Amines represent important intermediates in chemical and biological processes. Herein, we describe the use of a nanostructured iron-based catalyst for the tandem reductive amination between nitroarenes and aldehydes using hydrogen as reductant. The nanostructured iron-catalyst is prepared by immobilization of an iron-phenanthroline complex onto a commercially available carbon support. In the reaction sequence a primary amine is formed in situ from the corresponding nitro compound. Reversible condensation with aldehydes forms the respective imines, which are finally reduced to the desired secondary amine. This synthesis of secondary amines is atom-economical and environmentally attractive using cheap and readily available organic compounds as starting materials.

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This protocol describes the preparation of cobalt-based nanocatalysts and their applications in environmentally benign redox processes for fine chemical synthesis. The catalytically active material consists of nanoscale Co3O4 particles surrounded by nitrogen-doped graphene layers (NGrs), which have been prepared by pyrolysis of phenanthroline-ligated cobalt acetate on carbon. The resulting materials have been found to be excellent catalysts for the activation of both molecular oxygen and hydrogen; in all tested reactions, water was the only by-product. By applying these catalysts, green oxidations of alcohols and hydrogenation of nitroarenes for the synthesis of nitriles, esters and amines are demonstrated. The overall time required for catalyst preparation and for redox reactions is 35 h and 10-30 h, respectively.

In this protocol, we describe the preparation of nanoscale iron oxide-based materials and their use in the catalysis of different hydrogenation reactions. Pyrolysis of a Fe(OAc)2-phenanthroline complex on carbon at 800 °C under argon atmosphere results in the formation of nanoscale Fe2O3 particles surrounded by nitrogen-doped graphene layers. By applying these catalysts, the hydrogenation of structurally diverse and functionalized nitroarenes to anilines proceeds with excellent selectivity. Furthermore, we have shown that one-pot reductive amination of carbonyl compounds with nitroarenes is also possible in the presence of these iron oxide catalysts. We report herein the synthesis of more than 40 amines, which are important feedstocks and key intermediates for pharmaceuticals, agrochemicals and polymers. The detailed preparation of the catalysts and the procedures for the hydrogenation processes are presented. The overall time required for the catalyst preparation and for the hydrogenation reactions are 35 h and 20-35 h, respectively.

Heterogenized non‐noble metal‐based catalysts allow for cost‐efficient and environmentally benign hydrogenations. Here, we have developed a straightforward reductive amination methodology using molecular hydrogen in the presence of a Co3O4/NGr@C catalyst system. Various carbonyl compounds were transformed with secondary amines to the corresponding tertiary amines with good to excellent yields and selectivity. The Co3O4/NGr@C catalyst is recycled up to five times without significant loss of activity.