Electronic‐Effect‐Guided Bifunctional Iron Catalyst for the Copolymerization of Epoxides and Anhydrides: Enabling the Synthesis of High Molecular Weight Polyesters

ABSTRACT Ring‐opening copolymerization (ROCOP) of epoxides and anhydrides using metal‐based catalysts is a promising route to synthesize polyesters. However, conventional catalysts suffered from inadequate activity and tolerance to impurities that are essential for synthesizing high‐performance polyesters. Herein, a new electronic‐effect‐guided design principle was adopted to develop a novel bifunctional (salen)Fe(III) catalyst with outstanding efficiency. The electron‐withdrawing effect of the cocatalyst decreased the electron density at the iron center, which enhanced the catalytic activity of the (salen)Fe(III) catalyst. In contrast to conventional systems that required mol% catalyst loadings, the bifunctional (salen)Fe(III) catalyst maintained activity at an extremely low loading of 0.005 mol% and achieved an unprecedented turnover number of 19,000. Notably, the bifunctional (salen)Fe(III) catalyst emerged as the first example of organometallic complexes to synthesize polyesters with high molecular weights up to 254 kDa and high polyester selectivity over 98%. The high molecular weight polyesters showed remarkable thermal stability and high tensile strength comparable to commodity plastics. Moreover, the catalyst exhibited robust tolerance to impurities. This feature enabled the ROCOP of epoxides and anhydrides to proceed in air using commercial monomers without further purification, which was not accessible by previous catalysts.