Robust Bio-derived Polyoxometalate Hybrid for Selective Aerobic Oxidation of Benzylic C(sp³)–H Bonds

Utilization of natural resources to construct functional catalytic materials for challenging organic reactions is of great importance in the chemical community, which has achieved significant attention. Herein, we describe the synthesis of a robust bio-derived polyoxometalate (POM) hybrid by the reaction of the naturally occurring phytic acid (PhyA) with MoO3, and the obtained hybrid was denoted PhyA–Mo. Systematic studies revealed that the multi-phosphate structure of PhyA enabled the synthesized PhyA–Mo to simultaneously possess a higher concentration of surface-active oxygen species and more negatively charged Mo sites, which played the role of catalytically active sites for aerobic oxidation. These two types of active sites together enabled the PhyA–Mo to show outstanding catalytic activity for aerobic oxidation of benzylic C(sp3)–H in different substrates to generate various carbonyl compounds without using any additional initiator. Importantly, the fact of realizing aerobic oxidation of benzylic C(sp3)–H bonds efficiently over POM-based materials in the absence of any radical initiator represented the main finding and the major breakthrough. Especially, this work provided a general and useful strategy to improve the catalytic performance of POM-based materials by using phosphoric acids containing multi-phosphate groups

Efficient and Mild Transfer Hydrogenolytic Cleavage of Aromatic Ether Bonds in Lignin-Derived Compounds over Ru/C

Cleavage of aromatic ether bonds is crucial for the valorization of lignin and its fragments, which is challenging under mild conditions because the bonds are very stable. Herein, we found that Ru/C could efficiently catalyze the cleavage of the aromatic ether bonds in various lignin-derived compounds via a transfer hydrogenolytic route using isopropanol as the hydrogen resource. Various lignin-derived compounds could be efficiently cleaved over commercial Ru/C to generate the corresponding aliphatic alkanes, aliphatic alcohols and aromatic derivatives under milder conditions. A mechanism study indicated that the reaction occurred through the direct cleavage of aromatic ether bonds or the formation of the reaction intermediate cyclohexyl phenyl ether

Natural Product Glycine Betaine as an Efficient Catalyst for Transformation of CO₂ with Amines to Synthesize <i>N</i>‑Substituted Compounds

Transformation of carbon dioxide (CO₂) into value-added chemicals is of great importance, and use of natural products as a catalyst is very interesting. Herein, we used the naturally occurring glycine betaine as an efficient and renewable catalyst for the formation of a C–N bond between CO₂ and amines using PhSiH₃ as the reductant. The effects of different factors on the reaction were studied. It was demonstrated that the catalyst was very active for the reactions, and a broad range of amine substrates could be converted with satisfactory yields. Moreover, the selectivity to different <i>N</i>-substituted compounds could be controlled by the molar ratio of reactants (i.e., CO₂, amines, and PhSiH₃) and the reaction temperature. In the catalytic cycle, the carbon oxidation state of CO₂ could be reduced to +2, 0, and −2, respectively, and thus, the corresponding formamides, aminals, and methylamines were produced via successive two-electron reduction steps

Base-Free Aerobic Oxidation of Alcohols over Copper-Based Complex under Ambient Condition

Cu-based complex formed from Cu­(OAc)₂ and [2,2′]-bipyridinyl-5,5′-dicarboxylic acid diethyl ester (BPYDCDE) ligand was synthesized for the first time. It was found that the complex could catalyze aerobic oxidation of alcohols to aldehydes or ketones very efficiently without any external base at ambient temperature and pressure, and the yield of the desired product reached >99% in 2–5 h. Combination of experimental and theoretical studies showed that the ligand enhanced the electron population on the Cu center by a ligand-to-metal charge transfer (LMCT) effect, which made OAc^– in the complex have the appropriate alkalinity and be a good leaving group, and the Cu center and the OAc^– catalyze the reaction cooperatively. Moreover, the amount of OAc^– in the complex was much less than that of the external base added in the catalytic systems reported, suggesting that the basic anion in the complex is more efficient for promoting the reaction than the external base added

Metal-Oxide-Catalyzed Efficient Conversion of Cellulose to Oxalic Acid in Alkaline Solution under Low Oxygen Pressure

Conversion of cellulose into value-added chemicals and/or fuels has attracted worldwide attention due to the dwindling fossil fuel reserves and concerns over global warming. Herein, the conversion of microcrystalline cellulose into oxalic acid in homogeneous NaOH solution catalyzed by metal oxides under low oxygen pressure was reported. The effects of metal oxides, reaction temperature, reaction time, and oxygen pressure on the yields of the major products were studied. The results showed that a high yield of organic acids, mainly including oxalic acid, formic acid, glycolic acid, lactic acid, and acetic acid, could be obtained. Catalytic amounts of CuO could effectively improve the yield of oxalic acid. The yield of the oxalic acid could be as high as 41.5% with catalytic amount of CuO at oxygen pressure of 0.3 MPa and 200 °C for 2 h. A tentative reaction pathway for the selective oxidation of cellulose into small molecular organic acids in aqueous NaOH solution was investigated and proposed

Porous Hafnium Phosphonate: Novel Heterogeneous Catalyst for Conversion of Levulinic Acid and Esters into γ‑Valerolactone

Catalytic transfer hydrogenation (CTH) of levulinic acid (LA) and its esters to produce γ-valerolactone (GVL) is an important route for biomass transformation. Development of efficient and heterogeneous catalysts for the GVL production via CTH reaction of LA and its esters has attracted much attention. In this work, a new hafnium (Hf) containing organic–inorganic hybrid catalyst (Hf-ATMP) was prepared by the reaction of HfCl₄ and amino tri­(methylene phosphonic acid) and was used to catalyze the CTH reaction of LA and its esters to produce GVL using isopropanol as the hydrogen source. It was found that the prepared Hf-ATMP could catalyze the CTH reaction to provide satisfactory GVL yield, and the effects of reaction temperature, reaction time, and the amount of the catalyst on the reaction were studied in detail. Meanwhile, the Hf-ATMP could be reused at least five times without notable decrease in activity and selectivity. Systematic studies indicated that the acidity of Hf, the basicity of the phosphate groups, and the porosity of the prepared catalyst were the main reasons for the catalytic performance of Hf-ATMP in the CTH reaction of LA and its esters

Imidazolium-Based Ionic Liquids Catalyzed Formylation of Amines Using Carbon Dioxide and Phenylsilane at Room Temperature

The CO₂-involved synthesis of chemicals is of significance. In this work, we found that 1-alkyl-3-methylimidazolium ionic liquids (ILs) had high efficiency for catalyzing the formylation of amines using CO₂ and phenylsilane at room temperature, producing the corresponding formylated products in excellent yields under the metal-free condition. The ILs acted as bifunctional catalysts, which activated the Si–H bond of phenylsilane to react with CO₂ to form the formoxysilane intermediate and simultaneously activated the amine substrate through the hydrogen bond. Moreover, the imidazolium cation and the anions of the ILs showed an excellent synergistic effect on catalyzing the formylation of amines

Shape and Size Controlled Synthesis of MOF Nanocrystals with the Assistance of Ionic Liquid Mircoemulsions

In this work, the La-metal–organic frameworks (La-MOFs) were synthesized using lanthanum­(III) nitrate and 1,3,5-benzenetricarboxylic acid (BTC) in H₂O-in-1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF₆), bmimPF₆-in-water, and the bicontinuous microemulsions stabilized by surfactant TX-100. The MOFs prepared were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), powder X-ray diffraction (XRD), thermal gravimetric analysis (TGA), and FT-IR methods, and the microstructures of the microemulsions in the H₂O/bmimPF₆/TX-100 system were studied by small-angle X-ray scattering (SXAS) technique. It was shown that the dispersed droplets in the water-in-bmimPF₆, bicontinuous and bmimPF₆-in-water microemulsions were spherical, lamellar, and cylindrical, respectively. The shapes of the La-MOFs synthesized were similar to that of the droplets in the corresponding microemulsions. This indicated that the morphology of MOFs could be controlled by the microstructures of the microemulsions. On the basis of the systematic experimental results, the mechanism for controlling the morphology of the MOFs was proposed