Molecular catalysts have been shown to have high selectivity for CO2 electrochemical reduction to CO, but with current densities significantly below those obtained with solid‐state materials. By ...depositing a simple Fe porphyrin mixed with carbon black onto a carbon paper support, it was possible to obtain a catalytic material that could be used in a flow cell for fast and selective conversion of CO2 to CO. At neutral pH (7.3) a current density as high as 83.7 mA cm−2 was obtained with a CO selectivity close to 98 %. In basic solution (pH 14), a current density of 27 mA cm−2 was maintained for 24 h with 99.7 % selectivity for CO at only 50 mV overpotential, leading to a record energy efficiency of 71 %. In addition, a current density for CO production as high as 152 mA cm−2 (>98 % selectivity) was obtained at a low overpotential of 470 mV, outperforming state‐of‐the‐art noble metal based catalysts.
Iron porphyrin has been shown to be an exceptionally efficient supported homogeneous catalyst for the conversion of CO2 to CO in water once inserted in a flow cell. From neutral pH to alkaline conditions, selectivities larger than 98 % were systematically obtained, thanks to the high reactivity of the catalyst with CO2 and the low overpotential values that makes the HER pathway unfavorable.
The conversion of SO2 into arylsulfones under metal‐free conditions was achieved for the first time by reacting SO2 with (hetero)arylsilanes and alkylhalides in the presence of a fluoride source. The ...mechanism of this transformation was elucidated based on DFT calculations, which highlight the influence of SO2 in promoting C−Si bond cleavage.
SOO good: The conversion of SO2 into (hetero)arylsulfones under metal‐free conditions was achieved by reacting SO2 with (hetero)arylsilanes and alkylhalides in the presence of a fluoride source. The mechanism of this transformation was elucidated based on DFT calculations, which highlight the influence of SO2 in promoting C−Si bond cleavage.
Despite the hazardous nature of isocyanates, they remain key building blocks in bulk and fine chemical synthesis. By surrogating them with less potent and readily available formamide precursors, we ...herein demonstrate an alternative, mechanistic approach to selectively access a broad range of ureas, carbamates, and heterocycles via ruthenium-based pincer complex catalyzed acceptorless dehydrogenative coupling reactions. The design of these highly atom-efficient procedures was driven by the identification and characterization of the relevant organometallic complexes, uniquely exhibiting the trapping of an isocyanate intermediate. Density functional theory (DFT) calculations further contributed to shed light on the remarkably orchestrated chain of catalytic events, involving metal–ligand cooperation.
The cover picture shows a stylized potential energy surface landscape of thianthrenium anisole that undergoes cleavage upon electron transfer (DET). Understanding the different factors that govern ...the energy landscape is key to fine‐tune DET kinetics, a necessary requirement to use these processes as a chemical tool in selective and sustainable organic synthesis. See the Personal Account by N. von Wolff and M. Robert (DOI: 10.1002/tcr.202100151).
Glycolic acid is a useful and important α‐hydroxy acid that has broad applications. Herein, the homogeneous ruthenium catalyzed reforming of aqueous ethylene glycol to generate glycolic acid as well ...as pure hydrogen gas, without concomitant CO2 emission, is reported. This approach provides a clean and sustainable direction to glycolic acid and hydrogen, based on inexpensive, readily available, and renewable ethylene glycol using 0.5 mol % of catalyst. In‐depth mechanistic experimental and computational studies highlight key aspects of the PNNH‐ligand framework involved in this transformation.
A homogeneous ruthenium‐catalyzed reforming of aqueous ethylene glycol to glycolic acid and hydrogen is described. A plausible reaction mechanism, involving metal–ligand cooperation is proposed and supported by stoichiometric reactions, NMR studies, X‐ray crystallography and computational studies.
The electron is the ultimate redox reagent to build and reshape molecular structures. Understanding and controlling the parameters underlying dissociative electron transfer (DET) reactivity and its ...coupling with proton transfer is crucial for combining selectivity, kinetics and energy efficiency in molecular chemistry. Reactivity understanding and mechanistic elements in DET processes are traced back and key examples of current research efforts are presented, demonstrating a large variety of applications. The involvement of DET pathways indeed encompasses a broad range of processes such as photoredox catalysis, CO2 reduction and alcohol oxidation. Interplay between these experimental examples and fundamental mechanistic study provides a powerful path to the understanding of driving force‐rate relationships, which is crucial for the development of future generations of energy efficient catalytic schemes in redox organic chemistry.
Breaking bonds selectively in complex molecular systems is key in both energy related and synthetic applications. This personal account traces back how the fine understanding of dissociative electron transfer allowed for the development of systems ranging from late‐stage fluorination, photoredox catalysis to alcohol oxidation and small molecule activation.
The development of safe and energy efficient redox processes is key for a future sustainable organic chemistry and energy storage/vector applications. Molecular electrocatalysts have demonstrated ...their potential in the realm of CO2 reduction, however, successful implementations for the reduction of other carbonyl groups remain sporadic. Building on the reversibility of hydrogenation and dehydrogenation of carbonyls and alcohols, an overview of current molecular electrocatalytic systems is presented. Key mechanistic concepts are emphasized to facilitate the link with more mature schemes in transfer hydrogenation, proton‐ and CO2‐reduction. Thus, this work contributes to future catalyst generation development bridging fundamental aspects of electrochemical bond activation with molecular catalytic concepts in the context of societal challenges of today.
Molecular electrocatalysts have been efficiently used for CO2 reduction, however similar implementations for the reduction of other carbonyl groups are scarcely reported. Building on the reversibility of hydrogenation and dehydrogenation of carbonyls and alcohols, an overview of current molecular electrocatalytic systems is presented. Key mechanistic concepts are highlighted to facilitate the link with transfer hydrogenation, proton‐ and CO2‐reduction.
The guanidine 1,5,7‐triazabicyclo4.4.0dec‐5‐ene (TBD) and the substituted derivatives TBD–SiR2+ and TBD–BR2 reacted with SO2 to give different FLP–SO2 adducts. Molecular structures, elucidated by ...X‐ray diffraction, showed some structural similarities with the analogous CO2 adducts. Thermodynamic stabilities were both experimentally evidenced and computed through DFT calculations. The underlying parameters governing the relative stabilities of the different SO2 and CO2 adducts were discussed from a theoretical standpoint, with a focus on the influence of the Lewis acidic moiety.
SO2 activation: Frustrated Lewis Pairs (FLPs) based on a guanidine scaffold substituted with boryl or silylium Lewis acidic moieties can activate SO2 and CO2. Experimental and computational results showed how the Lewis acidity of the FLP can facilitate the activation of the small molecule, from structural and energetic perspectives.
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