Ring-opening polymerization of ε-caprolactone with a macrocyclic tetracarbene indium complex

Area of Science:

• Organometallic Chemistry
• Polymer Chemistry
• Coordination Chemistry

Background:

• Indium(III) complexes are versatile catalysts in organic synthesis.
• Tetracarbene ligands offer unique coordination environments.
• Macrocyclic ligands provide rigidity and control over metal center geometry.

Purpose of the Study:

• To synthesize novel chiral tetracarbene indium(III) complexes.
• To investigate the structural characteristics of these complexes.
• To evaluate the catalytic activity of the indium ethoxide complex in polymerization reactions.

Main Methods:

• Synthesis of a rigid dianionic macrocyclic tetra-NHC ligand.
• Coordination of the ligand with indium(III) precursors.
• Structural characterization of the resulting bromide and ethoxide complexes.
• Catalytic testing of the indium ethoxide complex for ring-opening polymerization.

Main Results:

• Successful synthesis of the first chiral tetracarbene indium(III) complexes.
• Structural similarity observed between the macrocyclic indium tetra-NHC complexes and analogous salen complexes.
• The indium ethoxide complex demonstrated effective promotion of living ring-opening polymerization of ε-caprolactone.
• Polymerization proceeded efficiently at room temperature.

Conclusions:

• Chiral tetracarbene indium(III) complexes can be effectively synthesized using rigid macrocyclic ligands.
• These complexes represent a new class of chiral organometallic compounds with potential applications.
• The indium ethoxide complex is a promising catalyst for controlled polymerization of lactones.