Chelating ligands with one pyridine donor and one mesoionic carbene donor are fast establishing themselves as privileged ligands in homogeneous catalysis. The synthesis of several new Ir(III)-Cp*- ...and Os(II)-Cym complexes (Cp* = pentamethylcyclopentadienyl, Cym = p-cymene=4-isopropyl-toluene) derived from chelating pyridyltriazolylidenes where the additional pyridine donor was incorporated via the azide part of the triazole is presented. Furthermore, different 4-substituted phenylacetylene building blocks have been used to introduce electronic fine-tuning in the ligands. The ligands thus can be generally described as 4-(4-R-phenyl)-3-methyl-1-(pyridin-2-yl)-1H-1,2,3-triazol-5-ylidene (with R being H (L(1)), Me (L(2)), OMe (L(3)), CN (L(4)), CF3 (L(5)), Br (L(6)) or NO2 (L(7))). The corresponding complexes (Ir-1 to Ir-7 and Os-1 to Os-7) were characterized by standard spectroscopic methods, and the expected three-legged, piano-stool type coordination was unambiguously confirmed by X-ray diffraction analysis of selected compounds. Together with Ru(II) analogues previously reported by us, a total of 21 complexes were tested as (pre)catalysts for the transfer hydrogenation of carbonyl groups, showing a remarkable reactivity even at very low catalyst loadings. The electronic effects of the ligands as well as different substrates were investigated. Some mechanistic elucidations are also presented.
An asymmetric Rh-catalyzed transfer hydrogenation was developed for the conversion of α-enamidophosphonates to α-aminophosphonates (α-APs) using isopropanol as the hydride donor. This methodology is ...amenable to a broad substrate scope. A library of structurally diverse α-APs was synthesized in moderate to good yield and enantiomeric excess, having a methylene moiety at Cβ and aryl, heteroaryl or alkyl side chains.
Display omitted
Obtaining high selectivity of aromatic monomers from renewable lignin has been extensively pursued but is still unsuccessful, hampered by the need to efficiently cleave C–O/C–C bonds and inhibit ...lignin proliferation reactions. Herein, we report a transfer hydrogenolysis protocol using a heterogeneous ZnIn2S4 catalyst driven by visible light. In this process, alcoholic groups (CαH–OH) of lignin act as hydrogen donors. Proliferation of phenolic products to dark substances is suppressed under visible light illumination at low temperature (below 50 °C); formation of a light and transparent reaction solution allows visible light to be absorbed by the catalyst. With this strategy, 71–91% yields of phenols in the conversion of lignin β-O-4 models and a 10% yield of p-hydroxyl acetophenone derivatives from organosolv lignin are achieved. Mechanistic studies reveal that CαH–OH groups of lignin β-O-4 linkage are initially dehydrogenated on ZnIn2S4 to form a “hydrogen pool”, and the adjacent Cβ–O bond is subsequently hydrogenolytically cleaved to two monomers by the “hydrogen pool”. Thus, the dehydrogenation and hydrogenolysis reaction are integrated in one-pot with lignin itself as a hydrogen donor. This study shows a promising way of supplying phenolic compounds by taking advantages of both renewable biomass feedstocks and photoenergy.
The metal-oxide-catalyzed transfer hydrogenation of nitroarenes to anilines by hydrazine hydrate has been widely reported; however, the risk of explosion resulting from excess hydrazine hydrate and ...high temperatures and complex preparations of these catalysts immensely hinder their industrial application. Herein, we use a simple co-precipitation method to synthesize atomically dispersed Ce-doped α-Fe2O3 (Ce0.025-Fe2O3-350 °C), which can completely reduce nitroarenes using stoichiometric hydrazine hydrate at room temperature, where the parent α-Fe2O3 is inactive. A thorough characterization indicates that the incorporation of Ce into the crystal lattice of α-Fe2O3 reorganizes the electronic structure of the surrounding Fe, such that the Lewis acidity of Fe2O3 is enhanced, which is the key for the room-temperature decomposition of N2H4·H2O. The structure is also beneficial for the adsorption of nitroarene, leading to the weakening of the N–O bonds. Mechanistic experiments and DFT calculations demonstrate that the reduction proceeds through Ph-NO2 → Ph-NHOH → Ph-NH2 without the widely recognized Ph-NO intermediate. Moreover, Ce0.025-Fe2O3-350 °C exhibits good stability in a continuous-flow reaction.
The Front Cover illustrates the main function of noradrenaline in the human body. In the background are represented the human brain and heart, which are the main target organs for this molecule. The ...image in the foreground shows a synapse exchanging noradrenaline molecules, an important neurotransmitter of all the sympathetic nerves. Cover design by M. Zacchè. More information can be found in the Research Article by D. Padula, M. Zacchè et al.
The transformation of biomass platform compounds to value-added products is of great significance in biomass development. Herein, a series of wHfO2/SBA-15 (w = 0.7–12.5 wt%) catalysts were ...synthesized and applied to the catalytic transfer hydrogenation (CTH) of ethyl levulinate (EL) to γ-valerolactone (GVL) reaction. The physicochemical properties of the prepared samples have been characterized by XRD, N2 adsorption-desorption, ICP, FT-IR, SEM, TEM, XPS, UV–vis, 29Si NMR, NH3-TPD, and Pyridine-FTIR. The introduction of hafnium species could produce abundant Lewis acid sites (LAS) without altering the ordered mesoporous structure of SBA-15. In addition, part of Hf species entered the SBA-15 framework and formed a small amount of Brønsted acid sites (BAS). Among these catalysts, 10.4HfO2/SBA-15 showed an excellent catalytic performance, providing a very high EL conversion (96 %) and GVL selectivity (91 %) at 130 °C in 3 h using isopropanol as the H-donor. The high catalytic performance maybe related to the high surface area and large amount of LAS. Furthermore, this catalyst also showed a good stability and reusability.
Display omitted
•The wHfO2/SBA-15 catalyst was prepared by a simple post-impregnation method.•Catalytic transfer hydrogenation of EL to GVL was performed over wHfO2/SBA-15 catalyst.•96 % EL conversion and 91 % GVL yield were obtained over 10.4HfO2/SBA-15 catalyst at 130 °C.•The abundant Lewis acid sites played a key role in the high catalytic activity.
Display omitted
•Ni SAs-N@LC was fabricated through facile pyrolysis of lignin-Ni/Zn complex with melamine.•Unique Ni-N3 structure was formed by lignin coordination and melamine-derived N ...anchoring.•Ni SAs-N@LC showed excellent catalytic activity for transfer hydrogenation of VAN into MMP.•Ni-N3 promoted the adsorption of VAN-CHO end and increased hydrogen evolution capacity.•Ni SAs-N@LC had superior feasibility to lignin-derived aldehydes and good cycling durability.
Developing sustainable catalytic processes for catalytic transfer hydrogenation (CTHDO) of lignin-derived aldehydes to renewable fuels and chemicals is essential for scale valorization of vast underused lignin. Herein, the work contributes to the efficient and selective vanillin (VAN) CTHDO process using formic acid (FA) as the H-donor over a novel lignin-coordinated N-anchoring Ni single-atom catalyst (Ni SAs-N@LC). Ni SAs-N@LC was fabricated through facile pyrolysis of lignin-Ni/Zn complex mixed with melamine, in which lignin localized the Ni atoms through its negatively charged groups (e.g. phenolic OH) and the dispersed Ni atoms were further anchored by the N-doped carbon support to form Ni-N3 active structure. DFT calculations revealed that the Ni-N3 structure preferentially adsorbed the –CHO end of VAN and endowed the catalyst with superior hydrogen evolution capacity. Therefore, Ni SAs-N@LC exhibited outstanding catalytic performance (98.93% of VAN conversion and 97.3% of 2-methoxy-4-methylphenol selectivity) which was significantly higher than two reference catalysts Ni NPs@LC (without N-anchoring) and Ni@C (without lignin coordination and N-anchoring) as well as the previously reported Ni-based catalysts. Moreover, Ni SAs-N@LC presented excellent feasibility to the CTHDO of a wide range of lignin-derived aldehydes and exhibited superior cycling durability in FA system owing to its acid resistance property. Consequently, this work provides a facile preparation method for atomically dispersed biomass-based catalysts and further demonstrates its favorable applicability in the CTHDO of lignin-derived aldehydes.
Achieving hydrothermal hydrogenation and deoxygenation of bio-oil with high water content such as microalgae-based bio-oil still faces significant challenges. Traditional upgrading processes require ...a large amount of H2. The objective of current research uses methanol and formic acid as a hydrogen donor to achieve the hydrothermal hydrodeoxygenation of palmitic acid (a model of microalgae-based bio-oil) to prepare pentadecane over Pt/C catalyst without the need for additional H2 supply. The research findings have shown that the H2 supply mechanism of methanol and formic acid in synergy with palmitic acid hydrothermal hydrodeoxygenation is obviously different. Formic acid is directly decomposed to produce H2, while methanol undergoes aqueous steam reforming to produce H2 in synergy with palmitic acid hydrodeoxygenation. More importantly, methyl palmitate, a typical model compound of the first-generation biodiesel, achieved efficient deoxygenation without the addition of H2 and hydrogen donors. At 300 °C, the yield of pentadecane reached 91.25 % within 150 min. The hydrothermal stability test shows that the decrease in Pt content and specific surface area (SBET), as well as the destruction of pore structure, are the main reasons for the decrease in activity of the Pt/C catalyst after cycling. The H2 production efficiency of hydrogen donors possesses a significant impact on the hydrodeoxygenation of palmitic acid and therefore more efficient catalysts need to be developed.
Display omitted
•Palmitic acid deoxygenation was achieved without the need for additional H2 supplies.•The rate of methanol transfer hydrogenation of palmitic acid is much higher than that of external H2.•Efficient deoxygenation of methyl palmitate over Pt/C without the need for hydrogen donors and external H2.•The yield of pentadecane reached 91.25 % in hydrothermal deoxygenation of methyl palmitate at 300 °C.
