Catalytic Activity In Transfer Hydrogenation Research Articles

Optimizing Cu 3d Bands with Nanotubular SnO2 to Boost Their Catalytic Transfer Hydrogenation Activity.

Catalytic transfer hydrogenation (CTH) using Cu nanocatalysts offers significant advantages over direct high-pressure hydrogenation. However, the active hydrogen (H*) in this process exhibits poor adsorption and tends to release H2 readily due to the fully occupied 3d states of Cu. To address this issue, a tubular SnO2 support with electron-accepting ability was selected to host Cu nanoparticles, aiming to optimize the Cu 3d bands. The Cu/SnO2 nanohybrids were prepared through an electrospinning technique, followed by hydrothermal synthesis. As evidenced by X-ray photoelectron spectroscopy (XPS) binding energy shifts and density functional theory (DFT) simulations, some electrons from Cu transferred to SnO2 in the Cu/SnO2 nanohybrids due to their different work functions. Such electron transfer enables the Cu 3d orbitals to lose electrons and alters its valence configuration from 3d10 to 3d10-x, which enhances the adsorption of active H* atoms and thereby inhibits undesirable H2 release. The 15 wt % Cu/SnO2 exhibits improved catalytic hydrogenation of 4-nitrophenol with NaBH4, with an optimal normalized rate constant of 56.98 mg-1 min-1 and a turnover frequency of 4.82 min-1, surpassing most reported catalysts. The enhanced activity is attributed to the optimized electronic states, improved hydrogen adsorption, and the tubular structure of the support. This work might shed light on developing more non-noble metal nanocatalysts for CTH by tuning their d bands with appropriate oxide supports.

Enhanced transfer hydrogenation of bio-derived Ethyl levulinate to γ-valerolactone over Zr-based catalysts through a formic acid modification strategy

Conversion of biomass platform compounds to γ-Valerolactone (GVL) is of significant for biomass high-value utilization. In this study, a range of innovative zirconium-based catalysts (Zr-5ASA-X) were synthesized utilizing 5-aminosalicylic acid (5-ASA) as the ligand through a formic acid (FA) modification strategy. Zr-5ASA (2:1)-300 exhibited excellent catalytic activity for transfer hydrogenation of bio-derived ethyl levulinate (EL) to GVL with a high EL conversion of 98.8 % and GVL selectivity of 98.6 % in isopropanol under moderate reaction conditions (170 ℃ and 5 h). The characterization results revealed that H+ dissociated from FA combined with the electron donating group -NH2 to generate electron-withdrawing effects, further boosting the intensity of Zr4+ Lewis acid active sites. More importantly, the catalyst can repetitively use at least five runs without an obvious loss of activity. Finally, a kinetic model describing this reaction was established and the possible reaction mechanism was proposed.

Introducing Novel Redox-Active Bis(phenolate) N-Heterocyclic Carbene Proligands: Investigation of Their Coordination to Fe(II)/Fe(III) and Their Catalytic Activity in Transfer Hydrogenation of Carbonyl Compounds.

A simple and efficient procedure for synthesizing novel pincer-type tridentate N-heterocyclic carbene bisphenolate ligands is reported. The synthesis of pincer proligands with N,N'-disubstituted imidazoline core, 5 and 6, was carried out via triethylorthoformate-promoted cyclization of either N,N'-bis(2-hydroxy-3,5-di-tert-butylphenyl)cyclohexanediamine, 3, or N,N'-bis(2-hydroxyphenyl)cyclohexanediamine, 4, in the presence of concentrated hydrochloric acid. Cyclic voltammograms of the ligands revealed ligand-centered redox activity, indicating the noninnocent nature of the ligands. The voltammograms of the ligands exhibit two successive one-electron oxidations and two consecutive one-electron reductions. In contrast to previous reports, the redox-active ligands in this study exhibit one-electron oxidation and reduction processes. All products were thoroughly characterized by using 1H and 13C NMR spectroscopy. The base-promoted deprotonation of the proligands and subsequent reaction with iron(II) and iron(III) chlorides yielded compounds 7 and 8. These compounds are binuclear and tetranuclear iron(III) complexes that do not contain carbene functional groups. Complexes 7 and 8 were characterized by using elemental analysis and single-crystal X-ray crystallography. At low catalyst loadings, both 7 and 8 exhibited high catalytic activity in the transfer hydrogenation of selected aldehydes and ketones.

Influence of Charge Delocalization on Manganese Catalyzed Transfer Hydrogenation

AbstractHydrogen transfer reactions promoted by Mn(I)‐based catalysts are a recently emerged field of research. Herein, we demonstrate the crucial effect of charge delocalization on the catalytic activity in transfer hydrogenation. Therefore, we synthesized pyridyl‐pyrazole ligands and a pyridyl‐pyridazinone ligand which exhibit resonance structures upon deprotonation with varying capability to transfer charge to the manganese center. The corresponding Mn(I) complexes were characterized and their activity as catalyst in transfer hydrogenation of acetophenone was determined using in‐situ IR techniques. Kinetic data and DFT calculations reveal that the ligands are deprotonated throughout the catalytic cycle and that the catalysts in which resonance structures point towards more negative charge at the metal center are also the more active ones. Thus, we deliver ample evidence that for effective hydrogen transfer the manganese catalyst requires a ligand with a deprotonable moiety allowing efficient delocalization to the metal while geometrical access of the acidic proton to the substrate is not essential. Our findings highlight the importance of an anionic hydrido intermediate, where mesomerism allows an effective charge transfer to the metal. This may support the ongoing development of new manganese‐based catalysts.

BICAAC-Derived Covalent and Cationic Ir(I) Complexes: Application of Ir(BICAAC)Cl(COD) Complexes as Catalysts for Transfer Hydrogenation and Hydrosilylation Reactions.

The ambiphilic bicyclic (alkyl)(amino)carbenes (Me/iPrBICAAC) upon reaction with [IrCl(COD)]2 smoothly afford mononuclear Ir(I) complexes that have been spectroscopically and structurally characterized. These complexes exhibit good catalytic activity for transfer hydrogenation (TH) of 4-chlorobenzaldehyde using isopropyl alcohol (iPrOH), with turnover frequency values ranging between 6269 and 8093 h-1. Choosing the covalent complex Ir(MeBICAAC)Cl(COD) as a catalyst, a wide array of carbonyls and imines functionalized with electron-withdrawing and electron-donating substituents have been surveyed and afforded their reduced products in moderate-to-good yields. No detachment of the BICAAC unit from the Ir center was observed upon prolonged heating of Ir(MeBICAAC)Cl(COD) in toluene-d8 or isopropyl alcohol-d8, which evidenced good thermal stability of the catalyst. Complex Ir(MeBICAAC)Cl(COD) was also found to be catalytically active for the hydrosilylation of a variety of aldehydes using triethylsilane (Et3SiH).

Tuning Active Site Flexibility by Defect Engineering of Graphene Ribbon Edge‐hosted Fe−N3 Sites

AbstractNitrogen‐doped, carbon‐supported transition metal catalysts are excellent for several reactions. Structural engineering of M−Nx sites to boost catalytic activity is rarely studied. Here, we demonstrate that the structural flexibility of Fe−N3 site is vital for tuning the electronic structure of Fe atoms and regulating the catalytic transfer hydrogenation (CTH) activity. By introducing carbon defects, we construct Fe−N3 sites with varying Fe−N bond lengths distinguishable by X‐ray absorption spectroscopy. We investigate the CTH activity by density‐functional theory and microkinetic calculations and reveal that the vertical displacement of the Fe atom out of the plane of the support, induced by the Fe−N3 distortion, raises the Fe orbital and strengthens binding. We propose that the activity is controlled by the relaxation of the reconstructed site, which is further affected by Fe−N bond length, an excellent activity descriptor. We elucidate the origin of the CTH activity and principles for high‐performing Fe−N−C catalysts by defect engineering.

Tuning Active Site Flexibility by Defect Engineering of Graphene Ribbon Edge-hosted Fe-N3 Sites.

Nitrogen-doped, carbon-supported transition metal catalysts are excellent for several reactions. Structural engineering of M-Nx sites to boost catalytic activity is rarely studied. Here, we demonstrate that the structural flexibility of Fe-N3 site is vital for tuning the electronic structure of Fe atoms and regulating the catalytic transfer hydrogenation (CTH) activity. By introducing carbon defects, we construct Fe-N3 sites with varying Fe-N bond lengths distinguishable by X-ray absorption spectroscopy. We investigate the CTH activity by density-functional theory and microkinetic calculations and reveal that the vertical displacement of the Fe atom out of the plane of the support, induced by the Fe-N3 distortion, raises the Fe orbital and strengthens binding. We propose that the activity is controlled by the relaxation of the reconstructed site, which is further affected by Fe-N bond length, an excellent activity descriptor. We elucidate the origin of the CTH activity and principles for high-performing Fe-N-C catalysts by defect engineering.

Confinement effect induced Pd/UiO-66-rGO for efficient aromatic alkenes catalytic hydrogenation

A simple and adaptable synthetic method is reported here for synthesizing UiO-66-GO nanohybrid materials by modulating the growth and dispersion of UiO-66 on GO surfaces, using PdCl2 as the Pd source with thermal treatment at 120 °C without additional reduction to obtain Pd/UiO-66-rGO composite catalyst. Pd/UiO-66-rGO demonstrates excellent activity in catalytic transfer hydrogenation for C═C bond of aromatic alkenes by using HCOONH4 and water as hydrogen donor and solvent at 25 °C, with 99.6 % styrene conversion and 99.9 % selectivity to ethylbenzene. The confinement effect leads to ultra-small Pd NPs active sites evenly dispersed on Pd/UiO-66-rGO, which is the good catalytic performance of Pd/UiO-66-rGO results from. Additionally, UiO-66-rGO makes a protection effect to stabilize and prevent the Pd active sites leaching out, ensuring the cyclic stability of this catalyst.

Catalytic Transfer Hydrogenation Performance of Magnesium-Doped ZrO2 Solid Solutions

This is the first study to investigate the activity of a solid solution containing magnesium ions in a zirconia matrix in the catalytic transfer hydrogenation (CTH) of acetophenone with 2-pentanol. The results have shown that magnesium oxide is very highly active in CTH when physically mixed with zirconia. However, the same concentration of Mg2+ ions (Mg:Zr = 3:97) inserted into a zirconia lattice did not yield high activity in CTH. A higher concentration of Mg2+ ions (5%) was also tested in the two types of systems, i.e., a physical mixture of oxides and a solid solution. The increase in the concentration of Mg2+ ions in the physical mixture led to a pronounced increase in the activity of the system, whereas in the case of the solid solution it led to a slight decrease in activity. The impact of the zirconyl salt used in the synthesis was also examined, but showed little effect on the properties and activity of the systems. The study has also shown that the increase of the concentration of magnesium ions caused a decrease in the m-ZrO2 to t-ZrO2 ratio. Nevertheless, the rate of heating had an even bigger effect on this ratio.

Ru(II) complexes containing NOO donors of tridentate Schiff base ligands: Synthesis, characterization, crystal structure and catalytic activity in transfer hydrogenation of ketones

A new series of pincer type ruthenium(II) Schiff base complexes namely [Ru(CO)(PPh3)2(L1‒6)] (1–6) (where, L1‒6 ​= ​NOO ‒ donors of tri-dentate ligands) have been synthesized from ruthenium precursor such as [RuHCl(CO)(PPh3)3] containing tri-dentate Schiff bases ligands (H2L1‒H2L6). These ruthenium complexes were analyzed by elemental analysis and diverse characterizations such as FT‒IR, UV–Vis and NMR (1H and 31P) spectroscopy studies. The crystal structure of one of the complexes 5 ([Ru(CO)(PPh3)2L5]) was determined by single crystal X‒ray crystallography that revealed pincer type of coordination mode of complexes. Furthermore, complexes 1–6 have been utilized for transfer hydrogenation of aromatic ketones to secondary alcohols in the presence of i‒PrOH/KOH. The catalytic efficiency of complexes showed an efficient for transfer hydrogenation of ketones with alcohol as moderate to high conversions.

Mechanistic insights and comparative analysis of Ru(ii)–NNC pincer complexes with anionic-, protic-, and classical-NHCs for transfer hydrogenation of ketones

A series of Ru(ii)–NNC pincer-type complexes bearing anionic-, protic- and classical-NHC ligands are reported. Comparative analysis of catalytic activity in transfer hydrogenation of ketones is investigated both experimentally and computationally.

Highly Active Large Au Clusters and Even More Active Ag Nanoparticles Supported on Ceria-Zirconia: Impact of Particle Size and Potassium Ion Loading on Activity in Catalytic Transfer Hydrogenation

Although heterogeneous monometallic gold catalysts are commonly more active when the gold particles are smaller, this study shows that the reverse is true in the case of liquid phase catalytic transfer hydrogenation of acetophenone with 2-pentanol. Higher catalytic activity of larger gold particles, i.e., over 30 nm in diameter, than of smaller particles of average 4 nm in size was observed. Moreover, this effect was contradictory to that observed for supported monometallic silver catalysts in which the interaction with the support and hence particle size was shown to cause drastic changes in the activity in this reaction, with the large particles being completely inactive and tiny ones being the most active system studied. In this reaction, the ceria-zirconia solid solutions were used as the supports for the catalysts and both zirconium doped ceria, as well as cerium doped zirconia carriers were tested. The supports themselves exhibited little activity in this reaction. It was shown that the activity of the supports and catalysts depends on the Ce/Zr ratio and potassium content. Both types of catalysts showed excellent selectivity to 1-phenylethanol and conversion of acetophenone, although it was noted that a high loading of potassium carbonate in the gold catalysts propelled undesired reactions, thereby reducing the selectivity to 1-phenylethanol.

Catalytic transfer hydrogenation of biomass-derived furfural into furfuryl alcohol over zirconium doped nanofiber

The design of high-efficiency heterogeneous catalyst plays a central role for catalytic transfer hydrogenation (CTH) of biomass-derived furfural (FAL) into furfuryl alcohol (FOL). Herein, a novel zirconium doped polyacrylonitrile (PAN) nanofiber (Zr@PAN) was assembled via electrospinning technology. Systematic characterizations revealed that the high catalytic activity for CTH of FAL into FOL was provided by the cooperative effect between Lewis acid and Lewis base sites due to the chelation effect between zirconium ions and cyano-groups on PAN. Besides, a kinetic model specifying this reaction has been set up and showed a good correlation (R2 > 0.94) between the measured and predicted data, which can effectively monitor the process and tailor the reaction conditions to attain the desired product. Although the activity of Zr-20@PAN decreased after three cycles of recovery, the introduction of bridging agent, such as lignin and tea polyphenol, can solve the recovery defect well due to their abundant hydroxyl group or carboxyl group.

Efficiently catalytic transfer hydrogenation and fast separation of unsaturated alkene compounds over Pd/UiO-66 under green conditions

Stable Pd nanoparticles (Pd NPs) have been uniformly dispersed and immobilized into the metal-organic framework of UiO-66, Pd/UiO-66, by a facile impregnation reduction method. Pd/UiO-66 retains the integrity of the UiO-66 crystal structure and incorporated with ultrasmall Pd NPs(1.70 ± 0.32 nm). Using ammonium formate(AF) as a H-donor and water as solvent under green condition, the optimized 1.16 wt% Pd/UiO-66 catalyst exhibits remarkable activity in the catalytic transfer hydrogenation(CTH) of α-methylstyrene(AMS) into cumin(achieving 99.6% conversion of AMS and almost full selectivity to cumin with an extremely high turnover frequency value 456.7 h−1 at 323.15 K). Pd/UiO-66 also show superior catalytic activity in CTH of unsaturated alkene compounds to saturated compounds with excellent stability and recyclability. Furthermore, the as-formed saturated alkanes can be fast and automatic separated easily from the aqueous catalytic media. This study supplies a general method for immobilizing ultrafine Pd nanoparticles into crystalline MOFs and a “green” path for hydrogenation of unsaturated alkene compounds.

Aluminum‐Ligand Cooperative O−H Bond Activation Initiates Catalytic Transfer Hydrogenation

AbstractMolecular design ultimately furnishes improvements in performance over time, and this has been the case for Rh‐ and Ir‐based molecular catalysts currently used in transfer hydrogenation (TH) reactions for fine chemical synthesis. In this report, we describe a molecular pincer ligand Al catalyst for TH, (I2P2−)Al(THF)Cl (I2P=diiminopyridine; THF=tetrahydrofuran). The mechanism for TH is initiated by two successive Al‐ligand cooperative bond activations of the O−H bonds in two molecules of isopropanol (iPrOH) to afford six‐coordinate (H2I2P)Al(OiPr)2Cl. Stoichiometric chemical reactions and kinetic experiments suggest an ordered transition state, supported by polar solvents, for concerted hydride transfer from iPrO− to substrate. Metal‐ligand cooperative hydrogen bonding in a cyclic transition state is a likely support for the concerted hydride transfer event. The available data does not support involvement of an intermediate Al‐hydride in the TH. Proof‐of‐principle reactions including the conversion of isopropanol and benzophenone to acetone and diphenylmethanol with 90 % conversion in 1 h are described. The analogous hydride compound, (I2P2−)Al(THF)H, also cleaves the O−H bond in iPrOH to afford (HI2P−)Al(OiPr)H and (HI2P−)Al(OiPr)2, but no activity for catalytic TH was observed.

Organic acid-assisted design of zirconium-lignocellulose hybrid for highly efficient upgrading levulinic acid to γ-valerolactone

Acid treatment is the key to improve the physicochemical properties of metal-lignocellulosic hybrid, thus contributing to the catalytic performance for catalytic transfer hydrogenation (CTH) of carbonyl compounds to their corresponding alcohols. Herein, a series of organic acids were introduced to assist the design of Zr-Pennisetum sinese hybrid. Comprehensive studies demonstrated the dramatic changes of specific surface and acid/base sites of the prepared hybrid. Remarkably, formic acid-assisted Zr@PS-FA possessed the largest surface area and enhanced interaction effects between acids (Lewis acid and Brønsted acid) and Lewis base sites, which exhibited excellent catalytic activity for CTH of levulinic acid to γ-valerolactone with a high yield of 95.6% in isopropanol under moderate reaction conditions (180 °C and 1.5 h). Zr@PS-FA also showed remarkable cycle stability, and it could be consecutively used at least six runs without a significant loss in catalytic activity. More gratifyingly, Zr@PS-FA displayed a superior universality for CTH of various carbonyl compounds to their corresponding alcohols, demonstrating great potential for upgrading biomass-derived aldehydes/ketones.

Fast catalytic transfer hydrogenation of phenol to cyclohexanol over urea modified Ni@CN nanoparticles

The Ni@CN-450 catalyst preparedviadirect pyrolysis of Ni-MOF-74(N) exhibited superior catalytic activity in catalytic transfer hydrogenation.

Effect of cysteine thiols on the catalytic and anticancer activity of Ru(II) sulfonyl-ethylenediamine complexes.

We have synthesized a series of novel substituted sulfonyl ethylenediamine (en) RuII arene complexes 1-8 of [(η6-arene)Ru(R1-SO2-EnBz)X], where the arene is benzene, HO(CH2)2O-phenyl or biphenyl (biph), X = Cl or I, and R1 is phenyl, 4-Me-phenyl, 4-NO2-phenyl or dansyl. The 'piano-stool' structure of complex 3, [(η6-biph)Ru(4-Me-phenyl-SO2-EnBz)I], was confirmed by X-ray crystallography. The values of their aqua adducts were determined to be high (9.1 to 9.7). Complexes 1-8 have antiproliferative activity against human A2780 ovarian, and A549 lung cancer cells with IC50 values ranging from 4.1 to >50 μM, although, remarkably, complex 7 [(η6-biph)Ru(phenyl-SO2-EnBz)Cl] was inactive towards A2780 cells, but as potent as the clinical drug cisplatin towards A549 cells. All these complexes also showed catalytic activity in transfer hydrogenation (TH) of NAD+ to NADH with sodium formate as hydride donor, with TOFs in the range of 2.5-9.7 h-1. The complexes reacted rapidly with the thiols glutathione (GSH) and N-acetyl-L-cysteine (NAC), forming dinuclear bridged complexes [(η6-biph)2Ru2(GS)3]2- or [(η6-biph)2Ru2(NAC-H)3]2-, with the liberation of the diamine ligand which was detected by LC-MS. In addition, the switching on of fluorescence for complex 8 in aqueous solution confirmed release of the chelated DsEnBz ligand in reactions with these thiols. Reactions with GSH hampered the catalytic TH of NAD+ to NADH due to the decomposition of the complexes. Co-administration to cells of complex 2 [(η6-biph)Ru(4-Me-phenyl-SO2-EnBz)Cl] with L-buthionine sulfoximine (L-BSO), an inhibitor of GSH synthesis, partially restored the anticancer activity towards A2780 ovarian cancer cells. Complex 2 caused a concentration-dependent G1 phase cell cycle arrest, and induced a significant level of reactive oxygen species (ROS) in A2780 human ovarian cancer cells. The amount of induced ROS decreased with increase in GSH concentration, perhaps due to the formation of the dinuclear Ru-SG complex.

Ru(Ii) Complexes Containing Noo Donors of Tridentate Schiff Base Ligands: Synthesis, Characterization, Crystal Structure and Catalytic Activity in Transfer Hydrogenation of Ketones

Ru(Ii) Complexes Containing Noo Donors of Tridentate Schiff Base Ligands: Synthesis, Characterization, Crystal Structure and Catalytic Activity in Transfer Hydrogenation of Ketones

Hg(II) and Ru(II) complexes of mono- and dichalcogenides of bis(diphenylphosphino)amine chelating ligands: Synthesis, characterization and catalytic activity in transfer hydrogenation of acetophenone derivatives

Reactions of C10H7-1-N(PPh2)2 (1) and C10H7-1-N(P(Se)Ph2)2 (2) ligands with mercury(II)iodide in equimolar ratio gave cis-[HgI2{1-κ2 P,P}] (3) and cis-[HgI2{2-κ2 Se,Se}] (4). Also, refluxing of monooxidized thioyl and selenoyl bis(phosphino)amine ligands C10H7-1-N(P(E)Ph2)(PPh2) (E = S (5), Se (6)) with [Ru(CO)3Cl2]2 dimer afforded cis-[Ru(CO)2Cl2{5-κ2 P,S}] (7) and cis-[Ru(CO)2Cl2{6-κ2 P,Se}] (8). Complexes 3, 4, 7 and 8 were identified and characterized by multinuclear NMR (1H, 13C, 31P and 77Se NMR) and IR spectroscopy. The molecular structure of 5 was determined by single X-ray crystallography. 5 is the first structurally characterized example of this kind of κ2 P,S -bidentate ligand. The novel ruthenium(II) complexes 7 and 8 show high catalytic activity in the transfer hydrogenation of acetophenone derivatives to 1-phenylethanol derivatives in the presence of 2-propanol as the hydrogen source.