Time-resolved gas-phase kinetic study of the reaction of germylene with propene over the temperature range 293-415 K: the thermal stabilities of germiranes

Absolute rate constants have been obtained for the title reaction over the pressure range 1 - 100 Torr (in SF6 bath gas) and the temperature range 293-415 K, by means of laser flash photolysis to generate and monitor germylene, GeH2. The reaction showed the characteristic pressure dependence of a third-body assisted association reaction. The high pressure rate constants, obtained by extrapolation, gave the Arrhenius equation: log(k(infinity)/cm(3) molecule(-1) s(-1)) = ( -10.86 +/- 0.19) + (7.16 +/- 1.23 kJ mol(-1))/RT ln 10 The parameters correspond to a fast reaction occurring at ca. 59% of the collision rate at room temperature. Collision efficiencies for GeH2 pi -additions are not much less than those of SiH2. RRKM (Rice, Ramsperger, Kassel, Marcus) modelling, based on a variational transition state consistent with the kinetics, gave a good fit to the data, with the value of E-o = 105 kJ mol(-1) corresponding to DeltaH degrees = 122 +/- 12 kJ mol(-1) for 2-methylgermirane decomposition. This result in conjunction with other work shows that C-methyl substitution lowers the thermal stability of germirane, and that germiranes are ca. 50-60 kJ mol less stable to decomposition than their silirane counterparts. (C) 2001 Elsevier Science B.V. All rights reserved.