ChemCatChem

Capturing and converting CO2 through artificial photosynthesis using photoactive, porous materials is a promising approach for addressing increasing CO2 concentrations. Porphyrinic Zr-based metal-organic frameworks (MOFs) are of particular interest as they incorporate a photosensitizer in the porous structure. Herein, the initial step of the artificial photosynthesis is studied: CO2 sorption and activation in the presence of water. A combined vibrational and visible spectroscopic approach was used to monitor the adsorption of CO2 into PCN-222 and PCN-223 MOFs, and the photophysical changes of the porphyrinic linker as a function of water concentration...

Aza-substitution, the replacement of aromatic CH groups with nitrogen atoms, is an established medicinal chemistry strategy for increasing solubility, but current methods of accessing functionalized azaindoles are limited. In this work, indole-alkylating aromatic prenyltransferases (PTs) were explored as a strategy to directly functionalize azaindole-substituted analogs of natural products. For this, a series of aza-l-tryptophans (Aza-Trp) featuring N -substitution of every aromatic CH position of the indole ring and their corresponding cyclic Aza-l-Trp-l-proline dipeptides (Aza-CyWP), were synthesized as substrate mimetics for the indole-alkylating PTs FgaPT2, CdpNPT, and FtmPT1...

We present the use of Pd-complex-containing supported ionic liquid phases (SILPs) as a novel approach for continuous-flow allylic alkylation of N -nucleophiles. This immobilization strategy gave simple access to air-tolerating catalyst frameworks, providing rapid and convenient access to various achiral and chiral N -allylation products. Under optimized conditions, the flow-reaction could be maintained for 3.5 hours with constant product output; meanwhile, only a marginal 0.7 wt % of ionic liquid leaching and no detectable palladium-complex leaching could be observed...

Indole is a significant structural moiety and functionalization of the C-H bond in indole-containing molecules expands their chemical space, and modifies their properties and/or activities. Indole prenyltransferases (IPTs) catalyze the direct regiospecific installation of prenyl, C5 carbon units, on indole-derived compounds. IPTs have shown relaxed substrate flexibility enabling them to be used as tools for indole functionalization. However, the mechanism by which certain IPTs target a specific carbon position is not fully understood...

Imine reductases (IREDs) are NADPH-dependent enzymes with significant biocatalytic potential for the synthesis of primary, secondary, and tertiary chiral amines. Their applications include the reduction of cyclic imines and the reductive amination of prochiral ketones. In this study, twenty-nine novel IREDs were revealed through genome mining. Imine reductase activities were screened at pH 7 and 9 and in presence of either NADPH or NADH; some IREDs showed good activities at both pHs and were able to accept both cofactors...

Carbocycles are core skeletons in natural and synthetic organic compounds possessing a wide diversity of important biological activities. Herein, we report the development of an excited-state copper-catalyzed radical carbo-aroylation of unactivated alkenes to synthesize ketonylated tetralins, di- and tetrahydrophenanthrenes, and cyclopentane derivatives. The reaction is operationally simple and features mild reaction conditions that tolerate a broad range of functional groups. Preliminary mechanistic studies suggest a reaction pathway beginning with photoexcitation of [CuI-BINAP]2 and followed by a single electron transfer (SET), radical aroylation of unactivated alkenes, radical cyclization, and re-aromatization, affording the desired ketonylated carbocycles...

Artificial redox catalysts are typically limited by unfavorable scaling relations of reaction intermediates leading to a significant overpotential in multi-electron redox reactions such as for example the oxygen reduction reaction (ORR). The multicopper oxidase laccase is able to catalyze the ORR in nature. In particular the high-potential variants show a remarkably low overpotential for the ORR and apparently do not suffer from such unfavorable scaling relations. Although laccases are intensively studied, it is presently unknown why the overpotential for ORR is so low and a clear description regarding the thermodynamics of the catalytic cycle and the underlying design principles is lacking...

The mechanism and the reactive species involved in the oxidation of alkenes, and alcohols with H2 O2 , catalysed by an in situ prepared mixture of a MnII salt, pyridine-2-carboxylic acid and a ketone is elucidated using substrate competition experiments, kinetic isotope effect (KIE) measurements, and atom tracking with 18 O labelling. The data indicate that a single reactive species engages in the oxidation of both alkenes and alcohols. The primary KIE in the oxidation of benzyl alcohols is ca. 3.5 and shows the reactive species to be selective despite a zero order dependence on substrate concentration, and the high turnover frequencies (up to 30 s-1 ) observed...

Low-coordinate, open-shell 3d metal complexes have attracted great attention due to their critical role in several catalytic transformations but have been notoriously difficult to prepare and study due to their high lability. Here, we report the synthesis of a heteroleptic tri-coordinate amidoferrate that displays high catalytic activity in the regioselective hydrosilylation of alkenes.

Vanadium redox flow batteries (VRFBs) are appealing large-scale energy storage systems due to their unique properties of independent energy/power design. The VRFBs stack design is crucial for technology deployment in power applications. Besides the design, the stack suffers from high voltage losses caused by the electrodes. The introduction of active sites into the electrode to facilitate the reaction kinetic is crucial in boosting the power rate of the VRFBs. Here, an O-rich layer has been applied onto structured graphite felt (GF) by depositing WO3 to increase the oxygen species content...

Tandem catalysis stands out as a major instrument towards the intensification of existing and future chemical processes. Initially formulated in the field of homogeneous catalysis, the concept relies on the single-pot integration of two (or more) catalysts showing high specificity for mechanistically decoupled reactions, while being operational and compatible under a single set of operation conditions. Isolated metal atoms stabilized on solid carriers in single-atom catalysts (SACs) hold the potential to reconcile the high reaction specificities of mononuclear sites in molecular catalysts with an intrinsic catalyst compartmentalization on inorganic matrices...

The chemo- and stereoselective semi-hydrogenation of alkynes to alkenes is a fundamental transformation in synthetic chemistry, for which the use of precious 4d or 5d metal catalysts is well-established. In mankind's unwavering quest for sustainability, research focus has considerably veered towards the 3d metals. Given their high abundancy and availability as well as lower toxicity and noxiousness, they are undoubtedly attractive from both an economic and an environmental perspective. Herein, we wish to present noteworthy and groundbreaking examples for the use of 3d metal catalysts for diastereoselective alkyne semi-hydrogenation as we embark on a journey through the first-row transition metals...

Development of C-N coupling methodologies based on Earth-abundant metals is a promising strategy in homogeneous catalysis for sustainable processes. However, such systems suffer from deactivation and low catalytic activity. We here report that encapsulation of Cu(I) within the phenanthroyl-containing calix[8]arene derivative 1,5-(2,9-dimethyl-1,10-phenanthroyl)-2,3,4,6,7,8-hexamethyl- p -tert-butylcalix[8]arene ( C8 PhenMe6 ) significantly enhances C-N coupling activity up to 92 % yield in the reaction of aryl halides and aryl amines, with low catalyst loadings (2...

The commercialization of acidic proton exchange membrane water electrolyzers (PEMWE) is heavily hindered by the price and scarcity of oxygen evolution reaction (OER) catalyst, i. e. iridium and its oxides. One of the solutions to enhance the utilization of this precious metal is to use a support to distribute well dispersed Ir nanoparticles. In addition, adequately chosen support can also impact the activity and stability of the catalyst. However, not many materials can sustain the oxidative and acidic conditions of OER in PEMWE...

In this work, we discuss the role of manganese oxide as a promoter in Cu catalysts supported on graphitic carbon during hydrogenation of CO2 and CO. MnOx is a selectivity modifier in an H2 /CO2 feed and is a highly effective activity promoter in an H2 /CO feed. Interestingly, the presence of MnOx suppresses the methanol formation from CO2 (TOF of 0.7 ⋅ 10-3  s-1 at 533 K and 40 bar) and enhances the low-temperature reverse water-gas shift reaction (TOF of 5.7 ⋅ 10-3  s-1 ) with a selectivity to CO of 87 %C ...

The development of highly active and long-term stable electrocatalysts for the cathode of proton-exchange membrane fuel cells (PEMFC) is a paramount requirement for high performance and durable PEMFC stacks. In this regard, alloying Pt with rare earth metals (REM) has emerged as a promising approach. This short review summarizes and discusses the most relevant advances on Pt-REM alloy electrocatalysts, from bulk polycrystalline surfaces to carbon supported nanostructures, for the oxygen reduction reaction (ORR), and their implementation in PEMFCs, and is a starting point to establish the challenges in synthesis and design and properties goals for novel Pt-REM alloys...

Friedel-Crafts alkylation and acylation reactions are important methodologies in synthetic and industrial chemistry for the construction of aryl-alkyl and aryl-acyl linkages that are ubiquitous in bioactive molecules. Nature also exploits these reactions in many biosynthetic processes. Much work has been done to expand the synthetic application of these enzymes to unnatural substrates through directed evolution. The promise of such biocatalysts is their potential to supersede inefficient and toxic chemical approaches to these reactions, with mild operating conditions - the hallmark of enzymes...

It remains a real challenge to control the selectivity of the electrocatalytic CO2 reduction (eCO2 R) reaction to valuable chemicals and fuels. Most of the electrocatalysts are made of non-renewable metal resources, which hampers their large-scale implementation. Here, we report the preparation of bimetallic copper-lead (CuPb) electrocatalysts from industrial metallurgical waste. The metal ions were extracted from the metallurgical waste through simple chemical treatment with ammonium chloride, and Cux Pby electrocatalysts with tunable compositions were fabricated through electrodeposition at varying cathodic potentials...

Phenochalcogenazines such as phenoxazines and phenothiazines have been widely employed as photoredox catalysts (PCs) in small molecule and polymer synthesis. However, the effect of the chalcogenide in these catalysts has not been fully investigated. In this work, a series of four phenochalcogenazines is synthesized to understand how the chalcogenide impacts catalyst properties and performance. Increasing the size of the chalcogenide is found to distort the PC structure, ultimately impacting the properties of each PC...

Lipase/metal nanobiohybrids, generated by growth of silver or gold nanoparticles on protein matrixes are used as highly effective dual-activity heterogeneous catalysts for the production of enantiomerically enriched 2,5-dihydrofurans from allenic acetates in a one-pot cascade process combining a lipase-mediated hydrolytic kinetic resolution with a metal-catalyzed allene cycloisomerization. Incorporating a novel strategy based on enzyme-polymer bioconjugates in the nanobiohybrid preparation enables excellent conversions in the process...