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Date of Award

3-2011

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Chemistry

Supervisor

William J. Leigh

Language

English

Abstract

1, 1, 1,3,3,3-Hexamethyl-2,2-bis(3,4,5-trimethylphenyl)trisilane (43) has been synthesized and its photochemistry studied by steady state and nanosecond laser flash photolysis (NLFP) methods in solution. Photolysis of 43 in the presence of methanol leads to the formation of methoxybis(3,4,5-trimethylphenyl)silane (53) as the major product, resulting from the reaction of the alcohol with the reactive intermediate, bis(3,4,5-trimethylphenyl)silylene (1, SiTmp2).

The reactivity of SiTmp2 with various substrates such as methanol, acetone, CCl4, acetic acid, triethylsilane, cyclohexene, 1,3-dienes, bis(trimethylsilyl)acetylene (BTMSE), and O2 has been examined by NLFP techniques, and the results are compared to analogous data for diphenylsilylene (3). In almost all cases it was found that electronic factors reduce the absolute rate constants by a factor of ca. 2, except for the reactions with triethylsilane and BTMSE where a factor of ca. 5 rate retardation was observed. This indicates that in general the inductive electron-donating effect associated with six methyl groups on the aromatic rings has only a small effect on diarylsilylene reactivity. The reactivity of SiMes2 (2) with some substrates such as alcohols, CCl4, acetic acid, isoprene and BTMSE has also been studied. The rate constants for the reactions of SiMes2 and SiTmp2 with each substrate were compared to provide a quantitative assessment of steric effects of the ortho methyl groups in diarylsilylene reactivity. It has been observed that for substrates like acetone, acetic acid and O2 there is almost no sensitivity to steric effects, it is moderate in the cases of triethylsilane, CCl4 and methanol and high in the cases of alkenes, dienes and alkynes. This study is the first quantitative assessment of the individual effects of steric hindrance and electronics on the reactivities of diarylsilylenes.

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