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 NaOtBu, 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.