PRISM :: Browsing by Author "Piers, Warren E."

Browsing by Author "Piers, Warren E."

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Open Access
14-electron phosphonium alkylidenes in olefin metathesis: a synthetic and mechanistic study
(2006) Romero Guadjardo, Patricio Eduardo; Piers, Warren E.
Open Access
9-borafluorenes derivatives: chemical reduction and reactivity towards [Cp*A1(I)]4
(2002) Romero Guadjardo, Patricio Eduardo; Piers, Warren E.
Open Access
Activation of Si-H bonds across the nickel carbene bond in electron rich nickel PCcarbeneP pincer complexes
(Royal Society of Chemistry, 2015-11-27) Piers, Warren E.; LaPierre, Etienne A.; Spasyuk, Denis M.; Bi, David W.
Silicon–hydrogen bonds are shown to add to a nickel carbon double bond to yield nickel α-silylalkyl hydrido complexes. Kinetic and isotope labeling studies suggest that a concerted 4-centred addition across the Ni[double bond, length as m-dash]C bond is operative rather than a mechanism involving Si–H oxidative addition. This constitutes an example of Si–H bond activation via ligand cooperativity.
Open Access
B-diketiminato supported scandium thiolate complexes
(2005) MacInnis, Glen Daniel; Piers, Warren E.
Open Access
Boron-containing aromatic compounds: synthesis, characterization and reactivity
(2009) Wood, Thomas Kuchurean; Piers, Warren E.; Keay, Brian A.
Boron-containing derivatives of barrelene and benzobarrelene were generated in good to excellent yields by Diels-Alder reactions between Lewis base-stabilized borabenzene and strong dienophiles. The resultant Diels-Alder adducts were more stable when the Lewis base donor atom was nitrogen as opposed to phosphorus. All members of the family were found to be highly Lewis acidic, and the neutral donors which ligated the boron atom could not be removed/exchanged. Most compounds exhibited a high degree of thermal stability and underwent ill-defined decomposition only when heated to temperatures in excess of 200 °C. In selected cases the Diels-Alder reaction was found to be reversible and the free borabenzene, formed transiently through a retro-Diels-Alder reaction, could be trapped if a stronger dienophile was present in solution. When one of the barrelenes was treated with 3,6-di(2-pyridyl)-1,2,4,5-tetrazine, acetylene was removed to give the first 2,3-disubstituted borabenzene pyridine adduct. Additionally, syntheses were developed for boron-doped versions of the larger acenes: anthracene, naphthacene and pentacene. Boron-doped acenes, 9-boraanthracene, 5-boranaphthacene, and 6-borapentacene, were generated upon deprotonation of appropriately constructed precursors in which the boron atom was ligated by an Arduengo carbene (1,3-bis(2,4,6-trimethyl)imidazolidin-2-ylidene ). These molecules were more highly coloured than their corresponding all-carbon counterparts, an observable manifestation of their much smaller HOMO-LUMO gap. This decrease in HOMO-LUMO gap was found to be a result of an increase in the energy of the HOMO, and is attributable to the boron's presence in the acene's n system. Additionally, the smallest member of this family, 9-boraanthracene, was also found to react with strong dienophiles and 0 2 to form Diels-Alder adducts. During the course of this research, two stable spirocyclic boronium ions were also generated, both of which proved to be valuable starting materials for neutral boron-centred radicals.
Open Access
Boron-Nitrogen Analogues of Indene Containing Hydrocarbons
(2019-07-09) Morgan, Matthew Michael; Piers, Warren E.; Roesler, Roland; Sutherland, Todd C.; Hubert, Casey R. J.; Gilroy, Joe B.
Boron-nitrogen (BN) containing polycyclic aromatic hydrocarbons represent an important class of compounds of fundamental and applied interest. Despite their prevalence in main group chemistry, there remain few ways to efficiently synthesize large quantities of BN containing aromatic species. We developed a method for the preparation of 3-bora-9aza-indene heterocycles based on zirconocene mediated functionalization of the ortho-CH bonds of pyridines. Unlike other methods, the boron center in these heterocycles remains functionalized with a chloride ligand allowing the compounds to be further elaborated through halide abstraction or reduction. The utility of the method was demonstrated by applying it towards the preparation of 1,5-dibora-4a,8a-diaza BN analogs of the intriguing hydrocarbon s-indacene starting from 2,5-dimethylpyrazine. This allowed us to experimentally and computationally compare the BN doped derivative to the all-carbon analogue, providing new knowledge on the effect of main group substitutions on bonding in aromatic compounds. The developed synthetic method also provided us access to a new BN doped indenide species in large scale that allowed for its reactivity to be examined in depth. It was found that the reactivity of the nucleophilic indenide depended on which electrophile it was treated with. This divergent reactivity was investigated through reactions with alkyl halides and carbon dioxide and the mechanisms determined were supported through computational methods. Inspired by the properties of the indacene species, we targeted derivatives of BN doped dihydroindeno[1,2-b]fluorene. They were synthesized via electrophilic borylation, a mildly air-sensitive technique, and the end products were handled readily under atmospheric conditions. Through transmetallation via diarylzinc reagents a series of derivatives were synthesized which show broad absorption profiles and frontier energy levels amenable to their use in organic solar cell devices. Exploratory device parameters were studied and show moderate results with PCEs reaching 2% showing the possibility of molecules containing this framework in organic electronic devices.
Open Access
Bulky polyaromatic flurocarbons: main group complexes and their application as weakly coordinating anions
(2008) Smith, Joshua Coburn; Piers, Warren E.
Open Access
Cationic PCP iridaepoxide and carbene complexes for facile water elimination and activation processes
(2017-03) Piers, Warren E.; Doyle, Lauren E.; Bi, David W.
Iridaepoxide dihydride complexes of a PCP ligand bearing benzo[b]thiophene linkers are synthesized through ligand coopertive N2O and H2 activations. These neutral complexes also eliminate water at elevated temperatures to form the corresponding PCcarbeneP complexes which results in the formal hydrogenation of N2O to water. The synthesis of cationic iridaepoxide dihydride complexes are reported herein where the room temperature elimination of water is observed when a donating solvent is used. This supports a previously proposed mechanism for this water elimination where hydrides cis to the epoxide are required. Ir(I) and Ir(III) cationic PCcarbeneP complexes are also synthesized through protonation and through O–H oxidation additions of water and phenol.
Open Access
Chiral fluoraryl boranes and flurobinaphthyl derivatives for lewis acid catalysis
(2006) Morrison, Darryl James; Piers, Warren E.
Open Access
Design, synthesis and characterization of fluorescent organoboron and organosilicon compounds
(2011) Mercier, Lauren Gina; Piers, Warren E.
Open Access
Development of Phosphoryl-Bridged Viologens Toward Functional Materials
(2017) Stolar, Monika; Baumgartner, Thomas; Piers, Warren E.; Roesler, Roland; Husein, Maen; Morin, Jean-Francois
The 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.
Open Access
Direct Heteroarylation as an Efficient Route to High-Performance pi-Conjugated Materials for use as Non-Fullerene Acceptors in Organic Solar Cells
(2018-04-06) McAfee, Seth Malcolm; Welch, Gregory C.; Piers, Warren E.; Sutherland, Todd C.; Marriott, Robert A.; Luscombe, Christine K.
This thesis is focused on applying direct heteroarylation as an efficient and sustainable synthetic route to access high-performance pi-conjugated molecular materials for use as non-fullerene acceptors as part of the active layer component of organic solar cells. Chapter One introduces pi-conjugated materials, organic solar cells and the importance of developing sustainable and efficient methods to access high-performance materials. In Chapter Two, the discussion is focused on the optimization of cross-coupling reactions catalyzed by a robust and reusable silica-supported palladium catalyst for the synthesis of pi-conjugated materials (SM-1–3) following both traditional Stille or Suzuki couplings and highlighting the advantages of direct heteroarylation over these methods. Chapter Three focuses on expanding the substrate scope to more complicated building blocks, while also comparing direct heteroarylation to Sonogashira couplings and their respective influences on synthetic accessibility and optoelectronic properties (SM-4–5). Chapter Four applies the synthetic methods developed in Chapters Two and Three and extends these principles to the design and synthesis of a non-fullerene acceptor based on the organic dye isoindigo (SM-6). Chapter Five is a direct follow-up on the derivatization of the parent compound disclosed in Chapter Four and how synthetic modification through the versatile direct heteroarylation coupling can lead to improved device performance (SM-7–9). Chapter Six is focused on identify the most promising organic dye core structure to include between flanking perylene diimide units, an extension of previous designs utilizing isoindigo and phthalimide-flanking units (SM-10–14). Chapter Seven follows the optimization of the most promising non-fullerene acceptor from Chapter Six, with a diketopyrrolopyrrole dye core (SM-13), which was able to achieve a high power conversion efficiency of 5.6 %, which is among the best in its class. Chapter Eight explores a series of scalable donor materials that were screened with SM-13 to identify a more practical alternative to the expensive donor polymer PTB7-Th utilized in Chapter Seven and marks the conclusion of this thesis.
Open Access
Efficient Synthetic Methods for the Installation of Boron-Nitrogen Bonds in Conjugated Organic Molecules
(Royal Society of Chemistry, 2015-11-06) Piers, Warren E.; Morgan, Matthew M.
Polycyclic aromatic hydrocarbons in which one or more CC units have been replaced by isoelectronic BN units have attracted interest as potentially improved organic materials in various devices. This promise has been hampered by a lack of access to gram quantities of these materials. However, the exploitation of keystone reactions such as ring closing metathesis, borylative cyclization of amino styrenes and electrophilic borylation has lead to strategies for access to workable amounts of material. These strategies can be augmented by judicious postfunctionalization reactions to diversify the library of materials available. This Frontier article highlights some of the recent successes and shows that the long promised applications of BN-doped PAHs are beginning to be explored in a meaningful way.
Open Access
Electrophilic boranes for organic synthesis
(1998) Parks, Daniel James; Piers, Warren E.
Open Access
Fundamental investigation and practical application of a highly fluorinated 9-borafluroenes: a synthetic, structural and reactivity study
(2003) Chase, Preston Allen; Piers, Warren E.
Open Access
Isoelectric analogues polycyclic aromatic hydrocarbons incorporating boron and nitrogen
(2008) Bosdet, Michael John Davis; Piers, Warren E.
Open Access
Ligand Cooperative Iridium PCP Complexes for Small Molecule Activation
(2017) Doyle, Lauren Elizabeth; Piers, Warren E.; Heinekey, D. Michael; Baumgartner, Thomas; Roesler, Roland; Barclay, Paul
Simple 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.
Open Access
Ligand Design for Energy Conversion and Storage Applications
(2019-12-17) Heidebrecht, Joshua; Roesler, Roland; Piers, Warren E.; Van Humbeck, Jeffrey Francis
The contents of this thesis are divided into two topics that fall under the umbrella of energy conversion and storage. The first section focuses on tuning the standard reduction potential of the Fe3+/2+ redox couple with the aid of nitrogen-based ligands, in pursuit of an all-iron, water-based redox-flow battery. Also included is the synthesis and characterization of iron coordination complexes with redox-active ligands featuring quinone/hydroquinone functional groups. This study aims to exploit the potential of this system incorporating Fe3+/2+ and a redox non-innocent ligand for application in single-component redox-flow batteries. The second portion of the thesis targets homogeneous single-site catalysts for the electrochemical reduction of CO2. The ability of nickel and iron complexes incorporating a redox non-innocent bis(triazapentadienyl) ligand to promote this transformation was investigated. The nickel complex was identified as more promising and infrared spectroelectrochemistry was used to determine the fate of the metal during controlled potential electrolysis, as well as to identify the extent to which a large excess of ligand-based redox behavior impacts electrocatalytic CO2 reduction. The synthesis and characterization of other ligand scaffolds based on tetradentate bis(carbene) macrocycles and porphyrinoids is discussed, with alterations to the parent framework aimed at increasing solubility and stability during metal complexation. Also reported are efforts tailored towards the synthesis of ligands based on a bipyridine central donor with flanking phosphine chalcogenides. The phosphine oxide generated iron, nickel and rhenium complexes while the phosphine sulfide analog proved to be a surprisingly incompetent ligand.
Open Access
Mechanistic studies of B(C6F5)3-catalyzed reactions of Si and Sn reagents
(2001) Blackwell, James Munro; Piers, Warren E.
Open Access
New fluorescent dyes based on 2-(2-pyridyl)-n-arylanilido boron difluoride compounds
(2011) Araneda-Arango, Juan Felipe; Piers, Warren E.