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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

ELECTRONIC FACTORS OF CARBON - HYDROGEN AND DOUBLE-BONDED CARBON BOND ACTIVATION: EXPERIMENTAL INFORMATION FROM ULTRAVIOLET AND X-RAY PHOTOELECTRON SPECTROSCOPIES (CORE, VALENCE, OLEFIN).

KELLOGG, GLEN EUGENE. January 1985 (has links)
Principles of transition metal electronic structure are presented to enable an understanding of the activation of C-H and C=C bonds by metals. A multitechnique approach utilizing core and valence photoelectron spectroscopies (p.e.s.) and molecular orbital calculations has been used to gain these insights. In the first half of the dissertation three principles are developed: ligand additivity, core-valence ionization correlation, and ring methylation. In the latter half of the dissertation these principles are seen to be crucial for understanding ionization data for the C-H and C=C activated species. Additive (with respect to ligand substitution) electronic effects, including additive core and valence ionization potentials, are shown in the p.e.s. of phosphine substituted molybdenum carbonyls. These additive effects demonstrate that the electronic effects of ligand substitution are predictable from empirical models. The core-valence ionization correlation enables direct comparison of XPS (core) and UPS (valence) ionization data and allows separation of bonding and overlap induced valence shift effects from Coulombic and relaxation shift effects. In the study of trimethylphosphine substituted cyclopentadienylmanganese tricarbonyl complexes, both the ligand additivity and core-valence ionization correlation principles are less valid than for the molybdenum carbonyl complexes because of loss of the very influential carbonyl backbonding. Methylation of the cyclopentadienyl ring in this system adds another independent variable of electronic structure perturbation and enables separation of the one-center and two-center Coulombic contributions to the core shifts. The above principles are used in the later chapters to show that the initial activation of the C-H bond in alkenylmanganese tricarbonyl complexes is dominated by the interaction of the C-H sigma bonding level with empty metal acceptor levels. The activation stops at the agostic stage rather than proceeding to full β-hydribe abstraction because there is, in these molecules, no gain in the number of pi electrons between the allyl and diene hydride endpoints of the abstraction cycle. Activation of the C=C bond in the cyclopentadienylmetal olefins is similar for Co and Rh complexes despite little similarity in the valence ionization spectra. The spectral differences are largely caused by the relaxation energy differences between Co and Rh. These complexes also provide interesting examples of electron delocalization through the metal. Permethylation of the cyclopentadienyl ring shifts the olefin pi ligand ionizations more than the expected Coulombic shift.
2

Synthesis, characterization and reactivity of transition metal containing zeolites

Rossin, Joseph A. January 1986 (has links)
Transition metal containing zeolites (zeolite A and ZSM-5) were prepared by addition of various transition metal containing substrates to zeolite synthesis gels. Crystal growth data were recorded in order to determine the influence of the transition metal species on the rate of crystal growth. X-ray diffraction, oxygen adsorption, FTIR and SEM were utilized to evaluate crystal purity. X-ray photoelectron spectroscopy (XPS), chemical analysis and electron microprobe analysis were performed in order to ascertain the position (intrazeolitic versus surface) and homogeneity of the transition metal. It was concluded that intrazeolitic transition metals were produced by the novel procedure presented in this work. 1-Hexene hydroformylation by rhodium zeolite A showed intrazeolitic rhodium to migrate to the external surface of the zeolite. However, in the presence of a solution and surface rhodium poison, intrazeolitic rhodium was found to hydroformylate 1-hexene exclusively to heptanal. Ruthenium containing zeolite A was evaluated under CO-hydrogenation conditions. No migration of intrazeolitic ruthenium to the external surface of the zeolite was observed over the course of the reaction. The product distribution obtained for this catalyst did not follow a log normal behavior. Also, loss of zeolite crystallinity was observed following the reaction. Cobalt ZSM-5 was evaluated under CO-hydrogenation conditions. No migration of cobalt to the external surface of the zeolite occurred. XPS analysis of the catalyst following various stages of the reaction indicated that intrazeolitic cobalt was not reduced to the zero valent state. Consequently, the non-zero valent cobalt was not capable of hydrogenating carbon monoxide. / Ph. D.

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