Nitrogen Fixation via a Terminal Fe(IV) Nitride

Terminal iron nitrides (Fe N ) have been proposed as intermediates of (bio)catalytic nitrogen fixation, yet experimental evidence to support this hypothesis has been lacking. In particular, no prior synthetic examples of terminal Fe N species have been derived from N-2. Here we show that a nitrogen-fixing Fe-N-2 catalyst can be protonated to form a neutral Fe(NNH2) hydrazido(2-) intermediate, which, upon further protonation, heterolytically cleaves the N-N bond to release [Fe-IV N ](+ )and NH3. These observations provide direct evidence for the viability of a Chatt-type (distal) mechanism for Fe-mediated N-2-to-NH(3 )conversion. The physical oxidation state range of the Fe complexes in this transformation is buffered by covalency with the ligand, a feature of possible relevance to catalyst design in synthetic and natural systems that facilitate multiproton/multielectron redox processes.