Gas phase alkylation of phenyltrimethylgermanes

The reaction of Me(3)GeC(6)H(5) and Me(3)GeC(6)H(4)Me with Me(2)CH(+), Me(3)C(+), and Me(2)Cl(+) has been studied in the gas phase at pressures spanning from 1 Torr (chemical ionization mass spectrometry) to 1 atm (radiolytic technique). The reactions conform to the general model of electrophilic aromatic substitution reactions, proceeding via sigma-complex intermediates, which show a tendency to isomerize to arenium ions bearing a proton on the germylated carbon. Such 1,2-H shift processes occur in the time scale of 10(-8) s. The fate of the germylated arenium ions is controlled by competing deprotonation and degermylation reactions showing a behavior similar to their silicon analogues. The Me(3)X (X = Si, Ge) groups are seen to show a comparable electronic effect with regard to electrophilic attack at the unsubstituted ring positions of an attached phenyl group. (C) 1997 Elsevier Science B.V.