CYCLOSILASELENANES - PHOTOCHEMICAL AND THERMAL PRECURSORS OF SILANESELONES, REACTIVE INTERMEDIATES WITH A SILICON SELENIUM DOUBLE-BOND

Several cyclodi- and cyclotrisilaselenanes (R2SiSe)n (n = 2, 3) were prepared from in situ generated Na2Se and R2SiCl2. The properties of the cyclosilaselenanes depend on the groups attached to silicon, ranging from thermally unstable and air-sensitive yellow oils (R = Me, Et) to green crystals (R = Me3Si) that can be exposed to air for several days and withstand temperatures of 250-degrees-C under nitrogen. (R2SiSe)n will generate silaneselones, R2Si = Se, which are easily trapped with hexamethylcyclotrisiloxane, thermally and photolytically when R = Me, Et and n = 3 but only thermally when R = Me, Et and n = 2. For R = Ph, only the six-membered ring (n = 3) was isolated, which produced modest yields of Ph2Si = Se under thermal conditions but gave a complex mixture upon photolysis. Silylene extrusion is not an important reaction of cyclodi- and cyclotrisilaselenanes.