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• N-doped polymer supported cobalt catalyst was active for nitroarene reduction. • Both cobalt and cobalt oxide nanoparticles were detected on the catalyst. • The catalytically active species were cobalt nanoparticles. • Nitrogen centers on the polymer increased the catalytic activity of the system. • The catalytic system was recyclable up to five runs. A nitrogen-doped polymer supported cobalt catalyst (Co-pol) was synthesized by co-polymerization of a methacrylic β-ketoesterate cobalt complex with amidic co-monomers and subsequent calcination under dihydrogen. Co-pol was employed as active, selective and recyclable catalyst for nitroarene reduction in aqueous medium (Et 2 O/H 2 O) at room temperature with NaBH 4 as reducing agent. The catalysis was truly heterogeneous, as demonstrated by hot filtration tests, and the catalytic system prevented hydrodehalogenation when halonitroarenes were used as substrates. To keep its activity, Co-pol needed to be regenerated after duty by calcination under dihydrogen. Accurate STEM and EDS analyses detected a mixture of both cobalt(0) and cobalt oxide nanoparticles in the active catalyst and only cobalt oxide nanoparticles in the spent catalyst indicating that the real catalytically active species were cobalt(0) nanoparticles. A beneficial role of nitrogen atoms in the catalytic support was ascertained by synthetizing a new catalyst (Co-pol2) similar to Co-pol , but without nitrogen centers. Co-pol2 turned out much less active than Co-pol , thus suggesting a mechanism consisting of a support-assisted heterolytic splitting of dihydrogen (rather than involving the formation of Co–N interaction, not detected by XPS analysis) as operative in Co-pol system. [Display omitted] [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]