Methane activation by vanadium oxide cluster anions (V₂O₅)_NO^- (N = 1-18)

The reactivity of vanadium oxide cluster anions (V₂O₅)_NO^- (N = 1-18) that feature with vanadium oxyl radicals (V-O^⋅-) toward the most stable alkane, methane, at 273 K has been characterized by employing a newly home-made ship-lock type reactor coupled with a time-of-flight mass spectrometer. The rate constants were determined in the orders of magnitude of 10^-16-10^-18 cm³ molecule^-1 s^-1, which significantly breaks the detection limit of predecessors that the reactivity of metal-oxyl radicals (Mⁿ⁺-O^⋅-) with rate constants higher than 10^-14 cm³ molecule^-1 s^-1 could usually be measured. The dynamic structural rearrangement of the cluster skeleton has been proposed to account for the size-dependent reactivity of (V₂O₅)₁-₅O^- clusters, which may also function in tuning the reactivity of large-sized (V₂O₅)₆-₁₈O^- clusters. This work provides new insights into the mechanism of Mⁿ⁺-O^⋅--mediated C-H activation of methane at a strictly molecular level and expands the activity landscape of Mⁿ⁺-O^⋅- radicals.