The kinetics of secondary reactions in the iodination of monogermane. The effect of iodine substitution on the GeH bond dissociation energy

A study has been made both of secondary reactions occurring during the reaction of I 2 with GeH 4 , and of the direct reaction between I 2 and GeH 3 I. Both these studies show that the abstraction reaction\documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm I}^ \cdot + {\rm GeH}_{\rm 3} {\rm I} \to {\rm \dot GeH}_{\rm 2} {\rm I + HI} $$\end{document}occurs about 30 times faster than the reaction\documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm I}^ \cdot + {\rm GeH}_{\rm 4} \to {\rm \dot GeH}_{\rm 3} {\rm + HI} $$\end{document}in the temperature range of 425–446 K. This information is used to show that iodine substitution weakens Ge–H bonds by 14.4 ± 2.5 kJ/mol and that D (H 2 IGeH) = 332 ± 10 kJ/mol (79.3 kcal/mol). Possible reasons for the effects of halogen substituents on GeH and SiH bond strengths are discussed.