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

Inorg. Chem., 2011, 50 (15), pp 7317–7323

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

Matthew G. K. Thompson†, Stephen W. C. Walker‡, and J. Mark Parnis*†‡

mparnis@trentu.ca

Department of Chemistry, Chemical Sciences Building, 1600 West Bank Drive, Trent University, Peterborough, Ontario, Canada, K9J 7B8

Department of Chemistry, Chernoff Hall, 90 Bader Lane, Queen’s University, Kingston, Ontario, Canada, K7L 3N6

Abstract

Vanadium atoms were reacted with different partial pressures of propene in Ar under matrix-isolation conditions.  The products were observed using Fourier transform infrared (FTIR) spectroscopy.

Under dilute propene in Ar conditions, new features are observed in the IR spectra which correspond to a C–H insertion product, here identified 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. By increasing the partial pressure of propene, additional features corresponding to propane (C₃H₈) are observed.  The hydrogen-atom source for the observed hydrogenation is shown 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.

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