Theses and Dissertations at Montana State University (MSU)
Permanent URI for this communityhttps://scholarworks.montana.edu/handle/1/732
Browse
4 results
Search Results
Item Catalysis with early and late transition metals: C-H activation at tantalocene hydrides and oxidative addition at palladium solvato complexes(Montana State University - Bozeman, College of Letters & Science, 2021) Rehbein, Steven Mark; Chairperson, Graduate Committee: Sharon Neufeldt; Matthew J. Kania and Sharon R. Neufeldt were co-authors of the article, 'Experimental and computational evaluation of tantalocene hydrides for C-H activation of arenes' in the journal 'Organometallics' which is contained within this dissertation.; Steven M. Rehbein and Sharon R. Neufeldt were co-authors of the article, 'Solvent coordination to palladium can invert the selectivity of oxidative addition' in the journal 'Organometallics' which is contained within this dissertation.Herein we present our work on transition metal catalysis using metals from two sides of the periodic table: C-H activation catalyzed by early transition metals and cross-couplings catalyzed by late transition metals. In the first part, a synergistic experimental and computational approach was employed to investigate the possibility of extending the reactivity of bent tantalocene hydrides beyond aromatic C-H activation to enable activation of aliphatic substrates. In situ monitoring of the characteristic 1 H NMR metal hydride signals in the reaction of Cp 2TaH 3 and related complexes with deuterated aromatic substrates allowed for the evaluation of reaction kinetics of catalyst decomposition, H/D exchange, and off-cycle reactions. The insight gained from in situ reaction monitoring with aromatic substrates, combined with computational analyses, allowed for the extension of this chemistry to intra- and intermolecular aliphatic C-H activation. This work represents the first example of aliphatic C-H activation by homogeneous tantalum hydrides. In the second part, we provide compelling evidence that solvent coordination to palladium during oxidative addition of chloroaryl triflates can result in an inversion of chemoselectivity of this step. Previous investigations attributed a solvent-dependent switch in chemoselectivity to the propensity of polar solvents to stabilize anionic transition states of the type [Pd(P t Bu 3)(X)]- (X = anionic ligand). However, our detailed investigations show that solvent polarity alone is not a sufficient predictor of selectivity. Instead, solvent coordinating ability is selectivity-determining, with polar coordinating and polar noncoordinating solvents giving differing selectivity, even in the absence of anionic ligands 'X'. A solvent-coordinated bisligated transition state of the type Pd(P t Bu 3)(solvent) is implicated by density functional theory calculations. This work provides a new mechanistic framework for selectivity control during oxidative addition.Item Solid acid catalysts for biomass and sugar upgrading to furans(Montana State University - Bozeman, College of Engineering, 2019) Romo, Joelle Elise; Chairperson, Graduate Committee: Stephanie Wettstein; Nathan V. Bollar, Coy J. Zimmermann and Stephanie G. Wettstein were co-authors of the article, 'Conversion of sugars and biomass to furans using heterogeneous catalysts in biphasic solvent systems' in the journal 'ChemCatChem' which is contained within this thesis.; Ting Wu, Xinlei Huang, Jolie Lucero, Jennifer L. Irwin, Jesse Q. Bond, Moises A. Carreon and Stephanie G. Wettstein were co-authors of the article, 'SAPO-34/5A zeolite bead catalysts for furan production from xylose and glucose' in the journal 'ACS omega' which is contained within this thesis.Platform chemicals derived from biomass provide a viable alternative to petroleum-based fuels, chemicals, and materials. The efficient production of chemical building blocks, such as 5-hydroxymethylfurufral (HMF) and furfural, requires an optimized catalyst and reaction system, as well as an efficient system in which catalysts and products can be easily recovered. While homogeneous acid catalysts have historically been a popular choice for furan production, additional safety, material, and corrosion considerations motivates the exploration of heterogeneous solid acid catalysts. Furthermore, biphasic reaction systems, which use an organic solvent to continuously extract products, have shown increased furan yields over aqueous and monophasic systems and can allow for easy product recovery if the boiling point is selected carefully. One class of heterogeneous catalysts known as zeolites, has unique potential for furfural and HMF production with its controlled acidic and structural properties. A novel SAPO- 34/5A zeolite bead is presented in this thesis, showing promise in catalyst design for activity, product selectivity, and stability. The combination of optimized solvent systems with carefully designed solid acid catalysts lays a framework for the progression of platform chemical production from biomass. Additionally, a comprehensive review of heterogeneous catalysts for furan production in biphasic systems is presented here, which informs decisions on optimized solvent selection.Item Linear and nonlinear optical studies of molecular adsorption to silica/liquid interfaces(Montana State University - Bozeman, College of Letters & Science, 2015) Woods, Brittany Lauren Gray; Chairperson, Graduate Committee: Robert Walker; Rob Walker was a co-author of the article, 'pH effects on molecular adsorption and solvation of p-nitrophenol at silica/aqueous interfaces' in the journal 'Journal of physical chemistry A' which is contained within this thesis.; Jenna K. George, Alex M. Sherman, Patrik R. Callis and Robert A. Walker were co-authors of the article, 'Adsorption and aggregation at silica/methanol interface: the role of solute structure' submitted to the journal 'Journal of physical chemistry C' which is contained within this thesis.; Jenna K. George and Robert Walker were co-authors of the article, 'Spectroscopic solvation mechanisms at silica/acetonitrile interfaces' submitted to the journal 'Physical chemistry and chemical physics' which is contained within this thesis.Adsorption mechanisms at buried interfaces are difficult to predict a priori, with many interactions to consider including those between the substrate and solvent, the substrate and adsorbate, and the solvent and adsorbate. Studies described in this thesis examine the roles these variables have on controlling interfacial behavior, including molecular adsorption and aggregation at solid/liquid interfaces. Specifically, second harmonic generation (SHG) was employed to characterize adsorption environments and adsorption energies at different silica/liquid interfaces, due to the technique's surface specificity. Additionally, time resolved fluorescence was used to quantify emission lifetimes within these same interfacial regions. By systematically changing the substrate, solvent identity, and adsorbate functionality, the impact of each contribution was identified and quantified. Initial studies examined the role played by interfacial pH in controlling adsorption. Above pH 5, silica surfaces become negatively charged and promote two distinct adsorption mechanisms. Adsorption due to these mechanisms requires very long equilibration times (>3hrs). Subsequent experiments studied the role played by solvent identity on interfacial solvation. At a methanol/silica interface a non-polar interfacial environment was produced, independent of solute choice. Non-polar solvents conversely create polar interfacial solvation environments. At these different solid/liquid interfaces, similarly structured coumarin dyes, C151 and C152, were examined. Slight changes in structure lead to differing behaviors at the surface, C151 terminates at monolayer coverage while C152 shows clear signs of multilayer formation. This observation is explained by the difference in hydrogen bonding opportunities for each adsorbate: C151 can accept and donate H-bonds while C152 can only accept H-bonds, resulting in more degrees of freedom for C152 at an interface and thus the possibility of aggregation.Item The solvent selection expert system for azeotropic and extractive distillation(Montana State University - Bozeman, College of Engineering, 1994) Yang, Zuyin; Chairperson, Graduate Committee: Ronald W. Larsen; Lloyd Berg (co-chair)