Ruthenium(II) half-sandwich complexes containing thioamides: Synthesis, structures and catalytic transfer hydrogenation of ketones

A new family of cationic half-sandwich complexes of the type [(η6-cymene)Ru(PPh3)(L)]+ (L = bidentate monoanionic thioamide) have been synthesized and isolated as their tetraphenylborate salts. All the synthesized ruthenium(II) arene complexes are air stable and are fully characterized by elemental analysis, spectral and X-ray diffraction methods. In chloroform solution all the complexes exhibit characteristic metal to ligand charge transfer (MLCT) absorptions and ligand based transitions. Molecular structure of the complexes 2, 3 and 4 has been determined by single crystal X-ray crystallography indicates that the thioamide ligands are coordinated to ruthenium as a bidentate O, S donor and a typical piano stool geometry was observed around ruthenium(II) metal center. Complexes 1–5 were tested as catalysts in the transfer hydrogenation of aliphatic and aromatic ketones to secondary alcohols in the presence of 2-propanol/KOH. Further, the influence of base, reaction temperature and catalyst loading in this reaction was also evaluated to find out the most active catalyst.

Graphical abstractFive new ruthenium(II) arene thioamide complexes have been synthesized and characterized. The single crystal X-ray analysis of the complexes (2, 3 and 4) shows a typical three legged piano stool geometry around ruthenium metal. The complexes were found to be efficient catalysts in transfer hydrogenation of ketones.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Five new ruthenium(II) arene thioamide complexes are synthesized. ► Single crystal X-ray structure evidenced three legged piano-stool geometry. ► Synthesized complexes are efficiently used as catalyst for transfer hydrogenation reaction.