A rollover Ir(iii) complex of 2-(6-bromopyridin-2-yl)imidazo[1,2-a]pyridine

Abstract

Here in, we report a rollover iridacycle complex cis-[Ir(κ²-C–N-L₁)(κ²-N–N-L₁)Cl₂], which can be easily obtained as yellow solid, through the reaction of two equivalents of new 2-(6-bromopyridin-2-yl)imidazo[1,2-a]pyridine (L₁) type ligand and IrCl₃ in dimethylformamide at 70 °C for a week. Rollover complex have an unusual κ²-C–N-cyclometallated ligand fragment, which involves the C–H bond activation reaction in remote position on bromo-pyridine, with a second one in classic κ²-N–N-donor mode. The structure of both compounds was studied by NMR, IR, and high-resolution mass spectrometry. Rollover complex UV/Vis absorption spectrum showed a dominating π–π* absorption band at 350 nm. Excitation at 385 nm gave a narrow emission band with maximum at 541 nm, which was associated to ligand-centred emission. The ligand shows antiproliferative activities against breast cancer lines. Density Functional Theory (DFT) calculations suggest that the rollover C–H bond activation occurs after a first κ²-N–N coordination during the complexation of the second ligand and is supported by DMF molecules.