Reaction rate constants for singlet silylene and singlet germylene with water, methanol, ethanol, dimethyl ether and trifluoromethanol: Competition between H-atom migration and H₂ elimination

Abstract

Stationary points on the reaction potential energy surfaces of singlet silylene and singlet germylene with water, methanol, ethanol, dimethyl ether and trifluoromethanol have been used to predict reaction rate constants for temperatures between 100 and 1500 Kelvin. We have previously identified two new reaction channels on each reaction surface, except for reactions involving dimethyl ether [J. Phys. Chem. A, 2001, 105, 1185]. The previously unreported reaction channels involve H₂ elimination following the initial formation of an association complex. A simple Activated-Complex Theory (ACT) analysis predicts that in the case of singlet silylene reacting with water, the newly identified reaction channels are equally likely to be accessed as previously identified 1,2 H-atom migration channels. The H₂-elimination channels are slightly disfavored upon reaction of singlet silylene with methanol and ethanol, but become the preferred reaction channels with trifluoromethanol as the reaction partner. For reactions involving singlet germylene with water and with methanol, the ACT analyses predict that the H₂-elimination channels will occur in preference to 1,2 H-atom migration. Indeed, the room temperature rate constants for H₂ elimination from the germanium complexes are predicted to be approximately five orders of magnitude greater than for the H-atom migration channels.