Cation-π interactions enabling hard/soft Ti/Ag heterobimetallic cooperativity in lactide ring-opening polymerisation

Area of Science:

• Organometallic Chemistry
• Polymer Science
• Catalysis

Background:

• Ring-opening polymerization (ROP) is a key method for synthesizing polyesters.
• Developing efficient catalysts for ROP, especially at room temperature, remains a challenge.
• Heterobimetallic complexes offer unique reactivity profiles through cooperative effects.

Purpose of the Study:

• To investigate the catalytic activity of a Ti-salen complex combined with AgBArF in lactide ROP.
• To elucidate the mechanistic aspects and the role of cation-π interactions in the observed cooperativity.
• To understand the distinct roles of titanium and silver in the polymerization process.

Main Methods:

• Synthesis and characterization of the Ti-salen complex.
• Ring-opening polymerization experiments of lactide using the combined catalytic system.
• Kinetic studies to determine reaction rates and orders.
• Mechanistic investigations including spectroscopic analysis.
• Computational studies (e.g., DFT) to model intermediates and interactions.

Main Results:

• The Ti-salen/AgBArF system exhibits significant catalytic activity for lactide ROP at room temperature.
• Evidence for the formation of heterobimetallic species facilitated by cation-π interactions between the silver cation and the salen ligand.
• Both titanium and silver play crucial, cooperative roles in activating the monomer and facilitating chain propagation.
• The system demonstrates controlled polymerization characteristics.

Conclusions:

• The combination of a Ti-salen complex and AgBArF creates a highly active hard/soft heterobimetallic catalyst for lactide ROP.
• Cation-π interactions are pivotal in stabilizing the active heterobimetallic species and enabling cooperative catalysis.
• This study provides valuable insights into the design principles for cooperative bimetallic catalysts in polymerization.