C-H Activation by Iron-Vanadium Bimetallic Oxide Cluster Anions FeV 3 O 10 - and FeV 5 O 15 - : A Comparison with Scandium-Vanadium Oxide Clusters.

Late transition metal-bonded atomic oxygen radicals (LTM-O⋅ - ) have been frequently proposed as important active sites to selectively activate and transform inert alkane molecules. However, it is extremely challenging to characterize the LTM-O⋅ - -mediated elementary reactions for clarifying the underlying mechanisms limited by the low activity of LTM-O⋅ - radicals that is inaccessible by the traditional experimental methods. Herein, benefiting from our newly-designed ship-lock type reactor, the reactivity of iron-vanadium bimetallic oxide cluster anions FeV 3 O 10 - and FeV 5 O 15 - featuring with Fe-O⋅ - radicals to abstract a hydrogen atom from C 2 -C 4 alkanes has been experimentally characterized at 298 K, and the rate constants are determined in the orders of magnitude of 10 -14 to 10 -16  cm 3 molecule -1  s -1 , which are four orders of magnitude slower than the values of counterpart ScV 3 O 10 - and ScV 5 O 15 - clusters bearing Sc-O⋅ - radicals. Theoretical results reveal that the rearrangements of the electronic and geometric structures during the reaction process function to modulate the activity of Fe-O⋅ - . This study not only quantitatively characterizes the elementary reactions of LTM-O⋅ - radicals with alkanes, but also provides new insights into structure-activity relationship of M-O⋅ - radicals.