Effective and Reversible Carbon Dioxide Insertion into Cerium Pyrazolates.

Area of Science:

• Organometallic Chemistry
• Inorganic Chemistry
• Catalysis

Background:

• Cerium complexes with pyrazolate ligands offer unique reactivity.
• Carbon dioxide (CO2) utilization remains a key challenge in sustainable chemistry.

Purpose of the Study:

• To investigate the CO2 insertion capabilities of homoleptic cerium pyrazolate complexes.
• To explore the catalytic activity of these cerium complexes in cyclic carbonate formation.

Main Methods:

• Synthesis and characterization of cerium pyrazolate complexes.
• In situ IR and NMR spectroscopy for monitoring CO2 insertion/reversibility.
• Thermogravimetric analysis (TGA) for solid-state studies.
• Catalytic reactions using epoxides and CO2 under mild conditions.

Main Results:

• Quantitative and reversible CO2 insertion into both cerous [Ce(III)4] and ceric [Ce(IV)] pyrazolate complexes.
• Formation of a trimetallic ceric complex with CO2 insertion.
• Both cerous and ceric CO2 insertion products effectively catalyze cyclic carbonate synthesis from epoxides and CO2.
• Observed reduction of the ceric catalyst by tetra-n-butylammonium bromide (TBAB) in the absence of epoxide.

Conclusions:

• Homoleptic cerium pyrazolate complexes demonstrate efficient and reversible CO2 capture.
• These cerium complexes serve as effective catalysts for synthesizing cyclic carbonates under mild conditions.
• Understanding catalyst stability and potential side reactions (e.g., reduction) is crucial for optimizing catalytic processes.