Bimolecular Reaction Dynamics in the Phenyl–Silane System: Exploring the Prototype of a Radical Substitution Mechanism

We present a combined
experimental and theoretical investigation
of the bimolecular gas-phase reaction of the phenyl radical (C6H5) with silane (SiH4) under single
collision conditions to investigate the chemical dynamics of forming
phenylsilane (C6H5SiH3) via a bimolecular
radical substitution mechanism at a tetracoordinated silicon atom.
Verified by electronic structure and quasiclassical trajectory calculations,
the replacement of a single carbon atom in methane by silicon lowers
the barrier to substitution, thus defying conventional wisdom that
tetracoordinated hydrides undergo preferentially hydrogen abstraction.
This reaction mechanism provides fundamental insights into the hitherto
unexplored gas-phase chemical dynamics of radical substitution reactions
of mononuclear main group hydrides under single collision conditions
and highlights the distinct reactivity of silicon compared to its
isovalent carbon. This mechanism might be also involved in the synthesis
of cyanosilane (SiH3CN) and methylsilane (CH3SiH3) probed in the circumstellar envelope of the carbon
star IRC+10216.