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Browsing by Author "Fisk, John D., committee member"

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    Catalytically generated acyl triazoliums as versatile acylating reagents and progress toward the total synthesis of okilactomycin
    (Colorado State University. Libraries, 2013) Wheeler, Philip Andrew Merris, author; Rovis, Tomislav, advisor; Shi, Yian, committee member; Ferreira, Eric, committee member; Shores, Matthew, committee member; Fisk, John D., committee member
    The first chapter of this dissertation describes the development of reactions involving the NHC-catalyzed acylation of carbon and nitrogen nucleophiles. The overall goal of this work was to expand the scope of the NHC-redox reaction manifold and improve its applicability to the synthesis of products that would be useful to the organic chemistry community. An efficient and simple procedure for the preparation of amides from amine hydrochloride salts and α,β-unsaturated aldehydes was developed. This procedure was then applied to the asymmetric synthesis of α-fluoroamides which are valuable building blocks for the preparation of fluorinated compounds that are highly sought after in pharmaceutical, material, and agrichemical applications. The second chapter describes efforts toward the total synthesis of the complex polyketide natural product okilactomycin, enabled by the rhodium-catalyzed desymmetrization of 3,5-dimethylglutaric anhydride developed previously by our group. Progress includes construction of the entire carbon skeleton in two fragments, poised to be unified and elaborated to the natural product by closely precedented steps. This progress demonstrates the potential of the catalytic, enantioselective desymmetrization of anhydrides to build complexity in rapid fashion.
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    Elastic free-standing RTIL composite membranes for CO2/N2 separation based on sphere-forming triblock/diblock copolymer blends
    (Colorado State University. Libraries, 2016) Wijayasekara, Dilanji B., author; Bailey, Travis S., advisor; Fisk, John D., committee member; Kipper, Matthew, committee member; James, Susan, committee member
    The main focus of this dissertation was the development of a robust polymeric membrane material for separating CO2 from a gas mixture of CO2 and N2. Flu gas, which is mainly a mixture CO2 and N2, is the single largest form of anthropogenic CO2 emissions to the atmosphere. Capturing CO2 from flu gas is considered as a measure of controlling anthropogenic CO2 emissions. Existing CO2 capturing technologies for flu gas suffer from low efficiency and the low cost effectiveness. Adoption of membrane technology is comparatively the best route towards the economical separations. Challenges faced by existing CO2 separation membrane materials are the lack of high mechanical robustness and the processability required for fabrication of membrane units while maximizing their gas separation properties. We were able to form a novel membrane material that addresses each of these challenges. These novel membranes are based on highly swollen, self-standing films produced using sphere-forming PS-PEO diblock and PS-PEO-PS triblock copolymer blends. The intricate connectivity among spherical domains produced during melt-state assembly (prior to swelling), provides a framework that remains elastically tough even in the presence of large quantities of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIMTf2N) - a room temperature ionic liquid (RTIL) that has high selectivity for CO2 over N2. Further investigations on improving the robustness of these membranes and the gas separation properties were carried out based on two scenarios. First, potential of improving the thermal stability of these membranes by replacing the thermoplastic polystyrene with a thermoset moiety such as a chemically cross-linked polyisoprene (PI) was researched. Cross-linking chemistry utilized required a post-polymerization modification of PI and it was found that this oxidation modification of olefins on PI caused the decoupling of triblock copolymer in the blend and also substantially hindered melt-state self assembly. The membranes formed with this modification turned out to have inferior mechanical properties compared to the polystyrene based ones, most likely due to the above mentioned complications. Due to the time restrictions, this study was limited to just the identification of the existing challenges in the proposed strategy. Recommendations for addressing the challenges identified are also presented later in the dissertation. The second scenario for improving the performance of these membranes was to increase their productivity by improving both the CO2 permeability and maximizing the trans-membrane pressure differentials possible during operation. To accomplish this we focused on the development of an alternative matrix material (alternative for PEO) enriched with ionic groups. The goal was to increase matrix solubility in the RTIL (improved CO2 permeability) while simultaneously strengthening matrix-RTIL interactions for reduced leaching under higher pressure differentials. Synthetic routes to achieve this task involved a sequential polymerization of isoprene and ethoxy ethyl glycidyl ether (EEGE) monomers. Polymerization of EEGE to yield high molecular weight linear blocks proved to be extremely challenging due to the undesirable chain transfer reaction tendency of EEGE monomer. A great deal of research effort was spent characterizing various anionic reaction conditions and developing measures aimed at suppressing chain transfer. While ultimately unsuccessful, the results of these studies provide significant insight into the challenges of forming high molecular weight linear polyglycidols and will hopefully provide inspiration for the development of future synthetically successful strategies. A series of proof of concept experiments for transforming alcohol functionalities on this polymer system to imidazolium was also completed successfully. The dissertation concludes with a final project completed outside the main objective of the dissertation - a morphological characterization of a series of thermoplastic elastomers with unique molecular architectures. This work is reported separately in the appendix I.
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    Reaction development and mechanistic investigation of rhodium-catalyzed pyridine synthesis via C-H activation
    (Colorado State University. Libraries, 2014) Neely, Jamie M., author; Rovis, Tomislav, advisor; McNally, Andrew, committee member; Fisk, John D., committee member; Neilson, James R., committee member; Inamine, Julia M., committee member
    Described herein are two complementary rhodium-catalyzed methods for the synthesis of substituted pyridines from unsaturated oxime derivatives and alkenes. In the first, formal [4+2] cycloaddition of O-pivaloyl α, β-unsaturated oxime esters and activated terminal alkenes was discovered to proceed in high yields and with excellent selectivity for 6-substituted pyridine products. Mechanistic experiments were found to be consistent with a reversible C-H activation step and a C-N bond forming, N-O bond cleaving process en route to pyridine formation. Rhodium-catalyzed coupling using unactivated alkene substrates was shown to present important information regarding the influence of the alkene component on product distribution. In a second method, access to 5-substituted pyridine derivatives was achieved by decarboxylative annulation of α, β-unsaturated oxime esters and β-substituted acrylic acid derivatives. In this case, carboxylic acids were found to serve as traceless activating groups for selective alkene incorporation. A wealth of mechanistic insight was gained by identification of and decomposition studies regarding catalytically relevant rhodium complexes.
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    Utilizing silicon for the synthesis of tri- and tetrasubstituted olefins
    (Colorado State University. Libraries, 2013) Rooke, Douglas Alexander, author; Ferreira, Eric, advisor; Wood, John, committee member; Fisk, John D., committee member; Shores, Matthew, committee member; Peersen, Olve, committee member
    Functionalized organosilanes serve an important role as reactive precursors for a number of synthetic transformations. Consequently there is still great use for the development of new methods that allow for facile and efficient generation of organosilicon compounds. Herein, a number of such methods are described. The stereoselective syntheses of α-silylenones using catalytic PtCl2 are reported. Via alkyne activation, α-hydroxypropargylsilanes are converted to (Z)-silylenones through a highly selective silicon migration. A trans halosilylation of alkynes is also reported. Both the PtCl2 catalyzed silyl migration the halosilylation reaction proceed through a 1,2-silicon shift onto the activated alkyne intermediate in an anti fashion relative to the activating agent. Both reactions afford excellent yields and selectivity for the product tri- and tetrasubstituted alkenes. The high yielding Pt catalyzed hydrosilylation reactions of internal alkynes are described with a focus on understanding the factors that govern the regioselectivity of the process. Electronic, steric, and functional group properties all influence the selectivity, an understanding of which allows the selective formation of trisubstituted vinylsilanes, which are synthetically useful compounds for accessing stereodefined alkenes. Finally, efforts to show the synthetic utility of tri- and tetrasubstituted vinylsilanes for the formation of C-C bonds using Hiyama coupling and halodesilylation reactions are reported. Hiyama couplings of tetraorganosilanes with and without the use of fluoride activators are thoroughly evaluated. Coupling reactions with vinylsiloxanes are also shown. Finally, stereoretentive halodesilylation reactions are explored with the product vinylhalides subsequently subjected to Suzuki cross coupling conditions affording high yields of highly substituted all-carbon alkenes with good retention of alkene geometry.
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    Visualizing dynamics using 100 kHz 2D IR spectroscopy and microscopy
    (Colorado State University. Libraries, 2018) Tracy, Kathryn Marie, author; Krummel, Amber T., advisor; Levinger, Nancy E., committee member; Szamel, Grzegorz, committee member; Krueger, David A., committee member; Fisk, John D., committee member
    2D IR spectroscopy is a nonlinear optical method with the ability to characterize condensed phase chemical systems. It offers information regarding structure and dynamics of chemical systems. Recent efforts have been made to resolve spatially the molecular structure and dynamics of heterogeneous samples, which shows the feasibility of ultrafast 2D IR microscopy. To image more efficiently, we have moved away from the Ti:sapphire based laser systems and OPA systems that operate at one to several kHz typically used in 2D IR spectroscopy. Instead, for the first time we have demonstrated higher repetition rate, 2D IR spectroscopy at 100 kHz. Achieving this higher repetition rate was accomplished by utilizing advances in diode pumped ytterbium oscillators and amplifiers, and is based on an OPCPA utilizing Mg:PPLN followed by DFG in ZGP. Using this system, we have for the first time, demonstrated the interfacing of IR compatible microfluidics with 2D IR spectroscopy to examine the solvatochromic pseudo-halide anion, cyanate in cosolvent environments. This high repetition rate source also provided a path to 2D IR microscopy experiments that explore the dynamics of complex, heterogeneous, chemical systems. We have shown the chemical dynamics in a room temperature ionic liquid microdroplet. Spatially resolved time-dependent 2D IR signals reveal three regions with different chemical dynamics—the bulk, the interface, and a region between the bulk and interface. This demonstration provides proof-of-concept to use 2D IR microscopy on a wide array of additional chemical systems.