Selective low-temperature syntheses of facial and meridional tris-cyclometalated iridium(III) complexes

We have developed a selective low-temperature synthesis of fac and mer tris-cyclometalated Ir(III) complexes. The chloro-bridged dimers [Ir(CwedgeN)2Cl]2 (CwedgeN = cyclometalating ligand) are cleaved in coordinating solvents like acetonitrile to give neutral Ir(CwedgeN)2(NCCH3)Cl species which in turn are reacted with AgPF6 to give hexafluorophosphate salts of the bis-acetonitrile species [Ir(CwedgeN)2(NCCH3)2]PF6 for CwedgeN = 2,2'-thienylpyridine (thpy) and 2-phenylpyridine (ppy). These bis-acetonitrile complexes are excellent starting materials for the synthesis of tris-Ir(III) complexes. The complexes of the general formula fac-Ir(CwedgeN)3 were synthesized with the ligands thpy and ppy at 100 degrees C in o-dichlorobenzene from the corresponding [Ir(CwedgeN)2(NCCH3)2]PF6 complexes. The reaction of [Ir(CwedgeN)2(NCCH3)2]PF6 with thpy at room temperature did not give the expected tris complex but instead gave [Ir(thpy)2(N,S-thpy)]PF6, with the third chelating ligand complexed through the sulfur atom of the thiophene ring. [Ir(thpy)2Cl]2, [Ir(ppy)2Cl]2, Ir(thpy)2(NCCH3)Cl, [Ir(thpy)2(NCCH3)2]PF6, [Ir(ppy)2(NCCH3)2]PF6, and [Ir(thpy)2(N,S-thpy)]PF6 were structurally characterized by X-ray crystallography. Additionally, hydroxy-bridged dimers, [Ir(CwedgeN)2(OH)]2, were synthesized as starting materials for the selective synthesis of mer-Ir(CwedgeN)3 complexes at 100 degrees C in o-dichlorobenzene. A mechanism is proposed that may account for the selectivity observed in the formation of the mer-Ir(CwedgeN)3 and fac-Ir(CwedgeN)3 isomers in previous studies and the studies presented here.     

Diastereoselective formation of chiral tris-cyclometalated iridium (III) complexes: characterization and photophysical properties

Chiral, facial tris-cyclometalated Ir(III) complexes, fac-Delta-Ir(pppy)(3), fac-Lambda-Ir(pppy)(3), fac-Lambda-IrL (where pppy is (8R,10R)-2-(2'-phenyl)-4,5-pinenopyridine and L is a tripodal ligand comprising three pppy moieties connected through a mesityl spacer) have been synthesized and characterized. In IrL, NMR and CD studies indicate that only one diastereomer is formed, with the Lambda configuration at the metal center, whereas enantiopure pppy yields the fac-Lambda- and the fac-Delta-stereoisomer in a ratio 2:3. fac-Lambda-IrL was structurally characterized using X-ray crystallography. The luminescence properties including CPL, of the three complexes and their sensitivity to dioxygen were examined.     

Photophysical and electrochemical properties of heteroleptic tris-cyclometalated iridium(III) complexes

Mixed (difluoro)phenylpyridine/(difluoro)phenylpyrazole tris-cyclometalated iridium complexes were prepared in order to study the effect of fluorination and the pyridine/pyrazole ratio on the emission and electrochemical properties. Increasing fluorination and replacement of pyridine by pyrazole both leads to a widening of the HOMO-LUMO gap and generally leads to a blue shift in emission.     

Synthesis of facial cyclometalated iridium(III) complexes triggered by tripodal ligands

The tripodal ligands composed of the 1,3,5-trisubstituted cyclohexyl moiety as a molecular scaffold and 2-phenylpyridyl moieties as a coordination site were designed. The homoleptic cyclometalated fac-Ir(C^N)(3) complexes could be obtained by the reaction of IrCl(3)·nH(2)O with the designed tripodal ligands. The single crystal X-ray structure determination confirmed the fac configuration and a distorted octahedral geometry with three intramolecular cyclometalated 2-phenylpyridyl ligands surrounding the iridium metal center. Also, the cyclohexyl scaffold was found to serve as a flexible scaffold to induce the fac configuration. The thus-obtained homoleptic cyclometalated fac-Ir(C^N)(3) complexes exhibited a broad emission band in the emission spectra at 298 K.     

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).     

Synthesis and characterization of half-sandwich iridium(III) and rhodium(III) complexes bearing organochalcogen ligands

Reactions of [Cp*M(μ-Cl)Cl]₂ (M = Ir, Rh; Cp* = η⁵-pentamethylcyclopentadienyl) with bi- or tri-dentate organochalcogen ligands Mbit (L1), Mbpit (L2), Mbbit (L3) and [Tm^Me]⁻ (L4) (Mbit = 1,1′-methylenebis(3-methyl-imidazole-2-thione); Mbpit = 1,1′-methylene bis (3-iso-propyl-imidazole-2-thione), Mbbit = 1,1′-methylene bis (3-tert-butyl-imidazole-2-thione)) and [Tm^Me]⁻ (Tm^Me = tris (2-mercapto-1-methylimidazolyl) borate) result in the formation of the 18-electron half-sandwich complexes [Cp*M(Mbit)Cl]Cl (M = Ir, 1a; M = Rh, 1b), [Cp*M(Mbpit)Cl]Cl (M = Ir, 2a; M = Rh, 2b), [Cp*M(Mbbit)Cl]Cl (M = Ir, 3a; M = Rh, 3b) and [Cp*M(Tm^Me)]Cl (M = Ir, 4a; M = Rh, 4b), respectively. All complexes have been characterized by elemental analysis, NMR and IR spectra. The molecular structures of 1a, 2b and 4a have been determined by X-ray crystallography.     

Highly efficient, selective, and general method for the preparation of meridional homo- and heteroleptic tris-cyclometalated iridium complexes

A highly efficient and general method based on transmetalation with an organozinc reagent is developed for selective preparation of homo- and heteroleptic meridional tris-cyclometalated iridium complexes. The molecular structure of mer-Ir(1-piq)2(ppy) (2) has been determined by a single-crystal X-ray diffraction analysis. The emission properties of a series of meridional complexes are reported.     

"Click" synthesis of heteroleptic tris-cyclometalated iridium(III) complexes: Cu(I) triazolide intermediates as transmetalating reagents

Efficient synthesis of heteroleptic tris-cyclometalated Ir(III) complexes mer-Ir(C(/\)N)(2)(trpy) (trpy = 2-(1H-[1,2,3]triazol-4-yl)pyridine) is achieved by using the Cu(I)-triazolide intermediates formed in "click" reactions as transmetalating reagents. Ligand preparation and cyclometalation of Ir(III) is accomplished in one pot. The robust nature of click chemistry provides opportunities to introduce different functional groups to the cyclometalated system, for example, alkyl, perfluoroalkyl, and aryl moieties. All of the meridional isomers show short-lived phosphorescence at room temperature, both in solution and in the solid state. DFT calculations indicates that the phosphorescence of mer-Ir(C(/\)N)(2)(trpy) is attributed to the (3)MLCT and (3)LC mixed excited states, also supported by the broad spectral shape and hypsochromic shift upon media rigidification. The luminescence efficiency and excited state lifetimes of the cyclometalated complexes can be tuned by varying the substituents on the triazole ring, while the emission color is mainly determined by the phenylpyridine-based ligands. Moreover, the trpy ligand can acquire the N(/\)N chelating mode under selective reaction conditions. mer-Ir(C(/\)N)(2)(trpy) complexes isomerize into cationic [Ir(C(/\)N)(2)(N(/\)N_trpy)](+) species instead of their fac isomers upon heating or UV radiation. This can be explained by the strong trans influence exerted by the phenyl groups. The weakened Ir-C(trpy) bonds are likely to be activated and protonated, leading to the switch of the trpy ligand to a thermodynamically more stable N(/\)N chelating mode.     

Synthesis and characterization of rhodium(III), iridium(III), ruthenium(III) and osmium(III) complexes containing sterically hindered heterocyclic ligands

Summary Some thiazolidine-2-thione and thiomorpholin-3-one complexes of rhodium(lll), iridium(III), ruthenium(III) and osmium(III) have been prepared and characterized by chemical analysis, conductivity measurements, room temperature magnetic moment studies, electronic, i.r. and far i.r. spectra and n.m.r. measurements. From the magnetic properties it was concluded that the above ligands form low-spin complexes with all the metal ions. The position and multiplicity of the metal-halogen stretching modes in the far-i.r. region have been extensively investigated and discussed; the results are particularly useful in distinguishing between themer- andfac-isomers in the octahedral compounds of the ML₃ X₃ type. The wavelengths of the principal electronic absorption peaks have been accounted for quantitatively in terms of the crystal field theory and the various parameters have been calculated. On the basis of the electronic spectra a trigonal bipyramidal geometry,D _3h, has been established for the Ru(tm)₂Cl₃ complex; the Ir(rm)₂Cl₃ · H₂O complex has also been prepared. It is penta-coordinated and a trigonal bipyramidal environment is suggested for the iridium(III) ion.     

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).     

Ruthenium(III) and iridium(III) complexes with nicotine

A new chloride-dimethylsulfoxide-ruthenium(III) complex with nicotine trans-[Ru^IIICl₄(DMSO)[H-(Nicotine)]] (1) and three related iridium(III) complexes; [H-(Nicotine)]trans-[Ir^IIICl₄(DMSO)₂] (2), trans-[Ir^IIICl₄(DMSO)[H-(Nicotine)]] (3) and mer-[Ir^IIICl₃(DMSO)(Nicotine)₂] (4) have been synthesized and characterized by spectroscopic techniques and by single crystal X-ray diffraction (1, 2, and 4). Protonated nicotine at pyrrolidine nitrogen is present in complexes 1 and 3 while two neutral nicotine ligands are observed in 4. In these three inner-sphere complexes coordination occurs through the pyridine nitrogen. Moreover, in the outer-sphere complex 2, an electrostatic interaction is observed between a cationic protonated nicotine at the pyrrolidine nitrogen and the anionic trans-[Ir^IIICl₄(DMSO)₂]^¯ complex.     

Rhodium(III) and iridium(III) complexes of thioarylazoimidazoles: Synthesis,structure, spectral characterization,electrochemistry and DFT calculation

[M(SRaaiNR′)Cl₃] (M = Rh(III), Ir(III) and SRaaiNR′ = 1-alkyl-2-{(o-thioalkyl)phenylazo}imidazole) complexes are described in this article. The single crystal X-ray structure of one of the complexes, [Rh(SMeaaiNEt)Cl₃] (3b), shows a tridentate chelation of SMeaaiNEt via N(imidazole), N(azo) and S(thioether) donor centres. Spectral characterization has been done by IR, UV–Vis and ¹H NMR data. The electronic structure, redox properties and spectra are well supported by DFT and TDDFT computation on the complexes.     

Bright electrochemiluminescence of iridium(III) complexes

Electrochemiluminescence (ECL) of four bright iridium(III) complexes containing aryltriazole cyclometallated ligands is reported. The ECL mechanisms, spectra and high efficiencies via annihilation and coreactant paths have been investigated.     

Electrochemiluminescence of cyclometalated iridium (III) complexes

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Synthesis and characterization of iridium(III) cyclometalated complexes with oligonucleotides: insights into redox reactions with DNA

Heteroleptic cyclometalated complexes of Ir(III) containing the dipyridophenazine ligand are synthesized through the direct introduction of a functionalized dipyridophenazine ligand onto a bis(dichloro)-bridged Ir(III) precusor and characterized by 1H NMR, mass spectrometry, as well as spectroscopic and electrochemical properties. The excited state of the Ir(III) complexes have sufficient driving force to oxidize purines and to reduce pyrimidine nucleobases. Luminescence and EPR measurements of the Ir(III) complex with an unmodified dppz bound to DNA show the formation of a guanine radical upon irradiation, resulting from an oxidative photoinduced electron-transfer process. Evidence is also obtained indirectly for reductive photoinduced electron transfer from the excited complex to the thymine base in DNA. We have also utilized cyclopropylamine-substituted nucleosides as ultrafast kinetic traps to report transient charge occupancy in oligonucleotides when DNA is irradiated in the presence of noncovalently bound complexes. These experiments establish that the derivatized Ir(III) complexes, with photoactivation, can trigger the oxidation of guanine and the reduction of cytosine.     

Synthesis and characterization of phosphorescent cyclometalated iridium complexes

The preparation, photophysics, and solid state structures of octahedral organometallic Ir complexes with several different cyclometalated ligands are reported. IrCl3.nH2O cleanly cyclometalates a number of different compounds (i.e., 2-phenylpyridine, 2-(p-tolyl)pyridine, benzoquinoline, 2-phenylbenzothiazole, 2-(1-naphthyl)benzothiazole, and 2-phenylquinoline), forming the corresponding chloride-bridged dimers, CwedgeN2Ir(mu-Cl)2IrCwedgeN2 (CwedgeNis a cyclometalated ligand) in good yield. These chloride-bridged dimers react with acetyl acetone (acacH) and other bidentate, monoanionic ligands such as picolinic acid (picH) and N-methylsalicylimine (salH), to give monomeric CwedgeN2Ir(LX) complexes (LX = acac, pic, sal). The emission spectra of these complexes are largely governed by the nature of the cyclometalating ligand, leading to lambda(max) values from 510 to 606 nm for the complexes reported here. The strong spin-orbit coupling of iridium mixes the formally forbidden 3MLCT and 3pi-pi* transitions with the allowed 1MLCT, leading to a strong phosphorescence with good quantum efficiencies (0.1-0.4) and room temperature lifetimes in the microsecond regime. The emission spectra of the CwedgeN2Ir(LX) complexes are surprisingly similar to the fac-IrCwedgeN3 complex of the same ligand, even though the structures of the two complexes are markedly different. The crystal structures of two of the CwedgeN2Ir(acac) complexes (i.e., CwedgeN = ppy and tpy) have been determined. Both complexes show cis-C,C', trans-N,N' disposition of the two cyclometalated ligands, similar to the structures reported for other complexes with a "CwedgeN2Ir" fragment. NMR data (1H and 13C) support a similar structure for all of the CwedgeN2Ir(LX) complexes. Close intermolecular contacts in both (ppy)2Ir(acac) and (tpy)2Ir(acac) lead to significantly red shifted emission spectra for crystalline samples of the ppy and tpy complexes relative to their solution spectra.     

Voltammetric behaviour of dichlorobis(2,2′-bipyridine) iridium(III) and dichlorobis(1,10-phenanthroline) iridium(III) complexes

The electrochemical behaviour of [Ir(bipy)₂Cl₂]⁺ and [Ir(phen)₂Cl₂]⁺ (bipy = 2,2′-bipyridine; phen = 1,10-phenanthroline) has been investigated in N,N-dimethylformamide (DMF). In potential sweep voltammetry [Ir(bipy)₂Cl₂]⁺ exhibits four reduction peaks. The first two processes involve one electron and are reversible in our conditions. The third reduction step is irreversible and has been attributed to the addition of three electrons to [Ir(bipy)₂Cl₂]⁺ followed by fast liberation of ligands. The data obtained for the fourth peak are consistent with a one-electron reversible process. The behaviour of [Ir(phen)₂Cl₂]⁺ is more complicated than that found for the bipy complex. In this case in fact, in addition to the four peaks observed in the case of the bipy complex, two other peaks appear. The latter have been attributed to the reduction of phen molecules liberated by the reduction of the complex. A qualitative MO discussion of the nature of the molecular levels involved in the reduction processes is also reported.     

Studies on ruthenium(III), rhodium(III) and iridium(III) complexes of indazoles

Summary New complexes of the general formula M(L)₃Cl₃ and M(5-AInz)₂Cl₃ · n H₂O (where M = Ru^III, Rh^III and Ir^III; L = indazole and 5-nitroindazole; n=1–2) have been synthesized and characterised by elemental analysis, molar conductance, magnetic susceptibility and i.r. and electronic spectral measurements. All the complexes are covalent and apparently have an octahedral geometry. The ligands are monocoordinated through the pyrrole nitrogen. From the far i.r. spectra amer configuration has been assigned to the indazole and 5-nitroindazole complexes.     

Highly efficient phosphorescent iridium (III) diazine complexes for OLEDs: Different photophysical property between iridium (III) pyrazine complex and iridium (III) pyrimidine complex

The synthesis and luminescence of four new iridium (III) diazine complexes (1-4) were investigated. HOMO and LUMO energy levels of the complexes were estimated according to the electrochemical performance and the UV-Vis absorption spectra, showing the pyrimidine complexes have a larger increase for the LUMO than the HOMO orbital in comparison with the pyrazine complexes. Several high-efficiency yellow and green OLEDs based on phosphorescent iridium (III) diazine complexes were obtained. The devices emitting yellow light based on 1 with turn-on voltage of 4.1 V exhibited an external quantum efficiency of 13.2% (power efficiency 20.3 lm/W), a maximum current efficiency of 37.3 cd/A. The electroluminescent performance for the green iridium pyrimidine complex of 3 is comparable to that of the iridium pyridine complex (PPY)₂Ir(acac) (PPY = 2-phenylpyridine), which is among the best reported.