tesis doctoral
Application of low valent main group elements in small molecule activation reactions.
Fecha
2020Registro en:
10.7764/tesisUC/QUI/28482
Autor
Villegas, Nery Andrés
Institución
Resumen
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.