1,3-Migration of a methyl group from germanium to silicon in reactions of (Me3Si)2C(GeMe3)(SiMe2Br) with silver salts

Abstract

The compound TsiGeMe₂Cl (1)[Tsi =(Me₃Si)₃C] has been shown to react with AgO₂CCF₃ in CF₃CO₂H and with AgBF₄ or AgO₃SCF₃ in CH₂Cl₂ to give TsiGeMe₂Y (Y = O₂CCF₃, F, or O₃SCF₃). In contrast, reaction of (Me₃Si)₂C(GeMe₃)(SiMe₂Br)(2), (i) with AgO₂CCF₃ in CF₃CO₂H gives a 35 : 65 mixture of the unrearranged (Me₃Si)₂C(GeMe₃)(SiMe₂O₂CCF₃) and the rearranged TsiGeMe₂O₂CCF₃, (ii) with AgO₃SCF₃ in CH₂Cl₂ gives almost exclusively the rearranged TsiGeMe₂O₃SCF₃, and (iii) with AgBF₄ in CH₂Cl₂ gives a 70:30 mixture of unrearranged (Me₃Si)₂C(GeMe₃)(SiMe₂F) and the rearranged TsiGeMe₂F. It is suggested that the reactions of (2) involve anchimeric assistance to leaving of Br^– by an Me group of the GeMe₃ ligand, with formation of a cationic intermediate having an Me bridge between Ge and Si. Since compound (2) is much more reactive towards silver salts than TsiSiMe₂Br it appears that an Me group attached to Ge provides markedly more assistance than one attached to Si. The absence of rearrangement in reactions of (1) indicates that cationic intermediates are not formed in this case.