Synthesis and X-ray diffraction structures of novel half-sandwich Os(ii)-and Ru(ii)-hydroxamate complexes

Novel water soluble half-sandwich complexes of the general formulae [M(η ⁶-p-cym)(ha)] ₂(CF ₃SO ₃) ₂, [M(η ⁶-p-cym)(ha)Cl] or [M(η ⁶-p-cym) (ha)(py)]X (M = Os, Ru; ha = hydroxamate; py = pyridine; X = Cl ^- or CF ₃SO ₃ ^-), incorporating metal-containing entities and hydroxamates both with potential anti-proliferative features, were prepared and characterized by elemental analysis, spectroscopy (NMR, IR) and ESI mass spectrometry. The X-ray crystal structure of [Ru(η ⁶-p-cym) (μ-meaha)] ₂(CF ₃SO ₃) ₂ (5), [Os(η ⁶-p-cym)(meaha)Cl] (6), [Ru(η ⁶-p-cym)(phebha) Cl], (9), [Ru(η ⁶-p-cym)(bha)(py)](CF ₃SO ₃) (12) and [Ru(η ⁶-p-cym)(phebha)(py)](CF ₃SO ₃) (14), 6 is the first published structure of an organometallic Os(ii)-hydroxamate reported. The effect of size differences of the metal ions, the steric demand of the R _C and R _N substituents at the hydroxamate group and the type of the monodentate ligand co-present in the stoichiometry, along with the binding architecture of the half-sandwich metal(ii) hydroxamate complexes are discussed. A novel dinuclear, dihydroxo bridged complex [Os(η ⁶-p-cym)(py)(μ-OH)] ₂(CF ₃SO ₃) ₂ (16) is prepared and characterized by X-ray crystallography. Unexpected formation of a dinuclear oxo bridged Os ^II/Os ^VI complex [{Os(η ⁶-p-cym)(meaha)} (μ-O){Os(O)(meaha) ₂}]Cl (17) occurs, and the crystal and molecular structure has been determined by X-ray method. Complexes 1, 5-8, 10 and 14 were tested for their in vitro cytotoxicity, using human-derived ovarian cancer cell lines (A2780 and A2780 cisR), and showed no anti-proliferative effect in the concentration range (0-200 μM) studied.