%0 Journal Article
%A Hirao, Hajime
%A Chen, Hui
%A Carvajal, Maria Angels
%A Wang, Yong
%A Shaik, Sason
%D 2008
%T Effect of External Electric Fields on the C−H Bond Activation
Reactivity of Nonheme Iron−Oxo Reagents
%U https://acs.figshare.com/articles/journal_contribution/Effect_of_External_Electric_Fields_on_the_C_H_Bond_Activation_Reactivity_of_Nonheme_Iron_Oxo_Reagents/2950603
%R 10.1021/ja070903t.s003
%2 https://acs.figshare.com/ndownloader/files/4649482
%K electron donor
%K EF changes
%K TMC
%K mechanism
%K External Electric Fields
%X The effect of external electric fields (EFs) on the reactivity of nonheme iron(IV)−oxo species
toward alkanes is investigated computationally using density functional theory. It is shown that an external
EF changes the energy landscape of the process and thereby impacts the mechanisms, rates, and
selectivities of the reactions, in a manner dependent on the nature of the iron(IV)−oxo/alkane pair. When
the iron−oxo species is a good electron acceptor, like N4PyFeO2+, and the alkane is a good electron
donor, like toluene, the application of the EF changes the mechanism from hydrogen abstraction to electron
transfer. With cyclohexane, which is a poorer electron donor than toluene, the EF promotes hydride transfer
and generates a carbocation. However, in the reaction between a poorer electron acceptor TMC(SR)FeO+
and cyclohexane, the EF preserves the hydrogen abstraction/rebound mechanism but improves its features
by lowering the barriers for both the C−H activation and rebound steps; larger effects were observed for
the quintet-state reaction. In all cases, the EF effect obeys a selection rule; the largest effects are observed
when the EF vector is aligned with the FeO axis (z) and directed along the molecular dipole. As such, an
EF aligned in the direction of the electron flow from substrate to the iron−oxo center lowers the reaction
barrier and affects both the reactivity and selectivity of the molecular catalysts.
%I ACS Publications