Preparation of Tris-Heteroleptic Iridium(III) Complexes Containing a Cyclometalated Aryl-N-Heterocyclic Carbene Ligand

Abstract

A new class of phosphorescent tris-heteroleptic iridium(III) complexes has been discovered. The addition of PhMeImAgI (PhMeIm = 1-phenyl-3-methylimidazolylidene) to the dimer [Ir(μ-Cl)(COD)] (1; COD = 1,5-cyclooctadiene) affords IrCl(COD)(PhMeIm) (2), which reacts with 1-phenylisoquinoline, 2-phenylpyridine, and 2-(2,4-difluorophenyl)pyridine to give the respective dimers [Ir(μ-Cl){κ- C, C-(CH-ImMe)}{κ- C, N-(CH-isoqui)}] (3), [Ir(μ-Cl){κ- C, C-(CH-ImMe)}{κ- C, N-(CH-py)}] (4), and [Ir(μ-Cl){κ- C, C-(CH-ImMe)}{κ- C, N-(CFH-py)}] (5), as a result of the N-heterocyclic carbene (NHC)- and N-heterocycle-supported o-CH bond activation of the aryl substituents and the hydrogenation of a C-C double bond of the coordinated diene. In solution, these dimers exist as a mixture of isomers a (Im trans to N) and b (Im trans to Cl), which lie in a dynamic equilibrium. The treatment of 3-5 with Kacac (acac = acetylacetonate) yields isomers a (Im trans to N) and b (Im trans to O) of Ir{κ- C, C-(CH-ImMe)}{κ- C, N-(CH-isoqui)}(κ- O, O-acac) (6a and 6b), Ir{κ- C, C-(CH-ImMe)}{κ- C, N-(CH-py)}(κ- O, O-acac) (7a and 7b), and Ir{κ- C, C-(CH-ImMe)}{κ- C, N-(CFH-py)}(κ- O, O-acac) (8a and 8b), which were separated by column chromatography. The treatment of 6a with HX in acetone-water produces the protonation of the acac ligand and the formation of the bis(aquo) complex [Ir{κ- C, C-(CH-ImMe)}{κ- C, N-(CH-isoqui)}(HO)]X [X = BF (9a[BF]), OTf (9a[OTf])]. The salt 9a[BF] reacts with 2-(2-pinacolborylphenyl)-5-methylpyridine in the presence of 40 equiv of KPO to afford Ir{κ- C, C-(CH-ImMe)}{κ- C, N-(CH-isoqui)}{κ- C, N-(CH-Mepy)} (10a). Complexes 6a, 6b, 7a, 7b, 8a, 8b, and 10a are phosphorescent emitters (λ = 465-655 nm), which display short lifetimes in the range of 0.2-5.6 μs. They show high quantum yields both in doped poly(methyl methacrylate) films (0.34-0.87) and in 2-methyltetrahydrofuran at room temperature (0.40-0.93). From the point of view of their applicability to the fabrication of organic-light-emitting-diode devices, a notable improvement with regard to those containing two cyclometalated C,N ligands is achieved. The introduction of the cyclometalated aryl-NHC group allows one to reach a brightness of 1000 cd/m at a lower voltage and appears to give rise to higher luminous efficacy and power efficacy.

Luminescent Platinum(IV) Complexes Bearing Cyclometalated 1,2,3‐Triazolylidene and Bi‐ or Terdentate 2,6‐Diarylpyridine Ligands

“…[42,43] We anticipated that the donor properties of the triazolylidene moiety would benefit the emission efficiencies of cyclometalatedP t IV complexes by increasing the energy of deactivating excited states of LMCT character to ag reater extent than in the case of 2-arylpyridines. Cyclometalating aryl-NHC ligands have previously been employed for the synthesis of luminescentc omplexes of Ir III , [44][45][46][47][48][49][50][51][52] Pt II , [53][54][55][56] and Au III [57] with enhanced emission properties, often as non-chromophorics upporting ligands. However, most of them are normal 2-imidazolylidene-typea ryl-NHCs, whereas mesoionic aryl-NHCs have only been employed to prepare a limited number of luminescent Pt II complexeso ft he type [Pt(C^C*)(O^O)] (O^O = b-diketonate).…”

C1‐Symmetric [Ir(C^N1)(C^N2)(O^O)]‐Tris‐Heteroleptic Iridium(III)‐Complexes with the Preferentially Horizontal Orientation for High‐Performance Near‐Infrared Organic Light‐Emitting Diodes

“…Moreover, different from the one set of proton signals (Figure S2, Supporting Information) of the ( acac ) − in the C 2 ‐symmetric [Ir(C^N 1 ) 2 (O^O)]/[Ir(C^N 2 ) 2 (O^O)], the H atoms on the two ‐CH 3 groups in every ( acac ) − ancillary ligand were split into two sets of singlet signals, peaking at 1.86 and 1.76 ppm for 1 , 1.74 and 1.68 ppm for 2 or 1.73 and 1.61 ppm for 3 , respectively, indicating the desirable destruction of structural symmetry. [ 15–19 ] The C 1 ‐symmetric [Ir(C^N 1 )(C^N 2 )(O^O)]‐ tris ‐heteroleptic character of the representative Ir(III)‐complex 2 was further confirmed by its X‐ray crystallographic analysis (Tables S1 and S2, Supporting Information). As depicted in Figure , one ( iqbt ) − ligand, one ( ppy ) − ligand with the similar C^N chelation (C11^N1 or C18^N2) mode and one ( acac ) − ancillary ligand with the O^O‐chelate (O1^O2) mode coordinate to one Ir(III)‐center in a distorted octahedral geometry.…”

“…[ 14 ] In light of the transformation [ 15 ] of the 1 T nature in the C 1 ‐symmetric tris ‐heteroleptic Ir(III)‐complex composed of an Ir(III) ion and three different ligands, it is of notable interest on expanding that novel molecule‐engineered strategy to Ir(III)‐complex‐based NIR‐emitters, which should fill in the blank after previously reported NIR‐emissive [Ir(C^N) 3 ]‐ [ 8 ] and [Ir(C^N) 2 (L^X)]‐heteroleptic [ 9–11 ] Ir(III)‐complexes. Indeed, for C 1 ‐symmetric tris ‐heteroleptic Ir(III)‐complexes, their evident advantage lies in the potentially enriched inventory ([Ir(C^N 1 )(C^N 2 )(L^X)] (L^X = O^O or N^N), [ 15,16 ] [Ir(C^N 1 )(C^N 2 )(C^N 3 )], [ 17 ] [Ir(C^N 1 )(C^C 2 )(C^N 3 )], [ 18 ] [Ir(C^N 1 )(N^N 1 )(N^N 2 )], [ 19 ] etc.) compared to conventional [Ir(C^N) 3 ]‐ [ 8 ] and [Ir(C^N) 2 (L^X)]‐counterparts.…”

“…Herein, encouraged by the smooth color‐tuning [ 15–19 ] and good device performance [ 15 ] within the vivid visible (λ em = 465–600 nm) range of C 1 ‐symmetric tris ‐heteroleptic Ir(III)‐complexes, it is anticipated that an attractive structural design strategy to our C 1 ‐symmetric [Ir(C^N 1 )(C^N 2 )(O^O)]‐ tris ‐heteroleptic Ir(III)‐complexes 1 – 3 ( Scheme ) could offer an opportunity to give NIR emission. Especially through the strengthened 3 MLCT effect from the C 1 ‐symmetric spatial configuration, large k r and/or reduced k nr can be motivated toward the efficient NIR‐phosphorescence.…”

Phosphorescent Tris‐Bidentate IrIII Complexes with N‐Heterocyclic Carbene Scaffolds: Structural Diversity and Optical Properties

“…The chemical structures of the tris ‐heteroleptic complexes are depicted in Scheme . Esteruelas and co‐workers reported on a series of tris ‐heteroleptic compounds of general formula [Ir(C ^ N)(C ^ C)(O ^ O)], where O ^ O is an acac ligand . The procedure used a stepwise metalation of the 1‐phenyl‐3‐methylimidazolylidene onto the [Ir(µ‐Cl)(1,5‐cyclooctadiene)] 2 via silver‐NHC transfer agent, followed by a double cyclometalation via ortho ‐C–H activation under mild conditions in presence of the C ^ N ligand to afford the corresponding mixed chloro‐dimer.…”