Beyond Samarium Diiodide: Vistas in Reductive Chemistry Mediated by Lanthanides(II)

Reactions proceeding through open‐shell, single‐electron pathways offer attractive alternative outcomes to those proceeding through closed‐shell, two‐electron mechanisms. In this context, samarium diiodide (SmI2) has emerged as one of the most important and convenient‐to‐use electron‐transfer reagents available in the laboratory. Recently, significant progress has been made in the reductive chemistry of other divalent lanthanides which for many years had been considered too reactive to be of value to synthetic chemists. Herein, we illustrate how new samarium(II) complexes and nonclassical lanthanide(II) reagents are changing the landscape of modern reductive chemistry. Electron dance: Lanthanide(II)‐based electron‐transfer reagents, beyond the classic reagent samarium(II) iodide (SmI2, Kagan's reagent), are receiving increasing attention as new vehicles for the delivery of electrons and the orchestration of radical processes with power and precision (see scheme).