Ligand Tailoring Toward an Air-Stable Iron(V) Nitrido Complex

Area of Science:

• Inorganic Chemistry
• Organometallic Chemistry
• Coordination Chemistry

Background:

• High-valence iron nitrido complexes are crucial intermediates in various catalytic processes.
• Understanding the electronic and structural properties of these species is key to controlling reactivity.
• Previous studies on Fe(IV)≡N/Fe(V)≡N redox pairs are limited.

Purpose of the Study:

• To synthesize and characterize a novel air-stable iron(V) nitrido complex.
• To investigate the structural and electronic changes associated with the Fe(IV)≡N/Fe(V)≡N redox couple.
• To compare the new system with previously reported iron nitrido complexes.

Main Methods:

• Synthesis of a new supporting ligand, tris-[2-(3-mesityl-imidazol-2-ylidene)methyl]amine (TIMMN^Mes).
• Isolation and characterization of iron(IV) and iron(V) nitrido complexes using single-crystal X-ray diffraction.
• Spectroscopic analyses including ⁵⁷Fe Mössbauer, EPR, and UV/vis electronic absorption spectroscopy.
• Quantum chemical calculations to elucidate electronic structure and bonding.

Main Results:

• An air-stable iron(V) nitrido complex was successfully synthesized using the TIMMN^Mes ligand.
• Single-crystal X-ray diffraction revealed Fe≡N bond elongation and structural changes upon oxidation from Fe(IV) to Fe(V).
• The iron center in the Fe(V) complex adopts a geometry closer to the equatorial plane in a trigonal bipyramidal structure.
• Spectroscopic and computational data indicated reduced pyramidalization and Jahn-Teller distortion compared to other systems.

Conclusions:

• The TIMMN^Mes ligand facilitates the isolation of stable high-valence iron nitrido species.
• Structural and electronic factors, including pyramidalization and SOMO nature, govern the properties of the Fe(IV)≡N/Fe(V)≡N redox pair.
• This work provides new insights into the fundamental chemistry of iron nitrido complexes.