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%.