Unexpected Disproportionation of Tetramethylethylenediamine-Supported Perchlorodisilane Cl3SiSiCl3

The addition compound Cl3SiSiCl3·TMEDA was formed quantitatively by treatment of Cl3SiSiCl3 with tetramethylethylenediamine (TMEDA) in pentane at room temperature. The crystal structure of Cl3SiSiCl3·TMEDA displays one tetrahedrally and one octahedrally bonded Si atom (monoclinic, P21/n). 29Si CP/MAS NMR spectroscopy confirms this structure. Density functional theory (DFT) calculations have shown that the structure of the meridional isomer of Cl3SiSiCl3·TMEDA is 6.3 kcal lower in energy than that of facial coordinate species. Dissolving of Cl3SiSiCl3·TMEDA in CH2Cl2 resulted in an immediate reaction by which oligochlorosilanes SinCl2n (n = 4, 6, 8, 10; precipitate) and the Cl–-complexed dianions [SinCl2n+2]2– (n = 6, 8, 10, 12; CH2Cl2 extract) were formed. The constitutions of these compounds were confirmed by MALDI mass spectrometry. Additionally, single crystals of [Me3NCH2CH2NMe2]2[Si6Cl14] and [Me3NCH2CH2NMe2]2[Si8Cl18] were obtained from the CH2Cl2 extract. We found that Cl3SiSiCl3·TMEDA reacts with MeCl, forming MeSiCl3 and the products that had been formed in the reaction of Cl3SiSiCl3·TMEDA with CH2Cl2. X-ray structure analysis indicates that the structures of [Me3NCH2CH2NMe2]2[Si6Cl14] (monoclinic, P21/n) and [Me3NCH2CH2NMe2]2[Si8Cl18] (monoclinic, P21/n) contain dianions adopting an “inverse sandwich” structure with inverse polarity and [Me3NCH2CH2NMe2]+ as countercations. Single crystals of SiCl4·TMEDA (monoclinic, Cc) could be isolated by thermolysis reaction of Cl3SiSiCl3·TMEDA (50 °C) in tetrahydrofuran (THF).