An improved protocol where a pre-cursor, [Ru(Cl)2(NBD)(Py)2], is treated with ligands to form [RuCl2(bidentate ligand)(diamine)] pre-catalysts for ester hydrogenation is reported. This family of catalysts, as well as a range of ruthenium complexes of tridentate P^N^X (X = NR2, OH) ligands have been investigated in the hydrogenation of aromatic esters. A range of aromatic esters can be hydrogenated in high yields at temperatures between 30 °C and 100 °C.
