Preparation of Phosphorescent Iridium(III) Complexes with a Dianionic C,C,C,C-Tetradentate Ligand

The preparation and photophysical properties of heteroleptic iridium(III) complexes containing a dianionic C,C,C,C-tetradentate ligand and a cyclometalated phenylpyridine group are described. Complex [Ir(μ-OMe)(COD)]₂ (1, COD = 1,5-cyclooctadiene) reacts with 1,1-diphenyl-3,3-butylenediimidazolium iodide ([PhIm(CH₂)₄ImPh]I₂), in the presence NaO^tBu, to give [Ir(μ-I){κ⁴- C, C, C, C-[C₆H₄Im(CH₂)₄ImC₆H₄]}]₂ (2), which leads to {[Ir{κ⁴- C, C, C, C-[C₆H₄Im(CH₂)₄ImC₆H₄]}]₂(μ-OH)(μ-OMe)} (3) by treatment first with silver trifluoromethanesulfonate (AgOTf) in acetone-dichloromethane and subsequently with KOH in methanol. The reaction of 2 with AgOTf and acetonitrile affords the bis(solvento) complex [Ir{κ⁴- C, C, C, C-[C₆H₄Im(CH₂)₄ImC₆H₄]}(CH₃CN)₂]OTf (4). The latter promotes the pyridyl-supported heterolytic ortho-CH bond activation of the phenyl group of 2-phenylpyridine, 2-(2,4-difluorophenyl)pyridine, 2-( p-tolyl)pyridine, and 5-methyl-2-phenylpyridine to yield Ir{κ⁴- C, C, C, C-[C₆H₄Im(CH₂)₄ImC₆H₄]}{κ²- C, N-[Ar-py]} (Ar-py = C₆H₄-py (5), C₆H₂F₂-py (6), C₆H₃Me-py (7), C₆H₄-Mepy (8)) using (piperidinomethyl)polystyrene as an external base. Complexes 5-8 are blue-green emitters, which display short lifetimes (0.6-4.8 μs) and quantum yields close to unity in both doped poly(methyl methacrylate) films at 5 wt % and in 2-methyltetrahydrofuran at room temperature.