Theses and Dissertations - Department of Chemistry & Biochemistry
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Browsing Theses and Dissertations - Department of Chemistry & Biochemistry by Author "Arduengo, Anthony J."
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Item Computational thermodynamic studies of alkali and alkaline earth compounds, olefin metathesis catalysts, and borane -- azoles for chemical hydrogen storage(University of Alabama Libraries, 2010) Vasiliu, Monica; Dixon, David A.; University of Alabama TuscaloosaGeometry parameters, frequencies, heats of formation and bond dissociation energies are predicted for the alkali (Li, Na and K) hydrides, chlorides, fluorides, hydroxides, and oxides and alkaline earth (Be, Mg and Ca) fluorides, chlorides, oxides and hydroxides at the coupled cluster theory [CCSD(T)] level extrapolated to the complete basis set (CBS) limit. The calculations including core-valence correlation corrections with the aug-cc-pwCVnZ basis sets (n = D, T, Q and 5) are mostly in excellent agreement with the available experimental measurements. Additional corrections (scalar relativistic effects, vibrational zero-point energies, and atomic spin-orbit effects) were necessary to accurately calculate the total atomization energies and heats of formation. The results resolve a number of issues in the literature. CCSD(T)/CBS level calculations with additional corrections are used to predict the heats of formation, adiabatic and diabatic bond dissociation energies (BDEs) and Bronsted acidities and fluoride affinities for the model Schrock-type metal complexes M(NH)(CRR')(OH)_2 (M = Cr, Mo, W; CRR' = CH_2, CHF, CF_2) and MO_2(OH)_2 transition metal complexes. The metallacyclobutane intermediates formed by addition of C_2H_4 to M(NH)(CH_2)(OH)_2 and MO_2(OH)_2 are investigated at the same level of calculation. The electronegative groups bonded to the carbene carbon lead to less stable Schrock-type complexes as compared to the complexes with a CH_2 substituent. The Schrock compounds with M = Cr are less stable than with M = W or Mo. The heats of formation and bond dissociation energies (BDEs) for the pyrrole, pyrazole, imidazole, triazole and tetrazole borane adducts were predicted using an isodesmic approach based on G3MP2 calculations. As potential hydrogen storage substrates, dehydrogenation energies for the elimination of one H_2 molecule were predicted as well as thermodynamic properties relative to their acid-base behavior. The H_3B-N bonds to an sp^2 nitrogen are much stronger than those to an sp^3 nitrogen for the 5-membered rings. The B-N BDEs for the azolylborate adducts are much larger than for the neutral azole borane adducts. The azole adducts with more number of nitrogens in the ring and with more BH_3 molecules to the azole nitrogens are more acidic.Item Design and synthesis of phosphine ligands for palladium-catalyzed coupling reactions(University of Alabama Libraries, 2009) Brown, William Scott; Shaughnessy, Kevin H.; University of Alabama TuscaloosaThe synthesis and design of new phosphines is a continuing area of interest. In designing new phosphines there are a number of design features that need be considered. For palladium catalyzed coupling reactions, sterically demanding and electron releasing ligands are generally most effective in promoting the reaction. In evaluating the hydrophobic phosphines utilized in the Suzuki coupling, the neopentyl derivatives of TTBP (tri-tert-butylphosphine) were investigated. The effect of the addition of a neopentyl group increases the cone angle and impacts the electron donation by decreasing it relative to TTBP. The application in Suzuki coupling shows that a palladium catalyst with a neopentyl phosphine ligand demonstrates good to excellent yields with aryl bromides at room temperature. In the design of new phosphines, building in polar groups generates the ability to take advantage of using water as a solvent or co-solvent. The synthesis of the water soluble ligands DTBPPS (di-tert-butylphosphoniumpropane sulfonate) and DAPPS (di-adamantylphosphoniumpropane sulfonate) led to their testing in Sonogashira and Suzuki coupling reactions. Both ligands give catalysts that show good to excellent conversion of aryl bromides to products at room temperature. For aryl chlorides elevated temperatures are required. In expanding the water-soluble ligands into other palladium coupling reactions, DAPPS was developed in the carbonylation of aryl bromides. The palladium/DAPPS-catalyzed carbonylation coupling reactions show good to excellent conversion of aryl bromides to carbonylated products. This is the first example of a water-soluble alkylphosphine promoting carbonylation of an aryl bromide.Item Fused polycyclic imidazoles(University of Alabama Libraries, 2009) Iconaru, Luigi Iulian; Arduengo, Anthony J.; University of Alabama TuscaloosaThis dissertation presents the synthetic efforts toward the generation and stabilization of fused polycyclic poly(imidazole)s based nucleophilic poly(carbene)s. Chapter 1 reviews how fused nucleophilic carbenes have been employed very successfully in a wide variety of catalytic transformations - both as direct (organo-) catalysts and as ligands for catalytic metal centers. Chapter 2 details the study on the fused tricyclic system. In addition to the progress toward the stabilization of tricyclic tris(carbene) there is also presented the synthesis of fused tricyclic monocarbene precursors and the generation and dimerization of the fused tricyclic monocarbene. New methodology for preparation of imidazol(in)-2-ylidene by reduction of chloroimidazolinium salts with sodium-potassium alloy is described. Metal complexes of the targeted monocarbene have been prepared and fully characterized. Chapter 3 is focused on the chemistry of the saturated fused bicyclic system. Precursors for the fused bicyclic bis(carbene) and the fused bicyclic monocarbene have been prepared. The new methodology for preparation of imidazolin-2-ylidene is also applied on the bicyclic monocarbene precursors.Item Preparation of perfluorinated ionomers for fuel cell applications(University of Alabama Libraries, 2012) Sayler, Todd Stephen; Thrasher, Joseph S.; University of Alabama TuscaloosaOne of the major issues with the current membrane technology for polymer electrolyte membrane fuel cells is the low conductivity seen at low relative humidity. This dissertation discloses the preparation of perfluorinated polymers with higher densities of acid sites and higher conductivities to overcome this issue. These materials are prepared using a system designed to safely synthesize and polymerize tetrafluoroethylene (TFE) on a hundred gram scale. The copolymerization of TFE and perfluoro-2-(2-fluorosulfonylethoxy) propyl vinyl ether (PSEPVE) to prepare materials with varying ratios of the two monomers was carried out by solution, bulk, and emulsion polymerization techniques. Additionally, the homopolymer of PSEPVE has been prepared and characterized by MALDI-TOF mass spectrometry, which shows the low molecular weight distribution seen in other similar materials in the literature is due to a high rate of β-scission termination. Spectroscopic measurements and thermal analysis were carried out on these samples to obtain better characterization than was currently available. Producing polymers with a higher amount of PSEPVE, and thus higher density of acid sites, leads to the materials becoming water soluble after hydrolysis. However, addition of a curable ter-monomer allows the polymer chains to be crosslinked to regain water insolubility. Using this approach, water insoluble membranes with high densities of acid sites and conductivities up to 5.5 times higher than Nafion® 115, the standard benchmark for fuel cell membranes, have been produced. Preparation of high molecular weight, low EW copolymers of TFE and PSEPVE is difficult due to the reactivity ratios of the two monomers. Literature reactivity ratios for VDF and PSEPVE are more favorable for preparation of high molecular weight, low EW copolymers. Here, alternating copolymers of VDF and PSEPVE are prepared for the first time; where high molecular weight samples have been shown to possess low swelling characteristics in water. It has also been found the lower molecular weight samples that are soluble in perfluorohexane can be converted to perfluorinated polymers by direct fluorination with 20% elemental fluorine in nitrogen with 254 nm UV irradiation.Item Synthesis and chemistry of 4,5-functionalized imidazoles(University of Alabama Libraries, 2011) Cojocaru, Oana Andreea; Arduengo, Anthony J.; University of Alabama TuscaloosaThis dissertation presents recent developments in the synthesis and chemistry of five-membered ring annulated imidazoles. Both cyclopentadienyl- and heterocycle-annulated systems are discussed. Chapter 1 introduces imidazol-2-ylidenes and their importance in chemistry: these molecules are the first stable "bottle-able" carbenes that can be used and stored as common reagents. The effect that different annulation patterns have on the carbene center is discussed. The synthesis and stability of 4,5-annulated imidazol-2-ylidenes and their metallic complexes is also presented. Chapter 2 details the synthesis and chemistry of new 4,5-cyclopentadienyl annulated imidazol-2-thiones. The chemistry of these systems allows the synthesis of different precursors of the corresponding imidazol-2-ylidenes. Chapter 3 focuses on the synthesis of 4,5-heterocycle annulated imidazoles. Precursors of the thiophene-annulated imidazol-2-ylidene and precursors of the bis(imidazol-2-ylidene) phospholes have been prepared. The bis(imidazol-2-thione)-phosphole synthesized is also the precursor of the corresponding bis(carbene) phosphorus radical. The first Nazarov cyclization involving a divinyl-phosphine derivative was also achieved.Item Synthesis of trifluoronitromethane, CF₃NO₂: photochemical scale-up and a new thermogeneration method with a refined purification technique(University of Alabama Libraries, 2009) Hauptfleisch, John O.; Thrasher, Joseph S.; University of Alabama TuscaloosaThe research herein investigates two primary methods to synthesize trifluoronitromethane, CF₃NO₂. The first method, a photochemical synthesis, was discovered by the Thrasher group and published in 2002. This photochemical method was the first one-step method for generating CF₃NO₂ and uses trifluoroiodomethane, CF₃I, and nitrogen dioxide, NO₂, as the reactants. This process is initiated by a 420 nm blue light apparatus that splits the C-I bond. The optimization and scale-up of this reaction had not been previously investigated. The production of multiple grams of CF₃NO₂ in a single reaction turned out to be impractical due to the equilibrium of 2 NO₂ with N₂O₄. However, the ideal conditions for the maximum generation of CF₃NO₂ were found to be a total pressure of 0.3 atm, a stoichiometric ratio of 1.1 : 1 of NO₂ : CF₃I, a temperature of at least 55 °C, and a reaction time of 18 hours. Even though this method could not be scaled-up, it still represents the fastest and least expensive method for generating lab quantities of 1-3 grams of CF₃NO₂ via multiple reactions. Because of the aforementioned limitations of the photochemical method, a new method for generating larger quantities of CF₃NO₂ had to be discovered. This new method involves the homolysis of the C-I bond in CF₃I at approximately 200 °C in the presence of NO₂ in a pressure vessel. The increase in reaction temperature allows for the previous limitations due to the 2 NO₂ to N₂O₄ equilibrium to be overcome, allowing for larger quantities, 10-100 grams, of CF₃NO₂ to be produced in a single reaction. This method can be carried out over a large pressure range, 10-60 atm; similar reaction times, 18-24 hours; and with a modest increase in the yield to 35-50%. A detailed kinetics study of this new preparative route was carried out by following both the disappearance of CF₃I and the appearance of CF₃NO₂. The results yielded a C-I bond energy for CF₃I that is in agreement with literature values. A new purification method was also developed for the larger quantities of CF₃NO₂, and the thermal properties of CF₃NO₂ were investigated using an accelerating rate calorimetry (ARC). The molecule CF₃NO₂ was found to be stable to almost 300 °C.Item Total syntheses of (-)-curvularin and xestodecalactone a, formal total syntheses of (-)-citreofuran, (+)-12-oxo-curvularin, (+)-sporostatin, synthetic efforts toward (-)-caylobolide a(University of Alabama Libraries, 2014) De Joarder, Dripta; Jennings, Michael P.; University of Alabama TuscaloosaThis dissertation demonstrates total syntheses of Xestodecalactone A and Curvularin. Formal total syntheses of Sporostatin, 12-oxo-curvularin and Citreofuran are also described. The key reaction utilized in the construction of these fused resorcinylic macrolides, is Pd-catalyzed α-arylation of a α-bromo ester and boronic acid. The first chapter gives a brief introduction of natural products and its importance. Special attention was given to 1,5-diols. Different ways to prepare 1,5-diols and current methods available to determine the absolute and absolute stereochemistry of 1,5-diols were discussed in details. The second chapter highlights the underutilized Pd-catalyzed α-arylation reaction and its potential in the synthesis of resorcinylic macrolides. Critical analyses of various previous methods of α-arylation reactions were included. The third chapter recounts the total synthesis of (+)-xestodecalactone A and formal total synthesis of (+)-sporostatin. The fourth chapter illustrates the total synthesis of (-)-curvularin. It also includes its various biological activities and all the previous approaches. The fifth chapter explains formal syntheses of (-)-12-oxo-curvularin and (-)-citreofuran. The final chapter is dedicated to the synthetic effort toward (-)-caylobolide A, a unique 36 member macrolactone containing a contiguous pentand of 1,5-diol. Successful synthesis of two diastereomeric C25-C40 subunits and a potential 1,5-syn-polyol fragment were delineated.