Acid Catalysis via Acid‐Promoted Electron Transfer

This feature article focuses on acid catalysis in various redox reactions of not only organic compounds but also metal complexes, in particular metal‐oxygen complexes via acid‐promoted electron transfer (APET). On the other hand, proton‐coupled electron transfer (PCET) has been extensively studied in relation with important biological PCET reactions such as O2 reduction in respiration and water oxidation in photosynthesis. Because PCET is normally defined as simultaneous electron and proton transfer from the same substrate, acid‐promoted electron transfer using external acids is called APET in this article. Various types of chemical transformations exhibiting acid catalysis via APET discussed in this article include CC bond formation, CH bond oxidation, aromatic hydroxylation, and oxygen atom transfer reactions such as sulfoxidation and epoxidation reactions.