The Weakly Coordinating Tris(trichlorosilyl)silyl Anion

Abstract

Closely following the procedure for the preparation of the base-stabilized dichlorosilylene complex NHC^Dipp ⋅SiCl₂ reported by Roesky, Stalke, and co-workers (Angew. Chem. Int. Ed. 2009, 48, 5683-5686), a few crystals of the salt [NHC^Dipp -H⋅⋅⋅Cl⋅⋅⋅H-NHC^Dipp ]Si(SiCl₃ )₃ were isolated, aside from the reported byproduct [NHC^Dipp -H⁺ ⋅⋅⋅Cl^- ], and characterized by X-ray crystallography (NHC^Dipp =N,N-di(2,6-diisopropylphenyl)imidazo-2-ylidene). They contain the weakly coordinating anion Si(SiCl₃ )₃^- , which was also obtained in high yields upon deprotonation of the conjugate Brønsted acid HSi(SiCl₃ )₃ with NHC^Dipp or PMP (PMP=1,2,2,6,6-pentamethylpiperidine). The acidity of HSi(SiCl₃ )₃ was estimated by DFT calculations to be substantially higher than those of other H-silanes. Further DFT studies on the electronic structure of Si(SiCl₃ )₃^- , including the electrostatic potential and the electron localizability, confirmed its low basicity and nucleophilicity compared with other silyl anions.

Keywords: Brønsted acid; N-heterocyclic carbenes; silanes; silicon; weakly coordinating anions.