Silylene Does React with Carbon Monoxide: Some Gas-Phase Kinetic and Theoretical Studies

Time-resolved studies of the reaction of silylene, SiH 2, with CO have been carried out over the pressure range 10−500 Torr (with SF 6 as bath gas) at four temperatures in the range 299−477 K, using laser flash photolysis to generate and monitor SiH 2 . The second-order rate constants obtained were pressure dependent, indicating that the reaction is a third-body assisted association process close to its third-order limit. The second-order rate constants at a pressure of 100 Torr gave the following Arrhenius parameters: log( A /cm 3 molecule -1 s -1 ) = −13.92 ± 0.23, E a = −13.02 ± 1.62 kJ mol -1, where the uncertainties are single standard deviations. Ab initio calculations at the G2 level indicated formation of silaketene, H 2 SiCO, as the initial product. RRKM theoretical calculations, employing a variational transition state based on the ab initio surface, fitted the kinetic data very well with a dissociation enthalpy, H D °(H 2 Si−CO) = 89 kJ mol -1, in very good agreement with ab initio calculation. These studies show unequivocally that SiH 2 does react rapidly with CO and that an earlier gas-phase investigation was carried out under conditions unfavorable for the observation of reaction.