Steric and Electronic Effects Responsible for <i>N</i>,<i>O</i>- or <i>N</i>,<i>N</i>-Chelating Coordination of Pyrazolones Containing a Pyridine Ring in Ruthenium Arene Systems

Structural and electronic factors are crucial to rationalize the different N,O or N,N chelating coordination of pyrazolones containing a pyridine ring. The reactivity proligand 3-phenyl-1-(pyridin-2-yl)-5-pyrazolone (HLpy,ph) with (arene)Ru(II) fragment was explored. Neutral ionic complexes were obtained fully characterized, also by X-ray diffraction, revealing ligand coordinate in an unusual N,O-chelating fashion. Other ruthenium synthesized 3-methyl-1-(pyridin-2-yl)-5-pyrazolone (HLpy,me) 3-methyl-1-(pyridin-2-yl)-4-trifluoroacetyl-5-pyrazolone (HQpy,CF3). In these ligands adopt preferred N,N-chelating mode. Ligands theoretically analyzed density functional theory (DFT). most stable tautomer HLpy,ph matched well experimental behavior this structures Ru-complexes described calculations. thermodynamic stability N,O- N,N-coordination modes proposal for achievement N,O-coordination mode 1–4 proposed. Cytotoxicity tests performed against human ovarian carcinoma (A2780 Cisplatin-resistant A2780cis) nontumorigenic embryonic kidney (HEK293T) cell lines, showing free be more cytotoxic that ensuing complexes.