Direct Time-Resolved Study of the Kinetics of the Reaction of Silylene with Phenylsilane in the Gas Phase. Does SiH2 React with the Aromatic Ring?

Abstract

Laser flash photolysis studies of silylene, SiH2, generated by the 193 nm laser flash photolysis phenylsilane, PhSiH3, have been carried out to obtain rate constants for its bimolecular reaction with PhSiH3 itself, in the gas phase. The reaction was studied in SF6 (mostly at 10 Torr total pressure) over the temperature range 298−595 K. The rate constants (also found to be pressure independent) gave the following Arrhenius equation:log(k/cm3molecule−1s−1)=(−9.92±0.04)+(3.31±0.27)kJmol−1/RTln10Similar investigations of the reaction of silylene with benzene, C6H6, (295−410 K) gave data suggestive of the fact that SiH2 might be reacting with photochemical products of C6H6 as well as with C6H6 itself. However, in the latter system, apparent rate constants were sufficiently low to indicate that in the reaction of SiH2 with PhSiH3 addition to the aromatic ring was unlikely to be in excess of 3% of the total. Quantum chemical calculations of the energy surface for SiH2 + C6H6 indicate that 7-silanorcaradiene and 7-silacycloheptatriene are possible products but that PhSiH3 formation is unlikely. RRKM calculations suggest that 7-silanorcaradiene should be the initial product but that it cannot be collisionally stabilized under experimental conditions