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A series of Ni/SiO2 catalysts with different Ni content were prepared by sol-gel method for application in the synthesis of 2-methyltetrahydrofuran (2-MTHF) by hydrogenation of 2-methylfuran (2-MF). The catalyst structure was investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and temperature programmed reduction (TPR). It is found that structures and catalytic performance of the catalysts were highly affected by the Ni content. The catalyst with a 25% Ni content had an appropriate size of the Ni species and larger BET surface area and produced a higher 2-MF conversion with enhanced selectivity in 2-MTHF. [ABSTRACT FROM AUTHOR]

We report the synthesis and characterization of synthetic polymer aerogels based on dendritic-type urethane-norbornene monomers. The core of those monomers is based either on an aromatic/rigid (TIPM/Desmodur RE), or an aliphatic/flexible (Desmodur N3300) triisocyanate. The terminal norbornene groups (three at the tip of each of the three branches) were polymerized via ROMP using the inexpensive 1st generation Grubbs catalyst. The polymerization/gelation conditions were optimized by varying the amount of the catalyst. The resulting wet-gels were dried either from pentane under ambient pressure at 50 °C, or from t-butanol via freeze-drying, or by using supercritical fluid (SCF) CO2. Monomers were characterized with high resolution mass spectrometry (HRMS), 1H- and solid-state 13C-NMR. Aerogels were characterized with ATR-FTIR and solid-state 13C-NMR. The porous network was probed with N2-sorption and SEM. The thermal stability of monomers and aerogels was studied with TGA, which also provides evidence for the number of norbornene groups that reacted via ROMP. At low densities (<0.1 g cm−3) all aerogels were highly porous (porosity > 90%), mostly macroporous materials; aerogels based on the aliphatic/flexible core were fragile, whereas aerogels containing the aromatic/rigid core were plastic, and at even lower densities (0.03 g cm−3) foamy. At higher densities (0.2–0.7 g cm−3) all materials were stiff, strong, and hard. At low monomer concentrations all aerogels consisted of discrete primary particles that formed spherical secondary aggregates. At higher monomer concentrations the structure consisted of fused particles with the size of the previous secondary aggregates, due to the low solubility of the developing polymer, which phase-separated and formed a primary particle network. Same-size fused aggregates were observed for both aliphatic and aromatic triisocyanate-derived aerogels, leading to the conclusion that it is not the aliphatic or aromatic core that determines phase separation, but rather the solubility of the polymeric backbone (polynorbornene) that is in both cases the same. The material properties were compared to those of analogous aerogels bearing only one norbornene moiety at the tip of each branch deriving from the same cores. [ABSTRACT FROM AUTHOR]

An amide functionlized bidentate NHC-Pd complex was successfully prepared by a facile solvothermal methodology from a bridged bis-benzimidazolium chloride and K 2 PdCl 4. The new bidentate NHC-Pd complex has been effectively applied as catalyst in Suzuki-Miyaura cross-coupling reactions of aryl halides with arylboronic acids in neat water (yields up to 99.0%). [Display omitted] • A novel bidentate Pd-NHC complex has been synthesized. • The new bidentate Pd-NHC complex showed good activity for Suzuki coupling reaction. • Water was selected as the solvent for Suzuki-Miyaura cross-coupling. • The functional ligand Pd complex is distinctly influenced by the electronic and steric effects on the catalytic process. An amide functionlized bidentate NHC-Pd complex was successfully prepared by a facile solvothermal methodology from a bridged bis-benzimidazolium chloride and K 2 PdCl 4. The new bidentate NHC-Pd complex has been effectively applied as catalyst in Suzuki-Miyaura cross-coupling reactions of aryl halides with arylboronic acids in distilled water (yields up to 99.0%). The bridged bis-benzimidazolium ligand from the Pd complex, bearing the amide functional groups on the nitrogen atom, showed to distinctly influence the electronic and steric effects on the catalytic process. The potential of application of the new NHC-Pd catalyst in diverse C C bond forming processes, working under environmentally friendly conditions, is further outlined. [ABSTRACT FROM AUTHOR]

• First Pd@ZIF-92 nanocatalyst for efficient C(sp2)-C(sp2) cross-coupling reactions. • Post-synthetic modification of ZIF-90 to ZIF-92 and Pd@ZIF-92. • High catalytic activity and recyclability for reactions in pure water. • Environment-friendly, stable and robust nanocatalyst for cross-couplings. Herein the first ever Pd2+-decorated ZIF-92 nanostructure is readily accessed by post-synthesis modification (PSM) of the zeolitic imidazolate framework ZIF-90. Thus, the imidazolate linker of the ZIF-90 is functionalized with the hydroxyethylimino group, followed by anchoring the palladium catalytically active sites through a tight coordination of Pd2+ ions to both the N and O atoms of ZIF-92. The acquired data (by PXRD, EDS, SEM, XPS, ICP-AES) concerning the crystalline structure, elemental mapping and network configuration of the Pd@ZIF-92 catalyst confirmed its structure, before and after the cross-coupling reactions and following recycling. The Pd@ZIF-92 showed excellent catalytic activity (>99%) and chemoselectivity in Suzuki-Miyaura coupling proceeding in neat water, at very low Pd loading (0.009 mol%). Comparison of its performance with that of many reported Pd nanocatalysts operating in aqueous/protic media testifies to its superiority. The appealing gateway to this innovative, stable, robust, easily recoverable and reusable Pd@ZIF-92 nanostructure recommends its beneficial utilization in C(sp2)-C(sp2) cross-couplings and other sustainable, environmentally-friendly processes. [ABSTRACT FROM AUTHOR]