Improved Synthesis of Unsymmetrical N-Aryl-N′-alkylpyridyl ß-Diketimines Using Molecular Sieves and their Lithium Complexes

The synthesis of unsymmetrical β-diketimines with N-aryl-N′-alkyl substitution require at least two condensation steps and tedious purification procedures. An improvement in the preparation of four unsymmetrical N-aryl-N′-alkylpyridyl β-diketimine ligands (HL1–HL4) using 5-Å molecular sieves is reported. The synthesis of four Li complexes (LiL1, LiL2, LiL3, and LiL4) containing N-aryl-N′-alkylpyridyl β-diketimines ligands is also presented. All four Li complexes were fully characterized by ¹H NMR spectroscopic, ¹³C NMR spectroscopic, and elemental analyses. X-ray structure analysis and spectroscopic results indicate that the Li β-diketimine structures and ligand binding modes are governed by the bulkiness of the N-aryl substituent and the length of the pyridyl arm of the N-aryl-N′-alkyl β-diketiminate ligand.