Author/Authors :
N Wiberg، نويسنده , , H Auer، نويسنده , , S Wagner، نويسنده , , K Polborn، نويسنده , , Gerhard Kramer1، نويسنده ,
Abstract :
Dehalogenations of 1,2-disupersilyldisilanes R*H2SiSiHalHR*, R*HHalSiSiHalHR*, R*HHalSiSiHal2R* and R*Hal2SiSiHal2R* in THF with equimolar amounts of supersilyl sodium NaR* (R*=SitBu3=Supersilyl) lead slowly at room temperature (Hal=Cl) or fast even at −78°C (Hal=Br, I) under exchange of one halogen Hal for sodium Na to yellow–orange disilanides R*H2SiSiNaHR*, R*HHalSiSiNaHR*, R*HHalSiSiNaHalR* and R*Hal2SiSiNaHalR* (identification by protonation, methylation, silylation). These then, in the latter three cases, eliminate NaHal under formation of trans-1,2-disupersilyldisilenes R*XSiSiXR* with silicon-bound H and Hal atoms as X. Actually produced are R*HSiSiHR*, R*HSiSiBrR*, R*ClSiSiClR*, R*BrSiSiBrR* and R*ISiSiIR*. The intermediate existence of the disilenes could be proved by trapping them with diphenylacetylene (formation of [2+2] cycloadducts), with anthracene (formation of [4+2] cycloadducts), with benzophenone (formation of [2+2] cycloadducts), and/or with 2,3-dimethylbutadiene (formation of [2+2] and [4+2] cycloadducts as well as ene reaction products). Obviously, isomerization of the disilenes R*HalSiSiHalR* to silylenes R*Hal2SiSiR* is possible, the latter of which may be trapped by Et3SiH. In the absence of the mentioned traps, R*HSiSiHR* thermolizes under formation of cyclotrisilanes R*3Si3H3 and R*3Si3H2R with R=SiH2R* as well as cyclotetrasilanes R*4Si4H4, whereas R*HSiSiBrR* and R*BrSiSiBrR* react to an unidentified mixture of substances. The disilene R*ClSiSiClR* forms in the presence of its source R*Cl2SiSiNaClR* cyclotetrasilanes R*4Si4Cl4 obviously by way of insertion into the SiNa bond of the latter followed by elimination of NaCl. Finally, R*ISiSiIR* goes over into the cyclotrisilane R*3Si3I2R with R=SiI2R*, the formation of which could take place by way of [2+1] cycloaddition of the mentioned disilene and its isomer R*I2SiSiR*. In the presence of NaR*, the disilene R*HSiSiBrR* forms endo,exo- and endo,endo-bicyclotetrasilanes R*4Si4H2. Thereby, at room temperature the pure endo,endo isomer slowly transforms into an equilibrium mixture of the endo,endo and the endo,exo isomer in the mole ratio of 1:9 (the reactions of R*4Si4H2 with I2 lead to cyclotrisilanes R*3Si3HIR with R=SiHIR* and cyclotetrasilanes R*4Si4H2I2). On the other hand, the disilenes R*HalSiSiHalR* (Hal=Cl, Br, I) in the presence of NaR* quantitatively transform, possibly via the disilenides R*HalSiSiNaR* and cyclotetrasilenes R*4Si4Hal2, into the tetrahedrotetrasilane R*4Si4 (the tetrahedrane reacts with O2, I2, Na under formation of R*4Si4O2, R*4Si4I2, R*4Si4Na2). X-ray structure analyses are presented for cis,cis,trans-R*4Si4H2I2 as well as cis,trans,cis-R*4Si4Cl4 and the [2+2] cycloadducts of R*BrSiSiBrR* with Ph2CO and of R*ClSiSiClR* with CH2CMeCMeCH2.
