The power of trichlorosilylation: Isolable trisilylated allyl anions, allyl radicals, and allenyl anions

Abstract

Treatment of hexachloropropene (Cl2CC(Cl)-CCl3) with Si2Cl6 and [nBu4N]Cl (1 : 4 : 1) in CH2Cl2 results in a quantitative conversion to the trisilylated, dichlorinated allyl anion salt [nBu4N][Cl2CC(SiCl3)-C(SiCl3)2] ([nBu4N][1]). Tetrachloroallene Cl2CCCCl2 was identified as the first intermediate of the reaction cascade. In the solid state, [1]- adopts approximate Cs symmetry with a dihedral angle between the planes running through the olefinic and carbanionic fragments of [1]- of CC-Si//Si-C-Si = 78.3(1)°. One-electron oxidation of [nBu4N][1] with SbCl5 furnishes the distillable blue radical 1. The neutral propene Cl2CC(SiCl3)-C(SiCl3)2H (2) was obtained by (i) protonation of [1]- with HOSO2CF3 (HOTf) or (ii) H-atom transfer to 1 from 1,4-cyclohexadiene. Quantitative transformation of all three SiCl3 substituents in 2 to Si(OMe)3 (2OMe) or SiMe3 (2Me) substituents was achieved by using MeOH/NMe2Et or MeMgBr in CH2Cl2 or THF, respectively. Upon addition of 2 equiv. of tBuLi, 2Me underwent deprotonation with subsequent LiCl elimination, 1,2-SiMe3 migration and Cl/Li exchange to afford the allenyl lithium compound Me3Si(Li)CCC(SiMe3)2 (Li[4]), which is an efficient building block for the introduction of Me, SiMe3, or SnMe3 (5) groups. The trisilylated, monochlorinated allene Cl3Si(Cl)CCC(SiCl3)2 (6), was obtained from [nBu4N][1] through Cl-ion abstraction with AlCl3 and rearrangement in CH2Cl2 (1 forms as a minor side product, likely because the system AlCl3/CH2Cl2 can also act as a one-electron oxidant).