Tandem Selective Reduction of Nitroarenes Catalyzed by Palladium Nanoclusters
We report a catalytic tandem reduction of nitroarenes by sodium borohydride (NaBH4) in aqueous solution at ambient conditions, which can selectively produce five categories of nitrogen-containing compounds: anilines, N-aryl hydroxylamines, azoxy-, azo- and hydrazo- compounds. The catalyst is the in situ-generated ultrasmall palladium nanoclusters (Pd NCs, diameter of 1.3±0.3 nm) from the reduction of Pd(OAc)2 by NaBH4. These highly active Pd NCs are stabilized by the surface-coordinated nitroarenes, which inhibit the further growth and aggregation of Pd NCs. By controlling the concentration of Pd(OAc)2 (0.1-0.5 mol% of nitroarene) and NaBH4, the water/ethanol solvent ratio and the tandem reaction sequence, each of the five categories of N-containing compounds can be obtained with excellent yields (up to 98%) in less than 30 min at room temperature. This tunable catalytic tandem reaction works efficiently with a broad range of nitroarene substrates, which offers a green and sustainable method for rapid and large-scale production of valuable N-containing chemicals.