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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.

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.

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...