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

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.