Cooperative Ammonia Formation Catalyzed by Molybdenum and Samarium Complexes

A series of novel samarium complexes bearing cyclopentadienyl-amide chelate ligands were synthesized and characterized by X-ray analysis. The complexes function as effective proton-coupled electron transfer (PCET) catalysts, facilitating molybdenum-catalyzed ammonia formation from dinitrogen under ambient conditions. In this reaction system, the Sm complexes could be recycled over 300 times, and they increased the ammonia formation rate by sevenfold compared to that obtained for reactions occurring in the absence of such complexes. Experimental results and density functional theory calculations indicate that the Sm complexes undergo protonation and reduction to form Sm(II) complexes, which then accelerate proton and electron transfer to the Mo complexes via PCET processes from the terminal proton source and reductant. This paper presents the first successful example of Sm complexes that can function as efficient catalysts for 300 cycles, promoting proton and electron transfer in Mo-catalyzed ammonia formation.