Two‐Dimensional Covalent Organic Frameworks for Carbon Dioxide Capture through Channel‐Wall Functionalization

Ordered open channels found in two‐dimensional covalent organic frameworks (2D COFs) could enable them to adsorb carbon dioxide. However, the frameworks’ dense layer architecture results in low porosity that has thus far restricted their potential for carbon dioxide adsorption. Here we report a strategy for converting a conventional 2D COF into an outstanding platform for carbon dioxide capture through channel‐wall functionalization. The dense layer structure enables the dense integration of functional groups on the channel walls, creating a new version of COFs with high capacity, reusability, selectivity, and separation productivity for flue gas. These results suggest that channel‐wall functional engineering could be a facile and powerful strategy to develop 2D COFs for high‐performance gas storage and separation.     

水对Ni/MgAlO催化丙酮加氢的影响

研究了H2O对Ni/MgAlO催化剂上丙酮加氢为异丙醇的催化反应的影响。结果发现,在丙酮中添加少量H2O可提高丙酮转化率,但超过5%的H2O量则会显著降低催化剂活性。吸附量热结果表明,催化剂表面吸附少量H2O会明显降低异丙醇的吸附热,但对丙酮吸附热的影响较小,这也许是反应体系中少量的H2O能促进丙酮加氢活性的原因之一。当催化剂表面吸附较多H2O后,丙酮、异丙醇和H2的吸附热都降低了,因此反而抑制了丙酮的加氢反应。此外,红外光谱结果表明,预吸附水抑制了催化剂表面异丙醇脱氢生成丙酮,并抑制吸附的丙酮在表面生成烯醇盐或异丙叉丙酮等物种,这也许是少量水能促进丙酮加氢生成异丙醇的另一个重要原因。     

Adsorption on Mesoporous Metal–Organic Frameworks in Solution: Aromatic and Heterocyclic Compounds

Adsorption and desorption play major roles in separations, purification of water, waste streams, liquid fuels, catalysis, biomedicine and chromatography. Mesoporous metal–organic frameworks (MOFs) with pore sizes 2–50 nm are particularly suitable for adsorption of organic compounds in solution. Tens of thousands of aromatic and heterocyclic compounds are major components of liquid fuels, feedstock for industrial synthesis, solvents, dyestuffs, agricultural chemicals, medicinal drugs, food additives, and so forth. This Review provides a systematization and analysis of studies on adsorption/desorption on mesoporous MOFs in solution and their underlying chemical mechanisms. The (in)stability of mesoporous MOFs in water is critically discussed. Adsorption capacity and selectivity are covered for organic dyes, medicinal drugs, major components of liquid fuels, and miscellaneous industrial chemicals. Ionic interactions, Brønsted acid–base interactions, hydrogen bonding, coordination bonding, π–π interactions, and non‐specific interactions are covered amongst adsorption mechanisms. The effects of post‐synthetic modifications of mesoporous MOFs on their stability, adsorption capacity, selectivity, and mechanisms of adsorption and desorption are analyzed. To encourage research in this quickly growing field, we identify “niches” for which no application‐oriented and/or mechanistic studies were reported. Perspectives and limitations of a wide use of mesoporous MOFs as industrial sorbents are discussed.     

Unmasking the Action of Phosphinous Acid Ligands in Nitrile Hydration Reactions Catalyzed by Arene–Ruthenium(II) Complexes

The catalytic hydration of benzonitrile and acetonitrile has been studied by employing different arene–ruthenium(II) complexes with phosphinous (PR₂OH) and phosphorous acid (P(OR)₂OH) ligands as catalysts. Marked differences in activity were found, depending on the nature of both the P‐donor and η⁶‐coordinated arene ligand. Faster transformations were always observed with the phosphinous acids. DFT computations unveiled the intriguing mechanism of acetonitrile hydration catalyzed by these arene–ruthenium(II) complexes. The process starts with attack on the nitrile carbon atom of the hydroxyl group of the P‐donor ligand instead of on a solvent water molecule, as previously suggested. The experimental results presented herein for acetonitrile and benzonitrile hydration catalyzed by different arene–ruthenium(II) complexes could be rationalized in terms of such a mechanism.     

Cyclotetrabenzoin: Facile Synthesis of a Shape‐Persistent Molecular Square and Its Assembly into Hydrogen‐Bonded Nanotubes

Cyanide‐catalyzed benzoin condensation of terephthaldehyde produces a cyclic tetramer, which we propose to name cyclotetrabenzoin. Cyclotetrabenzoin is a square‐shaped macrocycle ornamented with four α‐hydroxyketone functionalities pointing away from the central cavity, the dimensions of which are 6.9×6.9 Å. In the solid state, these functional groups extensively hydrogen bond, resulting in a microporous three‐dimensional organic framework with one‐dimensional nanotube channels. This material exhibits permanent—albeit low‐porosity, with a Langmuir surface area of 52 m² g^?1. Cyclotetrabenzoin’s easy and inexpensive synthesis and purification may inspire the creation of other shape‐persistent macrocycles and porous molecular crystals by benzoin condensation.     

High Ethene/Ethane Selectivity in 2,2′‐Bipyridine‐Based Silver(I) Complexes by Removal of Coordinated Solvent

Following removal of coordinated CH₃CN, the resulting complexes [Ag^I(2,2′‐bipyridine)][BF₄] ( 1 ) and [Ag^I(6,6′‐dimethyl‐2,2′‐bipyridine)][OTf] ( 2 ) show ethene/ethane sorption selectivities of 390 and 340, respectively, and corresponding ethene sorption capacities of 2.38 and 2.18 mmol g^?1 when tested at an applied gas pressure of 90 kPa and a temperature of (20±1) °C. These ethene/ethane selectivities are 13 times higher than those reported for known solid sorbents for ethene/ethane separation. For 2 , ethene sorption reached 90 % of equilibrium capacity within 15 minutes, and this equilibrium capacity was maintained over the three sorption/desorption cycles tested. The rates of ethene sorption were also measured. To our knowledge, these are the first complexes, designed for olefin/paraffin separations, which have open silver(I) sites. The high selectivities arise from these open silver(I) sites and the relatively low molecular surface areas of the complexes.     

Identification of tert‐Butyl Cations in Zeolite H‐ZSM‐5: Evidence from NMR Spectroscopy and DFT Calculations

Experimental evidence for the presence of tert‐butyl cations, which are important intermediates in acid‐catalyzed heterogeneous reactions, on solid acids has still not been provided to date. By combining density functional theory (DFT) calculations with ¹H/¹³C magic‐angle‐spinning NMR spectroscopy, the tert‐butyl cation was successfully identified on zeolite H‐ZSM‐5 upon conversion of isobutene by capturing this intermediate with ammonia.     

Cobalt‐Catalyzed Allylation of Heterobicyclic Alkenes: Ligand‐Induced Divergent Reactivities

The allylation of heterobicyclic alkenes is presented for the first time. By using an inexpensive cobalt salt as the catalyst and easy‐to‐handle potassium allyltrifluoroborate as the reagent, an unprecedented formal hydroallylation of the bicyclic alkenes is realized in high efficiency. When a chiral cobalt/bis(phosphine) complex is used instead, the alternative ring‐opening products can be obtained in high yield and excellent enantioselectivity.