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Recently, N-substituted anilines have been the object of increasing research interest in the field of organic chemistry due to their role as key intermediates for the synthesis of important compounds such as polymers, dyes, drugs, agrochemicals and pharmaceutical products. Among the various methods reported in literature for the formation of C–N bonds to access secondary anilines, the one-pot reductive amination of aldehydes with nitroarenes is the most interesting procedure, because it allows to obtain diverse N-substituted aryl amines by simple reduction of nitro compounds followed by condensation with aldehydes and subsequent reduction of the imine intermediates. These kinds of tandem reactions are generally catalyzed by transition metal-based catalysts, mainly potentially reusable metal nanoparticles. The rapid growth in the last years in the field of metal-based heterogeneous catalysts for the one-pot reductive amination of aldehydes with nitroarenes demands for a review on the state of the art with a special emphasis on the different kinds of metals used as catalysts and their recyclability features.

Rhodium nanoparticles (Rh NPs) embedded in different amphiphilic core-crosslinked micelle (CCM) latexes (RhNP@CCM) have been synthesized by [RhCl(COD)(TPP@CCM)] reduction with H2 (TPP@CCM = core-anchored triphenylphosphine). The reduction rate depends on...

Dedicated to Prof. Rinaldo Poli on occasion of his 65th birthday.Weakly magnetic hematite (α-Fe 2 O 3 ) nanoparticles were synthesized by heating an amorphous polymer supported iron(III) complex (Fe_POL) at 400 °C for 4 h in air. The growth of nanoparticles (NPs) was studied by PXRD, heating the polymer from 150 °C to 400 °C at 25 °C intervals, revealing that, at all temperatures, the only crystalline phase detected is hematite. Conversely, annealing of Fe_POL at 400 °C for 4 h under nitrogen, yielded a material containing wüstite (FeO) as the only crystalline phase, supported onto pyrolised acrylamidic polymer. The synthesized materials were characterized by TXRF, PXRD, SEM-EDS, XPS, Raman and FTIR spectroscopy as well as by magnetic analysis. Differently from natural micrometric hematite, synthesised nano-hematite turned out to be an efficient and recyclable catalyst for the hydrogenation of nitroarenes to the corresponding anilines.

A nickel containing monomer, Ni(AAEMA)2 (AAEMA− = deprotonated form of 2‐(acetoacetoxy) ethyl methacrylate) is co‐polymerized with ethyl methacrylate (co‐monomer) and ethylene glycol dimethacrylate (cross‐linker). The obtained polymer is a green methacrylic resin containing Ni(II) centers homogeneously dispersed in the catalyst, which results insoluble in all common organic solvents and in water. The specific features of this material classify it as an amphiphilic resin, air and moisture stable, with the peculiarity to swell in halogenated solvents, acetone and water and to shrink in diethyl ether and petroleum ether. The polymer is calcined under reductive conditions (dihydrogen with initial pressure of 5 bar) following two procedures, differing from each other for the cooling conditions. In the first procedure, the calcined material is cooled under dihydrogen gas, while in the second one the cooling step occurs under air. After calcination, the green Ni(II)‐based co‐polymer turns into black resins, Ni‐res1 (obtained by cooling under hydrogen) and Ni‐res2 ((obtained by cooling under air). FESEM analyses show that both Ni‐res1 and Ni‐res2 support Ni nanoparticles with different morphologies, being the metal nanoparticles onto Ni‐res1 smaller than the ones dispersed in Ni‐res2, that have an urchin‐like shape. Both Ni‐based co‐polymers are tested as catalysts in the reduction of nitrobenzene with NaBH4. Ni‐res1 results more active and selective towards aniline with respect to Ni‐res2.

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Fe2O3 nanoparticles (NPs) with mean size of 50 nm ca. are synthesized starting from a porous organic polymer containing β‐ketoesterate Fe(III) sites (Fe‐POP), which is annealed at 400 °C under air for 30 min. During calcination, the organic material partially decomposes, and iron(III) oxide NPs onto an organic residue could be observed after annealing. The obtained NPs are characterized by SEM‐EDS, IR, and magnetic analyses and they are employed as active catalysts in the reduction of p‐bromonitrobenzene into p‐bromoaniline, using hydrazine hydrate in ethanol.