Monomeric siliconthiodichloride trapped by a Lewis base

Abstract

Thiophosgene (CSCl₂), a chemical reagent used in numerous organic syntheses, exists in the monomeric form while its heavier silicon analogue [siliconthiodichloride (SiSCl₂)] has been isolated so far as a dimer at room temperature and as a tetramer at 180 °C. Herein, we report on the first synthesis, isolation, and characterization of cyclic alkyl(amino) carbene (cAAC) stabilized siliconthiodichloride (cAAC)SiSCl₂ (3) in the neutral monomeric form. 3 is synthesized via reaction of (cAAC˙)₂Si₂Cl₄ (1) or (cAAC)₂Si₂Cl₂ (2) with S₈ in the temperature range of −78 to 20 °C. An NHC [NHC = N-heterocyclic carbene] analogue of 3 is not isolated when (NHC)SiCl₂ is reacted with S₈. The bright yellow colored compound 3 is soluble in polar organic solvents. It is stable at room temperature for a month under an inert atmosphere. 3 decomposes above 160 °C. The monomeric molecular structure of 3 has been unambiguously confirmed by X-ray single crystal diffraction. 3 is also characterized by NMR, UV-vis, and IR spectroscopy. The bonding and electron density distributions of 3 have been further studied by theoretical calculations.