A Ring-Opening Metathesis Polymerization Catalyst That Exhibits Redox-Switchable Monomer Selectivities

Area of Science:

• Organometallic Chemistry
• Polymer Science
• Catalysis

Background:

• Ring-opening metathesis polymerization (ROMP) is a versatile method for polymer synthesis.
• Developing catalysts with tunable activity and selectivity is crucial for advanced polymer architectures.
• Redox-active ligands offer a pathway to modulate catalyst behavior through external stimuli.

Purpose of the Study:

• To synthesize and characterize a novel ROMP catalyst supported by a redox-active N-heterocyclic carbene (NHC).
• To investigate the influence of the catalyst's oxidation state on its polymerization activity and selectivity.
• To demonstrate the utility of redox-switching for controlled copolymer synthesis.

Main Methods:

• Synthesis of a ruthenium-based catalyst featuring a redox-active NHC ligand.
• Polymerization of 1,5-cis,cis-cyclooctadiene and norbornene derivatives using the catalyst in neutral and reduced forms.
• Redox-switching the catalyst during polymerization to produce copolymers with controlled compositions and microstructures.

Main Results:

• The catalyst exhibited reversible reduction, enabling modulation of its electronic properties.
• In its neutral state, the catalyst showed higher activity for 1,5-cis,cis-cyclooctadiene polymerization compared to norbornene derivatives.
• Upon reduction, the catalyst's selectivity reversed, favoring norbornene derivative polymerization over 1,5-cis,cis-cyclooctadiene.

Conclusions:

• The developed redox-active NHC catalyst provides a unique platform for controlling ROMP.
• Oxidation state-dependent selectivity allows for the precise synthesis of copolymers with tailored properties.
• This approach offers a new strategy for designing advanced polymeric materials through external redox control.