Non-Adiabatic Reaction Dynamics in the Gas-Phase Formation of Phosphinidenesilylene, the Isovalent Counterpart of Hydrogen Isocyanide, under Single-Collision Conditions

The phosphinidenesilylene (HPSi; X1A') molecule was prepared via a directed gas-phase synthesis in the bimolecular reaction of ground-state atomic silicon (Si; 3P) with phosphine (PH3; X1A1) under single-collision conditions. The chemical dynamics are initiated on the triplet surface via addition of a silicon atom to the non-bonding electron pair of phosphine, followed by non-adiabatic dynamics and surface hopping to the singlet manifold, accompanied by isomerization via atomic hydrogen shift and decomposition to phosphinidenesilylene (HPSi, X1A') along with molecular hydrogen. Statistical calculations predict that silylidynephosphine (HSiP, X1Σ+) is also formed, albeit with lower yields. The barrier-less route to phosphinidenesilylene opens up a multipurpose mechanism to access the hitherto obscure class of phosphasilenylidenes through silicon-phosphorus coupling via reactions of atomic silicon with alkylphosphines under single-collision conditions in the absence of successive reactions of the reaction products, which are not feasible to prepare by traditional synthetic routes.