Hydrogenation Of Olefins Research Articles

Rhodium Single‐Atom Catalyst Design through Oxide Support Modulation for Selective Gas‐Phase Ethylene Hydroformylation

AbstractA frontier challenge in single‐atom (SA) catalysis is the design of fully inorganic sites capable of emulating the high reaction selectivity traditionally exclusive of organometallic counterparts in homogeneous catalysis. Modulating the direct coordination environment in SA sites, via the exploitation of the oxide support's surface chemistry, stands as a powerful albeit underexplored strategy. We report that isolated Rh atoms stabilized on oxygen‐defective SnO2 uniquely unite excellent TOF with essentially full selectivity in the gas‐phase hydroformylation of ethylene, inhibiting the thermodynamically favored olefin hydrogenation. Density Functional Theory calculations and surface characterization suggest that substantial depletion of the catalyst surface in lattice oxygen, energetically facile on SnO2, is key to unlock a high coordination pliability at the mononuclear Rh centers, leading to an exceptional performance which is on par with that of molecular catalysts in liquid media.

Rhodium Single-Atom Catalyst Design through Oxide Support Modulation for Selective Gas-Phase Ethylene Hydroformylation.

A frontier challenge in single-atom (SA) catalysis is the design of fully inorganic sites capable of emulating the high reaction selectivity traditionally exclusive of organometallic counterparts in homogeneous catalysis. Modulating the direct coordination environment in SA sites, via the exploitation of the oxide support's surface chemistry, stands as a powerful albeit underexplored strategy. We report that isolated Rh atoms stabilized on oxygen-defective SnO2 uniquely unite excellent TOF with essentially full selectivity in the gas-phase hydroformylation of ethylene, inhibiting the thermodynamically favored olefin hydrogenation. Density Functional Theory calculations and surface characterization suggest that substantial depletion of the catalyst surface in lattice oxygen, energetically facile on SnO2 , is key to unlock a high coordination pliability at the mononuclear Rh centers, leading to an exceptional performance which is on par with that of molecular catalysts in liquid media.

Sonochemically‐Induced Reduction of Alkenes to Alkanes with Ammonia

AbstractWith the progressive defossilization of our industry, hydrogen (H2) has been identified as a central molecule to store renewable electricity. In this context, ammonia (NH3) is now rapidly emerging as a promising hydrogen carrier for the future. This game change indirectly impacts the field of fine chemistry where hydrogenation reactions are widely deployed. In particular, the possibility of performing hydrogenation reactions using ammonia directly instead of hydrogen has become highly desirable but it remains a very difficult scientific task, which we address in this communication. Here we show that the N−H bond of NH3 can be cleaved within cavitation bubbles, generated by ultrasonic irradiation at a high frequency, leading to the in situ formation of a diimide, which then induces the hydrogenation of alkenes. Advantageously, this work does not involve any transition metal and releases N2 as a sole co‐product.

Sonochemically-Induced Reduction of Alkenes to Alkanes with Ammonia.

With the progressive defossilization of our industry, hydrogen (H2 ) has been identified as a central molecule to store renewable electricity. In this context, ammonia (NH3 ) is now rapidly emerging as a promising hydrogen carrier for the future. This game change indirectly impacts the field of fine chemistry where hydrogenation reactions are widely deployed. In particular, the possibility of performing hydrogenation reactions using ammonia directly instead of hydrogen has become highly desirable but it remains a very difficult scientific task, which we address in this communication. Here we show that the N-H bond of NH3 can be cleaved within cavitation bubbles, generated by ultrasonic irradiation at a high frequency, leading to the in situ formation of a diimide, which then induces the hydrogenation of alkenes. Advantageously, this work does not involve any transition metal and releases N2 as a sole co-product.

The nature of “hydrogen spillover”: Site proximity effects and gaseous intermediates in hydrogenation reactions mediated by inhibitor-scavenging mechanisms

Support effects in alkene and arene hydrogenations on metal catalysts attributed to “hydrogen spillover” are shown to reflect the desorption and hydrogenation of Pt-bound intermediates at acid-base pairs on certain oxides (e.g. Al2O3, TiO2, MgO). Toluene-H2 reactions on Pt nanoparticles dispersed on SiO2 (Pt/SiO2) occur on surfaces nearly saturated with a diverse pool of bound species differing in the locations of H-atoms and surface attachments. Their diverse coverages and reactivity cause Pt surfaces to become preferentially occupied by less reactive isomers at the expense of the more competent isomers that account for most hydrogenation turnovers. These less reactive species can desorb from Pt nanoparticles as gaseous methylcyclohexadiene molecules, which diffuse to and react at nearby oxide surfaces; such scavenging increases the relative abundance of the more reactive intermediates at Pt surfaces leading to the rate enhancements inaccurately denoted as “hydrogen spillover.” These rate enhancements become less pronounced as mean inter-function distances between Pt nanoparticles and acid-base pairs on oxide surfaces increase, and as methylcyclohexadiene molecules become less effectively scavenged as their rates of mass transfer become consequential. The Al2O3 surfaces considered here catalyze dihydrogen addition to cyclohexadiene and cyclohexene molecules (but not toluene); titration of acid-base pairs by propanoic acid suppresses such reactions, as well as the significant enhancements of toluene-H2 reaction rates observed when Al2O3 is mixed physically with Pt/SiO2. The rate enhancements conferred by these bifunctional routes represent a natural consequence of the diverse coverage and reactivity of many different species bound on crowded metal surfaces during arene and alkene hydrogenation reactions. Their desorption as partially-hydrogenated molecules enable their scavenging at a second function present within diffusion distances, without requiring inter-function contact or the surface diffusion of H atoms.

Discovery of a Thioxanthone-TfOH Complex as a Photoredox Catalyst for Hydrogenation of Alkenes Using p-Xylene as both Electron and Hydrogen Sources.

Hydrogenation of alkenes is one of the most fundamental transformations in organic synthesis, and widely used in the petrochemical, pharmaceutical, and food industries. Although numerous hydrogenation methods have been developed, novel types of catalysis with new mechanisms and new hydrogen sources are still desirable. Thioxanthone (TX) is widely used in energy-transfer photoreactions, but rarely in photoredox processes. Herein we show that a catalytic amount of TfOH as a co-catalyst can tune the properties of TX to make it a photoredox catalyst with highly enhanced oxidative capability in the hydrogenation of carbonylated alkenes with the cheap petroleum industrial product p-xylene serving as the hydrogen source. Deuterium can also be introduced by this method by using D2 O as the D source. To the best of our knowledge, this is the first example of using p-xylene as a hydrogen source.

Discovery of a Thioxanthone–TfOH Complex as a Photoredox Catalyst for Hydrogenation of Alkenes Using p ‐Xylene as both Electron and Hydrogen Sources

Hydrogenation of alkenes is one of the most fundamental transformations in organic synthesis, and widely used in the petrochemical, pharmaceutical, and food industries. Although numerous hydrogenation methods have been developed, novel types of catalysis with new mechanisms and new hydrogen sources are still desirable. Thioxanthone (TX) is widely used in energy-transfer photoreactions, but rarely in photoredox processes. Herein we show that a catalytic amount of TfOH as a co-catalyst can tune the properties of TX to make it a photoredox catalyst with highly enhanced oxidative capability in the hydrogenation of carbonylated alkenes with the cheap petroleum industrial product p-xylene serving as the hydrogen source. Deuterium can also be introduced by this method by using D2O as the D source. To the best of our knowledge, this is the first example of using p-xylene as a hydrogen source.

The Dependence of Olefin Hydrogenation and Isomerization Rates on Zirconium Metal–Organic Framework Structure

The Dependence of Olefin Hydrogenation and Isomerization Rates on Zirconium Metal–Organic Framework Structure

Green synthesis of Fe3O4@ZnO-supported Pd nanoparticles for oxidation and hydrogenation reactions in liquid systems

In this work Pd nanoparticles immobilized on a hybrid solid support comprised of Fe3O4 coated by a ZnO layer were synthesized by a green method which makes use of water, a biological substrate from a local plant (Rhamnidium elaeocarpum) and inexpensive Fe3+ and Zn2+ salts. 1H-NMR and 13C-NM revealed β-sitosterol as the main component of the biological substrate. The catalytic support containing Pd nanoparticles was applied in three model solid-liquid catalytic systems, namely: alcohol oxidation, nitrocompound reduction and olefin hydrogenation. For the alcohol oxidation, benzyl alcohol was used as the substrate in a solvent-free condition with high selectivity towards benzaldehyde, and a single sample of the catalyst could be recycled up to 11 times before any loss of activity could be detected. TOF (turnover frequency) as high as 13,686 h-1 for the substrate oxidation was achieved with an average yield rate of 45.4% for formation of benzaldehyde and 81.6% of average substrate conversion after 6 catalytic cycles. For the hydrogenation experiments using cyclohexene and 4-nitrophenol as model substrates, conversion as high as 96% to 4-aminophenol and cyclohexane, respectively, was achieved after 30 minutes of reaction. Furthermore, a single sample of the catalyst could be recycled for up to 17 times for the reduction of 4-nitrophenol, and 21 times in the hydrogenation of cyclohexene. Catalytic recycling for all studied reactions was straightforward after due to the superparamagnetic property of the material, and catalyst isolation after each batch could be rapidly carried out using a Nd magnet. These results suggests that a highly active and stable catalytic system based on Pd nanoparticles supported on a multifunctional solid could be fabricated using green and inexpensive biomass under operationally simple synthesis conditions.

Photocatalytic Hydrogenation of Olefins and Nitro-benzenes with Al–H2O on Pd-Doped Carbon Nitride

Key words palladium catalysis - hydrogenation - photocatalysis - carbon nitride - nitrobenzenes - olefins

Filling the Gaps in the Challenging Asymmetric Hydrogenation of Exocyclic Benzofused Alkenes with Ir−P,N Catalysts

AbstractHerein, we report a chiral phosphine‐triazole ligand for the Ir‐catalyzed asymmetric hydrogenation of exocyclic benzofused alkenes. Overcoming previous limitations, the catalytic system is able to successfully hydrogenate exocyclic olefins bearing a benzofused five‐ and six‐membered ring motif (ee's between 92 to 99%). The catalyst tolerates well the presence of several substituents and substitution patterns at both aromatic rings. The absence of a competing isomerization process together with the perfect fit of the olefins in the catalyst chiral pocket are key to surpass the previous limitations in the hydrogenation of both 5‐ and 6‐membered ring benzofused exocyclic olefins.magnified image

Selective synthesis of olefins via CO2 hydrogenation over transition-metal-doped iron-based catalysts

The catalytic hydrogenation of CO2 to olefins has received considerable attention. Herein, transition metal- and sodium-modulated iron-based catalysts were fabricated. Doping with zinc and copper favor the formation of Fe3O4 and Fe5C2 active phases, while adding manganese inhibits the formation of iron carbide. In addition, phase separation between copper and iron species occurs more readily under working conditions. Therefore, a zinc- and sodium-modulated Fe catalyst exhibited the best activity and stability. Moreover, copper was predicted to substantially decrease the energy barrier of the rate-determining step for the secondary hydrogenation of olefins and result in a much lower olefin-to-paraffin ratio. In addition, the ZnO/Fe5C2 interface facilitated the desorption of olefins from the catalyst surface and inhibited the undesirable secondary reaction of olefins, enabling a high selectivity toward olefins of 36.9 % C2–4= and 32.3 % C5+=. This study provides an exemplary new strategy for tuning the product selectivity of catalysts for olefin synthesis.

Magnesium Pincer Complexes and Their Applications in Catalytic Semihydrogenation of Alkynes and Hydrogenation of Alkenes: Evidence for Metal-Ligand Cooperation.

The development of catalysts for environmentally benign organic transformations is a very active area of research. Most of the catalysts reported so far are based on transition-metal complexes. In recent years, examples of catalysis by main-group metal compounds have been reported. Herein, we report a series of magnesium pincer complexes, which were characterized by NMR and X-ray single-crystal diffraction. Reversible activation of H2 via aromatization/dearomatization metal–ligand cooperation was studied. Utilizing the obtained complexes, the unprecedented homogeneous main-group metal catalyzed semihydrogenation of alkynes and hydrogenation of alkenes were demonstrated under base-free conditions, affording Z-alkenes and alkanes as products, respectively, with excellent yields and selectivities. Control experiments and DFT studies reveal the involvement of metal–ligand cooperation in the hydrogenation reactions. This study not only provides a new approach for the semihydrogenation of alkynes and hydrogenation of alkenes catalyzed by magnesium but also offers opportunities for the hydrogenation of other compounds catalyzed by main-group metal complexes.

Porous ZnFe2O4 sphere decorated with highly dispersed Pd nanoparticles as an efficient catalyst for the selective hydrogenation of styrene

• Pd nanoparticles of Pd/ZnFe 2 O 4 can be uniformly deposited on porous ZnFe 2 O 4 . • The styrene can be completely restored into ethylbenzene by Pd/ZnFe 2 O 4 in 80 min. • For Pd/ZnFe 2 O 4 photocatalysts, no byproducts or derivatives are formed. The catalytic hydrogenation of olefins is common and important in the chemical industry. In this work, the uniform Pd nanoparticles (∼2 nm) are anchored on the porous ZnFe 2 O 4 particles to develop the Pd/ZnFe 2 O 4 nanocomposites. We applied the Pd/ZnFe 2 O 4 hybrids into a model reaction, namely the hydrogenation of styrene. The styrene can be completely restored into ethylbenzene over Pd/ZnFe 2 O 4 within 80 min. Meanwhile, no byproducts or derivatives are formed during the whole photocatalytic process. Above photocatalytic performance is ascribed to the synergistic interaction of porous ZnFe 2 O 4 and highly dispersive Pd NPs. In addition, the kinetics study with an R-square value of more than 0.99 showed that the hydrogenation of styrene matches the zero-order kinetics model well.

Experimental and Kinetic Study of the Effect of using Zr- and Pt-loaded Metals on Y-zeolite-based Catalyst to Improve the Products of n-heptane Hydroisomerization Reactions

The escalating cost of Pt metal has prompted researchers to incorporate other metals into Pt/catalysts to reduce the amount of Pt. In this work, several bimetallic Pt-Zr/HY-zeolite catalysts were prepared by incorporating small amounts of the inexpensive Zr into the Pt/HY-zeolite to form an active and selective catalyst. Results showed that although half of the required platinum metal was used, the catalytic activity of the prepared Pt-Zr/HY bimetallic catalyst was higher than that of the monometallic (Pt or Zr)/HY catalysts, as a result of the improved Lewis acidity of that catalyst that resulted from the addition of the Zr metal; additionally, the branched alkanes' yield also increased. The optimum catalyst was bimetallic, containing 0.5 wt% Pt + 0.5 wt% Zr, which achieved the highest yield of isomers at 70.2 mol%, along with 82.61 and 84.98 mol% for conversion and selectivity, respectively, under 1 MPa and 250°C reaction conditions. In addition, the hydroisomerization reaction kinetic model was achieved, giving good predicted results in agreement with the experimental calculations, with an acceptable relative error. It was found that lower activation energies (about 44.5 kJ/mol) were needed for olefin hydrogenation to iso-paraffins, while higher activation energies were required for i-paraffin hydrocracking (about 138.1kJ/mol).

Advanced Application of Planar Chiral Heterocyclic Ferrocenes

This manuscript is reviewing the superior catalytic activity and selectivity of ferrocene ligands in a wide range of reactions: reduction of ketones, hydrogenation of olefins, hydroboration, cycloaddition, enantioselective synthesis of biaryls, Tsuji–Trost allylation. Moreover, the correlation between a ligand structure and its catalytic activity is discussed in this review.

1,5-Dichloroethanoanthracene Derivatives As Antidepressant Maprotiline Analogs: Synthesis, DFT Computational Calculations, and Molecular Docking

The chlorinated tetracyclic 1,5-dichloro-9,10-dihydro-9,10-ethanoanthracen-12-yl)-N-methylmethanamine 1, a maprotiline analog, has been synthesized via reduction and the Diels–Alder reaction followed by reductive amination of aldehyde 2.1D-NMR (DEPT) and 2D-NMR (HSQC, DQF-COSY) techniques were recruited for structural elucidation in addition to HRMS. Density functional theory calculations were performed to identify the possible isomers of the intermediate compound aldehyde 2; these calculations were in good agreement with experimental results where aldehyde 2 could exist in three isomers with comparable energies. In addition, the side chain of this aldehyde 2 was extended via the Wittig reaction to obtain the unsaturated ester 5 that was subjected to selective olefinic catalytic hydrogenation to obtain the corresponding saturated ester 6. Molecular docking simulation showed that all the compounds (1, 2, 5, and 6) have high antidepressant activities and form stable complexes with LeuT by inhibiting the neurotransmitter reuptake at the synapse and hence are good candidates as antidepressant drugs.

Influence of Surface Chemistry of Carbon Nanofibers on the Hydrodechlorination of Chloroform to Olefins

Functionalized carbon nanofibers (CNF) are fascinating materials to be used as supports in Pd-based catalysts for the treatment of waste chloroform (TCM) to produce light olefins through the catalytic hydrodechlorination (HDC). The CNF were functionalized by HNO3, HCl, and urea. Compared to the Pd supported on un-treated CNF, all the catalysts using functionalized CNF as support showed lower turnover frequency values with higher stability, owing to their smaller Pd nanoparticles (NPs). These smaller Pd NPs are formed due to the stronger metal–support interactions promoted by the higher concentration of surface groups on the functionalized catalysts. Since the smaller Pd NPs could hinder the hydrogenation of olefins to paraffins, the selectivity to olefins increased on the functionalized catalysts. Moreover, the N-doped CNF was successfully formed on the catalyst functionalized by urea. Since the nitrogen functional groups (pyridinic N and pyrrolic N) could provide much stronger metal–support interactions compared to the oxygen functional groups on the other catalysts, the catalyst functionalized by urea showed the smallest Pd NPs among the four catalysts, leading to the highest selectivity to light olefins.

Design and Synthesis of Pyrrolidinyl Ferrocene-Containing Ligands and Their Application in Highly Enantioselective Rhodium-Catalyzed Olefin Hydrogenation.

Herein, we report the design and synthesis of a series of chiral pyrrolidine-substituted ferrocene-derived ligands. The proficiency of this novel structural motif was demonstrated in the Rh-catalyzed asymmetric hydrogenation of dehydroamino acid esters and α-aryl enamides. The products were obtained with full conversions and excellent levels of enantioselectivities of up to >99.9% ee and 97.7% ee, respectively, using a BINOL-substituted phosphine-phosphoaramidite ligand which possesses planar, central, and axial chirality elements.

Cobalt-Catalyzed Enantioconvergent Hydrogenation of Minimally Functionalized Isomeric Olefins.

Investigation on asymmetric hydrogenation of olefins is of great importance in both pharmaceutical molecule synthesis and chemical industry due to the high demand for enantiopure compounds. The established methods often require geometrically pure olefins. The enantioconvergent reaction provided the possibility to access a single stereoisomer via hydrogenation of E/Z-olefin mixtures; however, a polar functional group next to the carbon-carbon double bond was usually necessary. Here, we reported a cobalt-catalyzed enantioconvergent hydrogenation of readily available minimally functionalized E/Z-olefin mixtures. This strategy shows good functional group tolerance and provides an alternative means to enantioconvergent transformation. The preliminary mechanistic studies indicated that cobalt-catalyzed isomerization was the key to achieve the convergent transformation.