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

Abstract

Reaction of AlEt 3 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 H 2O. The α-CH 2 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 CDCl 2CDCl 2 and DMSO- d 6, 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 Δ H ‡ = 135 kJ mol −1 and Δ S ‡ = 159 J K −1 mol −1 in CDCl 2CDCl 2 and at Δ H ‡ = 124 kJ mol −1 and Δ S ‡ = 151 J K −1 mol −1 in DMSO- d 6, 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 CHCl 3 with quantum yields of 7–23%.