Nitrogen Fixation via a Terminal Fe(IV) Nitride.

Area of Science:

• Inorganic Chemistry
• Catalysis
• Biochemistry

Background:

• Terminal iron nitrides (Fe≡N) are hypothesized intermediates in biological and chemical nitrogen fixation.
• Experimental evidence and synthetic examples of Fe≡N species derived from N2 have been scarce.

Purpose of the Study:

• To provide experimental evidence for terminal iron nitrides as intermediates in nitrogen fixation.
• To synthesize and characterize Fe≡N species directly from N2.
• To elucidate the mechanism of iron-mediated nitrogen conversion to ammonia.

Main Methods:

• Protonation of a nitrogen-fixing Fe-N2 catalyst.
• Characterization of reaction intermediates, including a hydrazido(2-) species.
• Analysis of N-N bond cleavage and ammonia release.

Main Results:

• A neutral Fe(NNH2) hydrazido(2-) intermediate was formed upon protonation of the Fe-N2 complex.
• Heterolytic N-N bond cleavage occurred, releasing [FeIV≡N]+ and ammonia (NH3).
• Direct experimental evidence for terminal Fe≡N species derived from N2 was obtained.

Conclusions:

• The findings support a Chatt-type (distal) mechanism for iron-mediated N2-to-NH3 conversion.
• Ligand covalency plays a role in buffering the oxidation states of iron complexes during catalysis.
• The study offers insights relevant to designing catalysts for synthetic and natural nitrogen fixation systems.