Time-resolved gas-phase kinetic study of the germylene addition reaction, GeH(2) + C(2)D(2).
Time-resolved studies of germylene, GeH(2), generated by laser flash photolysis of 3,4-dimethyl-1-germacyclopent-3-ene, have been carried out to obtain rate coefficients for its bimolecular reaction with C(2)D(2). The reaction was studied in the gas phase, mainly at a total pressure of 1.3 kPa (in SF(6) bath gas) at five temperatures in the range 298-558 K. Pressure variation measurements over the range 0.13-13 kPa (SF(6)) at 298, 397 and 558 K revealed a small pressure dependence but only at 558 K. After correction for this, the second-order rate coefficients gave the Arrhenius equation: log(k infinity/cm3 molecule(-1) s(-)1) = (-10.96 +/- 0.05) + (6.16 +/- 0.37 kJ mol-1)/RT ln 10. Comparison with the reaction of GeH(2) + C(2)H(2) (studied earlier) showed a similar behaviour with almost identical rate coefficients. The lack of a significant isotope effect is consistent with a rate-determining addition process and is explained by irreversible decomposition of the reaction intermediate to give Ge((3)P) + C(2)H(4). This result contrasts with that for GeH(2) + C(2)H(4)/C(2)D(4) and those for the analogous silylene reactions. The underlying reasons for this are discussed.
Thermochemistry of germanium and organogermanium compounds.
This article reviews the current state of thermochemistry (enthalpies of formation) of germanium and organogermanium compounds. While the emphasis is on data from experimental measurements, results of quantum chemical (ab initio) calculations are also included. We provide a set of current best values for GeX4 compounds (X = H, Me, F, Cl, Br, I) as well as mixed GeXnY4-n compounds. Also included are Ge/C/H, Ge/C/H/O and Ge/C/H/N compounds and Ge2 and Ge3 containing molecules. Further inclusions are data for species such as GeX3 (free radicals), GeX2 (germylenes) and π-bonded molecules which play prominent roles as intermediates in many thermal and photochemical reactions of germanium compounds. Bond dissociation enthalpies are derived for most commonly encountered Ge-X bonds. The evaluation of preferred values is assisted by exploiting relationships (increments, substituent effects) within specific series and between series.
Absolute rate constant for the reaction silylene + molecular deuterium
An absolute rate constant for the reaction of silylene with molecular deuterium at room temperature has been measured by laser resonance absorption flash kinetic spectroscopy. The rate constant is four orders of magnitude larger than previous data suggest and provides experimental support for recent ab initio theoretical results. 44 references, 5 figures.