Add time:07/14/2019         Source:sciencedirect.com

A series of bis-cyclometalated Ir(III) complexes (8–10, 12, 15, 17, 19, 21, 23, 25, 28, 29 and 33) bearing two chromophoric N∧C cyclometalated ligands derived from 2-(3,5-bis(trifluoromethyl)phenyl)-4-methylpyridine (1) and a third nonchromophoric ligand has been synthesized. A palladium-catalyzed cross-coupling reaction between 2-chloro-4-methylpyridine (2) and 3,5-bis(trifluoromethyl)phenylboronic acid (3) was used to prepare 2-(3,5-bis(trifluoromethyl)phenyl)-4-methylpyridine (1). Cyclometalation of (1) by IrCl3 was carried out in (MeO)3PO, with the formation of chloro-bridged dimer [N∧C]2Ir(μ-Cl)2Ir[C∧N]2 (8). Reaction of (8) with lithium 2,4-pentanedionate, lithium 2,2,6,6-tetramethyl-heptane-3,5-dionate (13), dipivaloyltrimethylsilylphosphine (14), 2,2-dimethyl-6,6,7,7,8,8,8-heptafluoro-3,5-octadione (16), 1,1,1,3,3,3-hexafluoro-2-pyridin-2-yl-propan-2-ol (18), 1,1,1,3,3,3-hexafluoro-2-pyrazol-1-ylmethyl-propan-2-ol (20), 2-diphenylphosphanylethanol (22), and 1-diphenylphosphanylpropan-2-ol (24), afforded octahedral iridium complexes 9, 12, 15, 17, 19, 21, 23 and 25, respectively. Complex 10, which contains three different ligands (L1 = N∧C of 1; L2 = N∧C of 4,4′-dimethyl-[2,2′]bipyridinyl 4; L3 = O∧O of 2,4-pentanedione), and complex 11, which contains no cyclometalated ligands (L1 = 4; L2 = L3 = Cl; L4 = O∧O of 2,4-pentanedione) were also isolated as minor products in a one-pot reaction between a 94:5 mixture of 1 and 4, IrCl3 and lithium 2,4-pentanedionate. Reaction of 8 with diphenylphosphanylmethanol (27) in 1,2-dichloroethane unexpectedly led to complexes 28 and 29. The reactions of 8 with benzoylformic acid resulted in the formation of hydroxyl-bridged dimer [N∧C]2Ir(μ-OH)2Ir[C∧N]2 (33). According to X-ray analyses, Ir-to-Ir distances in the crystal cell increase from 6.86 Å for 10 to 13.31 Å for 33. The angle theta, which represents the twisting of two cyclometalated C–Ir–N planes relative to each other, varies from 97.5° for 21 to 90.76 for complex 28. OLED devices were fabricated from several Ir complexes and preliminary results are discussed.

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