Homoleptic Magnesium Complexes of [NNN]‐Tridentate Pyrrolylaldiminate Ligands as Dual Efficient Catalysts for the Production and Open‐/Closed‐Loop Chemical Recycling of Polylactide

Abstract A series of well‐defined homoleptic magnesium complexes 1 – 9 bearing [NNN]‐tridentate pyrrolylaldiminate ligands were prepared and fully characterized by NMR spectroscopic techniques. Their application to the ring‐opening polymerization (ROP) of rac ‐lactide ( rac ‐LA) to produce polylactide was investigated under solution and bulk conditions. The polymerizations initiated by all complexes in the presence of benzyl alcohol proceeded to completion within 5 min at 70 °C. The polymerizations were controlled and living, as evidenced by the obtained predetermined molar mass PLAs with narrow dispersities. Kinetic investigations revealed an unexpected zero‐order rate dependence on monomer concentration. The NMR reaction studies revealed that the polymerizations proceeded via an insertion‐coordination mechanism in the presence or absence of benzyl alcohol. All complexes demonstrated the ability to facilitate PLA methanolysis into methyl lactate (Me‐La) under mild conditions at 50 °C, achieving complete PLA consumption ( X int = 100%) within 24 h and affording Me‐La in excellent yield and selectivity ( Y Me‐La = 83–99%, S Me‐La = 83–99%). The depolymerization of poly(L‐lactide) (PLLA) and commercial PLLAs to L‐LA monomer was demonstrated utilizing the complex 1 /glycerol ethoxylate (GEO) catalyst system at 160 °C under reduced pressure, resulting in high‐purity L‐LA.