Preparation of Phosphorescent Iridium(III) Complexes with a Dianionic C,C,C,C-Tetradentate Ligand.

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)]2 (1, COD = 1,5-cyclooctadiene) reacts with 1,1-diphenyl-3,3-butylenediimidazolium iodide ([PhIm(CH2)4ImPh]I2), in the presence NaOtBu, to give [Ir(µ-I){κ4- C, C, C, C-[C6H4Im(CH2)4ImC6H4]}]2 (2), which leads to {[Ir{κ4- C, C, C, C-[C6H4Im(CH2)4ImC6H4]}]2(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{κ4- C, C, C, C-[C6H4Im(CH2)4ImC6H4]}(CH3CN)2]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{κ4- C, C, C, C-[C6H4Im(CH2)4ImC6H4]}{κ2- C, N-[Ar-py]} (Ar-py = C6H4-py (5), C6H2F2-py (6), C6H3Me-py (7), C6H4-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.

Preparation of Tris-Heteroleptic Iridium(III) Complexes Containing a Cyclometalated Aryl-N-Heterocyclic Carbene Ligand.

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)]2 (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){κ2- C, C-(C6H4-ImMe)}{κ2- C, N-(C6H4-isoqui)}]2 (3), [Ir(µ-Cl){κ2- C, C-(C6H4-ImMe)}{κ2- C, N-(C6H4-py)}]2 (4), and [Ir(µ-Cl){κ2- C, C-(C6H4-ImMe)}{κ2- C, N-(C6F2H2-py)}]2 (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{κ2- C, C-(C6H4-ImMe)}{κ2- C, N-(C6H4-isoqui)}(κ2- O, O-acac) (6a and 6b), Ir{κ2- C, C-(C6H4-ImMe)}{κ2- C, N-(C6H4-py)}(κ2- O, O-acac) (7a and 7b), and Ir{κ2- C, C-(C6H4-ImMe)}{κ2- C, N-(C6F2H4-py)}(κ2- 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{κ2- C, C-(C6H4-ImMe)}{κ2- C, N-(C6H4-isoqui)}(H2O)2]X [X = BF4 (9a[BF4]), OTf (9a[OTf])]. The salt 9a[BF4] reacts with 2-(2-pinacolborylphenyl)-5-methylpyridine in the presence of 40 equiv of K3PO4 to afford Ir{κ2- C, C-(C6H4-ImMe)}{κ2- C, N-(C6H4-isoqui)}{κ2- C, N-(C6H4-Mepy)} (10a). Complexes 6a, 6b, 7a, 7b, 8a, 8b, and 10a are phosphorescent emitters (λem = 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/m2 at a lower voltage and appears to give rise to higher luminous efficacy and power efficacy.

Functionalized imido-bridged Ti(IV) complexes as new building blocks for supramolecular arrangements: generation of a 1D structure through a Mg-Cl···I-C halogen bonding interaction.

The new functionalized aryl-imido-bridged cyclopentadienyl titanium compounds [TiCl(η(5)-C5Me5){µ-NR}]2, R = 4-X-C6H4 (X = CN (2a), X = Cl (2b), X = I (2c), X = (OMe) (2d)); 3,5-(OMe)2C6H3 (2e) were prepared and their appropriateness as building blocks for constructing supramolecular structures was evaluated. The presence of a functional group in the para position within the aryl-imido ligand leads to the formation of 1D arrangement for 2a, 2c and 2d through halogen bonding or hydrogen bonding interactions. In particular, the imido titanium complex 2c forms a supramolecular chain with a [MgCl2·(THF)4] unit generated in the synthesis where the metallic fragments are connected by C-I···Cl-Mg halogen bonding interactions (XB), being the first example within group 2 metals where the XB motif M-Cl···I-C appears.