Insertion of unsaturated C–C Bonds into the O–H bond of an Iridium(III)-Hydroxo complex: formation of phosphorescent emitters with an asymmetrical β-Diketonate ligand

Abstract

A synthetic methodology to prepare iridium(III) emitters of the class [3b+3b+3b′] with two ortho-metalated 1-phenylisoquinolines and an asymmetrical β-diketonate has been discovered. The abstraction of the chloride ligands of the dimer [Ir(μ-Cl){κ2-C,N-(C6H4-isoqui)}2]2 (1, C6H5-isoqui = 1-phenylisoquinoline) with AgBF4 in acetone and the subsequent addition of water to the resulting solution affords the water solvate mononuclear complex [Ir{κ2-C,N-(C6H4-isoqui)}2(H2O)2]BF4 (2), which reacts with KOH to give the dihydroxo-bridged dimer [Ir(μ-OH){κ2-C,N-(C6H4-isoqui)}2]2 (3). Treatment of the latter with dimethyl acetylenedicarboxylate leads to Ir{κ2-C,N-(C6H4-isoqui)}2{κ2-O,O-[OC(CO2CH3)CHC(OCH3)O]} (4), as a result of the anti-addition of the O–H bond of a mononuclear [Ir(OH){κ2-C,N-(C6H4-isoqui)}2] fragment to the C–C triple bond of the alkyne and the coordination of one of the carboxylate substituents to the metal center. Complex 3 also reacts with α,β-unsaturated ketones. The reaction with 3-(4-methylphenyl)-1-phenylprop-2-en-1-one affords Ir{κ2-C,N-(C6H4-isoqui)}2{κ2-O,O-[OC(C6H5)CHC(p-C6H4Me)O]} (5), whereas methyl vinyl ketone gives a mixture of Ir{κ2-C,N-(C6H4-isoqui)}2{κ2-O,O-[OC(CH3)CHCHO]} (6) and Ir{κ2-C,N-(C6H4-isoqui)}2{κ2-O,O-[OC(CH3)CHC(CH═CH2)O]} (7). Complexes 5 and 6 are the result of the addition of the O–H bond of the mononuclear [Ir(OH){κ2-C,N-(C6H4-isoqui)}2] fragment to the C–C double bond of the α,β-unsaturated ketones and the coordination of the carbonyl group to the iridium center, to generate O,O-chelates which lose molecular hydrogen to aromatize into the asymmetrical β-diketonate ligands. Complexes 4–7 are phosphorescent emitters in the red spectral region (599–672 nm) in doped poly(methyl methacrylate) (PMMA) film at 5 wt % at room temperature and 2-methyltetrahydrofuran at room temperature and 77 K. They display short lifetimes (0.8–2.5 μs) and quantum yields in both doped PMMA films and in 2-methyltetrahydrofuran at room temperature depending on the substituents of the β-diketonate: about 0.6–0.5 for 4 and 6 and ca. 0.35 for 5 and 7.