Theoretical study on the synthesis of ortho-metallated iridium(III) complex

Abstract

Fac-tris(2-phenylpyridine)iridium(III)(Ir(ppy)3) is one of the useful luminescent materials for organic EL devices. Recently, it was found that Ir(acac)3 reacts with 2-phenylpyridine (ppyH) to produce Ir(ppy)3 in the presence of Bronsted acids with a high yield. In the present study, we tried to understand the detailed mechanism of the reaction and to explicate the effects of Bronsted acid on the reaction. The B3LYP/SDD level of theory was used to investigate the mechanism of the ligand exchange reaction with and without the acids. A proton addition to an oxygen atom in one of the acac ligand results in breaking an Ir-O bond and changing its structure to a five coordination geometry suitable for accepting an N donor of ppyH. It was confirmed that solvent molecule extracts a proton on the acac ligand before the ligand exchange reaction occurs. Without removing the proton on the ligand, we only obtained a TS producing a by-product in which the elimination of an acac ligand from Ir(acac)3 does not occur. In conclusion, a proton from Bronsted acid and including an H2O molecule are the key to exchanging the acac ligand to the ppyH one in an early stage of the reaction.