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.

Novel homoleptic and heteroleptic NHC carbene containing bis(tridentate) osmium(II) complexes have been designed, synthesized, and characterized, and their photophysical properties have been studied. The complex OsH6(PiPr3)2 (1) reacts with the tetrafluoroborate salts of 1,3-bis(3-methylbenzimidazolium-1-yl)benzene and 1,3-bis(3-methylimidazolium-1-yl)benzene, in dimethylformamide, under reflux to afford the hydride–carbonyl derivatives [OsH(CNHCCarylCbenzimidazolium)(CO)(PiPr3)2]BF4 (2) and [OsH(CNHCCarylCimidazolium)(CO)(PiPr3)2]BF4 (3), as a result of the direct metalation of one of the NHC units of the salts, the activation of the C–H bond at the 6-position of the bridged aryl group, and metal carbonylation by solvent decarbonylation. In contrast to the BF4 salts, under the same conditions, the iodide salts of 1,3-bis(3-methylbenzimidazolium-1-yl)benzene, 1,3-bis(3-methylimidazolium-1-yl)benzene, and 1,3-bis(3-methylbenzimidazolium-1-yl)-5-trifluoromethylbenzene undergo direct metalation of both NHC units and C–H bond activation of the bridged aryl group at the 2-position to give the respective osmium(IV) dihydrides [OsH2(CNHCCarylCNHC)(PiPr3)2]I (4a–6a), which by deprotonation with K t BuO yield the osmium(II) monohydrides OsH(CNHCCarylCNHC)(PiPr3)2 (7–9). The reactions of 7 with 1,3-bis(3-methylbenzimidazolium-1-yl)benzene tetrafluoroborate and of 9 with 1,3-bis(3-methylbenzimidazolium-1-yl)-5-trifluoromethylbenzene tetrafluoroborate lead to the homoleptic derivatives Os(CNHCCarylCNHC)2 (10, 11), whereas the reactions of 9 with the tetrafluoroborate salts of 1,3-bis(3-methylbenzimidazolium-1-yl)benzene and 1,3-bis(3-methylimidazolium-1-yl)benzene generate heteroleptic Os(CNHCCarylCNHC)(CNHCCaryl′CNHC) (12) and Os(CNHCCaryl′CNHC)(CNHC′CarylCNHC′) (13). Treatment of 7 with 3,5-bis(3-methylbenzimidazolium-1-yl)-2,6-dimethylpyridine tetrafluoroborate affords the salt [Os(CNHCCarylCNHC)(CNHCCaryl′CNHC)]BF4 (14), with Caryl′ being a pyridinium group. Its deprotonation generates the neutral heteroleptic derivative Os(CNHCCarylCNHC)(CNHCCaryl′CNHC) (15). Complexes 10–13 and 15 are emissive in the blue-green spectral region with high quantum yields in the solid state, which reach 0.62 for 11. OLEDs using this compound as an emitting material show blue emission (CIE coordinates: (0.14, 0.26)). The brightness of the device reaches 10000 cd/m2 at 9.5 V. The maximum external quantum efficiency (EQE) was 19.2% at 1000 cd/m2.

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%.

A MHC6 complex of a platinum group metal with a capped octahedral arrangement of donor atoms around the metal center has been characterized. This osmium compound OsH{κ(2) -C,C-(PhBIm-C6 H4 )}3 , which reacts with HBF4 to afford the 14 e(-) species [Os{κ(2) -C,C-(PhBIm-C6 H4 )}(Ph2 BIm)2 ]BF4 stabilized by two agostic interactions, has been obtained by reaction of OsH6 (PiPr3 )2 with N,N'-diphenylbenzimidazolium chloride ([Ph2 BImH]Cl) in the presence of NEt3 . Its formation takes place through the C,C,C-pincer compound OsH2 {κ(3) -C,C,C-(C6 H4 -BIm-C6 H4 )}(PiPr3 )2 , the dihydrogen derivative OsCl{κ(2) -C,C-(PhBIm-C6 H4 )}(η(2) -H2 )(PiPr3 )2 , and the five-coordinate osmium(II) species OsCl{κ(2) -C,C-(PhBIm-C6 H4 )}(PiPr3 )2 .

The preparation and photophysical properties of heteroleptic iridium(III) complexes containing a dianionic C,C,C,C-tetradentate ligand and a cyclometalated phenylpyridine group are described. Complex [Ir(μ-OMe)(COD)] (1, COD = 1,5-cyclooctadiene) reacts with 1,1-diphenyl-3,3-butylenediimidazolium iodide ([PhIm(CH)ImPh]I), in the presence NaOBu, to give [Ir(μ-I){κ- C, C, C, C-[CHIm(CH)ImCH]}] (2), which leads to {[Ir{κ- C, C, C, C-[CHIm(CH)ImCH]}](μ-OH)(μ-OMe)} (3) by treatment first with silver trifluoromethanesulfonate (AgOTf) in acetone-dichloromethane and subsequently with KOH in methanol. The reaction of 2 with AgOTf and acetonitrile affords the bis(solvento) complex [Ir{κ- C, C, C, C-[CHIm(CH)ImCH]}(CHCN)]OTf (4). The latter promotes the pyridyl-supported heterolytic ortho-CH bond activation of the phenyl group of 2-phenylpyridine, 2-(2,4-difluorophenyl)pyridine, 2-( p-tolyl)pyridine, and 5-methyl-2-phenylpyridine to yield Ir{κ- C, C, C, C-[CHIm(CH)ImCH]}{κ- C, N-[Ar-py]} (Ar-py = CH-py (5), CHF-py (6), CHMe-py (7), CH-Mepy (8)) using (piperidinomethyl)polystyrene as an external base. Complexes 5-8 are blue-green emitters, which display short lifetimes (0.6-4.8 μs) and quantum yields close to unity in both doped poly(methyl methacrylate) films at 5 wt % and in 2-methyltetrahydrofuran at room temperature.