A new class of phosphorescent tris-heteroleptic iridium(III) complexes has been discovered. The addition of PhMeImAgI (PhMeIm = 1-phenyl-3-methylimidazolylidene) to the dimer [Ir(μ-Cl)(COD)] (1; COD = 1,5-cyclooctadiene) affords IrCl(COD)(PhMeIm) (2), which reacts with 1-phenylisoquinoline, 2-phenylpyridine, and 2-(2,4-difluorophenyl)pyridine to give the respective dimers [Ir(μ-Cl){κ- C, C-(CH-ImMe)}{κ- C, N-(CH-isoqui)}] (3), [Ir(μ-Cl){κ- C, C-(CH-ImMe)}{κ- C, N-(CH-py)}] (4), and [Ir(μ-Cl){κ- C, C-(CH-ImMe)}{κ- C, N-(CFH-py)}] (5), as a result of the N-heterocyclic carbene (NHC)- and N-heterocycle-supported o-CH bond activation of the aryl substituents and the hydrogenation of a C-C double bond of the coordinated diene. In solution, these dimers exist as a mixture of isomers a (Im trans to N) and b (Im trans to Cl), which lie in a dynamic equilibrium. The treatment of 3-5 with Kacac (acac = acetylacetonate) yields isomers a (Im trans to N) and b (Im trans to O) of Ir{κ- C, C-(CH-ImMe)}{κ- C, N-(CH-isoqui)}(κ- O, O-acac) (6a and 6b), Ir{κ- C, C-(CH-ImMe)}{κ- C, N-(CH-py)}(κ- O, O-acac) (7a and 7b), and Ir{κ- C, C-(CH-ImMe)}{κ- C, N-(CFH-py)}(κ- O, O-acac) (8a and 8b), which were separated by column chromatography. The treatment of 6a with HX in acetone-water produces the protonation of the acac ligand and the formation of the bis(aquo) complex [Ir{κ- C, C-(CH-ImMe)}{κ- C, N-(CH-isoqui)}(HO)]X [X = BF (9a[BF]), OTf (9a[OTf])]. The salt 9a[BF] reacts with 2-(2-pinacolborylphenyl)-5-methylpyridine in the presence of 40 equiv of KPO to afford Ir{κ- C, C-(CH-ImMe)}{κ- C, N-(CH-isoqui)}{κ- C, N-(CH-Mepy)} (10a). Complexes 6a, 6b, 7a, 7b, 8a, 8b, and 10a are phosphorescent emitters (λ = 465-655 nm), which display short lifetimes in the range of 0.2-5.6 μs. They show high quantum yields both in doped poly(methyl methacrylate) films (0.34-0.87) and in 2-methyltetrahydrofuran at room temperature (0.40-0.93). From the point of view of their applicability to the fabrication of organic-light-emitting-diode devices, a notable improvement with regard to those containing two cyclometalated C,N ligands is achieved. The introduction of the cyclometalated aryl-NHC group allows one to reach a brightness of 1000 cd/m at a lower voltage and appears to give rise to higher luminous efficacy and power efficacy.
The air-and temperature-stable cationic compound [Pt(C^N)(CNXyl) 2 ]ClO 4 (6) could be prepared from 2 by addition of CNXyl (1:4 molar ratio) after the Clabstraction with AgClO 4. Compound [Pt(C^N-κC)(tht) 3 ]ClO 4 (7) was prepared similarly
ABSTRACT:The hexahydride complex OsH 6 (P i Pr 3 ) 2 (1) reacts with the BF 4 -salts of 1-phenyl-3-methyl-1-H-benzimidazolium, 1-phenyl-3-methyl-1-H-5,6-dimethyl-benzimidazolium, and 1-phenyl-3-methyl-1-H-imidazolium to give the respective trihydrideosmium(IV) derivatives OsH 3 ( 2 -C aryl ,C NHC )(P i Pr 3 ) 2 (2-4). The protonation of these compounds with HBF 4 ·OEt 2 produces the reduction of the metal center and the formation of the bis(dihydrogen)-osmium(II) complexes [Os( 2 -C aryl ,C NHC )(η 2 -H 2 ) 2 (P i Pr 3 ) 2 ]BF 4 (5-7). DFT calculations using AIM and NBO methods reveal that the Os-NHC bond of the Os-chelate link tolerates a significant π-backdonation from a doubly occupied d π (Os) atomic orbital to the p z atomic orbital of the carbene carbon atom. The π-accepting capacity of the NHC unit of the C aryl ,C NHC -chelate ligand, which is higher than those of the coordinated aryl group and phosphine ligands, enhances the electrophilicity of the metal center activating one of the coordinated hydrogen molecules of 5-7 towards the heterolysis. As a result, these compounds are strong Brønsted acid with pK a water values between 2.5 and 2.8. In acetonitrile the hydrogen molecules of 5 and 6 are displaced by the solvent, the resulting bis(solvento) compounds [Os( 2 -C aryl ,C NHC )(CH 3 CN) 2 (P i Pr 3 ) 2 ]BF 4 (8, 9) react with acetylacetonate (acac) and cis-1,2-bis(diphenylsphosphino)ethylene (bdppe) to give Os( 2 -C aryl ,C NHC )(acac)(bdppe) (10, 11) as a mixture of the two possible isomers, namely with P trans to the aryl group or to the NHC moiety.
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