The good samarium

Abstract

Until recently, attempts to regenerate SmI₂ to create a catalytic cycle have been hindered by the formation of stable oxygen adducts with the conjugate bases of employed proton sources such as water and alcohols. These researchers previously developed a system with the use of non-coordinating 2,6-dimethylpyridinium as proton donor that allows electrocatalytic cycling of the samarium reducing agent. Combining this now with a Mo pincer complex ([Mo]) that acts as an electrocatalyst for N₂ to NH₃ conversion, they are able to achieve catalytic turnover under an applied potential (8.4 equivalents compared to 0.3 equivalents with respect to Sm under stoichiometric conditions). The Faradaic (charge to product) efficiency of 82% reported compares well to existing non-aqueous Li-mediated systems and is achieved at a considerably less negative potential of −1.45 V (versus the ferrocene/ferrocenium couple).

While the efficiency and overpotential are quite promising, the limited turnover remains a significant issue when considering the practical implementation of such approaches. Nonetheless, the addition of the Sm-mediated scheme to the non-aqueous N₂R toolbox represents a significant boost to efforts in this direction.