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 new synthetic route to iridium(III) phosphorescent complexes of the [3b+3b+3b'] class, incorporating two cyclometalated 1-phenylisoquinoline units and an asymmetric β-diketonate ligand, was established. Starting from a chloride-bridged dimer, chloride abstraction with AgBF4 in acetone followed by water addition yielded a mononuclear water solvate. Subsequent treatment with KOH produced a dihydroxo-bridged dimer, which upon reaction with dimethyl acetylenedicarboxylate or α,β-unsaturated ketones underwent O-H bond addition across C-C triple or double bonds, respectively, generating asymmetric β-diketonate chelates. In the case of α,β-unsaturated ketones, molecular hydrogen loss drove aromatization of the chelate ring. The resulting complexes exhibited red-region phosphorescence (599–672 nm) in doped PMMA films (5 wt%) and in 2-methyltetrahydrofuran at room temperature and 77 K, with emission lifetimes of 0.8–2.5 μs and quantum yields ranging from approximately 0.35 to 0.6 depending on β-diketonate substitution.

Mechanism

The O-H bond of a mononuclear iridium hydroxo fragment adds across C-C triple bonds of alkynes or C-C double bonds of α,β-unsaturated ketones; subsequent carbonyl coordination to iridium and loss of molecular hydrogen drives aromatization to form asymmetric β-diketonate chelate ligands.