Evaluating molecular cobalt complexes for the conversion of N2 to NH3

Area of Science:

• Inorganic Chemistry
• Catalysis
• Sustainable Chemistry

Background:

• Molecular catalysts for nitrogen (N2) reduction to ammonia (NH3) are rare, primarily limited to molybdenum and iron systems.
• Developing efficient and selective catalysts for N2 fixation is crucial for sustainable ammonia production.

Purpose of the Study:

• To synthesize and characterize a novel molecular cobalt complex for N2 reduction.
• To investigate the catalytic activity of the cobalt complex in N2 reduction to NH3 using protons and electrons.
• To compare the performance of the cobalt complex with related iron and molybdenum systems and understand structure-activity relationships.

Main Methods:

• Synthesis of a tris(phosphine)borane cobalt-dinitrogen complex.
• Electrochemical and chemical reduction experiments to assess N2 conversion to NH3.
• Spectroscopic and structural analyses to elucidate catalyst properties.

Main Results:

• The synthesized cobalt complex generated superstoichiometric yields of ammonia (>200% NH3 per Co-N2 precursor).
• Ammonia yields, while modest compared to some Fe/Mo systems, demonstrate cobalt's potential as a N2 reduction catalyst.
• Comparative studies revealed high sensitivity of N2 reduction performance to catalyst structure and electronic properties.

Conclusions:

• Cobalt is a viable metal for molecular N2 reduction catalysts, expanding the scope beyond Mo and Fe.
• Catalyst performance is highly sensitive to structural and electronic factors like π basicity, charge state, and geometric flexibility.
• This work provides insights into designing future molecular catalysts for efficient N2 conversion.