Influence of Schiff Base and Lanthanide Metals on the Synthesis, Stability, and Reactivity of Monoamido Lanthanide Complexes Bearing Two Schiff Bases

The monoamido lanthanide complexes stabilized by Schiff base ligand L2LnN(TMS)2 (L = 3,5-But2-2-(O)-C6H2CHN-8-C9H6N, Ln = Yb (1), Y (2), Eu (3), Nd (4), and La (5)) were synthesized in good yields by the reactions of Ln[N(TMS)2]3 with 1.8 equiv of HL in hexane at room temperature. It was found that the stability of 1−5 depends greatly on the size of the lanthanide metals with the increasing trend of Yb ≈ Y 2]3 with the bulky bidentate Schiff base HL′ (L′ = 3,5-But2-2-(O)-C6H2CHN-2,6-Pri2-C6H3) afforded the monoamido lanthanide complexes L′2LnN(TMS)2 (Ln = Yb (9), Y (10), Nd (11), and La (12)). While the amine elimination with the less bulky Schiff base HL′′ (L′′ = 3,5-But2-2-(O)-C6H2CHN-2,6-Me2-C6H3) yielded the desired monoamido complexes with the small metals of Y and Yb, L′′2LnN(TMS)2 (Ln = Yb (13) and Y (14)), and the more stable tris-Schiff base complexes with the large metals of La and Nd, yielded L′′3Ln as the only product. Complexes 1−14 were fully characterized including X-ray crystal structural analysis. Complexes 1−5, 10, and 14 can serve as the efficient catalysts for addition of amines to carbodiimides, and the catalytic activity is greatly affected by the lanthanide metals with the active sequence of Yb < Y < Eu ≈ Nd ≈ La.