Evidence for Dynamic Chemical Kinetics at Individual Molecular Ruthenium Catalysts

Abstract

Catalytic cycles are typically depicted as possessing time-invariant steps with fixedr ates.Y et 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,w ith af ocus on ring-opening metathesis polymerization catalyzedb yt he second-generation Grubbs ruthenium catalyst. Fluorescence microscopyi su sed to probe the chemical kinetics of the reaction because the technique possesses sufficient sensitivity for the detection of single chemical reactions.I nsertion 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.Supportinginformation and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.

Single-Molecule Catalysis in the Palladium Cross-Coupling Reaction Cycle

“…The study of catalytic reactions at the single-molecule level has provided a modern perspective for investigating various chemical and biochemical processes with unprecedented spatial and temporal resolution. − When the reaction product or any intermediate in the catalytic cycle is a fluorescent species, the localization or tracking of the catalyst over time, using advanced optical fluorescence microscopy methods, allows for the direct measurement of the stochastic fluctuation of the reaction dynamics underlying the process. This approach enables the investigation of catalytic organic and inorganic reactions, enzyme reactions, and other complex processes at the single-molecule (SM), atom, or nanoparticle levels. − These methods surpass classical macroscopic kinetics under deterministic conditions because they offer a more specific analysis of the turnover frequency (TOF) of the catalyst using a very small amount of reactants, which is an important consideration in today’s research. The Suzuki–Miyaura cross-coupling reaction is widely applied in organic synthesis, representing one of the most crucial methods for extending the carbon framework in desired large organic compounds .…”

Single‐molecule fluorescence microscopy for imaging chemical reactions: Recent progress and future opportunities for advancing polymer systems

“…Further expansion of these studies into polymer tethers for catalysts was suggested as a future opportunity for additional studies, and several of these works were performed to fill the gap in polymer initiation via catalysis. 26,[153][154][155][156]…”

“…219 These studies were eventually expanded to determine individual molecule kinetics of ruthenium catalyst-governed ROMP which varied from bulk concentration kinetics for the same reaction. [154][155][156] At a molecular level, catalysis kinetics vary depending on local environments, and at low concentrations of substrate, single monomer insertion events could be imaged within the precipitated polymer. Therefore, these methods of reaction monitoring have been limited to polymers of substantial molecular weight but not of oligomeric growth toward reaching entanglement molecular weight.…”

“…Therefore, these methods of reaction monitoring have been limited to polymers of substantial molecular weight but not of oligomeric growth toward reaching entanglement molecular weight. Furthermore, the kinetic nonuniformity in polymerization catalysis was identified via smFL imaging of an isolated monomer insertion, 154,155 and this technique could potentially be applied to other systems to understand polymerizations and insertions in other systems which may not follow a ROMP mechanism. 156 Chemo-selectivity of polymerization catalysts for ROMP has been a growing field since the reporting of molecular level kinetics of norbornene polymerizations, which led to successful imaging of individual catalyst selectivity by Garcia et al (Figure 12).…”

Single-Molecule Observations Provide Mechanistic Insights into Bimolecular Knoevenagel Amino Catalysis

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