EPR detection of Fe(V)=O active species in nonheme iron-catalyzed oxidations

Very recently, in situ cryospray-assisted variable temperature mass spectrometry (VT-MS) has been used to obtain the first convincing evidence for a HO–FeV=O intermediate in the catalyst system [(Me2PyTACN)FeII(OTf)2] (4)/H2O2 (Me2PyTACN = 1-(2′-pyridylmethyl)-4,7-dimethyl-1,4,7-triazacyclononane, OTf = OSO2CF3). The herein presented EPR spectroscopic study of the same system witnesses the formation of S = 1/2 reactive iron species. Its EPR parameters, in combination with its reactivity pattern toward cyclohexene and with independently obtained VT-MS data, allow for its reasonable assignment to the reactive [(Me2PyTACN)FeV=O(OH)]2 + (4c) species.

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► High-valent intermediate of nonheme Fe/H2O2 catalyst system shows rhombic EPR signal.
► This intermediate is active toward cyclohexene oxidation.
► Based on EPR and MS data the active intermediate is assigned to a FeV = O species.