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Comptes Rendus Chimie
Volume 8, n° 8
pages 1326-1335 (août 2005)
Doi : 10.1016/j.crci.2004.12.012
Received : 24 June 2004 ;  accepted : 8 December 2004
Luminescent complexes of iridium(III) with 6′-phenyl-2,2′-bipyridine and 4′-aryl derivatives: N^C versus N^N coordination
 

Adam J.S. Bexon, J.A. Gareth Williams
Department of Chemistry, University of Durham, South Road, Durham DH1 3LE, UK 

*Corresponding author.
Abstract

The reaction of iridium terpyridyl trichloride, [Ir(tpy)Cl3 ], with the following ligands has been investigated: 6′-phenyl-2,2′-bipyridine (HL1), its 4′-tolyl-derivative (HL2), and an annelated version of the latter incorporating an ethylene bridge between C5′ and the pendent phenyl ring (HL3). Although all three are potentially C^N^N-coordinating ligands, none are found to bind in this way in the products isolated. Ligand HL1 binds through its two nitrogen atoms only, leading to a dicationic complex [Ir(tpy)(HL1-N ,N )Cl]2+, 1, with an ‘N5 Cl' coordination sphere. In contrast, the presence of the 4′-tolyl group in HL2 and HL3 favours cyclometallation of the central pyridine ring through position C3′, leading to N^C-binding and to the monocationic complexes [Ir(tpy)(L2-C 3′,N )Cl]+, 2, and [Ir(tpy)(L3-C 3′,N )Cl]+, 3. The cyclometallated complexes 2 and 3 are intensely luminescent in solution at room temperature (λ max =541 and 562 nm; τ =3.2 and 2.4 μs, respectively; =0.16 for both, in degassed CH3 CN at 295 K), probably arising from a state of primarily 3MLCT character. In contrast, the N5 -coordinated complex 1 is only weakly emissive under the same conditions. To cite this article: A.J.S. Bexon, J.A.G. Williams, C. R. Chimie 8 (2005) .

The full text of this article is available in PDF format.
Résumé

Les réactions du trichlorure d'iridium terpyridyle, [Ir(tpy)Cl3 ], avec les ligands suivants ont été étudiées : 6′-phényl-2,2′-bipyridine (HL1), un derivé avec un groupement p -tolyle en position C4′ et un analogue de ce dernier, comportant un pont éthylène entre la position C5′ et l'anneau phényle. Bien que ces ligands puissent, en principe, se lier au métal d'une façon C^N^N, aucun ne se comporte ainsi dans les produits isolés. La coordination du ligand HL1 se fait par les deux azotes seulement, ce qui mène au complexe [Ir(tpy)(HL1-N ,N )Cl]2+, 1, comportant une sphère de coordination « N5 Cl ». En revanche, la présence du groupement tolyle dans HL2 et HL3 favorise la cyclométallation de l'anneau pyridyle central, en position C3′, qui mène à une coordination C^N, d'où les complexes [Ir(tpy)(L2-C 3′,N )Cl]+, 2, et [Ir(tpy)(L3-C 3′,N )Cl]+, 3. Les complexes cyclométallés 2 et 3 présentent une émission intense en solution à température ambiante (λ max =541 et 562 nm; τ =3,2 et 2,4 μs respectivement; =0.16 pour tous les deux, dans CH3 CN degazé à 295 K), dont l'origine est probablement un état excité de caractère 3MLCT. En revanche, le complexe 1, avec sa sphère de coordination N5 , n'est que faiblement luminescent dans les même conditions. Pour citer cet article : A.J.S. Bexon, J.A.G. Williams, C. R. Chimie 8 (2005) .

The full text of this article is available in PDF format.

Keywords : Iridium, Luminescence, Terpyridine, Cyclometallation

Mots clés : Iridium, Luminescence, Terpyridine, Cyclométallation




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