Showing papers on "Transfer hydrogenation published in 2018"
TL;DR: In this article, the authors summarize the breakthroughs on the development of multiple catalytic technologies in the past decade, including direct hydrogenation using high-pressure hydrogen; transfer hydrogenation with reductive compounds; photocatalytic and electrocatalytic hydrogenation accompanied with water oxidation, and focus on how to understand the two key element steps including hydrogen dissociation and the activation of nitro group in the process of hydrogenation.
Abstract: Selective catalytic hydrogenation of nitroarenes is of great importance for dyestuff and pharmaceutical industry. A critical step toward the rational design of targeted catalysts is to determine their electronic structures and related reaction mechanism. In this review, we summarize the breakthroughs on the development of multiple catalytic technologies in the past decade, including direct hydrogenation using high-pressure hydrogen; transfer hydrogenation using reductive compounds; photocatalytic hydrogenation using hole scavenger; electrocatalytic hydrogenation accompanied with water oxidation. We focus on how to understand the two key element steps including hydrogen dissociation and the activation of nitro group in the process of hydrogenation, and design and fabricate nanostructured catalysts with desired activity and selectivity. For direct catalytic hydrogenation, representative catalysts include metal, metal oxide/sulfide/carbides/nitrides/boride, and functional carbon material, and the crucial factors to tune their activity and selectivity are discussed such as metal-support interaction, size effect, alloy effect, defect engineering, and so on. Catalytic transfer hydrogenation, photocatalytic and electrocatalytic hydrogenation, in which these catalysts abstracts hydrogen species from the hydrogen donor and stabilizes it on the catalyst surface, restricting active H* recombination, and then the active hydrogen species can be promptly transferred to nitroarenes for the hydrogenation. It is worth mentioning that the light harvesting and charge separation of photocatalyst and the conductivity of electrocatalyst should also be considered together for the overall performance. All these experiences lay the foundation for large scale production of anilines and guide the rational design of catalysts for other organic transformation reactions.
326 citations
TL;DR: The catalytic performance of ISAS-Co/OPNC in both reactions surpasses previously reported homogeneous and heterogeneous precious-metal catalysts and it is suggested that the Eley-Rideal mechanism is dominant.
Abstract: Single-atom catalysts (SACs) have been explored widely as potential substitutes for homogeneous catalysts. Isolated cobalt single-atom sites were stabilized on an ordered porous nitrogen-doped carbon matrix (ISAS-Co/OPNC). ISAS-Co/OPNC is a highly efficient catalyst for acceptorless dehydrogenation of N-heterocycles to release H2 . ISAS-Co/OPNC also exhibits excellent catalytic activity for the reverse transfer hydrogenation (or hydrogenation) of N-heterocycles to store H2 , using formic acid or external hydrogen as a hydrogen source. The catalytic performance of ISAS-Co/OPNC in both reactions surpasses previously reported homogeneous and heterogeneous precious-metal catalysts. The reaction mechanisms are systematically investigated using first-principles calculations and it is suggested that the Eley-Rideal mechanism is dominant.
146 citations
TL;DR: A series of highly crystalline, porous, hafnium-based metal-organic frameworks (Hf-MOFs) have been shown to catalyze the transfer hydrogenation reaction of levulinic ester to produce γ-valerolactone by using isopropanol as a hydrogen donor.
Abstract: A series of highly crystalline, porous, hafnium-based metal-organic frameworks (Hf-MOFs) have been shown to catalyze the transfer hydrogenation reaction of levulinic ester to produce γ-valerolactone by using isopropanol as a hydrogen donor. The results are compared with their zirconium-based counterparts. The role of the metal center in Hf-MOFs has been identified and reaction parameters optimized. NMR studies using isotopically labeled isopropanol provide evidence that the transfer hydrogenation occurs through a direct intermolecular hydrogen transfer route. The catalyst, Hf-MOF-808, can be recycled several times with only a minor decrease in catalytic activity. The generality of the procedure has been demonstrated by accomplishing the transformation with aldehydes, ketones, and α,β-unsaturated carbonyl compounds. The combination of Hf-MOF-808 with the Bronsted-acidic Al-Beta zeolite gives the four-step one-pot transformation of furfural to γ-valerolactone in good yield of 75 %.
106 citations
TL;DR: A new NCP-type pincer iridium complex (BQ-NCOP)IrHCl containing a rigid benzoquinoline backbone has been developed for efficient, mild TH of unactivated C-C multiple bonds with ethanol, forming ethyl acetate as the sole byproduct.
Abstract: The first general catalytic approach to effecting transfer hydrogenation (TH) of unactivated alkenes using ethanol as the hydrogen source is described. A new NCP-type pincer iridium complex (BQ-NCOP)IrHCl containing a rigid benzoquinoline backbone has been developed for efficient, mild TH of unactivated C–C multiple bonds with ethanol, forming ethyl acetate as the sole byproduct. A wide variety of alkenes, including multisubstituted alkyl alkenes, aryl alkenes, and heteroatom-substituted alkenes, as well as O- or N-containing heteroarenes and internal alkynes, are suitable substrates. Importantly, the (BQ-NCOP)Ir/EtOH system exhibits high chemoselectivity for alkene hydrogenation in the presence of reactive functional groups, such as ketones and carboxylic acids. Furthermore, the reaction with C2D5OD provides a convenient route to deuterium-labeled compounds. Detailed kinetic and mechanistic studies have revealed that monosubstituted alkenes (e.g., 1-octene, styrene) and multisubstituted alkenes (e.g., cy...
106 citations
TL;DR: This review summarises the most recent advances in Ir-NHC catalysis while revisiting all the classical reactions in which this type of catalyst has proved to be active, accompanied by an examination of the great variety of catalytic cycles hitherto reported.
Abstract: This review summarises the most recent advances in Ir–NHC catalysis while revisiting all the classical reactions in which this type of catalyst has proved to be active. The influence of the ligand system and, in particular, the impact of the NHC ligand on the activity and selectivity of the reaction have been analysed, accompanied by an examination of the great variety of catalytic cycles hitherto reported. The reaction mechanisms so far proposed are described and commented on for each individual process. Moreover, some general considerations that attempt to explain the influence of the NHC from a mechanistic viewpoint are presented at the end of the review. The first sections are dedicated to the most widely explored reactions that use Ir–NHCs, i.e., hydrogenation and transfer hydrogenation, for which a general overview that tries to compile all the Ir–NHC catalysts hitherto reported for these processes is provided. The next sections deal with hydrogen borrowing, hydrosilylation, water splitting, dehydrogenation (of alcohols, alkanes, aminoboranes and formic acid), hydrogen isotope exchange (HIE), signal amplification by reversible exchange and C–H bond functionalisation (silylation and borylation). The last section compiles a series of reactions somewhat less explored for Ir–NHC catalysts that include the hydroalkynylation of imines, hydroamination, diboration of olefins, hydrolysis and methanolysis of silanes, arylation of aldehydes with boronic acids, addition of aroyl chlorides to alkynes, visible light driven reactions, isomerisation of alkenes, asymmetric intramolecular allylic amination and reactions that employ heterometallic catalysts containing at least one Ir–NHC unit.
97 citations
TL;DR: In this paper, the first facile fabrication of active, inexpensive, and reusable cobalt nanoparticles (NPs) coated with a N,P-codoped carbon shell derived from naturally renewable biomass and earth-abundant, low-cost cobalt salt and PPh3 was reported.
88 citations
TL;DR: The Pd/g-C3N4 nanosheets as support materials can significantly boost the efficiency of Pd nanoparticles for the reduction of nitro compounds to primary amines.
81 citations
TL;DR: In this article, ordered mesoporous N-doped carbon (OMNC) encapsulating Co nanoparticles (NPs) have been prepared under direct polymerization between [Co(NH 2CH2CH2NH2)2]Cl2 and carbon tetrachloride through a hard template method.
Abstract: Ordered mesoporous N-doped carbon (OMNC) encapsulating Co nanoparticles (NPs) have been prepared under direct polymerization between [Co(NH2CH2CH2NH2)2]Cl2 and carbon tetrachloride through a hard template method. The catalysts (Co@OMNC) are pyrolyzed at various temperatures and characterized by elemental analysis, Brunauer–Emmett–Teller (BET), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). In the quinoline transfer hydrogenation with formic acid (FA) as the hydrogen source under a base-free condition, the encapsulated Co NPs are physically isolated from the acidic reaction solution, which prevents them from poisoning or leaching. The rich mesopores and N dopants afford enhanced adsorption of quinoline. Co@OMNC-700 (pyrolyzed at 700 °C) gives the best activity (98.8% conversion) as well as >99% 1,2,3,4-tetrahydroquinoline (THQ) selectivity at 140 °C for 4 h, exhibiting significantly improved performance compared to using H2 as the hydrogenation ...
81 citations
TL;DR: In this paper, the reduction of ketones with 2-propanol as reductant was achieved using an in-situ generated catalytic system based on manganese pentacarbonyl bromide, as metal precursor, and ethylenediamine as ligand.
79 citations
TL;DR: In this article, an indazolyl-pyridinyl-triazole ligand was synthesized and its iridium complex supported on hydrotalcite was characterized via X-ray power diffraction (XRD), XPS, energy dispersive Xray (EDX) spectroscopy and transmission electron microscopy (TEM).
68 citations
TL;DR: A series of novel ruthenium(II) complexes supported by a symmetrical NNN ligand exhibited good performance in transfer hydrogenation to form new C-C bonds using alcohols as the alkylating agents, generating water as the only byproduct.
Abstract: A series of novel ruthenium(II) complexes supported by a symmetrical NNN ligand were prepared and fully characterized. These complexes exhibited good performance in transfer hydrogenation to form new C–C bonds using alcohols as the alkylating agents, generating water as the only byproduct. A broad range of substrates, including (hetero)aryl- or alkyl-ketones and alcohols, were well tolerated under the optimized conditions. Notably, α-substituted methylene ketones were also investigated, which afforded α-branched steric hindrance products. A potential application of α-alkylation of methylene acetone to synthesize donepezil was demonstrated, which provided the desired product in 83% yield. Finally, this catalytic system could be applied to a one-pot double alkylation procedure with sequential addition of two different alcohols. The current protocol is featured with several characteristics, including a broad substrate scope, low catalyst (0.50 mol %) loadings, and environmental benignity.
TL;DR: In this paper, three manganese complexes were synthesized and tested for the asymmetric transfer hydrogenation (ATH) of acetophenone in 2-PrOH, and only the precatalyst 16, upon reaction with potassium tert-butoxide (KOtBu), generated an active system at 80 °C for the ATH of 1-phenylethanol in an enantiomeric excess (ee) of 42%.
TL;DR: In this paper, a brief overview of advances on ruthenium(II) N-heterocyclic carbene complexes (NHCs) applied for hydrogenation reactions undertaken during the last five years is provided.
TL;DR: In this article, the authors highlight the recent notable advances in homogeneous transfer hydrogenation using transition metal complexes, especially in direction to establish practical greener processes by upgrading the catalyst performance or by expanding the scope of reducible functional groups.
TL;DR: Comparative testing revealed PdNPs immobilized on lightly cross-linked phsophine-decoarted PEGylated polymer to be a highly efficient catalyst for the aqueous phase reduction of nitroarenes catalyzed by a nanoparticle-based system.
TL;DR: DFT calculations provide insights into the reaction mechanism as well as the origin of stereochemistry, affording novel spiroindolines in good yields and with excellent enantioselectivity.
Abstract: A highly efficient synthesis of enantioenriched spiroindolines by catalytic asymmetric dearomatization of indolyl dihydropyridines through a chiral phosphoric acid catalyzed enamine isomerization/spirocyclization/transfer hydrogenation sequence has been developed. This reaction proceeds under mild reaction conditions, affording novel spiroindolines in good yields (up to 88 %) with excellent enantioselectivity (up to 97 % ee). DFT calculations provide insights into the reaction mechanism as well as the origin of stereochemistry.
08 Jun 2018
TL;DR: A series of zirconium-based catalysts were prepared for the selective transfer hydrogenation of biomass-derived furfural (FFR) into furfuryl alcohol with lower alcohols as hydrogen sources, and Zr(OH)4 revealed good performance and stability after being repeated four times.
Abstract: A series of zirconium-based catalysts were prepared for the selective transfer hydrogenation of biomass-derived furfural (FFR) into furfuryl alcohol with lower alcohols as hydrogen sources. The sample structures were clearly characterized using various methods, such as X-ray powder diffraction, thermogravimetric analysis, scanning electron microscope, NH3-temperature-programmed desorption (TPD), CO2-TPD, and nitrogen physisorption. Excellent furfuryl alcohol yield of 98.9 mol % was achieved over Zr(OH)4 using 2-propanol as a hydrogen donor at 447 K. The poisoning experiments indicated that basic centers displayed pronounced effect for FFR transfer hydrogenation. Moderate monoclinic phase content in ZrO2-x enhanced the conversion rate and furfuryl alcohol selectivity, whereas acid-basic site density ratio had slight influence on FFR conversion. Besides, Zr(OH)4 revealed good performance and stability after being repeated four times. The possible mechanism for this transfer hydrogenation process over Zr(OH)4 catalyst with 2-propanol as the hydrogen source was proposed.
TL;DR: It was noteworthy that many readily reducible or labile functional groups such as nitro, cyano, ester, and halide did not undergo any change under the reaction conditions.
Abstract: A Cp*Ir complex bearing a functional bipyridonate ligand [Cp*Ir(2,2’-bpyO)(H2O)] was found to be a highly efficient and general catalyst for transfer hydrogenation of aldehydes and chemoselective transfer hydrogenation of unsaturated aldehydes with isopropanol under neutral conditions. It was noteworthy that many readily reducible or labile functional groups such as nitro, cyano, ester and halide did not undergo any change under the reaction conditions. Furthermore, this catalytic system exhibited highly activity for transfer hydrogenation of ketones with isopropanol. Notably, this research exhibited new potential of metal-ligand bifunctional catalysts for transfer hydrogenation.
TL;DR: A cyclometalated rhodium complex has been shown to perform highly selective and efficient reduction of aldehydes, deriving the hydrogen from methanol.
TL;DR: In this article, a highly efficient and chemoselective transfer hydrogenation of ketones in water has been successfully achieved with the newly developed iridium catalyst, which is used as a traceless hydride source.
TL;DR: This is the first systematic study on the effect of stereoelectronic tuning of ancillary orthometalated NHC ligand in Ru(II)-catalyzed transfer hydrogenations of various types of unsaturated compounds with broad substrate scope.
Abstract: In an effort to develop efficient Ru(II)–NHC-based catalyst considering their stereoelectronic effect for hydride-transfer reaction, we found that the ancillary NHC ligand can play a significant role in its catalytic performance. This effect is demonstrated by comparing the activity of two different types of orthometalated precatalysts of general formula [(p-cymene)(NHC)RuII(X)] (NHC = an imidazolylidene-based ImNHC, compound 2a–c, or a mesoionic triazolylidene-based tzNHC, compound 4) in transfer hydrogenation of carbonyl substrates. The electron-rich precatalyst, 2c, containing p-OMe-substituted NHC ligand performed significantly better than both unsubstituted complex 2a and p-CF3 substituted electron-poor complex 2b in ketone reduction. Whereas bulky mesoionic triazolylidene ligand containing complex 4 was found to be superior catalyst for aldehyde reduction and the precatalyst 2a is more suitable for the selective transfer hydrogenation of a wide range of aromatic aldimines to amines. To the best of o...
TL;DR: In this paper, well-dispersed Pd nanoparticles were anchored on g-C3N4 nanosheets, which were prepared by a liquid-phase exfoliation method.
Abstract: Well-dispersed Pd nanoparticles were anchored on g-C3N4 nanosheets, which were prepared by a liquid-phase exfoliation method. The hybrid material displayed excellent catalytic activity for the transfer hydrogenation of nitroarenes. The reactions can be conducted smoothly in water at room temperature with formic acid as hydrogen source. Aniline was produced in excellent yield (>99%; turnover frequency: 853), surpassing the majority of reported heterogeneous catalysts using formic acid or formates as hydrogen source. The increased activity of such a hybrid catalyst can be ascribed to the nitrogen-rich and amphipathic property of the carbon nitride support, the stable and uniform dispersed Pd nanoparticles and the Mott–Schottky effect between the g-C3N4 nanosheets and the metal nanoparticles. The heterogeneous Mott–Schottky catalyst can be reused for five cycles without any obvious loss of its catalytic activity.
TL;DR: Four neutral organometallic tethered complexes exhibit moderate antiproliferative activity toward human ovarian, lung, hepatocellular, and breast cancer cell lines and show potent catalytic activity in the transfer hydrogenation of NAD+ to NADH with formate as hydride donor in aqueous solution.
TL;DR: Results by varying the substitution pattern of the ligand are consistent with an out‐sphere mechanism for the H‐transfer, and good to excellent yields were obtained for a wide substrate scope with broad functional group tolerance.
Abstract: A catalytic system based on complexes comprising abundant and cheap manganese together with readily available aminotriazole ligands is reported. The new Mn(I) complexes are catalytically competent in transfer hydrogenation of ketones with 2-propanol as hydrogen source. The reaction proceeds under mild conditions at 80 °C for 20 h with 3 % of catalyst loading using either KO t Bu or NaOH as base. Good to excellent yields were obtained for a wide substrate scope with broad functional group tolerance. The obtained results by varying the substitution pattern of the ligand are consistent with an out-sphere mechanism for the H-transfer.
TL;DR: In this paper, the photocatalytic transformation of cinnamaldehyde (CAL) to form Cinnamyl alcohol (COL) in the presence of isopropanol was investigated under visible light and 365 nm UV light.
TL;DR: Pd nanoparticles anchored on a covalent triazine framework (Pd@CTF) were fabricated and employed to catalyze the transfer hydrogenation of nitro-compounds with formic acid as the hydrogen source as discussed by the authors.
Abstract: Pd nanoparticles anchored on a covalent triazine framework (Pd@CTF) were fabricated and employed to catalyze the transfer hydrogenation of nitro-compounds with formic acid as the hydrogen source. The results demonstrated that Pd@CTF displayed excellent catalytic activity and high chemoselectivity for the hydrogenation reaction at room temperature. Various substituted nitro-compounds were successfully converted to the corresponding amines in 0.2–2.5 h with other reducible functional moieties remaining intact. The high performance of Pd@CTF can be attributed to the synergistic interaction between the highly dispersed Pd nanoparticles and the covalent triazine framework support. The Pd@CTF catalyst can be readily reused for at least five consecutive runs without an obvious loss of its catalytic activity.
TL;DR: A multicomponent nanocatalyst system was fabricated for the transfer hydrogenation of nitrile compounds that contains palladium, copper, and iron, which are supported on the magnetite nanospheres, and the loading of palladium could be at the parts per million level.
TL;DR: In this paper, a visible-light photocalytic method for the chemoselective transfer hydrogenation of imines in batch and continuous flow is described, which utilizes Et3N as both hydrogen source and single-electron donor, enabling the selective reduction of amines derived from diarylketimines containing other reducible functional groups including nitriles, halides, esters, and ketones.
TL;DR: Transformation of ent-2k into a Pallidol analogue via a highly diastereo- and regioselective Friedel-Crafts benzylation of o-chloroanisole is presented and offers a practical access to a new class of conformationally rigid enantiopure 1,4-diols 2k-m having four contiguous chiral centers.