Iridium Tris Research Articles

A tautomerized ligand enabled meta selective C–H borylation of phenol

Remote meta selective C–H functionalization of aromatic compounds remains a challenging problem in chemical synthesis. Here, we report an iridium catalyst bearing a bidentate pyridine-pyridone (PY-PYRI) ligand framework that efficiently catalyzes this meta selective borylation reaction. We demonstrate that the developed concept can be employed to introduce a boron functionality at the remote meta position of phenols, phenol containing bioactive and drug molecules, which was an extraordinary challenge. Moreover, we have demonstrated that the method can also be applied for the remote C6 borylation of indole derivatives including tryptophan that was the key synthetic precursor for the total synthesis of Verruculogen and Fumitremorgin A alkaloids. The inspiration of this catalytic concept was started from the O–Si secondary interaction, which by means of several more detailed control experiments and detailed computational investigations revealed that an unprecedented Bpin shift occurs during the transformation of iridium bis(boryl) complex to iridium tris(boryl) complex, which eventually control the remote meta selectivity by means of the dispersion between the designed ligand and steering silane group.

Intrinsic and Catalyzed Photochemistry of Phenylvinylketone for Wavelength‐Sensitive Controlled Polymerization

AbstractReversible addition‐fragmentation chain transfer (RAFT) photopolymerization of phenylvinylketone (PVK) is investigated. The polymerization is investigated both in the presence of two photocatalysts (iridium tris(phenylpyridine (Ir(ppy)3) and zinc tetraphenylporphyrin (ZnTPP)). The polymerization was efficient in the absence of photocatalyst, and accelerated by Ir(ppy)3, whereas ZnTPP was found to lead to retardation of polymerization. In all cases, well‐controlled polymers were synthesized with linear growth in Mn with conversion and narrow molecular weight distributions. The observed photopolymerization kinetics were consistent with a Norrish Type 1 reaction of PVK to give two radicals. The polymerization kinetics were investigated as a function of wavelength, with the reaction rate being fastest with blue irradiation (440 nm), which is surprisingly far from the absorption maximum of PVK and Ir(ppy)3. Photodegradation of PVK was observed under UV irradiation, but the polymers were stable against visible light.

Highly efficient polymer phosphorescent light-emitting devices based on a new polyfluorene derivative as host

Several highly efficient iridium-complex polymer light-emitting devices (PLEDs) are fabricated, with a newly synthesized blue conjugated polymer, poly[(9,9-bis(4-(2-ethylhexyloxy)phenyl)-fluorene)-co-(3,7-dibenziothiene-S,S-dioxide15)] (PPF-3,7SO15), chosen as host. High luminous efficiencies of 7.4 cd·A−1 and 27.4 cd·A−1 are achieved in red and green PLEDs, respectively, by optimizing the doping concentrations of red phosphorescent dye iridium bis(1-phenylisoquinoline) (acetylacetonate) (Ir(piq)) and green phosphorescent dye iridium tris(2-(4-tolyl)pyridinato-N, C2′) (Ir(mppy)3). Furthermore, highly efficient white PLEDs (WPLEDs) with the Commission Internationale de l'Eclairage (CIE) coordinates of (0.35, 0.38) are successfully produced by carefully controlling the doping concentration of the iridium complex. The obtained WPLEDs show maximal efficiencies of 14.4 cd·A−1 and 10.1 lm·W−1, which are comparable to those of incandescent bulbs. Moreover, the electroluminescent spectrum of the white device with an initial luminance of about 1000 cd·m−2 is stable, subject to constant applied current stress, indicating that good device stability can be obtained in this system.

Porous Phosphorescent Coordination Polymers for Oxygen Sensing

Phosphorescent cyclometalated iridium tris(2-phenylpyridine) derivatives were designed and incorporated into coordination polymers as tricarboxylate bridging ligands. Three different crystalline coordination polymers were synthesized using a solvothermal technique and were characterized using a variety of methods, including single-crystal X-ray diffraction, PXRD, TGA, IR spectroscopy, gas adsorption measurements, and luminescence measurements. The coordination polymer built from Ir[3-(2-pyridyl)benzoate](3), 1, was found to be highly porous with a nitrogen BET surface area of 764 m(2)/g, whereas the coordination polymers built from Ir[4-(2-pyridyl)benzoate](3), 2 and 3, were nonporous. The (3)MLCT phosphorescence of each of the three coordination polymers was quenched in the presence of O(2). However, only 1 showed quick and reversible luminescence quenching by oxygen, whereas 2 and 3 exhibited gradual and irreversible luminescence quenching by oxygen. The high permanent porosity of 1 allows for rapid diffusion of oxygen through the open channels, leading to efficient and reversible quenching of the (3)MLCT phosphorescence. This work highlights the opportunity of designing highly porous and luminescent coordination polymers for sensing other important analytes.

Bonding modes, structures and fluxionality in rhodium and iridium tris(3,5-dimethylpyrazolyl)methane diene complexes

The structures adopted by a range of hydrotris(3,5-dimethylpyrazolyl)methane complexes [ML(2){HC(pz')(3)}](+) (M = Rh, Ir; L(2) = diene) have been investigated. There is low steric hindrance between ligands in [Rh(eta-nbd){HC(pz')(3)}](+) (nbd = norbornadiene) and [Rh(eta-dmbd){HC(pz')(3)}](+) (dmbd = 2,3-dimethylbuta-1,3-diene) resulting in kappa(3) co-ordination of the pyrazolylmethane. The complexes [M(eta-cod){HC(pz')(3)}](+) (cod = cycloocta-1,5-diene) (M = Rh, Ir) are kappa(2) co-ordinated with the free pyrazolyl ring positioned above and approximately parallel to the square plane about rhodium or iridium. The HC(pz')(3) complexes undergo fast exchange of the co-ordinated and unco-ordinated pyrazolyl rings on the NMR spectroscopic timescale. However, for [Rh(eta-dmbd){HC(pz')(3)}](+), the fluxional process is slowed at low temperatures, so that inequivalent pyrazolyl rings may be observed. A mechanism for the fluxional process is proposed involving dynamic interconversion between isomeric forms in solution. The bonding mode of the HC(pz')(3) ligand can be determined by (13)C NMR spectroscopy. The (13)C chemical shifts (for the sp(3) hybridised carbon of the ligand) show the general pattern, kappa(3) < 71.5 ppm < kappa(2). The electrochemical behaviour of the pyrazolylmethane complexes is related to the degree of structural change, which occurs on electron transfer and is compared with that of the pyrazolylborate analogues.

Blue and Near-UV Phosphorescence from Iridium Complexes with Cyclometalated Pyrazolyl or N-Heterocyclic Carbene Ligands

Two approaches are reported to achieve efficient blue to near-UV emission from triscyclometalated iridium(III) materials related to the previously reported complex, fac-Ir(ppz)(3) (ppz = 1-phenylpyrazolyl-N,C(2)'). The first involves replacement of the phenyl group of the ppz ligand with a 9,9-dimethyl-2-fluorenyl group, i.e., fac-tris(1-[(9,9-dimethyl-2-fluorenyl)]pyrazolyl-N,C(2)')iridium(III), abbreviated as fac-Ir(flz)(3). Crystallographic analysis reveals that both fac-Ir(flz)(3) and fac-Ir(ppz)(3) have a similar coordination environment around the Ir center. The absorption and emission spectra of fac-Ir(flz)(3) are red shifted from those of fac-Ir(ppz)(3). The fac-Ir(flz)(3) complex gives blue photoluminescence (PL) with a high efficiency (lambda(max) = 480 nm, phi(PL) = 0.38) at room temperature. The lifetime and quantum efficiency were used to determine the radiative and nonradiative rates (1.0 x 10(4) and 2.0 x 10(4) s(-1), respectively). The second approach utilizes N-heterocyclic carbene (NHC) ligands to form triscyclometalated Ir complexes. Complexes with two different NHC ligands, i.e., iridium tris(1-phenyl-3-methylimidazolin-2-ylidene-C,C(2)'), abbreviated as Ir(pmi)(3), and iridium tris(1-phenyl-3-methylbenzimidazolin-2-ylidene-C,C(2)'), abbreviated as Ir(pmb)(3), were both isolated as facial and meridianal isomers. Comparison of the crystallographic structures of the fac- and mer-isomers of Ir(pmb)(3) with the corresponding Ir(ppz)(3) isomers indicates that the imidazolyl-carbene ligand has a stronger trans influence than pyrazolyl and, thus, imparts a greater ligand field strength. Both fac-Ir(pmi)(3) and fac-Ir(pmb)(3) complexes display strong metal-to-ligand-charge-transfer absorption transitions in the UV (lambda = 270-350 nm) and phosphoresce in the near-UV region (E(0)(-)(0) = 380 nm) at room temperature with phi(PL) values of 0.02 and 0.04, respectively. The radiative decay rates for fac-Ir(pmi)(3) and fac-Ir(pmb)(3) (5 x 10(4) s(-1) and 18 x 10(4) s(-1), respectively) are somewhat higher than that of fac-Ir(flz)(3), but the nonradiative rates are two orders of magnitude faster (i.e., (2-4) x 10(6) s(-1)).

Photoemission and X-ray absorption spectroscopies of phosphorescent organic iridium complexes

Phosphorescent materials represent an attractive route to high-efficiency organic LEDs, since their maximum theoretical quantum efficiency is 100%, compared to the 25% of fluorescent materials. We have studied the electronic structure of three phosphorescent iridium complexes, the red-emitter Iridium bis (2-(2′-benzothienyl) pyridinato-N, C 3′) (acetylacetonate), the blue emitter, Iridium bis(2-(4,6- difluorophenyl) pyridinato-N,C 2′) picolinate, and the green emitter Iridium tris (2-(4-totyl)pyridinato N,C 2) using electron spectroscopies. The materials were evaporated in-situ onto a clean gold substrate in ulta-high vacuum. The valence band electronic structures were investigated using resonant photoemission, with the unoccupied states determined using X-ray absorption. The data suggests a hybridisation of the Ir 5d states with the π orbitals of the ligand. NEXAFS spectra are shown to be highly sensitive to the local environment.

Characterisation of thin films of organic phosphorescent materials using synchrotron radiation

Synchrotron radiation photoemission and X-ray absorption spectroscopy (NEXAFS) have been used to investigate the electronic structure of evaporated films of the phosphorescent organic iridium complexes iridium tris-(2-(4-totyl)pyridinato-N,C 2), iridium bis(2-(4,6-difluorophenyl)pyridinato-N,C 2)picolinate, and iridium bis(2-(2′-benzothienyl)pyridinato-N,C 3)-(acetylacetonate) and spin coated films of these materials in a polymer host. Resonant photoemission at the Ir N 6,7 edge indicates that the Ir 5d states are hybridised with the π orbitals of the organic ligands, in agreement with recent calculations. The nitrogen K-edge NEXAFS shows the difference in the unoccupied orbitals induced by the acetylacetonate group compared to those of the pyridinate ligands. Although the valence bands of the ex situ prepared films are not accessible to photoemission, the Ir 4f core levels remain visible, and demonstrate that the polymer host serves to lower the electron injection barrier in the iridium complexes in comparison to the pure films.

MO CVD obtaining composite coatings from metal of platinum group on titanium electrodes

In the present paper we report obtaining composite coatings based on platinum metals by means of CVD technique. Platinum-, iridium- and ruthenium-containing coatings were deposited onto titanium substrates. Platinum bis-(2,4-pentanedionate), iridium tris-(2,4-pentanedionate), and ruthenium tris-(2,4-pentanedionate) were used as precursors. Corrosion resistance of the obtained samples is investigated with respect to the deposition conditions (substrate temperature and flow rate of the gas reagent - oxygen). Investigation was carried out using the electrolysis in sea water simulated solutions under active evolution of oxygen. It is stated that platinum coatings exhibit longer mean lifetime, in comparison with iridium and ruthenium samples. Service lifetime of the best electrodes exceeded 600 hours.

Effect of the deposition temperature on the iridum film microstructure produced by metal-organic chemical vapour deposition: sample characterization using x-ray techniques

The iridium films were prepared by metal-organic chemical vapour deposition (MOCVD) via the pyrolysis of iridium tris(acetylacetonate) on glass and quartz surfaces at atmospheric pressure with hydrogen as an additive in the deposition temperature range 370–550 °C. The phase composition and the microstructure of the films have been studied by means of the X-ray phase analysis and small-angle X-ray scattering techniques. Only the crystal phase of metal iridium has been found. The films consist of chaotically oriented close-spaced particles of different shapes and sizes. Iridium crystallites and other inhomogeneities of electron density in the films have a mean size in the range 100–400 Å. The analysis has made it possible to assume the presence of particles of two shapes in Ir films: “compact” (the axial ratio is no lower than 1:3) and “flattened-out” (disks, cracks, plates and shells) particles. For all the samples, the mean thicknesses r of “flattened-out” particles with spherical shells taken as models of their shapes have been estimated. The value of r increases with increasing substrate temperature from 370 to 470 °C. The maximum volume share of “flattened-out” particles is observed in the 420–470 °C deposition temperature range. An increase or a decrease in substrate temperature in MOCVD processes leads to almost complete disappearance of the particles of this shape. The average radii R g of gyration and the maximum distances L max in particles have been estimated. In addition, the specific surfaces S/V of film material and the functions of volumetric distribution D v( R) of compact particles in Ir films have been calculated depending on the deposition temperature.

Alcohol activation by [Ir(COD)(tris(pyrazol-1-yl)methane)] + and [Ir(COD) (tris(pyrazol-1-yl)ethanel + cations: formation of alkoxycarbonyl derivatives [(tpzm)IrH(CO 2R′)(CO)] + and [(tpze)IrH(CO 2R′)] + (R′ = Me, Et, i-Pr)

The reactions of iridium and rhodium complexes derived from tris(pyrazolyl)-methane (tpzm) and tris(pyrazolyl)ethane (tpze) have been examined. One of the most interesting reactions involves the formation of alkoxycarbonyl derivatives of iridium tris(pyrazolyl)alkanes from carbon monoxide and alcohols. In the case of rhodium derivatives, a dimer of formula [(tpzm)] 2Rh 2(CO) 3](CIO 4 2 has been obtained. A careful 1H and 13C NMR study has allowed assignment of all the signals of the compound [(tpzm)IrH(CO 2Me)(CO)]BF 4.