Synthesis, Structure and Dehalogenation of the Disilene RClSi=SiClR [R = (tBu3Si)2MeSi]

The reaction of R*2MeSi−SiX2X′ (X/X′ = Cl/Br, Br/Cl) with NaR* (R* = supersilyl SitBu3) leads, probably via the silylenes R*2MeSi−SiX, to the trans-configurated disilene (R*2MeSi)ClSi=SiCl(SiMeR*2), which could be isolated as orange-red crystals. According to an X-ray structure analysis, the central SiClSi=SiClSi framework of the disilene − the formation mechanisms of which are discussed − is planar. The Si=Si double bond is as short as 2.163(4) Å and shows a band in the Raman spectrum at 589 cm−1. Due to its insolubility in organic solvents, no NMR spectra of the disilene in solution were obtained. The spatially overcrowded disilene is stable towards H2O, MeOH, HF, and NaR*. It melts at 228 °C with decomposition. Reduction of the disilene occurs with LiC10H8 in THF with formation of a reaction mixture containing a chlorine-free product that gives a low field 29Si NMR signal at δ = 91.5 (the region for unsaturated Si atoms). It transforms in solution with traces of oxygen into a substance which, according to mass spectrometry (chemical ionization), shows a mass for the disilyne R*2MeSi−Si≡Si−SiMeR*2 plus two oxygen atoms. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)