Dinitrogen (N2) fixation via an associative mechanism universally follows the distal pathway, while the alternating or enzymatic pathways involving diazene (HN═NH) are scarce, thereby making it difficult to elucidate associated pathways. Here, we present an η2-hydrazido (the diazene’s resonance form) involved hybrid pathway, in which the η1- to η2-hydrazido isomerization fills a missing link in N2 fixation for the generation of diazenes. This contrasts with the classic alternating pathway, where η2-hydrazido is considered to form via direct functionalization of a diazenido’s Nα (metal-bound nitrogen) atom. Moreover, oxidation triggers the reverse η2- to η1-hydrazido isomerization, a previously unknown transformation, establishing a redox-switchable interconversion. Mechanistic and computational studies reveal a dominant intramolecular mechanism for both isomerizations, governed by SiMe3 group migration between the two nitrogen atoms. Electronic structures identify hydrazyl radical anion character as essential for facilitating isomerization, positioning these species as a versatile platform for accessing diverse η2-hydrazido complexes and designing new transformations of reduced dinitrogen in synthetic systems.
Yin et al. (Mon,) studied this question.