Metal-Salen (M = Fe, Co, Ni, Cu, Zn) complexes were synthesized to catalyze the oxidation of benzoin to benzil with air as the “green” oxidizing reagent. The effects of temperature, base and solvent on M-Salen catalyzed oxidation of benzoin had been examined and optimized. The catalysis results showed that Co-Salen and Fe-Salen complexes were efficient to catalyze the oxidation reaction with yields over 80% while the catalytic activities of other three M-Salen complexes were poor. Moreover, the Co-Salen catalysis system could be reused three times with satisfied yield.
Salen-type Schiff bases, formed by the condensation of salicylaldehyde with diamines, serve as versatile tetradentate N 2 O 2 chelating ligands owing to their tunable electronic and steric structures. Their corresponding metal complexes have been extensively applied as highly efficient and stable catalysts in diverse transformations, particularly in ring-opening polymerization (ROP) reactions. In this study, two structurally related propanediamine-derived bis-Schiff base ligands were synthesized from 3,5-di-tert-butylsalicylaldehyde and corresponding diamines, along with a series of Ce-, Fe-, and Co-Salen complexes. A thorough investigation was conducted on their catalytic performances and influencing factors in the ROP of rac-lactide. The results indicate that the catalytic performance of these Salen-metal complexes is dual-influenced by both the ligand structure and the nature of the metal center. Among the investigated catalysts, the Ce-Salen complex exhibited higher catalytic activity and comparatively favorable M n and dispersity values compared to its Fe- and Co-based counterparts under identical conditions. This comparative study provides valuable insights into the metal-center effects in Salen-type catalysts and offers rational guidance for designing efficient catalysts for PLA synthesis.