Disilienes R*XSi=SiXR* (R* = SitBu(3)) with silicon-bound H and Hal-Atoms X: Formation, isomerization, reactions

Dehalogenations of 1,2-disupersilyldisilanes R*H2Si-SiHalHR*, R*HHalSi-SiHa lHR*, R*HHalSi-SiHal(2)R* and R*Hal(2)Si-SiHal(2)R* in THF with equimolar a mounts of supersilyl sodium NaR* (R* = SitBu(3) = Supersilyl) lead slowly a t room temperature (Hal = Cl) or fast even at - 78 degreesC (Hal = Br, I) u nder exchange of one halogen Hal for sodium Na to yellow-orange disilanides R*H2Si-SiNaHR*, R*HHalSi-SiNaHR*, R*HHalSi-SiNaHalR* and R*Hal(2)Si-SiNaHa lR* (identification by protonation, methylation, silylation). These then, i n the latter three cases, eliminate NaHal under formation of trans-1,2-disu persilyldisilenes R*XSi=SiXR* with silicon-bound H and Hal atoms as X. Actu ally produced are R*HSi=SiHR*, R*HSi=SiBrR*, R*ClSi=SiClR*, R*BrSi=SiBrR* a nd 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 (form ation 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(2)Si-SiR* is possible, the latter of which may be trapped by Et3SiH. In the absence of the mentioned traps, R*HSi=SiHR* thermolizes under formatio n of cyclotrisilanes R-3*Si3H3 and R-3*Si3H2R with R = SiH2R* as well as cy clotetrasilanes R-4*XSi4H4, 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*Cl2Si=SiNaClR* cyclotetrasilanes R-4*Si4Cl4 o bviously by way of insertion into the SiNa bond of the latter followed by e limination of NaCl. Finally, R*ISi=SiIR* goes over into the cyclotrisilane R-3*Si3I2R with R = SiI2R*, the formation of which could take place by way of [2 + 1] cycloaddition of the mentioned disilene and its isomer R*I2Si-Si R*. In the presence of NaR*, the disilene R*HSi=SiBrR* forms endo,exo- and endo,endo-bicyclotetrasilanes R-4*Si4H2. Thereby, at room temperature the p ure endo,endo isomer slowly transforms into an equilibrium mixture of the e ndo,endo and the endo,exo isomer in the mole ratio of 1:9 (the reactions of R-4*Si4H2 with I-2 lead to cyclotrisilanes R-3*Si3HIR with R = SiHIR* and cyclotetrasilanes R-4*Si4H2I2). On the other hand, the disilenes R*HalSi=Si HalR* (Hal = Cl, Br, I) in the presence of NaR* quantitatively transform, p ossibly via the disilenides R*HalSi=SiNaR* and cyclotetrasilenes R-4*Si(4)H al(2), into the tetrahedrotetrasilane R-4*Si-4 (the tetrahedrane reacts wit h O-2: I-2, Na under formation of R-4*Si4O2, R-4*Si4I2, R-4*Si4Na2). X-ray structure analyses are presented for cis,cis,trans-R-4*Si4H2I2 as well as c is,trans,cis-R-4*Si4Cl4 and the [2 + 2] cycloadducts of R*BrSi=SiBrR* with Ph2C=O and of R*ClSi=SiClR* with CH2=CMe-CMe=H-2. (C) 2001 Elsevier Science B.V. All rights reserved.