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Issue 40, 2019
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Synthesis, X-ray structure, photophysical properties, and theoretical studies of six-membered cyclometalated iridium(iii) complexes: revisiting Ir(pnbi)2(acac)

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Abstract

We have determined the X-ray structure of Ir(pnbi)2(acac) (pnbi = 2-phenanthren-9-yl-1-phenyl-1H-benzimidazole; acac = acetylacetonate), which exhibits a six-membered metallocycle around the Ir center. This result stands in sharp contrast to previously postulated structures of Ir(pnbi)2(acac), which assumed a five-membered metallocycle. In this paper, we focus on the relative stability of five- and six-membered Ir(C^N) ring structures. DFT calculations of the total energies of Ir-(C^N) complexes indicated that six-membered structures are more stable when bulky substituents are present in the benzimidazole unit. When the phenanthrene group of pnbi was replaced with a naphthalene moiety, DFT calculations predicted that five-membered cycles are more stable than six-membered rings, which was confirmed experimentally by a single-crystal X-ray diffraction analysis. The steric bulk of the phenanthrene-containing polyaromatic ring ligand thus induces greater interligand repulsion between the two ligands, which plays an important role in determining the cyclometalation route. The Ir complexes examined in this study exhibit red emission (λem ≈ 660 nm) with relatively low quantum yields.

Graphical abstract: Synthesis, X-ray structure, photophysical properties, and theoretical studies of six-membered cyclometalated iridium(iii) complexes: revisiting Ir(pnbi)2(acac)

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Publication details

The article was received on 20 Aug 2019, accepted on 26 Sep 2019 and first published on 27 Sep 2019


Article type: Paper
DOI: 10.1039/C9DT03392K
Dalton Trans., 2019,48, 15212-15219

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    Synthesis, X-ray structure, photophysical properties, and theoretical studies of six-membered cyclometalated iridium(III) complexes: revisiting Ir(pnbi)2(acac)

    K. Yamada, H. Mori, T. Sugaya, M. Tadokoro, J. Maeba, K. Nozaki and M. Haga, Dalton Trans., 2019, 48, 15212
    DOI: 10.1039/C9DT03392K

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