Arene ruthenium and pentamethylcyclopentadienyl rhodium and iridium complexes containing N,O-chelating ligands derived from piroxicam: Synthesis, molecular structure and cytotoxicity

The non-steroidal anti-inflammatory and anti-arthritic drug piroxicam (LH) reacts with arene ruthenium dichloride dimers in refluxing dichloromethane to give the complexes [(η6-arene)Ru(η2-N,O-L)Cl] (3: arene = C6H5Me, 4: arene = p-MeC6H4Pri, 5: arene = C6Me6). The reaction seems to proceed via the intermediates [(η6-arene)Ru(N-LH)Cl2], which can be observed for arene = C6H5Me (1) and isolated in the case of arene = p-MeC6H4Pri (2). The analogous reaction with pentamethylcyclopentadienyl rhodium and iridium gives the complexes [(η5-C5Me5)M(η2-N,O-L)Cl] (6: M = Rh, 7: M = Ir). The single-crystal X-ray structure analyses of the p-cymene ruthenium derivatives 4 and 2 show the metal atom in the archetypical piano stool geometry; in 4 the piroxicamato ligand is coordinated in a bidentate fashion through the pyridine nitrogen atom and the enolic oxygen atom, while in 2 the intact piroxicam ligand is coordinated in a monodentate fashion through the pyridine nitrogen atom. The piroxicamato complexes 3–5 are weakly cytotoxic towards human ovarian cancer cells.