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

Treatment of hexachloropropene (Cl(2)C[double bond, length as m-dash]C(Cl)–CCl(3)) with Si(2)Cl(6) and [nBu(4)N]Cl (1 : 4 : 1) in CH(2)Cl(2) results in a quantitative conversion to the trisilylated, dichlorinated allyl anion salt [nBu(4)N][Cl(2)C[double bond, length as m-dash]C(SiCl(3))–C(SiCl(3))(2)] ([nBu(4)N][1]). Tetrachloroallene Cl(2)C[double bond, length as m-dash]C[double bond, length as m-dash]CCl(2) was identified as the first intermediate of the reaction cascade. In the solid state, [1](−) adopts approximate C(s) symmetry with a dihedral angle between the planes running through the olefinic and carbanionic fragments of [1](−) of C[double bond, length as m-dash]C–Si//Si–C–Si = 78.3(1)°. One-electron oxidation of [nBu(4)N][1] with SbCl(5) furnishes the distillable blue radical 1˙. The neutral propene Cl(2)C[double bond, length as m-dash]C(SiCl(3))–C(SiCl(3))(2)H (2) was obtained by (i) protonation of [1](−) with HOSO(2)CF(3) (HOTf) or (ii) H-atom transfer to 1˙ from 1,4-cyclohexadiene. Quantitative transformation of all three SiCl(3) substituents in 2 to Si(OMe)(3) (2(OMe)) or SiMe(3) (2(Me)) substituents was achieved by using MeOH/NMe(2)Et or MeMgBr in CH(2)Cl(2) or THF, respectively. Upon addition of 2 equiv. of tBuLi, 2(Me) underwent deprotonation with subsequent LiCl elimination, 1,2-SiMe(3) migration and Cl/Li exchange to afford the allenyl lithium compound Me(3)Si(Li)C[double bond, length as m-dash]C[double bond, length as m-dash]C(SiMe(3))(2) (Li[4]), which is an efficient building block for the introduction of Me, SiMe(3), or SnMe(3) (5) groups. The trisilylated, monochlorinated allene Cl(3)Si(Cl)C[double bond, length as m-dash]C[double bond, length as m-dash]C(SiCl(3))(2) (6), was obtained from [nBu(4)N][1] through Cl(−)-ion abstraction with AlCl(3) and rearrangement in CH(2)Cl(2) (1˙ forms as a minor side product, likely because the system AlCl(3)/CH(2)Cl(2) can also act as a one-electron oxidant).