Generation and conversion of the transient 1,1-bis(trimethylsilyl)-2-(2,4,6-triisopropylphenyl)-silene

Article abstract of DOI:10.1016/0022-328X(95)05877-R

Treatment of 2,4,6-triisopropylbenzaldehyde with tris(trimethylsilyl)silylmagnesium bromide (2) gives 2,4,6-triisopropylphenyl-tris(trimethylsilyl)silyl-methanol (3) in approximately 70% yield and E-3,4-bis(2,4,6-triisopropylphenyl)-1,1,2,2-tetrakis(trimethylsilyl)-l,2-disilacyclobutane (5) (15%). 5 is the [2 + 2] head-to-head cyclodimer of the transient 1,1-bis(trimethylsilyl)-2-(2,4,6-triisopropylphenyl)-silene (4), formed by trimethylsilanolate elimination according to a Peterson mechanism from the magnesium alkoxide, derived from the alcohol 3. Deprotonation of 3 with MeLi at low temperature in ether produces a complex mixture of products, the main constituents being the silene dimer 5 (10%) and bis(trimethylsilyl)-2,4,6-triisopropylbenzyl-trimethylsiloxysilane (10) (60%), which is formed by readdition of the eliminated lithiumtrimethylsilanolate at the Si=C bond of 4. The deprotonation of 3 with MeMgBr or PhMgBr (activated by LiBr) in THF at room temperature results in the formation of the polysilane (Me₃Si)₃SiSi(SiM₃)₂CH₂(2,4,6-C₆H₂iPr₃) (13). Its generation indicates that there exists an equilibrium between the magnesium alkoxide derived from the alcohol 3 on one side, and the magnesium silanide 2 and 2,4,6-triisopropylbenzaldehyde on the other side. Possible pathways of the formation of the compounds mentioned, as well as of further by-products, are discussed. The 1,2-disilacyclobutane 5 is characterized by an X-ray crystal structure analysis.