Acetylides for the Preparation of Phosphorescent Iridium(III) Complexes: Iridaoxazoles and Their Transformation into Hydroxycarbenes and N,C(sp3),C(sp2),O-Tetradentate Ligands

The preparation of three families of phosphorescent iridium­(III) emitters, including iridaoxazole derivatives, hydroxycarbene compounds, and N,C­(sp3),C­(sp2),O-tetradentate containing complexes, has been performed starting from dimers cis-[Ir­(μ2-η2-CCR)­{κ2-C,N-(MeC6H3-py)}2]2 (R = tBu (1a), Ph (1b)). Reactions of 1a with benzamide, acetamide, phenylacetamide, and trifluoroacetamide lead to the iridaoxazole derivatives Ir­{κ2-C,O-[C­(CH2tBu)­NC­(R)­O]}­{κ2-C,N-(MeC6H3-py)}2 (R = Ph (2), Me (3), CH2Ph (4), CF3 (5)) with a fac disposition of carbons and heteroatoms around the metal center. In 2-methyltetrahydrofuran and dichloromethane, water promotes the C–N rupture of the IrC–N bond of the iridaoxazole ring of 3–5 to form amidate–iridium­(III)–hydroxycarbene derivatives Ir­{κ1-N-[NHC­(R)­O]}­{κ2-C,N-(MeC6H3-py)}2{C­(CH2tBu)­OH} (R = Me (6), CH2Ph (7), CF3 (8)). In contrast to 1a, dimer 1b reacts with benzamide and acetamide to give Ir­{κ4-N,C,C′,O-[py-MeC6H3-C­(CH2-C6H4)­NHC­(R)­O]}­{κ2-C,N-(MeC6H3-py)}­(R = Ph (9), Me (10)), which bear a N,C­(sp3),C­(sp2),O-tetradentate ligand resulting from a triple coupling (an alkynyl ligand, an amide, and a coordinated aryl group) and a C–H bond activation at the metal coordination sphere. Complexes 2–4 and 6–10 are emissive upon photoexcitation, in orange (2–4), green (6–8), and yellow (9 and 10) regions, with quantum yields between low and moderate (0.01–0.50) and short lifetimes (0.2–9.0 μs).