The main object of this study is to explore the possibility of using metallocene catalyst and reagent toe preparation syndiotactic polystyrene (sPS) framework connected with different polymer segments. Despite its enhanced thermal stability, the stereo-regular sPS generally has poor miscibility with other conventional polymers, which substantially limits its use in commerce. Therefore, chemical modifications on sPS were attempted in this study to hopefully introduce polar chain segments into the olefinic sPS chains and to possibly vary its properties and so, its miscibility with other polymers. Here, a novel metallocene catalyst prepared from (

Thesis (Ph. D.)--University of Texas at Austin, 1999. / Vita. Includes bibliographical references. Available also in a digital version from Dissertation Abstracts.

The transfer of electrons to and from a molecule is one of the more fundamental and important chemical processes. One such important example is the reduction-oxidation (redox) cycles in catalysts and enzymes. In the hydrogenase enzymes, adding and removing electrons is one of the key processes for generating H₂ from water molecules. Finding a direct free energy relation between the vertical ionization energies (IE(V)) measured spectroscopically by gas-phase photoelectron spectroscopy and the oxidation potentials (E(1/2)) measured thermodynamically in solution by cyclic voltammetry (CV) for molecules is an important aspect for developing effective catalysts. In this study, a series of organometallic compounds such as metallocenes were used for investigating the free energy relationships and catalysts inspired by the active sites of [FeFe]-hydrogenases enzymes were evaluated for their ability to produce H₂ from electrocatalytic reduction of weak acids. The first part of the dissertation explores metallocenes of the form (η⁵-C₅H₅)₂M (M= Fe, Ru, Os, Co, Ni) as the model for developing the free energy relation between gas phase ionization energies (IE(V)) and solution oxidation potentials (E(1/2)). It was found that computing the electronic properties of Cp₂Fe, Cp₂Ru, and Cp₂Os using VWN-Stoll and OPBE density functional theory (DFT) functional was successful with root mean square deviation (RMSD) of 0.02 eV between the experimental and calculated ionization energies. However, calculated ionization energies of Cp₂Co and Cp₂Ni were less successful with RMSD of 0.3 eV between the experimental and calculated ionization energies. Introduction of the B3LYP or M06 hybrid DFT functionals yielded much improved results (0.1 eV) over the previous combinations of DFT functional for Cp2Co and Cp2Ni. The energy relation between the two experimental measurements was established and further computational studies revealed that the solvation energy was the largest energy contribution between IE(V) and E(1/2) in the five studied metallocenes. The RMSD of the calculated oxidation potentials, after adjusting for the error in gas-phase ionization energies, was 0.09 V. The second part of the dissertation explores a series of catalysts inspired by the active sites of [FeFe]-hydrogenase enzymes; μ-(2,3-pyrazinedithiolato)diironhexacarbonyl (PzDT-cat), Fe₂(μ-X₂C₅H₈O)(CO)₆ (where X = S, Se, Te), and Fe₂(μ-1,3-SC₃H₆X)(CO)₆ (where X = Se and Te) for their ability to produce H₂ from weak acids utilizing the computational techniques and knowledge gained from the metallocene study. Even though the overall electronic perturbation from μ-(1,2-benzenedithiolato)diironhexacarbonyl (BDT-cat) to μ-(2,3-pyridinedithiolato)diironhexacarbonyl (PyDT-cat) to PzDT-cat is found to be small, the reduction potential of PzDT-cat was found to be 0.15 V less negative than that of BDT-cat resulting in less energy required for initiating electrocatalytic H₂ production over the BDT-cat and PyDT-cat. Lower reorganization energy has been achieved by substitutions of larger chalcogens at the Fe₂S₂ core. However, the electrocatalytic production of H₂ from acetic acid in acetonitrile was found to be diminished upon going from analogous S to Se to Te species. This is ascribed to the increase in the Fe–Fe bond distance with a corresponding increase in the size of the chalcogen atoms from S to Se to Te, disfavoring the formation of a carbonyl-bridged structure in the anion which is thought to be critical to the mechanism of H₂ production.

Würzburg, Univ., Diss., 2009.

Thesis (Ph. D.)--Florida State University, 2005. / Advisor: Rufina G. Alamo, Florida State University, FAMU-FSU College of Engineering, Dept. of Chemical and Biomedical Engineering. Title and description from dissertation home page (viewed Jan. 24, 2006). Document formatted into pages; contains xv, 209 pages. Includes bibliographical references.

Techn. Universiẗat, Diss., 2000--München.

Techn. Universiẗat, Diss., 2004--Darmstadt.

Fakultät für Chemie, Diss., 2005--Universität Bielefeld.

A homopolimerização de etileno foi investigada utilizando o catalisador (nBuCp)2ZrCl2 suportado em sílicas modificadas quimicamente com diferentes espaçadores. Dentre eles, foram utilizados Me3SiCl, Me2HSiCl, Ph3SiCl, polimetilhidrossiloxano (PMHS), GeCl4, SnCl4 ou PbCl2. As interações organossilano-sílica, zirconoceno-silanos suportados e zirconoceno suportadosilanos suportados foram estudadas através do método teórico ICONC. Os teores de metal foram determinados por Espectrometria de retroespalhamento Rutherford (RBS), enquanto a modificação química da superfície da sílica foi monitorado por Espectroscopia molecular no infravermelho com Transformada de Fourier (FT-IR) ou Espectroscopia molecular no infravermelho de refletância difusa (DRIFTS). As espécies zirconocenas superficiais foram investigadas por Espectroscopia de raio-X (XPS). A morfologia dos sistemas catalíticos e polímeros obtidos foram caracterizados por Microscopia eletrônica de varredura (SEM) e a distribuição de metal do sistema contendo PMHS foi estudada por Microssonda eletrônica (EPMA). Estes sistemas catalíticos produziram polietilenos com estreita polidispersidade e alta atividade catalítica utilizando metilaluminoxano como cocatalisador. Os efeitos da modificação química da sílica na performance catalítica são apresentados e discutidos. / The homopolymerization of ethylene was investigated using the catalysts of (nBuCp)2ZrCl2 supported on chemically modified silica with different spacers. The spacers used were Me3SiCl, Me2HSiCl, Ph3SiCl, polymethylhydrosiloxane (PMHS), GeCl4, SnCl4 or PbCl2. The organosilanes-silica, zirconocene-supported silanes and supported zirconocene-supported silanes interactions were studied by ICONC method. The metal contents were determined by Rutherford backscattering spectrometry (RBS), while the chemical modification of the silica surface was monitored by Fourier transform infrared spectroscopy (FT-IR) or Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The zirconocene surface species were investigated by X-ray spectroscopy (XPS). The morphology of these catalytic systems and polymers were evaluated by Scanning electron microscopy (SEM) and the metal distribution for the PMHS systems was studied by Electron microprobe analysis (EPMA). These catalytic systems produced polyethylene with a narrow molecular weight distribution and high catalyst activities using methylaluminoxane as co-catalyst. The effects of the chemical modification of the silica on the catalyst performance are presented and discussed.

A homopolimerização de etileno foi investigada utilizando o catalisador (nBuCp)2ZrCl2 suportado em sílicas modificadas quimicamente com diferentes espaçadores. Dentre eles, foram utilizados Me3SiCl, Me2HSiCl, Ph3SiCl, polimetilhidrossiloxano (PMHS), GeCl4, SnCl4 ou PbCl2. As interações organossilano-sílica, zirconoceno-silanos suportados e zirconoceno suportadosilanos suportados foram estudadas através do método teórico ICONC. Os teores de metal foram determinados por Espectrometria de retroespalhamento Rutherford (RBS), enquanto a modificação química da superfície da sílica foi monitorado por Espectroscopia molecular no infravermelho com Transformada de Fourier (FT-IR) ou Espectroscopia molecular no infravermelho de refletância difusa (DRIFTS). As espécies zirconocenas superficiais foram investigadas por Espectroscopia de raio-X (XPS). A morfologia dos sistemas catalíticos e polímeros obtidos foram caracterizados por Microscopia eletrônica de varredura (SEM) e a distribuição de metal do sistema contendo PMHS foi estudada por Microssonda eletrônica (EPMA). Estes sistemas catalíticos produziram polietilenos com estreita polidispersidade e alta atividade catalítica utilizando metilaluminoxano como cocatalisador. Os efeitos da modificação química da sílica na performance catalítica são apresentados e discutidos. / The homopolymerization of ethylene was investigated using the catalysts of (nBuCp)2ZrCl2 supported on chemically modified silica with different spacers. The spacers used were Me3SiCl, Me2HSiCl, Ph3SiCl, polymethylhydrosiloxane (PMHS), GeCl4, SnCl4 or PbCl2. The organosilanes-silica, zirconocene-supported silanes and supported zirconocene-supported silanes interactions were studied by ICONC method. The metal contents were determined by Rutherford backscattering spectrometry (RBS), while the chemical modification of the silica surface was monitored by Fourier transform infrared spectroscopy (FT-IR) or Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The zirconocene surface species were investigated by X-ray spectroscopy (XPS). The morphology of these catalytic systems and polymers were evaluated by Scanning electron microscopy (SEM) and the metal distribution for the PMHS systems was studied by Electron microprobe analysis (EPMA). These catalytic systems produced polyethylene with a narrow molecular weight distribution and high catalyst activities using methylaluminoxane as co-catalyst. The effects of the chemical modification of the silica on the catalyst performance are presented and discussed.