Approach to multi-electron reduction beyond two-electron reduction of CO2

Area of Science:

• Coordination Chemistry
• Photochemistry
• Electrochemistry
• Catalysis

Background:

• Carbon dioxide (CO2) utilization is crucial for sustainable chemistry.
• Ruthenium polypyridyl complexes are versatile catalysts for redox reactions.
• Understanding CO2 reduction mechanisms is key to developing efficient catalytic systems.

Purpose of the Study:

• To investigate the electrochemical and photochemical reduction of dicationic ruthenium complexes.
• To explore the catalytic conversion of CO2 into various chemical products.
• To develop novel systems for CO2 reduction mimicking biological processes.

Main Methods:

• Photo- and electrochemical reduction of [Ru(bpy)2(CO)2](2+) in aqueous solutions.
• Reaction of ruthenium complexes with proton sources and nucleophiles (Me2NH, BH4(-)).
• Synthesis and photochemical investigation of [Ru(bpy)2(pbn)](2+) for NAD/NADH mimicry.

Main Results:

• Reduction of [Ru(bpy)2(CO)2](2+) yielded CO and HCOOH, with mechanisms involving M-CO2 intermediates.
• Catalytic production of N,N-dimethylformamide (DMF) was achieved via reductive cleavage of a Ru-C(O)NMe2 bond.
• Six-electron reduction of CO2 to methanol (CH3OH) was demonstrated using BH4(-) as a hydride donor.
• Photochemical reduction of [Ru(bpy)2(pbn)](2+) produced a two-electron reduced form with 20% quantum yield.
• Regeneration of the catalyst and HCOO(-) formation occurred via hydride transfer from the reduced complex to CO2.

Conclusions:

• Ruthenium complexes can catalyze the reductive cleavage of M-CO2 and M-CO bonds for CO2 conversion.
• Renewable hydride donors offer a viable route for catalytic six-electron reduction of CO2 to methanol.
• The [Ru(bpy)2(pbn)](2+) complex effectively mimics the NAD/NADH redox couple, enabling light-driven CO2 reduction and regeneration.