Trisilane, isotetrasilane, neopentasilane, and cyclohexasilane have been prepared in gram scale. In‐situ cryo crystallization of these pyrophoric liquids in sealed capillaries on the diffractometer allows access to the single crystal structures of these compounds. Structural parameters are discussed and compared to gas‐phase electron diffraction structures from literature and with the results from quantum chemical calculations. Significantly higher packing indices are found for the silanes compared to the corresponding alkanes. Radiation with ultraviolet light (365 nm) and parallel ESR (EPR) measurement shows that cyclohexasilane is easily split into radicals, which subsequently leads to the formation of branched and chain‐like oligomers. The other compounds form no radicals under these conditions. NMR spectra of all four compounds have been recorded.
Disproportionation reactions of chlorosilane compounds in the presence of boron trichloride yield the compound H[B(SiCl 3 ) 4 ]. Spectroscopic analyses of the yellow-whitish solid with IR-, Raman-, and NMR-spectroscopy ( 29 Si, 11 B) show the presence of a highly symmetric anion containing boron, which is fourfold coordinated with silicon. Due to the high symmetry 1 J( 11 B, 29 Si) and even 1 J ( 10 B, 29 Si) couplings can be observed in the NMR spectra of the dissolved compound. The crystal structure analysis with a crystal obtained from toluene solution proves the existence of a highly symmetric borate anion, which is stabilized by four trichlorosilyl groups. The molecular structure consists of a para-protonated toluene cation and the weakly coordinating borate anion [B(SiCl 3 ) 4 ] À . Quantum chemical analysis of the tetrakis(trichlorosilyl)borate ion shows a negatively charged boron atom and the presence of polar SiÀ Cl and SiÀ B bonds. Highly reactive compounds [E(SiCl 3 ) n ] À which are stabilized solely by trichlorosilyl groups have been prepared with E=C, Si, Ge, P, S in recent years. The superacid H[B(SiCl 3 ) 4 ] represents a new member in this elusive compound family.
Linear α,ω‐diphosphaoligosilanes were prepared starting from 1,5‐dilithiodecaphenyl‐n‐pentasilane, Li(SiPh2)5Li, and chlorodiorganophosphanes. The compounds 1,5‐bis(diphenylphosphanyl)decaphenyl‐n‐pentasilane, (Ph2P)Si5Ph10(PPh2), 1,5‐bis(di‐iso‐propylphosphanyl)decaphenyl‐n‐pentasilane, (iPr2P)Si5Ph10(PiPr2), and 1,4‐bis(di‐iso‐propylphosphanyl)octaphenyl‐n‐tetrasilane, (iPr2P)Si4Ph8(PiPr2), were obtained in moderate to good yields and characterized with IR‐, Raman‐, UV‐, 31P‐, 29Si‐, and 1H‐NMR spectroscopy. Single crystal structure analyses of these three silanes show all‐transoid conformations of the atoms along the phosphorus‐silicon backbone of the molecules in the solid state. The silicon‐silicon and the silicon‐phosphorus‐bonds are elongated. This is caused by the complete substitution of these molecules by sterically demanding phenyl‐ and i‐propyl‐substituents and effective σ‐conjugation along the main chains. Hexadecaphenyl‐n‐heptasilane, Si7Ph16, was prepared for comparison with the other three compounds. The latter one shows a long wavelength UV‐absorption in the same region as 1,5‐bis(diphenylphosphanyl)decaphenyl‐n‐pentasilane.
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