Dinuclear vs. mononuclear complexes: accelerated, metal-dependent ring-opening polymerization of lactide

Area of Science:

• Organometallic chemistry
• Polymer science
• Catalysis

Background:

• Bis(phenoxy-imine) ligands are effective in coordinating metal centers.
• Ring-opening polymerization (ROP) is a key method for producing polyesters like polylactide.
• Dinuclear metal complexes offer unique catalytic properties compared to mononuclear counterparts.

Purpose of the Study:

• To synthesize and characterize dinuclear aluminum and indium complexes with a bis(phenoxy-imine) platform.
• To investigate the efficacy of these complexes as catalysts for the ring-opening polymerization of lactide.
• To compare the catalytic activity and mechanism of dinuclear aluminum and indium systems with their respective mononuclear analogs.

Main Methods:

• Synthesis of dinuclear aluminum and indium complexes.
• Catalytic polymerization of lactide using synthesized complexes.
• Kinetic studies to determine reaction pathways and activation energies.
• Analysis of reaction mechanisms for both aluminum and indium systems.

Main Results:

• Dinuclear aluminum complexes demonstrated a more favorable polymerization pathway with lower activation free energy compared to monoaluminum systems.
• No analogous trend was observed for the dinuclear indium systems when compared to mononuclear indium systems.
• The observed differences in catalytic performance were attributed to mechanistic variations in the ring-opening polymerization process.

Conclusions:

• Dinuclear aluminum complexes are highly effective catalysts for lactide polymerization, offering kinetic advantages over mononuclear systems.
• The catalytic behavior of indium complexes in lactide polymerization differs significantly from aluminum, suggesting a distinct ring-opening polymerization mechanism.
• The bis(phenoxy-imine) platform can be successfully employed to create dinuclear catalysts with tunable properties for polyester synthesis.