Ligand and catalysts preparation. Based on these considerations, we attempted to prepare the required ligand precursor (Scheme 2A). As a result, a straightforward route has been developed, in which a cheap staring material, benzene-1,2-diamine (3) was converted to 1,4-dihydroquinoxaline-2,3-dione ( ) by an acid-catalysed condensation with oxalic acid (5). The obtained dione 4