Diastereoselective Formation of Chiral Tris-Cyclometalated Iridium (III) Complexes:  Characterization and Photophysical Properties

Schaffner-Hamann, Christine; Zelewsky, Alex von; Barbieri, Andrea; Barigelletti, Francesco; Muller, Gilles; Riehl, James P.; Neels, Antonia

doi:10.1021/ja048655d

Cited by 177 publications

(107 citation statements)

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“…Here, optical isomers having shorter and longer retention times in the HPLC can be determined as the ∆ and Λ isomers, respectively, by comparing their circular dichroism (CD) spectra with those reported for the optically resolved diastereomeric Ir(ppy) 3 derivatives, the chiralities of which were determined by X-ray crystallography. [13][14][15][16] The CD spectra of the mer-∆, mer-Λ, fac-∆, and fac-Λ isomers in CH 3 CN are shown in Figure 1. The CD spectra of the enantiomers showed good mirror images of each other for both the mer and fac isomers.…”

Section: Resultsmentioning

confidence: 99%

Chirality in the Photochemical mer→fac Geometrical Isomerization of Tris(1‐phenylpyrazolato,N,C^2′)iridium(III)

et al. 2009

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Irradiation of the optically resolved mer-∆ isomer of tris(1-phenylpyrazolato,N,C 2Ј )iridium(III) with 366-nm light in CH 3 CN purged by argon at 25°C gave 59 % fac-∆ and 41 % fac-Λ (18 % ee) at the end of geometrical isomerization. Formation of the intermediate mer-Λ species was not observed, which is quite characteristic when compared with the corresponding thermal isomerization reaction. This enantiomeric

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Section: Resultsmentioning

confidence: 99%

Chirality in the Photochemical mer→fac Geometrical Isomerization of Tris(1‐phenylpyrazolato,N,C^2′)iridium(III)

et al. 2009

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“…4 Single diastereomers have been isolated e.g. [Ir(C^N*)] 3 and [Ir(C^N*) 2 (acac)] with enantiopure cyclometallating ligands, 7 or [Ir(C^N) 2 (X^Y*)] (X^Y* = amino acidate, 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, 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.…”

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confidence: 99%

Preparation of single enantiomers of chiral at metal bis-cyclometallated iridium complexes

Davies

Singh

et al. 2013

Chem. Commun.

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) with enantiopure X^Y ligands. However, these complexes have chirality at the ligand as well as the metal; hence, 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 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. 5The 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 DCMmethanol (2 : 1) at room temperature for 2-4 hours, to give 1a as a (1 : 1) mixture of diastereomers, DS and LS, in good combined 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 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 by X-ray crystallography 13 and the structures of LS-and DS-1a are shown in Fig. 1. 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 L configuration at the Ir centre (Fig. 1, left), whereas the other isomer shows a D configuration (Fig. 1, right). The change in chirality at the metal leads to different orientations of L1 with respect to the

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“…88 CPL has also been observed for fac-D-Ir(RR-pppy) 3 and fac-L-Ir(RR-pppy) 3 diastereomers where the chiral ligand RR-pppy is (8R,10R)-2-(2 0 -phenyl)-4,5-pinenopyridine. 154 In this work, equal weak magnitude, but opposite signed CPL, is reported for the two species, and this has been interpreted in terms of the lack of influence of the remote chiral centers (RR-pppy) on the chiral optical properties of Ir(III), the CPL being primarily due to the helical nature of the first coordination sphere. Applications of CPL to chiral transition metal complexes have been few due to the requirements that the complex must luminesce and have a significant amount of circular polarization.…”

Section: Circularly Polarized Luminescencementioning

confidence: 69%

Absolute Chiral Structures of Inorganic Compounds

Riehl

Kaizaki

2010

Physical Inorganic Chemistry

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Chiral inorganic compounds play increasingly important roles in current research efforts concerned with asymmetric catalysis, biochemistry, and supramolecular chemistry. Although our ability to determine precise chiral structures of inorganic compounds and relate these structures to chemical phenomena is a relatively recent achievement, this area of research has been a central and fundamental subject since the beginning of modern chemistry. The realization that substances other than those containing tetrahedral carbon atoms could occur as nonsuperimposable mirrorimage forms was first made by the "father of coordination chemistry" Alfred Werner at the end of the nineteenth century. 1 A critical consequence of his octahedral coordination theory was that certain isomers of six-coordinate metal complexes should exist as enantiomeric pairs. As early as 1897, Werner was speculating on whether or not he could verify the existence of mirror-image compounds from sixcoordinate octahedral geometry, and the preparation and resolution of a chiral molecular metal complex was finally achieved by his research colleagues Ernst Scholze and Victor L. King with the publication of the separation of the optical isomers (enantiomers) of cis-bromoamminebis(ethylenediamine)cobalt(III) salts in 1911. 2 Figure 5.1 illustrates the structure of the two possible mirror-image structures for this complex. The separated complexes were shown to possess equal and opposite optical rotations (OR) confirming their mirror-image relationship. Alfred Werner received the Nobel Prize in Chemistry for his development of the coordination theory 2 years after the publication of this milestone work in 1913.Following the experimental results of Werner and his colleagues, a number of theoretical attempts were made to correlate the sign and magnitude of the optical rotation to the exact chiral molecular structure of metal complexes. These approaches have been summarized by Richardson. 3 The term "absolute structure" is sometimes limited to a discussion of the structure of noncentrosymmetric crystals, and the term Physical Inorganic Chemistry: Principles, Methods, and Models Edited by Andreja Bakac

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Diastereoselective Formation of Chiral Tris-Cyclometalated Iridium (III) Complexes: Characterization and Photophysical Properties

Cited by 177 publications

References 49 publications

Chirality in the Photochemical mer→fac Geometrical Isomerization of Tris(1‐phenylpyrazolato,N,C^2′)iridium(III)

Chirality in the Photochemical mer→fac Geometrical Isomerization of Tris(1‐phenylpyrazolato,N,C^2′)iridium(III)

Preparation of single enantiomers of chiral at metal bis-cyclometallated iridium complexes

Absolute Chiral Structures of Inorganic Compounds

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Diastereoselective Formation of Chiral Tris-Cyclometalated Iridium (III) Complexes: Characterization and Photophysical Properties

Cited by 177 publications

References 49 publications

Chirality in the Photochemical mer→fac Geometrical Isomerization of Tris(1‐phenylpyrazolato,N,C2′)iridium(III)

Chirality in the Photochemical mer→fac Geometrical Isomerization of Tris(1‐phenylpyrazolato,N,C2′)iridium(III)

Preparation of single enantiomers of chiral at metal bis-cyclometallated iridium complexes

Absolute Chiral Structures of Inorganic Compounds

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Chirality in the Photochemical mer→fac Geometrical Isomerization of Tris(1‐phenylpyrazolato,N,C^2′)iridium(III)

Chirality in the Photochemical mer→fac Geometrical Isomerization of Tris(1‐phenylpyrazolato,N,C^2′)iridium(III)