Reductive samarium (electro)catalysis enabled by Sm^III-alkoxide protonolysis

Samarium diiodide (SmI₂) is a privileged, single-electron reductant deployed in diverse synthetic settings. However, generalizable methods for catalytic turnover remain elusive because of the well-known challenge associated with cleaving strong Sm^III-O bonds. Prior efforts have focused on the use of highly reactive oxophiles to enable catalyst turnover. However, such approaches give rise to complex catalyst speciation and intrinsically limit the synthetic scope. Herein, we leveraged a mild and selective protonolysis strategy to achieve samarium-catalyzed, intermolecular reductive cross-coupling of ketones and acrylates with broad scope. The modularity of our approach allows rational control of selectivity based on solvent, pK_a (where K_a is the acid dissociation constant), and the samarium coordination sphere and provides a basis for future developments in catalytic and electrocatalytic lanthanide chemistry.