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 Bronsted 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.