfortunately, attempts to isolate compound 7.lf from this reaction mixture were unsuccessful. To circumvent, or at the very least minimize, the undesired side reactions, a classical phospha-Peterson reaction was employed where, MesP(Li)SiMe3was prepared in situ by addition of MeLi to a colorless MesP(SiMe3)2solution in THF. The formation of MesP(Li)SiMe3was confirmed by 31P NMR spectroscopy (ô3ip = —187 in THF) and the reaction mixture was then treated with 4-benzoylpyridine at 60 °C. Upon stirring for 1 h, followed by addition of SiMe3CI to quench the LiOSiMe3,compound 7.lf was extracted from the reaction mixture and successively recrystallized using hexanes (3x) to yield the pure product (Yield = 8 %). The synthesis of phosphaalkene 7.lf was confirmed upon 31P NMR analysis of a solution of 7.lf in CD2I that revealed two signals (ô31 = 255.2 and 246.2 EIZ isomers) in the expected region (ô31pfor P-Mes phosphaalkenes > 200). The 1H NMR spectrum of 7.lf in CD2I exhibits a characteristic downfield doublet for the Aryl C-H bonds in the meta position of the pyridyl References start on page 139 Chapter 7 123 moiety as displayed in Figure 7.1 (ÔIH = 8.56 and 8.32 EIZ—7.lf). Attempts to purify compound 7.lf by distillation at 200 °C resulted in isolation of an orange-coloured solid (M = 22 300, PDI = 1.22) in low yield (6 %) from four successive precipitations into hexanes (200 mL). The polymer has been tentatively assigned as compound 7.2 but only GPC-LLS experiments have been conducted on the material and more structural characterization is needed to confirm the assignment. Both the base catalyzed phospha-Peterson and the conventional phospha Peterson reactions seem well suited to form P-Mes phosphaalkenes. The versatility offered by simply changing the ketone in the preparative procedure results in the convenient side group modification and could be applied to synthesize a wide range of new phosphaalkenes. Mes DI, r PhiPh I IP—Li + o=C P=C_ uv PCSiMe -LiOSiMe3 Me Mesjn 7.lf 7.2 Scheme 7.4 Preparation of 4-pyridyl phosphaalkene 7.lf using the phospha-Peterson reaction. The MesP(Li)(SiMe3)2species is combined with 4-benzoyl pyridine. The resultant phosphaalkene can be purified by recrystallization. E/Z CH-N 9 8 7 6 5 4 3 2 1 ppm Figure 7.1 1H NMR spectrum of compound 7.lf in CD2I.The diagnostic signals for the m pyridyl C-H protons are assigned above. References start on page 139 Chapter 7 124 7.2.2 X-ray crystallographic analysis of compounds 7.la, 7.lb and 7.lf X-ray structure determination of single crystals for compounds 7.la, 7.lb, and 7.lf were conducted at low temperature. Unfortunately, compound 7.lc could not be crystallographically characterized since attempts to recrystallize this compound from hexanes and toluene resulted in viscous yellow oils. The solid-state molecular structures of 7.la, 7.lb, and 7.lf are displayed in Figures 7.2, 7.3 and 7.4, respectively. Compound 7.1 a crystallizes as the Z isomer, 7.1 b crystallizes preferentially as the E isomer and 7.lf crystallizes as mixture of E/Z isomers (E isomer of 7.lf is displayed in Figure 7.4). The important metrical values of the crystallographically characterized phosphaalkenes are outlined in Table 7.1 and the cell constants and data collection values are displayed in Table 7.2. Table 7.1 Important metrical parameters for crystallographically characterized phosphaalkenes 7.la, 7.lb and 7.lf. 7.la 7.lb 7.lf Bond Lengths P=C 1.708(2) 1.696(2) 1.700(2) PCMes 1 .839(2) 1 .829(2) 1.839(2) CCtrans 1.492(2) 1.483(2) 1.496(2) C—C, 1.471(2) 1 .479(2) 1.496(2) Bond Angles LCMeSPC 106.1(1) 107.1(1) 107.8(1) LP=CCtrans 114.7(1) 116.5(1) 117.4(1) LP=C—CdS 128.8(1) 126.1(1) 125.1(1) LCcjsCCtrans 116.4(1) 117.4(1) 117.4(1) Angles Between Planesa Mes 71.8 67.1 72.2 Artrans 43.3 32.9 22.9 Ar1 39.9 48.9 55.7 a The angle between the mean plane of the specified aryl ring atoms to the mean plane C10PC( Ctrans)(Ccis) atoms. Compounds with localized (p—p)t bonds between phosphorus and carbon normally exhibit P=C bond lengths in the range of 1.61 — 1.71 A.4° The three compounds shown below have relatively long P=C bonds (1.69—1.71 A) especially compound 7.la (1 .708(2) A). The diethylamino moiety of compound 7.1 a is extremely donating as evidenced by the short CA.I— NEt2 bond (1 .376(2) A). Moreover, the angles around the N atom sum to 359.3° which is expected for an sp2 hybridized N atom but not for an sp3 hybridized atom. These observations References start on page 139 Chapter 7 125 clearly support donation of the lone pair centered on the nitrogen atom into the st-cloud of the aryl ring. A possible rationale for the long P=C bond is that the 4-NEt2-C6Hmoiety is donating electron density into the phosphaalkene bond causing the slight elongation observed (1.708(2) A) when compared to MesP=CPh2(1.692(3) A).24 The P-Mes bond lengths in all three solid- state molecular structures are shorter than the expected P-C single bond length (1.85 — 1.90 A)41 which suggests a slight degree of conjugation between the Mes group and P=C bond. However, the angles between the planes of the P=C bond and the mesityl groups are large (—70°) for all three compounds (7.la, 7.1 b, 7.lf) which is indicative of little to no conjugation between those moieties. The aryl substituents seem to have more it conjugation with the PC bonds than the mesityl rings in all three cases. This is evidenced by the smaller angles between planes of the aryl rings and P=C bonds (Table The angles surrounding the C atom of the P=C bond are essentially planar for all three compounds (—360°), but the moieties of compounds 7.la, 7.lb and 7.lf are bent further away from the P=C bond (L PC— C 125 — 128°) than the Artrans (L PCCtrans — 115 — 117°) groups. This suggests some degree of steric repulsion between the Mes and moieties. References start on page 139 Chapter 7 126 C15 C14 C16 C13 CDI \C17 C3 C9 I C19 C2C8 I I C22\ IC20 C24 C21 C6 C25C26 Figure 7.2 Solid state molecular structure of 7.la. Crystallized preferentially as the Z isomer. Thermal ellipsoids at 50% probability; hydrogen atoms are omitted for clarity. Selected bond lengths (A) and angles (°). P(l)—C(lO) = 1.708(2), P(l)—C(1) = 1.839(2), C(10)—C(11) = 1.492(2), N(1) )—C(20) = 1.376(2) N(1)—C(23) = 1.464; C(1)—P(1)—C(10) = 106.1(1), P(1)— C(10)—C(17) = 128.8(1), C(1l)—C(1O)--C(17) = 116.4(1), N(1)—C(20)—C(21) = 122.4(1), C(23)— N(1)—C(20) = 120.5(1), C(25)—N(1)—C(20) = 121 .7(1), C(25)—N(1)--C(23)= 117.1(1), References start on page 139 Chapter 7 127 :m cii C2 C20 C22 c19 Cl 8 C17 T cii C3J01 C12 C2C9 C16 C13 C61 015 C14 Figure 7.3 Solid state molecular structure of 7.1 b. Crystallized preferentially as the E isomer. Thermal ellipsoids at 50% probability; hydrogen atoms are omitted for clarity. Selected bond lengths (A) and angles (°). P(1)—C(10) = 1.696(2), P(1)—C(i) = 1.829(2), C(10)—C(1i) = 1.479(2), 0(1 0)—C(1 7) = 1.483(2), C(20)—Cl(1) = 1.737(2); 0(1 )—P(1 )-.-C(1 0) = 107.1(1), P(1 )— 0(1 0)—C(1 I )= 126.1(1), P(1 )—C(1 0)—C(1 7) = 116.5(1), C(1 9)—C(20)—Cl(1) = 119.1(1), C(21 )— C(20)—Cl(1) = 119.9(1). C21 Ni C22 C19 ‘\C17 C18 P1 010 C3 Cli Cl C16 C2 09 C12 01504 08 c13 C5 ‘ 014 06 Figure 7.4 Solid state molecular structure 7.lf. Crystallized as EIZ mixture. Thermal ellipsoids at 50% probability; hydrogen atoms are omitted for clarity. Selected bond lengths (A) and angles (°). P(1)—C(10) = 1.700(2), P(i)—C(1) = 1.839(2), C(10)—C(11) = 1.496(2), C(19)— N(1) = 1.363(3), C(21)—N(1) = 1.359(3); C(1)—P(1)—C(10) = 107.8(1), P(i)—C(10)—C(i7) = 117.4(1), P(1 )—C(1 0)—C(i I) = 125,1(1), C(2 I )—N(1 )—C(1 9) = 117.0(2). References start on page 139 Chapter 7 128 7.2.3 Preliminary investigations into the polymerization behavior of phosphaalkenes 7.1 a — 7.le. Compounds 7.la — 7.le have all been investigated as potential monomers for anionic PC bond polymerization. In an inert atmosphere glovebox at room temperature, compound 7.la could not be polymerized in glyme using BuLi as the initiator. The attempted polymerization was monitored after 13 days using 31P NMR spectroscopy and no signal corresponding to the expected poly(methylenephosphine) was observed. A small resonance at —40 ppm was visible in the 31P NMR spectrum which most likely results from addition of BuLi across the P=C bond forming a carbanion. Stoichiometric combination of BuLi with a solution of 7.la in glyme was analyzed by 31P NMR spectroscopy and revealed nearly quantitative formation of the same species at — 40 ppm. Further investigations are currently underway to ascertain why this monomer will not polymerize and to hopefully circumvent this undesired behavior. This is especially surprising since theCH2(H)(4-NMe-C64styrene analog does polymerize in the presence of anionic initiators.42 Compound 7.ld was combined with BuLI in glyme at room temperature and the reaction was stirred for 7 days. An aliquot was removed from the reaction mixture and analyzed by 31P NMR spectroscopy which revealed only 10% conversion from the monomeric MesP=C(Ph)(4-F-C6H4)to poly(methylenephosphine). Precipitation of the mixture into 50 mL of hexanes did not yield any polymer. The electron-withdrawing fluoro group may stabilize the propagating carbanionic species by drawing electron density into the aryl ring and thus, slowing the rate of propagation considerably. To date, compound 7.ld has not been polymerized with sufficient conversion to isolate any polymeric material. Compound 7.le was also treated with BuLi in an attempt to isolate a new poly(methylenephosphine). Surprisingly, no evidence for polymerization is observed. Upon addition of the initiator to a pale yellow solution of 7.le in glyme, a noticeable color change from yellow to red was immediately observed. However, analysis of the reaction by 31P NMR spectroscopy after two days did not reveal any signal in the region typical of References start on page 139 Chapter 7 129 poly(methylenephosphine). This result was particularly striking when one considers the anionic polymerization of styrene (7.3) and 2-vinyl pyridine (7.4). H H HH1 H H n RNa R C— C2—C—-cH: Na H’b óó 73 n-2 H H HH1 H HRN I In cc R C—C-+CH2-C—Cc: H’ô H (N rN ..N1 — LJ] &“N içi 74 n-2 + Scheme 7.5 Anionic polymerization of styrene versus 2-vinyl pyridine. Styrene and 2-vinylpyridine differ at only one position where a CH moiety in the aryl ring is replaced by a N atom but this small difference has a large affect on polymerization behavior. Both the phenyl and pyridyl groups promote nucleophilic attack at the terminal CH2 moiety because the carbanion that is formed is stabilized by electron delocalization onto the aryl rings (Scheme 7.5). However, when comparing the two monomers, the pyridyl moiety in 7.4 has an electronegative N atom, which inductively withdraws electron density from the olefinic bond. This polarization results in the CH2 moiety being more electropositive and thus much more susceptible to nucleophilic attack when compared to 7323 In addition, the N atoms of the growing poly(2-vinylpyridine) chain can also coordinate the Na counterion which is responsible for creating more “free” or solvent separated cation/anion pairs in solution (Scheme 7.5). As discussed in Chapter 3, “free” or solvent separated ion pairs contribute more to the overall rate of polymerization than “tight” or contact ion pairs. Therefore, a growing poly(2-vinylpyridine) chain will have not only have more “free” ions than a growing polystyrene chain but the 2-vinyl pyridine monomer is also more susceptible to nucleophilic attack. This results in a much higher rate constant of propagation for 2-vinyl pyridine polymerization (7.4 — k= 7300 L mor1 s1) when compared to styrene (7.3 — k= 950 L mor1 s1) under otherwise identical conditions.23 One would expect MesP=C(Ph)(2-Py) to exhibit a significant increase in the rate of References start on page 139 Chapter 7 130 propagation relative to MesP=CPh2analogously to 2-vinylpyridine polymerizing faster than styrene. The N atom of the 2-pyridyl ring should inductively withdraw electron density from the P=C bond in compound 7.le making it more electropositive and more susceptible to nucleophilic attack. Moreover, the N atom of the pyridyl moiety in compound 7.1 e should be able to coordinate the Li counterion providing more “free” anions in solution to increase the rate of polymerization. The surprising lack of polymerization for the 2-pyridyl phosphaalkene 7.le warrants further investigation to better understand this behavior. Compounds 7.lb and 7.lc undergo anionic polymerization in ethereal solvents to afford the desired poly(methylenephosphine)s 7.5 and 7.6, respectively (Scheme 7.6). Polymerizations were conducted under inert atmosphere using‘1BuLi as initiator at room temperature and the macromolecules were isolated with modest molecular weights (7.5: M = 17 200, PDI = 1.09; 7.6: M = 27 600, PDI = 1.25). Each polymer exhibits a broad resonance at —7 ppm in the 31P NMR spectrum. A representative 31P NMR spectrum of compound 7.5 is displayed in Figure 7.5. The polymerizations of 7.lb and 7.lc were not conducted with anionic polymerization grade monomer and consequently, the polymerizations did not proceed in a living fashion. Further investigations will focus on living polymerization of these monomers and chemically modifying the side groups to tune the properties of the resultant poly(methylenephosphine). Ph 1.BuLi r Phi — p—d 2.MeOH ‘Bu-l--P—C-lH 7.5 R = ---c(i---ci Mel R glyme, RT [MsR j 7.6 R = ---(J---Me Scheme 7.6 Synthesis of poly(methylenephosphines) 7.5 and 7.6 by combination of phosphaalkenes 7.lb and 7.lc with substoichiometric amounts of n-butyllithium in glyme at room temperature under inert atmosphere. References start on page 139 Chapter 7 131 * I I I I I 200 100 0 -100 -200 ppm Figure 7.5 31P NMR spectrum of compound 7.5. * indicates a slight amount of poly(methylenephosphine oxide). 7.3 Conclusions Several new P-Mes phosphaalkenes have been prepared and crystallographically characterized. These exhibit similar structural features to other carbon substituted P=C bonds. The solid-state molecular structure of compound 7.la indicated that the NEt2moiety was strongly electron donating and surprisingly, this species did not polymerize in the presence of anionic initiators. Compounds 7.lb and 7.lc polymerized using BuLi as the initiator and the isolable polymer 7.5 has a functional group (Cl) which can be exploited for post-polymerization modification. Compounds 7.la, 7.ld and 7.le did not yield isolable poly(methylenephosphine)s by anionic polymerization and further studies are underway to determine suitable polymerization conditions for these monomers. Investigations to polymerize compound 7.lf will be conducted in the future. References start on page 139 Chapter 7 132 7.4 Experimental Table 7.2 X-ray crystallographic data of 7.la, 7.lb and 7.lf Crystal 7.la 7.lb 7.lf Formula C52H60N2P C22H0PCI C21H20NP Formula Weight 774.96 350.80 317.35 Crystal System monoclinic triclinic orthorhombic Space Group C I 2/c I PT Pbca Color orange yellow yellow a(A) 16.897(5) 8.578(5) 17.343(5) b(A) 15.365(5) 10.737(5) 9.589(5) c(A) 18.081(5) 11.148(5) 20.860(5) a(°) 90.000(5) 68.773(5) 90.000(5) 109.968(5) 73.306(5) 90.000(5) y (°) 90.000(5) 86.855(5) 90.000(5) V(A3) 4412(2) 915.4(8) 3469(2) Z 4 2 8 T(K) 173(2) 173(2) 173(2) t(Mo Ka) (cmi 1.36 2.96 1.58 Crystal Size (mm) 0.50x0.50x0.80 0.30x0.70x0.80 0.40x0.45x0.65 DId. (g cm-3) 1.167 1.273 1.215 20 (max) (°) 56.2 55.8 55.6 No. of Reflections 32332 26895 26119 No. of unique data 5301 4336 4085 0.039 0.025 0.036 Reflections/parameters 20.54 19.71 19.27 ratio R1, wR2[l >20(l)]a 0.038; 0.087 0.041; 0.110 0.041; 0.098 R1, wR2 (all data)a 0.063; 0.102 0.052; 0.122 0.066; 0.113 GOF 1.03 1.05 1.05 = IlFol - IFIl I Z IF0. wR2 = [ (w (F0’ — Fe’)’ )I w(F’)’]11 7.4.1 Materials and general procedures All manipulations of air and/or water sensitive compounds were performed under pre purified nitrogen (Praxair, 99.998%) using standard high vacuum or Schienk techniques or in an Innovative Technology glovebox. Hexanes and dichloromethane were deoxygenated with nitrogen and dried by passing through a column containing activated alumina. THE was freshly distilled from sodium/benzophenone ketyl. CDCI3was distilled from P205 and degassed. CD2I and DMSO—d6were purchased from Cambridge Isotope Laboratories and were used as received. Methanol was degassed prior to use. 4-benzoylpyridine, 4-methylbenzophenone, 4- chlorobenzophenone were purchased from Aldrich and sublimed prior to use. 4- diethylaminobenzophenone was used as received from Aldrich. Both BuLi (1 .45M in hexanes) References start on page 139 Chapter 7 133 and MeLi (1.5 M in Et20) were purchased from Aldrich and used as received. Alkyllithium reagents were titrated prior to use. 1H, 13C, and 31P NMR spectra were recorded on either a Bruker Avance 300 MHz or Bruker Avance 400 MHz spectrometer. Chemical shifts are reported relative to residual CHCI3 (ô = 7.26 for 1H and and 77.16 for 13C), CHDCI2 (ô = 5.32 for 1H and and 54.00 for ‘3C). 85% H3P04was used as an external standard o = 0.0 for 31P. 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) HR5E (2 000 —4 000 000), HR4 (5 000 — 500 000) and HR2 (500—20 000), Waters 2410 differential refractometer ( = 920 nm), Wyatt tristar miniDAWN (laser light scattering detector operating at ). = 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 mLj. Refractive index increments were estimated by comparison of the concentration of the prepared polymer solution to the concentration calculated by the Waters 2410 differential refractometer. Elemental analysis was conducted at the University of British Columbia. 7.4.2 Preparation of MesP=C(Ph)(4-NEt2-5H4)7.la Liquid MesP(SiMe3)2(7 g, 0.024 mol) was added to a solution of 4- diethylaminobenzophenone (6.82 g, 0.024 mol) in dry THE (— 20 mL) under inert atmosphere. A catalytic amount (—0.05 g) of dry NaOH was added to the reaction mixture and upon stirring for several hours, the mixture turned bright orange. The reaction was stirred under N2 in an inert atmosphere glovebox for several days. Removal of an aliquot for analysis by 31P NMR spectroscopy revealed that the MesP(SiMe3)2had been completely consumed (ô31p = —162) and replaced by 2 signals at (ô = 211 and 209). Upon removal of the THE in vacuo, the mixture was transferred to a round bottom flask and fractionally distilled at high temperatures (> 200 °C). The distillate was recrystallized from hexanes and ground into a fine powder and dried in vacuo for several days at 55°C. Yield (2.17 g, 23%) op(l21.5 MHz; CD2IH3P04)211.0(1 P, s, EIZ References start on page 139 Chapter 7 134 isomer), 209.8 (IP, s, EIZ isomer). ÔH(300.l MHz, CD2I;SiMe4)7.50 (2H, m, E/ZAryl—H), 7.36 (4H, m, E/ZAryl—H), 7.07 (4H, m, E/ZAryl—H), 6.91 (2H, m, E/ZAryI—H), 6.79 (2H, s, E/Z Aryl—H), 6.70 (4H, m, E/Z AryI—H), 6.59 (2H, d, JPH = 9 Hz, E,’Z Mes—H), 6.32 (2H, d, JPH = 9 Hz, E’Z Mes—H), 3.39 (4H, q, JHH = 7 Hz, E/Z NCH2CH3),3.27 (4H, q, 3JHH = 7 Hz, E/Z NCH2CH3), 2.30 (6H, s, E,Zo—CH3),2.27 (6H, s, E/Zo—CH3),2.24 (3H, s, EIZp—CH3),2.17 (3H, s, E/Zp— CH3), 1.17 (6H, t, 3J- = 7.2 Hz, EIZ NCH2CH3), 1.09 (6H, t, 3JHH = 7.2 Hz, E/Z NCH2CH3).Low Res El: m/z 387 [M+, MesP=C(Ph)(4-NEt-64)],Anal. Calcd. forC26Ha0NP: C, 80.59; H, 7.80; N, 3.61. Found: C, 80.37; H, 7.86; N, 3.62. 7.4.3 Preparation of MesP=C(Ph)(4-Cl-C5H4)7.lb Liquid MesP(SiMe3)2(9.87 g, 0.033 mol) was added to a solution of 4- chlorobenzophenone (7.20 g, 0.033 mol) in dry THF (— 20 mL) under inert atmosphere. A catalytic amount (—0.05 g) of dry NaOH was added to the reaction mixture and upon stirring the mixture turned a bright yellow. The reaction was stirred under N2 in an inert atmosphere glovebox for several days. Removal of an aliquot for analysis by 31P NMR spectroscopy revealed that the MesP(SiMe3)2had been completely consumed (o31p = —162) and replaced by 2 signals at (631P = 239 and 237). Upon removal of the THE in vacuo, the mixture was transferred to a round bottom flask and fractionally distilled at high temperatures (> 190 °C). The distillate was recrystallized from hexanes and ground into a fine powder and dried in vacuo for several days at 55 °C. The E isomer (ö31p = 239) crystallized selectively. Yield (3.75 g, 32 %) op(12l .5 MHz; CD2IH3P04)238.1 (IP, Eisomer, s). H(3OO.l MHz, CD2I;SiMe4)7.46 (2H, m, E Ary[—H), 7.30 (2 H, d, JPH = 8.6 Hz, EAryl—H), 7.09 (3 H, m, EAryl—H), 6.86 (2H, d, EAryl—H), 6.72 (2H, s, EMes—H), 2.25(6 H, s, Eo—CH3),2.19(3 H, S, Ep—CH3).c(75.5MHz, CD2I; SiMe4 - unassigned) 192.2 (d, Jp = 45 Hz) 143.7 (s), 143.3 (d, Jp = 8 Hz), 143.0 (s), 140.4 (d, Jc = 7 Hz), 138.8 (s), 136.1 (d, Jc = 42 Hz), 134.8 (d, Jc = 6 Hz), 129.1 (s), 128.8 (d, Jp = 7 Hz), 128.7 (s), 128.4 (d, Jpc = 7 Hz), 127.7 (s) , 22.1 (s), 20.9 (s). Low Res El: m/z 350 [M+, References start on page 139 Chapter 7 135 MesP=C(Ph)(4-CIC6H4)],Anal. Calcd. forC22H01P: C, 75.32; H, 5.75. Found: C, 75.41; H, 5.97. 7.4.4 Preparation of MesP=C(Ph)(4-Me-C6H4)7.lc Liquid MesP(SiMe3)2(10.0 g, 0.034 mol) was added to a solution of 4- methylbenzophenone (6.62 g, 0.034 mcI) in dry THF (— 20 mL) under inert atmosphere. Catalytic (-0.05 g), dry NaOH was added to the reaction mixture. Over several hours, the mixture turned bright yellow. After several days of stirring under inert atmosphere, removal of an aliquot for analysis by 31P NMR spectroscopy revealed that the MesP(SiMe3)2had been completely consumed (ô31p = —162) and replaced by 2 signals at (o31p = 230 and 229). Upon removal of the THF in vacuo, the mixture was transferred to a round bottom flask and fractionally distilled at high temperatures (> 200 °C). The distillate was recrystallized from hexanes and ground into a fine powder and dried in vacuo for several days at 55 °C. Yield (4.61 g, 42 %). An EIZ mixture was isolated after recrystallization. op(l2l .5 MHz; CD2I H3P04) 229.9 (1P, s) 229.2 (1P, s). H(3OO.i MHz, CD2I;SiMe4)7.51 (2H, m, EIZAryI—H), 7.38 (4H, m, E/ZAryI—H), 7.13 (6H, dd, EIZ Aryl—H), 6.92 (2H, d, JHH = 7.2 Hz, EIZArjI—H), 6.82 (IH, s, EIZ Aryl—H), 6.79 (1 H, s, EIZ Aryl—H), 6.77 (2H, s, EIZ Mes—H), 6.74 (2H, s, EIZ Mes—H) 2.39 (3H, s, E/Z C6H4p—CH3)2.31 (6H, s, E/Z Mes o—CH3), 2.30 (6H, s, E/Z Mes o—CH3), 2.26 (3H, s, E’Z C6H4p—CH3), 2.24 (3H, s, E/Z Mes p—CH3), 2.22 (3H, s, E/Z Mes p—CH3). Low Res El: m/z 330 [M+, MesP=C(Ph)(4-MeC)], 7.4.5 Preparation of MesPC(Ph)(4-Pyr) 7.lf An ethereal solution of MeLi (1.4 M, 4.8 mL) was added to a colorless solution of MesP(SiMe3)2(2.0 g, 0.0067 mol) in THF (10 mL) at room temperature. The solution turned yellow upon addition of the MeLi and the reaction mixture was allowed to stir for I — 1.5 h at 60 °C. Analysis of the reaction mixture by 31P NMR spectroscopy revealed the in situ formation of MesP(Li)SiMe3,which was treated with 4-benzoyl pyridine (1 .23 g, 0.0067 mol) and References start on page 139 Chapter 7 136 subsequently the reaction mixture was allowed to stir for several hours. The formation of 7.lf was confirmed by 31P NMR spectroscopy with the appearance of two signals (ô31p = 255 and 246) in the 31P NMR spectrum. The solvent was removed in vacuo, and the product was extracted with hexanes (3 x 10 mL). Three successive recrystallizations from a minimal amount of hexanes produced the pure product in low yield. (Yield 0.160 g, 8%) ôp(l2l.S MHz; CDCI3 H3P04)255.2 (1 P, s) 246.2 (1 P, s). ÔH(300.l MHz, CDCI3;SiMe4)8.56 (2H, dd, E/Z N—CH), 8.32 (2H, dd, E/ZN—CH), 7.51-7.48 (2H, m, E/ZAryl—H)7.42—7.31 (5H, m, E’ZAryl—H), 7.16—7.05 (3H, m, E/Z AryI—H), 6.83 (2H, m, E/Z Aryl—H), 6.76 (2H, m, E,’Z Aryl—H), 6.71 (4H, s, E,Z Mes H), 2.26 (6H, s, E/Zo—CH3),2.24 (6H, s, E/Zo—CH3),2.21 (3H, s, E/Zp—CH3),2.20 (3H, s, E/Z p—CH3). Low Res El: mlz 317 (M+, MesP=C(Ph)-4-Pyr), Anal. Calcd. for C21H20PN: C, 79.47; H, 6.35; N, 4.41. Found: C, 79.15; H, 6.54; N, 4.32. 7.4.6 Isolation of poly(methylenephosphine) 7.2 from the distillation residue The brown residue from the distillation was dissolved in THF (20 mL) and added to a hexanes (Ca. 200 ml) which resulted in the precipitation of a yellow flaky solid. The polymer was precipitated four times from a concentrated THF solution with hexanes. The solid was dried in vacuo at 60° overnight. Yield = 0.589 g (6 %). GPC-LLS (THE): M = 22 300, PDI = 1.22. 7.4.7 Attempted Polymerization of Me5PC(Ph)(4-NEt2-6H4) Reaction was conducted with M:l ratio of 33:1. Addition of 19 1tL of BuLi (1.45 M in hexanes) by microsyringe to a stirring yellow solution of 7.la (0.350 g, 0.9 mmol) in glyme (5 mL) produced an immediate colour change from yellow to red. The reaction mixture was stirred for 13 days in an inert atmosphere glovebox and then an aliquot was removed for NMR analysis. A 31P NMR spectrum of the reaction mixture exhibited two signals for the EIZ isomers of the MesP=C(Ph)(4-NEt2-6H4)phosphaalkene but no broad signal corresponding to the desired poly(methylenephosphine) was observed. References start on page 139 Chapter 7 137 7.4.8 Attempted polymerization of MesP=C(Ph)(4-F-C6H4) Reaction was conducted with M:l ratio of 25:1. Addition of 23 tL of BuLi (1.36 M in hexanes) by microsyringe to a stirring yellow solution of 7.ld (0.275 g, 0.8 mmol) in glyme (2 mL) produced a colour change from yellow to red. The reaction mixture was stirred for 7 days in an inert atmosphere glovebox and an aliquot was removed for NMR analysis. A 31P NMR spectrum of the reaction mixture exhibited two signals for the EIZ isomers of the MesP=C(Ph)(4-F-C6H4)phosphaalkene and a small broad signal corresponding to the poly(methylenephosphine) was observed. Precipitation of the reaction mixture using hexanes (50 mL) did not yield any of the desired poty(methylenephosphine). 7.4.9 Attempted polymerization of MesP=C(Ph)(2-Py) Reaction was conducted with M:l ratio of 25:1. Addition of 24 tL of BuLi (1.36 M in hexanes) by microsyringe to a stirring yellow solution of 7.le (0.25 1 g, 0.79 mmol) in glyme (2 mL) produced a colour change from yellow to red. The reaction mixture was stirred for 2 days and 31P NMR analysis of the reaction mixture displays two signals for the EIZ isomers of the MesP=C(Ph)(2-Py) phosphaalkene and no signal corresponding to the poly(methylenephosphine) was observed. 7.4.10 Polymerization of MesP=C(Ph)(4-CI-C5H4)to form 7.5 Addition of 50 iL of BuLi (1 .45 M in hexanes) by microsyringe to a stirring yellow solution of 7.lb (0.600g. 1.72 mmol) in THF (3.0 mL) produced an immediate colour change from yellow to red. Precipitation of the reaction mixture after 2 d into hexanes (2 x 70 mL) resulted in the isolation of the substituted poly(methylenephosphine). (Yield 0.071 g, 12%). ôp(l2l.S MHz; CDCI3H3P04)—7 (1P, br). GPC-LLS (THF): M = 17200, PDI = 1.09; References start on page 139 Chapter 7 138 7.4.11 Polymerization of MesP=C(Ph)(4-Me-C6H4)to form 7.6 Addition of 13.5 1tL of “BuLl (1.45 M in hexanes) by microsyringe to a stirring yellow solution of 7.lc (0.350 g, 1.1 mmol) in glyme (2 mL) produced an immediate colour change from yellow to red. The reaction was monitored by 31P NMR spectroscopy and proceeded to approximately 90% conversion after 2 days. Precipitation of the reaction mixture into hexanes (2 x 70 mL) resulted in the isolation of the substituted poly(methylenephosphine). (Yield 0.247 g, 71 %). op(l 21.5 MHz; CDCI3H3P04)—7 (1 P, br). ÔH(300.l MHz, CDCI3;SiMe4)8 —6 (11 H, br, Aryl—H), 3—0.5 (12H, br, Mes—CH3 Ph—Me). GPC-LLS (THF): M = 27 600 PDI = 1.25. 7.4.12 X-ray crystallography Crystal Data and refinement parameters are listed in Table 7.1. All single crystal were immersed in oil and mounted on a glass fiber. Data were collected at 173±0.1K on a Bruker X8 APEX 2 diffractometer with graphite-monochromated Mo Ka radiation. Data was collected and integrated using the Bruker SAINT43 software package. All structures were solved by direct methods and subsequent Fourier difference techniques and refined anisotropically for all non- hydrogen atoms using the SHELXTL44crystallographic software package from Bruker-AXS. All data sets were corrected for Lorentz and polarization effects. Compounds 7.la and 7.lb did not exhibit any crystallographic complexity. Compound 7.lf crystallized as a mixture of E!Z isomers that produced some disorder in modelling atoms NI, N2, C14 and C20. Though the E isomer is shown in Figure 7.4, the Z isomer could also have been displayed. References start on page 139 Chapter 7 139 7.5 References 1. Odian, G., Principles of Polymerization, 4th Edition. Wiley: New York, 2004. 2. Rider, D. A.; Liu, K.; Eloi, J. C.; Vanderark, L.; Yang, L.; Wang, J. Y.; Grozea, D.; Lu, Z. H.; Russell, T. P.; Manners, I. ACS Nano 2008, 2, 263. 3. Wang, Z.; Masson, G.; Peiris, F. C.; Ozin, G. A.; Manners, I. Chem. Eur. J. 2007, 13, 9372. 4. Wang, X. S.; Wang, H.; Frankowski, D. J.; Lam, P. G.; Welch, P. M.; Winnik, M. A.; Hartmann, J.; Manners, I.; Spontak, R. J. Adv. Mater. 2007, 19, 2279. 5. Naka, K.; Umeyama, T.; Nakahashi, A.; Chujo, Y. Macromolecules 2007, 40, 4854. 6. Nagata, Y.; Chujo, Y. Macromolecules 2007, 40, 6. 7. Na, H. S.; Morisaki, Y.; Aiki, Y.; Chujo, Y. J. Polym. Sd. Part A: Polym. Chem. 2007, 45, 2867. 8. Wright, V. A.; Patrick, B. 0.; Schneider, C.; Gates, D. P. J. Am. Chem. Soc. 2006, 128, 8836. 9. Sebastian, M.; Hissler, M.; Fave, C.; Rault-Berthelot, J.; Odin, C.; Reau, R. Angew. Chem. mt. Ed. 2006, 45, 6152. 10. Baumgartner, T.; Wilk, W. Org. Lett. 2006, 8, 503. 11. Vanderark, L.A.; Clark, T. J.; Rivard, E.; Manners, I.; Slootweg, J. C.; Lammertsma, K. Chem. Commun. 2006, 3332. 12. Heilmann, J. B.; Scheibitz, M.; Qin, Y.; Sundararaman, A.; Jakle, F.; Kretz, T.; Bolte, M.; Lerner, H. W.; Hoithausen, M. C.; Wagner, M. Angew. Chem. Int. Ed. 2006, 45, 920. 13. Sundararaman, A.; Victor, M.; Varughese, R.; Jakie, F. J. Am. Chem. Soc. 2005, 127, 13748. 14. Mark, J. E.; Alicock, H. R.; West, R., Inorganic Polymers. Oxford University Press: 2005. 15. Chandrasekhar, V., Inorganic and Organometallic Polymers. Springer-Verlag: Berlin, 2005. 16. Manners, I. Angew. Chem. Int. Ed. EngL 1996, 35, 1602. References start on page 139 Chapter 7 140 17. Noonan, K. J. T.; Gates, D. P. Angew. Chem. mt. Ed. 2006, 45, 7271. 18. Tsang, C.-W.; Yam, M.; Gates, D. P. J. Am. Chem. Soc. 2003, 125, 1480. 19. Tsang, C. W.; Baharloo, B.; Riendi, D.; Yam, M.; Gates, D. P. Angew. Chem. mt. Ed. 2004, 43, 5682. 20. Gillon, B. H.; Patrick, B. 0.; Gates, D. P. Chem. Commun. 2008, 2161. 21. Noonan, K. J. T.; Patrick, B. 0.; Gates, D. P. Chem. Commun. 2007, 3658. 22. Hirao, A.; Loykulnant, S.; Ishizone, T. Prog. Polym. Sd. 2002, 27, 1399. 23. Szwarc, M., Carbanions, Living Polymers, and Electron Transfer Processes. Interscience: New York, NY, 1968. 24. Becker, G.; Uhi, W.; Wessely, H.-J. Z. Anorg. Allg. Chem. 1981, 479, 41. 25. Van der Does, T.; Bickeihaupt, F. Phosphorus Sulfur Silicon Relaf. Elem. 1987, 30, 515. 26. Jouaiti, A.; Geoffroy, M.; Bernardinelli, G. Chem. Commun. 1996, 437. 27. Jouaiti, A.; Geoffroy, M.; Bernardinelli, G. Tetrahedron Lett. 1993, 34, 3413. 28. Jouaiti, A.; Geoffroy, M.; Bernardinelli, G. Tetrahedron Lett. 1992, 33, 5071. 29. Kawanami, H.; Toyota, K.; Yoshifuj, M. J. Organomet. Chem. 1997, 535, 1. 30. lonkin, A. S.; Marshafl, W. J. Heteroatom Chem. 2002, 13, 662. 31. Termaten, A.; van der Slus, M.; Bickeihaupt, F. Eur. J. Org. Chem. 2003, 2049. 32. Daugulis, 0.; Brookhart, M.; White, P. S. Organometallics 2002, 21, 5935. 33. Yam, M.; Chong, J. H.; Tsang, C. W.; Patrick, B. 0.; Lam, A. E.; Gates, D. P. lnorg. Chem. 2006, 45, 5225. 34. van Staden, L. F.; Gravestock, D.; Ager, D. J. Chem. Soc. Rev. 2002, 31, 195. 35. Becker, G.; Becker, W.; Mundt, 0. Phosphorus Sulfur Relat. Elem. 1983, 14, 267. 36. Becker, G.; Gresser, C.; Uhi, W. Z. Naturforsch. 1981, 36b, 16. 37. Appel, R.; Knoll, F.; Ruppert, I. Angew. Chem. mt. Ed. EngI. 1981, 20, 731. 38. Yoshifuji, M.; Toyota, K.; Inamoto, N. Tetrahedron Left. 1985, 26, 1727. 39. Yoshifuji, M.; Toyota, K.; Inamoto, N.; Hirotsu, K.; Higuchi, T. Tetrahedron Left. 1985, 26, 6443. References start on page 139 Chapter 7 141 40. Appel, R., In Multiple Bonds and Low Coordination in Phosphorus Chemistry, ed.; Regitz, M.; Scherer, 0. J., Thieme: Stuttgart, 1990. 41. CRC Handbook of Chemistry and Physics. 84th edition. CRC Press, Boca Raton, Florida. 2003. 42. Se, K.; Kijima, M.; Fujimoto, T. Polym. J. 1988, 20, 791. 43. SAINT, Version 6.02. BrukerAXS Inc., Madison, Wisconsin, USA, 1999. 44. SHELXTL Version 5.1. BrukerAXS Inc., Madision, Wisconsin, USA, 1997. References start on page 139 142 Chapter 8 Summary and Future Directions 8.1 Summary The main theme of this thesis was two-fold: to develop controlled routes for the polymerization of phosphaalkenes and to expand upon the chemistry of functional polymers possessing phosphorus atoms in the main chain. Living polymerization of olefins has had a profound impact on the broad field of macromolecular chemistry.14The expansion of living polymerization techniques to monomers containing inorganic elements in the quest for materials exhibiting unique properties is an exciting prospect.5’6The similar reactivity of alkenes and phosphaalkenes and the previously reported addition polymerization of phosphaalkenes led us to attempt the living anionic polymerization of the MesP=CPh2phosphaalkene.79 In Chapter 2, the ambient temperature living anionic polymerization of phosphaalkenes was described. Several experiments were conducted to ascertain whether the polymerization proceeded in a living fashion. Performing the polymerization reaction in the glovebox, while rigorously excluding moisture and impurities provided the desired poly(methylenephosphine) with modest molecular weights and low polydispersities. Using 31P NMR spectroscopy it was confirmed that the MesP=CPh2phosphaa!kene was completely consumed and the living Bu[MesP—CPh2]Lihad formed quantitatively. Moreover, kinetic studies revealed the polymerization reaction follows pseudo 1st order kinetics up to 50% conversion with a small apparent rate constant of propagation (k = 21 L moM hj. Two separate experiments were performed to confirm that the molecular weight of the growing polymer chain increases linearly with conversion. By varying the concentration of BuLi in the polymerization, precise control over the polymer chain length was achieved. This living methodology was also expanded to the MesP=C(Ph)(4-OMe-C6H4)substituted monomer. Finally, to illustrate the living nature of the Chapter 8 143 P=C system, a block copolymer was prepared from styrene and MesP=CPh2.Treatment of a MesP=CPh2solution in glyme with living polystyryl anion resulted in the synthesis of the polystyrene-biock-poly(methylenephosphosph me) 2.6. Two separate copolymer experiments were conducted and the expected molecular weights were in reasonable agreement with those determined using triple detection GPC analysis. Upon confirmation of the living nature of phosphaalkene polymerization, the BuLi initiated living anionic polymerization of MesP=CPh2was studied at a variety of temperatures (T = 296.3, 301.8, 307.4, 313, 318.6, and 324.2 K) with a fixed monomerto initiator ratio (50:1). The consumption of monomer and formation of polymer were monitored by 31P NMR spectroscopy and the conversion data obtained was analyzed using first order kinetics. Up to 50 % conversion, the plot of In [M]d[M] vs. time was linear and apparent propagation rate constants (kr) were extracted (k = 21 — 150 L moE1h1; T = 296.3— 324.2 K, respectively). These rate constants were used to construct an Arrhenius Plot and the apparent activation energy for the polymerization of P=C bonds was estimated (Ea = 14.0 ± 0.9 kcal mol _1) The self-assembly of diblock copolymers is an area of current interest as their phase separation capabilities can result in the formation of controlled nanostructures.10 In particular, the potential to exploit block copolymer architectures as nanoscale tools to organize metals is attracting attention. Polyisoprene-block-poly(methylenephosphine) copolymers (4.2) were synthesized by combination of living polyisopropenyl lithium with a MesP=CPh2solution in THF. These copolymers were then coordinated to AuCI by treament of the P1—b—PM P copolymer with (tetrahydrothiophene)AuCl at room temperature. Both 31P NMR spectroscopy and GPC analysis confirmed the coordination of the AuCI moiety. Solution self-assembly of the metallated block copolymers from dilute solutions of heptane were analyzed using transmission electron microscopy revealing that both spherical and cylindrical morphologies of the Au-rich PMP domains were accessible simply by altering the chain lengths of the respective P1 and PMP blocks. References start on page 150 Chapter 8 144 Chapter 5 described some coordination chemistry of the poly(methylenephosphine) with two isoelectronic species; namely, BH3 and CH3.The potential reactivity of the phosphine polymer is modeled by examining the reactivity of molecular phosphines bearing similar substituents as the polymer. In particular, the phosphine-borane adducts Mes(Me)P(BH3)— CPh2H (5.4a) and Mes(Me)P(BH3)—C h2SI e(5.4b) are prepared from the reaction of BH3SMe2with either Mes(Me)P—CPhH(5.3a) or Mes(Me)P—CPh2Si e (5.3b). Treating 5.3a with MeOTf affords methylated model compound, [Mes(Me)P—CPhH]OTf(5.5). Reacting the poly(methylenephosphine) with BH3SMe2affords the phosphine-borane polymer n Bu[MesP(BH3)—CPh2]H(5.6) (M = 4.13 x ion, PDI = 1.26). In contrast, methylation of poly(methylenephosphine) gives n-Bu[MesP—CPh]- /—[MesP(Me)--CPHOTf(5.7) where approximately 50% of the phosphine moieties are methylated (from P NMR). In order to incorporate more functionality into the poly(methylenephosphine), Fe containing polymers were prepared. The ferrocenyl phosphaalkene Mes P=C(Ph)(Fc) (6.1) was prepared from MesP(Li)(SiMe3)and FcC(O)(Ph). This phosphaalkene was polymerized by anionic methods yielding a redox-active polymer (6.2: M = 9500 g mor1, PDI 1.21). One quasi-reversible oxidation was observed upon electrochemical oxidation of the polymeric species, this was assigned to the ferrocene-ferricinium redox couple. The monomer also exhibited some intense absorptions in the visible spectrum, which is indicative oht-conjugation between the P=C and ferrocenyl moiety. Chapter 7 described the synthesis of four new phosphaalkenes bearing new functional groups using the phospha-Peterson reaction. The four new phosphaalkenes MesP=C(Ph)(4- NEt2-C6H4),MesPC(Ph)(4-Cl-C6H4),MesPC(Ph)(4-Me-C6H4)and MesP=C(Ph)(4-Py) were characterized using NMR, x-ray analysis, mass spectrometry and elemental analysis. Some preliminary investigations to polymerize these new phosphalkenes were conducted and not all of the monomers can be polymerized using anionic methods. This was somewhat surprising and further investigations must be undertaken to better probe this behavior. References start on page 150 Chapter 8 145 In conclusion, P=C bonds have been shown to polymerize in a controlled fashion. Several block copolymer architectures bearing functional phosphine units in the polymer backbone have been synthesized by sequential anionic polymerization. Several new P=C monomers have been synthesized and polymerized in an attempt to tailor the properties of the resultant poly(methylenephosphine). 8.2 Future Work As this project has provided a controlled mild route to poly(methylenephosphine)s, the expansion of living polymerization techniques to other phosphaalkene monomers such as 6.1, 7.3b and 7.3c should be undertaken. These monomers have already been shown to polymerize by anionic methods and finding the optimal conditions for living polymerization seems to be a logical extension of this work. Expanding living polymerization to monomer 6.1 could provide access to redox active copolymers, perhaps forming micellar structures from simple redox chemistry, similar to the polystyrene-block-polyferrocenylsilane copolymers described in Chapter 1 (Section 1 4)12 Another crucial investigation in this work will be to investigate whether monomers MesP=C(Ph)(4-NEt2-6H4),MesP=C(Ph)(4-F-C6H4),MesP=C(Ph)(2-Py) and MesP=C(Ph)(4-Py) will polymerize by anionic methods if the polymerization conditions are modified. Why some of these monomers are not amenable to anionic polymerization is not yet understood and further investigation is necessary. In terms of future directions for the MesP=CPh2monomer there are many different copolymer architectures that should be synthesized for example, ABA triblock copolymers should be prepared. If styrene is initiated using the electron transfer reagent sodium naphthalide, it is known to polymerize in two directions forming two active chain ends (Scheme 8.1).13 These two Na stabilized ends could then be used to polymerize MesP=CPh2and form the triblock copolymer illustrated in Scheme 8.1, poly(methylenephosphine)-block-polystyrene b/ock-poly(methylenephosphine). References start on page 150 Chapter 8 146 H H CC head to head •c—c:eNae dimerization aeC—C—C—Ce NaO HPh PhH HPh Na naphthalide H H 2n b=c’ H Ph Ph EPh 1 IH Hi [H Hi [ Phi 2m [H Hi [H HiMes Ph Naj-C-Cj—[C-C4Na [PhMesJm[Ph HJ[H Phj LMesPhJ L’ HJLH Ph] Scheme 8.1 Preparation of ABA triblock copolymers where the A block is poly(methylenephosphine) and the B block is polystyrene. These copolymers would be called poly(methylenephosphirie)-b/ock-polystyrene-block-poly(methylenephos ph me). Another potentially accessible block copolymer that may possess intriguing self- assembly properties are poly(methyl methacrylate)-block-poly(methyienephosphine)s. Poly(methyl methacrylate) is known to form crystalline domains and in combination with the amorphous poly(methylenephosphine) interesting self-assembled structures should be accessible. Methyl methacrylate necessitates fairly special reaction conditions for polymerization to proceed in a living fashion.1416 As outlined in Scheme 8.2, the low temperature (-.78 °C) polymerization of methyl methacrylate using 1,1-diphenylhexyllithium proceeds in a living fashion. The living chain end of MesP=CPh2polymerization bears a strong resemblance to 1,1-diphenylhexyllithium in that the carbanion is doubly-benzylic. I propose that AB block copolymers where the A block is poly(methyenephosphine) and the B block is poly(methylmethacrylate) could be synthesized by initiating the methyl methacrylate polymerization at low temperature. This would potentially provide access to elastomeric polymers bearing phosphine functional groups. References start on page 150 Chapter 8 147 H Me ‘ I n C=C H Ph . H Ph H’ ‘CO2Me H Ph FH MeBuLi i I II “Bu—C-C—Li “Bu—C-C--4C--C-— Li H Ph l1 lh H Ph Li-i CO2Me H Me n C=C Ph “BuLl F Ph] H’ bO2Me Phi H Mern “Bu—P—C—fLi ‘“Buj—P—C—HC--C LiMes Ph LMes hJ [Mes Phim L O2Me ri Scheme 8.2 1,1-diphenylhexyllithium is prepared from 1,1-diphenylethylene and ii-butyl lithium and used to initiate living methyl methacrylate polymerization. The living chain end formed by polymerization of MesP=CPh2resembles 1,1-diphenyihexyllithium in terms of its nucleophilicity as they are both doubly-benzylic. Thus, living poly(methylenephosphine) should be a suitable initiator to polymerize methyl methacrylate and synthesize poly(methyl methacrylate)-b/ock-poly(methylenephosphine). New monomers for anionic polymerization are also of interest within the Gates group. Currently, P-Mes phosphaalkenes possessing aryl substituents on the carbon have been shown to polymerize but MesP=CR2systems bearing alkyl substituents have not yet been polymerized (R = alkyl). Recently, our collaborators reported the synthesis of the MesP=C(H)(Bu) phosphaalkene, and I suspect that anionic polymerization of this monomer should be possible under the appropriate reaction conditions.17The rate constant of propagation for this MesP=C(H)(tBu) polymerization should be much higher than 21 L mor1 h because the formed carbanion upon attack of the “BuLl initiator across the P=C bond would be much less stabilized. The tbutyl and H groups would not provide any resonance stabilization which is in sharp contrast to the two phenyl groups of the doubly-benzylic carbanion from MesP=CPh2polymerization (Scheme 8.3). References start on page 150 Chapter 8 148 Ph ‘7BuLI Ph PC ‘78u—P—C—Li Me Ph Meslh tBu BuLi ‘TBu—P—C—Li Me H MesI’l Scheme 8.3 Reaction of MesP=CPh2with BuLi forms a doubly henzylic carbanion. Addition ofBuLi across the MesP=C(H)(Bu) phosphaalkene will form a less stabilized carbanion because the t-butyl and H groups do not provide any resonance stabilization. The preparation of a thiophene-containing phosphaalkene could be of interest for preparing polymers with interesting optical or electronic properties (Scheme 8.4). The synthesis of this monomer should be possible using the base-catalyzed phospha-Peterson reaction. The polymer would possess not only a functional phosphine moiety but also a sulfur atom that could impart some interesting characteristics to the polymer. Possible avenues to further chemically functionalize the polymer include; exploring the coordination chemistry of the thiophiene, forming bimetallic polymers by coordinating the phosphine and sulfur atoms to metals, or substitution of the 5-position on the thiophene ring to impart more functional groups to the polymer structure. MesP(SiMe3)2+ o=cP KOH ,P=c 2M0H flBUP?JL Ph THF Mes Ph Mesl’h Scheme 8.4 Preparation of thiophene-containing phosphaalkene from the combination of Mes(SiMe3)2and benzoyl thiophene using the base catalyzed phospha-Peterson reaction. One of the earlier projects in the Gates group which was discussed in Chapter 1 involved the attempted cationic polymerization of the Mes*P=CH2phosphaalkene.1819 This compound was combined with substoichiometric quantities of HOTf which produces oligomers of up to 6 repeat units as determined by ESI mass spectrometry. I propose that this compound will undergo anionic polymerization by combining Mes*P=CH2and BuLi under identical reaction conditions for the MesP=CPh2phosphaalkene polymerization (Scheme 8.5). One reaction that References start on page 150 Chapter 8 149 Chi-Wing Tsang conducted in our laboratory prior to my arrival at UBC involved combination of Mes*P=CH2with MeLi in THF. As expected, the yellow Mes*P=CH2reaction solution turns deep red upon addition of the ethereal MeLi solution. However, the reaction was only stirred for 30 mm and precipitation from hexanes yielded no polymer. From Chapters 2 and 3, the MesP=CPh2polymerization with 2% BuLI requires 9 h to quantitatively convert to poly(methylenephosphine), therefore I suspect that anionic Mes*P=CH2polymerization will necessitate longer than 30 mm and this reaction should be revisited. H 1!’BuLi E Hi p 2.MeOH Mes* H [Mes* H j Scheme 8.5 Polymerization of Mes*P=CH2using n-butyl lithium as the initiator. MeOH is employed as an electrophile to quench the reactive anions after polymerization. The living anionic polymerization of phosphaalkenes has opened up new avenues of exploration for incorporating functional phosphine units into controlled macromolecular architectures. There remains much work to be done in this area, including making new block copolymer architectures such as the proposed poly(methylenephosphine)-blcck poly(methylmethacrylate) or attempting to make ABA triblock copolymers. The preliminary research in controlling the size and morphology of self-assembled block copolymer architectures described in Chapter 4 must be expanded upon including studies to attempt bulk phase self-assembly of PS-PM P copolymers. The polymerization behavior of phosphaalkenes must be studied in further detail as well as expanding upon the monomers that form polymers. The potential to prepare functional polymers with unique properties is of significant interest arid further exploration is needed into the area of phosphaalkene polymerization. References start on page 150 Chapter 8 150 8.3 References 1. Hadjichristidis, N.; Pitsikalis, M.; Pispas, S.; Iatrou, H. Chem. Rev. 2001, 101, 3747. 2. Smid, J.; Van Beylen, M.; Hogen-Esch, T. E. Prog. Polym. Sd. 2006, 31, 1041. 3. Darling, S. B. Prog. Polym. Sd. 2007, 32, 1152. 4. Domski, G. J.; Rose, J. M.; Coates, G. W.; Bolig, A. D.; Brookhart, M. Prog. Polym. Sd. 2007, 32, 30. 5. Mark, J. E.; Ailcock, H. R.; West, R., Inorganic Polymers. Oxford University Press: 2005. 6. Chandrasekhar, V., Inorganic and Organometallic Polymers. Springer-Verlag: Berlin, 2005. 7. Mathey, F. Angew. Chem. mt. Ed. 2003, 42, 1578. 8. Dillon, K. B.; Mathey, F.; Nixon, J. F., Phosphorus: The Carbon Copy. Wiley: West Sussex, 1998. 9. Tsang, C.-W.; Yam, M.; Gates, D. P. J. Am. Chem. Soc. 2003, 125, 1480. 10. Hamley, I. W., Block Copolymers in Solution. Wiley: 2005. 11. Hamley, I. W. Soft Matter2005, 1,36. 12. Rider, D. A.; Winnik, M. A.; Manners, I. Chem. Commun. 2007, 4483. 13. Szwarc, M., Carbanions, Living Polymers, and Electron Transfer Processes. Interscience: New York, NY, 1968. 14. Wiles, D. M.; Bywater, S. T Faraday Soc. 1965, 61,150. 15. Anderson, B. C.; Andrews, G. D.; Arthur Jr., P.; Jacobson, H. W.; Melby, L. R.; Playtis, A. J.; Sharkey, W. H. Macromolecules 1981, 14, 1599. 16. Varshney, S. K.; Hautekeer, J. P.; Fayt, R.; Jerome, R.; Teyssie, P. Macromolecules 1990, 23,2618. 17. Masuda, J. D.; Jantunen, K. C.; Ozerov, 0. V.; Noonan, K. J. T.; Gates, D. P.; Scott, B. L.; Kiplinger, J. L. J. Am. Chem. Soc. 2008, 130, 2408. 18. Tsarig, C. W.; Rohrick, C. A.; Saini, T. S.; Patrick, B. 0.; Gates, D. P. Organometallics 2004, 23, 5913. References start on page 150 Chapter 8 151 19. Tsang, C. W.; Rohrick, C. A.; Saini, T. S.; Patrick, B. 0.; Gates, D. P. Organometallics 2002, 21,1008. References start on page 150 152 Appendix A Iii O0 10.0 20.0 30.0 40.0 50.0 60.0 time (mm) Figure Al. - Refractive index traces of 2.3a (Table 2.1 entries 1-4) with increasing M (black trace — M:I = 100:1, blue trace — M:l = 50:1, pink trace — M:l = 33:1, green trace — M:I = 25:1. 153 1.0 0.5 0.0 10.0 20.0 30.0 40.0 50.0 60.0 time (mm) Figure A2. GPC trace of 2.3b (Table 2.1, entry 5). M = 11500 (red trace — viscometer signal, green trace — refractive index signal, black trace — laser light scattering signal). 0.0 10.0 20.0 30.0 40.0 50.0 60.0 time (mm) Figure A3. GPC trace of 2.3b (Table 2.1, entry 6) M = 14600. (red trace — viscometer signal, green trace — refractive index signal, black trace — laser light scattering signal). 154 Appendix B Table BI. Monomer conversion data collected for the polymerization of 3.1 using 2% BuLi as initiator at 296.3 K. percent conversion [Mia In [M0]I[M] Time (h)Entry mol L1determined by 31p NMR 1 0.0462 0.3753 0.0473 0.25 2 0.0888 0.3586 0.0929 0.5 3 0.1230 0.3451 0.1313 0.75 4 0.1597 0.3307 0.1740 1 5 0.1761 0.3242 0.1938 1.25 6 0.2084 0.3115 0.2336 1.5 7 0.2356 0.3008 0.2687 1.75 8 0.2647 0.2893 0.3075 2 9 0.2940 0.2778 0.3482 2.25 10 0.3210 0.2672 0.3872 2.5 11 0.3634 0.2505 0.4516 2.75 12 0.3826 0.2429 0.4823 3 13 0.4058 0.2338 0.5205 3.25 14 0.4336 0.2229 0.5684 3.5 15 0.4744 0.2068 0.6432 3.75 16 0.5075 0.1938 0.7082 4 17 0.5275 0.1859 0.7497 4.25 18 0.5599 0.1732 0.8207 4.5 19 0.5947 0.1595 0.9030 4.75 20 0.6208 0.1492 0.9697 5 21 0.6370 0.1428 1.01 35 5.25 22 0.6764 0.1273 1.1282 5.5 23 0.6963 0.1195 1.1917 5.75 24 0.7242 0.1085 1.2880 6 25 0.7577 0.0954 1.41 75 6.25 26 0.7764 0.0880 1.4979 6.5 27 0.8088 0.0753 1.6543 6.75 28 0.8361 0.0645 1.8087 7 29 0.8554 0.0569 1.9335 7.25 30 0.8858 0.0449 2.1696 7.5 31 0.9072 0.0365 2.3775 7.75 a[M] =3.1. [M0] = 0.394 mol L1. Molecular weight of isolated polymer 3.4 after quenching with W (M 13500, PDI = 1.07). 155 Table B2. Monomer conversion data collected for the polymerization of 3.1 using 2% BuLi as initiator at 301.8 K. percent Ent conversion [M]a In M 1/FM1 Time ‘ determined by mol L1 I. OJ L (h) 31P NMR 1 0.1016 0.3521 0.1071 0.5 2 0.1396 0.3372 0.1503 0.75 3 0.2038 0.3120 0.2279 1 4 0.2368 0.2991 0.2703 1.25 5 0.2811 0.2818 0.3300 1.5 6 0.3301 0.2626 0.4006 1.75 7 0.3729 0.2458 0.4667 2 8 0.4294 0.2236 0.5610 2.25 9 0.4664 0.2091 0.6281 2.5 10 0.5031 0.1947 0.6994 2.75 11 0.5590 0.1728 0.8187 3 12 0.5946 0.1589 0.9030 3.25 13 0.6327 0.1440 1.0016 3.5 14 0.6720 0.1285 1.1148 3.75 15 0.7220 0.1090 1.2802 4 16 0.7594 0.0943 1.4247 4.25 17 0.7910 0.0819 1.5656 4.5 18 0.8358 0.0643 1.8069 4.75 19 0.8575 0.0558 1.9485 5 20 0.8974 0.0402 2.2771 5.25 21 0.9111 0.0348 2.4201 5.5 [M] = 3.1. [M0] = 0.392 mol L’. Molecular weight of isolated polymer 3.4 after quenching with H(M= 15100, PDI = 1.02). 156 Table B3. Monomer conversion data collected for the polymerization of 3.1 using 2% BuLi as initiator at 307.4 K. percent conversion [M]a TimeEntry determined by mol L1 In [M0]/[M] (h) 31P NMR 1 0.0419 0.3770 0.0428 0.25 2 0.1132 0.3490 0.1201 0.5 3 0.1768 0.3239 0.1946 0.75 4 0.2428 0.2980 0.2781 1 5 0.3046 0.2737 0.3633 1.25 6 0.3577 0.2528 0.4427 1.5 7 0.3990 0.2365 0.5091 1.75 8 0.4716 0.2079 0.6380 2 9 0.5187 0.1894 0.7313 2.25 10 0.5654 0.1710 0.8333 2.5 11 0.6398 0.1417 1.0211 2.75 12 0.6823 0.1250 1.1467 3 13 0.7241 0.1086 1.2876 3.25 14 0.7684 0.0911 1.4629 3.5 15 0.8171 0.0720 1.6991 3.75 16 0.8560 0.0567 1.9380 4 17 0.8953 0.0412 2.2566 4.25 18 0.9169 0.0327 2.4877 4.5 [M] = 3.1. [M0] = 0.394 mol L . . Molecular weight of isolated polymer 3.4 after quenching with H (M = 13 800, PDI = 1.05). 157 Table B4. Monomer conversion data collected for the polymerization of 3.1 using 2% BuLi as initiator at 313.0 K. percent E conversion [M]a I M I M Timen determined by mol L1 ° (h) 1P NMR 1 0.0462 0.3738 0.0473 0.25 2 0.1585 0.3298 0.1726 0.5 3 0.2440 0.2963 0.2798 0.75 4 0.3388 0.2591 0.41 37 1 5 0.4579 0.2125 0.6124 1.25 6 0.5356 0.1820 0.7669 1.5 7 0.6101 0.1528 0.9418 1.75 8 0.6722 0.1285 1.1152 2 9 0.7565 0.0954 1.4125 2.25 10 0.8077 0.0754 1.6489 2.5 11 0.8484 0.0594 1.8866 2.75 12 0.8891 0.0435 2.1994 3 13 0.9223 0.0304 2.5552 3.25 14 0.9398 0.0236 2.8098 3.5 15 0.9476 0.0205 2.9493 3.75 a[M] = 3.1. [M0] = 0.392 mol L1. Molecular weight of isolated polymer 3.4 after quenching with H (M = 14 400, PDI = 1.09). Table B5. Monomer conversion data collected for the polymerization of 3.1 using 2% BuLi as initiator at 318.6 K. percent conversion [M]a TimeIn [M0]/[M]Entry determined by mol L1 (h) 31p NMR 1 0.0574 0.3739 0.0591 0.25 2 0.2462 0.2990 0.2826 0.5 3 0.4253 0.2280 0.5539 0.75 4 0.5578 0.1754 0.8159 1 5 0.7036 0.1176 1.2160 1.25 6 0.7979 0.0802 1.5989 1.5 7 0.8786 0.0481 2.1090 1.75 8 0.9065 0.0371 2.3702 2 9 0.9356 0.0256 2.7421 2.25 10 0.9418 0.0231 2.8433 2.5 a[M] = 3.1. [M0] = 0.397 mol L1. Molecular weight of isolated polymer 3.4 after quenching with H (M = 12300, PDI = 1.07). 158 Table B6. Monomer conversion BuLi as initiator at 324.2 K. data collected for the polymerization of 3.1 using 2% percent E conversion [M]a r,i vrr,ii Timentry . ifl LIvIoJILIvIjdetermined by mol L (h) 31P NMR 1 0.1266 0.3465 0.1353 0.25 2 0.3508 0.2575 0.4320 0.5 3 0.5253 0.1883 0.7452 0.75 4 0.6806 0.1267 1.1412 1 5 0.7736 0.0898 1.4855 1.25 6 0.8047 0.0775 1.6332 1.5 7 0.8665 0.0530 2.01 36 1.75 8 0.8903 0.0435 2.21 01 2 9 0.9015 0.0391 2.3172 2.25 a[M] = 3.1. [M0] = 0.397 mol L1. Molecular weight of isolated with H (M = 13 600, PDI = 1.05). Table B7. Monomer conversion BuLi as initiator at 296.3 K. polymer 3.4 after quenching data collected for the polymerization of 3.1 using 4% [M] = 3.1) [M0] = 0.395 mol L . Molecular weight of isolated polymer with W (M 8800, PDI = 1.09). percent conversion [Mia TimeEntry . In [M0]I[M]determined by mol L (h) 31P NMR 1 0.1147 0.3498 0.1219 0.5 2 0.1930 0.3189 0.2144 0.75 3 0.2174 0.3092 0.2451 1 4 0.2766 0.2858 0.3238 1.25 5 0.3116 0.2720 0.3734 1.5 6 0.3606 0.2526 0.4472 1.75 7 0.4072 0.2342 0.5229 2 8 0.4563 0.2148 0.6093 2.25 9 0.4870 0.2027 0.6675 2.5 10 0.5446 0.1799 0.7865 2.75 11 0.5802 0.1659 0.8679 3 12 0.6404 0.1421 1.0227 3.25 13 0.6854 0.1243 1.1563 3.5 14 0.7187 0.1112 1.2682 3.75 15 0.7650 0.0928 1.4484 4 16 0.8040 0.0774 1.6297 4.25 17 0.8512 0.0588 1.9052 4.5 3.4 after quenching 159 InvErSion—RecoVervTfl I[t]1[O] 1;a*A*exp(_t/T1) Region 1 om 236.199 to 234.433 pprü T11.329s 0 5 10 15 20 25 [s] Figure BI. T1 Inversion Recovery Sequence recorded for compound MesPCPh2.

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