Synthesis of Gold Complexes From Diphosphine Ligands and Screening Reactions of Heterocyclic Acetylacetonato (ACAC) Ligands with Transitional Metal Complexes (open access)

Synthesis of Gold Complexes From Diphosphine Ligands and Screening Reactions of Heterocyclic Acetylacetonato (ACAC) Ligands with Transitional Metal Complexes

Syntheses of diphosphine gold (I) complexes from gold THT and two ligands, 4, 5-bis (diphenylphosphino)-4-cyclopenten-1, 3-dione (BPCD) and 2,3-bis(diphenylphosphino)-N-phenylmaleimide (BPPM), were done separately. The reactions happened under ice conditions followed by room temperature conditions and produced two diphosphine gold (I) complexes in moderated yield. Spectroscopic results including nuclear magnetic resonance (NMR) and X-ray crystallography were used to study and determine the structures of the products formed. Moreover, X-rays of all newly synthesized diphosphine gold (I) complexes were compared with the known X-ray structures of other phosphine and diphosphine gold (I) complexes. There were direct resemblances in terms of bond length and angle between these new diphosphine gold (I) complex structures and those already published. For instance, the bond lengths and angles from the newly prepared diphosphine gold (I) complexes were similar to those already published. Where there were some deviations in bond angles and length between the newly synthesized structures and those already published, appropriate explanation was given to explain the deviation. Heterocyclic ligands bearing acetylacetonate (ACAC) side arm(s) were prepared from ethyl malonyl chloride and the heterocyclic compounds 8-hydroxylquinoline, Syn-2-peridoxyaldoxime, quinoxalinol and 2, 6-dipyridinylmethanol. The products (heterocyclic ACAC ligands) from these reactions were screened with transition metal carbonyl compounds …
Date: August 2015
Creator: Nyamwihura, Rogers
System: The UNT Digital Library
Novel Carborane Derived Semiconducting Thin Films for Neutron Detection and Device Applications (open access)

Novel Carborane Derived Semiconducting Thin Films for Neutron Detection and Device Applications

Novel carborane (B10C2H12) and aromatic compounds (benzene, pyridine, diaminobenzene) copolymers and composite materials have been fabricated by electron beam induced cross-linking and plasma enhanced chemical vapor deposition (PECVD) respectively. Chemical and electronic structure of these materials were studied using X-ray and ultra-violet photoelectron spectroscopy (XPS and UPS). UPS suggest that the systematic tuning of electronic structure can be achieved by using different aromatic compounds as co-precursors during the deposition. Furthermore, top of valence band is composed of states from the aromatic moieties implying that states near bottom of the conduction band is derived from carborane moieties. Current- voltage (I-V) measurements on the ebeam derived B10C2HX: Diaminobenzene films suggest that these films exhibit enhanced electron hole separation life time. Enhanced electron hole separation and charge transport are critical parameters in designing better neutron voltaic devices. Recently, PECVD composite films of ortho-carborane and pyridine exhibited enhanced neutron detection efficiency even under zero bias compared to the pure ortho-carborane derived films. This enhancement is most likely due to longer electron-hole separation, better charge transport or a combination of both. The studies determining the main factors for the observed enhanced neutron detection are in progress by fabricating composite films of carborane with other aromatic …
Date: August 2015
Creator: James, Robinson
System: The UNT Digital Library
Computational Modeling of Small Molecules (open access)

Computational Modeling of Small Molecules

Computational chemistry lies at the intersection of chemistry, physics, mathematics, and computer science, and can be used to explain the behavior of atoms and molecules, as well as to augment experiment. In this work, computational chemistry methods are used to predict structural and energetic properties of small molecules, i.e. molecules with less than 60 atoms. Different aspects of computational chemistry are examined in this work. The importance of examining the converged orbitals obtained in an electronic structure calculation is explained. The ability to more completely describe the orbital space through the extrapolation of energies obtained at increasing quality of basis set is investigated with the use of the Sapporo-nZP-2012 family of basis set. The correlation consistent Composite Approach (ccCA) is utilized to compute the enthalpies of formation of a set of molecules and the accuracy is compared with the target method, CCSD(T,FC1)/aug-cc-pCV∞Z-DK. Both methodologies are able to produce computed enthalpies of formation that are typically within 1 kcal mol-1 of reliable experiment. This demonstrates that ccCA can be used instead of much more computationally intensive methods (in terms of memory, processors, and time required for a calculation) with the expectation of similar accuracy yet at a reduced computational cost. The …
Date: December 2015
Creator: Weber, Rebecca J.
System: The UNT Digital Library
Fundamental Studies of Copper Corrosion in Interconnect Fabrication Process and Spectroscopic Investigation of Low-k Structures (open access)

Fundamental Studies of Copper Corrosion in Interconnect Fabrication Process and Spectroscopic Investigation of Low-k Structures

In the first part of this dissertation, copper bimetallic corrosion and its inhibition in cleaning processes involved in interconnect fabrication is explored. In microelectronics fabrication, post chemical mechanical polishing (CMP) cleaning is required to remove organic contaminants and particles left on copper interconnects after the CMP process. Use of cleaning solutions, however, causes serious reliability issues due to corrosion and recession of the interconnects. In this study, different azole compounds are explored and pyrazole is found out to be a potentially superior Cu corrosion inhibitor, compared to the most widely used benzotriazole (BTA), for tetramethyl ammonium hydroxide (TMAH)-based post CMP cleaning solutions at pH 14. Micropattern corrosion screening results and electrochemical impedance spectroscopy (EIS) revealed that 1 mM Pyrazole in 8 wt% TMAH solution inhibits Cu corrosion more effectively than 10 mM benzotriazole (BTA) under same conditions. Moreover, water contact angle measurement results also showed that Pyrazole-treated Cu surfaces are relatively hydrophilic compared to those treated with BTA/TMAH. X-ray photoelectron spectroscopy (XPS) analysis supports Cu-Pyrazole complex formation on the Cu surface. Overall Cu corrosion rate in TMAH-based highly alkaline post CMP cleaning solution is shown to be considerably reduced to less than 1Å/min by addition of 1 mM Pyrazole. In …
Date: December 2015
Creator: Goswami, Arindom
System: The UNT Digital Library
The Impact of Computational Methods on Transition Metal-containing Species (open access)

The Impact of Computational Methods on Transition Metal-containing Species

Quantum chemistry methodologies can be used to address a wide variety of chemical problems. Key to the success of quantum chemistry methodologies, however, is the selection of suitable methodologies for specific problems of interest, which often requires significant assessment. To gauge a number of methodologies, the utility of density functionals (BLYP, B97D, TPSS, M06L, PBE0, B3LYP, M06, and TPSSh) in predicting reaction energetics was examined for model studies of C-O bond activation of methoxyethane and methanol. These species provide excellent representative examples of lignin degradation via C-O bond cleavage. PBE0, which performed better than other considered DFT functionals, was used to investigate late 3d (Fe, Co, and Ni), 4d (Ru, Rh, and Pd), and 5d (Re, Os, and Ir) transition metal atom mediated Cβ -O bond activation of the β–O–4 linkage of lignin. Additionally, the impact of the choice of DFT functionals, basis sets, implicit solvation models, and layered quantum chemical methods (i.e., ONIOM, Our Own N-layered Integrated molecular Orbital and molecular Mechanics) was investigated for the prediction of pKa for a set of Ni-group metal hydrides (M = Ni, Pd, and Pt) in acetonitrile. These investigations have provided insight about the utility of a number of theoretical methods in …
Date: December 2015
Creator: Wang, Jiaqi
System: The UNT Digital Library
Thin Cr2O3 (0001) Films and Co (0001) Films Fabrication for Spintronics (open access)

Thin Cr2O3 (0001) Films and Co (0001) Films Fabrication for Spintronics

The growth of Co (0001) films and Cr2O3 (0001)/Co (0001) has been investigated using surface analysis methods. Such films are of potential importance for a variety of spintronics applications. Co films were directly deposited on commercial Al2O3 (0001) substrates by magnetron sputter deposition or by molecular beam epitaxy (MBE), with thicknesses of ~1000Å or 30Å, respectively. Low Energy Electron Diffraction (LEED) shows hexagonal (1x1) pattern for expected epitaxial films grown at 800 K to ensure the hexagonally close-packed structure. X-ray photoemission spectroscopy (XPS) indicates the metallic cobalt binding energy for Co (2p3/2) peak, which is at 778.1eV. Atomic force microscopy (AFM) indicates the root mean square (rms) roughness of Co films has been dramatically reduced from 10 nm to 0.6 nm by optimization of experiment parameters, especially Ar pressure during plasma deposition. Ultrathin Cr2O3 films (10 to 25 Å) have been successfully fabricated on 1000Å Co (0001) films by MBE. LEED data indicate Cr2O3 has C6v symmetry and bifurcated spots from Co to Cr2O3 with Cr2O3 thickness less than 6 Å. XPS indicates the binding energy of Cr 2p(3/2) is at 576.6eV which is metallic oxide peak. XPS also shows the growth of Cr2O3 on Co (0001) form a thin …
Date: December 2015
Creator: Cao, Yuan
System: The UNT Digital Library
Biological Applications of a Strongly Luminescent Platinum (II) Complex in Reactive Oxygen Species Scavenging and Hypoxia Imaging in Caenorhabditis elegans (open access)

Biological Applications of a Strongly Luminescent Platinum (II) Complex in Reactive Oxygen Species Scavenging and Hypoxia Imaging in Caenorhabditis elegans

Phosphorescent transition metal complexes make up an important group of compounds that continues to attract intense research owing to their intrinsic bioimaging applications that arise from bright emissions, relatively long excited state lifetimes, and large stokes shifts. Now for biomaging assay a model organism is required which must meet certain criteria for practical applications. The organism needs to be small, with a high turn-over of progeny (high fecundity), a short lifecycle, and low maintenance and assay costs. Our model organism C. elegans met all the criteria. The ideal phosphor has low toxicity in the model organism. In this work the strongly phosphorescent platinum (II) pyrophosphito-complex was tested for biological applications as a potential in vivo hypoxia sensor. The suitability of the phosphor was derived from its water solubility, bright phosphorescence at room temperature, and long excited state lifetime (~ 10 µs). The applications branched off to include testing of C. elegans survival when treated with the phosphor, which included lifespan and fecundity assays, toxicity assays including the determination of the LC50, and recovery after paraquat poisoning. Quenching experiments were performed using some well knows oxygen derivatives, and the quenching mechanisms were derived from Stern-Volmer plots. Reaction stoichiometries were derived from …
Date: December 2015
Creator: Kinyanjui, Sophia Nduta
System: The UNT Digital Library
Accurate Energetics Across the Periodic Table Via Quantum Chemistry (open access)

Accurate Energetics Across the Periodic Table Via Quantum Chemistry

Greater understanding and accurate predictions of structural, thermochemical, and spectroscopic properties of chemical compounds is critical for the advancements of not only basic science, but also in applications needed for the growth and health of the U.S. economy. This dissertation includes new ab initio composite approaches to predict accurate energetics of lanthanide-containing compounds including relativistic effects, and optimization of parameters for semi-empirical methods for transition metals. Studies of properties and energetics of chemical compounds through various computational methods are also the focus of this research, including the C-O bond cleavage of dimethyl ether by transition metal ions, the study of thermochemical and structural properties of small silicon containing compounds with the Multi-Reference correlation consistent Composite Approach, the development of a composite method for heavy element systems, spectroscopic of compounds containing noble gases and metals (ArxZn and ArxAg+ where x = 1, 2), and the effects due to Basis Set Superposition Error (BSSE) on these van der Waals complexes.
Date: December 2015
Creator: Peterson, Charles Campbell
System: The UNT Digital Library
Design, Synthesis, and Characterization of Aqueous Polymeric Hybrid Composites and Nanomaterials of Platinum(II) and Gold(I) Phosphorescent Complexes for Sensing and Biomedical Applications (open access)

Design, Synthesis, and Characterization of Aqueous Polymeric Hybrid Composites and Nanomaterials of Platinum(II) and Gold(I) Phosphorescent Complexes for Sensing and Biomedical Applications

The two major topics studied in this dissertation are the gold(I) pyrazolate trimer {[Au(3-R,5-R’)Pz]3} complexes in aqueous chitosan polymer and phosphorescent polymeric nanoparticles based on platinum(II) based complex. The first topic is the synthesis, characterization and optical sensing application of gold(I) pyrazolate trimer complexes within aqueous chitosan polymer. A gold(I) pyrazolate trimer complex, {[Au(3-CH3,5-COOH)Pz]3}, shows high sensitivity and selectivity for silver ions in aqueous media, is discussed for optical sensing and solution-processed organic light emitting diodes (OLEDs) applications. Gold(I) pyrazolate trimer complexes are bright red emissive in polymeric solution and their emission color changes with respect to heavy metal ions, pH and dissolved carbon dioxide. These photophysical properties are very useful for designing the optical sensors. The phosphorescent polymeric nanoparticles are prepared with Pt-POP complex and polyacrylonitrile polymer. These particles show excellent photophysical properties and stable up to >3 years at room temperature. Such nanomaterials have potential applications in biomedical and polymeric OLEDs. The phosphorescent hybrid composites are also prepared with Pt-POP and biocompatible polymers, such as chitosan, poly-l-lysine, BSA, pnipam, and pdadmac. Photoluminescent enhancement of Pt-POP with such polymers is also involved in this study. These hybrid composites are promising materials for biomedical applications such as protein labeling and …
Date: December 2015
Creator: Upadhyay, Prabhat Kumar
System: The UNT Digital Library
Design, Synthesis and Study of Supramolecular Donor – Acceptor Systems Mimicking Natural Photosynthesis Processes (open access)

Design, Synthesis and Study of Supramolecular Donor – Acceptor Systems Mimicking Natural Photosynthesis Processes

This dissertation investigates the chemical ingenuity into the development of various photoactive supramolecular donor – acceptor systems to produce clean and carbon free energy for the next generation. The process is inspired by the principles learned from nature’s approach where the solar energy is converted into the chemical energy through the natural photosynthesis process. Owing to the importance and complexity of natural photosynthesis process, we have designed ideal donor-acceptor systems to investigate their light energy harvesting properties. This process involves two major steps: the first step is the absorption of light energy by antenna or donor systems to promote them to an excited electronic state. The second step involves, the transfer of excitation energy to the reaction center, which triggers an electron transfer process within the system. Based on this principle, the research is focused into the development of artificial photosynthesis systems to investigate dynamics of photo induced energy and electron transfer events. The derivatives of Porphyrins, Phthalocyanines, BODIPY, and SubPhthalocyanines etc have been widely used as the primary building blocks for designing photoactive and electroactive ensembles in this area because of their excellent and unique photophysical and photochemical properties. Meanwhile, the fullerene, mainly its readily available version C60 is …
Date: December 2015
Creator: KC, Chandra Bikram
System: The UNT Digital Library
Electrochemical Synthesis and Applications of Layered Double Hydroxides and Derivatives (open access)

Electrochemical Synthesis and Applications of Layered Double Hydroxides and Derivatives

Layered double hydroxides (LDH) are a class of anionic clay with alternating layers of positive and negative charge. A metal hydroxide layer with divalent and trivalent metals with a positive charge is complemented by an interlayer region containing anions and water with a negative charge. The anions can be exchanged under favorable conditions. Hydrotalcite (Mg6Al2(OH)16[CO3]·4H2O) and other variations are naturally occurring minerals. Synthetic LDH can be prepared as a powder or film by numerous methods. Synthetic LDH is used in electrode materials, adsorbents, nuclear waste treatment, drug delivery systems, water treatment, corrosion protection coatings, and catalysis. In this dissertation Zn-Al-NO3 derivatives of zaccagnaite (Zn4Al2(OH)12[CO3]·3H2O) are electrochemically synthesized as films and applied to sensing and corrosion resistance applications. First, Zn-Al-NO3 LDH was potentiostatically electrosynthesized on glassy carbon substrates and applied to the electrochemical detection of gallic acid and caffeic acid in aqueous solutions. The modified electrode was then applied to the detection of gallic acid in green tea samples. The focus of the work shifts to corrosion protection of stainless steel. Modified zaccagnaite films were electrodeposited onto stainless steel in multiples layers to reduce defects caused by drying of the films. The films were deposited using a step potential method. The …
Date: August 2015
Creator: Kahl, Michael S.
System: The UNT Digital Library
Determination of Solute Descriptors for Illicit Drugs Using Gas Chromatographic Retention Data and Abraham Solvation Model (open access)

Determination of Solute Descriptors for Illicit Drugs Using Gas Chromatographic Retention Data and Abraham Solvation Model

In this experiment, more than one hundred volatile organic compounds were analyzed with the gas chromatograph. Six capillary columns ZB wax plus, ZB 35, TR1MS, TR5, TG5MS and TG1301MS with different polarities have been used for separation of compounds and illicit drugs. The Abraham solvation model has five solute descriptors. The solute descriptors are E, S, A, B, L (or V). Based on the six stationary phases, six equations were constructed as a training set for each of the six columns. The six equations served to calculate the solute descriptors for a set of illicit drugs. Drugs studied are nicotine (S= 0.870, A= 0.000, B= 1.073), oxycodone(S= 2.564. A= 0.286, B= 1.706), methamphetamine (S= 0.297, A= 1.570, B= 1.009), heroin (S=2.224, A= 0.000, B= 2.136) and ketamine (S= 1.005, A= 0.000, B= 1.126). The solute property of Abraham solvation model is represented as a logarithm of retention time, thus the logarithm of experimental and calculated retention times is compared.
Date: August 2015
Creator: Mitheo, Yannick K.
System: The UNT Digital Library
Molecules and Materials for Excitonic Solar Cells Using P-type Metal Oxide Semiconductors (open access)

Molecules and Materials for Excitonic Solar Cells Using P-type Metal Oxide Semiconductors

This dissertation has two intersecting foci; firstly, the discovery of a new methodology for the growth of high surface area cuprous oxide (Cu2O) substrates. Secondly, the synthesis and characterization of electron-accepting molecules, and their incorporation into excitonic solar cells (XSCs) using the Cu2O substrates as electrodes. Increasing the surface area of the semiconductor creates more locations for charge transfer to occur thus increasing the overall efficiency of the device. Zinc oxide (ZnO) has been widely studied, and can be easily grown into many different films with high surface area morphologies. The ZnO films serve as sacrificial templates that allow us to electrochemically grow new semiconductors with the same high surface area morphologies but composed of a material having more desirable electronic properties. A polymer can be applied over the surface of the ZnO nanorod films before etching the ZnO with a weak acid, thereby leaving a polymer nanopore membrane. Cathodic electrodeposition of Cu2O into the membrane nanopores gives Cu2O nanorods. Electron-accepting dyes are designed with tethers that allow for direct attachment to metal oxide semiconductors. After soaking, the semiconductor is coated with a monolayer of a dye and then the coated semiconductor films were made into various dye-sensitized solar cells …
Date: August 2015
Creator: Haynes, Keith M.
System: The UNT Digital Library
Self-assembly Polymeric Nanoparticles Composed of Polymers Crosslinked with Transition Metals for Use in Drug Delivery (open access)

Self-assembly Polymeric Nanoparticles Composed of Polymers Crosslinked with Transition Metals for Use in Drug Delivery

A major drawback of chemotherapy is the lack of selectively leading to damage in healthy tissue, which results in severe acute side effects to cancer patients. The use of nanoparticles as a drug delivery system has emerged as novel strategy to overcome the barriers of immunogenic response, controlled release of therapeutic, and targeting the toxicity only to cancerous cells. In this study, polymeric nanoparticles composed of transition metals and particles derived from natural biopolymers have been generated via self-assembly. For example, nanoparticles composed of cobalt crosslinked with albumin (Co-alb NPs) via Co-amine coordination chemistry of lysine residue were syntheisized in various sizes. The method to generate Co-alb NPs involves no thermal heat, organic solvent or any surfactants, which is ideal for the production of large amounts in a timely manner. The Co-alb NPs displayed exceptional stability under physiological conditions (pH 7.4) for several days with minor changes in size; however degradation could be triggered by reductant (reduced glutathione (GSH), 10 mM) with complete disappearance of particles in less than 2 hour. Numerous therapeutics that are highly effective toward cancer cells have been developed; however, many cannot be administered to patients due to poor solubility in water and pH dependent properties. …
Date: December 2015
Creator: Nguyen, Duong Thuy
System: The UNT Digital Library
Application of the Correlation Consistent Composite Approach to Biological Systems and Noncovalent Interactions (open access)

Application of the Correlation Consistent Composite Approach to Biological Systems and Noncovalent Interactions

Advances in computing capabilities have facilitated the application of quantum mechanical methods to increasingly larger and more complex chemical systems, including weakly interacting and biologically relevant species. One such ab initio-based composite methodology, the correlation consistent composite approach (ccCA), has been shown to be reliable for the prediction of enthalpies of formation and reaction energies of main group species in the gas phase to within 1 kcal mol-1, on average, of well-established experiment, without dependence on experimental parameterization or empirical corrections. In this collection of work, ccCA has been utilized to determine the proton affinities of deoxyribonucleosides within an ONIOM framework (ONIOM-ccCA) and to predict accurate enthalpies of formation for organophosphorus compounds. Despite the complexity of these systems, ccCA is shown to result in enthalpies of formation to within ~2 kcal mol-1 of experiment and predict reliable reaction energies for systems with little to no experimental data. New applications for the ccCA method have also been introduced, expanding the utility of ccCA to solvated systems and complexes with significant noncovalent interactions. By incorporating the SMD solvation model into the ccCA formulation, the Solv-ccCA method is able to predict the pKa values of nitrogen systems to within 0.7 pKa unit (less …
Date: May 2015
Creator: Riojas, Amanda G.
System: The UNT Digital Library
Computational Studies of C–H/C–C Manipulation Utilizing Transition Metal Complexes (open access)

Computational Studies of C–H/C–C Manipulation Utilizing Transition Metal Complexes

Density Functional Theory (DFT) is an effective tool for studying diverse metal systems. Presented herein are studies of a variety of metal systems, which can be applied to accomplish transformations that are currently difficult/impossible to achieve. The specific topics studied utilizing DFT include: 1) C–H bond activation via an Earth-abundant transition metal complex, 2) C–H bond deprotonation via an alkali metal superbase, 3) and amination/aziridination reactions utilizing a CuI reagent. Using DFT, the transformation to methanol (CH3OH) from methane (CH4) was examined. The transition metal systems studied for this transformation included a model FeII complex. This first-row transition metal is an economical, Earth-abundant metal. The ligand set for this transformation includes a carbonyl ligand in one set of complexes as well as a phosphite ligand in another. The 3d Fe metal shows the ability to convert alkyls/aryls to their oxidized counterpart in an energetically favorable manner. Also, “superbasic” alkali metal amides were investigated to perform C—H bond cleavage. Toluene was the substrate of interest with Cs chosen to be the metal of interest because of the highly electropositive nature of this alkali metal. These highly electrophilic Cs metal systems allow for very favorable C—H bond scission with a toluene substrate. …
Date: May 2015
Creator: Pardue, Daniel B.
System: The UNT Digital Library
Applications of Single Reference Methods to Multi-Reference Problems (open access)

Applications of Single Reference Methods to Multi-Reference Problems

Density functional theory is an efficient and useful method of solving single-reference computational chemistry problems, however it struggles with multi-reference systems. Modifications have been developed in order to improve the capabilities of density functional theory. In this work, density functional theory has been successfully applied to solve multi-reference systems with large amounts of non-dynamical correlation by use of modifications. It has also been successfully applied for geometry optimizations for lanthanide trifluorides.
Date: May 2015
Creator: Jeffrey, Chris C.
System: The UNT Digital Library
The Mechanisms of Human Glutathione Synthetase and Related Non-Enyzmatic Catalysis (open access)

The Mechanisms of Human Glutathione Synthetase and Related Non-Enyzmatic Catalysis

Human glutathione synthetase (hGS) is a homodimeric enzymes that catalyzes the second step in the biological synthesis of glutathione, a critical cellular antioxidant. The enzyme exhibits negative cooperativity towards the γ-glutamylcysteine (γ-GC) substrate. In this type of allosteric regulation, the binding of γ-GC at one active site significantly reduces substrate affinity at a second active site over 40 Å away. The presented work explores protein-protein interactions, substrate binding, and allosteric communication through investigation of three regions of hGS: the dimer interface, the S-loop, and the E-loop. Strong electrostatic interactions across the dimer interface of hGS maintain the appropriate tertiary and quaternary enzymatic structure needed for activity. The S-loop and E-loop of hGS form walls of the active site near γ-GC, with some residues serving to bind and position the negatively cooperative substrate. These strong interactions in the active site serve as a trigger for allosteric communication, which then passes through hydrophobic interactions at the interface. A comprehensive computational and experimental approach relates hGS structure with activity and regulation. ATP-grasp enzymes, including hGS, utilize ATP in the nucleophilic attack of a carboxylic acid in a reaction thought to proceed through the formation of an acylphosphate intermediate. Small metal cations are known …
Date: May 2015
Creator: Ingle, Brandall L.
System: The UNT Digital Library
Pathways for C—H Activation and Functionalization by Group 9 Metals (open access)

Pathways for C—H Activation and Functionalization by Group 9 Metals

As fossil fuel resources become more and more scarce, attention has been turned to alternative sources of fuels and energy. One promising prospect is the conversion of methane (natural gas) to methanol, which requires an initial activation of a C-H bond and subsequent formation of a C-O bond. The most well studied methodologies for both C-H activation and C-O bond formation involve oxidation of the metal center. Metal complexes with facile access to oxidation states separated by four charge units, required for two subsequent oxidations, are rare. Non-oxidative methods to perform C-H bond activation or C-O bond formation must be pursued in order for methane to methanol to become a viable strategy. In this dissertation studies on redox and non-redox methods for both C-H activation and C-O bond formation are discussed. In the early chapters C-O bond formation in the form of reductive functionalization is modeled. Polypyridine ligated rhodium complexes were studied computationally to determine the properties that would promote reductive functionalization. These principles were then tested by designing an experimental complex that could form C-O bonds. This complex was then shown to also work in acidic media, a critical aspect for product stabilization. In the later chapters, non-oxidative C-H …
Date: May 2015
Creator: Pahls, Dale R.
System: The UNT Digital Library
Transition Metal Catalyzed Oxidative Cleavage of C-O Bond (open access)

Transition Metal Catalyzed Oxidative Cleavage of C-O Bond

The focus of this thesis is on C-O bonds activation by transition metal atoms. Lignin is a potential alternative energy resource, but currently is an underused biomass species because of its highly branched structure. To aid in better understanding this species, the oxidative cleavage of the Cβ-O bond in an archetypal arylglycerol β-aryl ether (β–O–4 Linkage) model compound of lignin with late 3d, 4d, and 5d metals was investigated. Methoxyethane was utilized as a model molecule to study the activation of the C-O bond. Binding enthalpies (ΔHb), enthalpy formations (ΔH) and activation enthalpies (ΔH‡) have been studied at 298K to learn the energetic properties in the C-O bond cleavage in methoxyethane. Density functional theory (DFT) has become a common choice for the transition metal containing systems. It is important to select suitable functionals for the target reactions, especially for systems with degeneracies that lead to static correlation effects. A set of 26 density functionals including eight GGA, six meta-GGA, six hybrid-GGA, and six hybrid-meta-GGA were applied in order to investigate the performance of different types of density functionals for transition metal catalyzed C-O bond cleavage. A CR-CCSD(T)/aug-cc-pVTZ was used to calibrate the performance of different density functionals.
Date: May 2015
Creator: Wang, Jiaqi
System: The UNT Digital Library
Synthesis of Peropyrene and Tetracene Derivatives for Photochemical Applications (open access)

Synthesis of Peropyrene and Tetracene Derivatives for Photochemical Applications

A novel route for the synthesis of the polycyclic aromatic hydrocarbon peropyrene (Pp) is reported along with the efforts to synthesize derivatives of Pp, 2,2′- and 5,5′-linked tetracene dimers as candidates for study as singlet fission materials in photovoltaic devices. Peropyrene was synthesized by the McMurry coupling conditions from phenalenone and low-valent titanium species. The crystal structure of Pp is formed by π-stacked molecular pairs in a herringbone arrangement. The direct functionalization of Pp was studied, and several indirect methods for the functionalization of Pp via phenalenone derivatives are reported. Nucleophilicly dependent, regioselective Michael addition pathways for phenalenone are described. Phenalenone forms a nucleophilic complex with bispinacolatodiboron and yields chiral 3,3′-linked phenalenone dimers and a bicyclo[3.2.1]octane derivative product of an unusual 3,4 addition. An active complex product of phenalenone and (dimethylphenylsilyl)boronic acid pinacolic ester forms Pp directly. The synthesis of 2,2′- and 5,5′-linked tetracene dimers led to the study of the reduction of 1-arylprop-2-yn-1-ol derivatives via TFA-catalyzed hydride transfer from triethylsilane. Substrates with terminal and TMS-protected alkynes showed silane exchange upon reduction. A TMS-protected, terminal alkyne became triethylsilyl-protected by about 50% whereas only triethylsilyl-protected, terminal alkyne was observed from the reduction of an unprotected, terminal alkyne. A new conformational polymorph …
Date: May 2015
Creator: Rodríguez López, Marco Tulio
System: The UNT Digital Library