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Date of Award
James R. Bour
Selective C—H functionalization of organic molecules is one of the most desired transformations in organic synthesis. In recent years, many groups have turned to using supramolecular chemistries to perturb native selectivity in reactions that are predominantly sterically controlled. In instances where there is little steric differentiation, people have turned to the development of supramolecular strategies that involve a level of directionality between substrate and catalyst assemblies primarily through non-covalent interactions. More proximal functionalizations to directing groups on substrates were the first to evolve, however branching out to more distal positions proved to be a formidable challenge. To address this discrepancy, significant research has been devoted to the use of porous materials as a potential support for use in transition metal catalysis to selectively functionalize a wide variety of compounds. One notable material type that has found itself in catalytic applications are metal-organic frameworks (MOFs). Because of their ability to be fitted with different types of metal and organic components, MOFs can contain a variety of functionalities for specific purposes integrated into them. The extended crystalline lattices and rigid framework of MOFs results in fixed spatial relationships between their structural features, and our main interest is exploiting these fixed relationships to selectively functionalize C—H bonds. In the short term, I sought to develop highly selective MOFs as effective C—H borylation catalysts. The long-term goal for my projects is to establish MOFs as tools for small molecule synthesis. The central hypothesis of this work is that the pore environment of MOFs can be modified to control selectivity in otherwise non or poorly selective transformations. To test this hypothesis, I investigated two different modes of perturbing selectivity in borylation reactions: selectivity through confinement and selectivity from substrate docking. In confinement-affected borylation, UiO-67-type MOFs were investigated for size confinement effects that assist in directing substrates into transition states where the ortho borylated regioisomer predominates. In the substrate docking approach, I investigated the use of MOF (Zn) PCN-222 as a metalloporphyrin-based director for substrate docking via Zn—substrate interactions. We were able to observe borylation activity using this MOF catalyst but did not observe significant regioselectivity in our experiments. In parallel with these studies, I developed a new approach toward high throughput experimentation in small molecule MOF catalysis, which allowed us to dispense submilligram quantities of MOF into multiple wells and lead to more efficient workflow using Chembeads technology developed by Abbvie and the team of Noah Tu.
Duque, Jesse Brandon, "Metal-Organic Framework Catalysts For Selective C-H Borylation" (2022). Wayne State University Theses. 870.