Thermochemistry of silicon-containing compounds. Part 2.—The enthalpies of formation of the methylsilanes, an experimental study and review

Abstract

The redistribution reactions of the methylsilanes have been studied over an aluminium chloride catalyst at 398 K. Equilibrium constants have been measured for the reactions 2Me_nSiH_4-n⇌ Me_n+1SiH_3–n+Me_n–1SiH_5–n where n= 2 and 3 and an equilibrium constant has been estimated for the case n= 1 based on the Allen scheme. A third-law analysis of the equilibrium data is combined with the published enthalpies of formation of gaseous SiH₄ and Me₄Si to derive the values: [graphic omitted] Previous values, as well as that for ΔH^⊖_f(Me₄Si), are reviewed critically. Use of these figures together with published bond-dissociation energies permits the derivation of ΔH^⊖_f for the methylsilyl radicals, in particular ΔH^⊖_f(Me₃Si)=–3 ± 8 kJ mol^–1. Additionally, D(Me₃Si–Me)= 375 ± 9 kJ mol^–1 and the divalent-state stabilisation energy of Me₂Si = 134 ± 12 kJ mol^–1 are obtained.