FTIR Matrix-Isolation Study of the Reaction Products of Vanadium Atoms with Propene: Observation of Allylvanadium Hydride As a Precursor to Sacrificial Hydrogenation of Propene

Vanadium atoms have been reacted with different partial pressures of propene in Ar under matrix-isolation conditions, and the products have been observed using Fourier transform infrared (FTIR) spectroscopy. Under dilute propene in Ar conditions, new features are observed in the IR spectra corresponding to a C–H insertion product, identified here as H–V–(η³-allyl). Use of d₃-propene (CD₃–CHCH₂) demonstrates that the initial V-atom insertion occurs at the methyl group of the propene molecule, and DFT calculations have been used to support the identity of the initial product. Upon increasing the partial pressure of propene, additional features corresponding to propane (C₃H₈) are observed, with the hydrogen-atom source for the observed hydrogenation demonstrated to be additional propene units. Analysis of a systematic increase in the partial pressure of propene in the system demonstrates that the yield of propane correlates with the decrease of the allyl product, demonstrating the H–V(allyl) species as a reactive intermediate in the overall hydrogenation process. An overall mechanism is proposed to rationalize the formation of the insertion product and ultimately the products of hydrogenation, which agrees with previous gas-phase and matrix-isolation work involving propene and the related system, ethene.