Synthesis and reactivity of cyclopentadienyl-phenoxide samarium complexes for proton-coupled electron transfer in nitrogen fixation.

Cyclopentadienyl-phenoxide samarium complexes were synthesized, and their reactivity as a proton-coupled electron transfer (PCET) mediator was investigated in molybdenum-catalyzed ammonia formation. The samarium complexes, chelated by a 3,4-diphenylcyclopentadienyl-phenoxide ligand, mediated proton and electron transfer from a terminal proton source and reductant to molybdenum complexes through more than 130 catalytic cycles, resulting in efficient catalytic nitrogen fixation. The PCET-active Sm(II) intermediate was investigated using electrochemical measurements, NMR spectroscopy, and density functional theory (DFT) calculations. This study highlights the importance of developing samarium complexes as PCET catalysts for achieving sustainable, green ammonia synthesis.