Mononuclear Lanthanide(III) Complexes for Efficient Conversion of CO2 to Cyclic Carbonates.

Two new mononuclear Ln(III) compounds having a molecular formula [Dy(HL)3]·MeOH·H2O (1) and [Er(HL)3]·[Et3NCl]·H2O (2) are synthesized employing a polydentate pro-ligand (H2L) as the coordinating scaffold with the corresponding hydrated salts of lanthanide chloride, carried out in methanol solution using triethylamine (Et3N) as the base at room temperature. Both compounds were characterized through different spectroscopic and analytical techniques, including powder XRD, FT-IR spectroscopy, and elemental analysis. Structural characterization of the compounds in the solid state was accomplished using SC-XRD analysis. Each compound features a one-metal center, forming a mononuclear lanthanide compound. Both compounds exhibit catalytic effectiveness in the cycloaddition of epoxides and carbon dioxide to cyclic carbonates in good yields under solvent-free environment. Additionally, the impact of substituents on the cycloaddition reaction between several substituted epoxides and CO2 was investigated. A reaction mechanism has also been proposed.