Reaction rate constants for singlet silylene and singlet germylene with water, methanol, ethanol, dimethyl ether and trifluoromethanol: Competition between H-atom migration and H-2 elimination

Stationary points on the reaction potential energy surfaces of singlet sily lene and singlet germylene with water, methanol, ethanol, dimethyl ether an d trifluoromethanol have been used to predict reaction rate constants for t emperatures between 100 and 1500 Kelvin. We have previously identified two new reaction channels on each reaction surface, except for reactions involv ing dimethyl ether [J. Phys. Chem. A, 2001, 105, 1185]. The previously unre ported reaction channels involve H-2 elimination following the initial form ation of an association complex. A simple Activated-Complex Theory (ACT) an alysis predicts that in the case of singlet silylene reacting with water, t he newly identified reaction channels are equally likely to be accessed as previously identified 1,2 H-atom migration channels. The H-2-elimination ch annels are slightly disfavored upon reaction of singlet silylene with metha nol and ethanol, but become the preferred reaction channels with trifluorom ethanol as the reaction partner. For reactions involving singlet germylene with water and with methanol, the ACT analyses predict that the H-2-elimina tion channels will occur in preference to 1,2 H-atom migration. Indeed, the room temperature rate constants for H-2 elimination from the germanium com plexes are predicted to be approximately five orders of magnitude greater t han for the H-atom migration channels.