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The polymeric metal complex iron tris(dibenzoylmethane-polylactide), Fe(dbmPLA)3, was synthesized from d,l-lactide and Fe(dbmOH)3, a hydroxyl functionalized metalloinitiator. Reactions are fast relative to those with the dbmOH ligand initiator even when no Sn(oct)2 or DMAP catalyst is added, indicating that iron serves as both a dbm protecting group and a catalyst for lactide ring-opening polymerization (ROP). Kinetics experiments show good molecular weight control to ∼60−70% conversion (e.g., PDIs < 1.1; no evidence of transesterification via 1H NMR spectroscopic analysis; continued chain growth when Fe(dbmPLA)3 is heated with additional lactide monomer). For comparison, Fe(bdk)3 (bdk = β-diketonate) complexes were tested as lactide ROP catalysts using dbmOH and benzyl alcohol as the initiators. The red-orange Fe(dbmPLA)3 polymers were analyzed by GPC, 1H NMR and UV-vis spectroscopy. Demetalation with dilute HCl yields dbmPLA macroligands for chelation to other metals. The polymerization mechanism using Fe(dbmOH)3 as an initiator and catalyst is also discussed and results suggest ligand exchange prior to initiation may be involved.

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