The First Anticancer Tris(pyrazolyl)borate Molybdenum(IV) Complexes: Tested in Vitro and in Vivo—A Comparison of O,O‐, S,O‐, and N,N‐Chelate Effects

The synthesis, characterization and biological activity of molybdenum(IV) complexes containing Trofimenko's scorpionato ligand, hydrotris(3‐isopropylpyrazolyl)borate (Tp(iPr)), in addition to varying biologically active as well as other conventional ligands is described. Ligands employed include (O,O‐) (S,O‐) (N,N‐) donors that have been successfully coordinated to the molybdenum center by means of oxygen‐atom transfer (OAT) reactions from the known Mo(VI) starting material, Tp(iPr)MoO(2)Cl. The synthesized complexes were characterized by standard analytical methods and where possible by X‐ray diffraction analysis. The aqueous stability of the compounds was studied by means of UV/Vis spectroscopy and the impact of the attached ligand scaffolds on the oxidation potentials (Mo(IV) to Mo(V)) was studied by cyclic voltammetry. Utilizing polyvinylpyrrolidone (PVP) as a solubilizing agent, adequate aqueous solubility for biological tests was obtained. Anticancer activity tests and preliminary mode of action studies have been performed in vitro and in vivo.