Phosphasalen yttrium complexes: highly active and stereoselective initiators for lactide polymerization

Area of Science:

• Organometallic Chemistry
• Polymer Science
• Catalysis

Background:

• Salen ligands are widely used in catalysis.
• Iminophosphorane donors offer unique electronic and steric properties.
• Yttrium complexes are effective in polymerization reactions.

Purpose of the Study:

• To synthesize and characterize novel yttrium alkoxide complexes featuring phosphasalen ligands.
• To evaluate the catalytic activity of these complexes in lactide ring-opening polymerization.
• To compare the performance of phosphasalen ligands with traditional salen ligands in catalysis.

Main Methods:

• Synthesis of yttrium alkoxide complexes with phosphasalen ligands.
• Characterization using multinuclear NMR, mass spectrometry, elemental analysis, and X-ray diffraction.
• Lactide polymerization experiments to assess initiation rates and stereocontrol.

Main Results:

• Three yttrium alkoxide complexes with mono- and dinuclear structures were prepared and characterized.
• The complexes demonstrated rapid initiation for lactide polymerization with excellent control.
• The mononuclear complex achieved high stereocontrol in rac-lactide polymerization, yielding heterotactic polylactic acid (PLA).

Conclusions:

• Phosphasalen ligands are highly effective in yttrium-catalyzed lactide ring-opening polymerization.
• These ligands provide superior catalytic rates and stereocontrol compared to salen ligands.
• The enhanced performance is attributed to the strong donating ability and steric protection offered by phosphasalen ligands.