R. Becerra et R. Walsh, A gas-phase kinetic study of the reaction of germylene with trimethylsilane: absolute rate constants, temperature dependence and mechanism, PCCP PHYS C, 1(23), 1999, pp. 5301-5304
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.