A nanospherical ordered mesoporous Lewis acid polymer for the direct glycosylation of unprotected and unactivated sugars in water

Benzothiadiazole-Based Ordered Mesoporous Polymer as a Versatile, Metal-Free Heterogeneous Photocatalyst

Visible-light active heterogeneous organophotocatalysts have recently gained considerable interest in organic synthetic community. Ordered mesoporous polymers (OMPs) are highly promising as heterogeneous alternative to traditional precious metal/organic dyes-based photocatalysts. Herein, we report the preparation of a benzothiadiazole functionalized OMPs (BT-MPs) through a "bottom-up" strategy. High ordered periodic porosity, large surface area, excellent stability and rational energy-band structures guarantee the high catalytic activity of BT-MPs. As a result, at least six conversions, e. g., the [3+2] cycloaddition of phenols with olefins, the selective oxidation of sulfides, the C-3 thiocyanation of indole and the aminothiocyanation of β-keto ester, could be promoted smoothly by BT-MPs. In addition, BT-MPs was readily recovered with well maintaining its photocatalytic activity and could be reused for at least eight times. This study highlights the potential of exploiting photoactive OMPs as recyclable, robust and metal-free heterogeneous photocatalysts.

A TEMPO-Functionalized Ordered Mesoporous Polymer as a Highly Active and Reusable Organocatalyst

The properties of high stability, periodic porosity, and tunable nature of ordered mesoporous polymers make these materials ideal catalytic nanoreactors. However, their application in organocatalysis has been rarely explored. We report herein for the first time the incorporation of a versatile organocatalyst, 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO), into the pores of an FDU-type mesoporous polymer via a pore surface engineering strategy. The resulting FDU-15-TEMPO possesses a highly ordered mesoporous organic framework and enhanced stability, and shows excellent catalytic activity in the selective oxidation of alcohols and aerobic oxidative synthesis of 2-substituted benzoxazoles, benzimidazoles and benzothiazoles. Moreover, the catalyst can be easily recovered and reused for up to 7 consecutive cycles.

Porous Organic Polymers Containing Active Metal Centers for Suzuki-Miyaura Heterocoupling Reactions

A new generation of confined palladium(II) catalysts covalently attached inside of porous organic polymers (POPs) has been attained. The synthetic approach employed was straightforward, and there was no prerequisite for making any modification of the precursor polymer. First, POP-based catalytic supports were obtained by reacting one symmetric trifunctional aromatic monomer (1,3,5-triphenylbenzene) with two ketones having electron-withdrawing groups (4,5-diazafluoren-9-one, DAFO, and isatin) in superacidic media. The homopolymers and copolymers were made using stoichiometric ratios between the functional groups, and they were obtained with quantitative yields after the optimization of reaction conditions. Moreover, the number of chelating groups (bipyridine moieties) available to bind Pd(II) ions to the catalyst supports was modified using different DAFO/isatin ratios. The resulting amorphous polymers and copolymers showed high thermal stability, above 500 °C, and moderate-high specific surface areas (from 760 to 935 m² g^-1), with high microporosity contribution (from 64 to 77%). Next, POP-supported Pd(II) catalysts were obtained by simple immersion of the catalyst supports in a palladium(II) acetate solution, observing that the metal content was similar to that theoretically expected according to the amount of bipyridine groups present. The catalytic activity of these heterogeneous catalysts was explored for the synthesis of biphenyl and terphenyl compounds, via the Suzuki-Miyaura cross-coupling reaction using a green solvent (ethanol/water), low palladium loads, and aerobic conditions. The findings showed excellent catalytic activity with quantitative product yields. Additionally, the recyclability of the catalysts, by simply washing it with ethanol, was excellent, with a sp²-sp² coupling yield higher than 95% after five cycles of use. Finally, the feasibility of these catalysts to be employed in tangible organic reactions was assessed. Thus, the synthesis of a bulky compound, 4,4'-dimethoxy-5'-tert-butyl-m-terphenylene, which is a precursor of a thermal rearrangement monomer, was scaled-up to 2 g, with high conversion and 96% yield of the pure product.

Porous Organic Polymers with Thiourea Linkages (POP-TUs): Effective and Recyclable Organocatalysts for the Michael Reaction

As novel porous organic polymers with thiourea linkages, POP-TUs were successfully synthesized with tris(4-aminophenyl) amine (TAA) and 1,4-phenylene diisothiocyanate (PDT) under different conditions. The as-synthesized POP-TUs possess distinctly different morphological characteristics and can effectively catalyze the Michael reaction of trans-β-nitrostyrenes to diethyl malonate. Particularly, the POP-TU-2-catalyzed Michael reaction can proceed smoothly even using an ultralow catalyst dosage of 0.03 mol %, whose turnover number (TON) and turnover frequency (TOF) can reach up to 2700 and 25 h^-1, respectively. Besides, POP-TU-2 also exhibits excellent recyclability and reusability. Only 2% decline in the isolated yield was found after five consecutive runs. This work shows a significant improvement over previously reported thiourea-based catalysts and can offer an effective strategy for developing highly efficient heterogeneous organocatalysts.

Fabrication of Hollow Silica Nanospheres with Ultra-High Acid Density for Efficient Heterogeneous Catalysis

Hollow silica nanospheres with ultra-high acid density were fabricated successfully via sulfonation of phenyl-functionalized hollow silica nanospheres, which were synthesized through a single micelle (F127 (EO106PO70EO106))-templated method, with phenyltrimethoxysilane and tetramethoxysilane (TMOS) as silane precursors under neutral conditions. The density of sulfonic acid reached as high as 1.97 mmol/g. The characterization results of 31P-NMR using triethylphosphine oxide as a probe molecule suggested that the acid strength of hybrid solid acids could be systematically tuned by tuning the content of sulfonic acid and higher acid density results in stronger acid strength. Attributed to the unique hollow structure and high-acid density, the sulfonic acid-functionalized hollow silica nanospheres exhibited good catalytic performance in the condensation reaction of benzaldehyde with ethylene glycol. Notably, this study found that the catalytic activity was significantly influenced by the acid density and the ultra-high acid loading was beneficial for the activity due to the enhanced acid strength. This novel solid-acid catalyst also showed good recyclability and could be reused for at least 11 runs.

Microwave-Assisted Rapid Preparation of Mesoporous Phenolic Resin Nanospheres toward Highly Efficient Solid Acid Catalysts

A novel microwave-assisted polymerization and self-assembly protocol was developed to prepare ordered mesoporous phenolic resin (MPRN) with nanospherical morphology for the first time. This unique strategy dramatically saved the synthesis time about 2 days with an energy-efficient way. Owing to its abundant phenyl groups in the framework, it was easily transformed to benzenesulfonic acid-functionalized MPRN (SO₃H-MPRN) by simple sulfonation treatment. The obtained SO₃H-MPRN sample still possessed a large surface area, two-dimensional hexagonal mesoporous structure, and uniform spherical shape. Importantly, because of its intrinsic organic framework, the pore surface of SO₃H-MPRN was hydrophobic. Accordingly, it exhibited the excellent catalytic activity and selectivity in aqueous formaldehyde-participated Prins reaction and water-medium Fischer-indole reaction. On the basis of material characterizations and the control experiments, this remarkable catalytic performance could be ascribed to the synergetic effect derived from its short mesoporous channel and hydrophobic pore surface, which resulted in the decreased reactant diffusion limitation and the reduced water competitive adsorption. Also, it was stable in water because of the periodically arranged acid species in the resin framework and thus was easily recycled and used repetitively for at least five times.

Mesoporous metallic rhodium nanoparticles

Mesoporous noble metals are an emerging class of cutting-edge nanostructured catalysts due to their abundant exposed active sites and highly accessible surfaces. Although various noble metal (e.g. Pt, Pd and Au) structures have been synthesized by hard- and soft-templating methods, mesoporous rhodium (Rh) nanoparticles have never been generated via chemical reduction, in part due to the relatively high surface energy of rhodium (Rh) metal. Here we describe a simple, scalable route to generate mesoporous Rh by chemical reduction on polymeric micelle templates [poly(ethylene oxide)-b-poly(methyl methacrylate) (PEO-b-PMMA)]. The mesoporous Rh nanoparticles exhibited a ∼2.6 times enhancement for the electrocatalytic oxidation of methanol compared to commercially available Rh catalyst. Surprisingly, the high surface area mesoporous structure of the Rh catalyst was thermally stable up to 400 °C. The combination of high surface area and thermal stability also enables superior catalytic activity for the remediation of nitric oxide (NO) in lean-burn exhaust containing high concentrations of O₂.

Mesoporous noble metal nanostructures offer great promise in catalytic applications. Here, Yamauchi and co-workers synthesize mesoporous rhodium nanoparticles using polymeric micelle templates, and report appreciable activities for methanol oxidation and NO remediation.

Sweet potato-derived carbon nanoparticles as anode for lithium ion battery

Sweet potato is produced abundantly around the word and its derived nano-carbon delivers high capacity as anode for LIBs, which should satisfy the increasing need for anodes for LIBs.