Browsing by Author "Baumgartner, Thomas"
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- ItemOpen AccessConjugated main-group polymers for optoelectronics(Royal Society of Chemistry, 2013-08-07) He, Xiaoming; Baumgartner, ThomasThe last decade has witnessed great progress in conjugated polymers for application in optoelectronics. The biggest driving force for the field is to develop polymers with suitable HOMO and LUMO orbital energies, as well as high charge carrier mobility for improved performance in practical devices. Apart from the conventional donor–acceptor (D–A) strategy to tune the optoelectronic properties, the incorporation of main-group elements represents a promising new way to achieve a similar function, however, more efficiently, due to the intrinsic electronic properties of the main-group components. This review highlights the recent advances in main-group element-based conjugated polymers for application in optoelectronics, representatively focusing on Se-, Te-, P-, Si-, Ge-, and B-containing materials.
- ItemOpen AccessDevelopment of macromolecular phosphorus-containing viologens(2018-08-27) Striepe, Laura J.; Baumgartner, Thomas; Sutherland, Todd C.; Derksen, Darren J.; Roesler, Roland; Turner, Raymond JosephThis thesis highlights the development and strategy towards larger, macromolecule-based phosphoryl-bridged viologens, or “phosphaviologens”, as an electrode material for application in organic electronics. The general setup of a battery consists of an anode and cathode, separated by an electrolyte. Cathodic materials, or electron-donating p-type materials, have been well established in organic batteries. Their anodic counter-parts, or electron-accepting n-type materials have not seen as much success and require further investigation. The phosphaviologen, developed by the Baumgartner group, has seen significant progress as an n-type material and is investigated in larger systems throughout this thesis. The first research chapter discusses two new “star-shaped” phosphoryl-bridged viologens and their appreciable electron-accepting ability. The three- and four-pendant compounds were fully characterized, and their benefits and drawbacks are examined. The second research chapter discusses the synthetic strategy and attempts of incorporating the phosphaviologen within a larger polymeric material, that is cellulose nanocrystals, and highlights the difficulties associated. Later discussed is an interesting aggregate that is produced between the anionic cellulose nanocrystals and the cationic phosphaviologen molecules. Expanding on the previous chapter, the final research chapter highlights the efforts of developing highly charged phosphaviologen-containing polymers. Initially, various functionalized precursor polymer backbones were utilized with the phosphaviologen. An alternative route was explored with a bottom-up approach, investigating the polymerization of a polymerization-ready phosphaviologen monomer. This chapter closes with a promising outlook with reference to this topic. Lastly, this thesis concludes with the future direction of phosphaviologen aggregates, and the continuation of the development of a polymer-containing phosphaviologen. The overall goal of this thesis was motivated toward developing novel anodic materials for battery applications.
- ItemOpen AccessDevelopment of Phosphoryl-Bridged Viologens Toward Functional Materials(2017) Stolar, Monika; Baumgartner, Thomas; Piers, Warren E.; Roesler, Roland; Husein, Maen; Morin, Jean-FrancoisThe work in this thesis provides a new class of viologen-based materials, phosphoryl-bridged viologens, for applications in organic electronics. Each chapter focuses on the properties of the materials and their applicability to a specific application. In addition, the chapters build upon the synthesis and properties of each other leading to a better understanding of phosphoryl-bridged viologens and more sophisticated applications. Chapter Two utilized the beautiful electrochromic character of phosphoryl-bridged viologens for application in electrochromic devices. Successful functionalization with various benzyl-substituents led to modification of the reduction potential but preserved the colour of the species, leading to a proof-of-concept electrochromic device. Chapter Three built upon the synthesis from the previous chapter, expanding a library of monomer to a library including dimers and main-chain polymers with the phosphoryl-bridged viologen core. The materials discussed in this chapter resulted in hybrid organic/Li- ion battery half-cells with the potential application for fully organic batteries. While phosphoryl-bridged viologens are not the current front-runners in this field, they offer a unique property that allows for increased charge to mass ratios for a higher energy density material. In addition, the phosphoryl-bridged viologen utilized offer exceptionally charging/discharging stability, which is a current pitfall of Li-ion batteries. Chapter Four developed new functionalizations of phosphoryl-bridged viologens for anchoring onto inorganic nanoparticles or immobilized substrates increasing the utility of this family of materials. Phosphoryl-bridged viologens proved to be excellent electron-acceptors of photoexcited titanium dioxide electrons for potential applications in photocatalysis. In addition, this chapter features the stable methyl viologen and phosphoryl-bridged viologen radicals in water, where their brilliant colour is preserved over several hours. Finally this thesis concludes with an immediate outlook on these materials and their potential success in organic electronics. The goal of this thesis was to establish a new library of phosphoryl-bridged viologens and demonstrate preliminary applications as organic electronic materials.
- ItemOpen AccessDirect (Hetero)Arylation for the Efficient Synthesis of π-Conjugated Materials for use in Organic Electronics(2019-09-13) Welsh, Thomas; Welch, Gregory; Baumgartner, Thomas; Piers, Warren; Roesler, RolandThis thesis project details the use of direct (hetero)arylation (DHA) cross-coupling methods in the synthesis of π-conjugated organic materials. The materials are based on the A–π-core–A framework where A is an electron acceptor moiety, typically N-annulated perylene diimide (NPDI), and the π-core is a thiophene-based material with -H atoms sufficiently reactive for DHA activation. Chapter One introduces the DHA method and presents the proposed reaction mechanism and common reaction parameters. A summary of various functional organic materials synthesized via DHA methods is also given. In Chapter Two, the application of DHA to the functionalization of bithiophene material incorporating a phosphole moiety is presented. Focus is given to the NPDI-functionalized compound (NPDI)2Th2PO and its use as a non-fullerene acceptor in organic solar cells. This is followed up in Chapter Three with the synthesis via Stille coupling of a borane-functionalized species, (NPDI)2Th2B, and its properties and device performance are compared to the (NPDI)2Th2PO and (NPDI)2Th2 analogues. Due to the borane moiety, synthesis via DHA coupling was not possible. In Chapter Four, various DHA methods are screened for the functionalization of thieno[3,4-c]pyrrole-4,6-dione with NPDI ((NPDI)2TPD) and a detailed analysis of post-deposition treatments for the optimization of solid-state morphology is provided. Chapter Five expands upon the synthesis of tetrameric materials via DHA methods with focus on the synthesis and properties of (NPDI)4ThTh, where ThTh = thieno[3,2-b]thiophene. Chapter Six continues this work by detailing the attempts to synthesize the Se-annulated PDI analogue, (SePDI)4ThTh, via DHA methods. Chapter Seven further explores the DHA functionalization of SePDI by coupling with diketopyrrolopyrrole (DPP). The synthesis and characterization of SePDI–DPP–SePDI and SePDI–DPP–NPDI are given and their properties compared with the previously reported NPDI–DPP–NPDI. Chapter Seven also marks the conclusion of this thesis.
- ItemOpen AccessExploring Reactive Species in the Mechanism of Oxygen Reduction using Pentadentate Ligand-Supported Cobalt Complexes(2016) Fairburn, Laura; Piers, Warren; Roesler, Roland; Baumgartner, Thomas; Thangadurai, VenkataramanBuilding on the idea of a pentapyridine ligand, the Piers group has recently focused on the development of a family of boron-substituted pentadentate ligands (B2Pz4Py). This work will describe the expansion of preliminary research completed by Dr. Denis Spasyuk, involving newly synthesized cobalt complexes coordinated with a dianionic pentadentate phenyl-substituted diborate ligand. Instead of continuing with the phenyl-substituted ligand, the synthetic procedure for the ligand was adapted to make a tolyl-substituted version. The synthesis and characterization of cobalt(II) complexes and their propensity to bind O2 forming a binuclear μ-peroxo cobalt(III) complex was explored. The binding of oxygen was found to be reversible and that the O2 was activated towards protonation and that reduction of the products lead back to cobalt(II). The relevance of this chemistry to the Oxygen Reduction Reaction (ORR) was discussed. The catalytic ability of the complex to reduce oxygen was measured and preliminary results showed comparable activity to the previously studied oxygen reduction cobalt catalysts.
- ItemOpen AccessInvestigating Direct Heteroarylation Reactivity in the Synthesis of π-Conjugated Materials for use in Organic Solar Cells(2018-12-12) Payne, Abby-Jo; Welch, Gregory C.; Baumgartner, Thomas; Derksen, Darren J.; Maccallum, Justin L.; Bender, Timothy P.This thesis is focused on applying direct heteroarylation as an efficient synthetic route to access new π-conjugated molecular materials for use in organic solar cells. Chapter one introduces π-conjugated materials, organic solar cells, and design considerations in the development of sustainable and efficient methods towards accessing high-performance materials. Chapter two introduces a novel π-conjugated building block, indoloquinoxaline, which is available from inexpensive starting materials and can be accessed from a modular and high yielding synthesis. Its materials’ properties are investigated through its incorporation as a terminal unit in three different molecular constructs (1-3) using Stille couplings and the more economical direct heteroarylation coupling. Building directly from this work, chapter three focuses on the use of the indoloquinoxaline building block and its fluorinated derivative to access a series of π-extended squaraine dyes (4-7) via Sonogashira and direct heteroarylation couplings expanding the substrate scope of the latter more versatile and atom-economical cross-coupling. Chapter four applies the synthetic methods developed in chapters two and three and extends these principles to the design and synthesis of an asymmetric π-conjugated molecular structure combining the organic dyes, perylene diimide, diketopyrrolopyrrole, and indoloquinoxaline in a linear fashion via direct heteroarylation (8). The asymmetric compound 8 is exploited for its low energy absorption as a non-fullerene acceptor in organic solar devices. Adapting the synthetic protocols from chapter four, chapter five explores the incorporation and effect of a rylene building block new to organic electronics, N-(alkyl)benzothioxanthene- 3,4-dicarboximide (BTXI), on materials properties in order to learn more about its potential use in organic electronic applications (9-11). The three molecular semiconductors (9-11) are compared and evaluated in organic thin-film transistors and organic solar cells. Chapter six concludes this thesis detailing unprecedented direct heteroarylation reactivity which is uncovered and exploited in order to access a novel tetrameric perylene diimide (12) non-fullerene acceptor for organic solar cell applications.
- ItemOpen AccessLigand Cooperative Iridium PCP Complexes for Small Molecule Activation(2017) Doyle, Lauren Elizabeth; Piers, Warren E.; Heinekey, D. Michael; Baumgartner, Thomas; Roesler, Roland; Barclay, PaulSimple small molecules are perhaps the most fundamental components to synthetic chemistry, acting as the building blocks from which larger, more complex compounds are made. These simple molecules are also important in of themselves, sometimes as fuels, greenhouse gases, the water we drink, or the air we breathe. Studying the way in which these molecules behave and react is therefore of great importance. Organometallic chemistry has had considerable success in using transition metal complexes to manipulate small molecules and perform otherwise difficult transformations such as the splitting of water into H2 and O2 or the decomposition of harmful emissions such as CO2 or N2O. This thesis presents the synthesis of a new PCP pincer ligand framework bearing benzo[b]thiophene linking groups as an alternative to the parent ortho-phenylene linkers. This ligand was installed onto an iridium center via double C-H activation at the central carbon atom, resulting in a carbene donor which can be used in favorable metal-ligand cooperative processes. This design feature was used for the activation of N2O, where a series of “iridaepoxide” complexes were made through oxygen atom transfer to the iridium-carbon bond with the release of N2 gas. The formal hydrogenation of N2O to H2O was accomplished by reaction of the iridaepoxide species with H2. The mechanistic details of these processes were studied extensively and reveal a unique ligand cooperative system. Halide abstraction from several neutral iridium complexes was then performed to explore the reactivity of their cationic counterparts. This allowed for the use of milder conditions in previous reactions and for the formation of highly reactive species capable of numerous bond activations including the strong O-H bonds of water and alcohols.
- ItemOpen AccessLow Band Gap Molecular Dyes(2009) Szabo, Lisa; Wilson, Jordan; Linder, Thomas; Baumgartner, Thomas
- ItemOpen AccessMolecular engineering of phosphole-based conjugated materials(2012) Ren, Yi; Baumgartner, ThomasThe work in this thesis focuses on the molecular engineering of phosphorus-based conjugated materials. In the first part (Chapters Two and Three), new phosphorus-based conjugated systems were designed and synthesized to study the effect of the heteroelement on the electronic properties of the re-conjugated systems. The second part (Chapters Four and Five) deals with the self-assembly features of specifically designed phosphorus-based conjugated systems. In Chapter Two, electron-poor and electron-rich aromatic substituents were introduced to the dithienophosphole core in order to balance the electron-accepting and electron-donating character of the systems. Furthermore, an intriguing intramolecular charge transfer process could be observed between two dithienophosphole cores m a bridged bisphosphole-system. In Chapter Three, a secondary heteroelement (Si, P, S) was incorporated in the phosphorus-based conjugated systems. Extensive structure-property studies revealed that the secondary heteroelement can effectively manipulate the communication in phosphinine-based systems. The study of a heterotetracene system allowed for selectively applying distinct heteroatom (S/P) chemistries, which offers a powerful tool for the modification of the electronic structure of the system. More importantly, the heteroatomspecific electronic nature (S/P) can be utilized to selectively control different photophysical aspects ( energy gap and fluorescence quantum yield). Furthermore, additional molecular engineering of the heterotetracene provided access to well-defined 1 D microstructures, which opened the door for designing multi-functional self-assembled phosphorus-based materials. In Chapter Four, the self-organizing phosphole-lipid system is introduced, which combines the features of phospholipids with the electronics of phospholes. Its amphiphilic nature induces intriguing self-assembly features - liquid crystal and soft crystal architectures, both exhibiting well-organized lamellar structure at a wide range of temperatures. Importantly, its dynamic structure endows the phosphole-lipid system with intriguing external stimuli-responsive features allowing for the modification of the emission of the system without further chemical modification. Chapter Five describes how further molecular engineering allowed for access to a series of new highly fluorescent phosphole-lipid organogels. Remarkably, the externalstimuli responsive features of the system can be amplified in a donor-acceptor system accessible through changes in long distance fluorescence resonance energy transfer processes. In addition, the first fluorescent liquid phospholes could also be accessed in the context of the work on the new phosphole-lipid system.
- ItemOpen AccessPhospholes in Conjugated Polythiophenes(2012-09-06) Wilson, Jordan; Baumgartner, ThomasNew conjugated phenyl dithienophosphole-containing polythiophenes were synthesized and studied. These polymers displayed unique optoelectronic properties, with broad absorption profiles and tunable HOMO and LUMO energy levels. The first research chapter is focused on the design of dithienophosphole-containing polythiophenes for donor material applications in bulk heterojunction solar cells. Random copolymers containing 3,3’-didodecyl-2,2’-bithiophene coupled to varying amounts of dithienophosphole oxide and benzothiadiazole were synthesized via a developed Stille coupling protocol. Optoelectronic studies showed a dependence of the HOMO energy levels on dithienophosphole oxide, as well as a destabilization of the LUMO energy levels with increasing dithienophosphole oxide content. The second research chapter focused on chemical modifications of the P-center of dithienophosphole. Post-polymerization reactions were performed to yield fully and partially P-modified dithienophosphole-containing polythiophenes. P-modifications include a borane adduct, Au-complexation, Pd-complexation, and methylation. Pd-complexation formed an insoluble cross-linked copolymer. Optoelectronic studies showed P-modifications tune the HOMO and LUMO energy levels, without altering the energy bandgap.
- ItemOpen AccessPhosphorus-bridged 2,2'-bithiophenes, phenylpyridines and 4,4'-bipyridines: versatile materials for organic electronics(2011) Durben, Stefan; Baumgartner, Thomas
- ItemOpen AccessPi-Extension and Hypervalency of Conjugated Organophosphorus Compounds(2017) Grenon, Nicole; Baumgartner, Thomas; Sutherland, Todd; Derksen, Darren; MacCallum, JustinThe work of this thesis focuses on synthesizing and analyzing new electron-accepting materials that could be beneficial for the development of organic n-type materials for application in organic electronics. The first research chapter focuses on the synthesis of pyridine-extended dithienophosphole oxide compounds in attempts to combine the strong emission of the dithienophosphole oxide backbone with the exciting electrochemical properties of methylated viologens. The motivation for this research and the various synthetic approaches attempted will be discussed in detail. Further, reasoning for the unsuccessful nature of this project will be offered. In the second research chapter, intramolecular Lewis acid/base interactions are formed to produce new hypervalent phosphorus compounds with electron-accepting capabilities. Systematic phosphorus functionalization is performed to allow for manipulation and exploitation of the electrochemical and optical properties of the molecule. Finally, the interactions present in the compounds are rationalized using theoretical calculations.
- ItemOpen AccessRuthenium Mesoionic Carbene Complexes and their Applications in Energy Generation and Storage(2017) Brown, Douglas; Sutherland, Todd; Berlinguette, Curtis Paul; Baumgartner, Thomas; Ling, Chang-Chun; Rivrad, Eric; Trudel, Simon; Heyne, BelindaA series of bis(tridentate) ruthenium complexes bearing 2',6'-bis(1-(2,6-dimethyl-4-bromophenyl)-3-methyl-1,2,3-triazol-4-yl-5-idene)pyridine (C^N^C) have been synthesized and characterized. The complexes of the type [Ru(terpy)(C^N^C)]2+ and derivatives herein, exhibit longer excited state lifetimes (τ) than the archetypical [Ru(terpy)2]2+ (terpy = 2,2':6,2''-terpyridine; τ = 0.25 ns) by several orders of magnitude (τ ~ 8 μs). Their unique ligand geometry and robust sensitization of TiO2 offer insightful design considerations in both dye-sensitized solar cell (DSSC) and water oxidation. In Chapter 2, a series of ruthenium complexes were investigated for their emission properties, which exhibited some of the longest room temperature excited state lifetimes ever reported. Modifications of both ligand fragments were conducted with electron-donating groups and electron-withdrawing groups, which enabled fine-tuning of the triplet metal-to-ligand charge transfer (3MLCT) state. This was a result of destabilizing the normally thermally accessible deactivating triplet metal centered (3MC) state. The location of the lowest-unoccupied molecular orbital (LUMO) could be tuned to reside on either the terpy or C^N^C fragment through chemical modification. Chapter 3 provides details on the sensitization of TiO2 through the cooperative anchoring of phosphonate (-PO3H2) and carboxylate (-CO2H) groups and their performance in the DSSC. Using a combination of anchoring groups provided an opportunity to address the instability due to hydrolysis with the -PO3H2 group, while maintaining electronic communication through the preferred -CO2H. The geometry of the two tridentate ligands within the complexes permitted them to be bind through both ligands to the TiO2 surface. Temporal stability studies identified the cooperative binding approach successfully increased hydrolysis resistance and that the –CO2H moiety on the terpy ligand was critical for higher power conversion efficiencies (PCE ~ 0.2%). The absorption spectrum showed modest absorptions over the visible spectrum 400 to 650 nm (λmax ~ 470 nm ; ε up to 1.0 × 104 M-1cm-1), which limited the maximum PCE ~ 2% based on the solar spectrum. In Chapter 4, the cooperative anchoring strategy was exploited in the heterogenization of a molecular water oxidation catalyst. The title complex ([Ru(bpy-CO2H)(C^N^C-PO3H2)Cl]2+) investigated was anchored to TiO2 and the catalytic oxidation of water (~4.0 μA/cm2; TOF 0.0004s-1) was demonstrated.
- ItemOpen AccessSelective tuning of the exocyclic p-substituent of dithienophosophole: a structure-property study(2011) Chua, Chris Jansen; Baumgartner, Thomas
- ItemOpen AccessSelf-Assembly and Unique Phosphorus Chemistry of Dithienophospholes(2017) Wang, Zisu; Baumgartner, Thomas; Sutherland, Todd; Heyne, Belinda; Muench, Douglas; Tykwinski, RikIn this thesis, first, the self-assembly features of the dithienophosphole system were explored by controlling the structural features of the compounds. By varying different directing forces and tuning their strength, a wide variety of self-assembly motifs with interesting optoelectronic features was achieved. Second, the unique chemistry involving the exocyclic R substituent at the phosphorus centre of the phosphole was discussed. Direct functionalization of the phosphole post ring closing can be achieved conveniently through newly synthesized chlorophosphole precursors. Furthermore, an unprecedented method for the construction of P-P single bond was discussed in mechanistic detail.
- ItemOpen AccessSmall Molecule Activation at Ruthenium NCN and CCC-Pincer Complexes with a Central N-heterocyclic Carbene(2020-09-18) Jiang, Yanmin; Roesler, Roland; Piers, Warren E.; Baumgartner, Thomas; Fraser, Marie; Zargarian, DavitThe design of pincer ligands is one of the most crucial topics in organometallic chemistry, and these tridentate, meridional frameworks have been extensively investigated due to the ease by which their steric and electronic properties can be tuned. One of the most important features of transition metal pincer complexes is their reactivity towards bond activation of small molecules such as H2O, O2, CH4, CO2, N2 and NH3 that are naturally abundant, or renewable feedstocks. Meanwhile, studying the way in which these small molecules behave and react is of great importance.This thesis presents the synthesis of a novel, transformable NCN pincer ligand featuring a six-membered N-heterocyclic carbene (NHC) central donor and sterically encumbered pyridyl pendant arms. This ligand was installed onto transition metals through transmetalation. The uncharacteristic square pyramidal geometry of NCN-nickel and ruthenium complexes reflected the steric impact of the pendant pyridine rings. The ruthenium-mediated azide-nitrile cycloaddition reaction led to the formation of tetrazolato ligands. Rollover cyclometalation occurred in the rhodium complex during the synthesis, which resulted in a novel monoanionic NCC pincer scaffold. The shortest Ru-CNHC and Rh-CNHC bonds on record for the respective metal complexes were measured in their derivatives, attesting to the superior binding ability of the developed NCN and NCC-pincer ligands.The parent NCN-ruthenium pincer system can be transformed into an unprecedented, dianionic LX2-type CCC-ruthenium pincer scaffold via double rollover cyclometalation using potassium hydride. Monodentate phosphine ligands with bulky substituents proved effectively in stabilizing such a pincer framework. These metal complexes reacted with small molecules like H2, N2, CO2 and P4, and the binding mode of compressed dihydride ligand was confirmed from the X-ray crystallographic data, together with multinuclear NMR spectroscopic interpretations. Catalytic H/D scrambling between benzene-d6 and ammonia mediated by the CCC-ruthenium pincer complex incorporating PCy3 and compressed dihydride ligands, was accomplished through the activation of C-D and N-H bonds. Furthermore, this compressed dihydride nature allowed for the facile processes of olefin hydrogenation and dehydrogenative coupling of ammonia-borane, demonstrating versatile catalytic activities of the developed CCC-ruthenium pincer system herein.
- ItemOpen AccessStructure-property studies of conjugated 1,8-naphthalic anhydrides(2014-05-21) Woo, Alva Yuen Yiu; Baumgartner, ThomasThe work in this thesis focuses on investigating the structure-property relationships of conjugated 1,8-naphthalic anhdyrides. Two series of compounds, substituted at the 3- and 4-position of the naphthalic core were designed and synthesized using a variety of aryl groups with different donor strengths. This allowed detailed analysis on how the aryl groups, as well as the position, affect the electronic and photophysical properties of the system. Both series showed a range of quantum yields, intramolecular charge-transfer properties, good electron-accepting character, and good chemical stability. The properties of the two series were compared to one another. Fluorescence quantum yields were much higher in the 4-series than the 3-series and intramolecular charge transfer seemed to be more efficient in the 3-series. Electrochemical properties were comparable between the two series of compounds. Finally, a proof-of-concept and attempted synthesis towards the cyclic diketophosphanyl products was discussed.
- ItemOpen AccessSubstrate coordination and activation at a bis(N-heterocyclic carbene)nickel(0) fragment incorporating a siloxane linker(2019-08-27) Gendy, Chris; Roesler, Roland; Baumgartner, Thomas; Sutherland, Todd C.; Hill, Josephine M.; Stephan, Douglas W.This work hones in on the synthesis and reactivity of a novel bis(NHC)Ni0 fragment in pursuit of expanding the underexplored family of chelating bis(NHC) ligands in the stabilization of low-valent species. Contrasting current literature, which standardizes rigid and constraining ligand designs, our strategy employed a flexible ligand capable of accommodating a wide range of bite angles. Herein, the stoichiometric reactions of a novel chelated Ni0 complex are reported. Combination of bis(NHC)Ni0 with the main group fragments GeCl2 and P4 yielded non-traditional bonding scenarios with Ni0, which represent reactive intermediates along the path to oxidative addition. The archetypal Lewis acid, tris(pentafluorophenyl)borane was activated by Lewis basic bis(NHC)Ni0. This represents the first report of C-F cleavage of B(C6F5)3 by a transition metal. A redox event hosted by a nickel substituted borane complex was useful in tuning its Lewis acidity. Bolstering the representation of bis(NHC) ligands in the stabilization of Ni0, these studies provide insight into the reactivity of ligand designs that alter bite angles while unveiling electronic nuance important in oxidative addition reactions with low-valent group 10 transition metals.
- ItemOpen AccessSynthesis, Structure and Reactivity of Pincer Supported Nickel Carbenes and Related Complexes(2018-11-13) LaPierre, Etienne Alain; Piers, Warren E.; Baumgartner, Thomas; Roesler, Roland; Ponnurangam, Sathish; Johnson, Samuel A.The activation of abundant or renewable feedstocks such as H2O, O2, CH4, CO2, N2 and NH3 and the development of sustainable systems for their productive conversion to value-added products are necessary to meet the growing demand for chemical and energy products. Complicating this are the unique challenges presented by these substrates and the current reliance on expensive and sparse 2nd and 3rd row transition metals to effect these bond activations. This work centres on the further development of nickel carbene complexes as a platform for small molecule activation. These species had been previously demonstrated to heterolytically activate numerous acidic bonds, including the weakly acidic bonds of ammonia. The landscape of bond activations has been expanded beyond acidic substrates to include hydridic, industrially important silanes, coupled with detailed mechanistic studies. Insights gleaned through these studies allowed for rational ligand modifications to improve stability, facilitating the study of CO2 and CO activation, and the synthesis of an umpolung cationic nickel carbene. The polarity reversal of the Ni-C moiety resulted in reactivity distinct from its neutral analogue, as exemplified by the unique ligand centred activation of ammonia. Further, preliminary studies suggest these reverse-polarity carbenes may be competent in catalytic hydrodefluorination of alkyl fluorides, an important first step in moving Ni carbenes from academic curiosity to application. Preliminary work on the synthesis of isostructural Pt carbenes will also be presented, allowing for a comparison of the bonding and reactivity in group 10 carbenes.
- ItemOpen AccessSynthetic Strategies Towards Pi-Extended Dithienophospholes Available for Click Chemistry(2018-04-24) MacLean, Liisa; Baumgartner, Thomas; Welch, Gregory; Sutherland, Todd; Ling, Chang-ChunA series of highly luminescent P-acetylenyl functionalized dithieno[3,2-b:2’,3’-d]phospholes were attempted to be synthesized following the previously studied P-phenyl phosphole as a guide. The original synthesis pathway of forming the dithienophosphole scaffold first, then cross-coupling onto the 2,6-positions, then modifying the acetylene to be able to perform click chemistry saw many difficulties. An alternative route was explored where the cross-coupling reaction with a brominated bithiophene was performed first, then a ring closure reaction to form the phosphole was done. Finally, the emissive materials were able to be clicked onto benzyl azide as a proof-of-concept for an organic light-emitting polymer material for the potential application of solid-state lighting.