Copper-Catalyzed Asymmetric Sulfilimination Enabled by Chiral Bisoxazoline Ligands – Collaborative Research by Shaanxi Normal University Li Xingwei, Xiao Jichao / Northeast Normal University Zheng Guangfan Teams Published in CCS Chemistry 1. Resea
Created on 02.06
An Ultrafast Benchmark for Ring-Opening Metathesis Polymerization Catalysts: A Ruthenium Phosphinimine System Approaching the Diffusion Rate Limit
– Research by Kansas State University Peter E. Sues Team Published in JACS
1. Research Background and Significance
Olefin metathesis (OM) is a pivotal chemical transformation for constructing unsaturated carbon‑carbon double bonds. Among its variants, ring-opening metathesis polymerization (ROMP) utilizes ring strain release from cyclic olefins to drive polymer formation, with broad applications in automotive, electronics, and pharmaceutical industries. Conventional ROMP catalysts (e.g., Schrock-type Group VI metals and Grubbs-type ruthenium complexes) face limitations such as low catalytic rates, insufficient stability, and often require elevated temperatures. Developing high-efficiency catalytic systems is therefore urgently needed. Recently, the team of Prof. Peter E. Sues at Kansas State University reported a ruthenium phosphinimine complex (Ru1) that demonstrates exceptional ROMP performance for model substrates including norbornene (NBE), cyclooctene (COE), and cyclooctadiene (COD). Through kinetic analysis, decomposition pathway studies, and mechanistic validation, the team systematically evaluated Ru1’s catalytic efficiency, determining its turnover frequency (TOF), turnover number (TON), and rate constants, while clarifying its activation mechanism and substrate scope.
2. Catalytic Performance Data
Table 1. ROMP of Norbornene (NBE) Catalyzed by Ru1
Each data point represents the average of three independent experiments. TOF calculated based on initial rates and conversion at 2 s after catalysis initiation.
Table 2. ROMP of Cyclooctene (COE) Catalyzed by Ru1
TOF calculated based on initial rates and conversion at 2 s after catalysis initiation.
Table 3. ROMP of Cyclooctadiene (COD) Catalyzed by Ru1
TOF calculated based on initial rates and conversion at 1 s after catalysis initiation.
3. Key Advantages of the Ruthenium Phosphinimine Catalyst
3.1 Record-High Catalytic Activity Nearing Diffusion Limit
Ru1 achieves unprecedented efficiency in ROMP:
- For NBE: TOF up to 4.00×104s⁻¹, TON up to 232,000
- For COE: TOF up to 9.88×103s⁻¹, TON up to 240,000 These values significantly surpass conventional Schrock-type (e.g., vanadium-based NBE systems: TOF ~1.18×102s⁻¹) and Grubbs-type catalysts (e.g., 1st-generation Grubbs catalyst for COE: TOF ~0.1 s⁻¹). The rate constants for NBE (7.9×108M⁻¹·s⁻¹) and COE (9.6×107M⁻¹·s⁻¹) approach the diffusion-controlled limit, rivaling some of the fastest enzymatic systems (e.g., carbonic anhydrase).
3.2 Interchange Activation Mechanism Enables Substrate Concentration Control
Unlike the dissociative activation in traditional Grubbs catalysts, Ru1 follows an interchange ligand substitution pathway, exhibiting first-order dependence on monomer concentration. This allows reaction rates to be optimized by tuning substrate concentration – e.g., high COE concentration (5 M) suppresses bimolecular decomposition, achieving >96% conversion. The mechanism avoids activity loss from ligand dissociation and remains consistent across NBE, COE, and COD, providing a clear strategy for controlling ROMP kinetics.
3.3 Broad Substrate Compatibility and High Polymer Performance
Ru1 demonstrates excellent adaptability:
- 90% conversion for NBE, COE, and COD (up to 98% in some cases)
- Ultra-high molecular weights: >100 kg/mol for COE polymers; 30–95 kg/mol for NBE polymers
- Stability–activity balance: sterically hindered carbene intermediates from NBE suppress bimolecular decomposition; high COE concentration competitively inhibits degradation
- Limitations only arise with strongly coordinating or sterically demanding substrates (e.g., dimethyl norbornenedicarboxylate)
4. Industrial Support
To support further research, Anhui Kaitai Laibo will soon release the ruthenium phosphinimine catalyst, offering custom synthesis services.
5. Publication Details
Title: An Ultrafast Benchmark for Ring-Opening Metathesis Polymerization Catalysts: A Ruthenium Phosphinimine System Approaching the Diffusion Rate Limit
Authors: Jordan R. Gipper, Dean Afsar, Carson Cole, Sayantani Saha, Ryan J. Rafferty, Patricia R. Calvo, Peter E. Sues*
Journal: Journal of the American Chemical Society
DOI: 10.1021/jacs.5c14780