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Title: | Mechanistic Studies of the Reactions of Transient Diarylgermylenes and Tetraarylgermylenes in Solution |
Authors: | Huck, Lawrence A. |
Advisor: | Leigh, William J. |
Department: | Chemistry |
Publication Date: | May-2010 |
Abstract: | <p>The reactivity of diarylgermylenes (GeAr2, Ga-g) with tetrahydrofuran, diethylamine, acetic acid, carbon tetrachloride and isoprene has been studied in hexanes solution, while the reactivity of the germylene-Lewis bases complexes 37 and 44 with methanesulfonic acid and sodium hydroxide has been studied in methanol and THF solution. Dimerization of germylenes yields digermenes (Ar2Ge=GeAr2, DGa-g) and the reactivity of these species with diethylamine, acetic acid, and carbon tetrachloride has been examined. In addition to product studies, laser flash photolysis is used to generate and monitor these species over their lifetimes(< 20 μs) to determine absolute rate (k) and equilibrium (K) constants for the reactions. Aromatic substituent effects on k and K provide insight into the electronic demands of the transition state, while the effects of temperature on k and K leads to the activation and thermodynamic parameters, respectively.</p> <p>Reaction of germylenes with acetic acid yields the corresponding 0-H insertion product ( 40); a two-step mechanism is proposed, Lewis acid-base complexation followed by proton transfer. Generation of germylenes in THF and MeOH leads to the immediate formation of the corresponding Lewis acid-base complex (37 and 44). In both solvents, the decay of the complex is accelerated by methanesulfonic acid but in neither case could evidence for a germyl cation be found. The decay of the germylene-MeOH complex (44) is accelerated by NaOMe; in one case a germyl anion (52) was detected. Reaction of germylenes with CC14 gives products consistent with halogen atom abstraction by the germylene. The data suggest a mechanism involving fast reversible germylene-CC14 complexation followed by a rate-determining dissociative inner-sphere electron transfer to yield the Ph2GeCl/CCh radical pair ( 60), whose primary fate is cage escape. Data on the reactions of 37 with CC14 in hexanes containing THF and neat THF are most consistent with a mechanism that yields an ion pair. Germylenes are scavenged by isoprene to form the vinylgermirane 24 as the kinetic product, while the germacyclopentenes 23 are the thermodynamic products. An-complex (77) prior to formation of 24 is proposed. It is believed that 23 forms from a (1 +4) cycloaddition reaction of the germylene with isoprene rather than a [1,3]-sigmatropic rearrangement of 24.</p> <p>Digermenes react with acetic acid to yield products consistent with formal addition of acetic acid across the Ge=Ge bond; the kinetic data are consistent with nucleophilic attack by the carbonyl oxygen at germanium as the initial step in the reaction. Reaction of digermenes with CC14 gives the 1,2-dichlorodigermane. A double halogen atom abstraction mechanism, with the digermene behaving as an electron donor, is proposed.</p> |
Description: | Title: Mechanistic Studies of the Reactions of Transient Diarylgermylenes and Tetraarylgermylenes in Solution, Author: William J. Huck, Location: Mills |
URI: | http://hdl.handle.net/11375/19475 |
Appears in Collections: | Open Access Dissertations and Theses |
Files in This Item:
File | Description | Size | Format | |
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Huck_Lawrence_A_2010_05_phd.pdf | Title: Mechanistic Studies of the Reactions of Transient Diarylgermylenes and Tetraarylgermylenes in Solution, Author: William J. Huck, Location: Mills | 55.92 MB | Adobe PDF | View/Open |
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