Compounds of silicon. 146 [1] Unsaturated silicon compounds. 59 [2] On theway to a disilyne -Si Si-: Formation of RHSi=SiHR and indication of the intermediate formation of RSi SiR (R = SiH(SitBu(3))(2))

Reaction of R-2*HSi-SiHBr-SiFlBr-SiHR2* with an equimolar amount of NaR* x 2 THF in THF at -78 degreesC (R* = supersilyl = SitBu(3)) or reaction of R2 *ClSi-SiHBr-SiHBr-SiClR2* with a two-molar amount of NaR* x 2 THY in C6D6 a t room temperature leads in the first case to the yellow disilene (R-2*HSi) HSi=SiH(SiHR2*) (1) and to the red cyclotetrasilene [-R*HSi-R*Si=SiR*-SiHR* -] (3), respectively, in the latter case to the colorless bicyclotetrasilan e R-4*H2Si4 (4). The disilene 1 (for > Si= in Si-29-NMR: d of d at 141.32 p pm with (1)J(SiH) = 149.9 Hz, (2)J(SiH) = 0.9 Hz) slowly isomerizes at room temperature (tau (1/2) ca. 3 h) under formation of the colorless trisilacy clopentane [-CH2-SiH(SiH2SiHR2*)SiHR*-SitBu(2)-CMe2-] (2) and adds methanol e under formation of the colorless compound R-2*HSi-SiH2-SiH(OMe)-SiHR2*. A s initial stage of 3 the disilyne R-2*HSi-Si=Si-SiHR2* is in consideration, which by way of R*HSi=SiR*-SiR*=SiHR* may transform into 3. The characteri zation of 2 and 3 results among others from X-ray structure analyses, where by for 3 an unexpectable long double bond (2.36 Angstrom) has been found. T he identification of 4 results from comparison with an authentic sample (fo rmed from R*HBrSi-SiBr2R* and NaR* x 2 THF).