Iridium(III) Complexes Bearing a Formal Tetradentate Coordination Chelate: Structural Properties and Phosphorescence Fine-Tuned by Ancillaries

Abstract

Synthesis of the multidentate coordinated chelate N3C–H2, composed of a linked functional pyridyl pyrazole fragment plus a peripheral phenyl and pyridyl unit, was obtained using a multistep protocol. Preparation of Ir­(III) metal complexes bearing a N3C chelate in the tridentate (κ3), tetradentate (κ4), and pentadentate (κ5) modes was executed en route from two nonemissive dimer intermediates [Ir­(κ3-N3CH)­Cl2]2 (1) and [Ir­(κ4-N3C)­Cl]2 (2). Next, a series of mononuclear Ir­(III) complexes with the formulas [Ir­(κ4-N3C)­Cl­(py)] (3), [Ir­(κ4-N3C)­Cl­(dmap)] (4), [Ir­(κ4-N3C)­Cl­(mpzH)] (5), and [Ir­(κ4-N3C)­Cl­(dmpzH)] (6), as well as diiridium complexes [Ir2(κ5-N3C)­(mpz)2(CO)­(H)2] (7) and [Ir2(κ5-N3C)­(dmpz)2(CO)­(H)2] (8), were obtained upon treatment of dimer 2 with pyridine (py), 4-dimethylaminopyridine (dmap), 4-methylpyrazole (mpzH), and 3,5-dimethylpyrazole (dmpzH), respectively. These Ir­(III) metal complexes were identified using spectroscopic methods and by X-ray crystallographic analysis of representative derivatives 3, 5, and 7. Their photophysical and electrochemical properties were investigated and confirmed by the theoretical simulations. Notably, green-emitting organic light-emitting diode (OLED) on the basis of Ir­(III) complex 7 gives a maximum external quantum efficiency up to 25.1%. This result sheds light on the enormous potential of this tetradentate coordinated chelate in the development of highly efficient iridium complexes for OLED applications.

Pseudo-Tris(heteroleptic) Red Phosphorescent Iridium(III) Complexes Bearing a Dianionic C,N,C′,N′-Tetradentate Ligand

“…X-ray structure of one of the two independent molecules of 6b showing 50% thermal ellipsoid probability (hydrogen atoms have been omitted). Selected bond lengths (Å) and angles (degree) for both molecules: Ir(1)−C(1) = 1.993( 9), 1.996 (9), Ir(1)−C(19) = 2.096 (9), 2.118 (9), Ir(1)−C(29) = 2.080 (9), 2.071 (9), Ir(1)−N(1) = 1.984(7), 1.956 (8) Cations of salts 8 and 10 are the result of a hydrogen-transfer reaction at the metal coordination sphere from the aryl substituent of the incoming pyridine ligand to the phenyl unit of the benzyl group of the tetradentate ligand. In addition, a position exchange between the pyridyl and phenyl rings of the 2benzylpyridine moiety takes place; that is, in contrast to the previous complexes of this work, the phenyl substituent of the 2phenylisoquinoline moiety and the phenyl unit of the benzyl group are mutually trans disposed.…”

“…This anion uses the free nitrogen atom of the pyrazolate group to generate the green binuclear emitters B . 9 We have recently shown that the ortho -CH bond activation of both phenyl groups of 2-phenyl-6-(1-phenyl-1-(pyridin-2-yl)ethyl)pyridine gives a dianionic C , N , C ′, N ′-tetradentate 6tt′ ligand, which allows the access to blue-green and green iridium(III) emitters, C and D , of classes [6tt′ + 1m + 2m] and [6tt′ + 3b], respectively. 10 …”

“…This anion uses the free nitrogen atom of the pyrazolate group to generate the green binuclear emitters B. 9 We have recently shown that the ortho-CH bond activation of both phenyl groups of 2-phenyl-6-(1phenyl-1-(pyridin-2-yl)ethyl)pyridine gives a dianionic C,N,C′,N′-tetradentate 6tt′ ligand, which allows the access to blue-green and green iridium(III) emitters, C and D, of classes [6tt′ + 1m + 2m] and [6tt′ + 3b], respectively. 10 Complex D can be viewed as a pseudo-tris(heteroleptic) iridium(III) emitter with the metal coordination sphere formed by three different bidentate moieties, an orthometalated 2phenylpyridine, an orthometalated 2-benzylpyridine type ligand, and an acetylacetonate group (acac).…”

“…The 2,2′-(1-(6-(3-trifluoromethyl-1 H -pyrazol-5-yl)­pyridin-2-yl)­ethane-1,1-diyl)­dipyridine molecules afford monoanionic N , N ′, N ″, N ″-tetradentate ligands (7tt′), which stabilize sky-blue [7tt′ + 2b] emitters A , whereas exchanging one of the peripheral pyridine for a phenyl group leads to 2-(3-trifluoromethyl-1 H -pyrazol-5-yl)-6-(1-phenyl-1-(pyridyn-2-yl)­ethyl)­pyridine, which forms a dianionic N , N ′, C , N ″-tetradentate ligand 6tt′. This anion uses the free nitrogen atom of the pyrazolate group to generate the green binuclear emitters B . We have recently shown that the ortho -CH bond activation of both phenyl groups of 2-phenyl-6-(1-phenyl-1-(pyridin-2-yl)­ethyl)­pyridine gives a dianionic C , N , C ′, N ′-tetradentate 6tt′ ligand, which allows the access to blue-green and green iridium­(III) emitters, C and D , of classes [6tt′ + 1m + 2m] and [6tt′ + 3b], respectively …”

Phosphorescent Iridium(III) Complexes with a Dianionic C,C′,N,N′-Tetradentate Ligand

“…The new compound was also characterized by Xray diffraction analysis. 6), Ir1-C26 = 2.125( 6), Ir1-C29 = 2.144( 6), Ir1-C30 = 2.137( 6); N2-Ir1-N1 = 81.00 (17).…”