Configurational Flexibility of Epimeric β-Aminothioether-chelated Ruthenium(II) η6-Arene Complex Salts

Abstract

Five chiral β -aminothioethers were obtained via different routes orientated on literature protocols. Three of these β -aminothioethers were reacted with two di-μ-chloro-bis{chloro[η6-arene]- ruthenium(II)} derivatives, resulting in the title complex salts. The complex cations exhibit three stereocenters, viz. ruthenium and sulfur atoms and the chiral benzylic carbon atom of the chelate ligand backbone. Both, ruthenium and sulfur stereocenters epimerize into a mixture of four NMR distinguishable diastereomers in equilibrium, but the designed chiral benzylic carbon atom is stable under all conditions applied so far. The relative diastereomer concentrations in solution depend mainly on the spatial requirements of the η6-arene ligand rather than on the thioether moiety. Diastereomer ratios and the absolute configurations in solution were studied by NMR and CD spectroscopy. The spectroscopic results fit to the absolute X-ray crystal structure parameters determined for the diastereomers present in the crystalline state.