Chemoselective Hydrogenation Reactions Research Articles

Celite‐Polyaniline supported palladium catalyst for chemoselective hydrogenation reactions

Polyaniline coated on particles of celite is used as support to load palladium catalyst. This heterogenized Celite•PANI•Pd system, is used as an efficient catalyst for chemoselective hydrogenation reactions. The catalyst is characterized by usual spectral, analytical techniques and studied for hydrogenation reactions at ambient conditions. The mild reaction conditions allow the control over the reactions and excellent selectivity is achieved in number of conversions. Hydrogenation of a carbon–carbon double bond was favored over other polar π‐bond systems, while labile functional groups such as benzyl ether, benzyl esters, cyano, nitro and halogen remained unaffected. Primary amines were converted to N,N‐dimethyl amines with formaldehyde, the double bond of coumarin was selectively hydrogenated without opening of the lactone functionality.

NH2-MIL-125(Ti)-derived porous cages of titanium oxides to support Pt-Co alloys for chemoselective hydrogenation reactions.

The change of atom density induced structural collapse in the transformation process from metal-organic frameworks (MOFs) to their inorganic counterparts is a major challenge to the achievement of porous hollow structures. Herein, we develop an amino acid-mediated strategy for transformation of NH2-MIL-125(Ti) to successfully synthesize well-defined porous cages of titanium oxides (PCT) due to sheets serving as structural scaffolds. On this basis, PCT supported Pt-based nanoparticles are generated via a similar synthetic route, and are utilized to study the selective hydrogenation of carbonyl groups in α,β-unsaturated aldehydes, benefiting from the specific structures of PCT and tunable electronic structures of Pt mainly affected by doping with metal species such as Co. In this case, Pt-Co/PCT composites give 96% selectivity for cinnamyl alcohol at 100% conversion of cinnamaldehyde under 0.2 MPa H2 and 80 °C for 3 h. This research would offer a promising strategy for important organic transformations in academic and industrial research to selectively synthesize high-value-added products.

Enhanced Chemoselectivity in Pt–Fe@mSiO2 Bimetallic Nanoparticles in the Absence of Surface Modifying Ligands

Noble metal-based bimetallic nanoparticles (NPs) synthesized using colloidal methods always contain organic capping agents. These NPs show high selectivities in many chemoselective hydrogenation reactions benefitting from both capping agents and secondary metals. However, it is challenging to separately identify the role of the secondary metal and the capping agents in the bimetallic NPs because the complete removal of the capping agents can often cause their aggregation or structural/compositional changes. Herein we report the synthesis of Pt5Fex (x = 1, 2 and 4) bimetallic NPs capped by an inorganic mesoporous silica (mSiO2) shell, which could prevent NP aggregation during high-temperature treatment to remove capping agents. Using these Pt5Fex@mSiO2 NPs with a clean surface, we could demonstrate the role played independently by the bimetallic composition in the selective hydrogenation of cinnamaldehyde and furfural. Understanding the functions of the secondary metal and the surface modifying ligands on the selectivity enhancement of bimetallic NPs is necessary for the design of high-performance chemoselective catalysts.

Monodisperse Pd Nanotetrahedrons on Ultrathin MoO3–x Nanosheets as Excellent Heterogeneous Catalyst for Chemoselective Hydrogenation Reactions

Two-dimensional (2D) metal oxides are ideal host supports for constructing active hybrid catalysts in various organic reactions as they have large specific surface area, strong adsorption ability, and excellent thermal stability, which could serve as support and promoter to anchor noble metal nanoparticles with enhanced catalytic activity. Herein, a simple one-pot wet-chemical approach is developed for the synthesis of well-defined monodisperse Pd nanotetrahedrons on ultrathin MoO3–x nanosheets (Pd/MoO3–x). Novel 2D oxygen-deficient MoO3–x nanosheets are formed in the synthetic process, which can work as robust catalyst support. Furthermore, in situ growth route is beneficial for boosting chemical attachment and electronic communication between Pd nanotetrahedrons and MoO3–x nanosheets. Such a composite system that combines the advantages of electronic effect and strong metal–support interaction contributes to excellent performance for selective hydrogenation of α,β-unsaturated aldehydes with high convers...

A new strategy to transform mono and bimetallic non-noble metal nanoparticles into highly active and chemoselective hydrogenation catalysts

A new strategy to transform non-noble metal oxide nanoparticles (NPs) into highly active and selective metallic NPs as hydrogenation catalysts by a simple carbon coating process based on hydrothermal treatment with glucose is presented. During the carbon coating process, metal oxide NPs will be reduced to metallic NPs and covered by thin carbon layers, resulting in formation of Metal@C NPs. Through this method, monometallic Co@C has been prepared, which shows excellent activity and selectivity for chemoselectivity hydrogenation of substituted nitroarenes to corresponding anilines under mild conditions. Kinetic, isotopic and spectroscopic studies indicate that hydrogen dissociation-addition is the controlling step in chemoselective hydrogenation reaction with Co@C NPs. Stabilization and the reaction rate of metallic Co are improved by preparing bimetallic CoNi@C catalyst, leading to almost fivefold improved activity. Our preparation method enables to synthesize non-noble bimetallic CoNi@C nanoparticles with nearly one-order magnitude higher activity than any Co-based non-noble metal catalysts prepared by other methods, without necessity to involve the promoting role of metal-N interactions. At last, we also show the application of Co@C NPs for hydrogenation of levulinic acid to γ-valerolactone.

A novel nano-palladium catalyst for continuous-flow chemoselective hydrogenation reactions

Herein, we report a catalyst composed of palladium nanoparticles immobilized on polymeric resin for chemoselective hydrogenation reactions under flow conditions. The catalyst exhibits high activity and selectivity towards hydrogenation of CC double bond, as confirmed in the hydrogenation of 2-heptene and 6-methyl-5-hepten-2-one.

Amphipathic monolith-supported palladium catalysts for chemoselective hydrogenation and cross-coupling reactions

Monolithic polymer-supported, effective, and reusable palladium catalysts were developed for cross-coupling reactions and hydrogenation.

Unsupported Nanoporous Gold Catalyst for Chemoselective Hydrogenation Reactions under Low Pressure: Effect of Residual Silver on the Reaction

For the first time, H-H dissociation on an unsupported nanoporous gold (AuNPore) surface is reported for chemoselective hydrogenation of C≡C, C═C, C═N, and C═O bonds under mild conditions (8 atm H2 pressure, 90 °C). Silver doping in AuNPore, which was inevitable for its preparation through a process of dealloying of Au-Ag alloy, exhibited a remarkable difference in catalytic activity between two catalysts, Au>99Ag1NPore and Au90Ag10NPore.The former was more active and the latter less active in H2 hydrogenation, while the reverse tendency was observed for O2 oxidation. This marked contrast between H2 reduction and O2 oxidation is discussed. Further, Au>99Ag1NPore showed a high chemoselectivity toward reduction of terminal alkynes in the presence of internal alkynes which was not achieved using supported gold nanoparticle catalysts and other previously known methods. Reductive amination, which has great significance in synthesis of amines due to its atom-economical nature, was also realized using Au>99Ag1NPore, and the Au>99Ag1NPore/H2 system showed a preference for the reduction of aldehydes in the presence of imines. In addition to this high chemoselectivity, easy recovery and high reusability of AuNPore make it a promising heterogeneous catalyst for hydrogenation reactions.

Tailoring High-Performance Pd Catalysts for Chemoselective Hydrogenation Reactions via Optimizing the Parameters of the Double-Flame Spray Pyrolysis

Tuning the chemical composition during the synthesis is a widely used method to control the activity of catalysts. Here, we reported an alternative synthesis strategy to tune the catalytic properties of nanocatalysts without changing their precursors and compositions. We synthesized a series of Pd catalysts on the most popular SiO2-, Al2O3-, and silica–alumina supports using the double-flame spray pyrolysis (FSP) technique. It was observed that various flow rates used for the synthesis of catalysts with the same composition affected the formation of the catalyst particles and their structures to further tune the surface acidity due to the correlation between acidity and structure, but the flow rates did not influence the electronic properties of Pd particles. It was observed that surface OH groups could associate Pd for the hydrogenation, but Lewis acid sites could not, as Pd/SA-30 and Pd/SiO2 showed much higher activity than Pd/Al2O3 for the same Pd size and surface properties. For Pd catalysts with Bron...

ChemInform Abstract: Chemoselective Hydrogenation Reaction of Unsaturated Bonds in the Presence of an o‐Nitrobenzenesulfonyl Group.

AbstractHydrogenation of unsaturated compounds bearing the sensitive o‐nitrobenzenesulfonyl amide moiety affords the corresponding saturated compounds without loss of the nitro group, utilizing a hydrogen balloon and the Pd/MS3A catalytic system.

Chemoselective Hydrogenation Reaction of Unsaturated Bonds in the Presence of an o-Nitrobenzenesulfonyl Group

Chemoselective hydrogenation of unsaturated compounds bearing an o-nitrobenzenesulfonyl (Ns)-amide moiety, affording the corresponding saturated compounds, was accomplished efficiently without loss of the nitro group by using the Pd/MS3A catalyst and a H2 balloon. Partial hydrogenation of alkynes bearing an Ns group to corresponding cis alkenes was achieved with the combination of the Pd/BN catalyst and an additive (diethylenetriamine or acetic acid).

Ionic Liquid-Supported Pt Nanoparticles as Catalysts for Enantioselective Hydrogenation

Ionic liquid (IL)-supported metal nanoparticles (NPs) are under scrutiny as novel heterogeneous hydrogenation catalysts. Here we present a simple strategy to extend the scope of these catalysts from chemoselective hydrogenation reactions to enantioselective hydrogenations. Pt nanoparticles with a mean size of 2–3 nm and narrow size distribution were obtained by stabilization with water-insoluble ILs or both an IL and cinchonidine (CD) as chiral costabilizer. High reaction rates and enantioselectivities were achieved in the hydrogenation of methyl benzoylformate (MBF). This simple synthesis protocol opens the door to catalysts based on IL-supported chiral Pt group metal NPs.

Synergy between Pt and Au in Pt-on-Au Nanostructures for Chemoselective Hydrogenation Catalysis

Supported Au nanoparticles (Au NPs) have been identified as highly selective catalysts for the chemoselective hydrogenation reaction potential for advanced and greener syntheses of many special and fine chemicals in organic chemistry, but their potential for applications has been hampered by their generally observed low activity arising from the intrinsic nobleness of gold to H2 activation. This work deals with a synergy between Au NPs and their carrying Pt entities in Pt-on-Au nanostructures (coded as Ptm∧Au, m denoting the atomic Pt/Au ratio) for hydrocinnamaldehyde production in the chemoselective hydrogenation of cinnamaldehyde. Ptm∧Au immobilized on a noninteracting SiO2 support (Ptm∧Au/SiO2) showed activity 1–2 orders of magnitude higher than that of monometallic Pt/SiO2 and Au/SiO2 catalysts. The high activity of Ptm∧Au nanostructures also remained distinct on interacting support materials such as Al2O3 and carbon and when varying the reaction temperature, H2 pressure, or both. Kinetic assessments suggest that the hydrogenation reaction could occur according to a Langmuir–Hinshelwood mechanism, in which cinnamaldehyde adsorbed on the Au surface was attacked by hydrogen atoms activated by Pt entities in the nanostructured Ptm∧Au catalysts. Pt dispersion or the size of the Pt entities and Pt–Au boundary, as well, strongly affected this synergic catalysis.

Microwave‐Assisted Chemoselective Hydrogenation Reactions Incorporating Hydrogen as Reducing Agent

AbstractThe use of modern microwave equipment affords an easy and safe handling in the laboratory routine. The described quartz reactor system was tested in different reaction types to show its versatile applications. Various liquid‐phase hydrogenations were carried out successfully. The construction of the reactor allows the direct introduction of gases into the reaction mixture so that the reduction can be performed with gaseous hydrogen.

Scope and Selectivity of Heterogeneous Rh0‐Catalyzed Tandem Dehydrocoupling/Hydrogenation Using Me2NH·BH3 as a Stoichiometric H2 Source

AbstractThe catalytic dehydrocoupling of Me2NH·BH3 (1) by Rh/Al2O3 (2) has been shown to act as an efficient hydrogenation and reduction system for a variety of organic substrates. A range of functional groups have been reduced, but chloro, bromo and iodo substituents, epoxide and nitrile groups were found to be stable under the reaction conditions, allowing chemoselective hydrogenation reactions to be performed. This reduction has also been shown to proceed cleanly under atmospheric air for a few representative examples of alkene and nitro functional groups.

Chemoselective transfer hydrogenation reactions over nanosized γ-Fe2O3 catalyst prepared by novel combustion route

γ-Fe2O3 catalyst was prepared by the novel combustion route. The as synthesized catalyst was characterized by several analytical techniques such as XRD, SEM, TG-DTA, etc. Chemoselective reduction of nitro compounds was studied over γ-Fe2O3 using propan-2-ol as a hydrogen donor and KOH promotor in liquid phase reaction. The catalyst used for this synthetically useful transformation showed good activity.

Application of Immobilized Rhodium Catalyst Precursors in Enantio- and Chemoselective Hydrogenation Reactions

Two different homogeneous catalyst precursor complexes, i.e. [Rh(COD)2]BF4 and [Rh(COD)Cl]2, were immobilized on phosphotungstic acid-modified alumina to form γ-Al2O3/PTA/Rh(COD)2BF4 (1b) and γ-Al2O3/PTA/[Rh(COD)Cl]2 (2b), respectively. These immobilized complexes have been modified with (R,R)-MeDuPHOS to form the immobilized chiral catalysts γ-Al2O3/PTA/Rh((R,R)-MeDuPHOS)(COD)BF4 (1c) and γ-Al2O3/PTA/Rh((R,R)-MeDuPHOS)(COD)Cl (2c). It is shown that immobilization and subsequent modification by ligand exchange reactions of general precursor complexes is a powerful method to prepare chiral and achiral anchored rhodium catalysts. Enantioselective hydrogenation reactions show that the activity and selectivity differences between the homogeneous catalysts [((R,R)-MeDuPHOS)Rh(COD)]BF4 (1a) and the in situ prepared [((R,R)-MeDuPHOS)Rh(COD)]Cl (2a) are larger than the differences between the immobilized analogues (1c, 2c). At elevated temperature and H2 pressure the activity and selectivity of 1c are comparable to those of its homogeneous analogue. Complex 1b was also used to prepare γ-Al2O3/PTA/Rh(DiPFc)(COD)BF4 (1d) via a ligand exchange reaction with 1,1‘-bis(diisopropylphosphino)ferrocene (DiPFc). This complex was used as a selective and heterogeneous hydrogenation catalyst with special chemoselective hydrogenation properties. The described immobilized rhodium catalysts prepared from the general precursor complexes 1b and 2b display hydrogenation activity and selectivity comparable to those of their homogeneous analogues. Moreover, it is demonstrated that these catalysts can be reused multiple times with neither activity nor selectivity loss and that leaching can be minimized by using optimized reaction parameters.