Formylation of Amines by CO₂ Hydrogenation Using Preformed Co(II)/Nickel(II) Complexes

Area of Science:

• Catalysis
• Organometallic Chemistry
• Green Chemistry

Background:

• Formamide synthesis via CO2 hydrogenation typically requires high temperatures and precious metal catalysts.
• Existing catalysts often involve rare and toxic elements, posing environmental and economic challenges.
• Developing efficient, earth-abundant catalysts is crucial for sustainable chemical production.

Purpose of the Study:

• To evaluate cobalt(II) and nickel(II) complexes with dmpe and PNN ligands as precatalysts for CO2 hydrogenation to formamides.
• To identify highly active and selective catalysts using earth-abundant metals.
• To establish a more sustainable route for formamide synthesis.

Main Methods:

• Synthesis and characterization of five cobalt(II) and nickel(II) complexes with dmpe (1,2-bis(dimethylphosphino)ethane) and PNN ligands.
• Evaluation of these complexes as precatalysts in the hydrogenation of CO2 with secondary amines in DMSO.
• Quantification of catalytic activity using turnover number (TON) and analysis of product formation (e.g., dimethylformamide).

Main Results:

• [NiCl2(dmpe)] was identified as the most active precatalyst, achieving up to 6300 TON for dimethylformamide (DMF) synthesis.
• The catalyst demonstrated high efficiency at moderate temperatures, utilizing CO2, H2, and dimethylamine.
• This represents the highest activity reported for this transformation using an earth-abundant metal-phosphine complex.

Conclusions:

• Nickel and cobalt complexes, particularly [NiCl2(dmpe)], are effective precatalysts for CO2 hydrogenation to formamides.
• The use of abundant metals offers a sustainable alternative to precious metal catalysts.
• This research advances the development of efficient catalytic systems for CO2 conversion and valorization.