Mechanism of Oxidative Activation of Fluorinated Aromatic Compounds by N-Bridged Diiron-Phthalocyanine: What Determines the Reactivity?

The biodegradation of compounds with C-F bonds is challenging due to the fact that these bonds are stronger than the C-H bond in methane. In this work, results on the unprecedented reactivity of a biomimetic model complex that contains an N-bridged diiron-phthalocyanine are presented; this model complex is shown to react with perfluorinated arenes under addition of H2 O2 effectively. To get mechanistic insight into this unusual reactivity, detailed density functional theory calculations on the mechanism of C6 F6 activation by an iron(IV)-oxo active species of the N-bridged diiron phthalocyanine system were performed. Our studies show that the reaction proceeds through a rate-determining electrophilic C-O addition reaction followed by a 1,2-fluoride shift to give the ketone product, which can further rearrange to the phenol. A thermochemical analysis shows that the weakest C-F bond is the aliphatic C-F bond in the ketone intermediate. The oxidative defluorination of perfluoroaromatics is demonstrated to proceed through a completely different mechanism compared to that of aromatic C-H hydroxylation by iron(IV)-oxo intermediates such as cytochrome P450 Compound I.