The Suzuki reaction, which joins aryl halides with arylboronic acids to form carbon-carbon bonds and produce biaryl compounds, sits at the heart of modern organic synthesis. Biaryls appear in pharmaceuticals, herbicides, natural products, polymers, molecular wires, and liquid crystals, which is why the reaction earned Akira Suzuki a share of the Nobel Prize in Chemistry. Traditionally, the transformation relies on homogeneous palladium catalysts paired with elaborate ligands such as bulky phosphines or carbenes. Those ligands work well but bring baggage: they are often toxic, flammable, and expensive, and the reactions typically demand hazardous organic solvents. Worse, the dissolved catalyst cannot simply be filtered out, so precious palladium is lost and metal residues contaminate the product.

The new catalyst tackles both problems at once through clever architectural design. At its core sits a magnetite nanoparticle, chosen for its strong magnetic response, large surface area, thermal stability, and low toxicity. Bare magnetic nanoparticles, however, tend to aggregate, oxidize, and lose their magnetic character, so the team wrapped each core in a protective shell of periodic mesoporous organosilica, or PMO. Unlike ordinary mesoporous silica built from purely inorganic Si-O-Si frameworks, PMO incorporates organic groups directly into its pore walls, here in the form of ethylene bridges. That hybrid composition grants the shell enhanced chemical and thermal stability, high hydrophobicity, larger pore volume, and a high specific surface area, making it an ideal nanoreactor for organic transformations that involve water-insoluble substrates.

Synthesis proceeded in carefully staged steps. The researchers first prepared Fe3O4@SiO2 nanoparticles, dispersed them in a water-ethanol mixture by ultrasonication, and added the surfactant cetyltrimethylammonium bromide along with ammonia. Dropwise introduction of 1,2-bis(triethoxysilyl)ethane and tetramethyl orthosilica precursor, followed by static heating at 100 degrees Celsius for 72 hours, grew the ordered mesoporous organosilica shell around each magnetic core. Soxhlet extraction with an ethanol-hydrochloric acid mixture removed the surfactant template, opening the pore network. The team then grafted N1-(3-trimethoxysilylpropyl)diethylenetriamine onto the pore surfaces under argon and finally coordinated palladium acetate to the pendant amine groups, anchoring the catalytically active diethylenetriamine/palladium complex throughout the mesoporous channels.

Characterization left little doubt that the material had formed as designed. Fourier-transform infrared spectroscopy tracked each stage of the build: signals for the Fe-O bond of magnetite, the Si-O-Si framework, and the carbon-silicon bonds of the organosilica appeared as expected, while the disappearance of surfactant methylene peaks confirmed successful template extraction. A distinct band at 1560 wavenumbers revealed the carbon-nitrogen bonds of the grafted diethylenetriamine ligand, and a slight blue-shift after palladium loading signaled successful metal coordination. Thermogravimetric analysis showed the composite remains stable well beyond typical reaction temperatures, with staged weight losses corresponding to adsorbed solvent, surface amine ligands, and the ethylene bridges of the shell. Wide-angle powder X-ray diffraction preserved all six characteristic reflections of the cubic spinel magnetite structure, while a low-angle peak at 2.1 degrees confirmed the ordered mesoporosity of the shell.

Electron microscopy and magnetometry filled in the visual and physical picture. Scanning electron microscopy showed uniform, spherical particles, and transmission electron microscopy revealed the unmistakable core-shell architecture, with dark magnetic cores clearly contrasted against gray organosilica shells. Energy-dispersive X-ray spectroscopy and elemental mapping demonstrated that iron, silicon, carbon, oxygen, nitrogen, and palladium were all present and homogeneously distributed through the framework, evidence that the active palladium sites are spread evenly rather than clumped in hotspots. Vibrating sample magnetometry recorded a saturation magnetization of 16.12 emu per gram for the finished catalyst, lower than bare magnetite as expected for a coated particle, but still ample for rapid magnetic separation from a reaction slurry.

With the material in hand, the team optimized the Suzuki coupling of iodobenzene with phenylboronic acid as a model reaction, screening solvents, bases, temperatures, and catalyst loadings. The greenest option won decisively. Water, the ideal solvent from a sustainability standpoint, outperformed toluene, ethanol, and water-ethanol mixtures, delivering a 92 percent isolated yield at 50 degrees Celsius with just 0.15 mole percent catalyst and potassium carbonate as base. The result is less paradoxical than it seems. Although aryl halides dissolve poorly in water, the hydrophobic mesoporous PMO shell acts as a nanoreactor that concentrates organic substrates at the catalyst-water interface and within its lipophilic pores, placing them in intimate contact with the palladium sites. Water simultaneously provides the polar medium that potassium carbonate needs to activate the boronic acid and generate the reactive hydroxo-palladium species involved in transmetalation, so medium and material work synergistically.

The substrate scope proved impressively broad. Fifteen different aryl halides bearing varied functional groups reacted with phenylboronic acid in 20 to 90 minutes, furnishing biaryl products in 81 to 95 percent yields with no detectable by-products. Electron-withdrawing and electron-donating substituents alike were tolerated, and melting points of the isolated products matched literature values. A control experiment without the catalyst produced nothing, confirming its essential role. In a leaching test, the researchers halted a reaction at roughly half conversion, removed the catalyst magnetically, and watched the filtrate: no further reaction occurred over an hour, demonstrating that the catalysis is genuinely heterogeneous and that palladium stays anchored to the solid rather than dissolving into solution.

Recyclability, the Achilles heel of many supported catalysts, emerged as the standout feature. After each run, an external magnet pulled the catalyst free; a water wash and drying readied it for the next cycle. Eleven consecutive reactions proceeded without significant loss of yield or selectivity, and post-use analysis told a story of remarkable durability. The infrared spectrum of the recovered catalyst was indistinguishable from the fresh material, the X-ray diffraction pattern retained the pristine magnetite crystal structure, and scanning electron microscopy after twelve cycles still showed intact spherical particles. Benchmarking against seven previously reported palladium-based magnetic catalysts for Suzuki reactions, the new material matched or exceeded them all, operating at the lowest temperature of the comparison group in pure water while sustaining the highest number of reuse cycles.

The study offers a template for how thoughtful materials engineering can reconcile the competing demands of activity, sustainability, and practicality in catalysis. By combining a magnetic core for effortless recovery, a hydrophobic mesoporous organosilica shell that functions as a nanoscale reactor, and a robust amine-anchored palladium complex as the active site, the Yasouj University team has produced a catalyst that runs one of organic chemistry’s most valuable reactions in water, at mild temperature, with vanishingly small catalyst loadings, and with a service life measured in dozens of cycles. As pressure mounts on the pharmaceutical and fine chemical industries to eliminate toxic solvents, precious metal waste, and phosphine ligands from their processes, magnetically recoverable nanoreactors of this kind point toward a cleaner future for carbon-carbon bond formation.

Subject of Research: A magnetically recoverable core-shell periodic mesoporous organosilica-supported palladium nanocatalyst for aqueous Suzuki coupling reactions

Article Title: Core-shell structured magnetic periodic mesoporous organosilica supported diethylenetriamine/palladium complex as a highly recoverable nanocatalyst for Suzuki reaction

Article References: Norouzi, M., Elhamifar, D., & Shaker, M. (2026). Core-shell structured magnetic periodic mesoporous organosilica supported diethylenetriamine/palladium complex as a highly recoverable nanocatalyst for Suzuki reaction. Results in Chemistry, 31, Article 103907. https://doi.org/10.1016/j.rechem.2026.103907

Image Credits: AI Generated

DOI: 10.1016/j.rechem.2026.103907

Keywords: nanocatalysis, Suzuki reaction, palladium catalyst, magnetic nanoparticles, periodic mesoporous organosilica, core-shell structure, green chemistry, heterogeneous catalysis, biaryl synthesis, water as solvent, catalyst recyclability, diethylenetriamine ligand

The catalyst itself is a layered particle with a magnetic iron oxide core wrapped in a silica shell, functionalized with an amino-silane compound called APTES and topped with sulfonic acid groups. This architecture gives the material two useful qualities at once: reactive acidic sites on the surface that can drive organic reactions, and a magnetic core that lets the particles be pulled out of a reaction mixture with a simple magnet rather than by filtration. The team built the material in four steps, starting with iron chloride dissolved in the butterbur extract, then layering on silica, APTES, and finally the sulfonic acid groups through a reaction with 1,4-butane sultone.

Once the catalyst was in hand, the researchers put it to work in a four-component reaction combining α,β-unsaturated compounds, guanidine, activated acetylenic compounds, and methyl iodide. The products are methyliminopyridopyrimidines, a class of fused nitrogen-containing ring systems that sit at the heart of many drug candidates. Pyridopyrimidine frameworks are known to display antibacterial, antiviral, antitumor, antimalarial, and anti-inflammatory properties, making them attractive targets for medicinal chemists. The reaction ran in plain water at room temperature and finished within roughly two to three hours, producing yields between 78 and 92 percent across the series of compounds the team made.

The choice of water as the solvent is more than a nod to environmental fashion. Water can actively accelerate organic reactions through hydrogen bonding at the interface between the aqueous phase and organic reactants, a phenomenon recognized since K. Barry Sharpless’s work on on-water chemistry in 2005. In this case, the reaction performed poorly without a catalyst, and heating the mixture to 100 degrees Celsius offered no improvement over room temperature. Water, it turned out, was the best solvent among those tested, and the catalyst at a loading of just 0.02 grams per reaction delivered the highest yields.

Characterization of the new catalyst was thorough. X-ray diffraction confirmed the cubic crystal structure of the magnetite core with no damage from the coating process, and the average crystallite size came out at about 32.5 nanometers. Electron microscopy showed spherical, uniform core-shell particles, while vibrating sample magnetometry revealed superparamagnetic behavior. The saturation magnetization dropped from 76.4 emu per gram for bare iron oxide to 35.5 emu per gram after coating, but that remained plenty strong for magnetic separation from solution. Energy-dispersive X-ray spectroscopy and elemental mapping confirmed the expected distribution of iron, oxygen, silicon, carbon, nitrogen, and sulfur throughout the material.

The catalyst also proved durable. Thermogravimetric analysis showed that the organic surface groups survive up to roughly 500 degrees Celsius, and hot filtration tests indicated that the catalyst does not leach into solution during reactions, meaning the material is genuinely heterogeneous rather than dissolving and acting from the liquid phase. After each run the particles were collected with a magnet, washed, dried, and reused, with considerable retention of catalytic activity across cycles.

The mechanism behind the catalysis involves cooperative action between Lewis acid and Lewis base sites on the particle surface. Silicon, iron, and the sulfonic acid protons bind to the oxygen atoms of carbonyl groups in the starting materials, increasing the electrophilicity of the carbonyl carbon and making it more vulnerable to nucleophilic attack. Meanwhile, oxygen and nitrogen sites on the surface act as bases, stripping protons from the reactants to form key intermediates. Guanidine first reacts with the unsaturated compound, then the acetylenic component joins in, and finally an intramolecular cyclization closes the ring to form the pyridopyrimidine product.

Having built the molecules, the researchers turned to biology. They tested four of the new compounds for antioxidant activity using the DPPH radical scavenging assay, a standard method that measures a compound’s ability to neutralize a stable free radical. Compound 5c stood out with an IC50 value of 12.56 micrograms per milliliter, meaning it took only that concentration to inhibit half of the DPPH radicals. That compares with 9.26 for the industrial antioxidant BHT and 8.75 for TBHQ, placing the synthetic compound in genuinely competitive territory. A second assay, in which the compound’s ability to reduce ferric iron was measured spectrophotometrically, produced a similar ranking, with TBHQ leading, followed by BHT, then compound 5c.

Antibacterial testing followed using the disk diffusion method against both Gram-positive and Gram-negative bacterial strains, with streptomycin and gentamicin as clinical benchmarks. Six of the compounds, designated 5b, 5c, 5e, 5f, 5i, and 5j, showed strong activity against both categories of bacteria. The largest zone of inhibition was observed against Escherichia coli, a Gram-negative organism whose outer membrane typically makes it harder to kill than Gram-positive species. That a synthetic heterocycle built in water at room temperature can match broad-spectrum antibacterial patterns is the kind of result that catches the attention of drug discovery teams.

The catalyst had one more trick to demonstrate. The team tested its ability to reduce 4-nitrophenol, a toxic water pollutant produced by the dye, pesticide, and pharmaceutical industries, into 4-aminophenol, a far less harmful compound and a useful industrial intermediate. In the presence of sodium borohydride, the catalyst drove the reduction rapidly, with the yellow color of the nitrophenol solution fading to colorless within minutes, confirmed by the disappearance of the 400-nanometer absorbance peak and the appearance of a new peak near 300 nanometers. Without the catalyst, the borohydride alone made no meaningful progress even after 15 hours. Given that global dye and pigment production runs at roughly 700,000 tons per year and that most of these compounds harm aquatic life, a cheap, magnetic, plant-built catalyst that clears such pollutants from water in seconds-to-minutes timescales represents a practical piece of green chemistry with potential well beyond the laboratory bench.

Subject of Research: Green synthesis of iminopyridopyrimidine compounds using a bio-derived magnetic nanocatalyst

Article Title: Green synthesis and evaluation of biological activity of novel iminopyridopyrimidine employing APTES@SiO2@Fe3O4-SO3H as nanocatalyst

Article References: Shirangi, H. S., Hojjati, M., Noorzaei, M., & Rostami-Charati, F. (2026). Green synthesis and evaluation of biological activity of novel iminopyridopyrimidine employing APTES@SiO2@Fe3O4-SO3H as nanocatalyst. Journal of Saudi Chemical Society, 30(4), Article 51. https://doi.org/10.1007/s44442-026-00079-5

Image Credits: AI Generated

DOI: 10.1007/s44442-026-00079-5

Keywords: green chemistry, nanocatalyst, magnetite nanoparticles, pyridopyrimidine, Petasites hybridus, antioxidant, antibacterial, multicomponent reaction, 4-nitrophenol reduction, water as solvent, APTES, sulfonic acid