Two Synthetic Tools to Deepen the Understanding of the Influence of Stereochemistry on the Properties of Iridium(III) Heteroleptic Emitters

Two complementary procedures are presented to prepare cis-pyridyl-iridium­(III) emitters of the class [3b+3b+3b′] with two orthometalated ligands of the 2-phenylpyridine type (3b) and a third ligand (3b′). They allowed to obtain four emitters of this class and to compare their properties with those of the trans-pyridyl isomers. The finding starts from IrH5(PiPr3)2, which reacts with 2-(p-tolyl)­pyridine to give fac-[Ir­{κ2-C,N-[C6MeH3-py]}3] with an almost quantitative yield. Stirring the latter in the appropriate amount of a saturated solution of HCl in toluene results in the cis-pyridyl adduct IrCl­{κ2-C,N-[C6MeH3-py]}2{κ1-Cl-[Cl–H-py-C6MeH4]} stabilized with p-tolylpyridinium chloride, which can also be transformed into dimer cis-[Ir­(μ-OH)­{κ2-C,N-[C6MeH3-py]}2]2. Adduct IrCl­{κ2-C,N-[C6MeH3-py]}2{κ1-Cl-[Cl–H-py-C6MeH4]} directly generates cis-[Ir­{κ2-C,N-[C6MeH3-py]}2{κ2-C,N-[C6H4–Isoqui]}] and cis-[Ir­{κ2-C,N-[C6MeH3-py]}2{κ2-C,N-[C6H4-py]}] by transmetalation from Li­[2-(isoquinolin-1-yl)-C6H4] and Li­[py-2-C6H4]. Dimer cis-[Ir­(μ-OH)­{κ2-C,N-[C6MeH3-py]}2]2 is also a useful starting complex when the precursor molecule of 3b′ has a fairly acidic hydrogen atom, suitable for removal by hydroxide groups. Thus, its reactions with 2-picolinic acid and acetylacetone (Hacac) lead to cis-Ir­{κ2-C,N-[C6MeH3-py]}2{κ2-O,N-[OC­(O)-py]} and cis-Ir­{κ2-C,N-[C6MeH3-py]}2{κ2-O,O-[acac]}. The stereochemistry of the emitter does not significantly influence the emission wavelengths. On the contrary, its efficiency is highly dependent on and associated with the stability of the isomer. The more stable isomer shows a higher quantum yield and color purity.