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Molecular Modeling Study of Oxidative Degradation of Polyperfluoroethers Catalyzed by Iron Fluoride Surfaces : An Extended Hückel Theory Approach

Description: Extended Hückel methods are known to be a useful tool in understanding surface phenomena. Important quantities about atoms and chemical bonds can be obtained from this computationally simple method, although caution must be exercised in interpreting the results. Application of Extended Hückel calculations to large metal clusters reveals the role of d orbitals in solids. Basic ideas of constructing model compounds have been developed. Several model systems for surface chemisorption processes are constructed in order to understand the surface catalyzed oxidative degradation of polyperfluoroethers. The activation of oxygen molecules can be explained. The Lewis acid character of the iron fluoride surface can be predicted. Based on these results, mechanisms of the degradation processes are discussed.
Date: May 1995
Creator: Wang, Yanbin
Partner: UNT Libraries

Synthesis and characterization of molecules to study the conformational barriers of fluorocarbon chains

Description: Fluorocarbons are known to be stiffer than their hydrocarbon analogues, a property that underlines the extensive industrial application of fluorocarbon materials. Although there has been previous studies on the rotational barrier of molecules having fluorocarbon centers, a detailed systematic study is necessary to quantify flurocarbon stiffness. The molecules, Pyrene-(CF2)n-Pyrene, Pyrene-(CF2)n-F, Pyrene-(CH2)n-Pyrene and Pyrene-(CH2)n-H were therefore synthesized to enable the determination of the barrier to rotation of the carbon backbone in fluorocarbons. Conformational studies will be completed with steady-state and time-dependent emission spectroscopy.
Date: May 2000
Creator: Niyogi, Sandip
Partner: UNT Libraries

A Kinetic Study of the Recombination Reacton Na + SO₂ + Ar

Description: The recombination reaction Na + S02 + Ar was investigated at 787 16 K and at pressures from 1.7 to 80 kPa. NaI vapor was photolyzed by an excimer laser at 308 nm to create Na atoms, whose concentration was monitored by time-resolved resonance absorption at 589 nm. The rate constant at the low pressure limit is ko = (2.7 0.2) x 10-21 cm6 molecule-2 s~1. The Na-SO 2 dissociation energy E0 = 170 35 kJ mol1 was calculated with RRKM theory. The equilibrium constant gave a lower limit E0 > 172 kJ mol~ 1. By combination of these two results, E0 = 190 15 kJ mol~ 1 is obtained. The high pressure limit is k, = (1 - 3) x 10-10 cm3 molecule 1 s~1, depending on the extrapolation method used. Two versions of collision theory were employed to estimate k,.. The 'harpoon' model shows the best agreement with experiment.
Date: December 1990
Creator: Shi, Youchun
Partner: UNT Libraries

An NMR Investigation of Aryl Mercury Compounds

Description: A variable temperature ^13 C and ^199 Hg NMR study has been conducted for diphenyl-, bis(o-tolyl)-, bis(m-tolyl)-, and bis(2, 6-xylyl)mercury in dimethyl sulfoxide and 1,1,2,2 tetrachloroethane; ^13 C T1 relaxation times are reported as a function of temperature. Barriers to rotation of the aryl rings are obtained. Chemical shifts and couplings in CDCl_3 are given for bis(p-tolyl)-, bis(2, 5-xylyl)-, bis(mesityl)-,phenyl(o-tolyl)-, phenyl(m-tolyl)mercury, and the compounds listed above. The steric interactions of these aryl mercury compounds are discussed.
Date: May 1987
Creator: Rowland, Keith E. (Keith Edward)
Partner: UNT Libraries

Hydraulic Activity in Synthetic and Commercial Slags

Description: Slag, by itself, shows very little hydraulic activity. However, hydration is greatly accelerated by incorporation of the slag with Portland cement. This phenomenon is due to the activating role of calcium hydroxide released from the hydration of Portland cement. This study was aimed at finding other activators that will increase hydration in both synthetic and commercial slags. The effects of chemical composition and the aggregation state of the slag on the hydration process were also investigated. For the synthetic slags, the aggregation state was altered by different quenching techniques. The chemical composition was varied by synthesizing a series of slags. The degree of hydration was studied by developing a thermogravimetric analysis technique and the glass content was determined using microscopy. Minerals were determined using powder x-ray diffraction analysis.
Date: May 1982
Creator: Saad, Bahruddin bin
Partner: UNT Libraries

Vibrational Spectra and Potential Function of Tetrachlorocyclopropene

Description: The laser Raman spectra of tetrachlorocyclopropene in the liquid and solid phases have been recorded and vibrational assignments are presented. These results along with root mean squared vibrational amplitudes from electron diffraction data have been employed in a normal coordinate analysis in which a 19 parameter potential function is refined. This potential function, originally expressed in terms of compliance constants, is then used to derive the corresponding conventional and relaxed force constants.
Date: August 1981
Creator: Adame, I. Ernesto (Ignacio Ernesto)
Partner: UNT Libraries

A Computational Study on 18+δ Organometallics

Description: The B3LYP density functional has been used to calculate properties of organometallic complexes of Co(CO)3 and ReBr(CO)3, with the chelating ligand 2,3-bisphosphinomaleic anhydride, in 19- and 18-electron forms. The SBKJC-21G effective core potential and associated basis set was used for metals (Co/Re) and the 6-31G* basis set was used for all other elements. The differences of bond angles, bond distances, natural atomic charges and IR vibrational frequencies were compared with the available experimental parameters. The differences between the 19- and 18-electron systems have been analyzed. The results reveal that the 19th electron is mostly distributed over the ligand of 2,3-bisphosphinomaleic anhydride, although partially localized onto the metal fragment in 1 and 2*. Two different methods, IR-frequencies and natural atomic charges, were used to determine the value of δ. Present computed values of δ are compared with available experimental values, and predictions are made for unknown complexes.
Date: May 2002
Creator: Yu, Liwen
Partner: UNT Libraries

Kinetics of Sulfur: Experimental Study of the Reaction of Atomic Sulfur with Acetylene and Theoretical Study of the Cn + So Potential Energy Surface

Description: The kinetics of the reaction of atomic sulfur with acetylene (S (3P) + C2H2) were investigated experimentally via the flash photolysis resonance fluorescence method, and the theoretical potential energy surface for the reaction CN + SO was modeled via the density functional and configuration interaction computational methods. Sulfur is of interest in modern chemistry due to its relevance in combustion and atmospheric chemistry, in the Claus process, in soot and diamond-film formation and in astrochemistry. Experimental conditions ranged from 295 – 1015 K and 10 – 400 Torr of argon. Pressure-dependence was shown at all experimental temperatures. The room temperature high-pressure limit second order rate constant was (2.10 ± 0.08) × 10-13 cm3 molecule-1 s-1. The Arrhenius plot of the high-pressure limit rate constants gave an Ea of (11.34 ± 0.03) kJ mol-1 and a pre-exponential factor of (2.14 ± 0.19) × 10-11 cm3 molecule-1 s-1. S (3P) + C2H2 is likely an adduct forming reaction due to pressure-dependence (also supported by a statistical mechanics analysis) which involves intersystem crossing. The potential energy surface for CN + SO was calculated at the B3LYP/6-311G(d) level and refined at the QCISD/6-311G(d) level. The PES was compared to that of the analogous reaction CN + O2. Notable energetically favorable products are NCS + O, CO + NS, and CS + NO. The completed PES will ultimately be modeled at the CCSD(T) level (extrapolated to infinite basis set limit) for theoretical reaction rate analysis (RRKM).
Date: May 2013
Creator: Ayling, Sean A.
Partner: UNT Libraries

N-Heterocyclic Carbenes of the Late Transition Metals: A Computational and Structural Database Study

Description: A computational chemistry analysis combined with a crystallographic database study of the bonding in late transition metal N-heterocyclic carbene (NHC) complexes is reported. The results illustrate a metal-carbon bond for these complexes, approximately 4% shorter than that of a M-C single bond found in metal alkyl complexes. As a consequence of this result, two hypotheses are investigated. The first hypothesis explores the possibility of multiple-bond character in the metal-carbon linkage of the NHC complex, and the second, considers the change in the hybridization of the carbenoid carbon to incorporate more p character. The latter hypothesis is supported by the results. Analysis of these complexes using the natural bond orbital method evinces NHC ligands possessing trans influence.
Date: May 2005
Creator: Baba, Eduard
Partner: UNT Libraries

Raman Studies of Conformational Energies and Hydrogen Bonding in Alcohols

Description: The conformational energy differences have been determined for ethylene glycol, 2- chloroethanol, and 2,2- dichloroethanol in the neat liquid, DMSO, and H20 with Raman spectroscopy. Spectra in the 0-H valence region were utilized to determine the energy difference between interand intramolecularly hydrogen bonded species. It was found that the solvent effect on the relative stabilities of the gauche and trans rotamers of the alcohols differ significantly. The results also indicate that, unlike ethylene glycol, there is significant intramolecular hydrogen bond formation in the halogenated alcohols in the neat liquid phase. Stronger intramolecular hydrogen bond formation was observed in dichloroethanol than in 2-chloroethanol.
Date: August 1982
Creator: Maleknia, Simindokht
Partner: UNT Libraries

Vibrational Dephasing of Haloalkanes and Halobenzenes

Description: The Raman linewidths of the carbon-halogen stretching mode was measured as a function of temperature in ethyl bromide, isopropyl chloride, isopropyl bromide, t-butyl chloride, t-butyl bromide, chlorobenzene, bromobenzene, iodobenzene and o-dichlorobenzene. The vibrational relaxation times showed a very clear trend. Together with earlier work on methyl iodide, these results provide evidence that the vibrational dephasing efficiencies (T^-1_iso) of the carbon-halogen mode vary in the order of Cl > Br > I. Vibrational dephasing times were calculated from the Fischer-Laubereau Isolated Binary Collision Mode. If further work shows this transferability to extend to other types of skeletal modes in molecular systems, this would have significant ramifications on future vibrational lineshape studies.
Date: May 1983
Creator: Ho, Salina Yuen-Han
Partner: UNT Libraries

Kinetic Studies of the Reactions of Cl and Br with Silane and Trimethylsilane

Description: The temperature dependence of the reactions of halogen atoms Cl and Br with SiH4 and (CH3)3SiH have been investigated with the flash photolysis-resonance fluorescence technique. CCI4 and CH2Br2 were used as precursors to produce Cl and Br atoms, respectively. Experiments gave {k(Cl + SiH4) (295 - 472 K)} = (1.56 +0.11) x 10-1 exp[(2.0 + 0.2) kJ mol'/RT] cm3 s4, {k(Br + SiH4)(295 - 575 K)} = (9.0 + 1.5) x 10-" exp[-(17.0 + 0.6) Id mol'/RT] cm3 s', {k(Cl + (CH3)3SiH)(295 - 468 K)} = (1.24 0.35) x 104 exp[(1.3 + 0.8) Id mol4/RT] cm3 s', and {k(Br + (CH3)3SiH)(295 - 456 K)} = (7.6 + 3.3) x 1010 exp[-(28.4 + 1.3) Id mol'/RT] cm3 s'. The results were compared with values from earlier work.
Date: May 1992
Creator: Ding, Luying
Partner: UNT Libraries

Synthesis, Structure, and Solution Dynamics of Co₄(CO)₈(dmpe)(mu₄-PPh)₂

Description: Reaction of the tetracobalt cluster Co4(CO)10(t 4-PPh)2 with 1,2-bis(dimethylphosphino)ethane (dmpe) affords the bis-substituted cluster Co4(CO)8(dmpe)(t 4-PPh)2. The bidentate dmpe ligand is shown to bind to the cluster in a chelating fashion by IR, NMR, and X-ray diffractions analyses. The fluxional nature of the ancillary carbonyl groups has been studied by variable temperature 13C NMR measurements which reveal two distinct carbonyl scrambling pathways. The stability of the phosphine-ligated cluster has been examined using in situ Cylindrical Internal Reflection (CIR) Spectroscopy. The effect of the dmpe ligand on the cluster polyhedron will be discussed with respect to the observed crystallographic and spectroscopic results
Date: May 1990
Creator: Schulman, Cheryl Lutins
Partner: UNT Libraries

Syntheses and Structures of Substituted Polycyclic Molecules and Analysis of the Two-Dimensional NMR Spectrum of Thiele's Ester

Description: Diels-Alder cycloaddition of methylcyclopentadienes to 2,5-dibromo-p-benzoquinone was performed. A single, isomerically pure cycloadduct was isolated, whose structure was assigned via analysis of its 1-D and 2-D NMR spectra. Diels-Alder cycloaddition of methylcyclopentadienes to 2 -methoxy-p-benzoquinone was performed. A single, isomerically pure cycloadduct was isolated, whose structure was assigned via analysis of the 1-D and 2-D NMR spectra of this cycloadduct and its reduction product obtained via stereo-specific reduction with sodium borohydride in the presence of cerous chloride. The structure of Thiele's ester was assigned via analysis of its 1-D and 2-D NMR spectra.
Date: May 1990
Creator: Lu, Shao-Po
Partner: UNT Libraries

Syntheses and the Structures of Polymethylpolycyclic and Polycyclic "Cage" Molecules

Description: The structures of Diels-Alder cycloaddition of cyclopentadiene to 2,6-dimethyl-p-benzoquinone and methylcyclopentadiene to 2,6-dimethyl-p-benzoquinone were assigned by analysis of 1-D and 2-D proton and carbon-13 NMR spectra. The structures of the cycloadduct of methylcyclopentadiene to 2,6-dimethyl-p-benzoquinone and that of the corresponding intramolecular [2+2] photocyclization product were also obtained by single crystal X-ray structural analysis. As the second part of the study, a new polycyclic "cage" molecule, a substituted trishomocubane isomer, was synthesized. In this synthesis, reductive bond cleavage followed by Dieckmann condensation was employed. Wolff-Kishner reduction then was used to convert a β-keto ester "cage" molecule to the corresponding carboxylic acid. A compound that possesses twofold symmetry was isolated from reaction product mixture. The structure of this compound has been established by single crystal X-ray crystallography.
Date: May 1989
Creator: Zhao, Dalian
Partner: UNT Libraries

Exploring Inorganic Catalysis with Electronic Structure Simulations

Description: Organometallic catalysis has attracted significant interest from both industry and academia due to its wide applications in organic synthetic transformations. Example of such transformations include the reaction of a zinc carbenoid with olefins to form cyclopropanes. The first project is a computational study using both density functional and correlated wavefunction methods of the reaction between ethylene and model zinc carbenoid, nitrenoid and oxenoid complexes (L-Zn-E-X, E = CH2, NH or O, L = X = I or Cl). It was shown that cyclopropanation of ethylene with IZnCH2I and aziridination of ethylene with IZnNHI proceed via a single-step mechanism with an asynchronous transition state. The reaction barrier for the aziridination with IZnNHI is lower than that of cyclopropanation. Changing the leaving group of IZnNHI from I to Cl, changes the mechanism of the aziridination reaction to a two-step pathway. The calculation results from the epoxidation with IZnOI and ClZnOCl oxenoids suggest a two-step mechanism for both oxenoids. Another important example of organometallic catalysis is the formation of alkyl arenes from arenes and olefins using transition metal catalysis (olefin hydroarylation). We studied with DFT methods the mechanism of a novel Rh catalyst (FlDAB)Rh(TFA)(η2–C2H4) [FlDAB = N,N’ -bis(pentafluorophenyl)-2,3-dimethyl-1,4-diaza-1,3-butadiene; TFA = trifluoroacetate] that converts benzene, ethylene and air-recyclable Cu(II) oxidants to styrene. Possible mechanisms are discussed.
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Date: May 2016
Creator: Karbalaei Khani, Sarah
Partner: UNT Libraries

Thermochemical Investigation of Ternary Nonelectrolyte Mixtures

Description: Excess molar volumes have been determined for four ternary chlorobenzene + dibutyl ether + alkane mixtures at 25°C. Results of these measurements are used to test the applications and limitations of BAB, Redlich-Kister, Kohler and Hwang et al. cubic models. For the systems studied, Redlich- Kister, Kohler and Cubic models were found to provide reasonable predictions. Differences between experimental and predicted ΔV^ex_123 values were about ±0.020 cm^3mol^-1 or less at most ternary compositions. Solubilities are reported for anthracene in binary mixtures containing propanol and butanol with alkanes at 25°C. Results of these measurements are used to test the NIBS/Redlich-Kister expression. The three-parameter form of this expression is found to provide reasonable mathematical representation with deviations between experimental and back-calculated values being less than ±1%.
Date: December 1992
Creator: Teng, I-Lih
Partner: UNT Libraries

Computational Studies of Selected Ruthenium Catalysis Reactions.

Description: Computational techniques were employed to investigate pathways that would improve the properties and characteristics of transition metal (i.e., ruthenium) catalysts, and to explore their mechanisms. The studied catalytic pathways are particularly relevant to catalytic hydroarylation of olefins. These processes involved the +2 to +3 oxidation of ruthenium and its effect on ruthenium-carbon bond strengths, carbon-hydrogen bond activation by 1,2-addition/reductive elimination pathways appropriate to catalytic hydrogen/deuterium exchange, and the possible intermediacy of highly coordinatively unsaturated (e.g., 14-electron) ruthenium complexes in catalysis. The calculations indicate a significant decrease in the Ru-CH3 homolytic bond dissociation enthalpy for the oxidation of TpRu(CO)(NCMe)(Me) to its RuIII cation through both reactant destabilization and product stabilization. This oxidation can thus lead to the olefin polymerization observed by Gunnoe and coworkers, since weak RuIII-C bonds would afford quick access to alkyl radical species. Calculations support the experimental proposal of a mechanism for catalytic hydrogen/deuterium exchange by a RuII-OH catalyst. Furthermore, calculational investigations reveal a probable pathway for the activation of C-H bonds that involves phosphine loss, 1,2-addition to the Ru-OH bond and then reversal of these steps with deuterium to incorporate it into the substrate. The presented results offer the indication for the net addition of aromatic C-H bonds across a RuII-OH bond in a process that although thermodynamically unfavorable is kinetically accessible. Calculations support experimental proposals as to the possibility of binding of weakly coordinating ligands such as dinitrogen, methylene chloride and fluorobenzene to the "14-electron" complex [(PCP)Ru(CO)]+ in preference to the formation of agostic Ru-H-C interactions. Reactions of [(PCP)Ru(CO)(1-ClCH2Cl)][BAr'4] with N2CHPh or phenylacetylene yielded conversions that are exothermic to both terminal carbenes and vinylidenes, respectively, and then bridging isomers of these by C-C bond formation resulting from insertion into the Ru-Cipso bond of the phenyl ring of PCP. The QM/MM and DFT calculations on full complexes ...
Date: December 2007
Creator: Barakat, Khaldoon A.
Partner: UNT Libraries

Forensic Analysis of Ink on Documents Using Direct Analyte-Probed Nanoextraction Coupled Techniques

Description: Analzying questioned documents in a nondestructive nature has been an issue for the forensic science community. Using nondestructive techniques such as video spectral comparator does not give reliable information due to the variations in gray or color levels that are distinguished differently by analysts. Destructive techniques such as chromatography give dependable, qualitative and quantitative, information but involves altering the evidentiary value of these questioned documents. The paradox of document examination becomes a problem when document evidence is involved, especially when trying to preserve its evidentiary value and critical data is needed. Thus, a nondestructive technique has been developed to solve the loopholes in document examinations. Direct analyte-probed nanoextraction (DAPNe) is a nanomanipulation technique that extracts ink directly off the document for further examination. A watermark is left, at most, post-extraction. DAPNe utilizes a tip emitter, pre-filled with a solvent, which is controlled in x-, y-, and z-coordinates via joystick controller and aspirates/extracts using a pressure injector. The versatility of this technique lies within the solvent chemistry and its capability to be coupled to various types of instrumentation. The extraction solvent can be altered to target specific components in the ink. For example, a chelator may be added to target metal ions found in ancient inks or methanol may be added to target certain organic resins and binding agents found in modern inks. In this study, DAPNe has been coupled to nanospray ionization mass spectrometry, fluorescence microscopy, Raman spectroscopy, matrix-assisted laser desorption ionization mass spectrometry, and laser ablation to solve questioned document concerns in the area of falsified or forged documents, redacted documents, and aging studies.
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Date: May 2016
Creator: Huynh, Vivian
Partner: UNT Libraries

A Reinvestigation of the Kinetics and Mechanism of Ligand Exchange in Mu-(2,2,8,8-Tetramethyl-3, 7-Dithianonane)-Decacarbonylditungsten(0)

Description: This student is interested in reinvestigating the kinetics and mechanism of the bridged compound in l,2-dichloroethane with triisopropyl phosphite and in finding the reasons why the values of competition ratio k₋₂ /k₃ in this reaction are so large.
Date: August 1988
Creator: Liao, Jing-Piin
Partner: UNT Libraries

Diphosphine Ligand Activation Studies with Organotransition-Metal Compounds

Description: Thermolysis of CoRu(CO)7(m -PPh2) (1) in refluxing 1,2-dichloroethane in the presence of the diphosphine ligands 2,3-bis(diphenylphosphino)maleic anhydride (bma) and 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd) furnishes the new mixed-metal complexes CoRu(CO)4(μ -P-P)(μ -PPh2) [where P-P = bma (3); bpcd (6)], along with trace amounts of the known complex CoRu(CO)6(PPh3)(μ -PPh2) (4). The requisite pentacarbonyl intermediates CoRu(CO)5(μ -P-P)(μ -PPh2) [where P-P = bma (2); bpcd (5)] have been prepared by separate routes and studied for their conversion to CoRu(CO)4(μ -P-P)(μ -PPh2). The complexes 2/3 and 5/6 have been isolated and fully characterized in solution by IR and NMR spectroscopy. The kinetics for the conversion of 2→3 and of 5→6 were measured by IR spectroscopy in chlorobenzene solvent. On the basis of the first-order rate constants, CO inhibition, and the activation parameters, a mechanism involving dissociative CO loss as the rate-limiting step is proposed. The solid-state structure of CoRu(CO)4(μ -bma)(μ -PPh2) (3) reveals that the two PPh2 groups are bound to the ruthenium center while the maleic anhydride π bond is coordinated to the cobalt atom. Thermolysis of the cluster Ru3(CO)12 with the bis(phosphine)hydrazine ligand (MeO)2PN(Me)N(Me)P(OMe)2 (dmpdmh) in toluene at 75°C furnishes the known clusters Ru4(CO)12[μ -N(Me)N(Me)] (9) and Ru3(CO)11[P(OMe)3] (10), in addition to the new cluster Ru3(CO)10(dmpdmh) (8) and the phosphite-tethered cluster Ru3(CO)9[μ -P(OMe)3] (11). The simple substitution product Ru3(CO)10(dmpdmh), a logical intermediate to clusters 9-11, was synthesized by treating Ru3(CO)12 and dmpdmh with Me3NO in CH2Cl2 at room temperature, and independent thermolysis reactions using cluster 8 were shown to yield clusters 9-11. The tetrahedrane cluster FeCo2(CO)9(μ3-S) reacts with the redox-active ligand 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd) to give the disubstituted cluster FeCo2(CO)7(bpcd)(μ3-S) as the sole product. This diphosphine-substituted cluster contains a cobalt-bound, chelating bpcd ligand. The solid-state structure has been unequivocally established by X-ray diffraction analysis. Cyclic voltammetric studies on FeCo2(CO)7(bpcd)(μ3-S) reveal the presence of two quasireversible ...
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Date: December 2000
Creator: Wang, Jiancheng
Partner: UNT Libraries

Transition Metal Catalyzed Oxidative Cleavage of C-O Bond

Description: 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
Partner: UNT Libraries

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

Description: 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 in thermolytic reactions. The complexes formed were studied and investigated using NMR and X-ray crystallography. Furthermore, the X-ray structures of the heterocyclic ACAC ligand or ligand A and that of rhenium complex 1 were compared with similar published X-ray structures. The comparison showed there were some similarities in terms of bond length and bond angles.
Date: August 2015
Creator: Nyamwihura, Rogers
Partner: UNT Libraries

Synthesis and characterization of quinoxaline-functionalized, cage-annulated oxa- and thiacrown ethers and reaction chemistry of the diphosphine ligand 2,3-bis(diphenylphosphino)-N-p-tolylmaleimide (bmi) at triosmium carbonyl clusters.

Description: Quinoxaline-functionalized, cage-annulated oxa- and thiacrown ethers have been synthesized as possible specific metal host systems. The synthesis and characterization of quinoxaline-functionalized, cage-annulated oxa- and thiacrown ethers have been described. The characterization of these host systems have been fully achieved in solution by using various techniques such as IR, 1H NMR, and 13C NMR spectroscopic methods, high-resolution mass spectrometry (HRMS), elemental microanalysis, and X-ray crystallographic analysis in case of one quinoxaline-functionalized, cage-annulated oxacrown ether compound. The synthesis of the diphosphine ligand 2,3-bis(diphenylphosphino)-N-p-tolylmaleimide (bmi) is described. The substitution of the MeCN ligands in the activated cluster 1,2-Os3(CO)10(MeCN)2 by the diphosphine ligand bmi proceeds rapidly at room temperature to furnish a mixture of bridging and chelating Os3(CO)10(bmi) isomers and the ortho-metalated product HOs3(CO)9[μ-(PPh2)C=C{PPh(C6H4)}C(O)N(tolyl-p)C(O)]. Thermolysis of the bridging isomer 1,2-Os3(CO)10(bmi) under mild conditions gives the chelating isomer 1,1-Os3(CO)10(bmi), whose molecular structure has been determined by X-ray crystallography. The kinetics for the ligand isomerization have been investigated by UV-vis and 1H NMR spectroscopy in toluene solution over the temperature range of 318-348 K. On the basis of kinetic data conducted in the presence of added CO and the Eyring activation parameters, a non-dissociative phosphine migration across one of the Os-Os bonds is proposed. Orthometalation of one of the phenyl groups associated with the bmi ligand is triggered by near-UV photolysis of the chelating cluster 1,1- Os3(CO)10(bmi).
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Date: December 2006
Creator: Poola, Bhaskar
Partner: UNT Libraries