Gregory W. Sluggett

A TRANSIENT SPECTROSCOPIC STUDY OF THE PHOTOCHEMISTRY OF VINYLDISILANES

Abstract The chemistry of the reactive intermediates produced by direct irradiation of pentamethylvinyldisilane ( 1 ), 1,1,2,2-tetramethyl-1,2-divinyldisilane ( 2 ), and 1,1,1,2-tetramethyl-2,2-divinyldisilane ( 3 ) in hydrocarbon solution have been studied by steady state and laser flash photolysis techniques. All three disilanes yield silenes derived from photochemical [1,3]-trimethylsilyl migration as the major product, as has been shown by the products of steady state trapping experiments. Direct irradiation of the three disilanes in 3-methylpentane matrices at 77 K leads to the formation of products with absorption maxima at 270, 270 and 325 nm, respectively, which disappear upon warming and are hence assigned to the silenes. Nanosecond laser flash photolysis of the disilanes in deoxygenated hexane solution at ambient temperatures gives rise to transient species with the same absorption maxima as found in the matrix experiments, and which decay over several tens of microseconds with mixed pseudo-first and second order kinetics. The assignment of these transients to the corresponding silenes is supported by their absolute rate constants for reaction with methanol, t -butanol, acetic acid, acetone, 2,3-dimethyl-1,3-butadiene (DMB), cyclohexene and oxygen, which vary over the range 10 5 –10 8 M −1 s −1 , depending on the reagent and the silene. The transient spectrum and reactivity of one of the silenes have also been examined in acetonitrile solution. The variation in spectroscopic properties and reactivity as a function of structure is discussed, and compared to previously reported data for closely related reactive silenes.