Synergistic effects of core-shell poly(ionic liquids)@ZIF-8 nanocomposites for enhancing additive-free CO2 conversion.

The present study, for the first time, reports the fabrication of core-shell poly(ionic liquids)@ZIF-8 nanocomposites through a facile in-situ polymerization strategy. These composites exhibited exceptional structural characteristics including high specific surface areas and the integration of high-density Lewis acid/base and nucleophilic active sites. The structure-activity relationship, reusability, and versatility of the poly(ionic liquids)@ZIF-8 composites were investigated for the cycloaddition reaction between CO2 and epoxide. By optimizing the composites structures and their catalytic performance, PIL-Br@ZIF-8(2:1) was identified as an exciting catalyst that exhibits high activity and selectivity in the synthesis of various cyclic carbonates under mild or even atmospheric pressure or simulated flue gas conditions. Moreover, the catalyst demonstrated excellent structural stability while maintaining its catalytic activity throughout multiple usage cycles. By combining DFT calculations, we investigated the transition states and intermediate geometries of the cycloaddition reaction in different coordination microenvironments, thereby proposing a synergistic catalytic mechanism involving multiple active sites.

A theoretical study on novel neutral noble gas compound F4XeOsF4.

A noble gas compound containing a triple bond between xenon and transition metal Os (i.e. F4XeOsF4, isomer A) was predicted using quantum-chemical calculations. At the MP2 level of theory, the predicted Xe-Os bond length (2.407 Å) is between the standard double (2.51 Å) and triple (2.31 Å) bond lengths. Natural bond orbital analysis indicates that the Xe-Os triple bond consists of one σ-bond and two π-bonds, a conclusion also supported by atoms in molecules (AIM) quantum theory, the electron density distribution (EDD) and electron localization function (ELF) analysis. The two-body (XeF4 and OsF4) dissociation energy barrier of F4XeOsF4 is 15.6 kcal mol-1. The other three isomers of F4XeOsF4 were also investigated; isomer B contains a Xe-Os single bond and isomers C and D contain Xe-Os double bonds. The configurations of isomers A, B, C and D can be transformed into each other.

Reaction induced robust Pd x Bi y /SiC catalyst for the gas phase oxidation of monopolistic alcohols.

Reaction induced Pd x Bi y /SiC catalysts exhibit excellent catalytic activity (92% conversion of benzyl alcohol and 98% selectivity of benzyl aldehyde) and stability (time on stream of 200 h) in the gas phase oxidation of alcohols at a low temperature of 240 °C due to the formation of Pd0-Bi2O3 species. TEM indicates that the agglomeration of the 5.8 nm nanoparticles is inhibited under the reaction conditions. The transformation from inactive PdO-Bi2O3 to active Pd0-Bi2O3 under the reaction conditions is confirmed elaborately by XRD and XPS.

Synthesis of 1,2-Dihydroquinazolines via Rearrangement of Indazolium Salts.

A convenient synthesis of 1,2-dihydroquinazolines via rearrangement of indazolium salts was described. A mechanistic study using isotope labeling experiment revealed that the rearrangement passes through cleavage of N-N bond/ring opening after basic deprotonation of 2-benzyl in indazolium salts to yield intermediate E, which proceeds in an intramolecular N-nucleophilic addition to form the observed product. Computational analyses imply that the pathway of the rearrangement is determined by the energy barriers of the ring-closing process and the stability of the product.

Can there be a multi-bond between noble gas and metal? A theoretical study of F2XeMoF2.

A new noble gas compound containing a Xe-Mo double bond, F2XeMoF2, was theoretically constructed and studied based on DFT and ab initio calculations. The CCSD(T)-calculated Xe-Mo bond length of 2.518 Å was comparable to the standard value of 2.56 Å. The bonding energy (32.3 kcal mol-1) was even higher than that of the Xe-Au bond in the well-known XeAuF complex (24.1 kcal mol-1). The result of natural bond orbital (NBO) analysis indicates that there is a σ-bond and a π-bond between the Xe and Mo atoms in F2XeMoF2. The properties of the Xe-Mo double bond were also analyzed with the atoms in molecules (AIM) approach and natural resonance theory (NRT).

Theoretical investigation of HNgNH3(+) ions (Ng = He, Ne, Ar, Kr, and Xe).

The equilibrium geometries, harmonic frequencies, and dissociation energies of HNgNH3(+) ions (Ng = He, Ne, Ar, Kr, and Xe) were investigated using the following method: Becke-3-parameter-Lee-Yang-Parr (B3LYP), Boese-Matrin for Kinetics (BMK), second-order Møller-Plesset perturbation theory (MP2), and coupled-cluster with single and double excitations as well as perturbative inclusion of triples (CCSD(T)). The results indicate that HHeNH3(+), HArNH3(+), HKrNH3(+), and HXeNH3(+) ions are metastable species that are protected from decomposition by high energy barriers, whereas the HNeNH3(+) ion is unstable because of its relatively small energy barrier for decomposition. The bonding nature of noble-gas atoms in HNgNH3(+) was also analyzed using the atoms in molecules approach, natural energy decomposition analysis, and natural bond orbital analysis.

Insights into hydrogen bond donor promoted fixation of carbon dioxide with epoxides catalyzed by ionic liquids.

Catalytic coupling of carbon dioxide with epoxides to obtain cyclic carbonates is an important reaction that has been receiving renewed interest. In this contribution, the cycloaddition reaction in the presence of various hydrogen bond donors (HBDs) catalyzed by hydroxyl/carboxyl task-specific ionic liquids (ILs) is studied in detail. It was found that the activity of ILs could be significantly enhanced in the presence of ethylene glycol (EG), and EG/HEBimBr were the most efficient catalysts for the CO2 cycloaddition to propylene oxide. Moreover, the binary catalysts were also efficiently versatile for the CO2 cycloaddition to less active epoxides such as styrene oxide and cyclohexene oxide. Besides, the minimum energy paths for this hydrogen bond-promoted catalytic reaction were calculated using the density functional theory (DFT) method. The DFT results suggested that the ring-closing reaction was the rate-determining step in the HEBimBr-catalyzed cycloaddition reaction but the EG addition could remarkably reduce its energy barrier as the formation of a hydrogen bond between EG and the oxygen atom of epoxides led this process along the standard SN2 mechanism. As a result, the ring-opening reaction became the rate-determining step in the EG/HEBimBr-catalyzed cycloaddition reaction. The work reported herein helped the understanding and design of catalysts for efficient fixation of CO2 to epoxides via hydrogen bond activation.

Predicted organic noble-gas hydrides derived from acrylic acid.

The Ar-, Kr-, and Xe-insertion compounds into acrylic acid, i.e., C2H3COONgH (Ng = Ar, Kr, and Xe), have been studied by ab initio calculations. The geometry optimization, frequency calculation, and stability were investigated at the MP2/aug-cc-pVTZ (aug-cc-pVTZ-PP) level of theory. Two configuration isomers, i.e., s-cis syn (isomer A) and s-cis anti (isomer B), were optimized for each molecule. Using the s-cis syn structure (isomer A) as an example, we performed natural bond orbital (NBO) analysis, natural energy decomposition analysis (NEDA), and atom-in-molecules (AIM) analysis to investigate the bonding nature of these noble-gas compounds. Our study predicts the existence of Kr- and Xe-derivatives of acrylic acid and the instability of Ar-related compounds.