A Continuum of Proton-Coupled Electron Transfer Reactivity

ConspectusProton-coupled electron transfer (PCET) covers a wide range of reactions involving the transfer(s) of electrons and protons. The best-known PCET reaction, hydrogen atom transfer (HAT), has been studied in detail for more than a century. HAT is generally described as the concerted transfer of a hydrogen atom (H• ≡ H+ + e–) from one group to another, Y + H–X → Y–H + X, but a strict definition of HAT has been difficult to establish. Distinctions are more challenging when the transfer of “H•” involves e– and H+ that transfer to/from spatially distinct sites or even completely separate reagents (multiple-site concerted proton–electron transfer, MS-CPET). MS-CPET reactivity is increasingly proposed in biological and synthetic contexts, and some reactions typically described as HAT more resemble MS-CPET. Despite that HAT and MS-CPET reactions “look different,” we argue here that these reactions lie on a reactivity continuum, and that they are governed by many of the same key parameters. This Account wa...