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.