Combined Experimental and Theoretical Study on Aromatic Hydroxylation by Mononuclear Nonheme Iron(IV)−Oxo Complexes

The hydroxylation of aromatic compounds by mononuclear nonheme iron(IV)−oxo complexes, [FeIV(Bn-tpen)(O)]2+ (Bn-tpen = N-benzyl-N,N‘,N‘-tris(2-pyridylmethyl)ethane-1,2-diamine) and [FeIV(N4Py)(O)]2+ (N4Py = N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine), has been investigated by a combined experimental and theoretical approach. In the experimental work, we have performed kinetic studies of the oxidation of anthracene with nonheme iron(IV)−oxo complexes generated in situ, thereby determining kinetic and thermodynamic parameters, a Hammett ρ value, and a kinetic isotope effect (KIE) value. A large negative Hammett ρ value of −3.9 and an inverse KIE value of 0.9 indicate that the iron−oxo group attacks the aromatic ring via an electrophilic pathway. By carrying out isotope labeling experiments, the oxygen in oxygenated products was found to derive from the nonheme iron(IV)−oxo species. In the theoretical work, we have conducted density functional theory (DFT) calculations on the hydroxylation of benze...