The first examples of 1,10-phenanthroline-2,9-diamides bearing CF3-groups on the side amide substituents were synthesized. Due to stereoisomerism and amide rotation, such complexes have complicated behavior in solutions. Using advanced NMR techniques and X-ray analysis, their structures were completely elucidated. The possibility of the formation of complex compounds with lanthanoids nitrates was shown, and the constants of their stability are quantified. The results obtained are explained in terms of quantum-chemical calculations.
An efficient approach to the synthesis of diamides of 4,7-difluoro-1,10-phenanthroline-2,9-dicarboxylic acid was elaborated. Direct nucleophilic substitution with 4,7-dichloro-1,10-phenanthroline precursors opened access to difluoro derivatives in high yield. As a result, four new fluorinated ligands were prepared in up to 88% yield. Their structure was proved by a combination of spectral methods and X-ray data. A set of lanthanoid complexes was prepared to demonstrate the utility of new ligands. The structure of the complexes was studied in solid state (IR-spectroscopy, X-ray diffraction) and in solution (NMR-spectroscopy).
Three pyrrolidine-derived phenanthroline diamides were studied as ligands for lutetium trinitrate. The structural features of the complexes have been studied using various spectral methods and X-ray. The presence of halogen atoms in the structure of phenanthroline ligands has a significant impact on both the coordination number of lutetium and the number of solvate water molecules in the internal coordination sphere. The stability constants of complexes with La(NO3)3, Nd(NO3)3, Eu(NO3)3, and Lu(NO3)3 were measured to demonstrate higher efficiency of fluorinated ligands. NMR titration was performed for this ligand, and it was found that complexation with lutetium leads to an approximately 13 ppm shift of the corresponding signal in the 19F NMR spectrum. The possibility of formation of a polymeric oxo-complex of this ligand with lutetium nitrate was demonstrated. Experiments on the liquid–liquid extraction of Am(III) and Ln(III) nitrates were carried out to demonstrate advantageous features of chlorinated and fluorinated pyrrolidine diamides.
An efficient approach to unsymmetrical 1,10-phenanthroline-2,9-dicarboxamides based on the bifunctional reactivity of 4-oxo-7-haloderivatives is reported. These substrates exhibit orthogonal reactivity, enabling selective nucleophilic aromatic substitution at the C7 position alongside electrophilic functionalization of the 4-oxo group under mild conditions. Reactions with a broad range of C-, N-, and O-nucleophiles afford 4-oxo-7-functionalized products in high yields, while subsequent transformations of azido- and hydroxy-substituted derivatives further demonstrate the synthetic versatility of this platform. The observed chemoselectivity is reflected in the highly selective O-functionalization of the 4-oxogroup, with alkylation proceeding under mild conditions. The developed strategy provides a general route to structurally diverse unsymmetrical derivatives and highlights the potential of 4-oxo-7-halo-systems as bifunctional building blocks.