Isolable Photoreactive Polysilyl Radicals

Abstract

Reaction of silyl substituted dichlorosilanes with lithiosilanes in hexane leads exclusively to the corresponding stable silyl radicals. Two radicals, the new (t-Bu(2)MeSi)(2)HSi(t-Bu(2)MeSi)(2)Si* (1) and the previously isolated (t-Bu(2)MeSi)(3)Si* (2), were isolated and fully characterized including by X-ray crystallography. This one-step method is general and was applied for the synthesis of other silyl radicals. Upon irradiation radical 1 (yellow solution in hexane) decays to yield the corresponding disproportionation products, silane and disilene (blue colored). In contrast, radical 2 is photostable in the absence of additives, but it abstracts hydrogen from triethylsilane and 2-propanol upon irradiation. DFT calculations and irradiation experiments with lambda > 400 nm suggest that SOMO-1 --> SOMO excitation, which provides better electron accepting properties to the radical, is responsible for the photoreactivity of 1 and 2.