The preparation, photophysical properties, and applicability to the fabrication of organic light-emitting diodes (OLEDs) of new phosphorescent bis(tridentate) [5t + 4t'] iridium(III) molecules are described. Treatment of [Ir(μ-OMe)( 4 -COD)]2 (1; COD = 1,5cyclooctadiene) with 5-tert-butyl-1,3-bis(3-isopropylimidazolium)benzene diiodide ([ i PrHImC6H3(5-t Bu)HIm i Pr][I]2), in the presence of KI, leads to [IrI(μ-I){κ 3 -C,C,C-[ i PrImC6H2(5-t Bu)Im i Pr]}]2 (2). This complex reacts with 2-(1H-imidazol-2-yl)-6-phenylpyridine (HNIm-pyC6H5) and 2-(1H-benzimidazol-2-yl)-6-phenylpyridine (HNBzimpyC6H5), in the presence of Na2CO3, to afford the bis(tridentate) derivatives Ir{κ 3 -C,C,C-[ i PrImC6H2(5-t Bu)Im i Pr]}{κ 3 -N,N,C-[NImpyC6H4]} (4) and Ir{κ 3 -C,C,C-[ i PrImC6H2(5-t Bu)Im i Pr]}{κ 3 -N,N,C-[NBzimpyC6H4]} (5). Complexes 4 and 5 are phosphorescent emitters (em = 482−590 nm), which display observed lifetimes in the range 1.2−11.7 μs. They show high quantum yields in both doped poly(methyl)methacrylate) films and in 2-methyltetrahydrofuran at room temperature ( = 0.73−0.49). Complex 5 has demonstrated to be suitable to be used as a reasonably efficient phosphorescent greenish-yellow emitter for OLED devices with electroluminescence max of 552 nm and maximum external quantum efficiency (EQE) of 12%.
The catalytic activity in the hydrosilylation of terminal alkynes by the unsaturated hydrido iridium(III) compound [IrH(κ3-hqca)(coe)] (1), which contains the rigid asymmetrical dianionic ONO pincer ligand 8-oxidoquinoline-2-carboxylate, has been studied. A range of aliphatic and aromatic 1-alkynes has been efficiently reduced using various hydrosilanes. Hydrosilylation of the linear 1-alkynes hex-1-yne and oct-1-yne gives a good selectivity toward the β-(Z)-vinylsilane product, while for the bulkier t-Bu-CCH a reverse selectivity toward the β-(E)-vinylsilane and significant amounts of alkene, from a competitive dehydrogenative silylation, has been observed. Compound 1, unreactive toward silanes, reacts with a range of terminal alkynes RCCH, affording the unsaturated η1-alkenyl complexes [Ir(κ3-hqca)(E-CHCHR)(coe)] in good yield. These species are able to coordinate monodentate neutral ligands such as PPh3 and pyridine, or CO in a reversible way, to yield octahedral derivatives. Further mechanistic aspects of the hydrosilylation process have been studied by DFT calculations. The catalytic cycle passes through Ir(III) species with an iridacyclopropene (η2-vinylsilane) complex as the key intermediate. It has been found that this species may lead both to the dehydrogenative silylation products, via a β-elimination process, and to a hydrosilylation cycle. The β-elimination path has a higher activation energy than hydrosilylation. On the other hand, the selectivity to the vinylsilane hydrosilylation products can be accounted for by the different activation energies involved in the attack of a silane molecule at two different faces of the iridacyclopropene ring to give η1-vinylsilane complexes with either an E or Z configuration. Finally, proton transfer from a η2-silane to a η1-vinylsilane ligand results in the formation of the corresponding β-(Z)- and β-(E)-vinylsilane isomers, respectively.
Molecular phosphorescent heteroleptic bis-tridentate iridium(III) emitters have been prepared via η -arene intermediates. In the presence of 4.0 mol of AgOTf, the complex [(IrCl{κ -N,C,N-(pyC HMe py)})(μ-Cl)] (1; pyC H Me py=1,3-di(2-pyridyl)-4,6-dimethylbenzene) reacted with 9-(6-phenylpyridin-2-yl)-9H-carbazole (PhpyCzH) and 2-phenoxy-6-phenylpyridine (PhpyOPh) to give [Ir{κ -N,C,N-(pyC HMe py)}{κ -C,N,C'-(C H pyCzH)}]OTf (2) and [Ir{κ -N,C,N-(pyC HMe py)}{κ -C,N,C'-(C H pyOPh)}]OTf (3). The X-ray diffraction structures of 2 and 3 reveal that the carbazolyl and phenoxy substituents of the C,N,C' ligand coordinate to the metal center to form an η -arene π bond. Treatment of 2 and 3 with KOtBu led to the deprotonation of the coordinated carbon atom of the η -arene group to afford the molecular phosphorescent [5t+4t'] heteroleptic iridium(III) complexes [Ir{κ -N,C,N-(pyC HMe py)}{κ -C,N,C'-(C H pyCz)}] (4) and [Ir{κ -N,C,N-(pyC HMe py)}{κ -C,N,C'-(C H pyOC H )}] (5). These complexes are green emitters that display short lifetimes and high quantum yields of 0.73 (4) and 0.87 (5) in the solid state.
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