Cyclic ruthenium-alkylidene catalysts for ring-expansion metathesis polymerization

Area of Science:

• Organometallic Chemistry
• Polymer Science
• Catalysis

Background:

• Ring-expansion metathesis polymerization (REMP) is crucial for synthesizing cyclic polyolefins.
• Developing efficient and stable catalysts is key to advancing REMP.
• N-heterocyclic carbene (NHC) ligands on ruthenium (Ru) centers are promising for metathesis catalysis.

Purpose of the Study:

• To synthesize and evaluate novel cyclic Ru-alkylidene catalysts for REMP.
• To investigate the impact of tether length and NHC ligand electronics on catalyst performance.
• To optimize catalyst design for efficient polymerization of cyclooctene.

Main Methods:

• Synthesis of modular cyclic Ru-alkylidene complexes with varying tether lengths and NHC ligands.
• Structural characterization using NMR spectroscopy and single-crystal X-ray diffraction.
• Evaluation of catalytic activity in cyclooctene polymerization, measuring propagation rates, chain transfer, and stability.

Main Results:

• Increasing tether length enhanced polymerization rates but decreased catalyst stability.
• Shorter tethers (5- or 6-carbon) facilitated intramolecular chain transfer and catalyst release.
• Electronic modification of NHC ligands (backbone saturation) significantly increased polymerization rates.
• Developed catalysts are bench-stable and highly active for REMP.

Conclusions:

• Catalyst design involving tether length and NHC ligand saturation is critical for efficient REMP.
• Optimized cyclic Ru catalysts offer a promising route to cyclic polyolefins.
• The modular approach allows fine-tuning of catalyst properties for specific applications.