Hydrogenation Of Acetophenone Research Articles

Facile Synthesis of P25@Pd Core-Shell Catalyst with Ultrathin Pd Shell and Improved Catalytic Performance in Heterogeneous Enantioselective Hydrogenation of Acetophenone

Heterogeneous enantioselective hydrogenation is an ideal method for synthesizing important chiral compounds in pesticides and pharmaceuticals. Up to the present, supported noble-metal catalysts are most widely studied in heterogeneous enantioselective hydrogenations. However, it is found that the weak interactions existing on the surface of support may have negative effects on the enantioselectivity. Herein, a new category of TiO2 (Aeroxide® P25) supported Pd catalyst with ultrathin Pd shell was successfully prepared via a simple strategy based on the reduction of PdI carbonyl complex. Characterization results show that a well-dispersed ultrathin Pd shell with an average thickness of ~1.0 nm and a Pd loading of 36 wt.% was formed over the surface of P25 support. By excluding the negative weak interactions from the support, the P25@Pd core-shell catalyst with unique electronic properties of Pd exhibits higher activity and enantioselectivity than that of Pd/P25 catalyst prepared by the impregnation method and unsupported Pd black catalyst in the enantioselective hydrogenation of acetophenone.

Phosphorus as a promoter of a nickel catalyst to obtain 1-phenylethanol from chemoselective hydrogenation of acetophenone

Two catalysts were prepared using monodisperse pre-synthetized nanoparticles of metallic nickel and nickel phosphides with the same average diameter. Both nanoparticles species were deposited on the same support: mesoporous silica nano-spheres of MCM-41. This support is suitable to inhibit agglomeration and sintering processes during preparation steps. Therefore, two supported and activated catalysts with the same average nanoparticles diameter were obtained. They differ only in the nature of the active species: metallic nickel and nickel phosphides. The effect of the presence of a second element (phosphorus), more electronegative than nickel, on the activity and selectivity in the chemoselective hydrogenation of acetophenone was studied. The reaction conditions were: H2 pressure of 1 MPa, 80 °C using n-heptane as solvent. With the aim to understand the catalytic results, nanoparticles, support and catalysts were carefully characterized by X-ray diffraction, diffuse light scattering, transmission electron microcopy, high resolution transmission electron microcopy, selected area electron diffraction, scanning electron microcopy, Fourier transformer infrared spectroscopy, N2 adsorption at -196 °C, atomic absorption, H2 and CO chemisorption and volumetric oxidation. Considering these results and geometric and electronic characteristics of the surface of both active species, a change in the adsorption intermediate state of acetophenone in presence of phosphorus is proposed to explain the hydrogenation chemoselectivity of nickel phospides.

Electrostatically enhanced catalytic phase transfer hydrogenation of acetophenone under low external electric field

The oriented external electric field (OEEF) promoted phase transfer catalysis (PTC) reaction is reported for the first time. It was demonstrated experimentally that an OEEF can act as promoter or inhibitor for the phase transfer hydrogenation of acetophenone depending on its direction. Organic solvents showed differing influences on the reaction, attributed to different electrical conductivities. A non-linear dependence of product yield on OEEF potential was also discovered. This work presents a methodology for promoting PTC reactions in the absence of a chemical phase transfer agent and shows promise for significantly improving the performance of organic reactions in biphasic liquid systems.

High-index facets of Pt[sbnd]Fe nanowires induce steric effect on selective hydrogenation of acetophenone

For selective hydrogenation of substrates that contain diversified unsaturated groups, it is difficult to address the dilemma between activity and selectivity. Herein, we developed PtFe nanowires with abundant high-index facets which created steric effect for improved selectivity without occupying or passivating active sites. During the selective hydrogenation of acetophenone, the turnover frequency number of PtFe nanowires was 97.7 min−1 at 70 °C, 5.7 times higher than that (17.2 min−1) of cubic counterparts. The selectivity for C = O groups over PtFe nanowires reached 91.7% at a conversion of 99.3%, whereas that over nanocubes was only 60.2% at a conversion of 98.4%. The high CO selectivity of PtFe nanowires was attributed to the steric effect, where the stepped surfaces composed of high-index facets selectively adsorbed CO bonds and inhibited the adsorption of aromatic rings.

Pyridine‐Stabilized Rhodium Nanoparticles in Ionic Liquids as Selective Hydrogenation and Transfer Hydrogenation Catalysts

Rhodium nanoparticles (RhNPs) stabilized with pyridine‐based ligands in the ionic liquid [BMIM][BF4] (RhNPs‐I to III) were synthesized from the organometallic precursor [Rh(µ‐OMe)COD]2 under dihydrogen pressure. The pyridine‐stabilized RhNPs showed smaller size compared to the ligand free RhNPs‐V and presented higher activity and selectivity in the hydrogenation of acetophenone to 1‐phenylethanol. In the case of pyridine‐capped RhNPs‐I, the system was reused for several runs without loss of activity and selectivity. Nitrobenzene was reduced to aniline with dihydrogen in the presence of RhNPs‐I with moderate activity. When the hydrogen source was formic acid‐Et3N azeotrope (transfer hydrogenation) the reaction was completed within minutes with high selectivity. Under transfer hydrogenation conditions, it was possible to apply the catalytic system RhNPs‐I in multistep processes for the generation of substituted arylic amines through the reductive N‐alkylation of nitrobenzene and benzaldehyde; and the synthesis of substituted pyrroles through the nitroarene reduction/Paal‐Knorr condensation.

Ruthenium(II) half-sandwich complexes containing N-substituted 5-nitrobenzimidazole: Synthesis, structures and catalytic transfer hydrogenation of ketones

In this study,N-substituted 5-nitrobenzimidazole ligands were reacted with [RuCl2(p-cymene)]2 and the corresponding complexes were prepared and their structure were elucidated by elemental analysis, IR and NMR spectroscopic techniques. The synthesized Ru(II) complexes were tested as catalysts for the transfer hydrogenation (TH) of acetophenone to secondary alcohols in the presence of KOH using 2–propanol as a hydrogen source at 82 ºC. This complexes was found to be an active catalyst in the catalytic transfer hydrogenation of ketones.

Asymmetric transfer hydrogenation of ketones using Ru(0) nanoparticles modified by Chiral Thiones

The catalytic asymmetric transfer hydrogenation (ATH) of acetophenone in isopropanol by Ru(0) nanoparticles (NPs) obtained by the in‐situ reduction of Ru (II) half‐sandwich complexes of chiral 2‐oxazolidinethiones and 2‐thiozolidinethiones was examined and compared with the catalytic activity of Ru(0) NPs formed in‐situ by the reduction of [Ru(p‐cymene)(Cl)2]2 in presence of optically active ligands such as (S)‐4‐isobutylthiazolidine‐2‐thione, (S)‐4‐Isopropyl‐2(−2‐pyridinyl)‐2‐oxazoline, (8S, 9R)‐(−)‐cinchonidine, (S)‐leucinol, (S)‐phenylalaninol, and (S)‐leucine. Three of the best catalytic systems were then examined for ATH of thirteen aromatic ketones with different electronic and steric properties. A maximum of 24% ee was obtained using NPs generated from the Ru (II) half‐sandwich complex with (S)‐4‐isobutylthiazolidine‐2‐thione in the TH of acetophenone. The NPs were characterized by TEM and DLS measurements. Kinetic studies and poisoning experiments confirmed that the reaction is catalyzed by the chiral NPs formed in‐situ. Complete characterization of the complexes, including the X‐ray crystallographic characterization of two complexes, was also carried out.

Surfactant free synthesis of Au@Ni core-shell nanochains in aqueous medium as efficient transfer hydrogenation catalyst

A surfactant free aqueous phase synthesis method is reported for the generation of highly lattice mismatched Au@Ni core-shell nanochains without using any expensive and hazardous organic ligands. As synthesised Au@Ni nanochain structures showed high thermal stability and bulk oxidation resistance up to 300 °C. In situ near ambient pressure XPS (NAPXPS) analysis has been done for the bare Au@Ni nanochain surfaces under oxygen atmosphere and at different temperatures which showed evidence for the surface oxidation resistance of naked Au@Ni nanochains up to 200 °C. Ligand or capping agent free Au@Ni nanochain surfaces are found to be highly active for transfer hydrogenation of acetophenone to 1-phenyl ethanol an important commodity in perfumery industry.

Syntheses, structures and immobilization of arene-ruthenium complexes bearing phosphine ligands with methoxysilyl groups

Condensation of 3-aminopropyltrimethoxysilane and chlorodiphenylphosphine in the molar ratio of 1:1 and 1:2 in the presence of Et3N in toluene afforded aminophosphine (CH3O)3Si(CH2)3NHPPh2 (L1) and bisphosphinoamine (CH3O)3Si(CH2)3N(PPh2)2 (L2) with methoxysilyl groups, respectively. Treatment of [(η6-C6H6)RuCl2]2 with L1 in refluxing tetrahydrofuran gave a mononuclear ruthenium phosphine complex [(η6-C6H6)RuCl2(κ1-P-L1)] (1). Reaction of [(η6-p-cymene)RuCl2]2 with L2 under the similar condition gave a dinuclear ruthenium phosphine complex [(η6-p-cymene)Ru(μ-Cl)3RuCl(κ2-P,P-L2)] (2). Complexes 1 and 2 were characterized by microanalyses, IR and NMR spectroscopies, and their structures were also established by single-crystal X-ray diffraction. Immobilization of complexes 1 and 2 on SBA-15, and characterization of these hybrid heterogeneous catalysts were studied by transmission electron microscopy (TEM), IR and low pressure N2 adsorption/desorption measurement. The heterogeneous catalysts were also briefly tested for transfer hydrogenation of acetophenone.

Rh(III)Cp* and Ir(III)Cp* Complexes of 1-[(4-Methyl)phenyl]-3-[(2-methyl-4′-R)imidazol-1-yl]triazenide (R = t-Bu or H): Synthesis, Structure, and Catalytic Activity

A series of iridium and rhodium complexes have been synthesized using as ligand a triazenide monofunctionalized with an imidazole substituent. Steric hindrance at the imidazole moiety induced differences in the coordination modes as well in the catalytic behavior of complexes 4–7. Complexes 4–7 were tested in the transfer hydrogenation of acetophenone and 5-alken-2-ones. The hydrogenation of either the double bond or the carbonyl group in 5-alken-2-ones, showed to be selective in the presence of 6, 7, and 10 and has a dependence on the presence or absence of base. Control experiments point out that the imidazole moiety in the structure of complexes 4–7 speeds-up the catalysis.

Hydrogenation of Acetophenone at Room Temperature and Atmospheric Pressure over Pt-Containing Catalysts Supported on Reducible Oxides

Complete conversion of acetophenone is achieved over 1% Pt/CеО2–ZrО2 catalyst in 2 h at room temperature and atmospheric pressure. Catalysts supported on the synthesized cerium–zirconium carriers show abnormally high hydrogen absorption in the temperature range of −50 to +25°С, and significantly exceed the activity of commercial samples in acetophenone hydrogenation.

Mixed thioalkyl-azoimine (SNN′)/α-diimine–ruthenium complexes: synthesis, characterization, DFT calculations, crystal structure and application as pre-catalysts for hydrogenation of acetophenone

Eight ruthenium complexes having thioalkyl-azoimine (SNN) ligands of two general types have been synthesized: (a) [Ru(L)(bipy)Cl](PF6) where {bipy = bipyridine, L = (2-SR)C6H4N=NC(COCH3)=NC6H4X, R = Ph (X = H, L1, 1; X = CH3, L2, 2; X = F, L3, 3); R = Me, (X = H, L4, 4)} and (b) [Ru(L1)(N–N)Cl](PF6) {N–N = 4,4-dimethyl-2,2′-bipyridine (dmbipy) (5), (1,10-phenanthroline) phen (6), 3,4,7,8-tetramethyl-1,10-phenanthroline (tetrmphen) (7), 5-5-chloro-1,10-phenanthroline (Clphen) (8). The crystal structures for 1 and 6 as well as for L2 are reported; the crystal structures of 1 and 6 show that L1 is bound to the ruthenium center as κ3[S,N,N′]. The complexes have been characterized by IR, UV/Vis and NMR spectroscopy as well as electrochemical (CV) techniques. The effect of groups X, the substituent R and N–N bidentate ligands on the electronic properties of the resulting mononuclear ruthenium complexes was investigated. The catalytic activity of these complexes was tested in the liquid-phase hydrogenation of acetophenone.

Toward Green Production of Chewing Gum and Diet: Complete Hydrogenation of Xylose to Xylitol over Ruthenium Composite Catalysts under Mild Conditions.

Xylitol is one of the most famous chemicals known to people as the essential ingredient of chewing gum and as the sugar alternative for diabetics. Catalytic hydrogenation of biomass-derived xylose with H2 to produce high-value xylitol has been carried out under harsh reaction conditions. Herein, we exhibit the combination of Ru NPs with an environmentally benign MOF (ZIF-67) to afford a heterogeneous composite catalyst. Complete conversion of xylose with 100% selectivity to xylitol was achieved at 50°C and 1 atm H2. This is the first successful attempt to produce xylitol with ambient pressure H2 as well as the first time to achieve a 100% selectivity of xylitol for applicable catalysts. We also proved the universality of the Ru@ZIF-67 towards other hydrogenation processes. Under 1 atm H2, we achieved 100% conversion and >99% selectivity of 1-phenylethanol at 50°C for the hydrogenation of acetophenone. This is also the first report of hydrogenating acetophenone to 1-phenylethanol under 1 atm H2, which confirms that our result not only contributes to enhance the industrial yields of xylitol and reduces both the economical and energy costs but also provides new perspectives on the other hydrogenation process with H2.

Insight into catalyst speciation and hydrogen co-evolution during enantioselective formic acid-driven transfer hydrogenation with bifunctional ruthenium complexes from multi-technique operando reaction monitoring.

Transfer hydrogenation of acetophenone from formic acid/triethylamine mixtures catalysed by the Ikariya-Noyori complex [(mesitylene)RuCl(R,R)-(TsDPEN)] has been investigated using simultaneous high-resolution FlowNMR and FlowUV-Vis spectroscopies coupled with on-line sampling head-space mass spectrometry and chiral high-performance liquid chromatography using an integrated, fully automated recirculating flow setup. In line with previous observations, the combined results show a gradual switch from formic acid dehydrogenation to hydrogen transfer mediated by the same Ru-hydride complex, and point to a Ru-formate species as the major catalyst intermediate. Hydrogen bonding in the formic acid/triethylamine mixture emerges as a sensitive 1H NMR probe for the transfer hydrogenation activity of the system and can be used to locate optimum reaction conditions.

Simple NMR predictors of catalytic hydrogenation activity for [Rh(cod)Cl(NHC)] complexes featuring fluorinated NHC ligands.

A series of imidazolium salts precursors for N-heterocyclic carbenes (NHCs) featuring fluoroaryl substituents have been prepared along with their selenides and rhodium complexes. Tests of the catalytic activity of the [Rh(cod)Cl(NHC)] complexes in the transfer hydrogenation of acetophenone with iPrOH shows that the rhodium complexes bearing fluorinated NHCs are better than their non-fluorinated counterparts. The order of activity being 4-F-C6H4 < 2,4-F2-C6H3 < 2,4,5-F3-C6H2 < 2,6-F2-C6H3 < 2,4,6-F3-C6H2. This order of reactivity is consistent with a number of simple NMR measures of the electronic properties of these systems, including 1JCH of the NHC·HBF4 salts, δ(77Se) of the NHC selenides and 1JRh-C and δ(13Ccarbene) of the [Rh(cod)Cl(NHC)] complexes.

Rapid transfer hydrogenation of acetophenone using ruthenium catalysts bearing commercially available and readily accessible nitrogen and phosphorous donor ligands

The screening, synthesis and testing of Ru complexes generated from commercially available ligands or ligands that can be synthesised in one step, is described. The catalysts were tested for activity in the transfer hydrogenation of acetophenone by isopropanol, a probe reaction for hydrogen transfer processes between oxygenated species, often found in applications such as biomass upgrading and fine and specialty chemical synthesis. Ligand screening was conducted by in situ catalyst generation and examined NPN and NNN pincer type ligands bearing NH or CN functional groups. The most active transfer hydrogenation catalysts were found to be those bearing NH functionality, either as amino groups or as benzimidazole groups. Well-defined catalyst precursors were subsequently synthesised, including the novel complex [Ru(1)PPh3(Cl)2] (where (1) = bis(3-aminopropyl)phenylphosphine), the first reported Ru complex for this NPN ligand. Established (PN)2 and PP/NN ketone hydrogenation catalysts were also screened for transfer hydrogen capability, of which [Ru(PhPN)2Cl2] (where PhPN = 2-(diphenylphosphino)ethylamine) was the most active. Subsequently, [Ru(1)PPh3(Cl)2], [Ru(PhPN)2Cl2] and [Ru(4)(PPh3)2Cl][Cl] (where (4) = 2,6-bis(2-benzimidazolyl)pyridine) were investigated more closely to compare rate constants (determined by reaction profile regression analysis) as a more accurate measure of catalyst activity over commonly reported turn over frequencies (TOF). The effect of the reaction products on the catalyst activity was evaluated using feed spiking experiments. Catalyst deactivation was shown to be prevalent and subsequently incorporated into a simple kinetic model which enabled more accurate reaction profile fitting and provided rate constants for both the transfer hydrogenation step and deactivation reaction.

DFT and AIMD prediction of a SNS manganese pincer complex for hydrogenation of acetophenone

An aliphatic SNS manganese pincer complex is computationally predicted as a promising catalyst for the hydrogenation of acetophenone to 1-phenylethanol. Density functional theory (DFT) calculations indicate that the total free energy barrier is 26.6 kcal/mol. Detailed reaction dynamics processes of two key steps, methanol assisted H2 cleavage and hydrogenation of acetophenone, are analyzed by using ab initio molecular dynamics (AIMD) simulations. Our AIMD simulation results confirmed the proposed catalytic mechanism based on DFT calculations and revealed that the H2 cleavage happens between 0.3 and 0.7 ps, while the hydride transfer from Mn to carbon happens at around 0.1 ps.

Selective catalytic hydrogenation of acetophenone to1-phenylethanoloverCo/mordenite in water

The selective catalytic hydrogenation of acetophenone (AP)to 1-phenylethanol (PhE) has been studied in water, ethanol and n-hexanesolvent over Co/mordenite. It was shown that the highest yield of PhE (99.9%) was obtained in water solvent. The adsorption of AP hindered the adsorption of PhE in water, which in turn reduced the rate of hydrogenolysis of PhE to ethylbenzene (EB).By increasing the reaction temperature the hydrogenolysis of PhE to EB is promoted. The water phase was collected after reaction and reused successfully. The yield of PhE was 96.1% when the AP concentration in solution and the catalyst loading increased to three times. The neutral and alkaline conditions were beneficial to the hydrogenation of AP to PhE in water.

Catalytic activity in transfer hydrogenation using ruthenium (II) carbonyl complexes containing two 1,8-naphthyridine as N-monodentate ligands

A new series of novel complexes of type cis-[Ru(CO)2Cl2(L)2], L = 2-phenyl-1,8-naphthyridine, 2-(4′-nitrophenyl)-1,8-naphthyridine, 2-(4′-bromophenyl)-1,8-naphthyridine, 2-(4′-methylphenyl)-1,8-naphthyridine, 2-(3′-methoxyphenyl)-1,8-naphthyridine, 2-(2′-methoxyphenyl)-1,8-naphthyridine and 2-(4′-methoxyphenyl)-1,8-naphthyridine have been successfully synthesized and characterized. We found that the complexes can be directly synthesized from [RuCl2(CO)2]2 with high yield. The crystallographic structures of complex cis-[RuCl2(CO)2(2-(4′-methoxyphenyl)-1,8-naphthyridine-κN8)2] and cis-[RuCl2(CO)2(2-(2′-methoxyphenyl)-1,8-naphthyridine-κN8)2] have been established by X-ray single crystal diffraction studies, which indicate an octahedral geometry with two 1,8-naphthyridine ligands coordinated to the metal in a N-monodentate fashion. The ruthenium(II) complexes have been studied as catalysts in the transfer hydrogenation of acetophenone. We found that complexes show moderate activities and a 100% selectivity. The best turnover frequency (390 h−1) is found for cis-[RuCl2(CO)2(2-(4′-methoxyphenyl)-1,8-naphthyridine-κN8)2] when the substrate/catalysis ratio was 1000/1. The catalytic conditions were optimized using different substrate/catalyst and base/catalyst ratios.

The enantioselective hydrogenation of acetophenone over Pd concave tetrahedron nanocrystals affected by the residual adsorbed capping agent polyvinylpyrrolidone (PVP)

One promising way to develop efficient noble-metal catalysts is to induce the exposure of specific catalytically active facets of nanocrystals through shape-controlled syntheses. However, as for the as-prepared noble-metal nanocrystals, there are commonly residual capping agents adsorbed on the metal surfaces, which have complex effects on the catalytic activity and selectivity in different catalytic reactions. In this paper, by taking polyvinylpyrrolidone (PVP), the most commonly used capping agents in the shape-controlled synthesis of noble-metal nanocrystals, as an example, we systematically studied the surface-modification effects of residual capping agents in the enantioselective hydrogenation of acetophenone. It was found for the first time that the residual PVP adsorbed on the Pd concave tetrahedron nanocrystals is detrimental to the enantioselectivity, negative to the activity, while positive to increase the chemoselectivity to the carbonyl group. The loss of enantioselectivity over PVP-stabilized Pd concave tetrahedron nanocrystals is probably due to that the residual PVP adsorbed on the Pd surface can interact with the chiral modifier S-proline and prevent the requisite interaction between S-proline and acetophenone co-adsorbed on the Pd surfaces. Thus, the prochiral interaction complexes which play a significant role in determining the enantioselectivity cannot be formed. KBH4 treatment or hot water reflux offers feasible methods to further reduce the amount of residual PVP adsorbed on the Pd nanocrystals and to achieve enantioselectivity in the enantioselective hydrogenation of acetophenone. This study provides useful information to reveal the essence of enantiodifferentiation in heterogeneous enantioselective hydrogenations, which is beneficial for the design of efficient synthetic protocols and the shape-controlled synthesis of noble-metal nanocrystals to obtain pure enantiomers.