Reprinted from the Journal of the American Chemical Society, 119, 466-471 (1997).

© American Chemical Society, 1997.

Direct Detection and Characterization of a Transient 1-Silaallene Derivative in Solution.

Corinna Kerst, Cerrie W. Rogers, Ralph Ruffolo and William J. Leigh*

Contribution from the Department of Chemistry, McMaster University, Hamilton, Ontario, Canada L8S 4M1

Abstract: Direct irradiation of trimethylsilylethynyl-pentamethyldisilane in hydrocarbon solution affords a mixture of reactive intermediates which have been detected and identified using laser flash photolysis techniques, and trapped as the methanol adducts in steady state irradiation experiments. Flash photolysis of air-saturated hexane solutions of the disilane allows detection of a transient species assigned to 1,1-dimethyl-3,3-bis(trimethylsilyl)-1-silaallene, along with a non-decaying species assigned to 1,1-dimethyl-2,3-bis(trimethylsilyl)-1-silacyclopropene. These were identified on the basis of their UV absorption spectra and for the former, by its reactivity toward characteristic silene quenchers. The 1-silaallene is a minor photoproduct, but it is readily observable in transient absorption experiments because it absorbs relatively strongly, with absorption maxima considerably to the red of those of the 1-silacyclopropene. The 1-silaallene reacts with water, methanol, acetic acid, and acetone (k = 10⁶-10⁷ M^-1s^-1), but exhibits low reactivity toward aliphatic dienes and O₂. In the absence of silene quenchers, the transient absorptions due to the silaallene decay with second-order kinetics. Steady state irradiations in the presence of methanol afford methanol-addition products consistent with the formation of the silaallene and silacyclopropene, along with bis(trimethylsilyl)acetylene as the major product. The suspected coproduct, dimethylsilylene, has also been identified by laser flash photolysis of nitrogen-saturated solutions of the disilane.