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.