Structure and Chemistry of the Heteronuclear Oxo-Cluster [VPO4]•+: A Model System for the Gas-Phase Oxidation of Small Hydrocarbons

Abstract

The heteronuclear oxo-cluster [VPO₄]^•+ is generated via electrospray ionization and investigated with respect to both its electronic structure as well as its gas-phase reactivity toward small hydrocarbons, thus permitting a comparison to the well-known vanadium-oxide cation [V₂O₄]^•+. As described in previous studies, the latter oxide exhibits no or just minor reactivity toward small hydrocarbons, such as CH₄, C₂H₆, C₃H₈, n-C₄H₁₀, and C₂H₄, while substitution of one vanadium by a phosphorus atom yields the reactive [VPO₄]^•+ ion; the latter brings about oxidative dehydrogenation (ODH) of saturated hydrocarbons, e.g., propane and butane as well as oxygen-atom transfer (OAT) to unsaturated hydrocarbons, e.g. ethene, at thermal conditions. Further, the gas-phase structure of [VPO₄]^•+ is determined by IR photodissociation spectroscopy and compared to that of [V₂O₄]^•+. DFT calculations help to elucidate the reaction mechanism. The results underline the crucial role of phosphorus in terms of C–H bond activation of hydrocarbons by mixed VPO clusters.