Unexpected Disproportionation of Tetramethylethylenediamine-Supported Perchlorodisilane Cl₃SiSiCl₃

Abstract

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, <i>P</i>2₁/<i>n</i>). ²⁹Si CP/MAS NMR spectroscopy confirms this structure. Density functional theory (DFT) calculations have shown that the structure of the <i>meridional</i> isomer of Cl₃SiSiCl₃·TMEDA is 6.3 kcal lower in energy than that of <i>facial</i> coordinate species. Dissolving of Cl₃SiSiCl₃·TMEDA in CH₂Cl₂ resulted in an immediate reaction by which oligochlorosilanes Si_<i>n</i>Cl_2<i>n</i> (<i>n</i> = 4, 6, 8, 10; precipitate) and the Cl^–-complexed dianions [Si_<i>n</i>Cl_2<i>n</i>+2]^2– (<i>n</i> = 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, <i>P</i>2₁/<i>n</i>) and [Me₃NCH₂CH₂NMe₂]₂[Si₈Cl₁₈] (monoclinic, <i>P</i>2₁/<i>n</i>) contain dianions adopting an “inverse sandwich” structure with inverse polarity and [Me₃NCH₂CH₂NMe₂]⁺ as countercations. Single crystals of SiCl₄·TMEDA (monoclinic, <i>Cc</i>) could be isolated by thermolysis reaction of Cl₃SiSiCl₃·TMEDA (50 °C) in tetrahydrofuran (THF)