Selective synthesis and photophysical properties of phosphorescent heteroleptic iridium(III) complexes with two different bidentate groups and two different monodentate ligands

Abstract

Rational synthetic procedures for the preparation of phosphorescent heteroleptic iridium(III) complexes, with controlled stereochemistry, of general formula IrX{κ2-N,C-(qui-C6H4)}(acac)(PiPr3) and their photophysical properties are reported. The d4 pentahydride IrH5(PiPr3)2 (1) promotes the chelate-supported C–H bond activation of 2-phenylquinoline to give IrH2{κ2-N,C-(qui-C6H4)}(PiPr3)2 (2), which affords the five-coordinate monohydride [IrH{κ2-N,C-(qui-C6H4)}(PiPr3)2]BF4 (3) by protonation with HBF4. Treatment of 3 with potassium acetylacetonate (Kacac) yields the hydrido target compound IrH{κ2-N,C-(qui-C6H4)}(acac)(PiPr3) (4). Phenylacetylene and acetylene insert into the Ir–H bond of 3 to form the five-coordinate alkenyl derivatives [Ir((E)-CH═CHR){κ2-N,C-(qui-C6H4)}(PiPr3)2]BF4 (R = Ph (5), H (6)). Similarly to 3, complexes 5 and 6 react with K(acac) to give Ir((E)-CH═CHR){κ2-N,C-(qui-C6H4)}(acac)(PiPr3) (R = Ph (7), H (8)). The chloride counterpart of 4, 7, and 8 has been obtained by starting from IrCl3(tht)3 (9; tht = tetrahydrotiophene). Treatment of this compound with triisopropylphosphine and 2-phenylquinoline leads to the five-coordinate species IrCl2{κ2-N,C-(qui-C6H4)}(PiPr3) (10). The use of triphenylphosphine instead of triisopropylphosphine affords the PPh3 analogue IrCl2{κ2-N,C-(qui-C6H4)}(PPh3) (11). Complexes 10 and 11 react with K(acac) to give IrCl{κ2-N,C-(qui-C6H4)}(acac)(PR3) (PR3 = PiPr3 (12), PPh3 (13)). The six-coordinate compounds 4, 7, 8, 12, and 13 are yellow-orange emissive upon photoexcitation, with short lifetimes and quantum yields increasing in the sequence 7 (CH═CHPh) < 12 (Cl) < 8 (CH═CH2) < 4 (H), as the contribution of the metal center to the HOMO of the complexes also increases.