The kinetics of the gas‐phase reaction between iodine and phenylsilane and the bond dissociation energy D (C 6 H 5 SiH 2 H)

The title reaction has been investigated in the temperature range of 490‐573 K. Initial reactant pressures were varied in the range of 0.2‐5.2 torr (I 2 ) and 2‐20 torr (C 6 H 5 SiH 3 ). The rate of iodine consumption, monitored spectrophotometrically, was found to obey\documentclass{article}\pagestyle{empty}\begin{document}$$ - \frac{{d[{\rm I}_{\rm 2}]}}{{dt}} = \frac{{k_{3/2} [{\rm I}_{\rm 2}]^{{\raise0.7ex\hbox{$1$} \!\mathord{\left/ {\vphantom {1 2}}\right.\kern-\nulldelimiterspace} \!\lower0.7ex\hbox{$2$}}} [{\rm C}_{\rm 6} {\rm H}_{\rm 5} {\rm SiH}_{\rm 3}]}}{{1 + k'[HI]/[I_2]}}$$\end{document}both by initial rate and integrated equation fitting procedures. The effect of added initial HI conformed to this expression. The data are consistent with a conventional I‐atom propagated chain reaction, and for the step\documentclass{article}\pagestyle{empty}\begin{document}$${\rm I}^{\rm .} + {\rm C}_{\rm 6} {\rm H}_{\rm 5} {\rm SiH}_{\rm 3} \to {\rm C}_{\rm 6} {\rm H}_{\rm 5} \mathop {\rm S}\limits^{\rm .} {\rm iH}_{\rm 2} + {\rm HI}$$\end{document}the rate constant is given by\documentclass{article}\pagestyle{empty}\begin{document}$${\rm log}k_1 (dm^3 /mol \cdot s) = (11.52 \pm 0.08) - (76.8 \pm 0.8{\rm kJ/mol})/RT{\rm ln}10$$\end{document}From this is derived the bond dissociation energy value C 6 H 5 SiH 2 H = 374 kJ/mol(88 kcal/mol). A comparison with other SiH dissociation energy values indicates that the “silabenzyl” stabilization energy is small, ≈7 kJ/mol.