Chelating diimines of the kind bis(arylimino)acenaphtene (Ar-BIAN) and bis(phenylimino)phenanthrene (Ph-BIP) are very effective promoters for the Ru-3(CO)(12) catalysed reduction of nitroarenes to anilines by CO/H2O. Their promoting efficiency for this catalytic system is higher than the one of any previously reported ligand. The corresponding quinones are also promoters for the same reaction and a comparison between several ligands under the same experimental conditions is reported. The reaction can be performed without any other solvent except water, but yields are better if ethanol is also added. The reduction is chemoselective for the nitro group with respect to olefins and keto groups.