Date of Award
Doctor of Philosophy
Thomas J. Barton
The generation of silathiones is shown to be possible by the retroene elimination of propene from allylthiodimethylsilane and 1-allylthio-1-hydrido-1,2,2,2-tetramethyldisilane. This retroene reaction of allylthiodimethylsilane has a very low activation energy (E[subscript] a = 36.3 kcal/mol, log A = 11.3), when compared with carbon, oxygen or nitrogen homologs. The low activation energy is probably due to the strong Si-S [pi] bond and the weak S-C bond. The low log A indicates that the formation of propene and silathione is via a 1,5-hydrogen shift from a six-centered transition state.;The trapping of (trimethylsilyl)methylsilathione by butadiene afforded a 5-membered ring (1-trimethylthio)-1-methyl-1-silacyclopent-3-ene) which is presumably due to the migration of a silyl group of silathione from silicon to sulfur to generate a silylene which was trapped by butadiene. This is the first example of a silathione-silylene isomerization.;Another route demonstrated to generate silathione was the reaction of a silylene, Me[subscript]2Si:, with carbon disulfide. Dimethylsilylene is thought to form a transient 3-membered ring with CS[subscript]2 and the elimination of carbon sulfide produces dimethylsilathione.;The other method to produce silathione was the [beta]-elimination of bis(trimethylsilythio)dimethylsilane. The [beta]-elimination has an activation energy (E[subscript] a = 33.8 kcal/mol, log A = 10.5).;The second example of a silathione-silylene isomerization was observed in the pyrolysis of 1,1-bis(trimethylsilythio)-1,2,2,2-tetramethyldisilane. The [beta]-elimination of hexamethyldisilathiane initially produced trimethylsilylmethylsilathione whose trimethyl silyl group migrated from silicon to sulfur to give a corresponding silylene. This silylene was trapped by butadiene to yield a 5-membered ring. The possibility of formation of silylene via [alpha]-elimination was ruled out by the result that the [alpha]-elimination of methylthiopentamethyldisilane had a high activation energy (E[subscript] a = 53.0 kcal/mol, log A = 14.2), while the [beta]-elimination of bis(trimethylsilythio)dimethylsilane had a low activation energy (E[subscript] a = 33.8 kcal/mol, log A = 10.5).
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Chong Bok Kim
Kim, Chong Bok, "Gas-phase generations and rearrangement of silathiones, R2Si=S " (1990). Retrospective Theses and Dissertations. 9516.