LOW-TEMPERATURE PHOTOCHEMISTRY OF OXY-SUBSTITUTED TRISILANES

Several new oxy-substituted trisilanes RO(Mes)Si(SiMe3)2 were synthesized and photolyzed in hydrocarbon matrices at 77 K to give silylenes, RO(Mes)Si:. The silylenes with R = mesityl and 2,6-diisopropylphenyl showed UV spectra that varied with matrix viscosity, attributed to conformational changes as the silylene relaxed to its equilibrium geometry. The structures of the two hindered (aryloxy)trisilanes 2a and 2c were determined by X-ray crystallography. Crystal data: 2c, R = phenyl, a = 16.609 (3) Å, b = 18.081 (3) Å, c = 20.029 (3) Å, orthorhombic, Pbca, Z = 8; 2a, R = 2,6-diisopropylphenyl, a = 13.078 (2) Å, b = 12.054 (3) Å, c = 15.111 (3) Å, β = 102.05 (1)°, monoclinic, P21/c, Z = 4. Their geometries about the central silicon atom were related to the UV properties of their respective silylenes. The solution-phase irradiation of the trisilane with R = 2,6-diisopropylphenyl at -60OC led to the isolation of the first heteroatom-substituted cyclotrisilane, [RO(Mes)Si]3, whose structure was determined by X-ray crystallography: space group P1, a = 15.541 (2) Å, b = 17.707 (3) Å, c = 11.989 (2) Å, α = 109.70 (1)°, β = 109.60 (1)°, γ = 78.86 (1)°, Z = 2. © 1990, American Chemical Society. All rights reserved.