Spectral, structural and DFT studies of platinum group metal 3,6-bis(2-pyridyl)-4-phenylpyridazine complexes and their ligand bonding modes

Reactions of 3,6-bis(2-pyridyl)-4-phenylpyridazine (Lph) with [(η6-arene)Ru(μ-Cl)Cl]2 (arene = C6H6, p-iPrC6H4Me and C6Me6), [(η5-C5Me5)M(μ-Cl)Cl]2, (M = Rh and Ir) and [(η5-Cp)Ru(PPh3)2Cl] (Cp = C5H5, C5Me5 and C9H7) afford mononuclear complexes of the type [(η6-arene)Ru(Lph)Cl]PF6, [(η5-C5Me5)M(Lph)Cl]PF6 and [(Cp)Ru(Lph)(PPh3)]PF6 with different structural motifs depending on the π-acidity of the ligand, electronic properties of the central metal atom and nature of the co-ligands. Complexes [(η6-C6H6)Ru(Lph)Cl]PF61, [(η6-p-iPrC6H4Me)Ru(Lph)Cl]PF62, [(η5-C5Me5)Ir(Lph)Cl]PF65, [(η5-Cp)Ru(PPh3)(Lph)]PF6, (Cp = C5H5, 6; C5Me5, 7; C9H7, 8) show the type-A binding mode (see text), while complexes [(η6-C6Me6)Ru(Lph)Cl]PF63 and [(η5-C5Me5)Rh(Lph)Cl]PF64 show the type-B binding mode (see text). These differences reflect the more electron-rich character of the [(η6-C6Me6)Ru(μ-Cl)Cl]2 and [(η5-C5Me5)Rh(μ-Cl)Cl]2 complexes compared to the other starting precursor complexes. Binding modes of the ligand Lph are determined by 1H NMR spectroscopy, single-crystal X-ray analysis as well as evidence obtained from the solid-state structures and corroborated by density functional theory calculations. From the systems studied here, it is concluded that the electron density on the central metal atom of these complexes plays an important role in deciding the ligand binding sites.