Bromination and C–C Cross-Coupling Reactions for the C–H Functionalization of Iridium(III) Emitters

The orthometalated phenyl groups of the dimer [Ir­(μ-Cl)­{κ²-C,N-(C₆H₃Me-py)}₂]₂ have been selectively brominated, at para-position with regard to the Ir–C bonds, with N-bromosuccinimide. The bromination leads to [Ir­(μ-Cl)­{κ²-C,N-(C₆H₂MeBr-py)}₂]₂, which affords the mononuclear derivatives Ir­{κ²-C,N-(C₆H₂MeBr-py)}₂{κ²-O,N-[OC­(O)-py]}, Ir­{κ²-C,N-(C₆H₂MeBr-py)}₂{κ²-O,O-(acac)}, and Ir­{κ²-C,N-(C₆H₂MeBr-py)}₂{κ²-C,N-[C₆H₄-Mepy]} by replacement of the chloride bridges by a picolinate anion, an acac group, and an orthometalated 2-phenyl-5-methylpyridine ligand, respectively. Complexes Ir­{κ²-C,N-(C₆H₂MeBr-py)}₂{κ²-O,O-(acac)} and Ir­{κ²-C,N-(C₆H₂MeBr-py)}₂{κ²-C,N-[C₆H₄-Mepy]} have been subsequently postfunctionalized by means of palladium-catalyzed Suzuki–Miyaura cross-coupling to give Ir­{κ²-C,N-(C₆H₂MeR-py)}₂{κ²-O,O-(acac)} (R = Me, Ph) and Ir­{κ²-C,N-(C₆H₂Me₂-py)}₂{κ²-C,N-[C₆H₄-Mepy]}. These [3b + 3b + 3b′] mononuclear compounds are green-yellow emitters (488–580 nm) upon photoexcitation, in doped poly­(methyl methacrylate) (PMMA) film at 5 wt % at room temperature and 2-methyltetrahydrofuran (2-MeTHF) at room temperature and at 77 K. They display lifetimes in the range 1.0–5.0 μs and quantum yields in PMMA films and in 2-MeTHF at room temperature between 0.84 and 0.40.