Mechanistic Investigation of Improved Syntheses of Iridium(III)-Based OLED Phosphors

Treatment of [IrCl3(tht)3] (tht = tetrahydrothiophene) with a stoichiometric amount of PPh3 gave the monosubstitution product [Ir(tht)2(PPh3)Cl3] (5), whose synthesis, particularly that leading to the effective preparation of OLED phosphors, was studied and optimized to achieve the best product yields. Thus, the independent treatment of 5 with 2,4-difluorophenylpyridine (dfppyH) or with variable amounts of benzyldiphenylphosphine (bdpH) gave rise to the formation of the cyclometalation products [Ir(dfppy)(tht)(PPh3)Cl2] (7), [Ir(bdp)(bdpH)(tht)Cl2] (8), and [Ir(bdp)(PPh3)(tht)Cl2] (10), depending on the stoichiometry and conditions employed. Upon further treatment with 5-pyridyl-3-trifluoromethyl-1H-pyrazole (fppzH), these Ir(III) complexes 7, 8, and 10 were capable of yielding the phosphors [Ir(dfppy)(fppz)2] (1), [Ir(bdp)2(fppz)] (4), and [Ir(bdp)(fppz)2] (2), respectively. The general mechanism en route to their formation was studied and discussed.