Kinetics of the Same Reaction Monitored over Nine Orders of Magnitude in Concentration: When Are Unique Subensemble and Single‐Turnover Reactivity Displayed?

Abstract

Essentially no information is knowna bout the behavior of individual molecular catalysts under reaction conditions.T his is ar esult of the averaging inherent to traditional analytical techniques.H erein, ac ombined fluorescence microscopyand 1 HNMR spectroscopystudy reveals that unique (that is,non-ensemble averaged) distributions and timevariable kinetics from molecular ruthenium catalysts within growing polynorbornene occur and are detectable between 10 À9 m and 10 À6 m of substrate,s urprisingly just 1000-fold less concentrated than at ypical laboratory bench-scale reaction. The kinetic states governing single-turnover events are determinable by overlayo ft he signal arising from individual monomer insertion reactions with that from polymer growth from neighboring catalysts.

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 The ability to image this reaction is attributed to rapid diffusion rates of norbornene monomer relative to the growing polymer chains, leading to a high resolution for spatial localization. 154,156,219,226 However, this technique relied on the ruthenium catalyst being in the active state, and the polymer could not be imaged otherwise. 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.…”

“…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).…”

“…Recent progress in this area highlights the importance of single-molecule microscopy of catalysts for determining local heterogeneities in ensemble averaging measurements. [154][155][156]222 Imaging a wider variety of catalyzed polymerizations could expand the horizons of smFL by monitoring the activity of the individual catalysts and comparing that to the bulk kinetics of a reaction. Additionally, the development of new techniques, like COMPEITS shows significant promise for the visualization of a variety of catalytic polymerization processes.…”