Exploring synthetic pathways to cationic heteroleptic cyclometalated iridium complexes derived from dipyridylketone

Abstract

Reactions between 2,2′-dipyridylketone (L1) and different amines gave a series of iminic ligands, and their chemical reductions produced the related amines. The organic ligands were employed in the syntheses of the corresponding new phosphorescent six-member ring bis-cyclometalated heteroleptic iridium(III) complexes of general formula [Ir(ppy)₂(L)]⁺ (ppy = 2-phenylpyridine), namely IrLn. The metal complexes containing N-(dipyridin-2-ylmethylene)butan-1-amine (IrL2), N-(dipyridin-2-ylmethyl)butan-1-amine (IrL5), N-(dipyridin-2-ylmethyl)butane-1,4-diamine with amino groups protected by Boc (IrL6-Boc) and TFA (IrL6-TFA), and N-(dipyridin-2-ylmethyl)-N-methylbutan-1-amine (IrL8) were characterized and their electronic and spectroscopic properties interpreted by DFT calculations. Organoiridium complexes containing amines and imines were found to have high and low photoemission quantum yields, respectively, and their features rationalized by quantum mechanic calculations. Some of these complexes show reasonable quantum yields (up to 13%), long lifetime (up to 2.3 μs) and high stability. Complementary and alternative synthetic pathways to get cationic heteroleptic cyclometalated Ir complexes bearing a tethered primary amino group have been explored with the aim to obtain organometallic phosphorescent derivatives suitable for surface functionalization.