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1. Mechanistic investigations on a homogeneous ruthenium Guerbet catalyst in a flow reactor

   https://doi.org/10.1039/D1RE00551K  

   Wang, Nicholas M.; Dillon, Sam; Guironnet, Damien (March 2022, Reaction Chemistry & Engineering)

   A mechanistic investigation on the ethanol self-condensation reaction (Guerbet reaction) catalyzed by a bis(pyridylimino)isoindolate Ru( ii ) catalyst was performed using a specifically designed continuously-stirred tank reactor (CSTR). Leveraging vapor–liquid equilibrium, the homogeneous catalyst was maintained in the reactor at a constant concentration by dissolving it in a non-volatile solvent while volatile substrates were fed continuously. The activity of the catalyst was monitored by analyzing the vapor exiting the reactor (reagents and products) using an in-line gas chromatograph. The formation of C 6 products demonstrates the catalyst's reactivity towards butanol, and the detection of solely saturated products implies that hydrogenation is fast under the reaction conditions. These observations led us to perform a detailed study of the hydrogenation step that provided evidence for a hydrogen-transfer pathway. The corresponding reaction mechanism for the Guerbet reaction was established. 

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2. A DNA-conjugated small molecule catalyst enzyme mimic for site-selective ester hydrolysis

   https://doi.org/10.1039/C7SC04554A  

   Flanagan, Moira L.; Arguello, A. Emilia; Colman, Drew E.; Kim, Jiyeon; Krejci, Jesse N.; Liu, Shimu; Yao, Yueyu; Zhang, Yu; Gorin, David J. (January 2018, Chemical Science)

   The challenge of site-selectivity must be overcome in many chemical research contexts, including selective functionalization in complex natural products and labeling of one biomolecule in a living system. Synthetic catalysts incorporating molecular recognition domains can mimic naturally-occurring enzymes to direct a chemical reaction to a particular instance of a functional group. We propose that DNA-conjugated small molecule catalysts (DCats), prepared by tethering a small molecule catalyst to a DNA aptamer, are a promising class of reagents for site-selective transformations. Specifically, a DNA-imidazole conjugate able to increase the rate of ester hydrolysis in a target ester by >100-fold compared with equimolar untethered imidazole was developed. Other esters are unaffected. Furthermore, DCat-catalyzed hydrolysis follows enzyme-like kinetics and a stimuli-responsive variant of the DCat enables programmable “turn on” of the desired reaction. 

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3. A deep neural network for oxidative coupling of methane trained on high-throughput experimental data

   https://doi.org/10.1088/2515-7655/aca797  

   Ziu, Klea; Solozabal, Ruben; Rangarajan, Srinivas; Takáč, Martin (December 2022, Journal of Physics: Energy)

   Abstract In this work, we develop a deep neural network model for the reaction rate of oxidative coupling of methane from published high-throughput experimental catalysis data. A neural network is formulated so that the rate model satisfies the plug flow reactor design equation. The model is then employed to understand the variation of reactant and product composition within the reactor for the reference catalyst Mn–Na₂WO₄/SiO₂at different temperatures and to identify new catalysts and combinations of known catalysts that would increase yield and selectivity relative to the reference catalyst. The model revealed that methane is converted in the first half of the catalyst bed, while the second part largely consolidates the products (i.e. increases ethylene to ethane ratio). A screening study of $⩾3400$combinations of pairs of previously studied catalysts of the form M1(M2) ${}_{1-2}$M3O_x/support (where M1, M2 and M3 are metals) revealed that a reactor configuration comprising two sequential catalyst beds leads to synergistic effects resulting in increased yield of C₂compared to the reference catalyst at identical conditions and contact time. Finally, an expanded screening study of 7400 combinations (comprising previously studied metals but with several new permutations) revealed multiple catalyst choices with enhanced yields of C₂products. This study demonstrates the value of learning a deep neural network model for the instantaneous reaction rate directly from high-throughput data and represents a first step in constraining a data-driven reaction model to satisfy domain information. 

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4. Bimetallic nickel-palladium nanoparticles supported on multi-walled carbon nanotubes for Suzuki and Sonogashira cross-coupling reactions in continuous flow

   Coker, Katherine A; Winkleman, Harlee B; Siamaki, Ali R (March 2024, ACS; American Chemical Society (CAS))

   NA (Ed.)

   The advancement of metal-catalyzed carbon-carbon bond forming reactions represents one of the most significant contributions to contemporary organic synthesis. Innovations in the area of palladium catalyzed homogeneous cross-coupling catalysis have dominated this area of chem. and are playing an increasingly important role in the area of pharmaceutical drug discovery and development. However, the use of these catalysts under homogeneous conditions has limited their com. viability due to product contamination as a direct result of inability to effectively sep. the catalyst from the reaction product. Ligand-free heterogeneous catalysis presents a promising option to address this problem as evidenced by the significant increase in research activity in this area. We have recently developed a simple, one-step method for the preparation of bimetallic nickel-palladium nanoparticles supported on multi-walled carbon nanotubes (Ni-Pd/MWCNTs) under mech. shaking in a ball- mill. The preparation method is very fast and straightforward which does not require any chems., solvents, or addnl. ligands. Notably, the concentration of palladium can be lowered to a min. amount of 1% and replaced by more abundant and less expensive nickel nanoparticles while effectively catalyzing the reaction. The as-prepared nanoparticles demonstrated remarkable catalytic activities in cross-coupling catalysis such as Suzuki and Sonoga shira reactions with functionalized substrates in batch with high turnover number in a single catalytic reaction. Batch operations have several inherent limitations that include reproducibility, scalability, and reactor productivity. Continuous flow chem. has been considered as an alternative approach in academic and industrial processes due to its efficient and innovative synthetic design. The low palladium loading and excellent recyclability of the catalyst make this an affordable and clean option for cross-coupling catalysis under continuous flow conditions, a feature that enables the large-scale industrial and pharmaceutical applications of this method in the future. 

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5. Enzyme-like catalysis by single chain nanoparticles that use transition metal cofactors

   https://doi.org/10.1039/d1cc05578j  

   Xiong, Thao M.; Garcia, Edzna S.; Chen, Junfeng; Zhu, Lingyang; Alzona, Ariale J.; Zimmerman, Steven C. (January 2022, Chemical Communications)

   We report a modular approach in which a noncovalently cross-linked single chain nanoparticle (SCNP) selectively binds catalyst “cofactors” and substrates to increase both the catalytic activity of a Cu-catalyzed alkyne-azide cycloaddition reaction and the Ru-catalyzed cleavage of allylcarbamate groups compared to the free catalysts. 

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