Study of the Bonding Modes of Di-2-pyridyl ketoxime Ligand towards Ruthenium, Rhodium and Iridium Half Sandwich Complexes

The bonding modes of the ligand di-2-pyridyl ketoxime towards half-sandwich arene ruthenium, Cp*Rh and Cp*Ir complexes were investigated. Di-2-pyridyl ketoxime {pyC(py)NOH} react with metal precursor [Cp*IrCl2](2) to give cationic oxime complexes of the general formula [Cp*Ir{pyC(py)NOH}Cl]PF6 (1a) and [Cp*Ir{pyC(py)NOH}Cl]PF6 (1b), for which two coordination isomers were observed by NMR spectroscopy. The molecular structures of the complexes revealed that in the major isomer the oxime nitrogen and one of the pyridine nitrogen atoms are coordinated to the central iridium atom forming a five membered metallocycle, whereas in the minor isomer both the pyridine nitrogen atoms are coordinated to the iridium atom forming a six membered metallacyclic ring. Di-2-pyridyl ketoxime react with [(arene) MCl2](2) to form complexes bearing formula [(p-cymene)Ru{pyC(py)NOH}Cl]PF6 (2); [(benzene)Ru{pyC(py)NOH}Cl]PF6 (3), and [Cp*Rh{pyC(py)NOH}Cl]PF6 (4). In case of complex 3 the ligand coordinates to the metal by using oxime nitrogen and one of the pyridine nitrogen atoms, whereas in complex 4 both the pyridine nitrogen atoms are coordinated to the metal ion. The complexes were fully characterized by spectroscopic techniques.