Development of a practical non-noble metal catalyst for hydrogenation of N-heteroarenes

Air-Stable Arene Manganese Complexes as Catalysts for the Syngas-Assisted Direct Reductive Amination, Cyanation of Aldehyde, and CO2 Fixation by Epoxide with High Functional Groups Tolerance

Manganese complexes [(arene)Mn(CO)3]+ were prepared in one step from arenes and Mn(CO)5Br. They were found to be efficient catalysts in the carbonyl cyanation with TMSCN, CO2 fixation by epoxides, and direct reductive amination in the presence of syngas. The amination reaction tolerated various reducible functional groups. The synergy of carbon monoxide and hydrogen in syngas provides high efficiency of the catalytic system. The developed protocols do not require an inert atmosphere, and the catalysts can be handled in air.

Ambient hydrogenation of solid aromatics enabled by a high entropy alloy nanocatalyst

Hydrogenation is a versatile chemical process with significant applications in various industries, including food production, petrochemical refining, pharmaceuticals, and hydrogen carriers/safety. Traditional hydrogenation of aromatics, hindered by the stable π-conjugated phenyl ring structures, typically requires high temperatures and pressures, making ambient hydrogenation a grand challenge. Herein, we introduce a PdPtRuCuNi high entropy alloy (HEA) nanocatalyst, achieving an exceptional 100% hydrogenation of carbon-carbon unsaturated bonds, including alkynyl and phenyl groups, in solid 1,4-bis(phenylethynyl)benzene (DEB) at 25 °C under ≤1 bar H2 and solventless condition. This results in a threefold higher hydrogen uptake for DEB-contained composites compared to conventional Pd catalysts, which can only hydrogenate the alkynyl groups with a ~ 27% conversion of DEB. Our experimental results, complemented by theoretical calculations, reveal that PdPtRu alloy is highly active and crucial in enabling the hydrogenation of phenyl groups, while all five elements work synergistically to regulate the reaction rate. Remarkably, this newly developed catalyst also achieves nearly 100% reactivity for ambient hydrogenation of a broad range of aromatics, suggesting its universal effectiveness. Our research uncovers a novel material platform and catalyst design principle for efficient and general hydrogenation. The multi-element synergy in HEA also promises unique catalytic behaviors beyond hydrogenation applications.

Combined Computational and Experimental Study Reveals Complex Mechanistic Landscape of Brønsted Acid-Catalyzed Silane-Dependent P═O Reduction

The reaction mechanism of Brønsted acid-catalyzed silane-dependent P═O reduction has been elucidated through combined computational and experimental methods. Due to its remarkable chemo- and stereoselective nature, the Brønsted acid/silane reduction system has been widely employed in organophosphine-catalyzed transformations involving P(V)/P(III) redox cycle. However, the full mechanistic profile of this type of P═O reduction has yet to be clearly established to date. Supported by both DFT and experimental studies, our research reveals that the reaction likely proceeds through mechanisms other than the widely accepted "dual activation mode by silyl ester" or "acid-mediated direct P═O activation" mechanism. We propose that although the reduction mechanisms may vary with the substitution patterns of silane species, Brønsted acid generally activates the silane rather than the P═O group in transition structures. The proposed activation mode differs significantly from that associated with traditional Brønsted acid-catalyzed C═O reduction. The uniqueness of P═O reduction originates from the dominant Si/O═P orbital interactions in transition structures rather than the P/H-Si interactions. The comprehensive mechanistic landscape provided by us will serve as a guidance for the rational design and development of more efficient P═O reduction systems as well as novel organophosphine-catalyzed reactions involving P(V)/P(III) redox cycle.

Reduction of sulfoxides catalyzed by the commercially available manganese complex MnBr(CO)5

A new methodology for the reduction of a wide variety of aliphatic and aromatic sulfoxides catalyzed by the air-stable, cheap and commercially available manganese catalyst MnBr(CO)5 with excellent yields is reported in this work. The catalytic system MnBr(CO)5/PhSiH3 is highly chemoselective, allowing the effective reduction of the SO bond in the presence of different functional groups.

Manganese Pentacarbonyl Bromide as Regeneration Catalyst Enabled Biomimetic Asymmetric Reduction

Using readily available manganese pentacarbonyl bromide as a regeneration catalyst, biomimetic asymmetric reduction of imines including quinoxalinones, benzoxazinones, and benzoxazine has been successfully developed in the presence of transfer catalyst chiral phosphoric acids, providing the chiral amines with high yields and enantioselectivities.

Unveiling Mechanistic Complexity in Manganese-Catalyzed C-H Bond Functionalization Using IR Spectroscopy Over 16 Orders of Magnitude in Time

ConspectusAn understanding of the mechanistic processes that underpin reactions catalyzed by 3d transition metals is vital for their development as potential replacements for scarce platinum group metals. However, this is a significant challenge because of the tendency of 3d metals to undergo mechanistically diverse pathways when compared with their heavier congeners, often as a consequence of one-electron transfer reactions and/or intrinsically weaker metal-ligand bonds. We have developed and implemented a new methodology to illuminate the pathways that underpin C-H bond functionalization pathways in reactions catalyzed by Mn-carbonyl compounds. By integrating measurements performed on catalytic reactions with in situ reaction monitoring and state-of-the-art ultrafast spectroscopic methods, unique insight into the mode of action and fate of the catalyst have been obtained.Using a combination of time-resolved spectroscopy and in situ low-temperature NMR studies, we have shown that photolysis of manganese-carbonyl precatalysts results in rapid (<5 ps) CO dissociation─the same process that occurs under thermal catalytic conditions. This enabled the detection of the key states relevant to catalysis, including solvent and alkyne complexes and their resulting transformation into manganacycles, which results from a migratory insertion reaction into the Mn-C bond. By systematic variation of the substrates (many of which are real-world structurally diverse substrates and not simple benchmark systems) and quantification of the resulting rate constants for the insertion step, a universal model for this migratory insertion process has been developed. The time-resolved spectroscopic method gave insight into fundamental mechanistic pathways underpinning other aspects of modern synthetic chemistry. The most notable was the first direct experimental observation of the concerted metalation deprotonation (CMD) mechanism through which carboxylate groups are able to mediate C-H bond activation at a metal center. This step underpins a host of important synthetic applications. This study demonstrated how the time-resolved multiple probe spectroscopy (TRMPS) method enables the observation of mechanistic process occurring on time scales from several picoseconds through to μs in a single experiment, thereby allowing the sequential observation of solvation, ligand substitution, migratory insertion, and ultimate protonation of a Mn-C bond.These studies have been complemented by an investigation of the "in reaction flask" catalyst behavior, which has provided additional insight into new pathways for precatalyst activation, including evidence that alkyne C-H bond activation may occur before heterocycle activation. Crucial insight into the fate of the catalyst species showed that excess water played a key role in deactivation to give higher-order hydroxyl-bridged manganese carbonyl clusters, which were independently found to be inactive. Traditional in situ IR and NMR spectroscopic analysis on the second time scale bridges the gap to the analysis of real catalytic reaction systems. As a whole, this work has provided unprecedented insight into the processes underpinning manganese-catalyzed reactions spanning 16 orders of magnitude in time.

Facile Transfer Hydrogenation of N-Heteroarenes and Nitroarenes Using Magnetically Recoverable Pd@SPIONs Catalyst

Catalysts with active, selective, and reusable features are desirable for sustainable development. The present investigation involved the synthesis and characterization of bear-surfaced ultrasmall Pd particles (<1 nm) loaded onto the surface of magnetic nanoparticles (8-10 nm). The amount of Pd loading onto the surface of magnetite is recorded as 2.8 wt %. The characterization process covered the utilization of scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), transmission electron microscopy (TEM), inductively coupled plasma (ICP), and X-ray photoelectron spectroscopy (XPS) methods. The Pd@Fe3O4 catalyst has shown remarkable efficacy in the hydrogenation of quinoline, resulting in the production of >99% N-ring hydrogenated (py-THQ) product. Additionally, the catalyst facilitated the conversion of nitroarenes into their corresponding aniline derivatives, where hydrogen was achieved by H2O molecules with the aid of tetrahydroxydiboron (THDB) as an equilibrium supportive at 80 °C in 1 h. The high efficiency of a transfer hydrogenation catalyst is closely related to the metal-support synergistic effect. The broader scope of functional group tolerance is evaluated. The potential mechanism underlying the hydrogenation process has been elucidated through the utilization of isotopic labeling investigations. The application of the heterocyclic compound hydrogenation reaction is extended to formulate the medicinally important tubular polymerization inhibitor drug synthesis. The investigation of the recyclability of Pd@Fe3O4 has been conducted.

Chemoselective Heterogeneous Hydrogenation of Sulfur Containing Quinolines under Mild Conditions

Sulfur, alongside oxygen and nitrogen, holds a prominent position as one of the key heteroatoms in nature and medicinal chemistry. Its significance stems from its ability to adopt different oxidation states, rendering it valuable as both a polarity handle and a hydrogen bond donor/acceptor. Nevertheless, the poisonous nature of its free electron pairs makes sulfur containing substrates inaccessible for many catalytic protocols. Strong and (at low temperatures) irreversible chemisorption to the catalyst's surface is in particular detrimental for heterogeneous catalysts, possessing only few catalytically active sites. Herein, we present a novel heterogeneous Ru-S catalyst that tolerates multiple sulfur functionalities, including thioethers, thiophenes, sulfoxides, sulfones, sulfonamides, and sulfoximines, in the hydrogenation of quinolines. The utility of the products was further demonstrated by subsequent diversifications of the sulfur functionalities.

Transfer Hydrogenation of N- and O-Containing Heterocycles Including Pyridines with H3N-BH3 Under the Catalysis of the Homogeneous Ruthenium Precatalyst

In this study, we report a transfer hydrogenation protocol that utilizes borane-ammonia (H3N-BH3) as the hydrogen source and a commercially available RuCl3·xH2O precatalyst for the selective aromatic reduction of quinolines, quinoxalines, pyridines, pyrazines, indoles, benzofurans, and furan derivatives to form the corresponding alicyclic heterocycles in good to excellent isolated yields. Applications of this straightforward protocol include the efficient preparation of useful key pharmaceutical intermediates, such as donepezil and flumequine, including a biologically active compound.

Colloidal ruthenium catalysts for selective quinaldine hydrogenation: Ligand and solvent effects

Colloidal Ru nanoparticles (NP) display interesting catalytic properties for the hydrogenation of (hetero)arenes as they proceed efficiently in mild reaction conditions. In this work, a series of Ru based materials was used in order to selectively hydrogenate quinaldine and assess the impact of the stabilizing agent on their catalytic performances. Ru nanoparticles stabilized with polyvinylpyrrolidone (PVP) and 1-adamantanecarboxylic acid (AdCOOH) allowed to obtain 5,6,7,8-tetrahydroquinaldine with a remarkable selectivity in mild reaction conditions by choosing the suitable solvent. The presence of a carboxylate ligand on the surface of the Ru NP led to an increase in the activity when compared to Ru/PVP catalyst. The stabilizing agent had also an impact on the selectivity, as carboxylate ligand modified catalysts promoted the selectivity towards 1,2,3,4-tetrahydroquinaldine, with bulky carboxylate displaying the highest ones.

Adaptive Catalysts for the Selective Hydrogenation of Bicyclic Heteroaromatics using Ruthenium Nanoparticles on a CO2 -Responsive Support

Ruthenium nanoparticles (NPs) immobilized on an amine-functionalized polymer-grafted silica support act as adaptive catalysts for the hydrogenation of bicyclic heteroaromatics. Whereas full hydrogenation of benzofuran and quinoline derivatives is achieved under pure H2 , introducing CO2 into the H2 gas phase leads to an effective shutdown of the arene hydrogenation while preserving the activity for the hydrogenation of the heteroaromatic part. The selectivity switch originates from the generation of ammonium formate species on the surface of the materials by catalytic hydrogenation of CO2 . The CO2 hydrogenation is fully reversible, resulting in a robust and rapid switch between the two states of the catalyst adapting its performance in response to the feed gas composition. A variety of benzofuran and quinoline derivatives were hydrogenated to fully or partially saturated products in high selectivity and yields simply by altering the composition of the feed gas from H2 to H2 /CO2 . The adaptive catalytic system thus provides controlled access to valuable products using a single catalyst rather than two specific and distinct catalysts with static reactivity.

Diastereoselective construction of carbo-bridged polyheterocycles by a three-component tandem annulation reaction

By a hydroamination-induced tandem annulation process, we herein report a new three-component reaction for room temperature construction of carbo-bridged polyheterocycles with exclusive diastereoselectivity, which features readily available feedstocks, catalyst-free conditions, good substrate and functionality compatibility, no need for transition metal catalysts, and high step and atom efficiency. The products are formed via initial formation of 1,2-dihydro-3H-pyrazol-3-one nucleophiles from but-2-ynedioates and hydrazine followed by 2,4-difunctionalization of N-heteroarenium salts. Given that the obtained products possess structurally important tetrahydroquinoline and pyranopyrazole motifs, the developed chemistry is anticipated to be further applied to the discovery of functional molecules including biomedical ones.

An Atomically Dispersed Mn-Photocatalyst for Generating Hydrogen Peroxide from Seawater via the Water Oxidation Reaction (WOR)

In this work, we have fabricated an aryl amino-substituted graphitic carbon nitride (g-C₃N₄) catalyst with atomically dispersed Mn capable of generating hydrogen peroxide (H₂O₂) directly from seawater. This new catalyst exhibited excellent reactivity, obtaining up to 2230 μM H₂O₂ in 7 h from alkaline water and up to 1800 μM from seawater under identical conditions. More importantly, the catalyst was quickly recovered for subsequent reuse without appreciable loss in performance. Interestingly, unlike the usual two-electron oxygen reduction reaction pathway, the generation of H₂O₂ was through a less common two-electron water oxidation reaction (WOR) process in which both the direct and indirect WOR processes occurred; namely, photoinduced h⁺ directly oxidized H₂O to H₂O₂ via a one-step 2e^- WOR, and photoinduced h⁺ first oxidized a hydroxide (OH^-) ion to generate a hydroxy radical (^•OH), and H₂O₂ was formed indirectly by the combination of two ^•OH. We have characterized the material, at the catalytic sites, at the atomic level using electron paramagnetic resonance, X-ray absorption near edge structure, extended X-ray absorption fine structure, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, magic-angle spinning solid-state NMR spectroscopy, and multiscale molecular modeling, combining classical reactive molecular dynamics simulations and quantum chemistry calculations.

Transition Metal-Doped C20 Fullerene-Based Single-Atom Catalysts with High Catalytic Activity for Hydrogen Dissociation Reaction

Hydrogen dissociation is a key step in almost all hydrogenation reactions; therefore, an efficient and cost-effective catalyst with a favorable band structure for this step is highly desirable. In the current work, transition metal-based C₂₀ (M@C₂₀) complexes are designed and evaluated as single-atom catalysts (SACs) for hydrogen dissociation reaction (HDR). Interaction energy (E _int) analysis reveals that all the M@C₂₀ complexes are thermodynamically stable, whereas the highest stability is observed for the Ni@C₂₀ complex (E _int = -6.14 eV). Moreover, the best catalytic performance for H₂ dissociation reaction is computed for the Zn@C₂₀ catalyst (E _ads = 0.53 eV) followed by Ti@C₂₀ (E _ads = 0.65 eV) and Sc@C₂₀ (E _ads = 0.76 eV) among all considered catalysts. QTAIM analyses reveal covalent or shared shell interactions in H₂* + M@C₂₀ systems, which promote the process of H₂ dissociation over M@C₂₀ complexes. NBO and EDD analyses declare that transfer of charge from the metal atom to the antibonding orbital of H₂ causes dissociation of the H-H bond. Overall outcomes of this study reveal that the Zn@C₂₀ catalyst can act as a highly efficient, low-cost, abundant, and precious metal-free SAC to effectively catalyze HDR.

Designing New Magnesium Pincer Complexes for Catalytic Hydrogenation of Imines and N-Heteroarenes: H2 and N-H Activation by Metal-Ligand Cooperation as Key Steps

Utilization of main-group metals as alternatives to transition metals in homogeneous catalysis has become a hot research area in recent years. However, their application in catalytic hydrogenation is less common due to the difficulty in heterolytic cleavage of the H-H bond. Employing aromatization/de-aromatization metal-ligand cooperation (MLC) highly enhances the H₂ activation process, offering an efficient approach for the hydrogenation of unsaturated molecules catalyzed by main-group metals. Herein, we report a series of new magnesium pincer complexes prepared using PNNH-type pincer ligands. The complexes were characterized by NMR and X-ray single-crystal diffraction. Reversible activation of H₂ and N-H bonds by MLC employing these pincer complexes was developed. Using the new magnesium complexes, homogeneously catalyzed hydrogenation of aldimines and ketimines was achieved, affording secondary amines in excellent yields. Control experiments and DFT studies reveal that a pathway involving MLC is favorable for the hydrogenation reactions. Moreover, the efficient catalysis was extended to the selective hydrogenation of quinolines and other N-heteroarenes, presenting the first example of hydrogenation of N-heteroarenes homogeneously catalyzed by early main-group metal complexes. This study provides a new strategy for hydrogenation of C═N bonds catalyzed by magnesium compounds and enriches the research of main-group metal catalysis.

Hydrogen Dissociation Reaction on First-Row Transition Metal Doped Nanobelts

Zigzag molecular nanobelts have recently captured the interest of scientists because of their appealing aesthetic structures, intriguing chemical reactivities, and tantalizing features. In the current study, first-row transition metals supported on an H₆-N₃-belt[6]arene nanobelt are investigated for the electrocatalytic properties of these complexes for the hydrogen dissociation reaction (HDR). The interaction of the doped transition metal atom with the nanobelt is evaluated through interaction energy analysis, which reveals the significant thermodynamic stability of TM-doped nanobelt complexes. Electronic properties such as frontier molecular orbitals and natural bond orbitals analyses are also computed, to estimate the electronic perturbation upon doping. The highest reduction in the HOMO-LUMO energy gap compared to the bare nanobelt is seen in the case of the Zn@NB catalyst (4.76 eV). Furthermore, for the HDR reaction, the Sc@NB catalyst displays the best catalytic activity among the studied catalysts, with a hydrogen dissociation barrier of 0.13 eV, whereas the second-best catalytic activity is observed for the Zn@NB catalyst (0.36 eV). It is further found that multiple active sites, i.e., the presence of the metal atom and nitrogen atom moiety, help to facilitate the dissociation of the hydrogen molecule. These key findings of this study enhance the understanding of the relative stability, electronic features, and catalytic bindings of various TM@NB catalysts.

cis-Selective Hydrogenation of Aryl Germanes: A Direct Approach to Access Saturated Carbo- and Heterocyclic Germanes

A catalytic approach of synthesizing the cis-selective saturated carbo- and heterocyclic germanium compounds (3D framework) is reported via the hydrogenation of readily accessible aromatic germanes (2D framework). Among the numerous catalysts tested, Nishimura's catalyst (Rh2O3/PtO2·H2O) exhibited the best hydrogenation reactivity with an isolated yield of up to 96%. A broad range of substrates including the synthesis of unprecedented saturated heterocyclic germanes was explored. This selective hydrogenation strategy could tolerate several functional groups such as -CF3, -OR, -F, -Bpin, and -SiR3 groups. The synthesized products demonstrated the applications in coupling reactions including the newly developed strategy of aza-Giese-type addition reaction (C-N bond formation) from the saturated cyclic germane product. These versatile motifs can have a substantial value in organic synthesis and medicinal chemistry as they show orthogonal reactivity in coupling reactions while competing with other coupling partners such as boranes or silanes, acquiring a three-dimensional structure with high stability and robustness.

Manganese-Catalyzed Hydrogenative Desulfurization of Thioamides

Earth-abundant transition metal catalysis has emerged as an important alternative to noble transition metal catalysis in hydrogenation reactions. However, there has been no Earth-abundant transition metal catalyzed hydrogenation of thioamides reported so far, presumably due to the poisoning of catalysts by sulfur-containing molecules. Herein, we described the first manganese-catalyzed hydrogenative desulfurization of thioamides to amines or imines. The key to success is the use of MnBr(CO)₅ instead of commonly-employed pincer-manganese catalysts, together with simple NEt₃ and CuBr. This protocol features excellent selectivity on sole cleavage of the C=S bond of thioamides, in contrast to the only known Ru-catalyzed hydrogenation of thioamides, and unprecedented chemo-selectivity tolerating vulnerable functional groups such as nitrile, ketone, aldehyde, ester, sulfone, nitro, olefin, alkyne and heterocycle, which are usually susceptible to common hydride-type reductive protocols.

Screening of Palladium/Charcoal Catalysts for Hydrogenation of Diene Carboxylates with Isolated-Rings (Hetero)aliphatic Scaffold

A series of seven palladium-containing composites, i.e., four Pd/C and three Pd(OH)₂/C (Pearlman's catalysts), was prepared using modified common approaches to deposition of Pd or hydrated PdO on charcoal. All the composites were tested in the catalytic hydrogenation of diene carboxylates with the isolated-ring scaffold, e.g., 5,6-dihydropyridine-1(2H)-carboxylates with 2-(alkoxycarbonyl)cyclopent-1-en-1-yl and hex-1-en-1-yl substituents at the C(4)-position. The performance of the composites was also studied via the hydrogenation of quinoline as a model reaction. The composites were characterized by transmission and scanning electron microscopy (TEM and SEM), powder X-ray diffraction, and low-temperature N₂ adsorption. It was found that the composites containing Pd nanoparticles (NPs) of 5-40 nm size were the most efficient catalysts for the hydrogenation of dienes, providing the reduced products with up to 90% yields at p(H₂) = 100 atm, T = 30 °C for 24 h. The method of Pd NPs formation had more effect on the catalyst performance than the size of the NPs. The catalytic performance of Pearlman's catalysts (Pd(OH)₂/C) in the hydrogenation of dienes was comparable to or lower than the performance of the Pd/C systems, though the Pearlman's catalysts were more efficient in the hydrogenation of quinoline.

Efficient Hydrogenation of N-Heterocycles Catalyzed by NNP-Manganese(I) Pincer Complexes at Ambient Temperature

Manganese-catalyzed hydrogenation reactions have aroused widespread interest in recent years. Among the catalytic systems described, especially PNP- and NNP-Mn pincer catalysts have been reported for the hydrogenation of aldehydes, ketones, nitriles, aldimines and esters. Furthermore, NNP-Mn pincer compounds are efficient catalysts for the hydrogenolysis of less reactive amides, ureas, carbonates, and carbamates. Herein, the synthesis and application of specific imidazolylaminophosphine ligands and the corresponding Mn pincer complexes are described. These new catalysts have been characterized and studied by a combination of experimental and theoretical investigations, and their catalytic activities have been tested in several hydrogenation reactions with good to excellent performance. Especially, the reduction of N-heterocycles can be performed under very mild conditions.

Remarkable Single Atom Catalyst of Transition Metal (Fe, Co & Ni) Doped on C2N Surface for Hydrogen Dissociation Reaction

Currently, hydrogen is recognized as the best alternative for fossil fuels because of its sustainable nature and environmentally friendly processing. In this study, hydrogen dissociation reaction is studied theoretically on the transition metal doped carbon nitride (C₂N) surface through single atom catalysis. Each TMs@C₂N complex is evaluated to obtain the most stable spin state for catalytic reaction. In addition, electronic properties (natural bond orbital NBO & frontier molecular orbital FMO) of the most stable spin state complex are further explored. During dissociation, hydrogen is primarily adsorbed on metal doped C₂N surface and then dissociated heterolytically between metal and nitrogen atom of C₂N surface. Results revealed that theFe@C₂N surface is the most suitable catalyst for H₂ dissociation reaction with activation barrier of 0.36 eV compared with Ni@C₂N (0.40 eV) and Co@C₂N (0.45 eV) complexes. The activation barrier for H₂ dissociation reaction is quite low in case of Fe@C₂N surface, which is comparatively better than already reported noble metal catalysts.

Core-Shell Nano-Cobalt Catalyzed Chemoselective Reduction of N-Heteroarenes with Ammonia Borane

An easily prepared core-shell heterogeneous nanocobalt catalyst was reported, which could achieve selective reduction of N-heteroarenes with ammonia borane under mild conditions and ambient atmosphere. Various quinoline, quinoxaline, naphthyridine, isoquinoline, acridine, and phenanthroline derivatives were hydrogenated with high selectivity and efficiency. Notably, substrates bearing sensitive functional groups under molecular hydrogen reduction conditions, such as cyano, ester, and halogens were well tolerated by the catalytic system. Moreover, with our novel method several bioactive molecules were prepared. Also, this catalyst could be applied in the liquid organic hydrogen storage system by reversible hydrogenation and dehydrogenation of heteroarene in high efficiencies.

Electrocatalytic hydrogenation of quinolines with water over a fluorine-modified cobalt catalyst

Room temperature and selective hydrogenation of quinolines to 1,2,3,4-tetrahydroquinolines using a safe and clean hydrogen donor catalyzed by cost-effective materials is significant yet challenging because of the difficult activation of quinolines and H₂. Here, a fluorine-modified cobalt catalyst is synthesized via electroreduction of a Co(OH)F precursor that exhibits high activity for electrocatalytic hydrogenation of quinolines by using H₂O as the hydrogen source to produce 1,2,3,4-tetrahydroquinolines with up to 99% selectivity and 94% isolated yield under ambient conditions. Fluorine surface-sites are shown to enhance the adsorption of quinolines and promote water activation to produce active atomic hydrogen (H*) by forming F⁻-K⁺(H₂O)₇ networks. A 1,4/2,3-addition pathway involving H* is proposed through combining experimental and theoretical results. Wide substrate scopes, scalable synthesis of bioactive precursors, facile preparation of deuterated analogues, and the paired synthesis of 1,2,3,4-tetrahydroquinoline and industrially important adiponitrile at a low voltage highlight the promising applications of this methodology.

Selective hydrogenation of quinolines with easy-to-handle hydrogen donors and cost-effective catalysts is desirable. Here electrocatalytic quinoline hydrogenation to 1,2,3,4-tetrahydroquinolines is reported with water over a fluorine-modified cobalt.

Access to Unexplored 3D Chemical Space: cis ‐Selective Arene Hydrogenation for the Synthesis of Saturated Cyclic Boronic Acids

A new class of saturated boron‐incorporated cyclic molecules has been synthesized employing an arene‐hydrogenation methodology. cis‐Selective hydrogenation of easily accessible, and biologically important molecules comprising benzoxaborole, benzoxaborinin, and benzoxaboripin derivatives is reported. Among the various catalysts tested, rhodium cyclic(alkyl)(amino)carbene [Rh‐CAAC] (1) pre‐catalyst revealed the best hydrogenation activity confirming turnover number up to 1400 with good to high diastereoselectivity. A broad range of functional groups was tolerated including sensitive substituents such as −F, −CF₃, and −silyl groups. The utility of the synthesized products was demonstrated by the recognition of diols and sugars under physiological conditions. These motifs can have a substantial importance in medicinal chemistry as they possess a three‐dimensional structure, are highly stable, soluble in water, form hydrogen bonds, and interact with diols and sugars.

Obstructed Surface States as the Descriptor for Predicting Catalytic Active Sites in Inorganic Crystalline Materials

The discovery of new catalysts that are efficient and sustainable is a major research endeavor for many industrial chemical processes. This requires an understanding and determination of the catalytic origins, which remains a challenge. Here, a novel method to identify the position of active sites based on searching for crystalline symmetry-protected obstructed atomic insulators (OAIs) that have metallic surface states is described. The obstructed Wannier charge centers (OWCCs) in OAIs are pinned by symmetries at some empty Wyckoff positions so that surfaces that accommodate these sites are guaranteed to have metallic obstructed surface states (OSSs). It is proposed and confirmed that the OSSs are the catalytic activity origins for crystalline materials. The theory on 2H-MoTe₂ , 1T'-MoTe₂ , and NiPS₃ bulk single crystals is verified, whose active sites are consistent with the calculations. Most importantly, several high-efficiency catalysts are successfully identified just by considering the number of OWCCs and the symmetry. Using the real-space-invariant theory applied to a database of 34 013 topologically trivial insulators, 1788 unique OAIs are identified, of which 465 are potential high-performance catalysts. The new methodology will facilitate and accelerate the discovery of new catalysts for a wide range of heterogeneous redox reactions.

Manganese-Catalyzed Asymmetric Formal Hydroamination of Allylic Alcohols: A Remarkable Macrocyclic Ligand Effect

A unique family of chiral peraza N₆ -macrocyclic ligands, which are conformationally rigid and have a tunable saddle-shaped cavity, is described. Utilizing their manganese(I) complexes, the first example of earth-abundant transition metal-catalyzed asymmetric formal anti-Markovnikov hydroamination of allylic alcohols was realized, providing a practical access to synthetically important chiral γ-amino alcohols in excellent yields and enantioselectivities (up to 99 % yield and 98 % ee). The single-crystal structure of a Mn^I complex indicates that the manganese atom coordinates with the chiral dialkylamine moiety in a bidentate fashion. Further DFT calculations revealed that five of the six nitrogen atoms in the ligand were engaged in multiple noncovalent interactions with Mn, an isopropanol molecule, and a β-amino ketone intermediate via coordination, hydrogen bonding, and/or CH⋅⋅⋅π interactions in the transition state, showing a remarkable role of the macrocyclic framework.

Manganese-catalyzed hydrogenation, dehydrogenation, and hydroelementation reactions

The emerging field of organometallic catalysis has shifted towards research on Earth-abundant transition metals due to their ready availability, economic advantage, and novel properties. In this case, manganese, the third most abundant transition-metal in the Earth's crust, has emerged as one of the leading competitors. Accordingly, a large number of molecularly-defined Mn-complexes has been synthesized and employed for hydrogenation, dehydrogenation, and hydroelementation reactions. In this regard, catalyst design is based on three pillars, namely, metal-ligand bifunctionality, ligand hemilability, and redox activity. Indeed, the developed catalysts not only differ in the number of chelating atoms they possess but also their working principles, thereby leading to different turnover numbers for product molecules. Hence, the critical assessment of molecularly defined manganese catalysts in terms of chelating atoms, reaction conditions, mechanistic pathway, and product turnover number is significant. Herein, we analyze manganese complexes for their catalytic activity, versatility to allow multiple transformations and their routes to convert substrates to target molecules. This article will also be helpful to get significant insight into ligand design, thereby aiding catalysis design.

Basic Promotors Impact Thermodynamics and Catalyst Speciation in Homogeneous Carbonyl Hydrogenation

Homogeneously catalyzed reactions often make use of additives and promotors that affect reactivity patterns and improve catalytic performance. While the role of reaction promotors is often discussed in view of their chemical reactivity, we demonstrate that they can be involved in catalysis indirectly. In particular, we demonstrate that promotors can adjust the thermodynamics of key transformations in homogeneous hydrogenation catalysis and enable reactions that would be unfavorable otherwise. We identified this phenomenon in a set of well-established and new Mn pincer catalysts that suffer from persistent product inhibition in ester hydrogenation. Although alkoxide base additives do not directly participate in inhibitory transformations, they can affect the equilibrium constants of these processes. Experimentally, we confirm that by varying the base promotor concentration one can control catalyst speciation and inflict substantial changes to the standard free energies of the key steps in the catalytic cycle. Despite the fact that the latter are universally assumed to be constant, we demonstrate that reaction thermodynamics and catalyst state are subject to external control. These results suggest that reaction promotors can be viewed as an integral component of the reaction medium, on its own capable of improving the catalytic performance and reshaping the seemingly rigid thermodynamic landscape of the catalytic transformation.

The Rise of Manganese-Catalyzed Reduction Reactions

Recent developments in manganese-catalyzed reducing transformations—hydrosilylation, hydroboration, hydrogenation, and transfer hydrogenation—are reviewed herein. Over the past half a decade (i.e., 2016 to the present), more than 115 research publications have been reported in these fields. Novel organometallic compounds and new reduction transformations have been discovered and further developed. Significant challenges that had historically acted as barriers for the use of manganese catalysts in reduction reactions are slowly being broken down. This review will hopefully assist in developing this research area, by presenting a clear and concise overview of the catalyst structures and substrate transformations published so far.

1 Introduction

2 Hydrosilylation

3 Hydroboration

4 Hydrogenation

5 Transfer Hydrogenation

6 Conclusion and Perspective

Electrocatalyst decomposition pathways: torsional strain in a second sphere proton relay shuts off CO2RR in a Re(2,2′-bipyridyl)(CO)3X type electrocatalyst

Group 7 tris(carbonyl) bipyridine complexes have been well explored as important CO2 reduction reaction (CO2RR) electrocatalysts and now represent an excellent platform for catalyst design.

Manganese-catalyzed transfer semihydrogenation of internal alkynes to E-alkenes with iPrOH as hydrogen source

The Mn-catalyzed transfer semihydrogenation of internal alkynes to E-alkenes is reported herein, along with Mn-catalyzed hydration of α-keto alkynes. Mechanistic studies displayed an asymmetrical Mn-hydride species performing the catalytic turnover.