Abstract
The products of very low pressure pyrolysis (VLPP) of hexamethylcyclotri-silthiane (I), tetramethylcyclodisilthiane (II) and 3,3-dimethyl-3-silathietane (III) were isolated in Ar matrices and were studied by IR spectroscopy. The only pyrolysis product of I was cyclosilthiane II, a dimer of transient dimethylsilanthione (Me 2SiS) (IV). The starting material was recovered on pyrolysis of II. Thermal decomposition of III involves three intermediate unsaturated compounds: dimethylsilaethylene (Me 2 SiCH 2) (V) and thioformaldehyde (H 2CS) (VI), both isolated in Ar matrix at 10 K, as well as silanthione IV fixed in the matrix in a form of the cyclic dimer II. The latter was also observed in the study of copyrolysis of 1,1-dimethyl-1-silacyclobutane and thietane, being authentic sources of intermediates V and VI. IR spectra of starting compounds I, II and III isolated in Ar matrices were obtained. The theoretical structure of IV and force constant F(SiS) were determined by the CNDO/2 method. With regard to CNDO/2 errors, SiS bond distance and F(SiS) are equal to 1.993 Å and 4.72 mdyn/Å, respectively. Calculation of normal vibrations resulted in the following values of vibrational frequencies of dimethylsilanthione (cm −1): 884 ν s(SiC 2) ( A 1), 735 ν as(SiC 2) ( B 2), 626 ν s(SiS) ( A 1), 200 ⪯ CSiC ( A 1).
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