Evidence for an Alternative to the Oxygen Rebound Mechanism in C-H Bond Activation by Non-Heme FeIVO Complexes

The hydroxylation of alkanes by heme (FeO)-O-IV species occurs via the hydrogen abstraction/oxygen rebound mechanism. It has been assumed that non-heme (FeO)-O-IV species follow the heme (FeO)-O-IV paradigm in C-H bond activation reactions. Herein we report theoretical and experimental evidence that C-H bond activation of alkanes by synthetic non-heme Few complexes follows an alternative mechanism. Theoretical calculations predicted that dissociation of the substrate radical formed via hydrogen abstraction from the alkane is more favorable than the oxygen rebound and desaturation processes. This theoretical prediction was verified by experimental results obtained by analyzing iron and organic products formed in the C-H bond activation of substrates by non-heme (FeO)-O-IV complexes. The difference in the behaviors of heme and non-heme (FeO)-O-IV species is ascribed to differences in structural preference and exchange-enhanced reactivity. Thus, the general consensus that C-H bond activation by high-valent metal-oxo species, including non-heme (FeO)-O-IV, occurs via the conventional hydrogen abstraction/oxygen rebound mechanism should be viewed with caution.