NH₃ formation from N₂ and H₂ mediated by molecular tri-iron complexes

Area of Science:

• Inorganic Chemistry
• Catalysis
• Sustainable Chemistry

Background:

• Biological nitrogen fixation converts N₂ to NH₃ at ambient conditions via nitrogenase.
• Industrial ammonia synthesis (Haber-Bosch process) requires high temperatures and pressures.
• Development of efficient molecular iron catalysts for ammonia synthesis remains a challenge.

Purpose of the Study:

• To synthesize and characterize a novel iron complex capable of ammonia synthesis.
• To investigate the catalytic activity of the iron complex under mild conditions.
• To explore the mechanism of ammonia formation using the developed catalyst.

Main Methods:

• Synthesis of a tri(iron)bis(nitrido) complex, [(Cp'Fe)₃(μ₃-N)₂], via reduction of a precursor under N₂.
• Reaction of the iron complex with H₂ under ambient temperature and low pressure in solution.
• Solid-state transformation of the nitrido complex to an imido species upon H₂ addition, studied via single-crystal X-ray diffraction.

Main Results:

• The synthesized [(Cp'Fe)₃(μ₃-N)₂] complex efficiently produces ammonia (NH₃) from N₂ and H₂ at 22°C and 1-4 bar.
• A unique solid-gas, single-crystal-to-single-crystal transformation occurs, converting the nitrido complex to a bis(imido) species with H₂ addition.
• The resulting [(Cp'Fe)₃(μ₃-NH)₂] species further reacts to form NH₃ in solution.

Conclusions:

• A novel iron complex demonstrates efficient ammonia synthesis under mild conditions, mimicking biological nitrogen fixation.
• The study reveals an unprecedented solid-state transformation pathway relevant to catalytic cycles.
• This work provides a promising molecular catalyst for sustainable ammonia production.