Synthesis and Characterization of Facial and Meridional Tris-cyclometalated Iridium(III) Complexes

Tamayo, Arnold; Alleyne, Bert D.; Djurovich, Peter I.; Lamansky, Sergey; Tsyba, Irina; Ho, Nam Nhat; Bau, Robert; Thompson, Mark E.

doi:10.1021/ja034537z

Cited by 1,209 publications

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“…This is consistent with conversion 55 of mer to fac isomers of [Ir(ppy) 3 ] requiring heating to > 200 C. 17 The previous reports of non-equal ratio of diastereomers with amino acidates 5,8 and phenol oxazolines 6 may reflect difficulties in isolation by column chromatography rather than an intrinsic diastereoselectivity.…”

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confidence: 84%

Atropisomerism in a thermally switchable, cyclometallated iridium complex

et al. 2012

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5,8,9 , phenol oxazoline 6 ) with enantiopure X^Y ligands. However, these complexes have chirality at the ligand as well as the metal; hence, 25 the aim of this work was to prepare, on a synthetically useful scale, homochiral cyclometallated Ir(III) complexes which are only chiral at the metal.Our strategy was to prepare diastereomeric complexes [Ir(C^N) 2 (X^Y*)], separate the diastereomers, then remove the 30 chiral auxiliary by protonation and replace it with another bidentate ligand. A similar strategy has recently been applied by Meggers for the synthesis of homochiral trisbidentate ruthenium complexes, 10 and in 2012 was applied to iridium complexes for the first time. 5 35 The dimer [Ir(ppz) 2 Cl] 2 (a, Hppz = phenylpyrazole) was reacted with 2.2 equiv of (S)-Na(L1) 11,12 in a mixture of DCM/ methanol (2:1) at room temperature for 2-4 hrs, to give 1a as a (1:1) mixture of diastereomers, ∆S and ΛS, in good combined 45 yields (>75%) (Scheme 1). The reaction was repeated with only 0.8 equiv of (S)-Na(L1) per dimer and the 1 H NMR spectrum of the product showed a 1:1 ratio of the two diastereomers along with the unreacted excess dimer. This suggests that there is no diastereoselectivity in the synthesis and there is an equal 50 probability for the formation of the two diastereomers. The diastereomers of 1a could be separated by crystallisation from different solvents and they do not interconvert in solution, suggesting the chirality at the metal is stable at room temperature. The absolute configuration of both diastereomers was determined 55 by X-ray crystallography 13 and the structures of S-and S-1a are shown in Fig. 2. 14 The structures show that both isomers have cis carbon atoms and trans nitrogen atoms for the C^N ligands and S configuration at the chiral carbon atom of the oxazoline ligand; one isomer has a Λ configuration at the Ir centre (Fig. 2 60 left), whereas the other isomer shows a ∆ configuration (Fig. 2 right). The change in chirality at the metal leads to different orientations of L1 with respect to the [Ir(C^N) 2 ] fragment. In the ΛS isomer the pyrazole [N(4)-C(12)] pointing towards the oxazoline nitrogen is on the unsubstituted side of the oxazoline 65 and there is no steric conflict. In contrast, in the ∆S isomer, the pyrazole [N(2)-C(3)] pointing towards the oxazoline nitrogen is on the same side as the isopropyl which leads to steric congestion which is clearly evident in the planarity of L1 (Fig. 2 right). Thus, in the ΛS isomer the angle between the planes of the 70 phenol and the oxazoline is less than 3 whilst in the ∆S isomer the corresponding angle is > 20.The structures are retained in solution as determined by key NOEs between the X^Y ligand and the [Ir(C^N) 2 ] fragment (see ESI Fig S1). In ΛS-1a the isopropyl group lies above a ppz ligand

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confidence: 84%

Atropisomerism in a thermally switchable, cyclometallated iridium complex

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“…39 An interesting design feature of these bridges is that they provide a short conjugative pathway between the two Ir centers. We now present a series of new diiridium complexes (13)(14)(15)(16) featuring different cyclometalated ligands. In all cases the diastereomers have been separated and characterized by their single-crystal X-ray structures.…”

Section: Introductionmentioning

confidence: 99%

Synthesis, Diastereomer Separation, and Optoelectronic and Structural Properties of Dinuclear Cyclometalated Iridium(III) Complexes with Bridging Diarylhydrazide Ligands

et al. 2017

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(2017) 'Synthesis, diastereomer separation, and optoelectronic and structural properties of dinuclear cyclometalated iridium(III) complexes with bridging diarylhydrazide ligands. ', Organometallics., 36 (5). pp. 981-993.Further information on publisher's website:https://doi.org/10.1021/acs.organomet.6b00887Publisher's copyright statement:This document is the Accepted Manuscript version of a Published Work that appeared in nal form in Organometallics, copyright c 2017 American Chemical Society after peer review and technical editing by the publisher. To access the nal edited and published work see https://doi.org/10.1021/acs.organomet.6b00887. Additional information:Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. ABSTRACT: A series of diiridium complexes 13-16 bridged by diarylhydrazine ligands and cyclometalated by phenylpyridine or phenylpyrazole ligands was synthesized. In all cases the ɅΔ meso and ɅɅ/ΔΔ rac diastereomers were separated and characterized by single-crystal X-ray diffraction, revealing intramolecular - stacking between arenes of the bridging and cyclometalating ligands. Density functional theory (DFT) calculations show that in general the HOMOs are mainly localized on the iridium centers, the cyclometalating phenyl moieties and the central hydrazide components of the bridging ligands, while the LUMOs are primarily localized on the N-heterocycles (pyridine or pyrazole) of the cyclometalating ligands. This series of complexes, especially with the separated diastereomers, provides an ideal opportunity to study the effects of subtle structural changes on the optoelectronic properties of diiridium systems: significant differences are observed between the rac and meso isomers in some cases. A cyclic voltammetric study of the electrochemical properties of the eight complexes reveals strong intramolecular interactions between the iridium centers. The photophysical properties are reported in solution, and in rigid poly(methyl methacrylate) (PMMA) or 2-methyltetrahydrofuran (2-MeTHF) (at 77 K) matrices where some of the complexes are strongly emissive in the turquoise and green regions (Φ PL 42-68 ±10%) due to matrix-induced restricted intramolecular motion (RIM).

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“…7,8 The absorption spectrum of the suspension of the hybrid 2 in ethanol shows intense bands appearing at 280 nm and 450 nm, which are attributed to the characteristic absorption of the core unit of the complex 1, supporting successful attachment of the complex 1 on the MWCNTs.…”

Section: Ligandmentioning

confidence: 87%

“…7,8 Consequently, we thought that hybrid systems of the phosphorescent d 6 Ir(III) complex with a long lifetime 7 and CNTs could show excellent performance for photovoltaic applications.…”

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Luminescence Quenching of a Novel Phosphorescent Ir(III) Complex/MWCNT Hybrid

Huh¹,

Park²,

Choi³

et al. 2012

Bulletin of the Korean Chemical Society

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Electron donor-acceptor hybrid systems have received great interest in photovoltaic applications, [1][2][3][4][5] in which photoinduced electrons of photosensitizers convert to electrical energy via electron transfer to electron acceptors. The electron transfer efficiency is determined by the competition between recombination of the excited electrons to the ground state and electron transfer of the excited electrons to acceptors. Consequently, the photosensitizer with a slow rate of recombination, which means a long lifetime for the excited electrons, could be a good candidate for achieving high electron transfer efficiency in donor-acceptor hybrids. Phosphorescence, emissive decay of the excited electrons to the ground state through intersystem crossing between singlet and triplet states by a strong spin-orbit coupling, shows a longer lifetime for the excited electrons than fluorescence, emissive decay between singlet states.6 Here, we present the synthesis of a novel Ir-based phosphorescent complex and demonstrate its excellent luminescence quenching when it forms a hybrid complex with multiwall carbon nanotubes (MWCNTs). The system shows an almost 100% quenching efficiency of the excited electrons. To the best of our knowledge, this is the first investigation of a Ir-based phosphorescent photosensitizer for possible photovoltaic applications.Carbon nanotubes (CNTs) composed of an extended π-electron system with one dimensional structure have been used for photovoltaic applications as an electron acceptor of donor-acceptor hybrid systems because of their high electron mobility. CNTs have often showed excellent electron transfer efficiency in hybrid systems containing fluorescent photosensitizers, such as porphyrins, pyrenes, polymers, and organometallic compounds.7,8 Consequently, we thought that hybrid systems of the phosphorescent d 6 Ir(III) complex with a long lifetime 7 and CNTs could show excellent performance for photovoltaic applications.In the CNT-based hybrid systems, the systems containing covalently tethered photosensitizers on CNTs have frequently showed good performances, such as good stability and high electron transfer efficiency.9 Thus, we designed a novel tris-cyclometalated iridium(III) complex [Ir(ppy) 2 (hppy)] (1), bis(2-phenylpyridyl)-4-(4'-hydroxyphenyl)-2-phenylpyridyliridium(III), that has one -OH end group and synthesized by heating dichloro-bridged dimer [(ppy) 2 Ir(µ-Cl) 2 (ppy) 2 ] with two-fold amount of 4-hydroxyphenyl-2-phenylpyridine (hppy) (see the experimental section and supporting information (SI)). Such -OH group is useful for covalent attachment of the Ir complex on -COOH groups of functionalized MWCNTs via esterification (Figure 1). Complex 1 showed a long excited-state lifetime (500 ± 6 ns) studied by time-resolved measurement when it was excited at 450 nm, confirming that it is a phosphorescent complex (inset in Figure 2(b)).7,10 On the other hand, fluorescent materials usually have a shorter lifetime, below several tens of nanoseconds. 6Carboxyl acid groups on the MW...

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Synthesis and Characterization of Facial and Meridional Tris-cyclometalated Iridium(III) Complexes

Cited by 1,209 publications

References 64 publications

Atropisomerism in a thermally switchable, cyclometallated iridium complex

Atropisomerism in a thermally switchable, cyclometallated iridium complex

Synthesis, Diastereomer Separation, and Optoelectronic and Structural Properties of Dinuclear Cyclometalated Iridium(III) Complexes with Bridging Diarylhydrazide Ligands

Luminescence Quenching of a Novel Phosphorescent Ir(III) Complex/MWCNT Hybrid

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