Catalytic Dehydrogenation Of Alcohols Research Articles

Pincer Nickel-Catalyzed Olefination of Alcohols with Benzylphosphine Oxides.

N,N,P-Pincer nickel complexes effectively catalyze reaction of alcohols with benzylphosphine oxides to form alkenes in good yields. The protocol suits for a wide scope of substrates and generates only E-configurated alkenes. The method also shows good compatibility of functional groups. Methoxy, methylthio, trifluoromethyl, ketal, fluoro, chloro, bromo, thienyl, and furyl groups are tolerated. The mechanism studies support that the reaction proceeds through catalytic dehydrogenation of alcohols to aldehydes or ketones followed by condensation with benzyldiphenylphosphine oxides in the presence of KOtBu.

Zeolitic Imidazolium Frameworks-Derived Ru-Based Composite Materials Enable the Catalytic Dehydrogenation of Alcohols to Carboxylic Acids

The metal-catalyzed dehydrogenation of alcohols without any oxidant or additive has been demonstrated as an atom-economic and environmentally friendly strategy for carboxylic acid synthesis. Among the various catalysts applied to this transformation, Ru-based homogeneous ones have been the most extensively studied owing to their remarkable catalytic activity. However, these catalysts required multiple complicated synthesis steps. In addition, they were either difficult to recycle or their recovery processes were relatively tedious. Therefore, a series of Ru-containing heterogeneous catalysts with zeolitic imidazolium frameworks (ZIFs)-derived materials were designed and fabricated. A thorough screening of various parameters was conducted, and it was found that the material obtained by loading a Ru concentration of 0.05 mol/L into Co species embedded in porous N-doped carbon (Ru0.05@Co-NC) had the best catalytic performance in this transformation, affording a handful of carboxylic acid products from the corresponding aromatic or aliphatic alcohols in moderate to high yields. Additionally, the catalyst showed remarkable recyclability as it could be recycled eight times with stable activity fluctuation (45–52%). It is noteworthy that catalyst recycling was convenient and fast, which could be realized simply by an external magnet. Moreover, the stable morphology and structure of Ru0.05@Co-NC, along with its high specific surface area, hierarchical pore structure, high porosity, and other properties, jointly contributed to its high catalytic activity and good recyclability. Furthermore, the stability and activity of Ru0.05@Co-NC were further evaluated through acid etching experiments, which revealed that some Ru species could stably exist in concentrated acids and play a pivotal role in promoting this catalytic process.

Nanostructured bimetallic Zn/Co in N-doped carbon as an efficient catalyst for the alcohol dehydrogenation to carboxylic acids under solvent-free conditions

The catalytic alcohol dehydrogenation to carboxylic acids has been demonstrated as an atom-economic and environmental-friendly synthetic method. However, the reported catalysts either require relatively complicated synthesis or exhibit high activity only in the presence of a solvent. Therefore, it is still in high demand to obtain catalysts that feature facile synthesis and perform well even without any solvent. Herein, a series of nanostructured bimetallic Zn/Co species embedded in N-doped hierarchical porous carbon were fabricated in a facile and green manner. More significantly, the best-performing material (Zn/Co@NC-800) was identified as the first heterogeneous catalyst to enable this transformation under solvent-free conditions. Moreover, the as-prepared composites were comprehensively investigated to determine their structural and morphological properties, which rationalized the superiority of Zn/Co@NC-800 over the other synthesized materials. Further studies signified that Co sites (both Co0 and Co2+) and N species (mainly pyridinic N) were probably involved in this process, functioning as the Lewis acid site and basic site, respectively. Hopefully, this study could provide a simple and sustainable method for carboxylic acid synthesis.

Efficient and Stable Cu‐Cu2O@NC Catalysts for Selective Catalytic Conversion of Glycerol to Lactic Acid

AbstractDeveloping efficient Cu‐based catalysts for catalytic conversion of glycerol to lactic acid has attracted much attention because of the low cost and high activity. However, construction of efficient Cu‐based catalysts with high stability for aqueous reactions at high temperatures still remains a challenge. Herein, highly dispersed Cu0 and Cu2O nanoparticles encapsulated by N‐doped C (Cu‐Cu2O@NC) were constructed by calcination of Cu‐based MOF for the catalytic dehydrogenation of glycerol to lactic acid under N2 atmosphere. The Cu‐Cu2O@NC‐400 catalyst exhibited 100 % conversion of glycerol with 84.8 % selectivity to lactic acid at 220 °C for 90 min. The Cu‐Cu2O@NC‐400 catalyst could be reused for eight times with almost no loss in the catalytic activity. The Cu‐Cu2O@NC‐400 catalyst is stable in the harsh reaction conditions, for the aggregation of Cu nanoparticles is avoided due to the confinement effect. The Cu‐Cu2O@NC‐400 catalyst demonstrated high catalytic activity and superior reusability benefitting from the N‐doping and highly dispersed Cu nanoparticles embedded in N‐doped C. This work will pave the way for designing efficient catalysts with high stability for catalytic dehydrogenation of alcohols.

Efficient Synthesis of C3-Alkylated and Alkenylated Indoles via Manganese-Catalyzed Dehydrogenation.

The catalytic dehydrogenation of alcohols is essential for the sustainable production of valuable products. This provides a new strategy for green organic synthesis in chemical industries. Herein, we describe a manganese-based catalytic system that enables the efficient synthesis of C3-alkylated indoles from benzyl alcohols and indoles via the borrowing hydrogen process. Furthermore, dehydrogenative coupling of 2-arylethanols and indoles yields C3-alkenylated indoles. Meanwhile, reacting 2-aminophenethanol instead of indoles can also obtain the corresponding indole products with high selectivity under the same conditions.

Homogeneously catalyzed acceptorless dehydrogenation of alcohols: A progress report

• Acceptorless dehydrogenation of alcohols to high value chemicals by homogeneous catalysts. • Acceptorless dehydrogenation of alcohols for future applications as hydrogen storage systems. • Multifunctional ligands in the coordination sphere of a metal center to improve catalytic activity. • Novel metal–ligand cooperativity to enable non-precious metal catalysis. Catalytic dehydrogenation of alcohols represents an attractive approach for future applications as hydrogen storage systems and clean synthesis of fine chemicals. Herein, an overview of recent progress in homogeneously catalyzed acceptorless alcohol dehydrogenation is presented. In Nature, dehydrogenation of alcohols is efficiently catalyzed by multiple metalloenzymes where a non-noble metal–ligand interplay is key to activate and transform a substrate. We highlight the introduction of multifunctional cooperative ligands in the coordination sphere of the metal center in order to improve catalytic activity under photochemical, electrochemical or thermal conditions. Moreover, metal–ligand cooperativity is crucial for an easy transition to first row metal based catalysis, as we have seen in the recent years.

Reinvestigating Catalytic Alcohol Dehydrogenation with an Iridium Dihydroxybipyridine Catalyst

The examined catalyst [Cp*Ir(H2O)(6,6′-dhbp)]2+ (1; 6,6′-dhbp = 6,6′-dihydroxy-2,2′-bipyridine) was reported in 2012 as a highly efficient (92% conversion) and selective catalyst for the conversion...

On the importance of the crystalline surface structure on the catalytic activity and stability of tailored unsupported cobalt nanoparticles for the solvent-free acceptor-less alcohol dehydrogenation

Unsupported nanoparticles are now recognized as model catalysts to evaluate the intrinsic activity of metal particles, irrespectively of that of the support. Co nanoparticles with different morphologies, rods, diabolos and cubes have been prepared by the polyol process and tested for the acceptorless catalytic dehydrogenation of alcohols under solvent-free conditions. Rods crystallize with the pure hcp structure, diabolos with a mixture of hcp and fcc phases, while the cubes crystallize in a complex mixture of hcp, fcc and ε-Co phases. All the cobalt particles are found to be highly selective towards the oxidation of a model secondary alcohol, octan-2-ol, into the corresponding ketone while no significant activity is found with octan-1-ol. Our results show the strong influence of particle shape on the activity and catalytic stability of the catalysts: Co nanorods display the highest conversion (85%), selectivity (95%) and recyclability compared to Co diabolos and Co cubes. We correlate the nanorods excellent stability with a strong binding of carboxylate ligands on their {1 1 2¯ 0} facets, preserving their crystalline superficial structure, as evidenced by phase modulation infrared reflection absorption spectroscopy.

Revised Mechanisms of the Catalytic Alcohol Dehydrogenation and Ester Reduction with the Milstein PNN Complex of Ruthenium

The combined experimental/DFT computational study of RuH2(CO)[Et2NCH2PyCH2Pt-Bu2] (2) suggests that this dihydride is the catalyst of the acceptorless alcohol dehydrogenation and ester hydrogenatio...

Metal-ligand cooperativity in a ruthenium(II) complex of bis-azoaromatic ligand for catalytic dehydrogenation of alcohols

Herein a new Ru-phosphine complex (1) with molecular formula [RuL(PPh3)Cl2] is reported where L is a redox active pincer ligand 2,6-bis(phenylazo)pyridine. The isolated complex has been characterized by usual spectroscopic techniques including single crystal X-ray crystallographic analysis. Complex 1 efficiently catalyzes aerobic oxidation of a wide range of primary and secondary benzylic, allylic, heterocyclic, alicyclic alcohols under mild conditions and is found to be superior over several other Ru (0, +2 and +3), Ru-H and Ru-PPh3 catalysts. Mechanistic studies indicate that a transient Ru-H intermediate is formed in the catalytic cycle which gets switched into a Ru-hydrazo intermediate via hydrogen-walking mechanism. The catalyst is regenerated by aerial oxidation producing H2O2 as a by-product.

An Azoaromatic Ligand as Four Electron Four Proton Reservoir: Catalytic Dehydrogenation of Alcohols by Its Zinc(II) Complex.

Electroprotic storage materials, though invaluable in energy-related research, are scanty among non-natural compounds. Herein, we report a zinc(II) complex of the ligand 2,6-bis(phenylazo)pyridine (L), which acts as a multiple electron and proton reservoir during catalytic dehydrogenation of alcohols to aldehydes/ketones. The redox-inactive metal ion Zn(II) serves as an oxophilic Lewis acid, while the ligand behaves as efficient storage of electron and proton. Synthesis, X-ray structure, and spectral characterizations of the catalyst, ZnLCl2 (1a) along with the two hydrogenated complexes of 1a, ZnH2LCl2 (1b), and ZnH4LCl2 (1c) are reported. It has been argued that the reversible azo-hydrazo redox couple of 1a controls aerobic dehydrogenation of alcohols. Hydrogenated complexes are hyper-reactive and quantitatively reduce O2 and para-benzoquinone to H2O2 and para-hydroquinone, respectively. Plausible mechanistic pathways for alcohol oxidation are discussed based on controlled experiments, isotope labeling, and spectral analysis of intermediates.

Exclusively Ligand-Mediated Catalytic Dehydrogenation of Alcohols.

Design of an efficient new catalyst that can mimic the enzymatic pathway for catalytic dehydrogenation of liquid fuels like alcohols is described in this report. The catalyst is a nickel(II) complex of 2,6-bis(phenylazo)pyridine ligand (L), which possesses the above requisite with excellent catalytic efficiencies for controlled dehydrogenation of alcohols using ligand-based redox couple. Mechanistic studies supported by density functional theory calculations revealed that the catalytic cycle involves hydrogen atom transfer via quantum mechanical tunneling with significant kH/kD isotope effect of 12.2 ± 0.1 at 300 K. A hydrogenated intermediate compound, [NiIICl2(H2L)], is isolated and characterized. The results are promising in the context of design of cheap and efficient earth-abundant metal catalyst for alcohol oxidation and hydrogen storage.

Insight into Varied Reaction Pathways for O–H and N–H Bond Activation by Bis(imino)pyridine Complexes of Al(III)

The activation of O–H bonds in alcohol substrates is the initial step in acceptor-less catalytic dehydrogenation of alcohols. At room temperature, the bis(imino)pyridine-ligated aluminum hydride compound, denoted as (PhI2P2–)AlH (1), activates O–H bonds in alcohols through a metal–ligand cooperative pathway to afford the phenoxide and benzyloxide complexes with protonated ligand: (PhHI2P1–)Al(OR)H, where R = Ph, Bn. Thermochemical measurements indicate that the amido nitrogen of the protonated ligand in (PhHI2P1–)Al(OPh)H is far more basic (pKa = 36–45) than the analogous proton for the previously reported (PhHI2P1–)Al(NHPh)H (pKa = 10–14), and this is consistent with reactivity we observe, where (PhHI2P1–)Al(OPh)H complexes do not intramolecularly liberate H2. The inability of (PhHI2P1–)Al(OR)H to release H2 upon heating precludes access to a four-coordinate Al center and results in an inability of 1 to dehydrogenate benzyl alcohol to benzaldehyde. These observations also lend further support to the mech...

Mechanism of N,N,N-Amide Ruthenium(II) Hydride Mediated Acceptorless Alcohol Dehydrogenation: Inner-Sphere β-H Elimination versus Outer-Sphere Bifunctional Metal–Ligand Cooperativity

The reversible transformations between ketones and alcohols via sequential hydrogenation–dehydrogenation reactions are efficiently achieved using a single precatalyst HRu(bMepi)(PPh3)2 (bMepi = 1,3-bis(6′-methyl-2′-pyridylimino)isoindolate). The catalytic mechanism of HRu(bMepi)(PPh3)2 mediated acceptorless alcohol dehydrogenation (AAD) has been investigated by a series of kinetic and isotopic labeling studies, isolation of intermediates, and evaluation of Ru(b4Rpi)(PPh3)2Cl (R = H, Me, Cl, OMe, OH) complexes. Two limiting dehydrogenation scenarios are interrogated: inner-sphere β-H elimination and outer-sphere bifunctional double hydrogen transfer. Isotopic labeling experiments demonstrated that the proton and hydride transfer in a stepwise manner. Catalyst modifications suggest that the imine group on the bMepi pincer scaffold is not necessary for catalytic alcohol dehydrogenation. Evaluation of the kinetic experiments and catalyst modifications suggests a pathway whereby HRu(bMepi)(PPh3)2 operates via ...

Palladium on Carbon‐Catalyzed Aqueous Transformation of Primary Alcohols to Carboxylic Acids Based on Dehydrogenation under Mildly Reduced Pressure

AbstractThe catalytic dehydrogenation of alcohols to carbonyl products is a green sustainable oxidation with no production of waste except for hydrogen, which can be an energy source. Additionally, a reusable heterogeneous catalyst is valuable from the viewpoint of process chemistry and water is a green solvent. We have accomplished the palladium on carbon (Pd/C)‐catalyzed dehydrogenation of primary alcohols to carboxylic acids in water under a mildly reduced pressure (800 hPa). The reduced pressure can be easily controlled by the vacuum controller of the rotary evaporator to remove the excess of generated hydrogen, which causes the reduction (reverse reaction) of aldehydes to alcohols (starting materials) and other undesirable side reactions. The present method is applicable to the reaction of various aliphatic and benzylic alcohols to the corresponding carboxylic acids, and the Pd/C could be reused at least 5 times.magnified image

Reversible catalytic dehydrogenation of alcohols for energy storage

Reversibility of a dehydrogenation/hydrogenation catalytic reaction has been an elusive target for homogeneous catalysis. In this report, reversible acceptorless dehydrogenation of secondary alcohols and diols on iron pincer complexes and reversible oxidative dehydrogenation of primary alcohols/reduction of aldehydes with separate transfer of protons and electrons on iridium complexes are shown. This reactivity suggests a strategy for the development of reversible fuel cell electrocatalysts for partial oxidation (dehydrogenation) of hydroxyl-containing fuels.

ChemInform Abstract: Rhodium‐on‐Carbon Catalyzed Hydrogen Scavenger‐ and Oxidant‐Free Dehydrogenation of Alcohols in Aqueous Media.

The efficient and catalytic dehydrogenation of alcohols is a clean approach for preparing carbonyl compounds accompanied only by the generation of hydrogen gas. We have accomplished the heterogeneous rhodium-on-carbon catalyzed dehydrogenation of secondary, as well as primary, alcohols to the corresponding ketones and carboxylic acids in water under basic conditions.

Rhodium-on-carbon catalyzed hydrogen scavenger- and oxidant-free dehydrogenation of alcohols in aqueous media

The efficient and catalytic dehydrogenation of alcohols is a clean approach for preparing carbonyl compounds accompanied only by the generation of hydrogen gas. We have accomplished the heterogeneous rhodium-on-carbon catalyzed dehydrogenation of secondary, as well as primary, alcohols to the corresponding ketones and carboxylic acids in water under basic conditions.

Electron-Rich PNP- and PNN-Type Ruthenium(II) Hydrido Borohydride Pincer Complexes. Synthesis, Structure, and Catalytic Dehydrogenation of Alcohols and Hydrogenation of Esters

Electron-rich PNP- and PNN-type ruthenium(II) hydrido borohydride pincer complexes, [RuH(BH4)(tBu-PNP)] (tBu-PNP = (2,6-bis(di-tert-butylphosphinomethyl)pyridine) (5) and [RuH(BH4)(tBu-PNN)] (tBu-PNN = 2-di-tert-butylphosphinomethyl-6-diethylaminomethylpyridine) (6), were prepared from their corresponding N2-bridged dinuclear Ru(II) complexes [(tBu-PNP)RuCl2]2(μ-N2) (3) and [(tBu-PNN)RuCl2]2(μ-N2) (4), respectively. The X-ray structure of 5 reveals a BH4– anion η2 coordinated to ruthenium through two bridging hydrides. A variable-temperature 1H NMR study of 6 exhibits interesting fluxional behavior of the BH4– ligand. Similarly, the Ru(II) hydrido borohydride complex 9, in which the BH4– moiety is coordinated in a η1 bonding mode, was obtained by reaction of [RuCl2(PPh3)(iPr-PNP)] (iPr-PNP = 2,6-bis(diisopropylphosphinomethyl)pyridine) (8) with two equivalents of NaBH4 at room temperature. The hydrido borohydride pincer complexes 5, 6, and 9 catalyze the acceptorless dehydrogenative coupling of primary al...

Osmium and Ruthenium Catalysts for Dehydrogenation of Alcohols

A series of pincer-type complexes of Os and Ru have been synthesized and investigated in catalytic alcohol dehydrogenation. The hydrides OsHCl(CO)[HN(C2H4PiPr2)2] and OsH2(CO)[HN(C2H4PiPr2)2] possess good air, moisture, and thermal stability and are outstanding versatile dehydrogenation catalysts for primary alcohols for reactions of transfer hydrogenation, dehydrogenative coupling, and amine alkylation.