Spatial Distribution of Nitrogen Binding Sites in Metal-Organic Frameworks for Selective Ethane Adsorption and One-Step Ethylene Purification.

The one-step purification of ethylene (C2 H4 ) from mixtures containing ethane (C2 H6 ) and acetylene (C2 H2 ) is an industrially important yet challenging process. In this work, we present a site-engineering strategy aimed at manipulating the spatial distribution of binding sites within a confined pore space. We realized successfully by incorporating nitrogen-containing heterocycles, such as indole-5-carboxylic acid (Ind), benzimidazole-5-carboxylic acid (Bzz), and indazole-5-carboxylic acid (Izo), into the robust MOF-808 platform via post-synthetic modification. The resulting functionalized materials, namely MOF-808-Ind, MOF-808-Bzz, and MOF-808-Izo, demonstrated significantly improved selectivity for C2 H2 and C2 H6 over C2 H4 . MOF-808-Bzz with two uniformly distributed nitrogen binding sites gave the optimal geometry for selective ethane trapping through multiple strong C-H⋅⋅⋅N hydrogen bonds, leading to the highest C2 H2 /C2 H4 and C2 H6 /C2 H4 combined selectivities among known MOFs. Column breakthrough experiments validated its ability to purify C2 H4 from ternary C2 H2 /C2 H4 /C2 H6 mixtures in a single step.

Enantioselective Reductive Homocoupling of Allylic Acetates Enabled by Dual Photoredox/Palladium Catalysis: Access to C2-Symmetrical 1,5-Dienes.

Transition-metal-catalyzed reductive coupling reactions have emerged as powerful protocols to construct C-C bonds. However, the development of enantioselective C(sp3)-C(sp3) reductive coupling remains challenging. Herein, we report a highly regio-, diastereo-, and enantioselective reductive homocoupling of allylic acetates through cooperative palladium and photoredox catalysis using diisopropylethylamine or Hantzsch ester as a homogeneous organic reductant. This straightforward protocol enables the stereoselective construction of C(sp3)-C(sp3) bonds under mild reaction conditions. A series of C2-symmetrical chiral 1,5-dienes were easily prepared with excellent enantioselectivities (up to >99% ee), diastereoselectivities (up to >95:5 dr), and regioselectivities (up to >95:5 rr). The resultant chiral 1,5-dienes can be directly used as chiral ligands in asymmetric synthesis, and they can be also transformed into other valuable chiral ligands.

Catalytic Conversion of Carbohydrates to Levulinate Ester over Heteropolyanion-Based Ionic Liquids.

An efficient one-pot approach for the production of levulinate ester from renewable carbohydrates is demonstrated over heteropolyanion-based ionic liquid (IL-POM) catalysts with alcohols as the promoters and solvents. The relationships between the structure, acidic strength, and solubility of the IL-POM in methanol and the catalytic performance were studied intensively. A cellulose conversion of 100 % could be achieved with a 71.4 % yield of methyl levulinate over the catalyst [PyPS]3 PW12 O40 [PyPS=1-(3-sulfopropyl)pyridinium] at 150 °C for 5 h. This high efficiency is ascribed to the reasonably high activity of the ionic liquid (IL) catalyst and reaction coupling with rapid in situ esterification of the generated levulinic acid with the alcohol promoter, which allows the insolubility of cellulose encountered in biomass conversion to be overcome. Furthermore, the present process exhibits high feedstock adaptability for typical carbohydrates and handy catalyst recovery by a simple self-separation procedure through temperature control.

The dehydration of fructose to 5-hydroxymethylfurfural efficiently catalyzed by acidic ion-exchange resin in ionic liquid.

The efficient dehydration of fructose to 5-hydroxymethylfurfural (HMF) was developed in ionic liquids (ILs) with acidic ion-exchange resins as catalyst. By screening different resins and ILs respectively, it was found that the structure of resins and ILs had a prominent effect on the dehydration of fructose. In 1-butyl-3-methylimidazolium chloride ([Bmim]Cl), D001-cc resin showed a high activity. And then the effects of reaction temperatures, dosages of D001-cc, and different initial fructose loadings on the dehydration of fructose were studied in detail. The system of D001-cc resin and [Bmim]Cl exhibited a constant activity at 75°C for 20 min and a 86.2% yield of HMF was obtained after seven recycles. At 75°C for 20 min, a 93.0% yield of HMF from the dehydration of fructose was obtained.