General synthesis of primary amines via reductive amination employing a reusable nickel catalyst

Reusable catalysts based on earth-abundant metals with a broad applicability in organic synthesis are a key to a more sustainable production of fine chemicals, pharmaceuticals and agrochemicals. Herein, we report on a nanostructured nickel catalyst for the general and selective synthesis of primary amines via reductive amination, employing ammonia dissolved in water. Our catalyst, which operates at low temperature and pressure, is highly active, reusable and easy to handle. The synthesis from a specific nickel complex and γ-Al2O3 is straightforward, with the ligand–metal combination of this complex being crucial. Aldehydes (including purely aliphatic ones), aryl–alkyl, dialkyl and diaryl ketones can all be converted smoothly into primary amines. In addition, the amination of pharmaceuticals, bioactive compounds and natural products is demonstrated. Many functional groups—including hydrogenation-sensitive examples—are tolerated. We expect that our findings will inspire others to develop reusable and nanostructured earth-abundant metal catalysts for complex organic transformations. Reusable catalysts based on earth-abundant metals could offer inexpensive and sustainable routes in organic synthesis. Here a nickel catalyst—formed by pyrolysis of a nickel complex on a γ-Al2O3 support—is shown to be highly active for synthesis of primary amines via reductive amination. The catalyst operates with aqueous ammonia and either aldehydes or ketones, tolerating a wide range of functional groups.