Proton donor effects on the reactivity of SmI₂. Experimental and theoretical studies on methanol solvation vs....

Proton donors are important components of many reactions mediated by samarium diiodide (SmI₂). The addition of water to SmI₂ creates a reagent system that enables the reduction of challenging substrates through proton-coupled electron-transfer (PCET). Simple alcohols such as methanol are often used successfully in reductions with SmI₂ but often have reduced reactivity. The basis for the change in reactivity of SmI₂-H₂O and SmI₂-MeOH is not apparent given the modest differences between water and methanol. A combination of Born-Oppenheimer molecular dynamics simulations and mechanistic experiments were performed to examine the differences between the reductants formed in situ for the SmI₂-H₂O and SmI₂-MeOH systems. This work demonstrates that reduced coordination of MeOH to Sm(ii) results in a complex that reduces arenes through a sequential electron proton transfer at low concentrations and that this process is significantly slower than reduction by SmI₂-H₂O.