The Weakly Coordinating Tris(trichlorosilyl)silyl Anion

Closely following the procedure for the preparation of the base‐stabilized dichlorosilylene complex NHCDipp⋅SiCl2 reported by Roesky, Stalke, and co‐workers (Angew. Chem. Int. Ed. 2009, 48, 5683–5686), a few crystals of the salt [NHCDipp−H⋅⋅⋅Cl⋅⋅⋅H−NHCDipp]Si(SiCl3)3 were isolated, aside from the reported byproduct [NHCDipp−H+⋅⋅⋅Cl−], and characterized by X‐ray crystallography (NHCDipp=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 NHCDipp 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.