Pseudo-Tris(heteroleptic) Red Phosphorescent Iridium(III) Complexes Bearing a Dianionic C,N,C′,N′‑Tetradentate Ligand

1-Phenyl-3-(1-phenyl-1-(pyridin-2-yl)­ethyl)­isoquinoline (H₂MeL) has been prepared by Pd­(N-XantPhos)-catalyzed “deprotonative cross-coupling processes” to synthesize new phosphorescent red iridium­(III) emitters (601–732 nm), including the carbonyl derivative Ir­(κ⁴-cis-C,C′-cis-N,N′-MeL)­Cl­(CO) and the acetylacetonate compound Ir­(κ⁴-cis-C,C′-cis-N,N′-MeL)­(acac). The tetradentate 6e-donor ligand (6tt′) of these complexes is formed by two different bidentate units, namely, an orthometalated 2-phenylisoquinoline and an orthometalated 2-benzylpyridine. The link between the bidentate units reduces the number of possible stereoisomers of the structures [6tt′ + 3b] (3b = bidentate 3e-donor ligand), with respect to a [3b + 3b′ + 3b″] emitter containing three free bidentate units, and it permits a noticeable stereocontrol. Thus, the isomers fac-Ir­(κ⁴-cis-C,C′-cis-N,N′-MeL)­{κ²-C,N-(C₆H₄-py)}, mer-Ir­(κ⁴-cis-C,C′-cis-N,N′-MeL)­{κ²-C,N-(C₆H₃R-py)}, and mer-Ir­(κ⁴-trans-C,C′-cis-N,N′-MeL)­{κ²-C,N-(C₆HR-py)} (R = H, Me) have also been selectively obtained. The new emitters display short lifetimes (0.7–4.6 μs) and quantum yields in a doped poly­(methyl methacrylate) film at 5 wt % and 2-methyltetrahydrofuran at room temperature between 0.08 and 0.58. The acetylacetonate complex Ir­(κ⁴-cis-C,C′-cis-N,N′-MeL)­(acac) has been used as a dopant for a red PhOLED device with an electroluminescence λ_max of 672 nm and an external quantum efficiency of 3.4% at 10 mA/cm².