Coordination and extraction of lanthanides(III) with tripodal ligands on the triphenylphosphine oxide platform: Effect of uncoordinating substituents

Abstract

A ligand system containing three carbamoyl moieties secured onto a triphenylphosphine oxide platform (2-R2NC(O)CH2OC6H4)3PO, where R = Me (1), Bu (2), and cyclo-Hex (3) has been developed for lanthanide complexation and extraction from aqueous solutions. The influence of non-coordinating alkyl substituents at the nitrogen atoms in the carbamoyl side arms on coordination and extraction properties of tripodal ligands 1–3 was studied. Two new ligands 1 and 3 with alkyl substituents of different bulkiness were synthesized and characterized by spectroscopic methods. Single-crystal X-ray structures have been determined for ligands 1 and 2. The selected coordination chemistry of ligands 1–3 with Ln(NO3)3 (Ln = La, Nd, Lu) has been evaluated. The 1:1 complexes of all ligands 1–3 were synthesized and characterized via elemental analysis and IR spectroscopy; in addition, the crystal structure of the ligand 1 complex with neodymium nitrate was determined by X-ray diffraction. Solution structure of 1:1 complexes was examined by IR and multinuclear (1H, 13C, and 31P) NMR spectroscopy. A formation of 1:2 complexes with lanthanum and lutetium nitrates (IR, NMR, ESI-MS) has been examined and structure of the major components of 1:2 complexes solutions has been suggested for ligands 1–3. Preliminary extraction studies of Ln(III) (Ln = La, Nd, Eu, Lu) from 3 M NH4NO3 into 1,2-dichloroethane show that ligands 2 and 3 recover lanthanides much better than their mono analog [2-(Bu2NC(O)CH2O)-5-Et-C6H3]P(O)Ph2 and known extractant Ph2P(O)CH2C(O)NBu2.