Derek Gates
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Dissertations completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest dissertations.
The full abstract for this thesis is available in the body of the thesis, and will be available when the embargo expires.
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This thesis outlines the results from the projects undertaken as a part of my PhD studies: the synthesis of novel phosphaalkenes and the investigation of the reactivities of phosphaalkenes towards various N-heterocyclic carbenes (NHCs) or electrophiles.Chapter 1 serves as a general introduction of the properties and reactivities of phosphaalkenes, N-heterocyclic carbenes and abnormal N-heterocyclic carbenes.Chapter 2 describes the kinetic studies of the abnormal reactions between IMes with MesP=CPh₂, MesP=C(4-C₆H₄F)₂ and MesP=C(4-OMeC₆H₄)₂, respectively. The kinetic and thermodynamic data are calculated in order to compare with DFT calculations. During the study, it is noticed the abnormal reaction is catalyzed by a base whereas hindered by an acid.In Chapter 3, metathesis reactions of phosphaalkenes (MesP=CPh₂, PhP=CPh₂ and o-TolP=CPh₂) mediated by NHCs are discussed. This features the first discovery of the metathesis of a P=C bond. In addition, several novel NHC−phosphinidenes adducts are synthesized from the reactions between NHCs and PhP=CPh₂, o-TolP=CPh₂.Chapter 4 discusses the synthesis of several new phosphaalkenes. These phosphaalkenes are designed in an effort to explore the isolable monomers for the polymerization of P=C bonds. Amongst these phosphaalkenes, (TMOP)P=CPh₂, ArFP=CPh₂ and PhP=C(PhNEt₂)₂ are noticeably stable as monomers whereas PhP=C(PhOMe)₂ and PhP=CPh(PhNEt₂) dimerize as 1,2-diphosphetanes in the solid state. In Chapter 5, the novel addition reactions between various phosphaalkenes and a cationic cyclophosphine [(Lc)₄P₄]⁴⁺ (Lc = Me₂IⁱPr) to afford three-membered rings featuring a P−P bond are described. Furthermore, preliminary results regarding the conversion of the cationic cyclophosphine to potential phospha-Wittig reagents and the study of their reactivities are also presented. Finally, Chapter 6 serves to summarize this thesis work.
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This dissertation outlines the development of Brønsted acids and their application as single-component initiators for the cationic polymerization of olefins. Solid weighable Brønsted acids are of particular interest in the generation and stabilization of highly reactive cations. Weakly coordinating anions (WCAs) facilitate the isolation of Brønsted acids and play a critical role in the carbocationic polymerization of vinyl monomers. Chapter 1 gives an introduction to the mechanism of cationic polymerization and the challenges associated with it. The chapter also describes important initiator systems that are used in cationic polymerization and provides an overview of main group element-based WCAs that have been previously reported. Chapter 2 outlines the application of the known tris(tetrachlorobenzenediolato)phosphate,[P(1,2-O₂C₆Cl₄)₃] ̄, as a WCA in the stabilization of reactive cations. The isolated Brønsted acids H(L)₂[P(1,2-O₂C₆Cl₄)₃] (L = THF, DMF) were employed as effective single-component initiators for the cationic polymerization of n-butyl vinyl ether and p-methoxystyrene at various temperatures. Notably, high molecular weight poly(p-methoxystyrene) was obtained with an unexpected branched structure. Chapter 3 describes three potential routes to afford Hellwinkel’s salt, [P(C₁₂H₈)₂][P(C₁₂H₈)₃]. A pentavalent phosphorane, P(C₁₂H₈)₂(C₁₂H₉), and an unprecedented product, [P(C₁₂H₈)(C₂₄H₁₆)][P(C₁₂H₈)₃], were isolated and characterized. The cation [P(C₁₂H₈)(C₂₄H₁₆)]⁺ is formally derived from the insertion of an additional biphenyl unit into the known [P(C₁₂H₈)₂]⁺. Chapter 4 highlights the synthesis and characterization of several amine salts and an alkali metal salt featuring a hexacoordinate anion, [P(C₆H₄CO₂)₃] ̄. The basicity of [P(C₆H₄CO₂)₃] ̄ was examined using IR spectroscopy and found to be comparable to [ClO₄] ̄ and [N(SO₂CF₃)₂] ̄. Chapter 5 describes the synthesis and characterization of two different Brønsted acids with the cation moiety [H(OEt₂)₂]⁺. The Brønsted acids were employed as highly effective single-component initiators for the cationic polymerization of n-butyl vinyl ether, styrene, ⍺-methylstyrene and isoprene at different temperatures. Remarkably, high molecular weight polystyrene and poly(⍺-methylstyrene) were obtained. A predominantly rich syndiotactic poly(⍺-methylstyrene) (rr up to 90%) was isolated from a polymerization at –78 °C. Chapter 6 provides a summary of the thesis work and postulates future considerations in the field.
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Phosphorus-containing flame retardants were synthesized and a variety of strategies for rendering them non-leachable were investigated. Chapter 1 gives a history of flame retardants, with a focus on the issues associated with their usage. An introduction to the mechanisms of flame retardancy and the effect of flame retardants on the thermal degradation of polymeric materials is also given. An overview of the different methods of incorporating phosphorus-containing flame retardants into polymeric materials is included. Chapter 2 described the synthesis of a poly(methylene phosphine) and its oxide by the addition polymerization of MesP=CPh₂. These polymers are moderately effective non-leachable flame retardants when tested by thermogravimetric analysis, Technical Association of Pulp and Paper Industry (TAPPI) Standard Method T461 cm-00, and Limiting Oxygen Index (LOI).The C-H activated microstructure of two poly(methylene phosphine)s, synthesized by the anionic polymerization of ArP=CPh₂ (Ar = 2,4,6-trimethylphenyl, Mes; 2,6-dimethylphenyl, Xyl), is investigated in Chapter 3 using model chemistry and NMR spectroscopic analysis. A mechanism for the anionic polymerization of phosphaalkenes in which a C-H activation occurs is proposed based on kinetic studies, isotopic labelling, and theoretical calculations.The synthesis of the molecular cyclophosphazene-based flame retardant hexakis(2-aminoethyl)aminophosphazene is reported in Chapter 4. This phosphazene is an effective yet leachable flame retardant for paper when tested by thermogravimetric analysis, TAPPI Standard Method T461 cm-00, and LOI. An attempt to covalently link hexakis(2-aminoethyl)aminophosphazene to carboxylatesin pulp via carbodiimide coupling is described in Chapter 5. While unsuccessful, carbodiimidecoupling can be employed in the synthesis of several simpler phosphazene-amide derivatives.In Chapter 6, a non-leachable flame retardant treatment for paper using hexakis(2-aminoethyl)aminophosphazene and sodium carboxymethyl cellulose is described. The efficacyof the treatment is evaluated by TAPPI Standard Method T461 cm-00, LOI, and SEM-EDS. Thesolid precipitate formed in the reaction between hexakis(2-aminoethyl)aminophosphazene andcarboxylmethyl cellulose is studied using solid-state CP/MAS ¹³C NMR and IR spectroscopy,and the interactions between hexakis(2-aminoethyl)aminophosphazene and carboxylmethylcellulose is modelled using an ammonium-containing phosphazene and carboxylate salt.
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The thesis outlines the synthesis and photophysical properties of novel macromolecules that contain phosphorus atoms. Significantly, the fluorescence properties of the polymers prepared in this thesis are dependent on the chemical environment at phosphorus. These materials have the potential to be useful sensors for analytes that react with the phosphine moieties in these polymers.Chapter 1 introduces conjugated polymers and details known examples of phosphorus-containing polymers of this class that have been previously reported. A particular focus is the synthesis of these materials, as well as their photophysical properties. The known examples of molecular phosphine sensors are also presented. Chapters 2 and 3 focus on the anionic polymerization of phosphaalkene monomers to make novel poly(methylenephosphine)s, (PMPs) that contain fluorescent polyaromatic substituents. The synthesized polymers exhibited “turn on” fluorescence upon oxidation of the phosphorus centres. Notably, the C-pyrenyl PMP synthesized in Chapter 3 was also fluorescent in the solid state when the phosphine centres were oxidized.Chapter 4 describes the synthesis and photophysical properties of poly(p-phenylenediethynylene phosphine)s, PPYPs, a new class of phosphorus-containing macromolecule. The polymers were prepared using a nickel-catalyzed coupling between phenyldichlorophosphine and dialkynes. The resulting materials displayed photophysical characteristics consistent with a degree of conjugation through the phosphorus centres within the polymer. Upon oxidation of the phosphorus atoms in PPYPs, “turn on” emission was observed. Remarkably oxidized PPYPs were also fluorescent in the solid state and therefore may have application as solid-state sensors or as OLEDs. Chapter 5 describes the study of a fluorene-containing PPYP as a fluorescent sensor for metal analytes. Remarkably the polymer exhibited a substantial fluorescence increase upon coordination to gold and mercury ions whereas exposure of the polymer to other ions resulted in no fluorescence increase. Chapter 6 provides a summary of the work contained within this thesis, and future directions for these projects are postulated.
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This thesis outlines the polymerization and novel reactivity of enantiomerically pure compounds featuring the relatively uncommon phosphaalkene moiety. Chapter 1 introduces the chemistry of the phosphaalkene (Ar-P=CR₂) structural fragment. This motif is compared and contrasted to the established chemistry of C=N and C=C groups. Similarities and differences are highlighted by an examination of: (a) phosphaalkene synthesis, (b) phosphaalkene polymerization and (c) phosphaalkene-metal coordination.Chapter 2 details the addition reactions of MeM (M = MgBr, Li) nucleophiles to enantiomerically pure phosphaalkene-oxazoline 1.10a [PhAk-Ox, MesP=CPh(CMe₂Ox)]. Of note, the reaction of MeMgBr and PhAk-Ox is highly diastereoselective and affords a new P-chiral phosphine oxazoline ligand. Chapters 3 and 4 report the free radical initiated homo- and co-polymerizations (with styrene) of enantiomerically pure phosphaalkene-oxazolines 1.10a (Chapter 3) and 4.1a [MesP=CPh(3-C₆H₄Ox), Chapter 4]. The coordination of rhodium(I) to copolymers of 1.10a and styrene permits the isolation of novel macromolecular complexes. Additionally, polymers of 4.1a display unique spectroscopic signatures that permit the direct assignment of styrene-phosphaalkene linkages in the polymer backbone. Chapters 5 and 6 highlight the coordination chemistry of phosphaalkenes. Chapter 5 discusses the syntheses of κ³(PNN)-copper(I) complexes featuring enantiomerically pure pyridine-bridged phosphaalkene-oxazoline 5.1a [ArP=CPh(2-C₅H₃N-6-Ox)]. Chapter 6 explores the insertion of the P=C functional group into Pd–R bonds, permitting the synthesis of novel phosphapalladacyclopropanes (6.1a-b) and palladium(II) complexes featuring 1,2-dihydropyridinato donors (6.3 and 6.4). Chapter 7 provides perspective for the work contained within this thesis.
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Alkali metal salts of tris(benzenediolato)phosphate [1]–, K[1] and Na[1], were preparedand examined as halide abstraction reagents. Compound K[1] reacts with (dppp)PdCl₂ [dppp =1,3-bis(diphenylphosphino)propane] (1:1 ratio) or [(cod)RhCl]₂ (2:1 ratio) to afford[(dppp)Pd(μ-Cl)]₂[1]₂ and (cod)Rh[1], respectively. Brønsted acids H(DMSO)₂[1] andH(DMF)₂[1] were isolated as crystalline solids. The basicity of [1]– was examined using IRspectroscopy and determined to be comparable to [BF4]–. Brønsted acid H(DMF)₂[1] is effectivein the protonolysis of late transition metal-alkyl bonds. Its stoichiometric reaction with(dppe)PdMe₂ [dppe = 1,2-bis(diphenylphosphino)ethane] affords either[(dppe)Pd(NCMe)Me][1] (1:1 ratio) or [(dppe)Pd(NCMe)₂][1]₂ (1:2 ratio). Brønsted acidH(DMF)₂[1] initiates the cationic polymerization of n-butyl vinyl ether at 17 °C to affordmoderate molecular weight poly(n-butyl vinyl ether) (Mn = 10,000 g mol-¹, PDI = 2.80).Brønsted acids of tris(tetrachlorobenzenediolato)phosphate [2]–, H(OEt₂)₂[2] andH(OEt₂)(NCMe)[2], were isolated as crystalline solids. Brønsted acid H(OEt₂)₂[2] was shown tobe an effective initiator for the cationic polymerizations of n-butyl vinyl ether, styrene andisoprene. High molecular weight poly(n-butyl vinyl ether) was isolated from polymerization at–78 °C (Mn = 122,000 g mol-¹, PDI = 1.19). Atactic polystyrene of moderate molecular weightwas isolated from polymerization at –50 °C (Mn = 55,400 g mol-¹, PDI = 1.62). Moderatemolecular weight trans-polyisoprene was isolated from polymerization at –38 °C (Mn= 77,000 g mol-¹, PDI = 1.34).Poly(methylenephosphine) and poly(methylenephosphine) oxide were coated onto papersheets made from thermomechanical pulp. TAPPI (Technical Association of Pulp and PaperIndustry) Standard Method T461 cm-00 was used to evaluate the flame retardant properties of the polymers. Paper samples coated with the phosphorus-based polymers exhibited a higherdegree of charring when compared to untreated paper and were comparable to paper treated withthe monobasic ammonium phosphate standard.The microstructure of the 1-(2,2,6,6-tetramethylpiperidinyloxy)-1-phenylethane initiatedpoly(methylenephosphine) was examined by NMR spectroscopy. Evidence suggests theoccurrence of 1,5-hydrogen abstraction rearrangement during the propagation step ofpolymerization. The unexpected microstructure was modeled using PhCH₂P(Mes)CHPh₂.
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This thesis outlines the results from three projects undertaken as part of my Ph.D.studies, with Chapter 1 serving as a general introduction and Chapter 5 serving tosummarize the thesis.Chapter 2 details a Lewis acid-mediated methodology for preparingphosphaalkenes from silyl phosphines [RP(SiMe₃)₂; R = alkyl, aryl, silyl] and aldehydesor ketones. The scope of this methodology was explored and phosphaalkenestBuP=CHtBu (1), AdP=CHtBu (2), MesP=CHtBu (3) and MesP=CPh₂ (4) were preparedon preparative scales. For phosphaalkene 1, this reduced its synthesis from 11 weeks toless than one hour. Additionally, AlCl₃ and GaCl₃ adducts of phosphaalkenes 1 and 2were synthesized and characterized by X-ray crystallography.In Chapter 3, the reactions of phosphaalkenes 1 and 2 with potential cationicinitiators are discussed. For both phosphaalkenes, treatment with substoichiometricHOTf affords rare diphosphiranium cations. Mechanistic studies reveal that this processproceeds via phosphenium triflate intermediates. Unexpectedly, treatment with therelated MeOTf affords diphosphetanium cations via methylenephosphoniumintermediates. Additionally, it was found that the diphosphetanium cation formed fromphosphaalkene 1 would react with two additional equivalents of MeOTf to afford anunprecedented dicationic diphosphetanium.Finally, Chapter 4 describes the abnormal reaction of IMes, a N-heterocycliccarbene (NHC), with phosphaalkenes to afford novel 4-phosphino-2-carbenes.Interestingly, DFT calculations of plausible reaction intermediates suggest the reactionsproceed via free abnormal NHCs (aNHCs). The phosphino-functionalized NHC (5),derived from the reaction of IMes with MesP=CPh₂, was used to study the coordinationproperties of this novel class of ligands. Treating carbene 5 with substoichiometric(tht)AuCl (0.5 equiv) affords a biscarbene complex, indicating that AuCl is preferentiallycoordinated by the carbene functionality. P-coordination of AuCl occurs when carbene 5is treated with additional equivalents of AuCl, confirming the bifunctional nature of thisligand. Additionally, rhodium and iridium complexes of the type (NHC)M(CO) ₂Cl (M =Rh, Ir) were prepared and CO stretching frequencies of these complexes suggest thatcarbene 5 has similar donor properties as IMes.
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This thesis outlines the design, synthesis and utilization of phosphaalkene-based ligandsfor asymmetric catalysis.Transition metal catalysis studies that utilize achiral phosphaalkene-based ligands arereviewed in Chapter 1. In addition, the synthesis and reactivity of phosphaalkenes are brieflyintroduced in this chapter.The reactivity of a palladium(II) phosphaalkene complex [MesP=CPh(2-py)⋅PdCl₂]bearing the smaller P-Mes substituent compared to the traditional Mes* is described in Chapter2. This complex was found to be a competent catalyst for the Overman–Claisen rearrangementwith yields ranging from 33% to 91%.In Chapter 3, a modular route to a set of chiral phosphaalkene–oxazoline [PhAk–Ox,R′P=CR′′(C(i-Pr-Ox)R₂)] proligands is described. The synthetic route starts from a chiral poolmaterial (L-valine) and generates the P=C bond by a phospha-Peterson reaction. The electronicand steric properties of the proligands (R′, R′′ and R) were modified using this synthetic route.MesP=CPh(C(i-Pr-Ox)Me₂) was thermally polymerized to generate poly(methylenephosphine).The investigation of the coordination chemistry of PhAk–Ox proligands is described inChapter 4. Rhodium(I) and iridium(I) PhAk–Ox complexes were characterized by X-raycrystallography and NMR spectroscopy. Rhodium(I) PhAk–Ox complexes were found to beactive in the asymmetric allylic alkylation of ethyl (1-phenylallyl) carbonate with dimethylmalonate as a nucleophile. The optimal conditions generated products in 37% yield and 66% ee.The investigations of PhAk–Ox ligands in palladium(0) catalyzed allylic alkylation of1,3-diphenylpropenyl acetate using malonate type nucleophiles are reported in Chapter 5. Thestructural modification of the ligand through the incorporation of a gem-dimethyl group [MesP=CPh(C(4-i-Pr-5-Me₂-Ox)Me₂)] was needed to optimize yields (73–95%) andenantioselectivities (79–92%). Ring-closing metathesis processes were used to generateenantioenriched carbocycles.To conclude, the results presented in this dissertation represent the highest reportedenantioselectivities for a reaction utilizing a phosphaalkene-based ligand. These results alsoserve as a proof of concept that phosphaalkene ligands can be used in asymmetric catalysis.
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The initiation and termination steps of the anionic polymerization of P=C bonds have been modeled. The initiation step was investigated through the stoichiometric reaction ofMesP=CPh₂(1) with RL1 (R Me or n-Bu). In each case, the addition was highly regioselectivewith the formal attack of R at phosphorus to give the carbanion Li[Mes(R)P—CPh₂](R = Me(3a); n-Bu (3b)). To simulate the termination step, carbanions 3a and 3b were quenched in situwith various electrophiles: Mes(Me)P—CPh₂H (4a), Mes(n-Bu)P—CPh₂H (4b), Mes(Me)P—CPh₂Me (6a), Mes(Me)P—CPh₂—P(NEt₂)₂ (7a), Mes(Me)P—CPh₂—SiMe₂H (8a) and Mes(Me)P—CPh₂—SiMe₃(9a). The first use of MALDI-TOF MS in the study of the products of RLi (R = Me, n-Bu)initiated oligomerization of 1 is reported. The detected linear products R[MesP(=O)-CPh₂]nH withR—P and C—H end-groups are consistent with a chain growth mechanism. The oligomerization was extended to other monomers (MesP=CPhAr, Ar = p-C₆H₄F or p-C₆H₄OMe). The results suggest oligomers undergo fragmentation during MALDI-TOF analysis. The thermal reactions of M(CO)₆ (M = W, Mo, Cr) with polymer n-Bu[MesP-CPh₂]nH (10) and its model compound 4a are reported. IR was primarily used to determine the success of metal coordination in the polymer. EDXISEM and GPC-LLS were used to determine metal content of the materials. Most metallation was modest (>10%), however, as much as 20% was attained with Mo. The phosphorus-containing polymer 10 was found to be an effective ligand for gold(l) to afford n-Bu[MesP(AuCl)—CPh₂]nH 11, a new class of macromolecule with high gold content. The prepared model compound MeMesP(AuCI)—CPh₂H 12 was characterized by X-ray crystallography and NMR spectroscopy. Block copolymers containing phosphorus atoms in the backbone were prepared andmetallated with gold(l). The living polymerization of isoprene (I) and then phosphaalkene I affords block copolymers PIm-b-[MesP-CPh₂]n (13a: m = 308, n = 46; 13b: m = 222, n = 77). Treating PIm-b-[MesP-CPh₂]n with (tht)AuCI results in gold-containing macromolecules [Pl]mbMesP(AuCl)-CPh₂]n (14a and 14b). Upon dissolution in a polyisoprene selective solvent (n heptane), the metallated block copolymers assembled into micelles (14a: spherical; 14b: worm-like). The solution self-assemblies were examined by TEM and DLS.
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Master's Student Supervision
Theses completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest theses.
Rubber is a widely used material that plays an essential role in our daily life. However, the challenging reaction conditions make butyl rubber manufacturing very energy-intensive and difficult to control. Brønsted acids are efficient single component initiators for cationic polymerization with a simple functional cation, H⁺. The coordinating force between cations and anions is crucial for developing high-performance initiators. Weakly coordinating anions have moderate interaction force with cations. This thesis will focus on developing functional initiators containing Brønsted acids and weakly coordinating anions. The growth of the field of weakly coordinating anions has mainly relied on p-block elements such as boron, aluminum, phosphorus, and sulfur. Transition metal complexes have rarely been used as weakly coordinating anions. This thesis will show efforts on designing Ta(V)- or Nb(V)-containing steric bulky WCAs for stabilizing functional Brønsted acids. Chapters 2 and chapter 3 have shown eleven cationic initiators. Among all these cationic initiators, two of them contain anions featuring heptacoordinated Ta(V) with pentagonal bipyramid geometry. These are unprecedented Brønsted acids. H(DMF)₂[2.1] contains the [Ta(1,2-O₂C₆Cl₄)₂(1,2–O₂(OH)₂C₆Cl₄)₂(O=CHN(CH₃)₂)]– anion which has two chelated tetrachlorocatechol ligands, two monodentate tetrachlorocatechol ligands and another DMF ligand with an overall charge of was –1. In addition, [H(DMA)]₂[2.2] was isolated and crystallographically characterized. This Brønsted acid features the novel [Ta(1,2-O₂C₆Cl₄)₃(1,2– O₂(OH)₂C₆Cl₄)]²– dianion with three chelated tetrachlorocatechol and only one monodentate tetrachlorocatechol. Although not specifically tested herein, these new Brønsted acids form a foundation for the future design of novel initiators for cationic polymerization
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This thesis outlines the synthesis, characterization, and catalytic use of phosphorus containing copolymers. The incorporation of phosphorus imparts unique functionalities that allow for the use of polymeric ligands in catalysis.In Chapter 2, the gold metallated phosphorus containing copolymer (PMP-r-PS)-Au-Cl was used as a hydroamination catalyst for the intermolecular hydroamination of phenyl acetylene with aniline. At 5 mol% catalyst loading (5 mol% Au centres), the total product conversion was 99.6% at room temperature and 98.6% at 110°C. The (PMP-r-PS)-Au-Cl catalyst was also selective in producing only the Markovnikov product.In Chapter 3, the free radical copolymerization of PMP-r-PBA was investigated. The linkages between phosphaalkene (PA) and n-butyl acrylate (BA) residues were fully characterized by edHSQC NMR spectroscopy and GPC. The reactivity ratios between PA and BA monomers were determined using the Fineman-Ross linear method and the Mayo-Lewis graphical method. The reactivity ratios were rPA = 18.1, rBA = 0.670 and rPA = 22.7, rBA = 0.784 from both methods, respectively. The reactivity ratios suggested that a propagating PA• radical has a strong preference for homo-propagation and a propagating BA• radical has a slight preference for cross-propagation.To conclude, these instigations have opened the doors to new possibilities in the synthesis of PMP copolymers as well as their uses as catalyst supports in gold catalysis
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Phosphoranes P(OC₆H₄NR)₂(OC₆H₄NHR) [R = Me (2.2a), Ph (2.2b), C6F5 (2.2c)] were synthesized by treating PCl5 with the respective 2–aminophenol derivative (2.1a–c, 3.1 equiv). In one instance, an intermediate species, P(OC₆H₄NR)₂Cl [R = Me (2.3a)], was isolated and structurally characterized. Deprotonation of the amine moieties (–NHR) in phosphoranes 2.2a and 2.2b with a strong alkali–metal base (e.g. n–BuLi) in the presence of a strong–donor solvent (e.g. THF) afforded salts composed of the hexacoordinate P(V)–anions [P(OC₆H₄NR)₃]– (R = Me, [2.4a]– ; Ph, [2.4b]–). Employing precursor 2.2a, the salt Li(THF)₃fac–[2.4a] was isolated. The X–ray crystal of each enantiomer was determined and, to our knowledge, represents the first structurally characterized example of a salt containing a hexacoordinate P(V)N₃O₃ anion featuring P(V)–N bonds. Efforts have also been made to synthesize analogous hypervalent P(V)–derivatives with 1,2–phenylenediamine ligands. Following the synthetic methodology to prepare phosphoranes 2.2a, 2.2b and 2.2c, preliminary investigations with three symmetrical 1,2–phenylenediamine derivatives (3.1a–c) were conducted. No evidence for the formation of five– or six–coordinate product was observed. Instead, an interesting phosphonium cation featuring a four–coordinate phosphorus(V) moiety was isolated as a chloride salt, P(OC₆H₄NR)₂Cl [R = Me (3.2b)], which was characterized spectroscopically.
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Living polymerization is a useful technique that is used to synthesize macromolecules with controlled architectures and tailor-made properties. Although this technique is widely used for the polymerization of organic monomers, the living polymerization of inorganic monomers is exceedingly rare. The prospect of synthesizing new inorganic-organic hybrid macromolecules with tailor-made structures is quite attractive due to the chemical functionality imparted by the inorganic moiety. Our group has developed the living anionic polymerization of Mes-P=CPh₂ to give chemically functional homo- and block-copolymers with phosphine moieties in the polymer backbone. Thus far, copolymers with styrene and isoprene have been prepared. In Chapter 2, the first poly(methylenephophine)-block-poly(methylmethacrylate) (PMP-b-PMMA) block copolymers will be reported. PMP-b-PMMA's with a variety of chain lengths have been synthesized and fully characterized by NMR spectroscopy, gel permeation chromatography (GPC) and matrix-assisted laser desorption-mass spectrometry (MALDI-MS). To fully understand the process of polymerization, the activation energy (Ea) was determined for the secBuLi-initiated polymerization of Mes-P=CPh₂ in nonpolar solvent toluene with TMEDA coordinator (Ea = 16.7 ± 0.7 kcal·mol-¹). In Chapter 3, a simple route to “masked” phosphaalkenes bearing P-Ar (Ar = aryl) and C-H substituents will be explored. The design of monomers bearing substituents smaller than Mesityl at phosphorus and phenyl at carbon, e.g. Mes-P=CPh2, poses considerable synthetic challenge. The present results will provide evidence that a masked phosphaalkene compound has been prepared as a transient species using a masked approach. The research included in this thesis extends the variety of phosphaalkene-based block copolymers that can be prepared. It also offers new perspectives in synthesis masked phosphaalkene compounds.
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This thesis outlines the synthesis and properties of phosphorus containing polymers and their model compounds. The incorporation of phosphorus in these systems leads to interesting photophysical properties that are dependent on the chemical environment of the phosphorous atoms. The photophysical properties of these materials can be useful for fluorescent based sensing. Small-molecule model compounds were used for testing the viability of various alkynes for polymerization. Notably the synthesized model compounds were shown to display an affinity for metal salts, specifically for gold(I) and gold(III). Fluorenyl and thiophene containing derivatives were also synthesized along with the first example of a thiophene containing poly(p-phenylenediethynylene phosphine) (PPYP). These systems undergo fluorescence upon oxidation of the phosphorus centers and could be useful for the detection of reactive oxygen species.To increase the emissive properties of PPYPs, fluorenyl-containing derivatives were synthesized. These polymers were shown to be highly emissive upon oxidation (Φsoln = 0.30) and were tested as fluorescent-based sensors for a variety of metal analytes. Interestingly, the polymers and their corresponding model compounds displayed a large fluorescence increase upon coordination to gold(I) and gold(III) while the presence of other metals such as Rh(I) resulted in no significant fluorescence response. This research represents the first use of a polymer as a fluorescence-based sensor for the detection of gold ions.
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Butyl rubber is a polymer commonly found in everyday life and produced solely by cationic polymerization at −100 °C. The cationic polymerization of olefin monomers, like isobutylene and isoprene in butyl rubber, is very challenging. It is prone to side reactions which can lead to low molecular weight polymers with broad dispersities if the temperature of polymerization is not kept extremely low. Using Brønsted acids incorporating weakly coordinating anions (WCAs) as single component initiators has been an area of growing interest over recent years. WCAs are commonly comprised of main group elements, however in this thesis transition metal complexes are implemented instead to increase the steric bulk of the anions. A series of four Brønsted acids containing Group 5 metals have been synthesized, isolated and characterized. The cationic polymerization of n-butyl vinyl ether, styrene, α-methylstyrene and isoprene is studied for each of isolated single component initiators and have been shown to produce high molecular weight polymers at temperatures above −100 °C.
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This thesis outlines the results from the project undertaken as a part of my MSc studies: the abnormal reactions of phosphaalkenes with N-heterocyclic carbenes (NHCs) to afford novel 4-phosphino-2-carbenes (IMesP). The focus is on investigating the mechanism of these reactions.Chapter 1 serves as a general introduction of phosphaalkenes, N-heterocyclic carbenes, and abnormal N-heterocyclic carbenes. The possible mechanisms of abnormal reactions of NHCs proposed by other researchers are briefly discussed as well. Chapter 2 describes the kinetic studies of the abnormal reactions. Specifically, the kinetic studies of the reactions of IMes with MesP=CPh2, MesP=C(4-C6H4F)2 and MesP=C(4-OMeC6H4)2, respectively. The kinetic and thermodynamic data are calculated in order to compare with DFT calculations. During the study, it is noticed the abnormal reaction is catalyzed by base whereas hindered by acid.In Chapter 3, the reactions of MesP=CPh2 with other NHCs are discussed. The NHCs include IMes-d2 (IMes with deuterium at C4 and C5 positions), IMesMe2 (IMes with –CH3 groups at C4 and C5 positions) and IMesMe (IMes with a –CH3 group at C4 position). The deuterium labeling experiments with IMes-d2 are designed to gain further insight into the issues with respect to the proton transfer in the abnormal reactions. The result shows the proton transfers intermolecularly in the process to form IMesP. The experiments related to IMesMe2 and IMesMe are conducted in order to expand the scope of reactions of phosphaalkenes with NHCs. It is revealed that IMesMe2 and IMesMe do not react with phosphaalkenes in the abnormal way.Finally, Chapter 4 describes a few metallic complexes synthesized from IMesP. Treating IMesP with excessive W(CO)5CH3CN only affords a product with tungsten binding at the carbene functionality. More interestingly, some dinuclear complexes are obtained by reacting IMesP with Pd(cod)2Cl2 and (tht)AuCl.
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Addition polymerization of phosphaalkenes has been successfully used in the preparation of poly(methylenephosphine)s, but the candidate monomers are limited to phosphaalkenes bearing relatively bulky substituents like mesityl group. This thesis presents the investigations on the preparation and anionic polymerization of new phosphaalkene monomers bearing smaller substituents.In Chapter 1, the advantages of synthesizing inorganic polymers by addition polymerization is first introduced. Achievements in the synthesis of poly(methylenephosphine)s by addition polymerization of phosphaalkenes is briefly reviewed, followed by the illustration of the intriguing and challenging aspects of the preparation of phosphaalkenes bearing small substituents.In Chapter 2, studies on the anionic polymerization of XylP=CPh₂ are described. It was shown by the NMR characterization of the polymer obtained and the molecular model built for the polymerization that there was intramolecular H-transfer during the anionic polymerization. This isomerization should account for the slow propagation rate of the anionic polymerization of XylP=CPh₂.In Chapter 3, investigations on the preparation of PhP=CPh₂, o-TolP=CPh₂ and MesP=C(H)Ph by the phospha-Peterson reaction are presented. It was found that PhP=CPh₂ and o-TolP=CPh₂ had the tendency to dimerize and afford 1,2-diphosphetane upon formation. The coordination chemistry of PhP=CPh₂ and o-TolP=CPh₂ is also described with the characterization of W(CO)₄(PhP=CPh₂)₂ by single-crystal X-ray crystallography.The anionic polymerization of "masked phosphaalkenes" is an alternative route to polymers containing phosphorus atoms in the main chain without the use of isolated phosphaalkenes. The development of a facile synthetic pathway to "masked phosphaalkenes" is illustrated in Chapter 4.To conclude, results presented in this thesis pave the road to new poly(methylenephosphine)s by anionic polymerization.
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