A gas-phase kinetic study of the reaction of germylene with trimethylsilane: absolute rate constants, temperature dependence and mechanism

Time-resolved studies of germylene, GeH2, generated by laser flash photolys is of 3,4-dimethylgermacyclopentene-3, have been carried out to obtain rate constants for its bimolecular reaction with trimethylsilane, Me3SiH. The r eaction was studied in the gas-phase at 10 Torr total pressure in SF6 bath gas, at five temperatures in the range 295-528 K. The second order rate con stants fitted the Arrhenius equation: log(k/cm(3) molecule(-1) s(-1)) = (-1 2.15 +/- 0.06) + (11.58 +/- 0.44 kJ mol(-1))/RT ln 10. Experiments at other pressures showed that these rate constants were unaffected by pressure. GC evidence supports the formation of trimethylsilylgermane as product. The d ata are consistent with the involvement of an H-bridged complex as intermed iate, through an encounter controlled first step. Comparisons show that alk yl substituents in the substrate molecule activate Si-H bonds more selectiv ely than Ge-H bonds towards insertion by GeH2. GeH2 is a more selective, bu t less reactive, "heavy methylene'' than SiH2. Reasons for this behaviour a re discussed.