Tandem ammonia borane dehydrogenation and nitroarenes hydrogenation has been reported as a novel strategy for the preparation of aromatic amines. However, the practical application of this strategy is subjected to the high-cost and tedious preparation of supported noble metal nanocatalysts. The commercially available CuO powder is herein demonstrated to be a robust catalyst for hydrogenation of nitroarenes using ammonia borane as a hydrogen source under mild conditions. Numerous amines (even sterically hindered, halogenated, and diamines) could be obtained through this method. This monometallic catalyst is characteristic of support-free, excellent chemoselectivity, low-cost, and high recyclability, which will favor its future utilization in preparative reduction chemistry. Mechanistic studies are also carried out to clarify that diazene and azoxybenzene are key intermediates of this heterogeneous reduction.Aromatic amines serve as key intermediates for the production of a wide range of high value-added materials, including dyes, pharmaceuticals, polymers, agrochemicals, etc. The increasing demand for functionalized amines has continuously driven the development of green and economical synthetic methods for their scalable production. The sustainable reduction of aromatic nitro compounds represents one of the most straightforward, industrially applicable approaches to synthesize anilines. [1] Although remarkable progress has been made in the direct hydrogenation of nitroarenes using pressurized H 2 as a hydrogen source with non-noble metal catalysts, [2][3][4][5][6][7][8] the transfer hydrogenation could realize safe reductions under mild conditions without specialized reaction setups. Therefore, NaBH 4 , [9] HCOONH 4 , [10] HCOOH, [11] hydrazine hydrate, [12] silane, [13] and H 3 PO 3 [14] have emerged as alternative hydrogen storage materials for reduction of nitro compounds.Unlike the above hydrogen sources, ammonia borane (BH 3 · NH 3 , denoted as AB hereafter) has been generally considered as a practical reservoir for hydrogen storage and transport, due to its high hydrogen capacity (19.6 wt %), stability (solid at room temperature), safety, and nontoxicity. [15] Additionally, bulk quantities of AB are commercially available and affordable. Hydrogen evolution from AB can be expediently performed via hydrolysis in the presence of transition metals (BH 3 · NH 3 + 2H 2 O!NH 4 + + BO 2 À + 3H 2 "), and one-pot tandem AB dehydrogenation and unsaturated compound hydrogenation provides a viable strategy for the manufacture of valuable molecules. As a metal-free reductant, AB has been directly used to initiate the reduction of imines, [16] ketones, [17] aldehydes, [17] and even polarized olefins. [18] Although the reducing ability of AB is not strong enough on its own to initiate the direct hydrogenation of other unsaturated functional groups, the use of metal catalysts with this reagent resolves this challenge. There are numerous reports describing the use of AB as the hydrogen donor for the catalytic transfer hydrog...