Quantifying the electrostatic driving force behind Sml₂ reductions

(Equation Presented) The equilibrium constant for the electron transfer between Sml₂ and substituted benzophenones was determined. The electron transfer reactions are exothermic with ΔG_eq ranging from -5.1 to -1.6 kcal/mol. Redox potentials suggest that the electron transfer reactions should be endothermic by ca. 25 kcal/mol, contrary to the experimental observation. It is suggested that the change from endothermicity to exothermicity stems from the electrostatic attraction between the negatively charged radical anion and Sm^3-.