Modulation of the solubility properties of arene ruthenium complexes bearing stannyl ligands as potential anti-cancer agents

Cleavage of the known ruthenium dimer [RuCl2(η6-C6H5OCH2CH2OH)]2(1), bearing a hydrophilic substituent on the η6 coordinated aromatic ring, with the phosphine ligands: triphenyl phosphine, triphenyl phosphite, trimethyl phosphite, and 1,3,5-triaza-7-phosphaadamantane (PTA) afforded the known complexes [RuCl2(η6-C6H5OCH2CH2OH)(PPh3)] (2a), [RuCl2(η6-C6H5OCH2CH2OH){P(OPh)3}] (2b), [RuCl2(η6-C6H5OCH2CH2OH){P(OMe3)}] (2c), and [RuCl2 (η6-C6H5OCH2CH2OH)(PTA)] (4). The reaction of the known complex 2a with SnCl2afforded, by facile insertion of the SnCl2moiety into the Ru-Cl bond, the novel complex [RuCl(η6-C6H5OCH2CH2OH)(PPh3)(SnCl3)] (3a). Similarly, the reaction of complex 2b with SnCl2afforded the novel complex [RuCl(η6-C6H5OCH2CH2OH){P(OPh)3}(SnCl3)] (3b). Complexes 3a and 3b were fully characterized by spectroscopy (Infrared (IR) -spectroscopy, 1H, 31P and 119Sn Nuclear Magnetic Resonance (NMR) spectroscopy, UV-Vis spectroscopy and high resolution ESI-MS) and their thermal behaviour elucidated by Thermogravimetric Analysis (TGA). Density Functional Theory (DFT) calculations (Level of theory B3LYP, basis set for H, C, P, O, N and Cl is 6-31+G(d,p) and for Ru and Sn is DGDZVP) for complex 3a, 3b and 4 were also carried out, in particular to elucidate the bonding situation between Ru and Sn in complexes. The hitherto unprecedented anti-cancer activity of the complexes 2a – 2c as well as the novel stannyl complexes 3a and 3b were evaluated against MCF-7 (oestrogen receptor positive) human breast adenocarcinoma cell lines. All complexes show activity active against MCF-7 cell lines, indicating potential application as an anti-tumor agent