Disilene R*XSiSiXR* (R*=Si tBu 3) mit siliciumgebundenen H- und Hal-Atomen X: Bildung, Isomerisierung, Reaktionen

Abstract

Dehalogenations of 1,2-disupersilyldisilanes R*H 2SiSiHalHR*, R*HHalSiSiHalHR*, R*HHalSiSiHal 2R* and R*Hal 2SiSiHal 2R* in THF with equimolar amounts of supersilyl sodium NaR* (R*=Si tBu 3=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*H 2SiSiNaHR*, R*HHalSiSiNaHR*, R*HHalSiSiNaHalR* and R*Hal 2SiSiNaHalR* (identification by protonation, methylation, silylation). These then, in the latter three cases, eliminate NaHal under formation of trans-1,2-disupersilyldisilenes R*XSiSiXR* with silicon-bound H and Hal atoms as X. Actually produced are R*HSiSiHR*, R*HSiSiBrR*, R*ClSiSiClR*, R*BrSiSiBrR* and R*ISiSiIR*. 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*HalSiSiHalR* to silylenes R*Hal 2SiSiR* is possible, the latter of which may be trapped by Et 3SiH. In the absence of the mentioned traps, R*HSiSiHR* thermolizes under formation of cyclotrisilanes R* 3Si 3H 3 and R* 3Si 3H 2R with R=SiH 2R* as well as cyclotetrasilanes R* 4Si 4H 4, whereas R*HSiSiBrR* and R*BrSiSiBrR* react to an unidentified mixture of substances. The disilene R*ClSiSiClR* forms in the presence of its source R*Cl 2SiSiNaClR* cyclotetrasilanes R* 4Si 4Cl 4 obviously by way of insertion into the SiNa bond of the latter followed by elimination of NaCl. Finally, R*ISiSiIR* goes over into the cyclotrisilane R* 3Si 3I 2R with R=SiI 2R*, the formation of which could take place by way of [2+1] cycloaddition of the mentioned disilene and its isomer R*I 2SiSiR*. In the presence of NaR*, the disilene R*HSiSiBrR* forms endo, exo- and endo, endo-bicyclotetrasilanes R* 4Si 4H 2. 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* 4Si 4H 2 with I 2 lead to cyclotrisilanes R* 3Si 3HIR with R=SiHIR* and cyclotetrasilanes R* 4Si 4H 2I 2). On the other hand, the disilenes R*HalSiSiHalR* (Hal=Cl, Br, I) in the presence of NaR* quantitatively transform, possibly via the disilenides R*HalSiSiNaR* and cyclotetrasilenes R* 4Si 4Hal 2, into the tetrahedrotetrasilane R* 4Si 4 (the tetrahedrane reacts with O 2, I 2, Na under formation of R* 4Si 4O 2, R* 4Si 4I 2, R* 4Si 4Na 2). X-ray structure analyses are presented for cis, cis, trans-R* 4Si 4H 2I 2 as well as cis, trans, cis-R* 4Si 4Cl 4 and the [2+2] cycloadducts of R*BrSiSiBrR* with Ph 2CO and of R*ClSiSiClR* with CH 2CMeCMeCH 2.