Gas‐Phase Reactivity of Metavanadate [VO 3 ] − towards Methanol and Ethanol: Experiment and Theory

The gas‐phase reactivity of the metavanadate anion [VO 3 ] − 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. [VO 3 ] − dehydrated methanol to eliminate water and form [VO 2 (η 2 ‐OCH 2 )] − , which features an [η 2 ‐ C , O ‐OCH 2 ] 2− ligand formed by formal removal of two protons from methanol and which is isoelectronic with peroxide. [VO 3 ] − reacted with ethanol in an analogous manner to form [VO 2 (η 2 ‐OCHCH 3 )] − , as well as by loss of ethene to form [VO 2 (OH) 2 ] − . The calculations predicted that important intermediates in these reactions were the hydroxo alkoxo anions [VO 2 (OH)(OCH 2 R)] − (R: H, CH 3 ). These were predicted to undergo intramolecular hydrogen‐atom transfer to form [VO(OH) 2 (η 1 ‐OCHR)] − followed by η 1 ‐ O →η 2 ‐ C , O rearrangements to form [VO(OH) 2 (η 2 ‐OCHR)] − . The latter reacted further to eliminate water and generate the product [VO 2 (η 2 ‐OCHR)] − . This major product observed for [VO 3 ] − is markedly different from that observed previously for [NbO 3 ] − 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. The origin of this difference was examined theoretically and attributed to the intermediate alkoxo anion [NbO 2 (OH)(OCH 3 )] − preferring hydride transfer to form [HNbO 2 (OH)] − with loss of formaldehyde. This contrasts with the hydrogen‐atom‐transfer pathway observed for [VO 2 (OH)(OCH 3 )] − .