Activation of C–H bonds by a nonheme iron(iv)–oxo complex: mechanistic evidence through a coupled EDXAS/UV-Vis multivariate analysis

Abstract

The understanding of reactive processes involving organic substrates is crucial to chemical knowledge and requires multidisciplinary efforts for its advancement. Herein, we apply a combined multivariate, statistical and theoretical analysis of coupled time-resolved X-ray absorption (XAS)/UV-Vis data to obtain detailed mechanistic information for on the C–H bond activation of 9,10-dihydroanthracene (DHA) and diphenylmethane (Ph₂CH₂) by the nonheme Fe^IV–oxo complex [N4Py·Fe^IV(O)]²⁺ (N4Py = N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine) in CH₃CN at room temperature. Within this approach, we determine the number of key chemical species present in the reaction mixtures and derive spectral and concentration profiles for the reaction intermediates. From the quantitative analysis of the XAS spectra the transient intermediate species are structurally determined. As a result, it is suggested that, while DHA is oxidized by [N4Py·Fe^IV(O)]²⁺ with a hydrogen atom transfer-electron transfer (HAT-ET) mechanism, Ph₂CH₂ is oxidized by the nonheme iron–oxo complex through a HAT-radical dissociation pathway. In the latter process, we prove that the intermediate Fe^III complex [N4Py·Fe^III(OH)]²⁺ is not able to oxidize the diphenylmethyl radical and we provide its structural characterization in solution. The employed combined experimental and theoretical strategy is promising for the spectroscopic characterization of transient intermediates as well as for the mechanistic investigation of redox chemical transformations on the second to millisecond time scales.