Iridium(III) and rhodium(III) cyclometalated complexes containing sulfur and selenium donor ligands

Treatment of [M(Buppy)₂Cl]₂ (M=Ir (1), Rh (2); BuppyH=2-(4^′-tert-butylphenyl)pyridine) with Na(Et₂NCS₂), K[S₂P(OMe)₂], and K[N(Ph₂PS)₂]₂ afforded monomeric [Ir(Buppy)₂(S^∧S)] (S^∧S=Et₂NCS₂ (3), S₂P(OMe)₂ (4), N(PPh₂S)₂ (5)) and [Rh(Buppy)₂(S^∧S)] (S^∧S=Et₂NCS₂ (6), S₂P(OMe)₂ (7), N(PPh₂S)₂ (8)), respectively. Reaction of 1 with Na[N(PPh₂Se)₂] gave [Ir(Buppy)₂{N(PPh₂Se)₂}] (9). The crystal structures of 3, 4, 7, and 8 have been determined. Treatment of 1 or 2 with AgOTf (OTf=triflate) followed by reaction with KSCN gave dinuclear [{M(Buppy)₂}₂(μ-SCN)₂] (M=Ir (10), Rh (11)), in which the SCN⁻ ligands bind to the two metal centers in a μ-S,N fashion. Interaction of 1 and 2 with [Et₄N]₂[WQ₄] gave trinuclear heterometallic complexes [{Ir(Buppy)₂}₂(μ-WQ₄)] (Q=S (12), Se (13)) and [{Rh(Buppy)₂}₂{(μ-WQ)₄}] (Q=S (14), Se (15)), respectively. Hydrolysis of 12 led to formation of [{Ir(Buppy)₂}₂{W(O)(μ-S)₂(μ₃-S)}] (16) that has been characterized by X-ray diffraction.     

Synthesis, opto-physics, and electroluminescence of cyclometalated iridium (III) complex with alkyltrifluorene picolinic acid

To improve the opto-physics, electroluminescence, and dispersibility of iridium (III) complexes in polymer light-emitting devices, we synthesized and characterized two red-emitting heteroleptic cyclometalated iridium (III) complexes of (Piq)₂Ir(Tfl-pic) and (Piq)₂Ir(Brfl-pic), in which Piq is 1-phenylisoquinoline, Tfl-pic and Brfl-pic are alkyltrifluorene- and dibromoalkylfluorene-containing picolinic acid derivatives bridged with alkoxy chain, respectively. Compared to (Piq)₂Ir(pic) and (Piq)₂Ir(Brfl-pic), (Piq)₂Ir(Tfl-pic) exhibited higher thermal stability, better dispersibility and excellent quantum efficiency. High-efficiency red emission with a maximum current efficiency of 6.28 cdA⁻¹ and a maximum EL peak at 608 nm was obtained in the (Piq)₂Ir(Tfl-pic)-doped devices using a blend of poly(9,9-dioctylfluorene) and 2-(4-biphenyl)-5-(4-tert -butylphenyl)-1,3,4-oxadiazole as a host matrix.     

Synthesis and characterization of cyclometalated iridium(III) complexes containing pyrimidine-based ligands

New pyrimidine derivatives (pyr) have been synthesized using palladium-catalyzed Suzuki coupling reaction. These compounds can undergo cyclometalation with iridium trichloride to form bis-cyclometalated iridium complexes, (pyr)₂Ir(acac) (acac = acetylacetonate; pyr = cyclometalated pyr). The substituents at the both cyclometalated phenyl ring and pyrimidine ring were found to affect both electrochemical and photophysical properties of the complexes. Computation results on these complexes are consistent with the electrochemical and photophysical data. The complexes are green-emitting with good solution quantum yields at ∼0.30. Light-emitting devices using these complexes as dopants were fabricated, and the device performance at 100 mA/cm² are moderate: 9 (17 481 cd/m², 4.8%, 18 cd/A, 5.1 lm/W); 10 (18 704 cd/m², 4.9%, 18.9 cd/A, 4.7 lm/W); 13 (20 942 cd/m², 5.4%, 21.0 cd/A, 6.1 lm/W).     

Recent progress in functionalized electrophosphorescent iridium(III) complexes

Iridium(III) complexes are one of the most important electrophosphorescent dyes with tunable emissions in the range of visible and near infrared lights, high photoluminescence yields and short lifetimes for high-efficiency organic light-emitting diodes (OLED) with 100% exciton harvesting. This review summarizes the recent development of electroluminescent Ir³⁺ complexes functionalized with host-featured carrier-transporting groups, with emphasis on correlations between functionalization, optoelectronic properties and device performance. According to the introducing approaches, the complexes were sorted with conjugated and aliphatic linkages, as well as the types of functional groups. The modification effect on physical properties and the state-of-the-art device performances were discussed.     

The catalytic activity of a cyclometalated ruthenium(III) complex for aerobic oxidative dehydrogenation of benzylamines

The ruthenium(III) complex bearing benzo[h]quinoline as a cyclometalated ligand was synthesized and characterized by ESI-MS, elemental analysis, cyclic voltammetry and crystallography. The complex serves as an efficient catalyst for the aerobic oxidative dehydrogenation of benzylamines to the corresponding benzonitriles under mild conditions.     

Reactivity studies of cyclopentadienyl ruthenium(II), osmium(II) and pentamethylcyclopentadienyl iridium(III) complexes towards 2-(2′-pyridyl)imidazole derivatives

The reaction of [CpRu(PPh₃)₂Cl] and [CpOs(PPh₃)₂Br] with chelating 2-(2′-pyridyl)imidazole (N ∩ N) ligands and NH₄PF₆ yields cationic complexes of the type [CpM(N ∩ N)(PPh₃)]⁺ (1: M = Ru, N ∩ N = 2-(2′-pyridyl)imidazole; 2: M = Ru, N ∩ N = 2-(2′-pyridyl)benzimidazole; 3: M = Ru, N ∩ N = 2-(2′-pyridyl)-4,5-dimethylimidazole; 4: M = Ru, N ∩ N = 2-(2′-pyridyl)-4,5-diphenylimidazole; 5: M = Os, N ∩ N = 2-(2′-pyridyl)imidazole; 6: M = Os, N ∩ N = 2-(2′-pyridyl)benzimidazole). They have been isolated and characterized as their hexafluorophosphate salts. Similarly, in the presence of NH₄PF₆, [Cp∗Ir(μ-Cl)Cl]₂ reacts in dry methanol with N ∩ N chelating ligands to afford in excellent yield [Cp∗Ir(N ∩ N)Cl]PF₆ (7: N ∩ N = 2-(2′-pyridyl)imidazole; 8: N ∩ N = 2-(2′-pyridyl)benzimidazole). All the compounds have been characterized by infrared and NMR spectroscopy and the molecular structure of [1]PF₆, [2]PF₆ and [7]PF₆ by single-crystal X-ray structure analysis.     

Synthesis and characterization of cyclometalated iridium(III) complexes containing benzoxazole derivatives and different ancillary ligands

The synthesis, structures, electrochemistry, and photophysics of a series of cyclometalated iridium(III) complexes based on benzoxazole derivatives and different β-diketonate ligands are reported. These complexes have a general formula C^∧N₂Ir(LL′) [where C^∧N is a monoanionic cyclometalating ligand; 2-phenylbenzoxazolato (pbo), 2-(4-chlorophenyl)benzoxazolato (cpbo), 2-phenyl-5-chlorobenzoxazolato (pcbo), 2-(3,5-difluorophenyl)benzoxazole (fpbo), or 2-(2-naphthyl)benzoxazolato (nbo), and LL′ is an ancillary ligand; acetylacetonate (acac), dibenzoylmethanate (dbm), or 1,1,1,5,5,5-hexafluoroacetylacetonate (hfacac)]. The complexes (pcbo)₂Ir(acac) (3), (dfpbo)₂Ir(acac) (4), (cpbo)₂Ir(dbm) (7), (dfpbo)₂Ir(dbm) (8), and (dfpbo)₂Ir(hfacac) (9) have been structurally characterized by X-ray crystallography. All of the complexes show reversible oxidation between 0.45 and 1.07 V, versus Fc/Fc⁺, and have short luminescence lifetime (τ = 0.1-1.3 μs) at room temperature. Except complex 9, the radiative decay rate (k_r) and nonradiative decay rate (k_nr) of the (C^∧N)₂Ir(LL′) complexes have been determined by using the lifetime and quantum efficiency. The k_r ranges between 2.0 × 10³ and 3.0 × 10⁵ s⁻¹ and k_nr spans a narrower range of values (5.0 × 10⁵ to 7.0 × 10⁶ s⁻¹).     

Copper(I)-2-(2′-pyridyl)benzimidazole catalyzed N-arylation of indoles

CuI-2-(2′-pyridyl)benzimidazole catalyst system can serve efficiently to promote N-arylation of various indoles to afford the N-arylated indoles. The bidentate ligand, 2-(2′-pyridyl)benzimidazole was proved superior to monodentate nitrogen-based ligands and well-known bidentate ligands such as 2,2′-bipyridyl and 1,10-phenanthroline.     

Solution-processable high-efficiency bis(trifluoromethyl)phenyl functionalized phosphorescent neutral iridium(III) complex for greenish yellow electroluminescence

A novel and highly efficient bis(trifluoromethyl)phenyl functionalized iridium(III) complex is designed and synthesized. The complex shows intensive greenish yellow phosphorescence (525?nm with 563?nm as shoulder), high photoluminescence efficiency (0.90) and moderate full width at half maximum (72?nm). The bulky bis(trifluoromethyl)phenyl moiety introduced into the complex provides the excellent solubility and effective steric hindrance for solution-processed organic light-emitting diodes. The maximum power efficiency and current efficiency of electroluminescence are 4.13?lm/W and 9.54?cd/A, respectively.     

Solid-state electrochemiluminescence of a novel iridium（Ⅲ） complex

The solid-state ECL behavior of a water-insoluble bis-cyclometalated （pq）2Ir（N-phMA） complex is presented, in which pq is a 2-phenylquinoline anion and N-phMA is N-phenyl methacrylamide, a monoanionic bidentate ligand. The MWNTs/（pq）2Ir（N-phMA） film, MWNTs/Ru（bpy）3^2＋ film and （pq）2Ir（N-phMA） directly modified glassy carbon electrode were fabricated; only the MWNTs/（pq）2Ir（N-phMA） film can produce steady ECL in the presence of tri-n-propylamine as a coreactant.     

Synthesis of 2-substituted indoles by iridium (III)-catalyzed CH functionalization of N-phenylpyridin-2-amines

A highly regioselective synthesis of 2-substituted indoles was realized through Ir(III)-catalyzed CH functionalization of N-phenylpyridin-2-amines followed by the reaction with sulfoxonium ylides and intramolecular cyclization under mild conditions. The reaction completed with broad range of substrate scopes and gave various 2-substituted indoles in up to 98% yields.     

Thin-layer chromatographic separation of rhodium(III) and iridium(III, IV) by anion exchange

Summary The TLC behaviour of Rh(III), Ir(III) and Ir(IV) has been investigated in the two systems consisting of DEAE-cellulose or ECTEOLA-cellulose and 5 M HCl media containing H₂O₂. These systems, especially in combination with a simple chemical pretreatment of samples (with LiCl, HCl and H₂O₂), can effectively be applied to the complete separation of mixtures of Rh(III) and Ir(III) or Ir(IV) in a wide range of ratios and amounts (Rh: Ir=1100 to 1001).

---

Dünnschicht-chromatographische Trennung von Rhodium(III) und Iridium(III, IV) durch Anionenaustausch

Zusammenfassung Das dünnschicht-chromatographische Verhalten von Rh(III), Ir(III) und Ir(IV) wurde in H₂O₂-haltiger 5 M salzsaurer Lösung auf DEAE-sowie ECTEOLA-Cellulose untersucht. In Kombination mit einer einfachen chemischen Vorbehandlung der Probe (mit LiCl, HCl, H₂O₂) kann eine wirkungsvolle Trennung von Rh(III) und Ir(III) oder Ir(IV) über einen weiten Konzentrationsbereich erzielt werden (Rh: Ir=1100 bis 1001).

     

Heteroleptic half-sandwich Ru(II), Rh(III) and Ir(III) complexes based on 5-ferrocenyldipyrromethene

The synthesis and characterization of heteroleptic complexes with the formulations [(η⁶-arene)RuCl(fcdpm)] (η⁶-arene = C₆H₆, C₁₀H₁₄) and [(η⁵-C₅Me₅)MCl(fcdpm)] (M = Rh, Ir; fcdpm = 5-ferrocenyldipyrromethene) have been reported. All the complexes have been characterized by elemental analyses, IR, ¹H NMR and electronic spectral studies. Structures of [(η⁶-C₆H₆)RuCl(fcdpm)] and [(η⁶-C₁₀H₁₄)RuCl(fcdpm)] have been determined crystallographically. Chelating monoanionic linkage of fcdpm to the respective metal centres has been supported by spectral and structural studies. Further, reactivity of the representative complex [(η⁶-C₁₀H₁₄)RuCl(fcdpm)] with ammonium thiocyanate (NH₄SCN) and triphenylphosphine (PPh₃) have been examined.     

Synthesis,characterization, interactions with DNA and bovine serum albumin (BSA), and antibacterial activity of cyclometalated iridium(III) complexes containing dithiocarbamate derivatives

Three mononuclear cyclometalated iridium(III) complexes having dithiocarbamate ligands, [Ir^III(2-C₆H₄py)₂(L)] (where 2-C₆H₄py?=?2-phenylpyridine; and L¹H?=?4-MePipzcdtH, L²H?=?MorphcdtH, and L³H?=?4-BzPipercdtH for 1, 2, and 3, respectively), were synthesized from [Ir(2-C₆H₄py)₂Cl]₂·1/4CH₂Cl₂ by displacing the two bridging chlorides with one dithiocarbamate ligand. The complexes were characterized using physicochemical and spectroscopic tools along with structural analysis of [Ir(2-C₆H₄py)₂(L²)] (2) by single crystal X-ray diffraction. Structural analysis of 2 showed a distorted octahedron in which the nitrogen donor of one 2-phenylpyridine and the carbon donor of another 2-phenylpyridine are in axial positions, trans to one another. Electrochemical analysis by cyclic voltammetry showed the irreversible two-electron equivalent reduction voltammograms of 1, 2, and 3 attributable to Ir(III) to Ir(I). Electronic characterizations of these complexes are consistent with significant delocalization of the sulfur electron density onto the empty metal d-orbital. The intercalative interaction of the complexes with calf thymus DNA was evaluated using absorption, fluorescence quenching, and viscosity measurements. The binding affinities of these complexes with bovine serum albumin were estimated in terms of quenching constants using the Stern–Volmer equation. Study of antibacterial activities of the complexes by agar disk diffusion against some species of pathogenic bacteria was also performed.     

Oxidation of ketones by cerium(IV) in presence of iridium(III) chloride

Kinetic data, in iridium(III) chloride catalyzed oxidation of ethyl methyl ketone (EMK) and methyl propyl ketone (MPK) by cerium(IV) perchlorate in aqueous perchloric acid medium, suggest the formation of complex C₁ between cerium(IV) and organic substrate in the first equilibrium step, which in turn gives rise to another complex C₂ with the catalyst. This second complex in the rate-determining step gives rise to the intermediate products. Interestingly IrCl_3, which is considered to be a sluggish catalyst in alkaline media, was found to surpass the catalytic efficiency of even osmium and ruthenium in acidic media. Rate decreases in the beginning at low acid concentrations, but after reaching to a minimum it becomes directly proportional to acid concentrations. Probably on increasing the acid concentrations hydrolyzed species of ceric perchlorate gradually converts into the un-hydrolyzed species, which then accelerates the rate at higher [H⁺], resulting in the observed peculiar effect of hydrogen ions on the rate. Initial concentrations of cerium(IV) and acid determine the extent of reduction of cerium(IV) by water. Order of the reaction shows direct proportionality with respect to the oxidant and ketones at their low concentrations, but tends to become zeroth order at their higher concentrations. Rate of the reaction shows direct proportionality with respect to [IrCl₃] while change in ionic strength of the medium does not affect the reaction velocity. Parameters such as the energy of activation, free energy of activation and entropy data suggest that methyl propyl ketone forms the activated complex more easily compared to ethyl methyl ketone.     

Synthesis, characterization and photophysics of fluorene-alt-oxadiazole copolymers containing pendent iridium (III) complex moiety

A series of fluorene-alt-oxadiazole copolymers containing a pendent phosphor chromophore of the (piq)₂Ir(pic) complex were synthesized via the palladium-catalyzed Suzuki coupling reaction, where piq is 1-phenylisoquinoline and pic is picolinic acid. These copolymers exhibited a similar absorption spectrum with a peak at about 330 nm and a typical emission peak at 408 nm in CH₂Cl₂ from the fluorene-alt-oxadiazole backbone. However, a significantly red-shifted emission peak at about 625 nm was observed in the neat films of these copolymers, which are attributed to the pendent iridium (III) complex unit. Using these copolymers as single emission layer, the polymer light-emitting devices with a configuration of ITO/PEDOT:PSS/copolymers/LiF/Al exhibited a saturated red emission with a peak at 632 nm. Significant influence of the attached iridium (III) complex ratio on EL performance was presented. A maximum current efficiency of 1.2 cd/A at 63 mA/cm² and a maximum luminance of 1125 cd/m² at 12 V were achieved from the device with the copolymer containing iridium (III) complex in a 3% molar ratio.     

Polymerizable cationic iridium(III) complexes exhibiting color tunable light emission and their corresponding conducting metallopolymers

Cyclometalated iridium(III) complexes have been synthesized for use in a variety of photophysical applications, including polymer light emitting diodes (PLEDs). A series of new complexes with one electrochemically polymerizable ligand and two phenylpyridine(ppy)-based ligands have been prepared: [Ir(ppy)₂L][PF₆](1), [Ir(F-mppy)₂L][PF₆](2), and [Ir(Br-mppy)₂L][PF₆](3), where L = 3,8-bis(2,2′-bithien-5-yl)-1,10-phenanthroline. The ancillary ppy ligands can be easily varied synthetically to tune emission color of the monomer from blue–green to red. The solid state structure of complex 1 has been obtained by single crystal X-ray crystallography. Conducting polymer materials have been prepared by electropolymerization of monomers and were characterized through XPS analysis and spectroscopic studies.     

Cyclometalated rhodium(III) complex with phen-dione ligand

The novel cyclometalated Rh(III) complex, [Rh(phpy-κ²N,C^2′)₂(phen-dione)]PF₆, where phpy-κ²N,C^2′ is pyridine-2-yl-2-phenyl and phen-dione is 1,10-phenanthroline-5,6-dione has been prepared and characterized by elemental analysis, IR, ¹H NMR, and electronic absorption spectroscopies, cyclic voltammetry, and X-ray crystallography. The crystal structure of [Rh(phpy-κ²N,C^2′)₂(phen-dione)]PF₆·CH₃CN shows that the coordination geometry around the Rh(III) is a distorted octahedron, with bite angles of 76.13°-81.09° for all three bidentate ligands.     

Synergistic liquid-liquid extractive spectrophotometric determination of gold(III) using 1-(2′,4′-dinitro aminophenyl)-4,4,6-trimethyl-1,4-dihydropyrimidine-2-thiol

Synergistic liquid-liquid extractive spectrophotometric determination of gold(III) using 1-(2′,4′-dinitro aminophenyl)-4,4,6-trimethyl-1,4-dihydro pyrimidine-2-thiol [2′,4′-dinitro APTPT] has been described. Equal volumes (5 cm³) of the 2′,4′-dinitro APTPT (0.02 mol L⁻¹) in the presence of pyridine (0.5 mol L⁻¹) form an orange-red coloured ternary complex with gold(III) of molar ratio 1:1:1 at pH 1.8-2.4 with 5 min of shaking. The absorbance of coloured organic layer in 1,2-dichloroethane is measured spectrophotometrically at 445 nm against reagent blank. A pronounced synergism has been observed by the binary mixture of 2′,4′-dinitro APTPT and pyridine, which shows that the enhancement in the absorbance is observed in the presence of pyridine by the adduct formation in the organic phase. Beer's law was obeyed in the concentration range 2.5-20.0 μg mL⁻¹, with molar absorptivity and Sandell's sensitivity values of 8.7 × 10³ dm³ mol⁻¹ cm⁻¹ and 0.023 μg cm⁻² respectively. A repetition of the method was checked by finding relative standard deviation (R.S.D.) (n = 10) which was 0.17%. The composition of the gold(III)-2′,4′-dinitro APTPT-pyridine adduct was established by slope analysis, molar ratio and Job's method. The ternary complex was stable for more than 48 h. The influence of various factors such as pH, 2′,4′-dinitro APTPT concentration, solvent and pyridine on the degree of complexation has been established. A number of foreign ions tested for their interferences and use of suitable masking agents wherever necessary are tabulated, which show that selectivity of the method has been enhanced. The method is successfully employed for the determination of gold(III) in binary, synthetic mixtures and ayurvedic samples. The reliability of the method is assured by inter-comparison of experimental values, using an atomic absorption spectrometer.