(Electro)chemical N₂ Splitting by a Molybdenum Complex with an Anionic PNP Pincer-Type Ligand

Area of Science:

• Inorganic Chemistry
• Catalysis
• Nitrogen Fixation

Background:

• Molybdenum complexes with pincer ligands are established catalysts for nitrogen (N₂) reduction to ammonia (NH₃).
• Investigating ligand electronic properties is crucial for optimizing N₂ activation and catalytic efficiency.

Purpose of the Study:

• To evaluate the effect of an anionic PNP pincer ligand on a Molybdenum(III) complex for (electro)chemical N₂ splitting.
• To understand the role of enhanced electron-donating properties in N₂ activation and subsequent ammonia synthesis.

Main Methods:

• Synthesis and characterization of a Molybdenum(III) complex featuring an anionic PNP pincer ligand ([LMoCl₃]⁻).
• Catalytic testing for N₂-to-NH₃ conversion using samarium(II) iodide (SmI₂)/ethylene glycol.
• Electrochemical reduction under N₂ atmosphere and spectroscopic analysis (IR, UV/vis-SEC).

Main Results:

• The anionic PNP ligand enhances N₂ activation in the Mo(III) complex, facilitating N₂-to-NH₃ conversion.
• Mo(V) and Mo(IV) nitrido complexes were formed, with the Mo(V) complex showing comparable activity to the precursor.
• Spectroscopic data suggest N₂ splitting proceeds through an intermediate dimeric species, [(L(N₂)₂Mo⁰)₂μ-N₂]²⁻.

Conclusions:

• Anionic PNP ligands significantly improve the catalytic performance of Molybdenum complexes in N₂ reduction.
• The proposed dimeric intermediate offers insights into the mechanism of N₂ splitting.
• Optimized electrochemical reduction potentials can enhance nitrido complex yield, supporting the proposed mechanism.