Synthesis of reactive [Al(Et)(q′)2] (q′ = 2-methyl-8-quinolinolato) serving as a precursor of light emitting aluminum complexes: Reactivity, optical properties, and fluxional behavior of the aluminum complexes

Reaction of AlEt3 with 2-methyl-8-quinolinol gave ethylbis(2-methyl-8-quinolinolato)aluminum complex [Al(Et)(q′)2] 1. The complex 1 provided photoluminescent Al complexes by reactions with phenols, carboxylic acid, and H2O. The α-CH2 hydrogens in the Et group of 1 was diastereotropic as revealed by 1H NMR spectroscopy because of the presence of a chiral center at Al. The chirality at Al was dynamically lost at elevated temperature in CDCl2CDCl2 and DMSO-d6, as indicated by temperature dependent 1H NMR spectroscopy. This dynamic or fluxional behavior of 1 is explained by rotation of the 2-methyl-8-quinolinolato ligand. The kinetic parameters of the dynamic process were estimated at ΔH‡ = 135 kJ mol−1 and ΔS‡ = 159 J K−1 mol−1 in CDCl2CDCl2 and at ΔH‡ = 124 kJ mol−1 and ΔS‡ = 151 J K−1 mol−1 in DMSO-d6, respectively, at 350 K. Structures of some of the obtained Al complexes were confirmed by single-crystal X-ray crystallography. These Al complexes showed photoluminescence peaks at 492–507 nm in CHCl3 with quantum yields of 7–23%.

Graphical abstractReaction of AlEt3 with 2-methyl-8-quinolinol gave ethylbis(2-methyl-8-quinolinolato)aluminum complex [Al(Et)(q′)2] (1). The complex 1 gave photoluminescent Al complexes by reactions with phenols, picolinic acid, and H2O. The α-CH2 hydrogens in the Et group of 1 was diastereotropic as revealed by 1H NMR spectroscopy because of the presence of a chiral center at Al. The chirality at Al was dynamically lost at elevated temperature in CDCl2CDCl2 and DMSO-d6, as indicated by temperature dependent 1H NMR spectroscopy. Structures of some of the obtained Al complexes were confirmed by single-crystal X-ray crystallography. These Al complexes showed photoluminescence peaks at 492–507 nm in CHCl3 with quantum yields of 7–23%.Figure optionsDownload full-size imageDownload as PowerPoint slide