Neutral and cationic half-sandwich arene ruthenium, Cp*Rh and Cp*Ir oximato and oxime complexes: Synthesis, structural, DFT and biological studies

• Neutral oximato and cationic oxime complexes of Ru, Rh and Ir are isolated with substituted pyridyl oximes.
• DFT calculations demonstrate that the calculated values are in good agreement with the experimental data.
• Iridium based oximato and oxime complexes exhibited better activity than ruthenium and rhodium complexes.

The reaction of [(p-cymene)RuCl2]2 and [Cp*MCl2]2 (M = Rh/Ir) with chelating ligand 2-pyridyl cyanoxime {pyC(CN)NOH} leads to the formation of neutral oximato complexes having the general formula [(arene)M{pyC(CN)NO}Cl] {arene = p-cymene, M = Ru, (1); Cp*, M = Rh (2); Cp*, M = Ir (3)}. Whereas the reaction of 2-pyridyl phenyloxime {pyC(Ph)NOH} and 2-thiazolyl methyloxime {tzC(Me)NOH} with precursor compounds afforded the cationic oxime complexes bearing formula [(arene)M{pyC(ph)NOH}Cl]+ and [(arene)M{tzC(Me)NOH}Cl]+ {arene = p-cymene M = Ru, (4), (7); Cp*, M = Rh (5), (8); Cp*, M = Ir (6), (9)}. The cationic complexes were isolated as their hexafluorophosphate salts. All these complexes were fully characterized by analytical, spectroscopic and X-ray diffraction studies. The molecular structures of the complexes revealed typical piano stool geometry around the metal center within which the ligand acts as a NN′ donor chelating ligand. The Chemo-sensitivity activities of the complexes evaluated against HT-29 (human colorectal cancer), and MIAPaCa-2 (human pancreatic cancer) cell line showed that the iridium-based complexes are much more potent than the ruthenium and rhodium analogues. Theoretical studies were carried out to have a deeper understanding about the charge distribution pattern and the various electronic transitions occurring in the complexes.

Reaction of strongly electron withdrawing cyano substituted pyridyl oxime with metal precursor afforded the neutral oximato metal complexes due to the deprotonation of the oxime hydrogen whereas reaction of weakly electron donating substituted phenyl and methyl oximes yielded cationic oxime complexes. The iridium complexes were found to be more active against MIAPaCa-2 cancer cell line.Figure optionsDownload as PowerPoint slide