Hydrogen Transfer Agent Research Articles

Ammonia-Borane Dependent Transfer Hydrogenation of Carboxylic Esters to Primary Alcohols.

Here, we present a user-friendly protocol that uses bench-stable NH3·BH3 (AB) as the hydrogen transfer agent for the reduction of both aromatic and aliphatic esters without an external catalyst and base, delivering a structurally diverse array of primary alcohols (80-98% yields). The broad functional-group tolerance (halogen, boronic ester, -NO2, -OH, etc.) under environmentally acceptable conditions implies high practical utility. Further, a tandem catalytic conversion of a plastic waste polyethylene terephthalate (PET) bottle to 1,4-benzenedimethanol including fatty esters into respective fatty alcohols was shown.

Catalytic deoxydehydration of glycerol to allyl alcohol in the presence of mono-oxygenated rhenium diphosphine complexes

Allyl alcohol is a crucial organic intermediate in synthesizing polymeric compounds industrially produced by petroleum-derived propylene despite environmental concerns. In this study, we propose a system that utilizes cost-effective and renewable bio-resource, glycerol, as the starting material. In this regard, we conducted the reaction in the presence of mono-oxygenated rhenium diphosphine complexes as catalysts and alcohol as the solvent and hydrogen transfer agent. Among the tested complexes, the [ReOBr3(Xantphos)] complex combined with 2-propanol as a solvent and the reducing agent exhibited the most outstanding performance, yielding allyl alcohol with an exceptional efficiency of 100%. The structures of three newly synthesized complexes, [ReOBr3(Xantphos)], [ReOBr3(DPEphos)], and [ReOCl3(dppb)] were determined by X-ray single crystallography. These findings contribute to the advancement of allyl alcohol production, offering a more sustainable and environmentally friendly alternative to conventional petroleum-based methods.

Synthetic and DFT Modeling Studies on Suzuki–Miyaura Reactions of 4,5-Dibromo-2-methylpyridazin-3(2H)-one with Ferrocene Boronates, Accompanied by Hydrodebromination and a Novel Bridge-Forming Annulation In Vitro Cytotoxic Activity of the Ferrocenyl–Pyridazinone Products

This paper presented the efficiency of different Pd-based catalytic systems in a series of SM reactions of 4,5-dibromo-2-methylpyridazin-3(2H)-one with ferroceneboronic acid, ferrocene-1,1′-diboronoc acid, and its bis-pinacol ester. In addition to the disubstituted product, these transformations afford substantial amounts of isomeric 4- and 5-ferrocenyl-2-methylpyridazin-3(2H)-ones, and a unique asymmetric bi-pyridazinone-bridged ferrocenophane with a screwed molecular architecture. The reactions of phenylboronic acid, conducted under the conditions, are proven to be the most reductive in the conversions of ferroceneboronic acid, and produce 2-methyl-4,5-diphenylpyridazin-3(2H)-one as single product, supporting our view about solvent-mediated hydrodehalogenations that are supposed to proceed via the assistance of the ferrocenyl group present in the reaction mixture, or attached to the bromo-pyridazinone scaffold, which is constructed in the first SM coupling of the heterocyclic precursor. A comparative DFT modelling study on the structures and possible transformations of relevant bromo-, ferrocene- and phenyl-containing carbopalladated intermediate pairs was carried out, providing reasonable mechanisms suitable to account for the apparently surprising regioselectivity of the alternative hydrodebromination processes, and for the formation of the ferrocenophane product. Supporting the results of DFT modelling studies, the implication of DMF as a hydrogen transfer agent in the hydrodebromination reactions is evidenced by deuterium labelling experiments using the solvent mixtures DMF-d7–H2O (4:1) and DMF–D2O (4:1). The organometallic products display antiproliferative effects on human malignant cell lines.

Furfural and 5-(hydroxymethyl)furfural valorization using homogeneous Ni(0) and Ni(II) catalysts by transfer hydrogenation

The complex [dippeNi(COD)] (dippe =1,2-bis(diisopropyl phosphino)ethane) was used as a catalytic precursor in furfural (FF) and 5-(hydroxymethyl)furfural (HMF) valorization, along with formic acid as hydrogen transfer agent, to produce the corresponding alcohol in each case, with excellent yields (≥99%) and under mild conditions (5 h, 120 °C).The air-stable Ni(II)-catalyst precursor, [dippeNiCl2], was assessed in FF hydroamination, with a variety of anilines, using FA as hydrogen source (at 16 h and 120 °C), to produce furfuryl amines with an excellent yield and selectivity (89 to >99%). To our knowledge, this is the first report of reductive amination of FF to get furfuryl amines using a homogeneous Ni catalyst in a hydrogen transfer protocol.

Batch Reactor Study for Partial Upgrading of a Heavy Oil with a Novel Solid Hydrogen Transfer Agent

A novel solid hydrogen transfer agent (SHTA) based on an organic polymer containing fused-aromatic-ring units, supported in an inorganic matrix, was prepared and tested as a hydrogen donor in the u...

Fibrane the reduced derivative of fenofibrate

Synthetic routes for the preparation of (i) isopropyl 2-(4-(4-chlorobenzyl)phenoxy)-2-methyl propanoate (Reduced Fenofibrate, Fibrane) (2) from isopropyl 2-(4-(4-chlorobenzoyl)phenoxy)-2-methylpropanoate (Fenofibrate) (1) in a single step is established in good yield and purity under mild conditions. The newly synthesized derivative of Fenofibrate has been characterized by NMR and IR spectroscopy techniques. Selective conversion of biphenyl ketone moiety, in the presence of ester carbonyl group in Fenofibrate to its corresponding alkane can be performed by Pd catalyst reduction with hydrogen transfer agent ammonium formate.

Benzylamine as Hydrogen Transfer Agent: Cobalt-Catalyzed Chemoselective C=C Bond Reduction of β-Trifluoromethylated α,β-Unsaturated Ketones via 1,5-Hydrogen Transfer.

An efficient cobalt-catalyzed chemoselective reduction of β-CF3 -α,β-unsaturated ketones using benzylamine as hydrogen transfer agent involving intramolecular 1,5-hydrogen transfer is reported. The reaction proceeded smoothly with a relatively wide range of substrates including those bearing aromatic heterocycles such as a furyl ring system in high yields (74-92 %). This provides an efficient method for the synthesis of β-CF3 saturated ketones in one-pot. This methodology was also applied to the selective C=C reduction of other enone substrates bearing no β-CF3 -substituent, of which β-substituted or β,β-disubstituted enones are tolerated, giving the desired products in good yields (72-75 %). Mechanistic studies indicate that the reaction involves 1,5-hydrogen transfer.

Cobaloxime Catalysis: Selective Synthesis of Alkenylphosphine Oxides under Visible Light.

Direct activation of H-phosphine oxide to react with an unsaturated carbon-carbon bond is a straightforward approach for accessing alkenylphosphine oxides, which shows significant applications in both synthetic and material fields. However, expensive metals and strong oxidants are typically required to realize the transformation. Here, we demonstrate the utility of earth-abundant cobaloxime to convert H-phosphine oxide into its reactive radical species under visible light irradiation. The radical species thus generated can be utilized to functionalize alkenes and alkynes without any external photosensitizer and oxidant. The coupling with terminal alkene generates E-alkenylphosphine oxide with excellent chemo- and stereoselectivity. The reaction with terminal alkyne yields linear E-alkenylphosphine oxide via neutral radical addition, while addition with internal ones generates cyclic benzophosphine oxides and hydrogen. Mechanistic studies on radical trapping experiments, electron spin resonance studies, and spectroscopic measurements confirm the formation of phosphinoyl radical and cobalt intermediates that are from capturing the electron and proton eliminated from H-phosphine oxide. The highlight of our mechanistic investigation is the dual role played by cobaloxime, viz., both as the visible light absorber to activate the P(O)-H bond as well as a hydrogen transfer agent to influence the reaction pathway. This synergetic feature of the cobaloxime catalyst preforming multiple functions under ambient condition provides a convergent synthetic approach to vinylphosphine oxides directly from H-phosphine oxides and alkenes (or alkynes).

Anionic reverse microemulsion grafting of acrylamide (AM) on HydroxyEthylCellulose (HEC): Synthesis, characterization and application as new ecofriendly low-cost flocculant

New water-soluble cellulosic derivative based on HEC was successfully elaborated (HECc), and used as anionic coagulant-flocculant of colloidal systems Fe(OH)3 and to remove of heavy metal ions (Cu(II)) from aqueous media. HECc was synthesized in unconventional reverse microemulsion process using water as ecofriendly solvent and as hydrogen transfer agent, where cyclohexane was employed as continuous phase to reduce the hydrophobicity of the medium. The amide groups grafted on HEC main chain were saponified to increase the negative charge density, and then the zeta potential value of HECc derivative reached -45 mV. The proposed structure of HECc was confirmed by FTIR, 1H, 13C NMR and deept-135. The XRD technique was used to study the effect of grafting process on the crystalline order. Moreover, the morphological changes and the elementary composition of the surfaces were studied using scanning electron microscope equipped with EDX. The new HECc coagulant-flocculant showed a high coagulation-flocculation capacity toward Fe(OH)3 colloidal system at 35 μL as added volume of 0.5% flocculant solution. Moreover, the pH values showed an important effect (species distribution) on the coagulation-flocculation mechanism and on the flocculating capacity to remove (Cu (II).

Pd nanoparticles on green support as dip-catalyst: a facile transfer hydrogenation of olefins and N-heteroarenes in water.

Chemo- and regioselective hydrogenation methods using highly green sources, particularly from metal nanoparticles on plant stem as support and water, is an intensive research area, which is highly relevant to the development of green chemistry and technology in the 21st century. Here, the synthesis and activity of a heterogeneous catalytic system (called “dip-catalyst”) for the transfer hydrogenation of a series of styrenyl, unfunctionalized olefins, quinoline and other N-heteroarenes, are presented. It consists of Pd nanoparticles (15–20 nm) anchored on bio-processed jute plant (Corchorus genus) stem as the support. Pd nanoparticles were decorated on the green support (GS) jute stem by the in situ reduction of K2PdCl4 in aqueous medium at 70 °C, using formic acid as the reductant. The Pd@GS was characterized using SEM, EDS, XRD, FTIR, XPS and TEM. Elemental mapping revealed uniform distribution of Pd on the cellulose matrix of the jute stem. The catalyst was successfully applied to the chemoselective transfer hydrogenation of numerous styrenyl, unfunctionalized olefins. Its high functional group tolerance was investigated during the olefins hydrogenation in water. Furthermore, Pd@GS was capable of quantitative hydrogenation to selectively produce 1,2,3,4-tetrahydroquinoline (THQ) in water using stoichiometric amounts of tetrahydroxydiboron (THDB) at 60 °C with turn over frequency (TOF) 4938 h−1. This system is stable in water and displays excellent recyclability; it could be used for 32 consecutive cycles, without losing its original crystallinity or requiring replenishment.

Upgrading of petroleum vacuum residue using a hydrogen-donor solvent with acid-treated carbon

Hydrocarbon/carbon systems can be used to perform the hydrogen transfer reaction in heavy oil upgrading, as alternatives to metal catalysts and molecular hydrogen. In this study, a system comprising a hydrogen-donor solvent (tetralin) and acid-treated activated carbon was established to evaluate its ability as a hydrogen transfer agent to upgrade a vacuum residue (VR). The use of tetralin substantially decreased coke formation from 32.7 wt% to a negligible amount in VR upgrading at 450 °C because the solvent could act as a hydrogen donor and diluent for the coke precursors. The acid-treated activated carbon accelerated dehydrogenation of tetralin through hydrogen transfer in the upgrading, resulting in a higher residue conversion and moderate coke formation. In view of the phase behavior, the hydrogen transfer reaction could also be promoted by increasing the contact between the hydrogen acceptor and donor in the supercritical medium. In the VR upgrading using the activated carbon in supercritical tetralin, complete residue conversion was achieved with 47 wt% light fractions (gas and light oil) and 6 wt% coke at 450 °C and 5.33 MPa. The results indicate that the streams available in oil refinery processes, which are rich in hydrocarbons with hydrogen-donor abilities, have great potential for use in heavy oil upgrading.

Thermal decomposition of poly(styrene) in the presence of a hydrogen atom transfer agent

General-purpose poly(styrene) is conventionally prepared using radical techniques in which termination of polymerization occurs through radical coupling to form a head-to-head unit. Previous evidence has shown that the bond linking the head-to-head components can undergo homolysis under thermal stress. Styrene monomer is generated from the rapid depolymerization of the macroradicals generated to release styrene monomer. Poly(styrene) containing no head-to-head units, on the other hand, does not undergo similar decomposition. Furthermore, the presence of polymer additives such as a hydrogen transfer agent that can effectively trap the macroradicals generated by chain scission should inhibit chain unzipping to form monomer. A direct comparison of the stability of the polymer in the presence and absence of a hydrogen atom transfer agent is readily available by thermogravimetric techniques.

Hydrogen Adsorption Properties of Carbon Nanotubes and Platinum Nanoparticles from a New Ammonium-Ethylimidazolium Chloroplatinate Salt.

Self-supporting membranes built entirely of carbon nanotubes have been prepared by wet methods and characterized by Raman spectroscopy. The membranes are used as supports for the electrodeposition of Pt nanoparticles without the use of additional additives and/or stabilizers. The Pt precursor is an ad hoc synthesized ammonium-ethylimidazolium chloroplatinate(IV) salt, [NH3 (CH2 )2 MIM)][PtCl6 ]. The Pt complex was characterized using NMR spectroscopy, XRD, ESI-MS, and FTIR spectroscopy. The interaction between the Pt-carbon nanotubes nanocomposites and hydrogen is analyzed using electrochemical and quartz microbalance measurements under near-ambient conditions. The contribution of the Pt phase to the hydrogen adsorption on nanotube is found and explained by a kinetic model that takes into account a spillover event. Such a phenomenon may be exploited conveniently for catalysis and electrocatalysis applications in which the hybrid systems could act as a hydrogen transfer agent in specific hydrogenation reactions.

Stereocontrolled (Me3Si)3SiH-Mediated Radical and Ionic Hydride Transfer in Synthesis of 2,3,5-Trisubstituted THF.

2,3,5-Trisubstituted tetrahydrofurans were prepared stereoselectively through a two-step process involving the addition of an acyl radical to a β-silyloxy acrylic ester followed by an acid-catalyzed desilylation-ketalization sequence and a final oxocarbenium reduction step. High levels of 1,2- and 1,3-stereocontrol were attained when (Me3Si)3SiH was used as a radical followed by a ionic hydrogen transfer agent.

Potential application of Pd-Ni bimetallic nanoparticles dispersed in Al-pillared clay matrix as catalyst for hydrodechlorination of chloroanilines from aqueous sources

The Al-pillared clay (Al-P) was prepared by insertion of [AlO4Al12(OH)24(H2O)12]7+ clusters into the interlayer of montmorillonite clay and subsequent thermal activation. Al-pillared clay was used as an efficient inorganic matrix for dispersion of Pd-Ni bimetallic nanoparticles. The bimetallic nanoparticles were synthesized using chemical reduction method. The supported bimetallic catalysts were characterized using XRD, IR, UV–vis, TGA, sorptometric, FE-SEM-EDX and TEM techniques. The expansion of the interlayer space of the parent clay as a result of pillaring and its subsequent retention in the Pd-Ni/Al-P system was noted from XRD study. The structural integrity as well as electronic environment of the pillars and supported metal particles has been inferred from the FTIR and UV–vis study. FE-SEM study implies changes in morphological feature of the clay materials upon pillaring and dispersion of the bimetallic nanoparticles. The TEM study of the supported bimetallic system indicated well dispersion of the metal species with particle size in the range of 10–25nm. The Pd-Ni/Al-P system was used as an efficient heterogeneous catalyst for hydrodechlorination of chloroanilines under hydrogen transfer condition using hydrazine hydrate as hydrogen donating agent. The catalytic studies indicated that the bimetallic Pd-Ni system supported over Al-P is highly active for the reaction. The effect of various reaction parameters such as molar ratio of metallic components, temperature, and time, type of hydrogen transfer agents and functionality of substrate was studied in details.

Changing the Action of Iron from Stoichiometric to Electrocatalytic in the Hydrogenation of Ketones in Aqueous Acidic Media.

Cyclohexanone, a model compound chosen to conveniently represent small oxygenates present in the aqueous phase of biomass hydrothermal upgrading streams, was hydrogenated in the presence of electrodeposited iron(0) using aqueous formic or sulfuric acid as a hydrogen donor. Under these conditions, zero-valent iron is consumed stoichiometrically and serves as both a formic acid decomposition site and a hydrogen transfer agent. However, the resulting iron(II) can be used to continuously regenerate iron(0) when a potential is applied to the glassy carbon working electrode. Controlled potential electrolysis experiments show a 17% conversion of cyclohexanone (over 1000 seconds) to cyclohexanol with >80% efficiency of iron deposition from an iron(II) sulfate solution containing formic or sulfuric acid. In the absence of electrodeposited iron, formation of cyclohexanol could not be detected.

Catalytic activity of SBA-15-grafted indium tri-isopropoxide in chemoselective MPV reductions

Indium tri-isopropoxide-containing heterogeneous In(O i Pr)3–SBA-15 catalyst were synthesized by grafting method and were then used as catalyst in the Meerwein–Ponndorf–Verley (MPV) reduction of various carbonyl compounds using 2-propanol as the hydrogen transfer agent. The prepared new heterogeneous catalyst, In(O i Pr)3–SBA-15, was characterized in details by using XRD, 29Si NMR,13C NMR, TEM, N2 adsorption and ICP-OES. New heterogeneous catalyst has been studied in the chemoselective MPV reduction of unsaturated aldehydes and ketones. Good activity and selectivity to the reduced unsaturated alcohols, citronellol, cinnamalcohol, α-ionol, 3-methyl-2-butanol, geraniol, nerol were observed over indium tri-isopropoxide supported on silica. The In(O i Pr)3–SBA-15 catalyst is recyclable up to six cycles without any significant loss in its catalytic activity. Eventually, In(O i Pr)3–SBA-15 has been found that active catalyst in the MPV reactions of carbonyl compounds including unsaturated aldehydes and ketones with excellent conversion, selectivity and reusability.

Hydrodehalogenation of Halogenated Organic Contaminants from Aqueous Sources by Pd Nanoparticles Dispersed in the Micropores of Pillared Clays Under Transfer Hydrogenation Condition

Palladium nanoparticles dispersed in the micropores of the Al-pillared clay was prepared by chemical reduction of palladium chloride salt. The Al-pillared clay was prepared by insertion of [AlO4Al12(OH)24(H2O)12]7+ clusters into clay interlayer and subsequent thermal activation. The pillared clay supported system (Pd/Al–P) was characterized using XRD, IR, UV–Vis, SEM, TEM and sorptometric technique. The expansion of the interlayer space as a result of pillaring was noted for Pd/Al–P system from the XRD study. The TEM study of the supported system indicated well dispersion of the Pd species with particle size in the range of 5–30 nm. The supported Pd particles were used as an efficient heterogeneous catalyst for the hydrodehalogenation of halogenated organics under hydrogen transfer condition using hydrazine hydrate as hydrogen donating agent. The effect of various reaction parameters such as temperature, time, and nature of support, type of hydrogen transfer agents and functionality of substrate was studied in details. The catalytic study clearly indicated superior catalytic activity of the supported Pd system in presence of hydrazine hydrate as hydrogen donating agent. The Al-pillared clay as support influences the dispersion and catalytic activity of the supported Pd nanoparticles.

HAP-Pd(0): A Highly Efficient Recyclable Heterogeneous Catalyst for the Selective Reduction of Carbon–Carbon Double Bond in α,β-Unsaturated Ketones

A recyclable heterogeneous hydroxyapatite-supported palladium(0) catalyst was prepared by a simple procedure and successfully applied for the selective reduction of carbon–carbon double bond in α,β-unsaturated ketones using HCOONH4 as hydrogen transfer agent. The workup procedure is simple, and the catalyst could be recovered by simple filtration and recycled for five consecutive runs without significant loss of activity.

A smart palladium catalyst in ionic liquid for tandem processes

New catalytic systems based on in situ and preformed palladium nanoparticles in ionic liquids (characterised by TEM) starting from palladium acetate or dipalladiumtris(dibenzylideneacetone) have been applied in the synthesis of 4-phenylbutan-2-one (II), a model compound for the preparation of fragrances. Imidazolium-based ionic liquid containing a methyl hydrogenophosphonate anion leads to an efficient Pd-catalyzed tandem coupling/reduction process, taking advantage of the multi-role of this solvent (nanoparticles stabiliser, base, hydrogen transfer agent). The influence of the mono-phosphine ligands (1-3) on the catalyst has been evaluated, showing that the ligand-free palladium system turns into the most appropriate for the formation of II using Pd(OAc)(2) as precursor. Fine-tuning conditions involved in this multi-parameter process have led us to propose a plausible mechanism based on the hydrogen transfer coming from the methyl hydrogenophosphonate anion.