Configurationally flexible zinc complexes as catalysts for rac-lactide polymerisation

Area of Science:

• Coordination Chemistry
• Polymerization Catalysis
• Organometallic Chemistry

Background:

• Zinc complexes are increasingly investigated as catalysts for polymer synthesis.
• Developing efficient and selective catalysts for biodegradable polymers like polylactide is crucial.
• Ligand design plays a key role in tuning catalyst activity and polymer stereochemistry.

Purpose of the Study:

• To synthesize and characterize novel zinc complexes with different ligand environments.
• To evaluate the catalytic activity and stereoselectivity of these complexes in rac-lactide polymerization.
• To investigate the influence of ligand structure on catalyst performance.

Main Methods:

• Synthesis of dimeric and monomeric zinc complexes using various ligands.
• Characterization by X-ray diffraction and NMR spectroscopy.
• Catalytic testing in rac-lactide polymerization, monitoring conversion and polymer tacticity.

Main Results:

• A dimeric zinc complex (L1)2Zn2(μ-OR)2 showed moderate activity for heterotactic polylactide.
• Amide complexes reacted with ethanol to form highly active ethoxide catalysts (L2)ZnOEt and (L3)ZnOEt.
• (L3)ZnOEt achieved full conversion in 15 min, yielding polymers with a slight isotactic bias (Pm = 0.55-0.60).

Conclusions:

• The synthesized zinc complexes, particularly ethoxide derivatives, are highly effective catalysts for rac-lactide polymerization.
• Ligand structure, specifically the presence of a second donor arm, influences polymer tacticity.
• These catalysts offer a promising route to controlled synthesis of polylactide.