Unexpected Formation and Crystal Structure of the Highly Symmetric Carbanion [C(SiCl ₃ ) ₃ ] ^–

Disproportionation reactions of Si2Cl6 in the presence of [nBu4N]Cl in halogenated solvents yield the compound [nBu4N][C(SiCl3)3] (1). X-ray structure analysis of 1 proves the existence of a planar carbanion, which is stabilized by three trichlorosilyl groups. Quantum chemical analysis shows the presence of highly polar bonds in the anion. Planarization of the anion can be explained by the interaction of the occupied lone pair at the carbon atom with the antibonding σ* orbitals of the Si–Cl bonds (negative hyperconjugation).