Browsing by Author "Schaefer, Henry F."

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    Application of low valent main group elements in small molecule activation reactions.
    (2020) Villegas, Nery Andrés; Toro Labbé, Alejandro; Schaefer, Henry F.; Pontificia Universidad Católica de Chile. Facultad de Química
    Exceptional synthetic transformations have been achieved through the years by the use of transition metal catalysts. On the contrary, only a few industrialized processes use main group based catalysts due to its low reactivity and poor recovery from the reaction media. In this thesis, a detailed computational study of the application of main group elements acting as transition metals for the activation of small molecules is presented. The hydroboration of CO2 by group 14 NacNac derived systems and the activation of H2 by low valent aluminum species are studied. Low valent main group 14 elements (Si, Ge, Sn, and Pb) bearing charge 2+ and a N-Arylisopropyl--diketiiminate ligand were used for the transformation of CO2, aimed to yield in subsequent steps formic acid derivatives. It has been found that when going down in group 14, the reaction becomes more favored. This study suggests that Pb(II) is a preponderate candidate for hydroboration of CO2. We hope this study motivates future experimental work on main group catalysis, especially using low valent lead compounds.On the other hand, for the activation of H2 by aluminyl anions, it was found that the potassium atoms that help stabilize the dimeric form of the catalysts do not play a catalytic role in the activation of the gas. To explore substituent effect in geometry, electronic structure, and reactivity, simple AlR1R – 2 species were used as a model. High-level coupled-cluster geometry and energetics were obtained for each structure. In conclusion, donation and back-donation effects were found in these structures, resembling a TM behavior. Moreover, monosubstituted aluminyl anions reported lower activation energies concerning the disubstituted systems.Exceptional synthetic transformations have been achieved through the years by the use of transition metal catalysts. On the contrary, only a few industrialized processes use main group based catalysts due to its low reactivity and poor recovery from the reaction media. In this thesis, a detailed computational study of the application of main group elements acting as transition metals for the activation of small molecules is presented. The hydroboration of CO2 by group 14 NacNac derived systems and the activation of H2 by low valent aluminum species are studied. Low valent main group 14 elements (Si, Ge, Sn, and Pb) bearing charge 2+ and a N-Arylisopropyl--diketiiminate ligand were used for the transformation of CO2, aimed to yield in subsequent steps formic acid derivatives. It has been found that when going down in group 14, the reaction becomes more favored. This study suggests that Pb(II) is a preponderate candidate for hydroboration of CO2. We hope this study motivates future experimental work on main group catalysis, especially using low valent lead compounds.On the other hand, for the activation of H2 by aluminyl anions, it was found that the potassium atoms that help stabilize the dimeric form of the catalysts do not play a catalytic role in the activation of the gas. To explore substituent effect in geometry, electronic structure, and reactivity, simple AlR1R – 2 species were used as a model. High-level coupled-cluster geometry and energetics were obtained for each structure. In conclusion, donation and back-donation effects were found in these structures, resembling a TM behavior. Moreover, monosubstituted aluminyl anions reported lower activation energies concerning the disubstituted systems.
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    Radicals derived from acetaldehyde and vinyl alcohol
    (2017) Estep, Marissa L.; Villegas Escobar, Nery.; Morgan, W. James.; Winkles, Alexander T.; Abbott , Adam S.; Mullinax, J. Wayne.; Turner, Walter E.; Wang, Xiao-Yong.; Turney, Justin M.; Schaefer, Henry F.