Cycloreversion of the CO₂ trimer: a paradigmatic pseudopericyclic [2 + 2 + 2] cycloaddition reaction

Area of Science:

• Physical Chemistry
• Theoretical Chemistry
• Climate Science

Background:

• The experimental synthesis and characterization of the carbon dioxide (CO2) trimer have been recently achieved.
• This breakthrough offers potential new avenues for the withdrawal and storage of carbon dioxide, a major greenhouse gas.
• The CO2 trimer exhibits stability up to -40 °C with a limited lifetime, reverting to monomers under thermal stress.

Purpose of the Study:

• To theoretically investigate the reaction mechanism of the CO2 trimer's fragmentation into monomers.
• To analyze the electronic character of the transition state in the CO2 trimer fragmentation.
• To conduct a comparative study of isoelectronic fragmentations, including cyclohexane and benzene, and analyze [2+2] cycloreversions involving CO2 dimers/trimers.

Main Methods:

• Theoretical computational chemistry methods were employed.
• Analysis included energetic, magnetic, and electron localization/delocalization functions.
• Isoelectronic fragmentation reactions of cyclohexane and benzene were studied for comparison.

Main Results:

• The fragmentation mechanism of the CO2 trimer was theoretically elucidated.
• The transition state was identified as having a paradigmatic pseudopericyclic character.
• Comparative studies confirmed the pseudopericyclic nature in related cycloreversions involving CO2 dimers and trimers.

Conclusions:

• The CO2 trimer's dissociation mechanism is characterized by a unique pseudopericyclic transition state.
• This understanding contributes to the fundamental knowledge of molecular interactions and reactions.
• The findings support the potential for CO2 trimer utilization in greenhouse gas management strategies.