Evidence for Dynamic Chemical Kinetics at Individual Molecular Ruthenium Catalysts

Catalytic cycles are typically depicted as possessing time‐invariant steps with fixed rates. Yet the true behavior of individual catalysts with respect to time is unknown, hidden by the ensemble averaging inherent to bulk measurements. Evidence is presented for variable chemical kinetics at individu...

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Bibliographic Details
Published in:Angewandte Chemie (International ed.) 2018-02, Vol.57 (6), p.1572-1575
Main Authors: Easter, Quinn T., Blum, Suzanne A.
Format: Article
Language:English
Subjects:
Catalysis
Catalysts
Chemical kinetics
Chemical reactions
Fluorescence
Fluorescence microscopy
Kinetics
Metathesis
molecular catalysis
Polymerization
polymers
Reaction kinetics
reaction mechanisms
ring-opening metathesis
Ruthenium
single-molecule fluorescence microscopy
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Summary:Catalytic cycles are typically depicted as possessing time‐invariant steps with fixed rates. Yet the true behavior of individual catalysts with respect to time is unknown, hidden by the ensemble averaging inherent to bulk measurements. Evidence is presented for variable chemical kinetics at individual catalysts, with a focus on ring‐opening metathesis polymerization catalyzed by the second‐generation Grubbs’ ruthenium catalyst. Fluorescence microscopy is used to probe the chemical kinetics of the reaction because the technique possesses sufficient sensitivity for the detection of single chemical reactions. Insertion reactions in submicron regions likely occur at groups of many (not single) catalysts, yet not so many that their unique kinetic behavior is ensemble averaged. Time‐lapse polymerization: Fluorescence microscopy detects single‐insertion reactions of a green fluorescent probe as it is incorporated into polynorbornene by a molecular ruthenium ring‐opening metathesis polymerization (ROMP) catalyst. After initiation, the chemical kinetics for norbornene monomer insertion are unexpectedly time‐variant at the molecular ruthenium ROMP catalyst. Both abrupt and gradual changes in rate occur.
ISSN:1433-7851
1521-3773
DOI:10.1002/anie.201711314