Cooperative Initiation in a Dinuclear Indium Complex for CO₂ Epoxide Copolymerization.

Area of Science:

• Organometallic Chemistry
• Polymer Chemistry
• Catalysis

Background:

• Indium complexes are increasingly explored as catalysts in organic synthesis.
• Schiff base ligands offer versatile coordination environments for metal centers.
• The alternating copolymerization of CO2 and epoxides is a key reaction for sustainable polymer production.

Purpose of the Study:

• To synthesize and characterize novel dinuclear indium complexes.
• To investigate the catalytic activity of these complexes in the alternating copolymerization of carbon dioxide and cyclohexene oxide.
• To elucidate the mechanism of catalysis, particularly the role of dinuclearity.

Main Methods:

• Synthesis and characterization of neutral and cationic dinuclear indium complexes supported by Schiff base ligands.
• Evaluation of catalytic performance in copolymerization reactions under varying CO2 pressures and temperatures.
• Comparison of reactivity between dinuclear and mononuclear indium complexes.

Main Results:

• The neutral dinuclear indium chloride complex (±)-[(ONapNiN)InCl2]2 (4) demonstrated high conversion of cyclohexene oxide and excellent selectivity for poly(cyclohexene carbonate) formation.
• Catalysis proceeded efficiently without the need for cocatalysts at 80 °C and under CO2 pressures ranging from 2 to 30 bar.
• A significant difference in reactivity was observed between the dinuclear complex 4 and its mononuclear counterpart (±)-(NNiO)InCl2 (5).

Conclusions:

• Dinuclear indium complexes, particularly the neutral chloride complex 4, are highly effective catalysts for CO2/cyclohexene oxide copolymerization.
• The distinct reactivity of dinuclear versus mononuclear complexes suggests a cooperative initiation mechanism involving both indium centers.
• This study opens avenues for designing advanced dinuclear catalysts for sustainable polymer synthesis.