An Ultrafast Benchmark for Ring Opening Metathesis Polymerization Catalysts: A Ruthenium Phosphinimine System...

Area of Science:

• Organometallic Chemistry
• Polymer Science
• Catalysis

Background:

• Ruthenium complexes are pivotal in olefin metathesis.
• Understanding catalyst mechanisms is key to improving polymerization efficiency.
• Previous studies indicated ultrafast initiation and bimolecular decomposition for Ru1.

Purpose of the Study:

• To investigate a ruthenium phenylidene complex with a phosphinimine ligand (Ru1) as a ring-opening metathesis polymerization (ROMP) catalyst.
• To evaluate the catalytic activity and kinetics of Ru1 using norbornene (NBE), cyclooctene (COE), and cyclooctadiene (COD).
• To establish Ru1 as a benchmark for ultrafast metathesis polymerization.

Main Methods:

• Kinetic analysis of Ru1-catalyzed ROMP with NBE, COE, and COD.
• Determination of turnover frequencies (TOFs) and turnover numbers (TONs).
• Experimental measurement of rate constants for polymerization reactions.

Main Results:

• Kinetic analysis showed first-order dependence on monomer concentration, indicating rate-limiting interchange ligand substitution.
• Ru1 exhibited exceptional activity: TOFs up to 4.00 × 10^4 s^-1 and TONs up to 232,000 for NBE; TOFs up to 9.88 × 10^3 s^-1 and TONs up to 240,000 for COE; TOFs up to 1.80 × 10^2 s^-1 and TONs up to 2760 for COD.
• Rate constants approached diffusion limits (NBE: 7.9 × 10^8 M^-1·s^-1, COE: 9.6 × 10^7 M^-1·s^-1, COD: 1.1 × 10^5 M^-1·s^-1), rivaling enzymatic systems.

Conclusions:

• Ru1 is a highly active catalyst for ROMP, achieving unprecedented catalytic rates.
• The observed rates are among the highest reported for ROMP, establishing Ru1 as a benchmark system.
• This work advances the field of ultrafast metathesis polymerization.