Synthesis and photochemistry of monosilacycloalkenes and synthesis and photochemistry of arylcyclopentenyldisilanes
Three areas were the subject of photochemical studies. The first chapter describes the syntheses of a series of para-substituted arylcyclopentenyldisilanes and photochemical studies of the disilanes. The disilane bearing a p-cyano group exhibited a solvent polarity dependent, long wavelength fluorescence attributable to a lowest energy CT excited state, while other disilanes bearing hydrogen or methoxy at the para position showed no fluorescence or a normal $\pi,\pi$* fluorescence. The photochemistry of the p-cyano derivative in alcohol, and solutions of methanol in pentane provided, predominantly, products of TICT state. Linear relationships were found for double reciprocal plots of quantum yield for TICT product versus alcohol concentration and for Stern-Volmer quenching of fluorescence by methanol. The major, nonvolatile product was formed via regioselective nucleophilic attack at the terminal trimethylsilyl of the Si-Si bond. The photochemistry of the parent compound in methanol gave a complex distribution of photoproducts. In Chapter II, the photoalcoholyses of 1,1-dimethylsilacyclopent-2-ene and 1,1- dimethylsilacyclohex-2-ene were described. In the case of the silacyclopentene, three intermediates were identified utilizing methanol-O-d, 2,2,2-trifluoroethanol-$d\sb3$ and acetone as trapping agents. Two $\beta$-silyl stabilized cations were formed via photoprotonation, while the silene was produced through 1,3-carbon shift. Photolyses of silacyclohexene in various alcohols resulted in the formation of two products, which possibly shared the same silyl cation as an intermediate. The third project (Chapter III) involved photochemical studies of 1,1-dimethylsilacyclopent-3-ene, in which silicon is not directly attached to the double bond. Photolyses of silacyclopent-3-ene at 214 nm in methanol gave 1,3-butadiene, methoxytrimethylsilane, (Z)-2-butenylmethoxydimethylsilane and 3-butenylmethoxydi- methylsilane as primary products. According to quantum yields for product formation and viscosity effect, the predominant photoprocess is disengagement of dimethylsilylene, which is trapped by methanol in competition with 1,2-addition of the silylene to initially formed 1,3-butadiene.
"Synthesis and photochemistry of monosilacycloalkenes and synthesis and photochemistry of arylcyclopentenyldisilanes"
(January 1, 1993).
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