A novel and versatile precursor for the synthesis of highly preorganized tetradentate ligands based on phenanthroline and their binding properties towards lanthanides(III) ions

Rare earth elements (REEs) are vitally important for both high-tech industry and homeland security. Current industrial production and purification of REEs rely mostly on solvent extraction, for which, the overall extraction efficiency is largely determined by the organic ligands used as extractants. Ligands based on 1,10-phenantroline-2,9-diamides (PhenDA) are promising candidates and have been intensively investigated for both lanthanides (Lns) and/or lanthanides/actinides (Lns/Ans) separations. The synthetic drawback for current PhenDA derivatives lies in the equivalent usage of acyl chloride for the key precursors, thus limiting functional group tolerance and large-scale production of the extractants. Herein, we have demonstrated a new synthetic approach for mild reaction condition, high-yield synthesis of various types of PhenDA derivatives ranging from alkyl, aromatic to amino acid substituents. The synthetic procedures are relatively green for the absence of corrosive, volatile reagents and easy of product purification. The in-group Lns discrimination of one ligand is investigated in detail to demonstrate the separation potential. Considering the broad functional group tolerance of the current method and ease of large-scale production, we believe the methodology will broaden the ligands scope based on PhenDA and inspire new functionalities of Lns complexes.