Synthesis and reactivity of a novel oligosilyl anion

A highly efficient route for the preparation of the sterically overcrowded oligosilyl anion TBTSLi(THF)4 (3) {TBTS=Si[Si(SiMe3)2Me]3} in a large scale is reported. The reactions of HSiCl3 and SiCl4 with 3 do not give coupling products, instead they produce TBTSH and TBTSCl, probably as a result of steric interactions. On the contrary, PhSiF3 and SiF4 can be reacted with 3 to give TBTSSiF3 (5) and TBTSSiF2Ph (6), respectively, in excellent yields. The X-ray analysis revealed 6 to be a sterically overcrowded molecule, in which the SiF2Ph group is strongly shielded by the TBTS substituent. Despite the extensive space demand of the TBTS group, 5 and 6 can be transformed into TBTSSiH3 (7) and TBTSSiH2Ph (8) by treatment with LiAlH4. The controlled hydrolysis of 5 leads to the selective formation of TBTSSiF2OH (9), the first isolated difluorosilanol, which is stable towards condensation.