Ruthenium Arene Complexes with α-Aminoacidato Ligands: New Insights into Transfer Hydrogenation Reactions and Cytotoxic Behaviour

The RuII arene complexes [Ru(η6-p-cymene)(κ2N,O-aa)Cl] (aa = l-glutaminato, 1; l-homoserinato, 2; l-tyrosinato, 3; l-serinato, 4; l-prolinato, 5; trans-4-hydroxyl-l-prolinato, 6; l-threoninato, 7; glycinato, 8) were synthesized in high yields by the reactions of [Ru(η6-p-cymene)Cl2]2 with aa/MOH (M = Na, K). The salt [Ru(η6-p-cymene)(κ2N,O-l-serinato)(PPh3)][CF3SO3], 9[CF3SO3], was prepared in 68 % yield from 4 and AgSO3CF3/PPh3. All the products were fully characterized by analytical and spectroscopic methods, moreover the X-ray structures of 1 and 2 were elucidated by X-ray diffraction. Compounds 1–7 and 9[CF3SO3] were studied as catalytic precursors for the transfer hydrogenation reaction (THR) of acetophenone, using 2-propanol or sodium formate (in water) as hydrogen sources, under variable experimental conditions. The catalytic process was investigated also under microwave irradiation. In general, all the catalytic reactions selectively afforded 1-phenylethanol, and the best results were achieved with 5 and 6, in terms of both activity and enantioselectivity (enantiomeric excess up to 78 %). The in vitro cytotoxicity of 1, 4, 5 and 9[CF3SO3] was assessed towards the human pancreatic cancer cell line BxPC3 and the mouse embryo fibroblast Balb/3T3 Clone A31 cell line, all of the investigated compounds showing to be substantially inactive. The catalytic and biological results will be discussed in relation to the relevant chemical behaviour of the compounds in water solution.