Electrophile-promoted Fe-to-N₂ hydride migration in highly reduced Fe(N₂)(H) complexes

Abstract

One of the emerging challenges associated with developing robust synthetic nitrogen fixation catalysts is the competitive formation of hydride species that can play a role in catalyst deactivation or lead to undesired hydrogen evolution reactivity (HER). It is hence desirable to devise synthetic systems where metal hydrides can migrate directly to coordinated N₂ in reductive N–H bond-forming steps, thereby enabling productive incorporation into desired reduced N₂-products. Relevant examples of this type of reactivity in synthetic model systems are limited. In this manuscript we describe the migration of an iron hydride (Fe-H) to N_α of a disilylhydrazido(2-) ligand (Fe=NNR₂) derived from N₂ via double-silylation in a preceding step. This is an uncommon reactivity pattern in general; well-characterized examples of hydride/alkyl migrations to metal heteroatom bonds (e.g., (R)M=NR′ → M–N(R)R′) are very rare. Mechanistic data establish the Fe-to-N_α hydride migration to be intramolecular. The resulting disilylhydrazido(1-) intermediate can be isolated by trapping with CN^tBu, and the disilylhydrazine product can then be liberated upon treatment with an additional acid equivalent, demonstrating the net incorporation of an Fe-H equivalent into an N-fixed product.