Ruthenium(II) complexes incorporating salicylaldiminato-functionalized N-heterocyclic carbene ligands as efficient and versatile catalysts for hydration of organonitriles

Abstract

We describe a new synthetic procedure for synthesis of ruthenium(II) complexes containing salicylaldiminato functionalized mixed N-heterocyclic carbene (NHC) ligand and phosphine co-ligand. The complexes (3a–3d) have been obtained in good to excellent yields by transmetalation from the corresponding Ag–NHC complexes (2a–2d) as carbene transfer reagents. All the [Ru–NHC] complexes have been characterized by elemental analyses, spectroscopic methods as well as ESI mass spectrometry. The ligands 1a–1d show their versatility by switching to be O,N,C-chelating in these ruthenium(II) complexes. The resulting complexes have been evaluated as potential catalysts for the selective hydration of nitriles to primary amides, and related amide bond forming reactions, in environmentally friendly medium. The reaction tolerated ether, hydroxyl, nitro, bromo, formyl, pyridyl, benzyl and alkyl functional groups. The catalyst was stable for weeks and could be recovered and reused more than six times without significant loss of activity.