Hydrogen Transfer Reduction Research Articles

Insight into the reaction route and the effect of Brønsted and Lewis acid for alkylation of 5-Hydroxymethylfurfural

5-Hydroxymethylfurfural (HMF) can be upgraded to ether as fuel or fuel additives through conversion of the hydroxyl and aldehyde groups. The two groups are always involved in different catalytic reactions, such as etherification, acetalization, hydrogen transfer reduction, and even ring-opening reactions. This makes the etherification upgrading of HMF with high selectivity to desired product a great challenge. In the present wok, transformation of HMF in isopropanol was systematically investigated over different catalysts with Brønsted acid and Lewis acid sites. The effect of catalytic sites on product distribution and selectivity was studied. Moreover, several products, such as 5-isopropoxymethylfurfural, 5-isopropoxymethylfurfuryl alcohol, 5-isopropoxymethylfurfuryl alcohol, and 2,5-furandimethanol, were obtained with high selectivity, and the conversion pathway of HMF with alcohols on different catalytic sites was revealed under different catalytic conditions. The transformation of HMF to furan triether products over multi-site catalyst was realized for the first time based on the proposed reaction pathway with excellent activity and selectivity.

New metallophthalocyanine (M: Ni(II) and Fe(II)) complexes as efficient catalysts for transfer hydrogenation of various ketones

Hydrogen transfer reduction methods are attracting increasing attention from synthetic chemists in view of their operational simplicity. Therefore, the novel Ni(II) and Fe(II) tetra substituted metallophthalocyanines containing resorcinol and guaiacol groups were synthesized using microwave irradiation and characterized via elemental analysis, UV-Vis and FT-IR spectroscopy, and TGA. The comparison of the catalytic features of phthalocyanine based on metals is discussed in detail. These phthalocyanine-complexes were tested in transfer hydrogenation (TH) of ketones in the existence of KOH, utilizing 2-propanol as a hydrogen source. Examination of different carbonyl substrates revealed that Nickel (II) phthalocyanine, (Ni2) complex was a remarkable catalyst for the catalytic reduction of acetophenones (1.0 mol % of catalyst, 99 % conversion). Furthermore, we have discovered that the catalytic characteristics of this class of molecules are significantly influenced by both steric and electronic variables.

Selectivity-controllable hydrogen transfer reduction of α,β-unsaturated aldehydes over high-entropy catalysts

A selectivity-controllable H transfer reduction of α,β-unsaturated furanic aldehyde is developed using aliphatic alcohols as hydrogen sources in the presence of the high entropy CuCoAlNiFeOx catalyst.

In Situ Construction of Single-Site Ti Active Centers on Carbon Nitride for Photocatalytic Chemoselective Hydrogen Transfer Reduction

In this work, we report an in situ construction of single-site Ti active centers on a carbon nitride surface during photocatalytic processes for one-pot chemoselective hydrogen transfer reduction of nitroaromatics and domino-type reaction using Cp2TiCl2 and −OH-enriched carbon nitride (OHCN) as precatalysts. Due to the selective adsorption of nitro and the promotion of photogenerated charge transfer by single-site Ti active species and the formation of Ti3+, the system can achieve an efficient chemoselective reduction of nitroaromatics containing various substituents, especially sensitive substituents (C═C, C≡C, C═O, C═N, C≡N, C–X (X is halogen), etc.). The two processes of chemoselective reduction of nitroaromatics and oxidation of aromatic alcohols are photocatalytically coupled to form a complete photocatalytic cycle, which allows the simultaneous formation of two high-value-added products, aromatic amines and aromatic aldehydes. More valuable products like imines are obtained by effecting the reduction of the nitro moiety to −NH2 in the presence of aromatic alcohols that can react in a domino-type process. This work guides the in situ preparation of non-noble metallic single-site photocatalysts and provides a strategy for the photocatalytic synthesis of valuable organic compounds from nitroaromatics.

Iron-catalyzed reductive cyclization of nitroarenes: Synthesis of aza-heterocycles and DFT calculations

Research into environmentally friendly strategies for hydrogen transfer reduction is increasing, along with the need for more elaborate heterocyclic platforms. Within this context, we develop a new approach for substituted dihydrobenzo[c]carbazoles and indoles. These compounds were synthesized through an iron-catalyzed hydrogen transfer reduction of nitroarenes, followed by intramolecular cyclization. This transformation involves using a Knölker-type catalyst, Cs2CO3 as the base, and benzyl alcohol as the non-expensive and low volatile hydrogen donor. We synthesize 30 examples of aza-heterocycles with moderate to excellent yields by applying this strategy. Additionally, DFT calculations demonstrated that the pathway reaction could follow an anionic mechanism.

Direct Synthesis of Amides from Benzonitriles and Benzylic Alcohols via a KOt-Bu-Mediated MPV-type Hydrogen Transfer Process

Meerwein-Ponndorf-Verley (MPV)-type reduction between benzonitriles and benzylic alcohols under transition-metal-free conditions has been demonstrated for the first time. Using simple KOt-Bu as the base, various benzonitriles can be efficiently reduced by benzylic alcohols via hydrogen transfer reduction, and the resultant phenyl imine can react further with benzylic alcohols to give amides as the final product in which both the alcohols and the nitriles are incorporated. Preliminary mechanistic investigations indicated that the reaction may go through multiple MPV-type hydrogen transfer processes.

Achmatowicz approach to the asymmetric synthesis of (+)- and (−)-monanchorin

The full account of our development of a de novo asymmetric total synthesis of (+)-monanchorin has been reported. The optimized synthesis provided access to either enantiomer of the guanidine alkaloid natural product in nine steps from the commodity chemicals furan and caproic acid. The route relied upon the asymmetric Noyori hydrogen transfer reduction of an achiral acylfuran to introduce the absolute stereochemistry. In addition, an Achmatowicz rearrangement, a diastereoselective palladium-catalyzed glycosylation, a reductive amination and an acid-catalyzed bicyclic guanidine mixed acetal formation were used to complete the synthesis.

Nanometer-thick defective graphene films decorated with oriented ruthenium nanoparticles. Higher activity of 101 vs 002 plane for silane-alcohol coupling and hydrogen transfer reduction

Pyrolysis of ammonium alginate films containing Ru(NH3)6Cl3 leads to the formation of Ru nanoparticles (NPs) supported on defective graphene films. The procedure allows controlling the preferential facet orientation of small Ru NPs (5–20 nm), either 002 when the pyrolysis is carried out under Ar atmosphere or the 002 and 101 planes for pyrolysis in the presence of H2. Ru is a metal difficult to prepare in preferential facet orientation compared to noble metals due to its higher reactivity and smaller particle size. Theoretical calculations substantiated the inhibition of Ru(002) growth by H2 adsorption, with restructuration to Ru(002–101) NPs. The defective graphene films of about 15 nm thickness containing one of the two types of Ru NPs (150 ng/cm2) exhibit distinctive catalytic activity for the dehydrogenative coupling of silanes and alcohols and hydrogen transfer reduction of cyclohexanone. Comparison of turnover frequencies indicates that the 101 facet is more efficient than the 002 plane. Overall, this study illustrates that pyrolysis conditions can control the preferential crystallographic orientation of the growing Ru NPs and the relative catalytic activity of their specific crystallographic planes.

Selective reduction of aromatic halonitroarene to corresponding amine with Ru-gC3N4 as a catalyst in presence of sodium hypophosphite as a hydrogen source

This study reports an efficient heterogeneous catalyst Ru-gC3N4 (Ru-GCN) developed for the selective hydrogen transfer reduction reaction of nitroarenes to the corresponding amine. It helps to avoid multistep reaction in the field of organic synthesis. The catalyst Ru-gC3N4 shows excellent activity under the mild reaction parameters via using sodium hypophosphite as a hydrogen source and can be effective after many cycles without significant change in activity. The simply separable and recyclable heterogeneous Ru-gC3N4 catalyst is straight forward to operate, non-toxic, eco-friendly and at the same time replaces the comprehensive use of high pressurized hydrogen cylinder. Various types of material characterization and spectral methods such as PXRD, FTIR, SEM, TEM, XPS, and TGA are used to characterize the Ru-gC3N4 catalyst. All these properties such as good reusability and retained activity make our process sustainable and environmentally friendly. Aiming towards industrial potentiality, a gram scale experiment was reported using the developed protocol.

Iron-catalyzed chemoselective hydride transfer reactions

A Diaminocyclopentadienone iron tricarbonyl complex has been applied in chemoselective hydrogen transfer reductions. This bifunctional iron complex demonstrated a broad applicability in mild conditions in various reactions, such as reduction of aldehydes over ketones, reductive alkylation of various functionalized amines with functionalized aldehydes and reduction of α,β-unsaturated ketones into the corresponding saturated ketones. A broad range of functionalized substrates has been isolated in excellent yields with this practical procedure. To create your abstract, type over the instructions in the template box below. Fonts or abstract dimensions should not be changed or altered.

Selective reduction of alkynes to alkenes with hydrogen or formic acid catalyzed by cis,mer-[IrH2Cl(mtppms)3

In this work we have found, that the water-soluble cis,mer-[IrH2Cl(mtppms)3] (mtppms = monosulfonated triphenylphosphine Na-salt) was an excellent catalyst for reduction of terminal alkynes by hydrogen transfer from aqueous HCOOH/HCOONa mixtures. The conversions strongly depended on the pH of the reaction mixtures, and the highest rate of phenylacetylene transfer hydrogenation was observed at pH 3. The same dihydrido-Ir(III) complex actively catalyzed also the hydrogenation of terminal alkynes under mild conditions (T = 50 °C; P(H2) = 2–10 bar). Importantly, both the hydrogenation and hydrogen transfer reductions afforded exclusively the corresponding alkenes as products. Phenylacetylene and its substituted derivatives reacted smoothly, while benzylic and aliphatic alkynes were less reactive or did not react at all. It was also found, that an excess of the mtppms ligand inhibited the reaction. This was rationalized by formation of cisz-[IrH2(mtppms)4]+ which was also confirmed with multinuclear NMR spectroscopy. On the basis of the experimental results, a joint mechanism was suggested for both the hydrogenation and transfer hydrogenation pathways. The mechanism of hydrogenation and transfer hydrogenation of phenylacetylene was also studied by DFT calculations, which revealed several possibilities for protonation of a vinyl intermediate as the crucial step in formation of the styrene product.

Iron-Catalyzed Hydrogen Transfer Reduction of Nitroarenes with Alcohols: Synthesis of Imines and Aza Heterocycles.

A straightforward and selective reduction of nitroarenes with various alcohols was efficiently developed using an iron catalyst via a hydrogen transfer methodology. This protocol led specifically to imines in 30-91% yields, with a good functional group tolerance. Noticeably, starting from o-nitroaniline derivatives, in the presence of alcohols, benzimidazoles can be obtained in 64-72% yields when the reaction was performed with an additional oxidant, DDQ, and quinoxalines were prepared from 1,2-diols in 28-96% yields. This methodology, unprecedented at iron for imines, also provides a sustainable alternative for the preparation of quinoxalines and benzimidazoles.

Synergistic interaction between Ru and MgAl-LDH support for efficient hydrogen transfer reduction of carbonyl compounds under visible light

Coordinated Ru species, Ru/LDH, were applied to the reduction of carbonyl compounds via blue light irradiation under mild (45 °C, atmospheric argon pressure), ligand-free, and additive-free conditions. LDH can act as an efficient base catalyst to assist in formation of isopropoxide, requiring no additional base, because basic OH groups form an ordered distribution on LDH surface. The coordinated Ru species containing one OH and three oxygen atoms ligands deriving from the OH groups of LDH are a crucial component, for securing the active electron-deficient Ru species that favours formation of Ru-isopropoxide. The photocatalytic activity is related to the adsorption capacity of isopropyl alcohol near the electron-deficient Ru species and the formation of Ru-isopropoxide. The strong-metal-support interactions between Ru and LDH affect the coordination and the electronic surroundings of the Ru centres and have a significant effect on the photocatalytic activity.

A Facile One-pot Synthesis of Substituted Quinolines via Cascade Friedlander Reaction from Isoxazoles with Ammonium Formate-Pd/C and Ketones

The Friedlander reaction is the most commonly used method to synthesis substituted quinolines, the essential intermediates in the medicine industry. A facile one-pot approach for synthesizing substituted quinolines by the reaction of isoxazoles, ammonium formate-Pd/C, concentrated sulfuric acid, methanol and ketones using Friedlander reaction conditions is reported. Procedures for the synthesis of quinoline derivatives were optimized, and the yield was up to 90.4%. The yield of aromatic ketones bearing electron-withdrawing groups was better than the ones with electron-donating substituents. The structures of eight substituted quinolines were characterized by MS, IR, H-NMR and 13CNMR, which were in agreement with the expected structures. The mechanism for the conversion was proposed, which involved the Pd/C catalytic hydrogen transfer reduction of unsaturated five-membered ring of isoxazole to produce ortho-amino aromatic ketones. Then the nucleophilic addition of with carbonyl of the ketones generated Schiff base in situ, which underwent an intermolecular aldol reaction followed by the elimination of H2O to give production of substituted quinolines. This new strategy can be readily applied for the construction of quinolines utilizing a diverse range of ketones and avoids the post-reaction separation of the o-amino aromatic ketone compounds. The conventionally used o-amino aromatic ketone compounds in Friedlander reaction to prepare substituted quinoline are laborious to synthesize and are apt to self-polymerize. While oxazole adopted in this work can be prepared at ease by the condensation of benzoacetonitrile and nitrobenzene derivatives under the catalysis of a strong base. Moreover, the key features of this protocol are readily available starting materials, excellent functional group tolerance, mild reaction conditions, operational simplicity, and feasibility for scaling up.

Synthesis and characterization of silica‐coated magnetite nanoparticles modified with bis(pyrazolyl) triazine ruthenium(II) complex and the application of these nanoparticles as a highly efficient catalyst for the hydrogen transfer reduction of ketones

We present a facile and efficient method for modifying the surface of silica‐coated Fe3O4 magnetic nanoparticles (MNPs) with bis(pyrazolyl) triazine ruthenium(II) complex [MNPs@BPT–Ru (II)]. Field emission‐scanning electron microscopy, thermogravimetric/derivative thermogravimetry analysis, X‐ray powder diffraction, Fourier‐transform infrared spectroscopy, vibrating sample magnetometry, and energy‐dispersive X‐ray spectrometry analyses were employed for characterizing the structure of these nanoparticles. MNPs@BPT–Ru(II) nanoparticles proved to be a magnetic, reusable, and heterogeneous catalyst for the hydrogen transfer reduction of ketone derivatives. In addition, highly pure products were obtained with excellent yields in relatively short times in the presence of this catalyst. A comparison of this catalyst with those previously used for the hydrogen transfer reactions proved the uniqueness of MNPs@BPT–Ru(II) nanoparticle which is due to its inherent magnetic properties and large surface area. The presented method also had other advantages such as simple reaction conditions, eco‐friendliness, high recovery ability, easy work‐up, and low cost.

Tandem Hydrogenation/Hydrogenolysis of Furfural to 2-Methylfuran over a Fe/Mg/O Catalyst: Structure–Activity Relationship

The hydrodeoxygenation of furfural (FU) was investigated over Fe-containing MgO catalysts, on a continuous gas flow reactor, using methanol as a hydrogen donor. Catalysts were prepared either by coprecipitation or impregnation methods, with different Fe/Mg atomic ratios. The main product was 2-methylfuran (MFU), an important highly added value chemical, up to 92% selectivity. The catalyst design helped our understanding of the impact of acid/base properties and the nature of iron species in terms of catalytic performance. In particular, the addition of iron on the surface of the basic oxide led to (i) the increase of Lewis acid sites, (ii) the increase of the dehydrogenation capacity of the presented catalytic system, and (iii) to the significant enhancement of the FU conversion to MFU. FTIR studies, using methanol as the chosen probe molecule, indicated that, at the low temperature regime, the process follows the typical hydrogen transfer reduction, but at the high temperature regime, methanol dehydrogenation and methanol disproportionation were both presented, whereas iron oxide promoted methanol transfer. FTIR studies were performed using furfural and furfuryl alcohol as probe molecules. These studies indicated that furfuryl alcohol activation is the rate-determining step for methyl furan formation. Our experimental results clearly demonstrate that the nature of iron oxide is critical in the efficient hydrodeoxygenation of furfural to methyl furan and provides insights toward the rational design of catalysts toward C–O bonds’ hydrodeoxygenation in the production of fuel components.

Bimetallic Pd-Au/TiO2 Nanoparticles: An Efficient and Sustainable Heterogeneous Catalyst for Rapid Catalytic Hydrogen Transfer Reduction of Nitroarenes.

Anilines are one of the important chemical feedstocks and are utilized for the preparation of a variety of pharmaceuticals, agrochemicals, pigments, and dyes. In this context, the catalytic reduction of nitro functionality is an industrially vital process for the synthesis of aniline derivatives. Herein, we report an efficient nanosized bimetallic Pd–Au/TiO2 nanomaterial which is proved to be quite efficient for rapid catalytic hydrogen transfer reduction of nitroarenes into corresponding amines. Significantly, the reduction process is successful under solvent-free and mild green atmospheric conditions. Bimetallic Pd–Au nanoparticles served as the active center, and TiO2 played as a support in hydrogen transfer from the source hydrazine monohydrate. Typical results highlighted that the reactions were very rapid and the products were obtained in good to excellent yields. Significantly, the process was successful in the presence of a very low amount catalyst (0.1 mol %). Furthermore, the reaction showed good chemoselectivity and compatiblity with double or triple bond, aldehyde, ketone, and ester functionalities on the aromatic ring. Typical results indicated the true heterogeneous nature of the Pd–Au/TiO2 nanocatalyst, where the catalyst retained the activity, without loss of its activity.

Switching Selectivity in the Hydrogen Transfer Reduction of Furfural

AbstractSupported Cu catalysts and bare inorganic oxides have been tested in the reduction of furfural to furfuryl alcohol under hydrogen transfer reaction conditions by using butanol as a donor. Bare oxides like zirconia and alumina were found to be more active than the corresponding supported catalysts and in particular high surface Zirconia gave a quantitative transformation of the aldehyde into alcohol in 2,5 h at 140 °C according to a pure Meerwein‐Ponndorf‐Verley mechanism. Competitive dehydrogenation of the alcohol formed on the surface of Cu catalysts strongly reduces their activity although selectivity to alcohols on zirconia and alumina supported catalysts keeps very high. On the other hand catalysts with a well‐defined Lewis acid character such as highly dispersed Zirconia on Silica allowed to obtain up to 64% yield in 2‐butyl‐furfuryl‐ether under the same conditions.

Fluorobissulfonylmethyl Iodides: An Efficient Scaffold for Halogen Bonding Catalysts with an sp3-Hybridized Carbon–Iodine Moiety

The halogen-bond donors FBSM-I and FBDT-I, which contain an sp3-hybridized carbon–iodine (Csp3–I) moiety, were designed and synthesized. The highly electron-withdrawing nature of the fluorobissulfonyl-methane scaffold leads to the generation of σ-holes on the surface of the iodine atoms in FBSM-I and FBDT-I. Mukaiyama aldol reactions and hydrogen-transfer reductions are efficiently catalyzed by FBSM-I and FBDT-I under neutral and mild reaction conditions. The driving force for these transformations should be the halogen bonding induced by FBSM-I and FBDT-I, which was confirmed by DFT calculations, single-crystal X-ray diffraction analyses, and NMR titrations.

Nickel Nanoparticles Decorating Graphite Flake Surface Using Planetary Ball Milling: Physical Characterization and Methanol Electrooxidation Investigation

In recent years, several researches have been conducted in order to investigate the physical and chemical method for obtain the metallic nanoparticles, such as co-precipitation, hydrothermal, thermal decomposition of organometallic compounds, electrochemical, and ball milling method [1-4]. The particle size, shape and crystallinity depend on the selected synthesis method. In this sense the ball milling technique is one of the widely used to produce metallic nanoparticles, being the method feasible for large production [4]. A simple approach was proposed to obtain graphite surface decorated with nickel nanoparticles (Ni NPs) from dry ball milling process. Ni NPs were obtained after 40 h of high energy milling and 100, 200, 300 and 400 rpm ball rotation speeds. Both Ni NPs and graphite decorated samples were characterized by Scanning Transmission (STEM), Raman Spectroscopy, Scanning Electron Microscopy, X-ray diffraction pattern (XRD). The electrocatalytic activity of Ni/Graphite samples were evaluated from methanol oxidation in alkaline medium using electrochemical techniques. Good agreement between STEM and XRD results can be found, reporting average diameter size of 4.9 nm and average crystallite size of 5.50 nm for Ni NPs. The methanol electrooxidation electrocatalytic activity was more efficient for Ni/Graphite with 100 rpm compared to Ni/Graphite others. REFERENCES M. Freire, T.S. Ribeiro, I.F. Vasconcelos, J.C. Denardin, E.B. Barros, M. Giuseppe, L. Carbone, S.E. Mazzetto, P.B.A. Fechine, MZnFe2O4 (M = Ni, Mn) cubic superparamagnetic nanoparticles obtained by hydrothermal synthesis, J. Nanopart. Res. 15 (2013) 1-12.Alonso, P. Riente, J.A. Sirvent, M. Yus, Nickel nanoparticles in hydrogen-transfer reductions: Characterisation and nature of the catalyst, Appl. Catal. A 378 (2010) 42–51.Aghazadeh, A.N. Golikand, M. Ghaemi, Synthesis, characterization, and electrochemical properties of ultrafine b-Ni(OH)2 nanoparticles, Int. J. Hydrogen Energy 36 (2011) 8674-8679.F. de Carvalho, S.N. de Medeiros, M.A. Morales, A.L. Dantas, A.S. Carriço, Synthesis of magnetite nanoparticles by high energy ball milling Appl. Surf. Sci. 275 (2013) 84-87.