Highly selective synthesis of surface Fe^IV=O with nanoscale zero-valent iron and chlorite for efficient oxygen transfer reactions.

Abstract

High-valent iron-oxo species (Fe^IV=O) has been a long-sought-after oxygen transfer reagent in biological and catalytic chemistry but suffers from a giant challenge in its gentle and selective synthesis. Herein, we propose a new strategy to synthesize surface Fe^IV=O (≡Fe^IV=O) on nanoscale zero-valent iron (nZVI) using chlorite (ClO₂^-) as the oxidant, which possesses an impressive ≡Fe^IV=O selectivity of 99%. ≡Fe^IV=O can be energetically formed from the ferrous (Fe^II) sites on nZVI through heterolytic Cl-O bond dissociation of ClO₂^- via a synergistic effect between electron-donating surface ≡Fe^II and proximal electron-withdrawing H₂O, where H₂O serves as a hydrogen-bond donor to the terminal O atom of the adsorbed ClO₂^- thereby prompting the polarization and cleavage of Cl-O bond for the oxidation of ≡Fe^II toward the final formation of ≡Fe^IV=O. With methyl phenyl sulfoxide (PMS¹⁶O) as the probe molecule, the isotopic labeling experiment manifests an exclusive ¹⁸O transfer from Cl¹⁸O₂^- to PMS¹⁶O¹⁸O mediated by ≡Fe^IV=¹⁸O. We then showcase the versatility of ≡Fe^IV=O as the oxygen transfer reagent in activating the C-H bond of methane for methanol production and facilitating selective triphenylphosphine oxide synthesis with triphenylphosphine. We believe that this new ≡Fe^IV=O synthesis strategy possesses great potential to drive oxygen transfer for efficient high-value-added chemical synthesis.