Hydrogenation Of Dienes Research Articles

Novel approach to saturated amino acid derivatives with isolated (hetero)cyclic rings via the hydrogenation of dienes

Novel approach to saturated amino acid derivatives with isolated (hetero)cyclic rings via the hydrogenation of dienes

Screening of Palladium/Charcoal Catalysts for Hydrogenation of Diene Carboxylates with Isolated-Rings (Hetero)aliphatic Scaffold.

A series of seven palladium-containing composites, i.e., four Pd/C and three Pd(OH)2/C (Pearlman's catalysts), was prepared using modified common approaches to deposition of Pd or hydrated PdO on charcoal. All the composites were tested in the catalytic hydrogenation of diene carboxylates with the isolated-ring scaffold, e.g., 5,6-dihydropyridine-1(2H)-carboxylates with 2-(alkoxycarbonyl)cyclopent-1-en-1-yl and hex-1-en-1-yl substituents at the C(4)-position. The performance of the composites was also studied via the hydrogenation of quinoline as a model reaction. The composites were characterized by transmission and scanning electron microscopy (TEM and SEM), powder X-ray diffraction, and low-temperature N2 adsorption. It was found that the composites containing Pd nanoparticles (NPs) of 5-40 nm size were the most efficient catalysts for the hydrogenation of dienes, providing the reduced products with up to 90% yields at p(H2) = 100 atm, T = 30 °C for 24 h. The method of Pd NPs formation had more effect on the catalyst performance than the size of the NPs. The catalytic performance of Pearlman's catalysts (Pd(OH)2/C) in the hydrogenation of dienes was comparable to or lower than the performance of the Pd/C systems, though the Pearlman's catalysts were more efficient in the hydrogenation of quinoline.

Influence of Ni/Mo Ratio on Structure Formation of Ni–Mo Complex Compounds in NiMo/Al2O3 Catalysts for Selective Diene Hydrogenation

Influence of Ni/Mo Ratio on Structure Formation of Ni–Mo Complex Compounds in NiMo/Al₂O₃ Catalysts for Selective Diene Hydrogenation

Single-palladium-atom catalyst nestled in nine-atom gold “bowl” for regioselective hydrogenation

Achieving the goal of “catalysts by design” has long been a major dream for chemists. In the September issue of Chem , Shen et al. describe the design of a single-atom catalyst (SAC) consisting of a single palladium atom nestled in a 9-atom gold bowl for achieving regioselective hydrogenation of dienes. Achieving the goal of “catalysts by design” has long been a major dream for chemists. In the September issue of Chem , Shen et al. describe the design of a single-atom catalyst (SAC) consisting of a single palladium atom nestled in a 9-atom gold bowl for achieving regioselective hydrogenation of dienes.

Hydrogenation of 1,3-pentadiene on modified Pd-containing catalysts

Activity and selectivity of alumina-supported palladium catalysts, particularly the sulfurized ones, in the hydrogenation of 1,3-pentadiene to pentenes were investigated. Preliminary sulfurizing of palladium catalysts considerably enhances the selectivity to olefins in a wide range of the H2 /diene molar ratio (from 2.5 to 10). Samples activated in H2 at elevated temperatures demonstrate a higher activity toward diene hydrogenation. Palladium catalysts are more active at low temperatures of the reaction; however, the earlier studied sulfurized Ni catalysts compare well with palladium ones in terms of their selectivity to olefins and productivity, and are more selective in an excess of hydrogen. Modification of palladium with chromium, silver or lithium increases the selectivity to olefins.

Synthesis of new ruthenium complexes and their use as catalysts in the hydrogenation of diene compounds

Ruthenium half-sandwich complexes [Cp*Ru (diene compound)]+X− containing various commercially available diene compounds as ligands were tested as catalysts for the hydrogenation of diene compounds. Complexes containing acyclic, cyclic, bicyclic dienes, and α,β-unsaturated carboxylic acids and their derivatives as diene ligands were successfully prepared. The anionic part of the complexes (X−) was represented by triflate, perchlorate and tetrafluoroborate ions. Hydrogenations were carried out in homogeneous and heterogeneous arrangements. The desired products with Z-configuration of the double bond were formed with high selectivity (95–99%) in both cases. It was found out that selectivity was influenced neither by the type of diene ligand nor by the type of the anionic part of the complex. The hydrogenation rate was influenced by the type and the size of the diene ligand. The rate of hydrogenation of diene using complexes containing isolated cyclic or bicyclic ligands was the highest. The lowest reaction rates were observed using complexes with acyclic dienes. The influence of the type of the anionic part of the complex on the reaction rate was also studied. The lowest rate of hydrogenation was observed using complexes with tetrafluoroborate anion. The difference in reaction rates using complexes with triflate and perchlorate anions was not significant. This work added important information for the understanding the mechanism of diene hydrogenation using ruthenium half-sandwich complexes.

Recent advance in single-atom catalysis

Single-atom catalysts (SACs) have obtained a great deal of attention in many catalytic fields due to the high atom utilization efficiency and high catalytic activity. Recently, great achievements on SACs have been made for thermocatalysis, electrocatalysis, and photocatalysis which play an important role in obtaining value-added products. However, it remains a great challenge to fabricate SACs with high metal loading and investigate their reaction mechanisms. Therefore, it is necessary to highlight the recent development of SACs in these fields to guide future research. In this review, we overviewed the thermocatalysis applications of SACs in CO oxidation, preferential oxidation of CO, water-gas shift reaction, methane conversion, methanol steam reforming, aqueous-phase reforming of methanol, hydrogenation of alkynes and dienes, hydrogenation of CO, and hydrogenation of substituted nitroarenes. Moreover, the oxygen reduction reaction (ORR), hydrogen evolution reaction (HER), oxygen evolution reaction (OER), CO2 reduction reaction (CO2RR), and N2 reduction reaction (N2RR) for photocatalytic and electrocatalytic fields were also overviewed. Lastly, the opportunities and challenges of SACs were pointed out.

Synthesis of a hybrid Pd0/Pd-carbide/carbon catalyst material with high selectivity for hydrogenation reactions

We present a highly selective and active Pd carbon catalyst prepared by an easy hydrothermal synthesis method. This synthetic procedure allows the stabilization under mild conditions of interstitial carbon atoms on the surface of a Pd0 carbon catalyst. The so formed Pd carbide phase appears on the upper surface layers of the Pd carbon catalyst, as demonstrated by X-ray photoelectron depth profile analysis using variable synchrotron X-ray energies. The presence of carbon in the palladium carbide species modifies the electronic state of surface Pd atoms, resulting in more electron positive Pd species (Pdδ+). This influences the adsorption of reactants and reaction intermediates during the hydrogenation of alkynes, dienes and imines, resulting in high selectivities at practically 100% conversion.

From Palladium Clusters in Solutions to Supported Nanocatalysts for Hydrocarbon Synthesis

Literature data on palladium clusters obtained by the interaction of Pd(II) compounds in solutions with hydrogen are summarized and analyzed. The conclusion is drawn on the influence of ligands and reduction conditions on the polynuclearity of clusters and on the autocatalytic nature of their formation. Palladium clusters become active in the selective hydrogenation of alkynes and dienes only after their treatment with hydrogen containing traces of oxygen or hydrogen peroxide. Clusters containing phosphide ligands are active in the homogeneous hydrogenation of unsaturated hydrocarbons with a high selectivity being of a thermodynamic nature. Most of the distinctive features of nanocluster synthesis in solution are also observed in the synthesis of metal-containing nanoparticles on the support surface from precursors. Catalysts for the liquid-phase selective hydrogenation of phenylacetylene on the Pd supported on coal with a nanoparticle size of 2.8 ± 0.2 nm are obtained. This size is comparable with the size of clusters in solution. The mechanism for the reduction of palladium acetate on carbon is also autocatalytic and is similar to the same process in solutions. A kinetic study of the selective hydrogenation of phenylacetylene to styrene in the presence of Pd supported on coal shows that it is impossible to adequately describe the experimental data in the framework of the Langmuir, Hinshelwood, or Eley–Rideal mechanisms. It is proposed to use this mechanism in the framework of cluster (polynuclear) active sites on the surface of Pd particles capable of adsorbing more than one substrate molecule or its fragments on the same site. This approach makes it possible to describe the mechanisms of other reactions occurring in the presence of nanoscale heterogeneous supported catalysts: deoxygenation of fatty acids obtained from renewable raw materials to paraffins on supported palladium catalysts and olefins on supported nickel sulfide catalysts.

Regio- and Chemoselective Hydrogenation of Dienes to Monoenes Governed by a Well-Structured Bimetallic Surface.

Unprecedented surface chemistry, governed by specific atomic arrangements and the steric effect of ordered alloys, is reported. Rh-based ordered alloys supported on SiO2 (RhxMy/SiO2, M = Bi, Cu, Fe, Ga, In, Pb, Sn, and Zn) were prepared and tested as catalysts for selective hydrogenation of trans-1,4-hexadiene to trans-2-hexene. RhBi/SiO2 exhibited excellent regioselectivity for the terminal C═C bond and chemoselective hydrogenation to the monoene, not to the overhydrogenated alkane, resulting in a high trans-2-hexene yield. Various asymmetric dienes, including terpenoids, were converted into the corresponding inner monoenes in high yields. This is the first example of a regio- and chemoselective hydrogenation of dienes using heterogeneous catalysts. Kinetic studies and density functional theory calculations revealed the origin of the high selectivity: (1) one-dimensionally aligned Rh arrays geometrically limit hydrogen diffusion and attack to alkenyl carbons from one direction and (2) adsorption of the inner C═C moiety to Rh is inhibited by steric repulsion from the large Bi atoms. The combination of these effects preferentially hydrogenates the terminal C═C bond and prevents overhydrogenation to the alkane.

Supported metal catalysts at the single-atom limit – A viewpoint

AbstractAn account of recent work on supported single-atom catalyst design is given here for reactions as diverse as the low-temperature water-gas shift, methanol steam reforming, selective ethanol dehydrogenation, and selective hydrogenation of alkynes and dienes. It is of fundamental interest to investigate the intrinsic activity and selectivity of the active metal atom site and compare them to the properties of the corresponding metal nanoparticles and sub-nm clusters. It is also important to understand what constitutes a stable active metal atom site in the various reaction environments, and maximize their loadings to allow us to design robust catalysts for industrial applications. Combined activity and stability studies, ideally following the evolution of the active site as a function of catalyst treatment in real time are recommended. Advanced characterization methods with atomic resolution will play a key role here and will be used to guide the design of new catalysts.

Alkanethiolate-capped palladium nanoparticles for selective catalytic hydrogenation of dienes and trienes.

Selective hydrogenation of dienes and trienes is an important process in the pharmaceutical and chemical industries. Our group previously reported that the thiosulfate protocol using a sodium S-alkylthiosulfate ligand could generate catalytically active Pd nanoparticles (PdNP) capped with a lower density of alkanethio-late ligands. This homogeneously soluble PdNP catalyst offers several advantages such as little contamination via Pd leaching and easy separation and recycling. In addition, the high activity of PdNP allows the reactions to be completed under mild conditions, at room temperature and atmospheric pressure. Herein, a PdNP catalyst capped with octanethiolate ligands (C8 PdNP) is investigated for the selective hydrogenation of conjugated dienes into monoenes. The strong influence of the thiolate ligands on the chemical and electronic properties of the Pd surface is confirmed by mechanistic studies and highly selective catalysis results. The studies also suggest two major routes for the conjugated diene hydrogenation: the 1,2-addition and 1,4-addition of hydrogen. The selectivity between two mono-hydrogenation products is controlled by the steric interaction of substrates and the thermodynamic stability of products. The catalytic hydrogenation of trienes also results in the almost quantitative formation of mono-hydrogenation products, the isolated dienes, from both ocimene and myrcene.

Mechanistic insights into complete hydrogenation of 1,3-butadiene over Pt/SiO2: effect of Pt dispersion and kinetic analysis

Gas-phase hydrogenation of 1,3-butadiene was investigated over Pt/SiO2catalysts with the aim of understanding the complete hydrogenation of dienes.

Regeneration of an alumopalladium hydrogenation catalyst in the process of supercritical CO2 fluid extraction

Using a specially created experimental setup, the crossover character of a change in solubility is determined, and the approximate pressure at the upper crossover point is found (≈19 MPa). The modification of carbon dioxide with chloroform is shown to increase its solubility by 2–2.5 times on average within the above range of conditions. The supercritical CO2 fluid extraction (SCFE) process is studied as it applies to the regeneration of LD-265 alumopalladium hydrogenation catalyst. Dimethylsulfoxide and ethanol are selected as cosolvents (modifiers). Maximum regeneration efficiency is established at a 5.5–6.5 wt % concentration of cosolvents, and dimethylsulfoxide proves to be a more efficient cosolvent than ethanol. The diene and bromine numbers and styrene and methylcyclopentadiene conversions obtained on catalysts regenerated via SCFE satisfy the requirements for catalytic systems used in the selective hydrogenation of dienes in a benzene–toluene–xylene fraction.

Diene hydroaminomethylation via ruthenium-catalyzed C-C bond forming transfer hydrogenation: beyond carbonylation.

Under the conditions of ruthenium catalyzed transfer hydrogenation using 2-propanol as terminal reductant, 1,3-dienes engage in reductive C-C coupling with formaldimines obtained in situ from 1,3,5-tris(aryl)-hexahydro-1,3,5-triazines to form homoallylic amines. Deuterium labelling studies corroborate a mechanism involving reversible diene hydroruthenation to form an allylruthenium complex that engages in turn-over limiting imine addition. Protonolysis of the resulting amidoruthenium species releases product and delivers a ruthenium alkoxide, which upon β-hydride elimination closes the catalytic cycle. These transformations, which include enantioselective variants, represent the first examples of diene hydroaminomethylation.

The chemical behavior of terminally tert-butylated polyolefins.

The chemical behavior of various oligoenes 2 has been studied. The catalytic hydrogenation of diene 3 yielded monoene 4. Triene 7 was hydrogenated to diene 8, monoene 9 and saturated hydrocarbon 10. Bromine addition to 3 and 7 yielded the dibromides 17 and 18, respectively, i.e., the oligoene system has been attacked at its terminal olefinic carbon atoms. Analogously, the higher vinylogs 19 and 20 yielded the 1,8- and 1,10-bromine adduts 23 and 24, respectively, when less than 1 equivalent of bromine was employed. Treatment of tetraene 19 with excess bromine provided tetrabromide 25. In epoxidation reactions, both with meta-chloroperbenzoic acid (MCPBA) and dimethyldioxirane (DMDO) two model oligoenes were studied: triene 7 and tetraene 19. Whereas 7 furnished the rearrangement product 31 with MCPBA, it yielded the symmetrical epoxide 32 with DMDO. Analogously, 19 was converted to mono-epoxide 33 with MCPBA and to 34 with DMDO. Diels–Alder addition of 7 with N-phenyltriazolinedione (PTAD) did not take place. Extension of the conjugated π-system to the next higher vinylog, 19, caused NPTD-addition to the symmetrical adduct 37 in good yield. Comparable results were observed on adding NPTD (equivalent amount) to pentaene 20 and hexaene 21. Using 36 in excess provided the 2:1-adduct 40 from 21 and led to a complex mixture of adducts from heptaene 22. With tetracyanoethylene (TCNE) as the dienophile, tetraolefin 19 yielded the symmetrical adduct 43, although the reaction temperature had to be increased. Pentaene 20 and hexaene 21 led to corresponding results, adducts 44 and 45 being produced in acceptable yields. With nonaene 42 and TCNE the 2:1-adduct 48 was generated according to its spectroscopic data. Exploratory photochemical studies were carried out with tetraene 19 as the model compound. On irradiation this reacted with oxygen to the stable endo-peroxide 52.

A novel strategy for producing highly dispersed Pd particles on ZIF-8 through the occupation and unoccupation of carboxyl groups and its application in selective diene hydrogenation

We proposed a novel strategy for producing highly dispersed Pd particles on ZIF-8 via the anchoring effect of the carboxyl groups incorporated into the ligand of ZIF-8. The as-synthesized Pd nanoparticles supported on the in situ carboxyl-functionalized ZIF-8 showed excellent activity and selectivity for diene hydrogenation due to the high dispersion of Pd nanoparticles and the interaction between the Pd nanoparticles and carboxyl groups. This method opens a new and simple route for greatly improving the dispersion of supported Pd nanoparticles.

Mechanistic interpretation of selective catalytic hydrogenation and isomerization of alkenes and dienes by ligand deactivated Pd nanoparticles.

Unsupported thiolate-capped palladium nanoparticle catalysts are found to be highly substrate-selective for alkene hydrogenation and isomerization. Steric and poisoning effects from thiolate ligands on the nanoparticle surface control reactivity and selectivity by influencing alkene adsorption and directing either di-σ or mono-σ bond formation. The presence of overlapping p orbitals and α protons in alkenes greatly influences the catalytic properties of deactivated palladium nanoparticles leading to easily predictable hydrogenation or isomerization products.

ChemInform Abstract: Carboxy‐Directed Asymmetric Hydrogenation of α‐Alkyl‐α‐aryl Terminal Olefins: Highly Enantioselective and Chemoselective Access to a Chiral Benzylmethyl Center.

AbstractThe carboxy‐directed hydrogenation prohibits the isomerization of the terminal olefins, and realizes the chemoselective hydrogenation of various dienes.

Pd nanoparticles in dendrimers immobilized on silica-polyamine composites as catalysts for selective hydrogenation.

New heterogeneous hydrogenation catalysts, based on Pd nanoparticles and polypropyleneimine (PPI) dendrimers of the third generation that have been covalently grafted to a silica surface modified with polyallylamine (PAA) have been synthesized. The final products were characterized by TEM, XPS, and solid-state NMR spectroscopy. The synthesized materials are effective catalysts for selective hydrogenation of dienes to monoenes and phenyl acetylene to styrene at very high substrate/Pd ratios with turnover rates higher than related Pd nanoparticle catalysts. The synthesized catalysts can be reused without any loss of activity in the case of styrene and isoprene.