Multinuclear metal catalysts in ring-opening polymerization of ε‑caprolactone and lactide: Cooperative and electronic effects between metal centers

Multinuclear metal complexes can effectively improve the catalytic activity of catalysts for ring-opening polymerization (ROP) of cyclic esters. If the catalytic metal centers are close enough to each other, they divide the labor of coordination-insertion reactions in polymerization processes. If the catalytic metal centers are too far apart, and the ligands connecting the catalytic metal centers can have resonance, their positive charge properties affect each other and thus affect the catalytic polymerization reaction in the same manner that electron-withdrawing groups do. This review focused on recent reports of multinuclear metal catalysts in ROP that exhibited higher catalytic activity than did mononuclear metal catalysts. The dilemma faced by the development of novel multinuclear metal complexes, and the strategies and the attention for designing catalysts are also provided.