A Tale of Two Complexes: Electro-Assisted Oxidation of Thioanisole by an "O-2 Activator/Oxidizing Species" Tandem System of Non-Heme Iron Complexes

We report two new Fe-III complexes [(LFeIII)-Fe-1(H2O)](OTf)(2) and [(LFeIII)-Fe-2(OTf)], obtained by replacing pyridines by phenolates in a known non-heme aminopyridine iron complex. While the original, starting aminopyridine [(L-5(2))Fe-II(MeCN)](PF6) complex is stable in air, the potentials of the new Fe-III/II couples decrease to the point that [(LFeII)-Fe-2] spontaneously reduces O-2 to superoxide. We used it as an O-2 activator in an electrochemical setup, as its presence allows to generate superoxide at a much more accessible potential (>500 mV gain). Our aim was to achieve substrate oxidation via the reductive activation of O-2. While (LFeIII)-Fe-2(OTf) proved to be a good O-2 activator but a poor oxidation system, its association with another complex (TPEN)Fe-II(PF6)(2) generates a complementary tandem couple for electro-assisted oxidation of substrates, working at a very accessible potential: upon reduction, (LFeIII)-Fe-2(OTf) activates O-2 to superoxide and transfers it to (TPEN)Fe-II(PF6)(2) leading in fine to the oxidation of thioanisole.