Novel half-sandwich Ru(II)-hydroxamate complexes: synthesis, characterization and equilibrium study in aqueous solution

Novel half-sandwich Ru(II)-benzohydroxamate complexes were synthesized. [Ru(eta(6)-p-cymene)(mu-bha)](2)Cl(2) (bhaH = benzohydroxamic acid) with (O,O) coordination of the ligand, was characterized by elemental analysis, spectroscopic ((1)H-NMR, IR) and ESI-MS methods. Replacement of the chloride of the precursor by CF(3)SO(3)(-) and reaction of the obtained [Ru(eta(6)-p-cym)(acetone)(3)](CF(3)SO(3))(2) with bhaH affords [Ru(eta(6)-p-cymene)(mu-bha)](2)(CF(3)SO(3))(2), the crystal and molecular structure of which has been determined by X-ray crystallography. In this complex, the first reported structure of an organometallic Ru(II)-hydroxamate, the carbonyl oxygens of the bha ligands coordinate to one of the Ru units and the hydroxamate oxygens bridge the two Ru atoms. Hydrolytic behaviour of [Ru(eta(6)-p-cym)Cl(x)(H(2)O)(3-x)]((2-x)+) (x = 0-3) present in aqueous solution and its complex forming capabilities with N-methyl-acetohydroxamic acid (meahaH) were studied by pH-potentiometric, (1)H-NMR, UV-Vis and ESI-MS methods. Formation constants of the various species present in solution are reported. The data are consistent with the formation of the stable, monomeric [Ru(eta(6)-p-cym)(meaha)](+) as the major species at physiological pH.