Photocatalytic Generation of a Ground-State Electron Donor Through Water Activation

Electron donors that can be excited to higher energy states through light absorption can achieve oxidation potentials as low as -3.0 V (vs. SCE). However, ground-state organic electron transfer reagents operating at such potentials remain underdeveloped, often necessitating multi-step syntheses and elevated reaction temperatures for activation. The longer lifetime of ground-state reagents is an advantage compared to most photoexcited single-electron reductants, which typically have relatively short lifetimes. In this study, catalytically generated phosphine oxide radical anions derived from phosphines and water applying redox catalysis are introduced as highly efficient single-electron reductants. The in situ generated radical anions are capable of reducing electron-rich aryl chlorides at potentials as low as -3.3 V (vs. SCE). Cyclic voltammetry studies and DFT calculations provide valuable insights into the behavior of these phosphorus-based ground-state electron donors. These findings do not only expand the chemistry of phosphoranyl radicals but also unlock the potential of in situ generated organic ground state electron donors that reach potentials comparable to elemental potassium.