title: Direct time-resolved study of the gas-phase reactions of germylene with ethyl- and diethylgermane: absolute rate constants, temperature dependences, and mechanism.
abstract: Time-resolved studies of germylene, GeH2, generated by the 193 nm laser flash photolysis of 3,4-dimethyl-1-germacyclopent-3-ene, have been carried out to obtain rate constants for its bimolecular reactions with ethyl- and diethylgermanes in the gas phase. The reactions were studied over the pressure range 1-100 Torr with SF6 as bath gas and at five temperatures in the range 297-564 K. Only slight pressure dependences were found for GeH2 + EtGeH3 (399, 486, and 564 K). The high pressure rate constants gave the following Arrhenius parameters: for GeH2 + EtGeH3, log A = -10.75 +/- 0.08 and Ea = -6.7 +/- 0.6 kJ mol-1; for GeH2 + Et2GeH2, log A = -10.68 +/- 0.11 and Ea = -6.95 +/- 0.80 kJ mol-1. These are consistent with fast, near collision-controlled, association processes at 298 K. RRKM modeling calculations are, for the most part, consistent with the observed pressure dependence of GeH2 + EtGeH3. The ethyl substituent effects have been extracted from these results and are much larger than the analogous methyl substituent effects in the SiH2 + methylsilane reaction series. This is consistent with a mechanistic model for Ge-H insertion in which the intermediate complex has a sizable secondary barrier to rearrangement.
authors.affiliation: Instituto de Quimica-Fisica Rocasolano, CSIC, C/Serrano 119, 28006 Madrid, Spain.
authors.forename: Rosa
authors.initials: R
authors.lastname: Becerra
authors.forename: Sergey E
authors.initials: SE
authors.lastname: Boganov
authors.forename: Mikhail P
authors.initials: MP
authors.lastname: Egorov
authors.forename: Irina V
authors.initials: IV
authors.lastname: Krylova
authors.forename: Oleg M
authors.initials: OM
authors.lastname: Nefedov
authors.forename: Robin
authors.initials: R
authors.lastname: Walsh