Evidence for an alternative to the oxygen rebound mechanism in C-H bond activation by non-heme FeIVO complexes

Abstract

The hydroxylation of alkanes by heme FeIVO species occurs via the hydrogen abstraction/oxygen rebound mechanism. It has been assumed that non-heme FeIVO species follow the heme FeIVO 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 Fe IVO 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 FeIVO complexes. The difference in the behaviors of heme and non-heme FeIVO 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 FeIVO, occurs via the conventional hydrogen abstraction/oxygen rebound mechanism should be viewed with caution. © 2012 American Chemical Society.