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.