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 λmax of 672 nm and an external quantum efficiency of 3.4% at 10 mA/cm2.