Use of spin traps in the study of silyl radicals in the gas phase

Abstract

The aim of this study was to probe the utility of the spin-trapping technique for the identification and estimation of radicals derived from organosilicon compounds in the gas phase. The methods of generation comprised electric discharge and mercury-sensitized photolysis; the traps were Me₃ C—NO and PhCNN(O)CMe₃. After establishing that the procedures were satisfactory, using toluene and n-hexane as radical sources, a range of monosilanes was studied. Several systems gave reasonable yields of spin-trap radicals. For example, SiMe₄ gave H₂CSiMe₃ adducts, Me₃SiH gave H₂CSi(H)Me₂ and Me₃Si· adducts and PhSiH₃ gave PhSiH₂ adducts. Certain chlorosilanes gave chlorine atom adducts using electric-discharge generation, but only very weak signals from unknown radical derivatives using the photolytic method.

In many other cases, such as Me₂SiH₂ and MeSiH₃, we were unable to detect any radical products despite extensive attempts under a wide range of conditions. We conclude that the technique is quite satisfactory for the detection of carbon-centred radicals, but is less reliable for the study of silyl radicals. In a few cases, we also used 2,6-di-t-butylquinone as a trap, but the results were less satisfactory than with the nitrone trap.