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DC Field | Value | Language |
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dc.contributor.advisor | Leigh, William J. | en_US |
dc.contributor.advisor | David J. H. Emslie, Ignacio Vargas-Baca | en_US |
dc.contributor.author | Kostina, Svetlana S. | en_US |
dc.date.accessioned | 2014-06-18T17:05:42Z | - |
dc.date.available | 2014-06-18T17:05:42Z | - |
dc.date.created | 2014-02-04 | en_US |
dc.date.issued | 2014-04 | en_US |
dc.identifier.other | opendissertations/8790 | en_US |
dc.identifier.other | 9859 | en_US |
dc.identifier.other | 5061639 | en_US |
dc.identifier.uri | http://hdl.handle.net/11375/13958 | - |
dc.description.abstract | <p>The complexation reactions of silylenes (SiMe<sub>2</sub>, SiPh<sub>2</sub> and SiMes<sub>2</sub>) and germylenes (GeMe<sub>2</sub>, GePh<sub>2</sub> and GeMes<sub>2</sub>) with a series of O-, S-, N- and P-donors have been studied in hexanes solution. The equilibrium constants for complexation of SiMes<sub>2</sub> and GeMes<sub>2</sub> with 7 Lewis bases were determined, and demonstrate that the silylene is more Lewis acidic than the germylene by ca. 1 kcal mol<sup>-1</sup>. Diethyl ether reacted with the six tetrellylenes with equilibrium constants that decrease in the order SiPh<sub>2</sub> > SiMe<sub>2</sub> > GePh<sub>2</sub> > GeMe<sub>2</sub> > SiMes<sub>2</sub> > GeMes<sub>2</sub>, establishing a trend in the Lewis acidities of the silylenes and germylenes. Experimental results are complemented by calculated (G4) binding enthalpies of the MMe<sub>2</sub>-donor complexes, which were found to correlate with Drago’s E and C parameters leading to the classification of SiMe<sub>2</sub> and GeMe<sub>2</sub> as borderline soft Lewis acids.</p> <p>A number of sigma-bond insertion reactions by transient silylenes was examined, namely the O-H, N-H and Si-O insertion reactions with alcohols, amines and siloxanes, respectively. In all cases the reactions were found to proceed via a two step mechanism in which the first step is a reversible formation of a Lewis acid-base complex. The second step was found to be a catalytic H-migration in the reactions with alcohols and amines; the catalysis by the alcohol is at least 10<sup>4</sup> times faster than that by the amine. Complexes of silylenes with alkoxysilanes and siloxanes transform into the final products via a unimolecular [1,2]-silyl migration.</p> <p>Chalcogen abstraction reactions by silylenes (SiMe<sub>2</sub>, SiPh<sub>2</sub>, SiTmp<sub>2</sub> and SiMes<sub>2</sub>) and germylenes (GeMe<sub>2</sub> and GePh<sub>2</sub>) from oxiranes (cyclohexene oxide (CHO) and propylene oxide (PrO)) and thiiranes (cyclohexene sulfide (CHS) and propylene sulfide (PrS)) were investigated by laser flash photolysis and steady-state photolysis methods. The results indicate that the reaction proceeds via a two step mechanism, in which the first step is a reversible complexation followed by a unimolecular decomposition of the complex to yield products of chalcogen abstraction, namely alkenes and the corresponding R<sub>2</sub>M=X transients (R = Me, Ph, Tmp and Mes, M = Si or Ge, X = O or S). Diphenylsilanethione was directly detected and identified on the basis of its spectra and reactivity with amines and alcohols. The O- and S- abstraction by silylenes proceed with ca. 50% efficiency; in contrast, no evidence for O-abstraction by GeMe<sub>2</sub> from CHO could be found, while propene was formed in ca. 35% yield in the reaction of GeMe<sub>2</sub> with PrS.</p> | en_US |
dc.subject | photochemistry | en_US |
dc.subject | silylene | en_US |
dc.subject | germylene | en_US |
dc.subject | kinetics | en_US |
dc.subject | thermodynamics | en_US |
dc.subject | spectroscopy | en_US |
dc.subject | Inorganic Chemistry | en_US |
dc.subject | Physical Chemistry | en_US |
dc.subject | Inorganic Chemistry | en_US |
dc.title | Mechanistic Aspects of the Complexation, Chalcogen Abstraction and Sigma Bond Insertion Reactions by Transient Silylenes and Germylenes in Solution | en_US |
dc.type | thesis | en_US |
dc.contributor.department | Chemistry and Chemical Biology | en_US |
dc.description.degree | Doctor of Philosophy (PhD) | en_US |
Appears in Collections: | Open Access Dissertations and Theses |
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fulltext.pdf | 8.53 MB | Adobe PDF | View/Open |
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