Authors
Yang Huang, Hehua Li, Haiyan Ma
Published in
Inorganic chemistry. Jun 22, 2026. Epub Jun 22, 2026.
Abstract
Novel ion-paired alkali metal complexes Na1-Na4 and K1, supported by hexadentate amino-bisphenolate ligands incorporating two pendant heterocyclic rings, were synthesized. In the solid state, the multidentate ligand in Na1 and Na4 coordinates to the metal center in a pentadentate fashion, leaving one heterocyclic ring uncoordinated; in solution, however, these complexes adopt symmetric and fluxional structures. Using benzyl alcohol (BnOH) as an initiator, all complexes efficiently catalyzed the ring-opening polymerization (ROP) of rac-LA at room temperature, delivering isotactically biased PLAs with high activities (TOF up to 37917h-1). At 223 K, the sodium complexes Na1-Na4 exhibited significantly enhanced isoselectivities (Pm = 0.78-0.89), while the potassium complex K1 remained less stereoselective (Pm = 0.64). Among them, Na1 displayed the highest activity and isoselectivity (TOF up to 2407 h-1; Pm = 0.87-0.89). Under optimized conditions ([rac-LA]0/[Na1]0/[BnOH]0 = 2500/1/2), Na1 afforded high-molecular-weight isotactic PLA (Mn = 134 kg/mol, Pm = 0.89). Further decreasing the temperature to 203 K improved the isoselectivity of Na1 to Pm = 0.92 with sufficient activity still retained (TOF = 245 h-1). Based on the ROP studies of L-LA, NMR-scale reactions, and MALDI-TOF mass spectrometric analysis of typical oligomers, it is proposed that at low temperature the ROP of rac-lactide is initiated via a ligand-assisted activated-monomer mechanism in the presence of BnOH.
PMID:
42329663
Bibliographic data and abstract were imported from PubMed on 22 Jun 2026.
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