Epoxides are an important chemical functional group, used in a wide variety of processes, from the small-scale production of pharmaceuticals to the large-scale production of propylene oxide. Current methods for production of epoxides require costly multi-step syntheses that use toxic or explosive reagents, result in low yields, and produce co-products that must be removed and often disposed. The development of an atom-efficient general method, preferably catalytic, for converting alkenes to epoxides using safe, cheap, and readily available molecular oxygen as the stoichiometric oxidant would be a great advance in both industrial and academic chemistry.
Presented here is a proposed catalytic cycle in which molecular oxygen is used as the stoichiometric oxidant for the epoxidation of alkenes. The cycle begins with a palladium hydride bearing a tridentate ligand. Molecular oxygen adds to the palladium hydride, forming a palladium hydroperoxide that will act as the active oxidant in the catalytic cycle. This palladium hydroperoxide then transfers one oxygen atom to an alkene, producing palladium hydroxide and the desired epoxide. Finally, the palladium hydride is regenerated from palladium hydroxide by addition of hydrogen gas and elimination of water.
Each individual step of this proposed catalytic cycle was studied computationally using density functional theory calculations. Specifically, the palladium-hydrogen bond dipole and the palladium-hydrogen bond length were examined in relation to formation of the palladium hydroperoxide; the effect of the electrophilicity of the alkene on the epoxidation was studied; and the relationship between the characteristics of the tridentate ligand and the mechanism of palladium-hydride regeneration were examined. Computational results and suggested direction for future experimental focus are presented.
|Advisor:||Kemp, Richard A.|
|Commitee:||Bear, David, Kirk, Martin, Wang, Wei|
|School:||The University of New Mexico|
|Department:||Chemistry and Chemical Biology|
|School Location:||United States -- New Mexico|
|Source:||DAI-B 73/12(E), Dissertation Abstracts International|
|Subjects:||Chemistry, Inorganic chemistry|
|Keywords:||Alkene, Catalytic cycle, Density functional theory, Epoxidation, Epoxide, Palladium|
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