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.