Reactions of SiCl2 with N2O, NO and O2

Abstract

The thermal route to dichlorosilylene by pyrolysis of Si₂Cl₆ has been investigated using both mass spectrometry and matrix isolation techniques. The formation of SiCl₂ in the gas phase was confirmed by employing a known “trapping” agent, namely buta-1,3-diene, which gave the product 1,2-dichloro-1-silacyclopent-3-ene. Dichlorosilylene was then reacted with N₂O and NO. The observed products in the mass spectrum from the N₂O reaction were SiCl₂O and its polymers and N₂. On reacting SiCl₂ with NO, SiCl₂O and its polymers, Cl₂ and N₂O were all observed. Infrared spectra of argon matrices supported these findings from mass spectrometry. A mechanism is proposed for this reaction based on these observations involving the intermediacy of cyclo-Cl₂SiO₂ and is supported by ab initio calculations at the MP2 and G3 levels. The reaction between SiCl₂ and O₂ has also been investigated. The products seen in this case were SiCl₂O and Cl₂. Ab initio calculations again suggest that cyclo-Cl₂SiO₂ is involved, and a chain mechanism seems the most likely route to Cl₂ formation. The calculations lead to ΔH_f° (SiO₂,g) = −276 ± 6 kJ mol⁻¹.