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.