Catalytic Transfer Hydrogenation Reaction Research Articles

Versatile functionalized mesoporous Zr/SBA-15 for catalytic transfer hydrogenation and oxidation reactions

Through this work, a family of sulfonamide functionalized mesoporous materials as sustainable heterogeneous catalysts has been successfully synthesized by employing sulfaguanidine, sulfathiazole, and sulfadiazine. The samples were fully characterized using a multitechnique approach. Such materials have proved to be highly versatile and catalytically active in both the advances in the hydrogenation of Levulinic acid through heterogeneous catalytic transfer hydrogenation (CTH) and oxidation reactions with a strong emphasis on discussing morphology and structure of versatile catalysts, plausible mechanism, and performance of the catalysts for biomass valorization of renewable feedstock. In particular, the prepared catalytic systems were tested in levulinic acid transformation into γ-Valerolactone, achieving a maximum conversion of 99% and a selectivity of 90% for the sulfaguanidine modified sample. The three nanocatalysts displayed good stability over four reuse cycles, and by considering the results of a hot filtration test, it is confirmed that the nature of the catalysis is heterogeneous as acid-base pairs and functionalized groups on catalytic activation of C–H and CO bonds for transfer hydrogenation of levulinic acid. Moreover, such samples also showed remarkable results in the oxidation of benzyl alcohol towards benzaldehyde, with conversion and selectivity values of 95% and 97%, respectively. The obtained catalytic results are highly promising for biomass upgrading processes, looking forward to a more sustainable future.

Co/N-codoped porous carbons derived from poly(Schiff base)/Co(II) complex as ultrahighly efficient catalysts for CTH of nitroarenes

Herein we report the scalable synthesis of Co/N-codoped porous carbon (Co/N-C) catalysts by pyrolyzing poly(Schiff base)/Co(II) complex. The strong Co(II)-binding affinity of poly(Schiff base) leads to the formation of uniformly distributed Co(0) nanoparticles, Co-Nx species, and N–C configurations, in which their catalytic contributions are confirmed and estimated by ligand-poisoning and acid-etching experiments and the Co-Nx species has been proved to be highly active for catalytic transfer hydrogenation (CTH) reaction. Consequently, the as-prepared Co-N/C-950 catalyst exhibits an ultrahigh activity for the CTH of 4-nitrophenol (4-NP) with a TOF of 226 mol4-NP molCo−1 min−1 (13560 h−1) together with an excellent selectivity for CTH of challenging nitroarenes. Moreover, the Co(0) nanoparticles embedded in the Co-N/C-950 catalyst can be further transformed to Co4N phase by a facile nitridation reaction, yielding Co4N-N/C-950 catalyst with even higher activity for the CTH of 4-NP (TOF up to 310 mol4-NP molCo−1 min−1).

Primary Vs. Secondary Alcohols Electrooxidation: Mechanistic Insights

Direct Alcohol Fuel Cells (DAFCs), mostly based on methanol or ethanol, have been in the spotlight in the past, due to alcohols’ high and easy availability, low cost, liquid form, low temperature operation and comparable theoretical mass energy densities in comparison with Hydrogen Fuel Cells.[1] However, 2-propanol fuel cells can be preferred for coupling with Liquid Organic Hydrogen Carriers (LOHCs), by creating a closed loop where 2-propanol is oxidized in a fuel cell to acetone and the latter is hydrogenated back to 2-propanol by the catalytic transfer hydrogenation reaction with a hydrogen-rich LOHC molecule.[2] Here, we characterize the products of 2-propanol oxidation on Pt and PtRu and find that the reaction is selective to acetone on both surfaces. Interestingly, the addition of ruthenium gives rise to an early oxidation peak close to the reversible potential, which is not present in 1-propanol oxidation.[3] The early onset of the 2-propanol oxidation leads to significantly larger Open Circuit Voltages (OCVs) for fuel cells based on 2-propanol compared to 1-propanol, when PtRu is used as the anode. By studying the oxidation of larger (C4 and C5) alcohols, we find that this is a unique characteristic of secondary alcohols on platinum-ruthenium bimetallic catalysts. Using a combination of Rotating Disc Electrode (RDE) measurements, Density Functional Theory (DFT) calculations and real-time product analysis with Electrochemical Real-Time Mass Spectrometry (EC-RTMS) we conclude that the unique feature of secondary alcohols stems from the difficulty in breaking their C-C bond, which prevents their dissociative adsorption at low potential and enables the optimal adsorption on platinum-ruthenium ensemble sites.[4] Acknowledgements I.M.-G, P.K, K.J.J.M. and I.K. acknowledge financial support by the Bavarian Ministry of Economic Affairs, Regional Development and Energy.F.C.-V. acknowledges funding from Spanish MICIUN RTI2018-095460-B-I00, Ramón y Cajal RyC-2015-18996 and María de Maeztu MDM-2017-0767 grants and partly by Generalitat de Catalunya 2017SGR13. O.P. thanks the Spanish MICIUN for a PhD grant (PRE2018-083811). We thank Red Española de Supercomputación (RES) for supercomputing time at SCAYLE (projects QS-2019-3-0018, QS-2019-2-0023, and QCM-2019-1-0034), MareNostrum (project QS-2020-1-0012), and CENITS (project QS-2020-2-0021). The use of supercomputing facilities at SURFsara was sponsored by NWO Physical Sciences, with financial support by NWO.

Ruthenium(II) Complex of a Tridentate Azoaromatic Pincer Ligand and its Use in Catalytic Transfer Hydrogenation of Aldehydes and Ketones with Isopropanol

AbstractIn this work, a new Ru(II) complex with the redox‐active pincer 2,6‐bis(phenylazo)pyridine ligand (L) is reported which acts as a metal‐ligand bifunctional catalyst for transfer hydrogenation reactions. The isolated complex [(L)Ru(PMe2Ph)2(CH3CN)](ClO4)2; [1](ClO4)2 is characterized by a host of spectroscopic measurements and X‐ray structure determination. It is diamagnetic and single‐crystal X‐ray structure analysis reveals that [1]2+ adopts a distorted octahedral geometry where L binds Ru center in meridional fashion. The observed elongation in the coordinated azo bond length (1.29 Å) is attributed to the extensive π‐back bonding, dπ(RuII)→π*(azo)L. The complex [1](ClO4)2 acts as an efficient catalyst, which brings about catalytic transfer hydrogenation reactions of a broad array of aldehydes and ketones in isopropanol and in inert conditions. The selectivity of the catalyst for aldehyde reduction over the other reducible functional groups such as nitro, nitrile, ester etc was also investigated. Mechanistic studies, examined by suitable control reactions and isotope labelling experiments, indicate synergistic participation of both ligand and metal centres via the formation of a fleeting Ru−H intermediate and hydrogen walking to the coordinated azo function of L.

A Pd-NP/AC‐CATALYZED TRANSFER‐HYDROGENATION OF MESITYL OXIDE TO METHYL ISOBUTYL KETONE USING SODIUM FORMATE AS HYDROGEN DONOR

Methyl isobutyl ketone (MIBK) is an α,β-unsaturated carbonyl compound, which is often used as solvent and extractor for antibiotics in the pharmaceutical industry. One alternative to the synthesis of MIBK from mesityl oxide (MO) is through catalytic transfer hydrogenation (CTH) using various organic compounds as hydrogen donors in the presence of a catalyst. The purpose of this study was to synthesize MIBK from MO through the CTH reaction using sodium formate as the hydrogen donor and Pd nanoparticles deposited on the activated charcoal (Pd-NP/AC) as the catalyst. Based on the Gas Chromatography-Mass Spectrometry (GC-MS) analysis, the conversion value of MO was obtained in 97.3% and the yield of the MIBK formation was 10.5%. Meanwhile, the highest selectivity was obtained in 17% at 40° C. The results show that sodium formate can effectively be used to reduce MO into MIBK in the presence of Pd-NP/AC catalyst at 70° C for 5 hours.

Theoretical insights into furfural reduction to furfuryl alcohol via the catalytic hydrogen transfer reaction catalyzed by cations exchanged zirconium-containing zeolites

The density functional theory has been employed to study the reduction of furfural to furfuryl alcohol via the catalytic transfer hydrogenation (CTH) reaction over cations exchanged zirconium (Zr) containing zeolites. From the calculations results, the reaction proceeds through the following three steps: (i) the dissociation of the hydroxyl (OH) group of i-propanol to form i-propoxide, (ii) the hydrogen transfer from i-propoxide to furfural and (iii) the formation of furfuryl alcohol. The Li-Zr-BEA zeolite shows higher catalytic activity than Li-Sn-BEA due to its lower activation free energy (25.8 vs 20.8 kcal/mol). The effect of cations (Li, Na and K) which are exchanged on Zr-BEA is also considered. Based on the activation energy of rate determining step and turn over frequencies (TOFs), the catalytic activity rises when the group period of an exchanged metal decreases. The finding shows that the exchange of cations in Zr-zeolite surface is a simple process to make a tunable catalyst for the catalytic transfer hydrogenation reaction. The effects of different zeolite frameworks (BEA, ZSM-5 and FAU) are also studied. The relative catalytic activity of Li-Zr-BEA and Li-Zr-ZSM-5 zeolite is found to be almost similar and higher than that of Li-Zr-FAU zeolite.

Wadsworth Emmons cyclopropanation mediated diastereoselective Syntheses of α-epoxy- trans-disubstituted cyclopropane and α-hydroxy-trans-disubstituted cyclopropane

The present work describes the diastereoselective Syntheses of α -epoxy- trans -disubstituted cyclopropane and α -hydroxy- trans -disubstitutedcyclopropane. The genesis of chirality in the targeted products is based on the exploitation of catalytic asymmetric transfer hydrogenation (CATHy) reaction. Asymmetric Cyclopropanation was carried out using Wadsworth–Emmons protocol. Among the surveyed conditions, employing TEPA, epoxide, NaH in toluene under reflux furnished the desired cyclopropane with 85% yield.

Ruthenium(ii)-catalyzed reductive N–O bond cleavage of N-OR (R = H, alkyl, or acyl) substituted amides and sulfonamides

A convenient method for the reductive cleavage of the N–O bonds of amide derivatives was developed using ruthenium(ii)-catalyzed transfer hydrogenation reaction.

Formic acid enabled selectivity boosting in transfer hydrogenation of 5-hydroxymethylfurfural to 2,5-furandimethanol on highly dispersed Co–Nx sites

Catalytic transfer hydrogenation (CTH) reaction is considered as a potential route for upgrading bio-based carbonyl compounds to their corresponding alcohols.

Advancements in multifunctional manganese complexes for catalytic hydrogen transfer reactions.

Catalytic hydrogen transfer reactions have enormous academic and industrial applications for the production of diverse molecular scaffolds. Over the past few decades, precious late transition-metal catalysts were employed for these reactions. The early transition metals have recently gained much attention due to their lower cost, less toxicity, and overall sustainability. In this regard, manganese, which is the third most abundant transition metal in the Earth's crust, has emerged as a viable alternative. However, the key to the success of such manganese-based complexes lies in the multifunctional ligand design and choice of appropriate ancillary ligands, which helps them mimic and, even in some cases, supersede noble metals' activities. The metal-ligand bifunctionality, achieved via deprotonation of the acidic C-H or N-H bonds, is one of the powerful strategies employed for this purpose. Alongside, the ligand hemilability in which a weakly chelating group tunes in between the coordinated and uncoordinated stages could effectively stabilize the reactive intermediates, thereby facilitating substrate activation and catalysis. Redox non-innocent ligands acting as an electron sink, thereby helping the metal center in steps gaining or losing electrons, and non-classical metal-ligand cooperativity has also played a significant role in the ligand design for manganese catalysis. The strategies were not only employed for the chemoselective hydrogenation of different reducible functionalities but also for the C-X (X = C/N) coupling reactions via HT and downstream cascade processes. This article features multifunctional ligand-based manganese complexes, highlighting the importance of ligand design and choice of ancillary ligands for achieving the desired catalytic activity and selectivity for HT reactions. We have also discussed the detailed reaction pathways for metal complexes involving bifunctionality, hemilability, redox activity, and indirect metal-ligand cooperativity. The synthetic utilization of those complexes in different organic transformations has also been detailed.

Bis-NHC–Ag/Pd(OAc)2 Catalytic System Catalyzed Transfer Hydrogenation Reaction

The bis-NHC–Ag/Pd(OAc)2 catalytic system (NHC = N-heterocyclic carbene), a combination of bis-NHC–Ag complex and Pd(OAc)2, was found to be a smart catalyst in the Pd-catalyzed transfer hydrogenation of various functionalized arenes and internal/terminal alkynes. The catalytic system demonstrated high efficiency for the reduction of a wide range of various functional groups such as carbonyls, alkynes, olefins, and nitro groups in good to excellent yields and high chemoselectivity for the reduction of functional groups. In addition, the protocol was successfully exploited to stereoselectivity for the transformation of alkynes to alkenes in aqueous media under air. This methodology successfully provided an alternative useful protocol for reducing various functional groups and a simple operational protocol for transfer hydrogenation.

Synergistic effect between Ni single atoms and acid–base sites: Mechanism investigation into catalytic transfer hydrogenation reaction

Catalytic Transfer Hydrogenation (CTH) of unsaturated functional groups to obtain high value-added products has attracted considerable attention in heterogeneous catalysis. Herein, we report a Ni single atoms (SAs) catalyst anchoring to MgAl mixed metal oxide (MMO) based on structural topotactic transformation from hydrotalcite precursor, which displays an excellent catalytic behavior toward CTH of cinnamaldehyde (CAL) to cinnamyl alcohol (COL) (conversion: 100%; selectivity: 100%; 2 h). A combination research including AC-STEM, XAFS and in situ CO-IR demonstrates that Ni species anchored by NiO coordination with different dispersion could be precisely obtained by tuning the reduction temperature: the Ni SAs (only NiO coordination) were obtained below 450 °C, and the NiNi coordination appears and increases gradually with the rise of the reduction temperature. The selective poisoning experiment, kinetic isotope effect (KIE), in situ FT-IR measurement and DFT calculation reveal the synergistic effect between metal Ni SAs and acid–base sites toward CTH of CAL. Specifically, the Ni SAs play a crucial role in dehydrogenation reaction of 2-propanol (2-POL) to supply activated H, the base sites induce α-CH cleavage in 2-POL (the rate-determining step), and the Lewis acid sites serve as the active center for CO adsorption in CAL molecule. This work demonstrates a synergetic effect between Ni SAs and acid–base sites, which would pave the way in the rational design and synthesis of high-performance SAs materials used in CTH reactions.

Efficient catalytic transfer hydrogenation reactions of carbonyl compounds by Ni(II)-diphosphine complexes

The catalytic transfer hydrogenation reactions of a series of aromatic and aliphatic carbonyl compounds were investigated using divalent Ni(II)-diphosphine complexes, [L2NiCl2] (where L2 = 1,1-bis(diphenylphosphino)methane (dppm), 1,2-bis(diphenylphosphino)ethane (dppe), 1,3-bis(diphenylphosphino)propane (dppp), 1,1-bis(diphenylphosphino)ferrocene (dppf), and N-butyl-N-(diphenylphosphino)-1,1-diphenylphosphinamine (dppba)). This is a single-step reaction in the presence of potassium hydroxide and isopropyl alcohol to afford the corresponding alcohols. This protocol tolerates other sensitive functional groups like olefinic double bonds and also achieves high chemoselectivity. All the reactions were monitored by GC and GC–MS. The plausible mechanism is also discussed. The method reported in the present article is simple, cost-effective, and provides excellent conversions. Nickel-diphosphine complexes appear as a potential alternative to expensive transition metal complexes.

Catalytic Transfer Hydrogenation of Arenes and Heteroarenes.

Transfer hydrogenation reactions are of great interest to reduce diverse molecules under mild reaction conditions. To date, this type of reaction has only been successfully applied to alkenes, alkynes and polarized unsaturated compounds such as ketones, imines, pyridines, etc. The reduction of benzene derivatives by transfer hydrogenation has never been described, which is likely due to the high energy barrier required to dearomatize these compounds. In this context, we have developed a catalytic transfer hydrogenation reaction for the reduction of benzene derivatives and heteroarenes to form complex 3‐dimensional scaffolds bearing various functional groups at room temperature without needing compressed hydrogen gas.

Sugars as Novel, Effective, and Renewable Hydrogen Sources in Dehydrogenation and Catalytic Transfer Hydrogenation Reactions

The applications of sugars as inexpensive, renewable, and nontoxic sources of hydrogen gas are systematically demonstrated by means of dehydrogenation and catalytic transfer hydrogenation reactions. The chiral bifunctional Noyori‐type catalyst, Cp*Ir(TsDPEN), is found to effectively, regioselectively, and stereoselectively dehydrogenate various sugars possessing different steric hindrance and stereochemistry. Furthermore, kinetics experiments for these dehydrogenation reactions reveal that many sugars are superior sources of hydrogen gas when compared with a traditional hydrogen donor, isopropanol. Applications of sugars in transfer hydrogenation with various hydrogen acceptors are also investigated.

One-pot synthesis of LaFeO3@C composites for catalytic transfer hydrogenation reactions: Effects of carbon precursors

Carbon encapsulated LaFeO3 perovskite composites (LaFeO3@C) were synthesized by a one-pot method and the effects of carbohydrates as carbon precursor on the activity of LaFeO3@C for catalytic transfer hydrogenation (CTH) reactions were investigated. The textural and surface properties (e.g., pore structure, surface acidity and basicity) of LaFeO3@C vary significantly with carbohydrates, which offer a facile route to tailor the sample by simply changing the carbon precursor. LaFeO3@C-M, using maltose as carbon precursor, shows the best catalyst for the CTH of furfural with isopropanol, with conversion and selectivity of 90.3 % and 94.3 %, respectively, owing to the surface La enrichment, rich oxygen functional groups / oxygen vacancy and matched surface acidity-basicity. This sample is also recyclable after post-treatment in N2 atmosphere and can be applied to catalytic hydrogenation of various carbonyl compounds. The current one-step synthesis method provides an efficient way to design carbon-containing composite catalysts with controllable properties for catalytic applications.

Magnetic Fe3O4 nanoparticles as easily separable catalysts for efficient catalytic transfer hydrogenation of biomass-derived furfural to furfuryl alcohol

Magnetic Fe3O4-12 nanoparticles, an easily separable heterogeneous catalyst, exhibits high catalytic performance in the catalytic transfer hydrogenation (CTH) reaction of biomass-derived furfural (FAL) to furfuryl alcohol (FOL) with 2-propanol (2-PrOH) as the hydrogen source (90.1 % FOL yield at 160 °C for 5 h). Comparing Fe3O4 nanoparticles with different particle sizes found that the smaller the nanoparticles, the larger the BET surface area, pore volume and pore diameter, resulting in more acid-base active sites through BET, SEM, TEM, NH3-/CO2-TPD and other characterizations. Moreover, a scaled-up CTH experiment of FAL and a stepwise reaction from xylose to FOL verified that the catalytic system has great industrial application prospects. A feasible flowchart of the chemical process from xylose to FOL was designed, which can realize the regeneration of biomass resources (xylose derived from corncob), the reuse and recycling of catalysts and solvents, and minimize the amount of solvents and pollutant emissions.

Manganese catalyzed transfer hydrogenation of biomass-derived aldehydes: Insights to the catalytic performance and mechanism

Manganese catalyzed transfer hydrogenation (CTH) of aldehydes is an attractive method for the synthesis of alcohols. Here, we report a novel and efficient MnO@C-N catalyst for the CTH of biomass-derived 5-hydroxymethylfurfural and other aldehydes to alcohols in high yields. Catalytic experimental studies showed that the MnO and nitrogen-doping are responsible for the high selectivity and high conversion, respectively. Isotopic labelling experiments demonstrated that the CTH of aldehydes to alcohols over MnO@C-N is via a route by direct hydrogen transfer. Kinetic studies revealed that the N-doping can improve the reaction rate and reduce the activation energy of the aldehydes conversion. DFT calculations also indicated that both pyridine N and pyrrolic N doping can reduce the energy barrier for acetone desorption by the interaction between N and hydroxyl-H of alcohol. Furthermore, MnO@C-N showed good recyclability for at least five reaction cycles. We anticipate that these results can drive progress in the manganese catalyzed transfer hydrogenation reaction.

Understanding the role of Al/Zr ratio in Zr-Al-Beta zeolite: Towards the one-pot production of GVL from glucose

The direct one-pot transformation of glucose into γ-valerolactone (GVL) can be accomplished by means of a cascade of reactions in which Brønsted acid-catalyzed transformations are combined with catalytic transfer hydrogenation (CTH) by using 2-propanol as sacrificial alcohol, avoiding the use of high-pressure hydrogen. Catalysts containing Zr Lewis acid sites have been successfully applied in CTH reactions while the acid-driven transformations can be preferentially promoted by Brønsted Al-related acidity. Here, we present the combination of Zr and Al as active sites within a BEA zeolite structure as catalyst, with the possibility of adjusting the Al/Zr ratio from ∞ (commercial H-Beta) to 0 (aluminium-free Zr-Beta), which show a scale of Brønsted/Lewis acid sites ratios. The Al/Zr ratio has a strong impact on the products distribution. As the Zr content increases, higher amount of GVL is obtained, leading to a maximum over the catalyst with high amount of Zr and low content of Al acid sites (Al/Zr = 0.2). An increase of reaction temperature, as well as reaction time, allows an enhancement of yields towards the desired products, leading to a maximum yield towards GVL of 24 mol% over Zr-Al-Beta (2.0), and a maximum yield towards isopropyl lactate of 26 mol% over Zr-Beta at 190 °C.

Catalytic Transfer Hydrogenation of Castor Oil Using Glycerol-Based Reaction

A catalytic transfer hydrogenation of castor oil using glycerol-based is a process of adding hydrogen to the castor oil to produce hydrogenated castor oil with the addition of 10% Pd/C as the catalyst and glycerol as a hydrogen donor. The reaction occurred at the reaction temperature of 178 °C for an hour. To prove whether glycerol can be one of the hydrogen donors like limonene that is commonly used, the research started by using pure glycerol as the hydrogen donor and as a control to determine the protocol. A direct heating apparatus connected with a reflux system was used for this experiment. The result from FTIR along with the melting point shows the formation of hydrogenated castor oil from this reaction. The increment in melting point value and the absence of C=C peak (1655.79 cm−1) from FTIR spectrum shows that the catalytic transfer hydrogenation successfully occurred. The melting point of the hydrogenated castor oil is 65 °C and the melting point of castor oil is − 7 °C. Therefore, it was proven that, the glycerol can be used as the hydrogen donor for the castor oil for a catalytic transfer hydrogenation reaction.