Tris- and tetrakis (lithiomethyl) silanes: An easy access to new building blocks for organosilicon compounds

Tris(lithiomethyl)silanes, RSi(CH2Li)(3), and tetrakis(lithiomethyl)silane, Si(CH2Li)(4), were prepared by the reductive C-S bond cleavage with lithiu m p,p'-di-tert-butylbiphenylide (LiDBB) and characterized by trapping with Bu3SnCl. The yields of the isolated trapping products were 42-81% (>95% NMR yield of the crude product), indicating a high-yield synthesis of the corr esponding poly(lithiomethyl)silane building blocks. Tetrakis(lithiomethyl)s ilane is the first compound containing four lithioalkyl groups without any stabilization of the metalated carbon atoms by pi -systems. Tetrakis(lithio methyl)silane was used for the synthesis of 2,2,3,3,7,7,8,8-octamethyl-2,3, 5,7,8-pentasilaspiro[4,6]nonane (10), a new spirocyclic disilane. The singl e-crystal X-ray diffraction study of 10 indicates two five-membered rings i n envelope conformation with ecliptically arranged methyl groups connected to a spiro compound by a central silicon atom. DFT geometry optimizations [ B3LYP/6-31G(d) level] and NMR calculations (GIAO method, HF/6-31 + G(d,p) l evel) of 10 confirm the observed conformation of 10 as an energetic minimum and support the experimental results.