Tripodal diglycolamides as highly efficient extractants for f-elements

Abstract

A series of new ligands bearing three diglycolamide functions preorganized at the C-pivot and trialkylphenyl platforms was synthesized. They are very efficient extractants for Am³⁺ and Eu³⁺ with an up to five times relative extraction ability for Eu³⁺. The distribution coefficients are up to 1000 times increased upon alkylation or arylation of the N-position of the diglycolamide moieties. The tripodal diglycolamides show a 1 : 1 metal to ligand stoichiometry as proven with three independent methods for the complexation of the 3-pentyl N-substituted diglycolamide ligand with Eu³⁺ (K = 2.5 × 10⁵ M⁻¹ in acetonitrile–water). A cage-like cryptand, containing three diglycolamide units, was prepared using a Eu³⁺ templated synthesis. However, it does not exhibit improved extraction properties.