Ru(ii) complexes containing dmso and pyrazolyl ligands as catalysts for nitrile hydration in environmentally friendly media

Abstract

The synthesis of two Ru-dmso complexes containing the ligands 2-(3-pyrazolyl)pyridine (pypz-H), and pyrazole (pz-H), [Ru^IICl₂(pypz-H)(dmso)₂], (2) and [Ru^IICl₂(pz-H)(dmso)₃], (3), has been described. Both complexes have been fully characterized in solution through ¹H-NMR and UV-Vis techniques and also in the solid state through monocrystal X-ray diffraction analysis. The redox properties of both complexes have also been studied by means of cyclic voltammetry. Exposure of 2 to visible light in acetonitrile produces a substitution of one dmso ligand by a solvent molecule generating a new complex, [Ru^IICl₂(MeCN)(pypz-H)(dmso)] (4). Also, UV-visible spectroscopy points out that complex 2 presents a thermal and photochemical substitution of dmso ligands in aqueous solution. Finally, the reactivity of complexes 2 and 3 has been tested with regard to the hydration of nitriles using water as a single solvent, displaying good efficiency and selectivity for the corresponding amide derivatives. In general, better performance is achieved with complex 3. Reuse of these catalysts in water and glycerol has been explored for the first time in ruthenium-mediated nitrile hydration catalysis.