Carbon dioxide activation with sterically pressured mid- and high-valent uranium complexes

Area of Science:

• Organometallic Chemistry
• Uranium Chemistry
• Carbon Dioxide Activation

Background:

• Sterically hindered uranium complexes are key to understanding reactivity.
• Triazacyclononane ligands offer tunable steric environments.
• Carbon dioxide activation remains a significant challenge in chemistry.

Purpose of the Study:

• To investigate carbon dioxide activation and transformation by sterically pressured uranium complexes.
• To synthesize and characterize high-valent uranium imido, oxo, and carbamate species.
• To elucidate the influence of ligand steric bulk on reaction mechanisms and product structures.

Main Methods:

• Synthesis and spectroscopic characterization of uranium complexes.
• X-ray crystallography to determine molecular structures.
• Electronic absorption, EPR spectroscopy, SQUID magnetization, and DFT studies for electronic structure analysis.

Main Results:

• Synthesis of uranium(V) imido complexes with a bent imido fragment and long U-N bond.
• Formation of uranium(V) terminal oxo species via isocyanate extrusion from CO2 reaction.
• Observation of uranium(V) carbamate intermediates and diphenyl ureate derivatives.
• Characterization of uranium(IV) carbamate complexes from CO2 insertion into U-N amide bonds.
• Demonstration of steric control by the ligand scaffold on carbamate coordination modes (monodentate vs. bidentate).

Conclusions:

• Sterically pressured uranium complexes effectively activate and transform carbon dioxide.
• The ligand's steric environment dictates the reaction pathway and the coordination of resulting carbamate species.
• High-valent uranium oxo complexes exhibit unusual electronic properties, suggesting novel bonding interactions.