Selective NH₃-to-N₂H₄ conversion electrocatalysed by ruthenium(ii)-cymene complexes.

Area of Science:

• Organometallic Chemistry
• Catalysis
• Inorganic Synthesis

Background:

• Ruthenium complexes are versatile catalysts in various chemical transformations.
• Developing efficient catalysts for ammonia oxidation is crucial for sustainable chemical processes.
• Pyridylpyrrole ligands offer tunable electronic and steric properties for metal complex design.

Purpose of the Study:

• To design and synthesize novel ruthenium(II)-cymene complexes with systematically modified pyridylpyrrole ligands.
• To investigate the impact of ligand modifications on the electrochemical properties of the complexes.
• To evaluate the catalytic activity and selectivity of these complexes for ammonia oxidation to hydrazine.

Main Methods:

• Synthesis and characterization of ruthenium(II)-cymene complexes with pyridylpyrrole ligands.
• Solid-state structural analysis using X-ray crystallography.
• Electrochemical studies including cyclic voltammetry and controlled potential coulometry.
• Kinetic and theoretical thermodynamic studies to elucidate reaction mechanisms.

Main Results:

• A series of ruthenium(II)-cymene complexes with varying electron-donating methyl groups on the pyridylpyrrole ligand were successfully synthesized.
• Electrochemical studies revealed that increasing methyl groups on the ligand significantly lowered the Ru(III/II) oxidation potential.
• The [4-NH3]PF6 complex demonstrated selective catalysis for ammonia oxidation to hydrazine with a high turnover number (453.2).
• Mechanistic studies suggested pathways involving bimolecular coupling of Ru(II)-aminyl species and ammonia nucleophilic attack on Ru(IV)-imide.

Conclusions:

• The electronic properties of ruthenium(II)-cymene complexes can be effectively tuned by modifying the pyridylpyrrole ligand.
• These complexes show promising catalytic activity and selectivity for the oxidation of ammonia to hydrazine.
• The findings provide insights into the mechanism of N-N bond formation in ammonia oxidation catalysis.