Hydrogen Transfer Research Articles

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.

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.

Strategic integration of national grid or solar photovoltaic power with the on-site hydrogen vehicle refueling station at the hydrogen energy laboratory, BCSIR, Bangladesh

The country's first on-site hydrogen refueling station (HRS) is installed at the Hydrogen Energy Laboratory, Bangladesh Council of Scientific and Industrial Research (BCSIR), and its performance is studied to penetrate and prepare the hydrogen refueling network for the future. The study fills the power conditioning and integration information gap to HRS and refueling performances of on-site HRS in the particular conditions of the country. Strategic integration of grid power to the HRS is materialized and its adaptation with on-site HRS. Low-cost frequency & voltage conversion (conversion of 50 Hz, 420 V, or 220 V to stable 60 Hz, 220 V, or 110 V) and its stabilization are successfully made. An initial pressure of 5 MPa and 10 MPa of the vehicle tank (two-time refueling conditions) at 25 °C fills with the hydrogen at the APRR of 5.07 & 6.39 by 5.91& 7.5 min accordingly whereas the target pressure is 35 MPa. Hydrogen transfer to the vehicle tank at the pressure established by SAE J2799 according to the APRR during refueling time. The system consumes 52.71 kW and 3.73 kW of power to produce and compress 1 kg of hydrogen. The temperature profile shows that at the maximum hydrogen flow rate of 20 g/s, the temperature rose to 56 °C maintaining the fueling protocol. The levelized cost of hydrogen (LCOHP) of on-site hydrogen production is $6.68 and the LCOHS&D of storage & dispensing of hydrogen is $1.07 using the grid electricity whereas it gets down to $3.74 and $0.76 for the case of solar PV. Hydrogen vehicles reduce 43% fuel cost (using grid power) as compared to diesel engines. The study also depicts that a solar-powered hydrogen fleet is a better option for replacing fossil fuels and in shaping a sustainable transport system. The economic analyses provide the net present value (NPV20) and benefit and cost ratio (BCR) of the on-site HRS are 0.09 million and 1.18 at the discount rate of 9.5% which corresponds to the investment to the on-site HRS is feasible and free of risk.

Study on the Formation Mechanism of NOx Precursors During Density Functional Theory Pyrolysis of Leucine and Proline

ABSTRACT Incineration is an efficient method of resource utilization for kitchen waste. As an important stage of incineration, pyrolysis not only degrades kitchen waste but also generates pollutants such as nitrogen oxides. It is necessary to conduct in-depth research on the nitrogen conversion mechanism during its pyrolysis process. Most of the nitrogen in kitchen waste is concentrated in protein/amino acids. This article is based on the density functional theory calculation method, selecting typical compounds leucine and proline in kitchen waste as research objects, and studying their pyrolysis mechanism and the formation path of NOx precursors. A possible path for the cleavage of C-C/C-N bonds caused by hydrogen transfer to form NH3 and HCN has been proposed. Finally, it has been theoretically proven that the pyrolysis process of leucine tends to generate NH3 rather than HCN. And it was clarified that low energy barriers and high reaction rates are the reasons for the difference in production of these two NOx precursors. Meanwhile, the differences in the generation characteristics of NOx precursors for proline at different pyrolysis temperatures were theoretically explained. Finally, it was elucidated that leucine and proline preferentially undergo decarboxylation to complete the deoxygenation process, and the reason for the difference in CO production during the pyrolysis of the two amino acids was explained. In addition, this study found that the pyrolysis of leucine occurred preferentially than that of proline under the same conditions, and the yield of NOx precursor produced by leucine was higher than that of proline.

Heterogeneously catalyzed reductive depolymerization of lignin to value-added chemicals.

Lignin is an abundant renewable source of aromatics, but its complex heterogeneous structure poses challenges for its depolymerization and valorization. Heterogeneously catalyzed reductive depolymerization (HCRD) has emerged as a promising approach, utilizing heterogeneous catalysts to facilitate selective bond cleavage in lignin and hydrogen transfer to stabilize the products under mild conditions. This review provides a comprehensive understanding of the hydrogen transfer mechanisms in HCRD involving different hydrogen sources including molecular hydrogen, alcohols, formic acid, etc., and the native hydrogen donor groups in lignin. Recent advances in catalyst design for efficient lignin depolymerization are systematically discussed, focusing on precious metal-based (Pt, Ru, Pd) and non-precious metal-based catalysts. Factors influencing catalyst performance, such as metal-support interactions, promoters, and synergistic effects, are highlighted. The diverse array of high-value aromatic chemicals obtained from HCRD is overviewed. Finally, the significance of HCRD in the context of lignin valorization and the development of integrated biorefineries is discussed, underscoring its potential to contribute to a sustainable bioeconomy.

Employing Ammonia for the Synthesis of Primary Amines: Recent Achievements over Heterogeneous Catalysts.

Primary amines represent highly privileged chemicals for synthesis of polymers, pharmaceuticals, agrochemicals, coatings, etc. Consequently, the development of efficient and green methodologies for the production of primary amines are of great importance in chemical industry. Owing to the advantages of low cost and ease in availability, ammonia is considered as a feasible nitrogen source for synthesis of N-containing compounds. Thus, the efficient transformation of ammonia into primary amines has received much attention. In this review, the commonly applied synthetic routes to produce primary amines from ammonia were summarized, including the reductive amination of carbonyl compounds, the hydrogen transfer amination of alcohols, the hydroamination of olefins and the arylation with ammonia, in which the catalytic performance of the recent heterogeneous catalysts is discussed. Additionally, various strategies to modulate the surface properties of catalysts are outlined in conjunction with the analysis of reaction mechanism. Particularly, the amination of the biomass-derived substrates is highlighted, which could provide competitive advantages in chemical industry and stimulate the development of sustainable catalysis in the future. Ultimately, perspectives into the challenges and opportunities for synthesis of primary amines with ammonia as N-resource are discussed.

Physically hybrid Zr(OH)4 + CuO catalyzed selective aniline oxidation: A new Ph‐N˙$$ \dot{\mathbf{N}} $$OH mediated mechanism

AbstractDeveloping the sustainable and cost‐effective heterogeneous catalytic system for controlling chemoselectivity holds substantial importance in fine organic chemicals. Herein we construct a unique Zr(OH)4 + CuO physically hybrid system for selective oxidation of anilines. Zr(OH)4 alone leads to azoxybenzene formation, and Zr(OH)4 + CuO shifts the reaction favorably toward nitrosobenzene. The proximity study indicates Zr(OH)4 + CuO outperforms its counterparts synthesized through methods like ball‐milling, loading, and coprecipitation, because the closer proximity exhibits stronger chemical interaction, restricting the activity of Zr‐OH hydroxyl sites. Through mechanistic experiments, in situ DRIFT‐IR and DFT calculations, a new Ph‐OH intermediate mechanism is firstly proposed. Two Ph‐OH self‐condensate to form azoxybenzene for only Zr(OH)4, whereas Zr(OH)4 + CuO could promote rapid transformation of Ph‐OH to nitrosobenzene on CuO through a hydrogen transfer process. Moreover, Zr(OH)4 + CuO displays good recyclability and robust scalability. This is the first report demonstrating the utilization of a physically hybrid catalyst to adjust the selectivity of the aniline oxidation reaction.

Iridium Complexes with Bidentate Pyridinylidene/N-Amidate Ligands for Transfer Hydrogenation Catalysis.

A series of iridium pentamethylcyclopentadienyl (Cp*) complexes, [Cp*Ir(κ2-RLp/m)Cl], that contain the strongly coordinating bidentate ligands RLp/m were synthesized. The donor groups of the bidentate ligands were an N-amidate and either a para-pyridinylidene remote N-heterocyclic carbene (RLp) or a meta-pyridinylidene remote N-heterocyclic carbene (RLm). For each type of bidentate ligand, a set of iridium complexes was synthesized, which differed only according to the substituents (R) on the phenyl ring associated with the amidate group. The iridium complexes were all fully characterized and molecular structures were obtained by single-crystal X-ray diffraction studies for representative examples. The complexes were found to be good precatalysts in iso-propanol for the transfer hydrogenation of benzaldehyde to give benzyl alcohol. The catalytic activity correlated with the Hammett σm/p parameters of the phenyl ring substituents, with more electron-donating substituents leading to increased catalytic activity. In all cases, the meta-pyridinylidene complexes, [Cp*Ir(κ2-RLm)Cl], performed better than the corresponding para analogues, [Cp*Ir(κ2-RLp)Cl].

Dynamic Kinetic Resolution of β-Cyano α-Ketoesters via Asymmetric Transfer Hydrogenation.

An efficient rhodium-catalyzed asymmetric transfer hydrogenation of β-cyano α-ketoesters via dynamic kinetic resolution has been developed. Despite the challenge posed by multiple functional groups, the reaction proceeded smoothly under mild conditions, generating versatile synthons with two adjacent stereocenters in high yields with excellent enantio- and diastereoselectivities. Furthermore, the power of this strategy is highlighted by the scale-up reaction and the follow-up synthesis of cytoxazone and paclitaxel intermediates.