Degree Type

Dissertation

Date of Award

2002

Degree Name

Doctor of Philosophy

Department

Chemistry

First Advisor

Thomas J. Barton

Abstract

In order to further examine the driving forces behind the thermal rearrangement of an olefin to a carbene found in 1,1-dimethyl-2-methylenesilacyclobutane, methylenegermacyclobutanes were synthesized via Barbier-type coupling of 2,4-dibromo-1-butene and dichlorogermanes (Me2GeCl2, Et2GeCl 2, Bu2GeCl2, PhMeGeCl2) with activated magnesium. The methylenegerma-cyclobutanes synthesized were kinetically unstable and tended to decompose, probably through ring-opening polymerization. The latter two compounds, 1,1-dibutyl-2-methylenegermacyclo-butane and 1-methyl-2-methylene-1-phenylgermacyclobutane could be isolated, although both compounds gradually decomposed over a few days. The thermal behavior of 1,1-dibutyl-2-methylenegermacyclobutane was studied. Thermal rearrangement to 1,1-dibutyl-1-germacyclopent-3-ene and 1,1-dibutyl-1-germacyclopent-2-ene was observed as a minor decomposition pathway. Germylene extrusion is thought to be the major decomposition pathway. However, the expected insertion product of the germylenes into the starting material was not observed. Trapping experiments with 2,3-dimethyl-1,3-butadiene similarly did not provide any evidence for the presence of dibutylgermylenes.;In order to further examine the decomposition mechanism of diakylgermylenes, the thermal decomposition of a series of di-n-hexylgermylene precursors has been investigated and their Arrhenius parameters measured. The gas phase decomposition of di-n-hexylgermylene was proposed to proceed through a mechanism of intramolecular beta C-H insertion to form an intermediate germirane, followed by either elimination of hexene or a 1,2-hydrogen shift to reform germylene. The presence of dihexylgermylene and hexylgermylene was demonstrated by means of trapping experiments with 2,3-dimethyl-1,3-butadiene in the thermolysis of the low temperature germylene precursor ethylmethyl(trimethylsilyl)germane.;The flow pyrolysis of diallyldimethylgermane was also investigated. Arrhenius parameters of Ea = 54.2 +/- 0.8 kcal/mol and Log (A/s-1) 13.36 +/- 0.2 were measured. The main decomposition pathway is proposed to be through consecutive Ge-C homolytic cleavage of allyl groups.;The thermal and photolytic behavior of (Z)-1,1-dimethyl-2-phenyl-4-phenylmethylene-silacyclobut-2-ene were studied in the hopes that a rare 1,2-silicon rearrangement to a carbene would be observed. Photolysis at 350 nm or thermolysis in a sealed tube at 250°C gave the same product, apparently through cis-trans isomerization of the external phenylmethylene moiety. Thus, the result was inevitably an inseparable mixture of (E)-1,1-dimethyl-2-phenyl-4-(phenylmethylene)silacyclobut-2-ene, and the starting material in a 1:1 ratio. Derivatization of the compounds via alcoholysis for the purposes of characterization produced ring opened products (E,Z)-1,4-diphenyl-1-(ethoxydimethylsilyl)-1,3-butadiene and (E,E)-1,4-diphenyl-2-(ethoxydimethylsilyl)-1,3-butadiene, which also proved to be inseparable.

DOI

https://doi.org/10.31274/rtd-180813-96

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu

Copyright Owner

Nathan Robert Classen

Language

en

Proquest ID

AAI3073442

File Format

application/pdf

File Size

220 pages

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