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Lithium half-salen complexes: Synthesis, structural characterization and studies as catalysts for rac-lactide ring-opening polymerization

DOI: 10.1002/ejoc.202100981 DOI Help

Authors: Yali Zhou (University of Edinburgh) , Gary S. Nichol (University of Edinburgh) , Jennifer A. Garden (University of Edinburgh)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: European Journal Of Organic Chemistry , VOL 2021 , PAGES 5557 - 5568

State: Published (Approved)
Published: October 2021
Diamond Proposal Number(s): 22240

Open Access Open Access

Abstract: Seven lithium complexes supported by sterically and electronically diverse phenoxyimine ligands were synthesized and characterized by X-ray diffraction, NMR spectroscopy and elemental microanalysis. These complexes show high activity (kobs ≤7.43×10−2 s−1) for rac-lactide ring-opening polymerization (ROP) in the presence of co-initiator benzyl alcohol (BnOH), with the exception of Li4 which features an unusual polymeric ladder structure. Overall, the catalyst activity correlates to the aggregation state; the catalysts with low aggregation states display increased propagation rates attributed to improved metal accessibility and kinetic mobility. The nature of the ligand substituents and solvent influence the catalyst aggregation in both the solid- and solution-state. While the lithium complexes can initiate rac-lactide ROP without BnOH, the addition of this co-initiator significantly increases the polymerization rate by switching the mechanism from a coordination-insertion to an activated monomer pathway, changing the resultant poly(lactic acid) architecture from cyclic to linear.

Journal Keywords: Ligand design; Lithium; Reaction mechanisms; Ring-opening polymerization; Substituent effects

Subject Areas: Chemistry, Materials

Instruments: I19-Small Molecule Single Crystal Diffraction

Added On: 26/10/2021 09:49


Discipline Tags:

Molecular Complexes Physical Chemistry Catalysis Chemistry Materials Science Polymer Science Organometallic Chemistry

Technical Tags:

Diffraction Single Crystal X-ray Diffraction (SXRD)