Ultrafast Infrared Studies of the Reaction Mechanism of Silicon−Hydrogen Bond Activation by η⁵-CpV(CO)₄

The photochemical Si−H bond activation reaction by the group VB, d⁴ organometallic compound η⁵-CpV(CO)₄ (Cp = C₅H₅) has been studied in neat triethylsilane under ambient conditions. The spectral evolutions of the metal-bonded CO stretching bands were monitored from 300 fs to 800 ps following UV photolysis using femtosecond pump−probe spectroscopic methods. The reactive intermediates observed on the ultrafast time scale were also studied using density functional theory as well as ab initio quantum chemical modeling. It was found that photolysis of vanadium tetracarbonyl resulted in the formation of tricarbonyls in either the singlet or triplet electronic state following CO loss. The subsequent reaction was partitioned into two pathways by the initial solvation of the tricarbonyls through the Si−H bond or an ethyl group of the solvent molecule. Knowledge of the elementary reaction steps including changes in molecular morphology and electronic multiplicity allowed a comprehensive description of the chemical reactivity.