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

Abstract

Novel water soluble half-sandwich complexes of the general formulae [M(η⁶-p-cym)(ha)]₂(CF₃SO₃)₂, [M(η⁶-p-cym)(ha)Cl] or [M(η⁶-p-cym)(ha)(py)]X (M = Os, Ru; ha = hydroxamate; py = pyridine; X = Cl⁻ or CF₃SO₃⁻), 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(η⁶-p-cym)(μ-meaha)]₂(CF₃SO₃)₂ (5), [Os(η⁶-p-cym)(meaha)Cl] (6), [Ru(η⁶-p-cym)(phebha)Cl], (9), [Ru(η⁶-p-cym)(bha)(py)](CF₃SO₃) (12) and [Ru(η⁶-p-cym)(phebha)(py)](CF₃SO₃) (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(η⁶-p-cym)(py)(μ-OH)]₂(CF₃SO₃)₂ (16) is prepared and characterized by X-ray crystallography. Unexpected formation of a dinuclear oxo bridged Os^II/Os^VI complex [{Os(η⁶-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.