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Ammonia (NH

A new series of ether-linked, per-fluorinated organic polymers bearing azo- (-N = N-) and azomethane (-C = N-) organic linkers was reported. The synthetic methodology relied on applying the nucleophilic aromatic substitution reaction (NAS) to fluorinated linkers (e.g. decafluorobiphenyl and hexaflourobenzene) and diols of azo- and azomethane linkers. The successful formation of the new structures revealing ether-linkage substitution of selected fluorine sites was confirmed by 1H-, 13C-, 19F-NMR and FTIR. All polymers were thermally stable in the range of 350–500 °C due to the variation of fluorine and nitrogen contents. The extended conjugation of the polymers was confirmed by the changes in the UV-Vis spectra of the organic linkers and their corresponding polymers. A notable hypsochromic shift was observed in all cases, which was more pronounced with azo-based fluorinated chains due to the H-bonding on the nitrogen sites, chain conformations and planarity. The optical band gap (Eg) of the polymers was determined from the UV-Vis. The Eg values of azo-based fluorinated polymers were higher by 1eV compared to their corresponding linkers. The 19F-NMR analysis confirmed two types of NAS on both the ortho- and para- positions of the fluorinated linkers. These connections created the possibility of developing cross-linked frameworks beside the open-chain confirmation with tailored hydrophobic nature. The cross-linking formation was characterized by porosity measurements, including surface area (SA), pore size and pore volume. The highest measured values were recorded for the azo-based polymer (DAB-Z-1h), which reached 438 m2/g and a pore volume of 0.35 cm3/g. A surface area of 105 m2/g was the lowest for the open-chain azomethane-based polymer (DAB-A-1O) with a pore volume of 0.0872 cm3/g. The beneficial formation of porous structures with varied hydrophobic nature was investigated as adsorbents for separating water/benzene, water/phenol and the selective binding of methane/carbon dioxide gases from the air. The most hydrophobic polymers that contain the decafluorbiphenyl linker were suitable for benzene separation, and the superior methane uptake values were 6.14 and 3.46 mg/g, for DAB-Z-1O and DAB-A-1O, respectively. On the other hand, DAB-Z-1h, with the highest surface area (438 m2/g) and rich with nitrogen sites, has the highest CO2 uptake at 298 K (17.25 mg/g).

Palladium catalyzed cross-coupling reactions represent a significant advancement in contemporary organic synthesis as these reactions are of strategic importance in the area of pharmaceutical drug discovery and development. Supported palladium-based catalysts are highly sought-after in carbon–carbon bond forming catalytic processes to ensure catalyst recovery and reuse while preventing product contamination. This paper reports the development of heterogeneous Pd-based bimetallic catalysts supported on fumed silica that have high activity and selectivity matching those of homogeneous catalysts, eliminating the catalyst's leaching and sintering and allowing efficient recycling of the catalysts. Palladium and base metal (Cu, Ni or Co) contents of less than 1.0 wt% loading are deposited on a mesoporous fumed silica support (surface area SABET = 350 m2 g−1) using strong electrostatic adsorption (SEA) yielding homogeneously alloyed nanoparticles with an average size of 1.3 nm. All bimetallic catalysts were found to be highly active toward Suzuki cross-coupling (SCC) reactions with superior activity and stability for the CuPd/SiO2 catalyst. A low CuPd/SiO2 loading (Pd: 0.3 mol%) completes the conversion of bromobenzene and phenylboronic acid to biphenyl in 30 minutes under ambient conditions in water/ethanol solvent. In contrast, monometallic Pd/SiO2 (Pd: 0.3 mol%) completes the same reaction in three hours under the same conditions. The combination of Pd with the base metals helps in retaining the Pd0 status by charge donation from the base metals to Pd, thus lowering the activation energy of the aryl halide oxidative addition step. Along with its exceptional activity, CuPd/SiO2 exhibits excellent recycling performance with a turnover frequency (TOF) of 280 000 h−1 under microwave reaction conditions at 60 °C. Our study demonstrates that SEA is an excellent synthetic strategy for depositing ultra-small Pd-based bimetallic nanoparticles on porous silica for SCC. This avenue not only provides highly active and sintering-resistant catalysts but also significantly lowers Pd contents in the catalysts without compromising catalytic activity, making the catalysts very practical for large-scale applications.