Suzuki–Miyaura Cross-Coupling Reactions for Increasing the Efficiency of Tris-Heteroleptic Iridium(III) Emitters

C-H, N-H, and O-H Bond Activations to Prepare Phosphorescent Hydride-Iridium(III)-Phosphine Emitters with Photocatalytic Achievement in C-C Coupling Reactions

Complex IrH5(PiPr3)2 (1) activates two different σ-bonds of 3-phenoxy-1-phenylisoquinoline, 2-(1H-benzimidazol-2-yl)-6-phenylpyridine, 2-(1H-indol-2-yl)-6-phenylpyridine, 2-(2-hydroxyphenyl)-6-phenylpyridine, N-(2-hydroxyphenyl)-N'-phenylimidazolylidene, and 1,3-di(2-pyridyl)-4,6-dimethylbenzene to give IrH{κ3-C,N,C-[C6H4-isoqui-O-C6H4]}(PiPr3)2 (2), IrH{κ3-N,N,C-[NBzim-py-C6H4]}(PiPr3)2 (3), IrH{κ3-N,N,C-[Ind-py-C6H4]}(PiPr3)2 (4), IrH{κ3-C,N,O-[C6H4-py-C6H4O]}(PiPr3)2 (5), IrH{κ3-C,C,O-[C6H4-Im-C6H4O]}(PiPr3)2 (6), and IrH{κ3-N,C,C-[py-C6HMe2-C5H3N]}(PiPr3)2 (7), respectively. The activations are sequential, with the second generally being the slowest. Accordingly, dihydride intermediates IrH2{κ2-C,N-[C6H4-isoqui-O-C6H5]}(PiPr3)2 (2d), IrH2{κ2-N,N-[NBzim-py-C6H5]}(PiPr3)2 (3d), IrH2{κ2-N,N-[Ind-py-C6H5]}(PiPr3)2 (4d), and IrH2{κ2-N,C-[py-C6HMe2-py]}(PiPr3)2 (7d) were characterized spectroscopically. Complexes 3 and 5 are green phosphorescent emitters upon photoexcitation, exhibiting good absorption over a wide range of wavelengths, emission quantum yields about 0.70 in solution, long enough lifetimes (10-17 μs), and reversible electrochemical behavior. In agreement with these features, complex 3 promotes the photocatalytic α-amino C(sp3)-H arylation of N,N-dimethylaniline and N-phenylpiperidine with 1,4-dicyanobenzene and 4-cyanopyridine under blue LED light irradiation. The C-C coupling products are isolated in high yields with only 2 mol % of photocatalyst after 24 h.

Two Synthetic Tools to Deepen the Understanding of the Influence of Stereochemistry on the Properties of Iridium(III) Heteroleptic Emitters

Two complementary procedures are presented to prepare cis-pyridyl-iridium(III) emitters of the class [3b+3b+3b'] with two orthometalated ligands of the 2-phenylpyridine type (3b) and a third ligand (3b'). They allowed to obtain four emitters of this class and to compare their properties with those of the trans-pyridyl isomers. The finding starts from IrH5(PiPr3)2, which reacts with 2-(p-tolyl)pyridine to give fac-[Ir{κ2-C,N-[C6MeH3-py]}3] with an almost quantitative yield. Stirring the latter in the appropriate amount of a saturated solution of HCl in toluene results in the cis-pyridyl adduct IrCl{κ2-C,N-[C6MeH3-py]}2{κ1-Cl-[Cl-H-py-C6MeH4]} stabilized with p-tolylpyridinium chloride, which can also be transformed into dimer cis-[Ir(μ-OH){κ2-C,N-[C6MeH3-py]}2]2. Adduct IrCl{κ2-C,N-[C6MeH3-py]}2{κ1-Cl-[Cl-H-py-C6MeH4]} directly generates cis-[Ir{κ2-C,N-[C6MeH3-py]}2{κ2-C,N-[C6H4-Isoqui]}] and cis-[Ir{κ2-C,N-[C6MeH3-py]}2{κ2-C,N-[C6H4-py]}] by transmetalation from Li[2-(isoquinolin-1-yl)-C6H4] and Li[py-2-C6H4]. Dimer cis-[Ir(μ-OH){κ2-C,N-[C6MeH3-py]}2]2 is also a useful starting complex when the precursor molecule of 3b' has a fairly acidic hydrogen atom, suitable for removal by hydroxide groups. Thus, its reactions with 2-picolinic acid and acetylacetone (Hacac) lead to cis-Ir{κ2-C,N-[C6MeH3-py]}2{κ2-O,N-[OC(O)-py]} and cis-Ir{κ2-C,N-[C6MeH3-py]}2{κ2-O,O-[acac]}. The stereochemistry of the emitter does not significantly influence the emission wavelengths. On the contrary, its efficiency is highly dependent on and associated with the stability of the isomer. The more stable isomer shows a higher quantum yield and color purity.

High-yielding synthesis of cyclometallated iridium complexes with hydrogen bond-rich ligands

A library of cyclometallated iridium(III) complexes with a strong H-bonding motif in their ancillary ligand was synthesized, characterized and their photophysical properties measured. Demonstrated herein is a general synthetic high yield procedure for these compounds. We ascribe these yields to the use of an intermediary primer ligand. This de novo strategy circumnavigates the standard synthetic issues of H-bond rich ligand precursors (self-aggregation and poor solubility in organic solvents).

Ligand Design and Preparation, Photophysical Properties, and Device Performance of an Encapsulated-Type Pseudo-Tris(heteroleptic) Iridium(III) Emitter

The organic molecule 2-(1-phenyl-1-(pyridin-2-yl)ethyl)-6-(3-(1-phenyl-1-(pyridin-2-yl)ethyl)phenyl)pyridine (H3L) has been designed, prepared, and employed to synthesize the encapsulated-type pseudo-tris(heteroleptic) iridium(III) derivative Ir(κ6-fac-C,C',C″-fac-N,N',N″-L). Its formation takes place as a result of the coordination of the heterocycles to the iridium center and the ortho-CH bond activation of the phenyl groups. Dimer [Ir(μ-Cl)(η4-COD)]2 is suitable for the preparation of this compound of class [Ir(9h)] (9h = 9-electron donor hexadentate ligand), but Ir(acac)3 is a more appropriate starting material. Reactions were carried out in 1-phenylethanol. In contrast to the latter, 2-ethoxyethanol promotes the metal carbonylation, inhibiting the full coordination of H3L. Complex Ir(κ6-fac-C,C',C″-fac-N,N',N″-L) is a phosphorescent emitter upon photoexcitation, which has been employed to fabricate four yellow emitting devices with 1931 CIE (x:y) ∼ (0.52:0.48) and a maximum wavelength at 576 nm. These devices display luminous efficacies, external quantum efficiencies, and power efficacies at 600 cd m-2, which lie in the ranges 21.4-31.3 cd A-1, 7.8-11.3%, and 10.2-14.1 lm W1-, respectively, depending on the device configuration.

Palladium immobilized on guanidine functionalized magnetic nanoparticles: a highly effective and recoverable catalyst for ultrasound aided Suzuki–Miyaura cross-coupling reactions

The Fe3O4@SiO2-TCT-Gua-Pd catalyst anchored with guanidine moiety on Fe3O4 nanoparticles was synthesised for Suzuki–Miyaura cross coupling reaction.

Acetylides for the Preparation of Phosphorescent Iridium(III) Complexes: Iridaoxazoles and Their Transformation into Hydroxycarbenes and N,C(sp3),C(sp2),O-Tetradentate Ligands

The preparation of three families of phosphorescent iridium(III) emitters, including iridaoxazole derivatives, hydroxycarbene compounds, and N,C(sp³),C(sp²),O-tetradentate containing complexes, has been performed starting from dimers cis-[Ir(μ²-η²-C≡CR){κ²-C,N-(MeC₆H₃-py)}₂]₂ (R = ^tBu (1a), Ph (1b)). Reactions of 1a with benzamide, acetamide, phenylacetamide, and trifluoroacetamide lead to the iridaoxazole derivatives Ir{κ²-C,O-[C(CH₂^tBu)NC(R)O]}{κ²-C,N-(MeC₆H₃-py)}₂ (R = Ph (2), Me (3), CH₂Ph (4), CF₃ (5)) with a fac disposition of carbons and heteroatoms around the metal center. In 2-methyltetrahydrofuran and dichloromethane, water promotes the C-N rupture of the IrC-N bond of the iridaoxazole ring of 3-5 to form amidate-iridium(III)-hydroxycarbene derivatives Ir{κ¹-N-[NHC(R)O]}{κ²-C,N-(MeC₆H₃-py)}₂{═C(CH₂^tBu)OH} (R = Me (6), CH₂Ph (7), CF₃ (8)). In contrast to 1a, dimer 1b reacts with benzamide and acetamide to give Ir{κ⁴-N,C,C',O-[py-MeC₆H₃-C(CH₂-C₆H₄)NHC(R)O]}{κ²-C,N-(MeC₆H₃-py)}(R = Ph (9), Me (10)), which bear a N,C(sp³),C(sp²),O-tetradentate ligand resulting from a triple coupling (an alkynyl ligand, an amide, and a coordinated aryl group) and a C-H bond activation at the metal coordination sphere. Complexes 2-4 and 6-10 are emissive upon photoexcitation, in orange (2-4), green (6-8), and yellow (9 and 10) regions, with quantum yields between low and moderate (0.01-0.50) and short lifetimes (0.2-9.0 μs).

Divergent Approach for Tris-Heteroleptic Cyclometalated Iridium Complexes Using Triisopropylsilylethynyl-Substituted Synthons

Bis-heteroleptic cyclometalated iridium complexes of the form Ir(L^a)₂(acac), where L^a is a substituted 2-phenylpyridine derivative and acac is an acetylacetonato ligand, are a useful class of luminescent organometallic complexes for a range of applications. Related tris-heteroleptic complexes of the form Ir(L^a)(L^b)(acac) offer the potential advantage of greater functionality through the use of two different cyclometalated ligands but are, in general, more difficult to obtain. We report the synthesis of divergent bis- and tris-heteroleptic triisopropylsilylethynyl-substituted intermediate complexes that can be diversified using a “chemistry-on-the-complex” approach. We demonstrate the methodology through one-pot deprotection and Sonogashira cross-coupling of the intermediate complexes with para-R-aryliodides (R = H, SMe, and CN). The photophysical and electrochemical behaviors of the resultant bis- and tris-heteroleptic complexes are compared, and it is shown that the tris-heteroleptic complexes exhibit subtly different emission and redox properties to the bis-heteroleptic complexes, such as further red-shifted emission maxima and lower extinction coefficients, which can be attributed to the reduced symmetry. It is demonstrated, supported by DFT and time-dependent DFT calculations, that the charge-transfer character of the emission can be altered via variation of the terminal substituent; the introduction of an electron-withdrawing cyano group in the terminal position leads to a significant red shift, while the introduction of an SMe group can substantially increase the emission quantum yield. Most notably, this convenient synthetic approach reduces the need to perform the often challenging isolation of tris-heteroleptic complexes to a single divergent intermediate, which will simplify access to families of complexes of the form Ir(L^a)(L^b)(acac).

Alkynyl Ligands as Building Blocks for the Preparation of Phosphorescent Iridium(III) Emitters: Alternative Synthetic Precursors and Procedures

Alkynyl ligands stabilize dimers [Ir(μ-X)(3b)₂]₂ with a cis disposition of the heterocycles of the 3b ligands, in contrast to chloride. Thus, the complexes of this class—cis-[Ir(μ₂-η²-C≡CPh){κ²-C,N-(C₆H₄-Isoqui)}₂]₂ (Isoqui = isoquinoline) and cis-[Ir(μ₂-η²-C≡CR){κ²-C,N-(MeC₆H₃-py)}₂]₂ (R = Ph, ^tBu)—have been prepared in high yields, starting from the dihydroxo-bridged dimers trans-[Ir(μ-OH){κ²-C,N-(C₆H₄-Isoqui)}₂]₂ and trans-[Ir(μ-OH){κ²-C,N-(MeC₆H₃-py)}₂]₂ and terminal alkynes. Subsequently, the acetylide ligands have been employed as building blocks to prepare the orange and green iridium(III) phosphorescent emitters, Ir{κ²-C,N-[C(CH₂Ph)Npy]}{κ²-C,N-(C₆H₄-Isoqui)}₂ and Ir{κ²-C,N-[C(CH₂R)Npy]}{κ²-C,N-(MeC₆H₃-py)}₂ (R = Ph, ^tBu), respectively, with an octahedral structure of fac carbon and nitrogen atoms. The green emitter Ir{κ²-C,N-[C(CH₂^tBu)Npy]}{κ²-C,N-(MeC₆H₃-py)}₂ reaches 100% of quantum yield in both the poly(methyl methacrylate) (PMMA) film and 2-MeTHF at room temperature. In organic light-emitting diode (OLED) devices, it demonstrates very saturated green emission at a peak wavelength of 500 nm, with an external quantum efficiency (EQE) of over 12% or luminous efficacy of 30.7 cd/A.

Acetylide ligands have been employed as building blocks to prepare orange and green iridium(III) phosphorescent emitters, with an octahedral structure of fac carbon and nitrogen atoms. In OLED devices, the emitter Ir{κ²-C,N-[C(CH₂^tBu)Npy]}{κ²-C,N-(MeC₆H₃-py)}₂ demonstrates very saturated green emission at a peak wavelength of 500 nm, with a luminous efficacy of 30.7 cd/A.

Phosphorescent Ir(III) complexes derived from purine nucleobases

We report the preparation and the study of new types of neutral and cationic phosphorescent heteroleptic Ir(III) complexes derived from 6-phenylpurine nucleosides and nucleotides. Neutral complexes of general formula Ir(C^N)₂(acac) 7, and 8a-c (HC^N = 9-substituted-6-phenyl purine) are orange-red emissive upon photoexcitation, with short lifetimes and good quantum yields (0.42-0.65) in both PMMA films and 2-MeTHF at room temperature. In turn, cationic complexes [Ir(C^N)₂(dtb-bpy)][PF₆] 9, 12a and 12c (dtb-bpy = 4,4'-di-tert-butyl-2,2'-dipyridine) are yellow-green emitters with moderate quantum yields (0.24-0.32).

Pseudo-Tris(heteroleptic) Red Phosphorescent Iridium(III) Complexes Bearing a Dianionic C,N,C',N'-Tetradentate Ligand

1-Phenyl-3-(1-phenyl-1-(pyridin-2-yl)ethyl)isoquinoline (H₂MeL) has been prepared by Pd(N-XantPhos)-catalyzed “deprotonative cross-coupling processes” to synthesize new phosphorescent red iridium(III) emitters (601–732 nm), including the carbonyl derivative Ir(κ⁴-cis-C,C′-cis-N,N′-MeL)Cl(CO) and the acetylacetonate compound Ir(κ⁴-cis-C,C′-cis-N,N′-MeL)(acac). The tetradentate 6e-donor ligand (6tt′) of these complexes is formed by two different bidentate units, namely, an orthometalated 2-phenylisoquinoline and an orthometalated 2-benzylpyridine. The link between the bidentate units reduces the number of possible stereoisomers of the structures [6tt′ + 3b] (3b = bidentate 3e-donor ligand), with respect to a [3b + 3b′ + 3b″] emitter containing three free bidentate units, and it permits a noticeable stereocontrol. Thus, the isomers fac-Ir(κ⁴-cis-C,C′-cis-N,N′-MeL){κ²-C,N-(C₆H₄-py)}, mer-Ir(κ⁴-cis-C,C′-cis-N,N′-MeL){κ²-C,N-(C₆H₃R-py)}, and mer-Ir(κ⁴-trans-C,C′-cis-N,N′-MeL){κ²-C,N-(C₆HR-py)} (R = H, Me) have also been selectively obtained. The new emitters display short lifetimes (0.7–4.6 μs) and quantum yields in a doped poly(methyl methacrylate) film at 5 wt % and 2-methyltetrahydrofuran at room temperature between 0.08 and 0.58. The acetylacetonate complex Ir(κ⁴-cis-C,C′-cis-N,N′-MeL)(acac) has been used as a dopant for a red PhOLED device with an electroluminescence λ_max of 672 nm and an external quantum efficiency of 3.4% at 10 mA/cm².

The proligand 1-phenyl-3-(1-phenyl-1-(pyridine-2-yl)ethyl)isoquinoline is used to generate a new family of neutral phosphorescent red iridium(III) emitters containing a tetradentate ligand, formed by two different bidentate units, and a third bidentate ligand with a good stereocontrol of the resulting [6tt′ + 3b] products. One of the new emitters has been used in the fabrication of an OLED device.

Palladium-Catalyzed C-H Bond Arylation of Cyclometalated Difluorinated 2-Arylisoquinolinyl Iridium(III) Complexes

The utility of C-H bond functionalization of metalated ligands for the elaboration of aryl-functionalized difluorinated-1-arylisoquinolinyl Ir(III) complexes has been explored. Bis[(3,5-difluorophenyl)isoquinolinyl](2,2,6,6-tetramethyl-3,5-heptanedionato) iridium(III) undergoes Pd-catalyzed C-H bond arylation with aryl bromides. The reaction regioselectively occurred at the C-H bond flanked by the two fluorine atoms of the difluoroaryl unit, and on both cyclometalated ligands. This post-functionalization gives a straightforward access to modified complexes in only one manipulation and allows to introduce thermally sensitive functional groups, such as trifluoromethyl, nitrile, benzoyl, or ester. The X-ray crystallography, photophysical, and electrochemical properties of the diarylated complexes were investigated. Whatever the nature of the incorporated substituted aryl groups is, all obtained complexes emit red phosphorescence (622-632 nm) with similar lifetimes (1.9-2 μs).

Insertion of Unsaturated C-C Bonds into the O-H Bond of an Iridium(III)-Hydroxo Complex: Formation of Phosphorescent Emitters with an Asymmetrical β-Diketonate Ligand

A synthetic methodology to prepare iridium(III) emitters of the class [3b+3b+3b'] with two ortho-metalated 1-phenylisoquinolines and an asymmetrical β-diketonate has been discovered. The abstraction of the chloride ligands of the dimer [Ir(μ-Cl){κ²-C,N-(C₆H₄-isoqui)}₂]₂ (1, C₆H₅-isoqui = 1-phenylisoquinoline) with AgBF₄ in acetone and the subsequent addition of water to the resulting solution affords the water solvate mononuclear complex [Ir{κ²-C,N-(C₆H₄-isoqui)}₂(H₂O)₂]BF₄ (2), which reacts with KOH to give the dihydroxo-bridged dimer [Ir(μ-OH){κ²-C,N-(C₆H₄-isoqui)}₂]₂ (3). Treatment of the latter with dimethyl acetylenedicarboxylate leads to Ir{κ²-C,N-(C₆H₄-isoqui)}₂{κ²-O,O-[OC(CO₂CH₃)CHC(OCH₃)O]} (4), as a result of the anti-addition of the O-H bond of a mononuclear [Ir(OH){κ²-C,N-(C₆H₄-isoqui)}₂] fragment to the C-C triple bond of the alkyne and the coordination of one of the carboxylate substituents to the metal center. Complex 3 also reacts with α,β-unsaturated ketones. The reaction with 3-(4-methylphenyl)-1-phenylprop-2-en-1-one affords Ir{κ²-C,N-(C₆H₄-isoqui)}₂{κ²-O,O-[OC(C₆H₅)CHC(p-C₆H₄Me)O]} (5), whereas methyl vinyl ketone gives a mixture of Ir{κ²-C,N-(C₆H₄-isoqui)}₂{κ²-O,O-[OC(CH₃)CHCHO]} (6) and Ir{κ²-C,N-(C₆H₄-isoqui)}₂{κ²-O,O-[OC(CH₃)CHC(CH═CH₂)O]} (7). Complexes 5 and 6 are the result of the addition of the O-H bond of the mononuclear [Ir(OH){κ²-C,N-(C₆H₄-isoqui)}₂] fragment to the C-C double bond of the α,β-unsaturated ketones and the coordination of the carbonyl group to the iridium center, to generate O,O-chelates which lose molecular hydrogen to aromatize into the asymmetrical β-diketonate ligands. Complexes 4-7 are phosphorescent emitters in the red spectral region (599-672 nm) in doped poly(methyl methacrylate) (PMMA) film at 5 wt % at room temperature and 2-methyltetrahydrofuran at room temperature and 77 K. They display short lifetimes (0.8-2.5 μs) and quantum yields in both doped PMMA films and in 2-methyltetrahydrofuran at room temperature depending on the substituents of the β-diketonate: about 0.6-0.5 for 4 and 6 and ca. 0.35 for 5 and 7.