An Isolable Silicon Dicarbonate Complex from Carbon Dioxide Activation with a Silylone

The first isolable molecular silicon dicarbonate complex (bis-NHC)Si(CO3)(2) 2 (bis-NHC=H2C[{NC(H)=C(H)N(Dipp)}C:](2), Dipp=2,6-iPr(2)C(6)H(3)) was synthesized by facile reaction of the bis-N-heterocyclic carbene stabilized silylone (bis-NHC)Si 1, bearing a zero-valent silicon atom, with carbon dioxide. The monomeric silicon dioxide complex (bis-NHC)SiO2 3 supported by the bis-NHC ligand was proposed as a key intermediate resulting from double oxygenation of the zero-valent silicon atom in 1 by two molar equivalents of CO2 under liberation of CO; its subsequent Lewis acid-base reaction with CO2 leads to 2 which has been fully characterized including an single-crystal X-ray diffraction analysis. Its electronic structure, spectroscopic data and the thermochemistry of the formation have been studied quantum-chemically.