1013: DFT INSIGHTS ON HOMOPOLYMERIZATION OF CYCLIC ESTERS PROMOTED BY FE(II) PYRIDYLAMIDO CATALYST

Transitioning toward a sustainable and circular economy necessitates the development of alternative materials to replace non-degradable, fossil-derived plastics such as polyolefins. Among biodegradable polymers, poly(lactic acid) (PLA) has gained significant attention due to its increasing production and broad applicability. The development of material properties aligned with circular economy principles are focusing on various cyclic esters (lactones) in both homo- and copolymerization. This approach can develop materials that can be chemically recycled to their monomers (CRM), a critical objective for sustainability^[1]. Recent studies have reported the synthesis of novel three-coordinate heteroleptic [N, N]Fe^II(N(SiMe₃)₂) complexes with bidentate monoanionic pyridylamido ligands (Fig. 1a), which have demonstrated high efficiency and activity in the ring-opening polymerization (ROP) of lactide (LA) and ε-caprolactone (ε-CL)^[2],[3]. Recently, these catalysts have been employed in the ROP of less reactive cyclic esters, such as δ-hexalactone (δ-HL), δ-nonalactone (δ-NL), and ε-decalactone (ε-DL). This study presents a preliminary computational investigation into the homopolymerization mechanisms of δ-HL and ε-CL (Fig. 1b) using density functional theory (DFT). The main goal is to explore the polymerization pathways facilitated by Fe(II) catalysts, with particular focus on the complexities introduced by the -N(SiMe₃)₂ group. We propose alternative mechanisms to the classical pathways reported in the literature (Fig. 1c). Our analysis incorporates experimental evidence to validate these mechanisms, providing insights into catalyst structure-reactivity relationships.