Synthesis, characterization and interactions with 9-methylguanine of ruthenium(II) η6-arene complexes with aromatic diimines

Abstract

The complexes of the formula [(η6-arene)Ru(L)Cl]PF6, where arene is benzene (bz) or p-cymene (cym) and L is 2,(2′-pyridyl)quinoline (pqn), were synthesized and characterized by means of NMR spectroscopic techniques, HR-ESI mass spectrometry and, in the case of [(η6-cym)Ru(pqn)Cl]PF6, by X-ray single crystal diffraction. Their resistance in hydrolysis was also studied. A comparative NMR study of their 9-methylguanine (9-MeG) complexes, [(η6-arene)Ru(pqn)(9-MeG)](PF6)2, with similar diimine complexes revealed that the unimpeded rotation of 9-MeG is hindered by interactions between the 9-MeGO6 and the p-cymene aromatic proton H2 and, by the bulky shape of the pqn. This conformation forces the 9-MeGH8 to be in close proximity to the aromatic ring system of pqn. NMR spectroscopic techniques lead to the conclusion that the strong shielding effect on 9-MeGH8 depends on the extension of the aromatic system of the ligand. Also, we conclude that the strong deshielding on the 9-MeGNH1 is influenced by both the N7 ruthenation of 9-MeG and the addendum electron density in the 9-MeG ring system, due to the proximity to the aromatic ring system of pqn.