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.