Cobalt complex with a tetradentate aminopyridine ligand: a single-component and efficient catalytic system for the cycloaddition reactions of CO2 and epoxides†

A simple and commercially viable synthetic route for tetradentate aminopyridine ligands composed of diamine and pyridine has been developed. A series of novel cobalt complexes incorporating these tetradentate aminopyridine ligands were subsequently synthesized. The single crystal of one such cobalt complex was characterized, revealing coordination through four N atoms in a cis-α topology. This cobalt complex was successfully employed as a single-component catalyst for the synthesis of cyclic carbonates from epoxides and carbon dioxide at 90 °C under 2.5 MPa CO₂ pressure in solvent-free conditions. The catalyst exhibited excellent recyclability and stability, as confirmed by infrared radiation (IR) spectra and inductively coupled plasma (ICP) analyses. Additionally, a single-Co catalytic mechanism for the cycloaddition reaction was investigated using density functional theory (DFT). Notably, a reaction mechanism has been proposed in which the epoxide is activated following the release of a Br⁻ ion from the cobalt complex.