Hexa cyclotrisilane

Further cycloaddition reactions of silylenes generated by the photolysis of cyclotrisilanes have been published since Weidenbruch and coworkers summarized these reactions in an excellent review. Different siliranes were prepared by [2+1]-cycloaddition of di-t-butylsilylene to various alkenes and dienes (Scheme 6)46. Quite interesting results are obtained from the photolysis of hexa-i-butylcyclotrisilane in the presence of unsaturated five-membered ring compounds47 (Scheme 7). With cyclopentadiene and furane, [4 + 2]-cycloaddition of the photolytically generated disilene occurs only as a side reaction. Furthermore, [2 + 1]-cycloaddition of the intermediately formed silylene is highly favored and siliranes are primarily obtained. A totally different course is observed for the reaction in the presence of thiophene. The disilene abstracts the sulfur atom with the formation of the 1,2-disilathiirane as the major product with an extremely short Si—Si distance of 230.49 pm. 

Photolysis of cyclotrisilane 72, in the presence of five-membered ring compounds, produces l,l-di- /t-butyl-2,2-dimethyl-l-silacyclopropene 37 when reacted with cyclopentadiene (Equation 16), o o-3,3,6,6,7,7-hexa-/i t/-butyl-3,6,7-trisilacyclo-8-oxatricyclo[3.2.1.0 ]octane 38 and l,l-di-fem-butyl-2,2-dimethyl-l-silacyclopropane 39 when reacted with furan (Equation 17), and 2,2,6,6-tetra-/i m-butyl-2,6-disilabicyclo[3.1.01]hex-3-ene 40 when reacted with thiophene (Equation 18), among other products <19950M5695>. These products were characterized by H, and Si NMR, and for the furan derivative 38, also by X-ray diffraction studies. 

Hexa-substituted cyclotrisilanes have been shown to be excellent precursors of disilenes. Tetraisopropyldisilene (280), for example, can be obtained by photoextrusion of di-isopropylsilylene (281) from hexaisopropylcyclotrisilane (282). Z- and E-substituted disilenes have similarly been obtained on photodecomposition of tri-t-butyl-trimesitylcyclotrisilanes photochemically induced Z,E-isomerization has been reported in this disilene. ... 

Preparation of hexa-tert-butyl-cyclotrisilane (t-Bu2Sil3 270 Preparation of 1,1-di-tert-butyl-siliranes 271 Preparation of 1,1-di-tert-butyl-iminosiletans 272 References 273... 

Hexa-fert-butyl-cyclotrisilane is an efficient precursor for di-terf-silylene and tetra-terf-butyl-disilene (1). Both species are formed upon irradiation with a suitable light source emitting in the UV region between 200 and 400 nm. Low- or high-pressure mercury lamps can he used, or suitahle LEDs. 

Upon irradiation of hexa-terf-hutyl-cyclotrisilane in the presence of olefins such as cyclopentane, cyclohexane, styrene, or allylhenzene the corresponding siliranes are formed in good to excellent yields. The colorless liquids can be separated from the less-volatile reaction products of the disilene via distillation under reduced pressure (4). Interestingly, conjugated olefins such as 2,3-dimethyl-buta-l,3-diene, isoprene, 2,3-dimethoxy-buta-l, 3-diene, cyclohexa-1,3-diene, or cyclopenta-1,3-diene, reacted not yield the expected five-membered rings but the corresponding vinyl-siliranes (4). The nonconjugated alkene norbomadiene also reacts selectively to the endo-silirane (4). 

Preparation of hexa-tert-butyl-cyclotrisilane (t-Bu2Si 3... 

A solution of 0.637 g (1.49 mmol) hexa-terf-butyl-cyclotrisilane and 1.54 g (18.7 mmol) cyclohexane in 100 mL n-hexane is irradiated with a low-pressiue mercury lamp at room temperature under stirring. Due to the formation of tetra-terf-butyl-disilene the solution turns yellow-orange after about 50 min. Further irradiation yields a colorless solution after 3 h. The photolysis is stopped, the solvent is removed under vacuum, and the residue is separated by short-path distillation at 42—44°C/0.01 mbar to yield a colorless liquid product. In many cases the purity of the obtained colorless silirane is sufficient after distillation. In case of the cyclohexene-derived silirane 7,7-di-terf-butyl-7-silabicyclo[4.1.0] heptane recrystallization at 52°C using 2 mL ethyl acetate as a solvent was successful yielding 208 mg (0.927 mmol) of the silirane. Mp 26-28°C. 

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