Catalytic Activity For Hydrogenation Research Articles

Mechanical activation assisted synthesis of atomically dispersed cobalt catalysts supported on N, P co-doped cellulose-derived carbon for nitrobenzene hydrogenation

Modulating the coordination structure of active center atoms of atomically dispersed metal catalysts has emerged as a critical strategy to further enhance the catalytic performance for selective hydrogenation. Herein, we report the successful synthesis of atomically dispersed cobalt catalysts supported on N, P co-doped cellulose-derived carbon (Co1/NPC) via a mechanical activation assisted synthesis method. The introduction of P and N atoms modifies the electronic structure of Co atoms by forming Co–Nx and Co–Px structures, enhancing their ability to dissociate H2 and adsorb nitroarenes, thereby significantly boosting the hydrogenation activity. Consequently, the Co1/NPC catalyst demonstrates outstanding catalytic activity for the selective hydrogenation of nitrobenzene, achieving 99 % conversion and selectivity with a high TOF of 507 h−1, far outperforming the benchmark Co1/NC (TOF of 4 h−1) and CoNPs/NPC catalysts (TOF of 10 h−1). Moreover, Co1/NPC catalysts possess exceptional stability and satisfactory universality. This study provides an efficient and practical catalyst for the production of nitroanilines via the selective hydrogenation of nitroarenes.

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.

Preparation of Sustainable Ni/SiO2 Catalysts from Rice Husk by Different Methods for CO2 Methanation.

Silicon dioxide (SiO2) from rice husk can be extracted and be used as support for Ni-based catalysts. The impregnation method (IM) is usually used for preparing Ni/SiO2 catalysts, but its catalytic activity in CO2 hydrogenation to CH4 remains unsatisfactory. In this work, we explored alternative preparation methods, using ammonia evaporation method (AEM) and hydrothermal method (HM) to prepare the catalysts. The results showed that the catalysts prepared by AEM and HM were significantly superior to that prepared by IM. Notably, the catalyst synthesized by AEM from sustainable silica exhibited the best performance, achieving 81.69 % CO2 conversion and over 99 % methane selectivity at low reaction temperature of 300 °C. The characterization techniques indicate that the Ni/SiO2-AEM catalyst can form nickel phyllosilicate with lamellar structure, leading to better Ni dispersion and higher specific surface area. Furthermore, the results of in-situ DRIFTS have revealed the potential catalytic mechanism over Ni/SiO2 catalysts, indicating that it involves pathways with both the CO* and HCOO* as the key intermediates.

A very simple synthesis of defect-rich PdAg nanosponges for highly selective hydrogenation of furfural

Furfuryl alcohol (FA) is an important chemical and has extensive applications in varied fields. To realize the highly selective hydrogenation of furfural (FF) to produce FA, the key is the preparation of the catalysts with excellent performance. Herein, a very simple wet chemical method is developed for the one-step preparation of PdAg nanosponges (NSs). Specifically, with Pd(OAc)2 and AgNO3 as precursors, and ethylene glycol (EG) as both solvent and reducing agent, PdAg NSs can be grown and assembled at mild temperature of 40 °C. Throughout the reaction, no any surfactants and additional reducing agents are applied. The as-prepared PdAg NSs possess 3D self-supported alloy structures, “clean” surface, abundant pores, high specific surface area and rich defects. In the FF hydrogenation reaction at 60 °C under 1.5 MPa H2 pressure in the mixed solvent of ethanol and water (1 : 4 in volume ratio), the self-supported PdAg-1 NSs (1 : 1 in Pd/Ag molar ratio) exhibit superior catalytic performance than other PdAg NSs, pure Pd sample and commercial Pd/C (10%). With PdAg-1 NSs as catalyst in the absence of support, 100% FF can be converted and the selectivity toward FA is as high as 97.1% at 36.0 h of reaction. After 4 cycles, PdAg-1 NSs still maintain the high catalytic activity in FF hydrogenation and high selectivity toward FA, which may originate from the 3D self-supported structures, high specific surface area, “clean” surface, rich defects and electronic synergistic effect between Pd and Ag. This simple fabrication of PdAg NSs introduces new ideas for the synthesis of other nanostructured bi- and multi-metallic catalysts for highly selective FF hydrogenation to FA and other advanced applications.

Copper single atoms decorated iridium nanoparticles for the selective hydrogenation of bromonitrobenzene

The interaction between metals is an important factor to modify the catalytic roles of metallic catalysts, and it is highly desirable to reveal the relationship between metal-metal interaction and catalytic performance. Three types of Ir-Cu catalysts including Cu single atoms modified Ir nanoparticles and Ir-Cu alloy catalysts are prepared to observe the modifying role of Cu on Ir. Under relatively high temperature treatment, Ir-Cu alloy can be produced from Cu single atoms and Ir nanoparticles. The selectivity to bromoaniline (BAN) over Cu/C-Ir catalyst can be up to 99.9 % at the 100 % conversion of bromonitrobenzene (BNB), which is higher than that over Ir/C (94.3 %) and Ir-Cu/C alloy catalyst (98.5 %). The turnover frequencies (TOFs) of Cu/C-Ir catalysts are evidently lower than that of the Ir-Cu/C alloy catalyst, though their dispersions are higher than that of Ir-Cu/C alloy catalyst. The electronic transfer from Cu single atoms to Ir nanoparticles not only weakens the hydrogen adsorption ability but reduces the number of active sites available for splitting hydrogen molecules into hydrogen atoms, leading to a decrease in the catalytic activity for the selective hydrogenation of BNB. The interaction exerted by unalloyed Cu single atoms on Ir nanoparticles differs from that of alloyed Cu on Ir, which may be the possible reason for the different catalytic performance between Cu single atoms modified Ir nanoparticles and Ir-Cu alloy.

Regioselective encapsulation of Pd clusters in hollow polycrystalline shell

Zeolite catalysts have been widely applied in petroleum and chemical industries. Nano/hierarchical structure could improve the utilization efficiency of active sites, especially for metal species encapsulated in zeolites. However, the uniformity of zeolite surface and crystallinity would decrease, leading to low stabilization effect. Herein, we developed a seed-directed method to prepare Pd clusters (∼1.3 nm) regioselectively encapsulated in hollow polycrystalline shell of Silicalite-1 zeolite. In nitrobenzene hydrogenation reaction, the optimized Pd@S-1-hp showed a high conversion of 92.2 % at 110 °C, which is 40 % higher than that of Pd clusters in bulk zeolite. Sub-nano Pd species in polycrystalline shell could significantly shorten the diffusion length on the basis of strong microporous confinement effect. Catalytic hydrogenation activity remained stable after six cycles. This structure could be extended to heterogeneous reactions suffering from diffusion limitation.

Structural design and electronic regulation of atomically dispersed Mo-S4 sites by second shell N species reconfiguration for intensifying hydrogen spillover

Intensifying hydrogen spillover by regulating the atomic local structures catalysts is crucial for improving the hydrogenation performance, but still hugely challenging. Herein, we report a robust single-atom catalyst featuring Mo-S4 sites in the first shell modulated with N atoms in the second shell (Mo-S4-N/C) by an efficient cyclodextrin supramolecular self-assembly pyrolysis strategy for intensifying hydrogen spillover in slurry-phase hydrocracking of vacuum residue (VR). We discovered that the H2 is activated at the single-atom Mo-S4 sites efficiently and the spillover of active hydrogen is accelerated by the reconfiguration of N species in the second shell. Remarkably, the Mo-S4-N/C catalyst demonstrates excellent catalytic hydrogenation activity with high turnover frequency calculated for total metals up to 0.46 s−1, the VR per pass conversion of 61 wt.%, liquid product yield of 94 wt.%, and the low coke content of 0.6 wt.%, along with good stability, respectively. Theoretical calculations revealed that the N species in the second shell regulated the electronic structure of Mo-S4 sites, promoting the migration of active hydrogen species by reducing the transfer energy barrier of hydrogen spillover, thus enhancing the hydrogenation performance. This work proposed a strengthened hydrogen spillover mechanism from the atomic scale for hydrogenation reaction, offering novel concepts for designing and developing high-performance hydrogenation catalysts.

Sustainable Formate Production via Highly Active CO2 Hydrogenation Using Porous Organometallic Polymer with Ru-PNP Active Sites.

Efforts to combine the advantages of homogeneous catalysts in terms of activity with the ease of separation process offered by heterogeneous catalysts continue to be actively pursued in the field of catalyst development. Heterogeneous catalysts were synthesized from Ru-MACHO organometallic compounds, recognized for their high hydrogenation catalytic activity linked to the active site of the Ru-PNP motif, through direct polymerization utilizing the Friedel-Crafts reaction. These catalysts were then applied for the conversion of greenhouse gas carbon dioxide (CO2) into formate via hydrogenation, exhibited with a record-high turnover frequency of 31,700 and a productivity of 36,100 kgformate/(kgcatalyst·d). Furthermore, the facile separation characteristics and recyclability of the heterogeneous catalysts were confirmed.

Mo2Ti2C3TX MXene performance in catalytic CO2 hydrogenation and its promotion with single Pt atoms

Mo2Ti2C3Tx MXene materials, bare or loaded with strongly anchored single Pt atoms, were investigated using various methods, including STEM, XPS, XAS and DFT calculations. Upon Pt impregnation, the delaminated Mo-rich MXene surface undergoes partial oxidation, which is reversed by an H2 thermal treatment at 400 °C. The optimized MXene shows high catalytic activity for CO2 hydrogenation to CO and smaller amounts of methane and methanol. Around and above the pretreatment temperature of 400 °C, the MXene is gradually defunctionalized from O- and F-containing groups and depleted in carbidic carbon, leading to deactivation. Single Pt atoms are cationic after impregnation, and reduce upon H2 treatment, filling surface Mo vacancies. Pt addition increases the MXene activity, in particular by facilitating H2 dissociation, but has little effect on the single-atom catalyst selectivity and on the rate dependence upon reactant partial pressures. The lowest Pt loading leads to the highest turnover frequency, indicating that the MXene surface sites are key to CO2 activation.

One-step green synthesis of Au@Pd concave nanocubes in deep eutectic solvents and their highly catalytic activities for selective hydrogenation

Concave nanomaterials possess superior properties, but their synthesis usually requires complicated steps, specific conditions and additional reagents (surfactants, capping agents, seeds, etc.). Herein, the well-defined Au@Pd concave nanocubes (CNCs) is facile one-step fabricated in a deep eutectic solvent (DES, named reline) composed of choline chloride (ChCl) and urea. It is found that the reline is crucial to the formation of Au@Pd CNCs. Owing to the concave core-shell structures, and electronic effects between Au core and Pd shell, Au@Pd CNCs exhibited excellent catalytic performance, and recovery convenience in the selective hydrogenation of 4-nitrostyrene. Specifically, under normal temperature and pressure conditions (25°C, 0.1 MPa), 4-nitrostyrene can be completely hydrogenated to 4-nitroethylbenzene within 7.0 min. After five cycles, Au@Pd CNCs still maintain the highly catalytic activity and 100 % selectivity toward 4-nitroethylbenzene. It is expected that well-constructed Au@Pd CNCs also display advanced potentials in other applications.

Effect of Cu incorporation on Fe-based catalysts for selective CO2 hydrogenation to olefins

The process of converting CO2 into sustainable chemical feedstock and fuels through reaction with renewable hydrogen has been regarded as a promising direction in energy research. The enhancement of CO2 hydrogenation efficiency to produce valuable hydrocarbons (specifically olefins) on Fe catalysts through Cu modification has been extensively researched. However, there is ongoing vigorous debate regarding the impact of these modifications on catalytic properties and the underlying mechanism. When compared to unprompted iron-based catalysts for CO2 hydrogenation, the choice of desired products, such as C2-C4 and C5+, is relatively low. So, promoters are frequently employed to customize and enhance product distribution. This study investigates how adding Cu to Fe-based supported catalysts affects their performance in converting CO2 to hydrocarbons, with a specific emphasis on the interaction between Fe and Cu. To achieve this goal, catalysts were created using co-precipitation methods, varying the distribution of Fe and Cu within them. A set of composite catalysts underwent testing in a fixed bed setup using a reactant gas mixture at 350 °C and 30 bar pressure. Analysis techniques such as XRD, SEM, TEM, NH3-TPD, H2-TPR, and N2 adsorption-desorption isotherms revealed the presence of iron-copper interaction within the composite catalysts. This interaction between the two components synergistically enhances the catalytic activity in CO2 hydrogenation.

Bifunctional heterostructured nitrogen-doped carbon-layer-loaded NiSe2-FeSe2 electrocatalyst for efficient water splitting

Developing high-performance, eco-friendly bifunctional electrocatalysts is crucial to popularizing water electrolysis for hydrogen production, but it still presents major challenges. Here, we develop a composite material with NiSe2-FeSe2 heterostructure loaded on N-doped carbon layers by utilizing the metal-organic framework as a sacrificial template (NiSe2-FeSe2/NC). According to microstructural studies, direct contact between NiSe2 and FeSe2 induces charge transfer and enhances conductivity, while sensible arraying of NiSe2-FeSe2/NC nanosheets fully exposes active sites and protects catalysts from violent reaction processes. The NiSe2-FeSe2/NC heterostructured catalysts show excellent bifunctional catalytic activity for hydrogen and oxygen evolution reactions, with overpotentials of 54 and 232 mV at 10 mA cm−2, respectively. Moreover, NiSe2-FeSe2/NC also retains superiority in a two-electrode system, needing lower voltage to drive the overall water splitting at 10 mA cm−2 (1.53 V) than Pt/C||RuO2 as well as long-term stability. This work introduces a novel concept for developing state-of-the-art non-noble metal catalysts for hydrogen production and new insights into interface engineering.

CO2 hydrogenation to methanol over Cu-CeO2-ZrO2 catalysts: The significant effect of metal-support interaction

CO2 hydrogenation to methanol is an important pathway to achieving carbon neutrality, with metal-support interaction (MSI) being crucial in the design and optimization of catalysts for this process. In this study, Cu-CeO2-ZrO2 catalysts (CuCe + Zr, CuZr + Ce, CeZr + Cu, and CuCeZr) with different interactions between metal Cu and supports were successfully prepared. We mainly address the problem that how the MSI affects the catalytic performance. The CuCeZr prepared by one step solid-phase method shows the optimal catalytic activity and stability for CO2 hydrogenation, even better than the benchmark commercial Cu-ZnO-Al2O3 catalyst for syngas to methanol. Based on the investigation of the structure-performance relationship of catalysts, we propose that the excellent catalytic activity of CuCeZr is mainly determined by its largest surface area of metallic Cu (SCu) and the most amount of Cu species at Cu-support interface, both resulting from the strongest MSI between metallic Cu and CeO2-ZrO2 support. Furthermore, in situ DRIFTS showed that the strong SMI in CuCeZr promotes the formation of formate and its rapid transfer to methoxy, thereby efficiently producing methanol. This work reveals the intrinsic active sites of Cu-CeO2-ZrO2 catalysts from a MSI perspective, providing useful insights for researchers to design highly efficient Cu-based catalysts.

Hydrogen spillover enhances the selective hydrogenation of α,β-unsaturated aldehydes on the Cu–O–Ce interface

The industrially important selective hydrogenation of α,β-unsaturated aldehydes to allyl alcohol is still challenging to realize using heterogenous hydrogenation catalysts. Supported Cu catalysts have shown moderate selectivity, yet low activity for the reaction, due to the electronic structure of Cu. By anchoring atomically dispersed Pd atoms onto the exposed Cu surface of Cu@CeO2, we report in this work that hydrogen spillover activates the inert metal-oxide interfaces of Cu@CeO2 into highly effective and selective catalytic sites for hydrogenation under mild reaction conditions. The as-prepared catalysts exhibit much higher catalytic activity in the selective hydrogenation of acrolein than Cu@CeO2. Comprehensive studies reveal that atomically dispersed Pd species are critical for the activation and homolytic splitting of H2. The activated H atoms easily spill to the Cu–O–Ce interfaces as Cu–Hδ– and interfacial Ce–O–Hδ+ species, making them the active sites for hydrogenation of polar C=O bonds. Moreover, the weak adsorption of allyl alcohol on the Pd and Cu–O–Ce interfacial sites prevents deep hydrogenation, leading to selective hydrogenation of several α,β-unsaturated aldehydes. Overall, we demonstrate here a synergic effect between single atom alloy and the support for activation of an inert metal-oxide interface into selective catalytic sites.

Effect of Catalyst and Electrode Structures on the Operating Current Densities of Liquid Alkaline Water Electrolyzers

Liquid Alkaline Water Electrolyzers (LAWEs) stand out as the technology best-suited for cost-effective hydrogen production. They do not require expensive platinum group metal catalysts and have proven durability afforded by nickel-based electrodes and porous separators. While nickel electrodes and porous separators provide chemical stability in highly alkaline conditions, they do suffer from lower catalytic activity for hydrogen and oxygen evolution reactions (HER and OER), and separators possess higher ohmic resistance due to the absence of ion-conducting groups. Consequently, most LAWEs operate at low current densities ranging from 0.2 to 0.6 A/cm2, resulting in a bulky footprint and comparatively lower energy efficiency due to a reduced hydrogen production rate. To address these challenges, considerable efforts have been directed towards developing thin separators and efficient transition metal-based electrocatalysts for HER and OER in alkaline media. However, the majority of studies related to catalysts are limited to half cells, with only a limited number of catalysts evaluated in relevant LAWE configurations.In this work, we introduce a next-generation Zero-gap LAWE testing capability, benchmarked for performance through H2NEW consortia. Employing this setup, we have evaluated hydrogen and oxygen evolution catalysts under LAWE-relevant conditions on different electrode substrates, each offering a unique electrode structure. Our preliminary findings indicate that Zero-gap LAWEs, when coupled with NiMo cathode and NiFe-type anode catalysts, can operate at current densities exceeding 0.75 A/cm2 at approximately 1.8 V without compromising their short-term durability. In contrast, the benchmark cell exhibited a meager current density of around 0.22 A/cm2. In this presentation, effects of electrode structure, catalyst type, and other relevant parameters related to Zero-gap LAWEs will be discussed in detail. Acknowledgement:This research is supported by the U.S. Department of Energy (DOE) Hydrogen and Fuel Cell Technologies Office through the Hydrogen from Next-generation Electrolyzers of Water (H2NEW) consortium.

Defect Engineering in Ce-Based Metal-Organic Frameworks toward Enhanced Catalytic Performance for Hydrogenation of Dicyclopentadiene.

Defective metal-organic frameworks (MOFs) have shown great potential for catalysis due to abundant active sites and adjustable physical and chemical properties. A series of Ce-based MOFs with different defect contents were synthesized via a modulator-induced defect engineering strategy with the aid of the cell pulverization technique. The effects of modulators on the pore structure, morphology, valence distribution of Ce, and Lewis acidity of Ce-MOF-801 were systematically investigated. Among the different samples studied, the optimal Ce-MOF-801-50eq sample exhibited remarkable catalytic activity for DCPD hydrogenation, achieving a conversion rate of 100%, which is significantly higher compared to other Ce-MOF-801-neq samples as well as the Zr-MOF-801-50eq and Hf-MOF-801-50eq samples. The enhanced catalytic performance of Ce-MOF-801-50eq can be attributed to advantages provided by defect engineering, such as the high specific surface area, proper pore size distribution, abundant unsaturated metal sites, and Ce3+/Ce4+ atom ratio, which have been supported by various characterizations. This study provides important insights into the rational design of Ce-MOFs in the field of catalytic DCPD hydrogenation.

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.

Light-enhancing ketone transfer hydrogenation catalyzed by diphosphine phenanthroline ruthenium complexes

The cationic phenanthroline ruthenium derivatives [Ru(OAc)(dppb)(NN)]OAc (NN = phen 1, imidazo[4,5-f][1,10]phenanthroline 2) have been obtained in high yield by reaction of the acetate [Ru(OAc)2dppb] with the corresponding NN ligand. The dinuclear cyclometalated [(dppb)(η2-OAc)(Ru(µ-NN-phenimid-NC)Ru(η2-OAc)(dppb)]OAc (3) has been prepared from 2 with [Ru(OAc)2(dppb)] via elimination of acetic acid. The characterization of these compounds has been carried out by NMR, FT-IR, UV–Vis, conductivity and cyclic voltammetry measurements. These derivatives display catalytic activity in the transfer hydrogenation of aromatic and aliphatic cyclic ketones at S/C up to 2000 in presence of NaOiPr in 2-propanol. An increase of the rate (up to 8 times) has been observed upon irradiation at 30 and 60 °C (300 W Xenon Arc Lamp light source). Control experiments show that [Ru(OiPr)2(dppb)(phen)] (1A), formed from 1 by substitution of the acetate with the isopropoxide ligand, shows a stronger emission compared to 1 and that 1A is quenched by NaOiPr, affording the dihydride [Ru(H)2(dppb)(phen)] (1C) via a photo induced β-H elimination.

Tailoring metal-support interactions via spatial confinement of Ni/CeO2 interfaces on h-BN for efficient CO2 methanation

Modulating metal-support interactions is critical for improving catalytic activity and product selectivity for CO2 hydrogenation. Such modulation can be achieved by modifying the metal nanoparticles as well as the supports. Here, we prepared a novel catalyst, in which Ni nanoparticles were dispersed on CeO2 and hexagonal boron nitride (h-BN) hybrid supports. The introduction of h-BN to Ni/CeO2-BN effectively improves the dispersion of Ni nanoparticles. More importantly, the abundant Ni-CeO2 interfacial sites with enriched oxygen vacancies are formed over h-BN edge sites. The dispersed Ni species are anchored on CeO2 via a unique interfacial structure, with electron-rich Ni (Niδ−) species. At the interfacial sites on Ni/CeO2-BN, the synergy between oxygen vacancies and Niδ−, which enhances CO2 activation and H2 dissociation, respectively, renders superior catalytic performance for CO2 methanation. In situ DRIFTS suggests formate as key rate-limiting intermediates on Ni-CeO2 sites, while the formation of B-H bonds further promotes hydrogen activation and subsequently the catalytic performance. The modulation of metal-support interactions by spatial confinement effect by BN offers a new paradigm for designing metal/oxide catalysts for chemical transformations that requires bifunctionality as CO2 hydrogenation.

New half-sandwich ruthenium(II) complexes of chelating (SS) organochalcogen ligands and their application as transfer hydrogenation catalysts

Room temperature reactions of [(η6-arene)Ru(μ-Cl)Cl]2 (arene = p-cymene) with three new bidentate (SS) organochalcogen ligands, 2a–c (2a: 1,1’-ethylenebis(3-ethyl-imidazole-2-thione), 2b: 1,1’-ethylenebis(3-propyl-imidazole-2-thione), 2c: 1,1’-methylenebis(3-ethyl-imidazole-2-thione)), and in situ anionic exchange with KPF6 afforded the corresponding new 18-electron half-sandwich [(η6-arene)RuLCl]PF6 complexes 3a–c (3a: L = 2a, 3b: L = 2b, 3c: L = 2c). The Ru(II) complexes and the organochalcogen ligands were fully characterized by spectroscopic and analytical techniques. Solid state single crystal X-ray diffraction analysis of 3a–c displayed the Ru(II) center in the expected piano stool geometry. The catalytic activities of the half-sandwich ruthenium complexes toward the transfer hydrogenation of ketones to their corresponding alcohols were investigated using 2-propanol as a hydrogen source and solvent. All three Ru(II) complexes exhibited excellent catalytic activity for the transfer hydrogenation of ketones in the order 3b > 3a > 3c at an appreciably low catalyst loading of 0.5 mol% under a minimal alkaline condition of 10 mol% KOH. The catalytic activities of the complexes are influenced by the length of the alkyl spacer and the steric bulk of the N-substituents on the chelating organochalcogen ligand framework.