Octahedral Iridium Complexes Research Articles

Bis[3,5-di-fluoro-2-(pyridin-2-yl)phen-yl](4,4'-di-meth-oxy-2,2'-bi-pyridine)-iridium(III) hexa-fluorido-phosphate.

The title cyclo-metalated distorted octa-hedral iridium complex, [Ir(C11H6F2N)2(C12H12N2O2)]PF6, exhibits elongated Ir-N bonds to the dimeth-oxy bi-pyridine ligand [2.128 (3) and 2.136 (3) Å] where these nitro-gen atoms are trans to the Ir-C bonds of the two cyclo-metalating di-fluoro-phenyl-pyridine ligands. The angles between the mean planes of the phenyl and pyridyl fragments within the individual ligands range from 3.5 (2) to 11.4 (2)° to deviate slightly from coplanarity.

Peripheral Ligand Effect on the Photophysical Property of Octahedral Iridium Complex: o-Aryl Substitution on the Phenyl Units of Homoleptic IrIII(C∧C)3 Complexes (C∧C = 1-Phenyl-3-methylimidazolin-2-ylidene-C,C2') for Deep Blue Phosphorescence.

To evaluate the efficacy of ortho-arylation in the second coordination sphere of octahedral iridium complex, a series of homoleptic N-heterocyclic carbene (NHC)-based Ir(C∧CR)3-type complexes were designed and prepared by introducing various substituents (R = H, Me, Ph, MePh, and diMePh) at the ortho-position of the aryl unit of the orthometalated phenyl group. In solution, an unnoticeable increase of emission quantum yields was observed within the variation of the ortho-substituent of the sterically demanding side-branch, a diMePh- group, showing the radiative quantum yield of mer-Ir(C∧CdiMePh)3 (ΦPL = 1.9%), being higher than that of the unsubstituted carbene-based mer-Ir(C∧CH)3 (ΦPL = 1.2%), due to a considerable difference in the nonradiative decay rate (knr = 65.40 × 105 s-1 for mer-Ir(C∧CdiMePh)3 vs knr = 141.1 × 105 s-1 for mer-Ir(C∧CH)3). Such a difference is attributed to the reduction of nonradiative pathway via the 3MLCT → 3MC transition by the widening gap between triplet emissive states and 3MC state, and a rigidity increase in structure by steric hindrance of bulky aryl substituent. In contrast, significant increase of emission quantum yield was observed in the films cast by spin coating, and fac-/mer-Ir(C∧CdiMePh)3 (ΦPL = 60.1/49.1%) were the most efficient ones among NHC-Ir(III) complexes, compatible with the assumption that the secondary coordination effect, i.e. a peripheral constraint, was put into action. As the substituent R increases in size on going from H, Me, Ph, MePh, to diMePh, notable structural changes in the periphery are evident, while an increase of emission quantum yields is also seen. Such a peripheral difference was under scrutiny first with X-ray structural studies, and its manifestation in photophysics was investigated along with quantum calculations that finally addressed the peripheral effect being maximized at R = diMePh. In the application of PhOLED, the mer-Ir(C∧CdiMePh)3-doped multilayer device showed highly enhanced efficiency with an external quantum efficiency (EQE) of up to 8.1%, compared to that of the mer-Ir(C∧CH)3-based device (1.2%), indicating the multiple positive effects of bulky aryl substitution of Ir(III) dopant. A deep-blue CIE chromaticity diagram (0.16, 0.09) was achieved from the device using mer-Ir(C∧CdiMePh)3 as a dopant.

Octahedral iridium complex catalyzed α-chlorination of 2-acyl imidazoles with tosyl chloride

An efficient and catalytic α-chlorination of 2-acyl imidazoles with readily available tosyl chloride catalyzed by an octahedral iridium complex under mild condition was reported. A range of 2-acyl imidazoles were converted to their corresponding α-chlorination products in good to excellent yields.

Metal-Templated Design: Enantioselective Hydrogen-Bond-Driven Catalysis Requiring Only Parts-per-Million Catalyst Loading.

Based on a metal-templated approach using a rigid and globular structural scaffold in the form of a bis-cyclometalated octahedral iridium complex, an exceptionally active hydrogen-bond-mediated asymmetric catalyst was developed and its mode of action investigated by crystallography, NMR, computation, kinetic experiments, comparison with a rhodium congener, and reactions in the presence of competing H-bond donors and acceptors. Relying exclusively on weak forces, the enantioselective conjugate reduction of nitroalkenes can be executed at catalyst loadings as low as 0.004 mol% (40 ppm), representing turnover numbers of up to 20 250. A rate acceleration by the catalyst of 2.5 × 10(5) was determined. The origin of the catalysis is traced to an effective stabilization of developing charges in the transition state by carefully orchestrated hydrogen-bonding and van der Waals interactions between catalyst and substrates. This study demonstrates that the proficiency of asymmetric catalysis merely driven by hydrogen-bonding and van der Waals interactions can rival traditional activation through direct transition metal coordination of the substrate.

Vibrational circular dichroism and chiroptical properties of chiral Ir(iii) luminescent complexes

The octahedral ionic Ir(iii) complex with a dual stereogenic centre of general formula Δ,Λ-(R,S)-[(ppy)2Ir(Me-Campy)]X, where ppy = 2-phenylpyridine and Me-Campy = 2-methyl-5,6,7,8-tetrahydroquinolin-8-amine, and the complex Λ-(R,S)-[(ppy)2Ir(H-Campy)]X, where ppy = 2-phenylpyridine, H-Campy = 8-amino-5,6,7,8-tetrahydroquinolines and X(-) = Cl(-) as a counterion in both cases, have been characterized by vibrational circular dichroism (VCD), which turns out to be efficacious in diastereomeric discrimination. Moreover, the single crystal X-ray structure of the complex Δ-(R)-[(ppy)2Ir(Me-Campy)]Cl is reported here. Density functional theory (DFT) calculations allow us to conclude that the most important doublet feature in the VCD spectra is associated with a clear vibrational exciton structure located on the two dissymmetrically disposed phenylpyridine ligands. The features in the VCD spectra associated with the (R) or (S)-central chirality configuration are identified and commented on. DFT calculations provide also the interpretation of electronic circular dichroism (ECD) spectra. Finally, circularly polarized luminescence (CPL) spectra are presented as an additional chiroptical characterization of these luminescent iridium complexes.

Crystal structure of chlorido-(η(2)-phenyl iso-thio-cyanate-κ(2) C,S)-mer-tris-(tri-methyl-phosphane-κP)iridium(I).

The molecule of the title compound, [IrCl(C7H5NS)(C3H9P)3], is a distorted octa-hedral iridium complex with three PMe3 ligands arranged in a meridional geometry, a chloride ion cis to all three PMe3 groups and the phenyl iso-thio-cyanate ligand bonded in an η(2)-fashion through the C and S atoms. The C atom is trans to the chloride ion and the S atom is responsible for a significant deviation from an ideal octa-hedral geometry. The geometric parameters for the metal-complexing phenyl isothiocyanate group are compared with other metal-complexed phenyl iso-thio-cyanates, as well as with examples of uncomplexed aryl iso-thio-cyanates.

Synthesis, structural characterization, and initial electroluminescent properties of bis-cycloiridiated complexes of 2-(3,5-bis(trifluoromethyl)phenyl)-4-methylpyridine

A series of bis-cyclometalated Ir(III) complexes ( 8– 10, 12, 15, 17, 19, 21, 23, 25, 28, 29 and 33) bearing two chromophoric N ∧C cyclometalated ligands derived from 2-(3,5-bis(trifluoromethyl)phenyl)-4-methylpyridine ( 1) and a third nonchromophoric ligand has been synthesized. A palladium-catalyzed cross-coupling reaction between 2-chloro-4-methylpyridine ( 2) and 3,5-bis(trifluoromethyl)phenylboronic acid ( 3) was used to prepare 2-(3,5-bis(trifluoromethyl)phenyl)-4-methylpyridine ( 1). Cyclometalation of ( 1) by IrCl 3 was carried out in (MeO) 3P O, with the formation of chloro-bridged dimer [N ∧C] 2Ir(μ-Cl) 2Ir[C ∧N] 2 ( 8). Reaction of ( 8) with lithium 2,4-pentanedionate, lithium 2,2,6,6-tetramethyl-heptane-3,5-dionate ( 13), dipivaloyltrimethylsilylphosphine ( 14), 2,2-dimethyl-6,6,7,7,8,8,8-heptafluoro-3,5-octadione ( 16), 1,1,1,3,3,3-hexafluoro-2-pyridin-2-yl-propan-2-ol ( 18), 1,1,1,3,3,3-hexafluoro-2-pyrazol-1-ylmethyl-propan-2-ol ( 20), 2-diphenylphosphanylethanol ( 22), and 1-diphenylphosphanylpropan-2-ol ( 24), afforded octahedral iridium complexes 9, 12, 15, 17, 19, 21, 23 and 25, respectively. Complex 10, which contains three different ligands (L 1 = N ∧C of 1; L 2 = N ∧C of 4,4′-dimethyl-[2,2′]bipyridinyl 4; L 3 = O ∧O of 2,4-pentanedione), and complex 11, which contains no cyclometalated ligands (L 1 = 4; L 2 = L 3 = Cl; L 4 = O ∧O of 2,4-pentanedione) were also isolated as minor products in a one-pot reaction between a 94:5 mixture of 1 and 4, IrCl 3 and lithium 2,4-pentanedionate. Reaction of 8 with diphenylphosphanylmethanol ( 27) in 1,2-dichloroethane unexpectedly led to complexes 28 and 29. The reactions of 8 with benzoylformic acid resulted in the formation of hydroxyl-bridged dimer [N ∧C] 2Ir(μ-OH) 2Ir[C ∧N] 2 ( 33). According to X-ray analyses, Ir-to-Ir distances in the crystal cell increase from 6.86 Å for 10 to 13.31 Å for 33. The angle theta, which represents the twisting of two cyclometalated C–Ir–N planes relative to each other, varies from 97.5° for 21 to 90.76 for complex 28. OLED devices were fabricated from several Ir complexes and preliminary results are discussed.

The Reaction of (PPri3)2H2Cl2Ir With Phosphines: Crystal and Molecular Structures of mer-cis-(PMe2Ph)2(PPri3)-cis-Cl2HIrIII and mer-cis-(PMe2Ph)2(PPri3)-trans-Cl2HIrIII

Ambient temperature reactions of the complex (PPri3)2H2Cl2IrIV (1) with ethyl-substituted monodentate phosphine ligands are shown to yield different product types to those obtained both with methyl-substituted analogues and with phosphine itself. With the phosphines PH3 and PMe3-nPhn (n = 0, 1) there is spontaneous reaction to give the complexes mer-trans-(Ppri3)2(PR3)H-trans-Cl2IrIII, whereas with PEt3-nPhn (n = 0-2) the reaction yields mer-cis-(PR3)2(PPri3)H-trans-Cl2IrIII complexes. Under reflux the phosphines PMe3 and PMe2Ph also yield mer-cis-(PR3)2(PPri3)H-trans-Cl2IrIII complexes [PR3 = PMe3 (2), Pme2Ph (3)]. The differing course of the reactions of (1) with PMe3 and with PEt3 has permitted the synthesis of mer-(Pme3)-trans-(PPri3)(PEt3)H-trans-Cl2IrIII, the first example of an octahedral iridium complex containing three different monodentate phosphine ligands. All of the products obtained have been fully characterized by 31P and 1H n.m.r. spectroscopy. Crystal structure analyses of (3) and of its photoisomer mer-cis-(PMe2Ph)2(PPri3)H-cis-Cl2IrIII (4) have been carried out to permit comparison of the metal-ligand bonding in these complexes with that in their previously characterized, sterically less crowded, tris-PMe2Ph analogues. Summary data are as follows: (3), triclinic, Pī, a 13.414(1), b 12.062(1), c 9.077(1) Ǻ, α 79.53(1), β 88.05(1), γ 79.47(1)° [T 158�3 K], Z 2, R 0.022, Rw 0.032 (4822 reflections); (4), monoclinic, P21/n, a 19.694(1), b 15.972(1), c 9.548(1) Ǻ, β 101.45(1)° (T 293�2 K), Z 4, R 0.026, Rw 0.032 (5476 reflections). Both molecules exhibit distorted octahedral coordination of the metal atom and appreciably greater steric strain than in their (Pme2Ph)3HCl2IrIII analogues. Metal-ligand distances to the mutually trans Pme2Ph and PPri3 ligands are 2.322(1) and 2.372(1)Ǻ, respectively, for (3), and 2.359(1) and 2.406(1)Ǻ for (4), and suggest that the thermodynamically favoured cis-dichloro isomer (4) is the more strained. The preparations of the complexes (PCy3)2H2Cl2IrIV (1a) and (PCy3)2H2Br2IrIV (1b) (Cy = cyclohexyl), and their reactions with the same phosphines as used with (1), are also reported.

Migratory insertion reactions of indenyliridium dialkyls and alkyl and aryl hydrides

This paper reports the migratory insertion chemistry of indenyliridium complexes described in the companion paper. Complexes of general formula ({eta}{sup 5}-Ind)(PMe{sub 3})Ir(R)(R{prime}), where R = alkyl or aryl and R{prime} = alkyl, aryl, or hydride (4-6) react with dative ligands L such as tert-butylisocyanide and CO. These transformations lead to {eta}{sup 5} to {eta}{sup 1} isomerization of the indenyl ligand, giving octahedral iridium complexes of general formula ({eta}{sup 1}-Ind)(PMe{sub 3})(L){sub 2}Ir(R)(R{prime}) (8, 9, 11). Treatment of the methyl aryl and dimethyl {eta}{sup 1}-indenyl complexes 9a, 9d, and 9e with trimethylamine oxide removes CO, allowing the indenyl ligand to reestablish {eta}{sup 5}-coordination by inducing CO migratory insertion to give acyl complexes 10. Reaction of {eta}{sup 1}-indenyl aryl and methyl hydrides 6 (as well as the dihydride ({eta}{sup 5}-Ind)(PMe{sub 3})IrH{sub 2} (7)) with CO leads to reductive elimination of arene, methane, or H{sub 2} rather than migratory insertion, forming ({eta}{sup 1}-Ind)-(CO){sub 3}(PMe{sub 3})Ir (12) as the organometallic product. In contrast, treatment of methyl and aryl hydrides 6 with alkynes leads to the methyl vinyl complexes ({eta}{sup 5}-Ind)(PMe{sub 3})Ir(Me)(CR{double_prime}C(R{prime})(H)) (13) and reaction of 6a with ethylene gives the methyl ethyl complex ({eta}{sup 5}-Ind)(PMe{sub 3})Ir(Me)(Et) (14). Isotope labeling, stereochemical, and kinetic studies have beenmore » carried out on the insertion reaction of 6a with 3,3-dimethyl-1-butyne. The results of these experiments are most consistent with a mechanism involving initial reversible coordination of alkyne to the metal center (probably with concurrent {eta}{sup 5}-{eta}{sup 3} isomerization of the indenyl ligand) followed by irreversible migration of the metal-bound hydrogen to the tert-butyl-substituted carbon of the alkyne and then rapid recoordination of the indenyl group. 22 refs., 3 figs., 2 tabs.« less

Theory of E.P.R. in low-spin ferric haemoproteins

Difficulty is found in fitting experimental g values for low-spin ferric haemoproteins to formulae based on a pure t 2 5 configuration. This is discussed and it is shown that it is almost certainly mainly due to neglect of configuration interaction with excited t 2 4 e states, a mechanism which was originally discussed by Thornley [8] for octahedral iridium complexes.