Trisilane determination

Mass-spectrometric research on silane decomposition kinetics has been performed for flowing [298, 302-306] and static discharges [197, 307]. In a dc discharge of silane it is found that the reaction rate for the depletion of silane is a linear function of the dc current in the discharge, which allows one to determine a first-order reaction mechanism in electron density and temperature [302, 304]. For an RF discharge, similar results are found [303, 305]. Also, the depletion and production rates were found to be temperature-dependent [306]. Further, the depletion of silane and the production of disilane and trisilane are found to depend on the dwell time in the reactor [298]. The increase of di- and trisilane concentration at short dwell times (<0.5 s) corresponds to the decrease of silane concentration. At long dwell times, the decomposition of di- and trisilane produces... 

The proton NMR spectral data of organopolysilanes have often been published incidental to preparative studies (51, 54, 62, 74, 108, 119, 177, 187, 190). Only recently has a systematic investigation to determine the chemical shifts and coupling constants in linear and cyclic permethylated polysilanes, and to study the effects of substituents on the NMR properties of methyl derivatives of disilane and trisilane been reported (see Table V-VII) (206). 

Methylated trisilanes Me Si3Xg (X = H, F, Cl, Br, 1, Ph, OMe) can serve as model compounds for the study of correlations between structures and Si chemical shifts, Si Si coupling constants, bond strengths and bond lengths, as determined with vibrational spectroscopy and electron diffraction or for the study of rotational isomerism of Si-Si bonds. A report of these ongoing activities is given in this work. 

The trisilane is inert to both air and moisture. Purity may be determined by gas chromatography and H NMR. The trisilane should be kept dry as traces of moisture would destroy the disilene formed in the photolysis step. 

To get an impression of the influence of the sample concentration on T, viscosity-dependent spectra of the trisilane PhaMeSi-SiMePh SiMePh2 were recorded and the NOE enhancement factors T determined. T decreases with increasing viscosity, as expected from literature [4]. But the expected minimum and the subsequent increase in Tt did not occur in the range we worked in. Table 3 lists the determined and calculated relaxation rates for the different silicon atoms in (Ph2MeSi )2Si MePh. 

An interestng attempt was made by Ramsey [20] to determine the nature of the reactive excited state of a cyclic trisilane by means of an orbital symmetry analysis of its photofragmentation. The question addressed was whether the relevant excitation might be to a low-lying 3d orbital rather than to an antibonding valence orbital, as is usually assumed. 

Chlorine reacts with decaphenylcyclopentasilane with surprisii ease to give 1,5-dichlorodecaphenyIpentasilane (58), 1,3-dichlorohexaphenyl-trisilane (59), and 1,2-dichlorotetraphenyldisilane (60), the quantity of each being determined by the reaction conditions. Extended reaction times resulted in no isolable compounds, only viscous polymeric oils being formed. 

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