The reactions of tetrachloroauric(III)
acid (
HAuCl4) with the
thioamides; 2-mercapto-benzothiazole (mbztH) and 5-ethoxy-2-mercapto-benzimidazole (EtmbzimH) lead to the desulfuration of the
ligands and the formation of the ionic complexes {[AuCl4]- [bztH2]+} (1), and {[AuCl4]- [EtbzimH2]+ (H2O)} (2) (where bztH2+ and EtbzimH2+ are the desulfurated
cations of the starting
ligands). The reaction of
HAuCl4 with 2-mercapto-nicotinic
acid (mnaH2), however results in the formation of 2-sulfonate-nicotininc
acid (C6H5NO5S) (3) with the simultaneous oxidation of the
sulfur atom. On the other hand, the reactions of the
gold(I) complex [Au(tpp)Cl] (4) (tpp =
triphenylphosphine (Ph3P)) with the
thioamides; 2-mercapto-thiazolidine (mtzdH), 2-mercapto-benzothiazole (mbztH) and 5-chloro-2-mercapto-benzothiazole (ClmbztH) in the presence of
potassium hydroxide resulted in the formation of the
gold(I) complexes of formulae [Au(tpp)(mtzd)] (5), [Au(tpp)(mbzt)] (6) and [Au(tpp)(Clmbzt)] (7) without
ligand desulfuration. All complexes have been characterized by elemental analysis, FT-IR, far-FT-IR,1H-NMR, spectroscopic techniques and X-Ray crystallography. The electrochemical behavior of 1, 2 and 4-7 complexes and the
ligands EtmbzimH, mbztH and mnaH2 was also studied in
acetonitrile and DMF using cyclic voltammetry. The results are in support of a mechanism of desulfuration of the
ligands by Au(III), involving a first oxidation of S to -SO3-, followed by a C-S bond cleavage. This is also supported by PM6 calculations of bond dissociation energies of the various compounds involved. Complexes 1, 2 and 4-7 were tested for in vitro cytotoxicity against
leiomyosarcoma cells and the results are discussed in relation with the geometry of the complexes and compared with those of
cisplatin and other metals. Complexes 1 and 5 showed higher activity than that of
cisplatin, while
HAuCl4 was inactive against
sarcoma cells.