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

Abstract

1-Phenyl-3-(1-phenyl-1-(pyridin-2-yl)ethyl)isoquinoline (H 2 MeL) 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(κ 4 - cis - C , C ′- cis - N , N ′-MeL)Cl(CO) and the acetylacetonate compound Ir(κ 4 - 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(κ 4 - cis - C , C ′- cis - N , N ′-MeL){κ 2 - C , N -(C 6 H 4 -py)}, mer -Ir(κ 4 - cis - C , C ′- cis - N , N ′-MeL){κ 2 - C , N -(C 6 H 3 R-py)}, and mer -Ir(κ 4 - trans - C , C ′- cis - N , N ′-MeL){κ 2 - C , N -(C 6 HR-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(κ 4 - 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/cm 2 .

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

“…Iridium(III) emitters with nonplanar tetradentate ligands are uncommon, 24 particularly those bearing different bidentate moieties, 25 and in special when the donor atoms of such moieties are different in identity and nature, as is occurring in 9 and 10 . Furthermore, in contrast to our new compounds, such ligands are generated from the coordination of organic molecules previously prepared.…”

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

“…This lack of structural diversity is a consequence of the retention of the stereochemistry of the mononuclear fragments of the dimers [Ir­(μ-Cl)­(3b) 2 ] 2 during the preparation reactions of the emitters. In the search for emitters with a cis disposition of the heterocycles, some linkers have been designed to tie them, but the rigidity of the resulting organic molecules greatly complicates the reactions usually employed for this type of synthesis . Thus, the stabilization of dimers [Ir­(μ-X)­(3b) 2 ] 2 with a cis disposition of the heterocycles of the 3b ligands is a target of prominent importance for the field.…”

Stepwise Access of Emissive Ir(III) Complexes Bearing a Multi-Dentate Heteroaromatic Chelate: Fundamentals and Applications

“…Alternatively, the non-planar tetradentate chelates, such as 2,2′-(1-(6-(3-trifluoromethyl-1 H -pyrazol-5-yl)­pyridin-2-yl)­ethane-1,1-diyl)­dipyridine and 2-phenyl-6-(1-phenyl-1-(pyridin-2-yl)­ethyl)­pyridine (e.g., N4-H and N2C2-H 2 of Chart ), , are expected to occupy three facial and one adjacent sites of the central Ir­(III) atom. Hence, unlike its planar counterpart, these tetradentate chelates would leave two cis-coordination sites for other incoming auxiliaries in completing the demanded octahedral structure. , …”

“…35 Alternatively, the non-planar tetradentate chelates, such as 2,2′-(1-(6-(3-trifluoromethyl-1H-pyrazol-5-yl)pyridin-2-yl)ethane-1,1-diyl)dipyridine and 2-phenyl-6-(1-phenyl-1-(pyridin-2-yl)ethyl)pyridine (e.g., N4-H and N2C2-H 2 of Chart 2), 36,37 cis-coordination sites for other incoming auxiliaries in completing the demanded octahedral structure. 36,38 Herein, we present the synthesis of Ir(III) complexes composed of tetradentate chelate LnH 2 , which showed structural designs relevant to its predecessors N4-H and N2C2-H 2 , c.f., Chart 2. This class of LnH 2 chelate is expected to impose two combined features: the phenyl appendage can be engaged in cyclometalation rather than simple coordination as expected for the pyridyl appendage.…”