Gas-phase reactivity of metavanadate [VO3](-) towards methanol and ethanol: Experiment and theory

The gas-phase reactivity of the metavanadate anion [VO3]- towards methanol and ethanol was examined by a combination of ion-molecule reaction and isotope labelling experiments in a quadrupole ion-trap mass spectrometer. The experimental data were interpreted with the aid of density functional theory calculations. [VO3](-) dehydrated methanol to eliminate water and form [VO2(eta(2)-OCH2)(-), which features an [eta(2)-C,O-OCH2](2-) ligand formed by formal removal of two protons from methanol and which is isoelectronic with peroxide. [VO3]reacted with ethanol in an analogous manner to form [VO2(eta(2)-OCHCH3)](-), as well as by loss of ethene to form \ [VO2(OH)(2)](-). The calculations predicted that important intermediates in these reactions were the hydroxo alkoxo anions [VO2(OH)(OCH2R)](-) (R: H, CH3). These were predicted to undergo intramolecular hydrogen-atom transfer to form [VO(OH)(2)(eta(2)-OCHR)](-) followed by eta(1)-O ->eta(2) -C,O rearrangements to form [VO(OH)(2)(eta(2)- OCHR)](-). The latter reacted further to eliminate water and generate the product [VO2(eta(2)-OCHR)](-). This major product observed for [VO3](-) is mark- edly different from that observed previously for [NbO3](-) containing the heavier Group 5 congener niobium. In that case, the major product of the reaction was an ion of stoichiometry [Nb, O-3, H-2](-) arising from the formal dehydrogenation of methanol to formaldehyde. T'he origin of this difference was examined theoretically and attributed to the intermediate alkoxo anion [NbO2(OH)(OCH3)](-) preferring hydride transfer to form [HNbO2(OH)]with loss of formaldehyde. This contrasts with the hydrogen-atom-transfer pathway observed for [VO2(OH)(OCH3)](-).