Reaction of Germylene with Sulfur Dioxide: Gas-Phase Kinetic and Theoretical Studies

Time-resolved studies of germylene, GeH2, generated by laser flash photolysis of 3,4-dimethyl-1-germacyclopent-3-ene at 193 nm, have been carried out to obtain rate constants for its bimolecular reaction with SO2. The reaction was studied in the gas phase, mainly at a total pressure of 10 Torr (in SF6 bath gas) at five temperatures in the range 295553 K. Pressure variation measurements over the range 1100 Torr (SF6) at 295, 408, and 553 K revealed no pressure dependence. The second-order rate constants at 10 Torr (SF6 bath gas) fit the Arrhenius equation log(k/cm(3) molecule(1) s(1)) = (-11.01 +/- 0.09) + (4.62 +/- 0.65 kJ mol(1))/RT ln 10, where the uncertainties are single standard deviations. The collisional efficiency is 19% at 298 K, and in kinetic terms the reaction resembles that of SiH2 with SO2 quite closely. Quantum chemical calculations at the B3LYP/aug-cc-pvQZ level suggest a mechanism occurring via the initial addition of GeH2 to one O atom of SO2 to form H2GeOSO which, via a 1,3-H shift followed by a cyclization, leads to a four-membered-ring species, cyclo-HGeO2SH(cis). A low-energy H2 elimination results in the formation of cyclo-GeO2S, a hitherto unknown compound. A number of other species on the enthalpy surface have been identified, including the novel Ge(OH)(2)S-..., a cyclic five-membered ring comprising an S atom stabilized by dihydroxygermylene. However, none of these other molecules seem to be involved as intermediates in this reaction, either because barriers to their formation or rearrangement are too high or because their enthalpies are insufficiently negative for them to be collisionally stabilized under experimental conditions. The reaction is compared and contrasted with that of SiH2 + SO2.