Isolable aryl-substituted silyl radicals: synthesis, characterization, and reactivity.

Isolable aryl-substituted silyl radicals (tBu2 MeSi)2(Ar)Si(·) (Ar = C6H5, 4-tBuC6H4, 4-PhC6H4, 3,5-tBu2C6H3) were synthesized by the reaction of the corresponding iodosilane with an equimolar amount of potassium graphite (KC8 ) in tetrahydrofuran (THF). The crystal structure of 3,5-tBu2C6H3 derivative, which was determined by X-ray crystallography, showed a planar geometry around the Si atom for the radical center. EPR studies of all four radicals revealed the lack of the delocalization of the unpaired electron over the aromatic ring. Reactivity and spectroscopic studies of the less-hindered phenyl-substituted silyl radical showed that it exists as an equilibrium mixture of the radical and its silene-type dimer in solution.