Mimicking the Constrained Geometry of a Nitrogen-Fixation Intermediate

Area of Science:

• Inorganic Chemistry
• Catalysis
• Materials Science

Background:

• Nitrogen reduction catalysts, both biological and industrial, utilize multinuclear binding sites with specific Fe-Fe distances.
• Molecular diiron systems typically form linear N₂ bridges to avoid steric hindrance.

Purpose of the Study:

• To synthesize model compounds that mimic the geometric features of N₂ binding in nitrogenase enzymes and Mittasch catalysts.
• To understand the high N₂-reduction activity observed in these catalytic systems.

Main Methods:

• Utilizing a geometrically flexible, dinucleating macrocycle to synthesize iron complexes.
• Characterizing the structure and N₂ binding mode of the resulting complex.

Main Results:

• Formation of a bridging N₂ ligand with an unusual Fe-Ct_N2-Fe angle of 150°.
• The macrocycle's cavity size prevented linear Fe-N₂-Fe unit formation.
• Observed distinct orbital interactions compared to linear configurations.

Conclusions:

• The unusual N₂ binding geometry approximates the α-N₂ binding mode on Fe(111) surfaces, preceding N₂ bond cleavage.
• This model compound provides insights into the mechanisms of efficient nitrogen reduction catalysts.