Hydrogen Transfer Research Articles

Tracking the coupling conversion of C1-C4 aldehydes with methanol-to-hydrocarbon reaction

Small-molecule aldehydes are promising additives to regulate product distribution in methanol-to-hydrocarbon (MTH) reaction. Herein, the co-feeding of C1-C4 aldehydes with methanol resulted in a significant increase in aromatic formation with the order: acetaldehyde > formaldehyde > propanal ≈ butanal. The mechanistic basis for this enhancement in aromatic production derived from both a direct participation pathway of aldehydes and an indirect pathway via driving the aromatic-based cycle. C2+ aldehydes could undergo multiple aldol-condensation on Brønsted acid sites to form larger alkenals, followed by sequential cyclization-dehydration reaction to cycloalkenes or aromatic species. The Prins reaction could be extended to all C1-C4 aldehydes with alkenes by generating the corresponding dienes. The hydrogen transfer from methanol to C2+ aldehydes produced C2+ olefins and formaldehyde, which would lead to extra formaldehyde-mediated aromatic formation pathway. The intricate evolution pathway of C1-C4 aldehydes in MTH reaction was constructed by detecting abundant oxygenate and hydrocarbon intermediates.

Identity of the Silyl Ligand in an Iron Silyl Complex Influences Olefin Hydrogenation: An Experimental and Computational Study.

In this study, we explore the selective synthesis of iron silyl complexes using the reaction of an iron mesityl complex (MesCCC)FeMes(Py) with various hydrosilanes. These resulting iron silyl complexes, (MesCCC)Fe(SiH2Ph)(Py)(N2), (MesCCC)Fe(SiMe2Ph)(Py)(N2), and (MesCCC)Fe[SiMe(OSiMe3)2](Py)(N2), serve as effective precatalysts for olefin hydrogenation. The key to their efficiency in catalysis lies in the specific nature of the silyl ligand attached to the iron center. Experimental observations, supported by density functional theory (DFT) simulations, reveal that the catalytic performance correlates with the relative stability of dihydrogen and hydride species associated with each iron silyl complex. The stability of these intermediates is crucial for efficient hydrogen transfer during the catalytic cycle. The DFT simulations help to quantify these stability factors, showing a direct relationship between the silyl ligand's electronic and steric properties and the overall catalytic activity. Complexes with certain silyl ligands exhibit better performance due to the optimal balance between the stability and reactivity of the key active catalyst. This work highlights the importance of ligand design in the development of iron-based hydrogenation catalysts.

Electrochemical Dimerization of o-Aminophenols and Hydrogen Borrowing-like Cascade to Synthesize N-Monoalkylated Aminophenoxazinones via Paired Electrolysis.

A novel electrocatalytic dimerization of o-aminphenols and a hydrogen borrowing-like cascade for synthesizing N-monoalkylated aminophenoxazinones have been developed. This electrocatalytic reaction uses a constant current mode in an undivided cell and is free of metal catalysis, open to the air, and eco-friendly. In particular, this protocol exhibits a wide substrate range and provides versatile N-monoalkylated aminophenoxazinones in medium to good yields. The results of our mechanistic research reveal that this protocol involves a cascade of electrochemical cyclocondensation of o-aminphenols and the hydrogen transfer process via paired electrolysis.

Optimization and reaction kinetics of catalytic transfer hydrogenation of 5‐hydroxymethylfurfural to 2, 5‐dimethylfuran over CuCoOx catalysts

Optimization and reaction kinetics of catalytic transfer hydrogenation of 5‐hydroxymethylfurfural to 2, 5‐dimethylfuran over CuCoOx catalysts

Efficient hydrogen transfer carriers: hydrogenation mechanism of dibenzyltoluene catalyzed by Mg-based metal hydride

Efficient hydrogen transfer carriers: hydrogenation mechanism of dibenzyltoluene catalyzed by Mg-based metal hydride

Pressure-induced generation of heterogeneous electrocatalytic metal hydride surfaces for sustainable hydrogen transfer

Metal hydrides are crucial intermediates in numerous catalytic reactions. Intensive efforts have been dedicated to constructing molecular metal hydrides, where toxic precursors and delicate mediators are usually involved. Herein, we demonstrate a facile pressure-induced methodology to generate a cost-effective heterogeneous electrocatalytic metal hydride surface for sustainable hydrogen transfer. Taking carbon dioxide (CO2) electroreduction as a model system and zinc (Zn), a well-known carbon monoxide (CO)-selective catalyst, as a model catalyst, we showcase a homogeneous-type hydrogen atom transfer process induced by heterogeneous hydride surfaces, enabling direct hydrogenation pathways traditionally considered “prohibited”. Specifically, the maximal Faradaic efficiency for formate is enhanced by ~fivefold to 83% under ambient conditions. Experimental and theoretical analyses reveal that unlike the distal hydrogenation route for CO2 to CO over pristine Zn, the Zn hydride surface enables direct hydrogenation at the carbon site of CO2 to form formate. This work provides a promising material platform for sustainable synthesis.

Emergence of meta-methylbenzyl alcohol in novel pathway of ethanol with methacrolein catalyzed by hydroxyapatite

Bioethanol, a renewable resource, can be converted into high value-added chemicals. Methylbenzyl alcohol in its ortho- and para-isomers has been successfully synthesized from ethanol upgrading over metal-modified hydroxyapatite (HAP). However, meta-methylbenzyl alcohol (3-MB-OH), a particularly valuable fine chemical, has yet to be produced from ethanol. Herein, we present a novel reaction pathway for the selective synthesis of 3-MB-OH over HAP by co-feeding ethanol with methacrolein. Notably, the selectivity of 3-MB-OH reached up to 36.2 % in our tests. Experiments using intermediates as reactants proved that the introduction of methacrolein definitively led to the production of 3-MB-OH, which was also confirmed by in-situ diffuse reflectance infrared Fourier-transform spectroscopy. Moreover, we inferred the co-conversion reaction pathway of ethanol and methacrolein. Density functional theory calculations indicated that ethanol preferentially underwent Meerwein-Ponndorf-Verley hydrogen transfer with methacrolein, resulting in acetaldehyde formation and subsequently promoting the synthesis of aromatic compounds.

Tuning the Electronic Properties of Azophosphines as Ligands and Their Application in Base-Free Transfer Hydrogenation Catalysis.

The design and tuning of new ligands is crucial for unlocking new reactivity at transition metal centers. Azophosphines have recently emerged as a new class of 1,3-P,N ligands in ruthenium piano-stool complexes. This work shows that the azophosphine synthesis can tolerate N-aryl substituents with strongly electron-donating and electron-withdrawing para-R groups and that the nature of this R group can affect the spectroscopic and structural properties of the azophosphines, as measured by NMR spectroscopy, UV-vis spectroscopy, single-crystal X-ray diffraction, and DFT studies. Azophosphines are shown to be relatively weak phosphine donors, as shown by analysis of the 1 J P-Se coupling constants of the corresponding azophosphine selenides, but the donor properties can be fine tuned within this area of chemical space. Monodentate and bidentate Ru-azophosphine complexes were prepared, and their first use as a catalyst was probed. The Ru-azophosphine complexes were found to promote the transfer hydrogenation of acetophenone to 1-phenylethanol without the requirement of a harsh base additive, and the bidentate complex was more active than the monodentate analogue.

Asymmetric Transfer Hydrogenation of Ketones Improved by PNN-Manganese Complexes.

Chiral manganese(I) complexes that contain carbocyclic-fused 8-amino-5,6,7,8-tetrahydroquinolinyl groups that are appended with distinct para-R substituents have proven to be effective catalysts in the asymmetric transfer hydrogenation (ATH) of a wide range of ketones (48 examples). Notably, Mn2 proved to be the most productive catalyst, allowing an outstanding turnover number of 8300 with catalyst loadings as low as 0.01 mol %. Furthermore, this catalytic protocol shows considerable promise for applications in the synthesis of chiral drugs such as Lusutrombopag.

Iron-Catalyzed Chemoselective Transfer Hydrogenation of α,β-Unsaturated Ketones Using H2O as a Surrogate of Hydrogen.

Sustainable and highly economical iron-catalyzed chemoselective reduction of C═C of α,β-unsaturated ketones has been established under mild reaction protocols. Water is used as a green and abundant surrogate of hydrogen and is scarcely used in organic synthetic transformations as a source of hydrogen. The developed protocol offers a broad spectrum for chemoselective transfer hydrogenation of α,β-unsaturated ketones. Moreover, the method was found to be highly effective for aryl and ferrocenyl α,β-unsaturated ketones consisting of one or two double bonds and with multiple functionalities. Moreover, the present method avoids prolonged reaction time, provides a wide range of substrates with excellent yield, and circumvents the tedious chromatographic workup.

Efficient cascade reactions involving esterification, hydrogen transfer, and lactonization for biomass conversion using MOF/Metal oxide composites as heterogeneous catalysts

Development of heterogeneous catalysts with both Brønsted and Lewis acid properties has proved to be promising and useful because they offer an efficient way to cascade reactions. In this study, we present the synthesis pathway and efficacy evaluation of new composites which combined by sulfonic acid functional group modified TiO2 and MIL-101, analyzing their structure-performance correlation as heterogeneous catalysts in cascade reactions involving esterification, hydrogen transfer, and lactonization. These composites possess an open porous structure (MOF and porous TiO2), as well as active sites including Lewis acid (unsaturated coordination metal), Lewis base (Ti-OH), and Brønsted acid (-SO3H). The role of these active sites and the synergies between them were investigated through the esterification of levulinic acid and the direct synthesis of γ-valerolactone from levulinic acid and furfural under cascade reactions. The composites exhibit a 100% ethyl levulinate (EL) yield at 120°C for 6 hours, with γ-valerolactone yields reaching up to 94.5% (160 °C, 9 h) and 89.5% (160 °C, 16 h) from levulinic acid and furfural, respectively. This synergistic effect of Lewis acid/base and Brønsted acid ensures efficient esterification. The presence of a sulfonic acid group promotes the lactonization reaction, while the Meerwein-Ponndorf-Verley reduction is facilitated by the dual Cr sites located adjacent to each other in the secondary building unit of MIL-101(Cr). Moreover, the double-porous structure of porous TiO2 and MIL-101(Cr) effectively guarantees the efficient mass transfer of reactants and intermediates, leading to enhanced synergistic effects that promote more efficient reaction conversion.

Single-Atom Co-N4 Sites Mediate C=N Formation via Reductive Coupling of Nitroarenes with Alcohols.

It remains challenging to construct C=N bonds due to their facile hydrogenation. Herein, a single Co atom catalyst was discovered to be active for the selective construction of C=N bonds toward the synthesis of imines and N-heterocycles via reductive coupling of nitroarenes with various alcohols, including inert aliphatic ones. DFT calculations and experimental data revealed that the transfer hydrogenation proceeded via the intramolecular hydride transfer and the transfer of H from the α-Csp3-H bond to the nitro group was the rate-determining step. The single Co atoms served as a bridge to transfer the electrons from the catalyst to the adsorbed alcohol molecules, resulting in the activation of the α-Csp3-H bond. Unlike metal nanoparticles, the C=N bonds in imine products can be reserved due to the large steric hindrance from substituents on C and N. DFT calculation also confirmed that transfer hydrogenation of the C=N bonds in imines is thermodynamically unfavored with a much higher energy barrier compared with the transfer hydrogenation of the -NO2 group (1.47 vs 1.15 eV).

Asymmetric 1,4-Reduction of Pyrano[2,3-b]indoles with Hantzsch Ester by Chiral Phosphoric Acid.

A highly regioselective and enantioselective transfer hydrogenation of pyrano[2,3-b]indoles with Hantzsch ester has been successfully realized using spiro-chiral phosphoric acid, affording a series of optically active 1,4-reductive adducts, 4,9-dihydropyrano[2,3-b]indoles, in 34-99% yields with 61-99% ee.

Dynamics of spontaneous mutations: implications of guanine–cytosine tautomers on chromatin integrity

This study investigates the origin and implications of spontaneous mutations within DNA, focusing on the dynamics of guanine–cytosine (GC) base pairs. We propose inter – and intramolecular hydrogen transfer as potential mechanisms for the formation of rare tautomers, which can significantly impact the structural conformity and operational integrity of chromatin. The nitrogenous bases in DNA are pivotal for genetic coding and protein synthesis, while chromatin plays a fundamental role in DNA compaction, organisation, gene expression control and genome integrity preservation. Our research identifies 56 previously unrecorded guanine–cytosine tautomers and explores diverse potential energy levels, leading to the discovery of 67 transition states across pathways. These transitions involve five distinct types of hydrogen transfer: N-H→N, N-H→O, N-H→C, C–H→N and O-H→N. Utilising an innovative approach, we establish a Markov chain to assess the probability of molecular production from the same source, unveiling insights into transitional dynamics. Furthermore, our study facilitates the identification of tautomers capable of swift conversion to the GC1 base pair, which is dependent on transition states and molecular pathways. Our findings contribute to a deeper understanding of spontaneous mutations and their impact on chromatin integrity, offering valuable insights for further research in this field.

Methanol-Mediated Hydrogen Transfer Reactions at Surface Lewis Acid Sites of H-SSZ-13

Methanol-Mediated Hydrogen Transfer Reactions at Surface Lewis Acid Sites of H-SSZ-13

Ir-Catalyzed Selective Reductive N-Formylation and Transfer Hydrogenation of N-Heteroarenes

Ir-Catalyzed Selective Reductive N-Formylation and Transfer Hydrogenation of N-Heteroarenes

Design, Synthesis and Evaluation of Photophysical and Biological Properties of Tetrafluoroacridine

Abstract1,4,5,8‐Tetrafluoroacridine was successfully synthesized from 1,4,5,8‐tetrafluoroacridone through transfer hydrogenation using an in‐house ruthenium pincer catalyst followed by in situ dehydration. The synthetic protocol involves the copper‐catalyzed coupling of 2‐amino‐3,6‐difluorobenzoic acid 1 and 1,4‐difluoro‐2‐iodobenzene 2 to obtain 3 followed by cyclization using polyphosphoric acid to get the 1,4,5,8‐tetrafluoroacridone 4. Common synthetic strategies for converting 4 to the 1,4,5,8‐tetrafluoroacridine 5 were unsuccessful and the transfer hydrogenation approach proved to be most fruitful. 1,4,5,8‐Tetrafluoroacridone 4 can be N‐methylated to give 9. The investigation into the photophysical properties of 4, 5, and 9 revealed that the average photoluminescence (PL) lifetime of the acridine derivatives was longer in the aqueous medium than in ethanol and methanol, indicating the influence of the solvent environment on the excited‐state dynamics. To assess their potential therapeutic applications, the cytotoxic activity of these compounds was evaluated against AGS and IMR‐32 cells, and compound 9 showed significant activity. The addition of methyl group to the acridone was found helpful in enhancing the solubility and biological activity.

Mn2(CO)10-catalyzed direct protic hydrogen transfer with unactivated alkenes

Transition-metal-catalyzed hydrogen-atom-transfer (HAT) reactions have proven to be effective strategies for obtaining important heterocycle scaffolds found in natural products. However, the electronic mismatch between metal catalysts and the protic hydrogen atom necessitates the use of excess oxidants and external reductive hydrogen sources in existing methods, which limit their practicality. To address this issue, we present a practical and efficient methodology for Mn₂(CO)₁₀-catalyzed intramolecular transfer of the protic hydrogen atom. A catalytic amount of tBuOOH is utilized promoting the HAT process, going beyond mere oxidation, thereby obviating the need for excess oxidants and external reductive hydrogen sources during the HAT process. Additionally, the dimeric manganese catalysis enables efficient dioxygenation, oxy-amination, oxy-sulfuration, and oxy-halogenation of alkenes. Comprehensive mechanistic studies have been done and suggest that a radical reaction pathway is involved in the proton transfer. This finding provides novel insights into the direct metal-catalyzed protic hydrogen atom-transfer reactions.

Isopropanol/Water Bi‐Solvent Enhanced the Catalytic Transfer Hydrogenation of Levulinic Acid to γ‐Valerolactone over Ru‐PC Catalyst

AbstractCatalytic transfer hydrogenation of levulinic acid (LA) to γ‐valerolactone (GVL) was attractive in biomass conversions since GVL is highly useful in different applications, such as polymer synthesis, fuel, and food. Various catalytic systems were reported for the reaction, yet harsh reaction conditions were generally required, which could restrict the scaling up of the reaction. Herein, we developed an effective and green bi‐solvent system of isopropanol/water for the catalytic transfer hydrogenation of LA to GVL over a ruthenium–phosphorous carbon (Ru‐PC) catalyst. It was found that the presence of water in the solvent system promoted the production of GVL from LA. The effect of isopropanol/water ratios and other reaction conditions were investigated, exhibiting that 93.8% yield of GVL was achieved using isopropanol/water ratio of 2.5:2.5 at 140 °C for 4 h and over Ru‐PC catalyst. Combining water and organic solvent not only reduced the usage of organic solvent but also created an effective bi‐solvent system for catalytic reactions.

Enantioselective Transfer Hydrogenation of α-Methoxyimino-β-keto Esters.

α-Methoxyimino-β-keto esters are reported to undergo highly enantioselective catalytic transfer hydrogenation using the Noyori-Ikariya complex RuCl(p-cymene)[(S,S)-Ts-DPEN] in a mixture of formic acid-triethylamine and dimethylformamide at 25 °C. The experimental study performed on over 25 substrates combined with computational analysis revealed that a Z-configured methoxyimino group positioned alpha to a ketone carbonyl leads to higher reactivity and mostly excellent enantioselectivity within this substrate class. Density functional theory calculations of competing transition states were used in rationalizing the origins of enantioselectivity and the possible role of the methoxyimino group in the reaction outcome.