Synthesis of rare-earth metal complexes with a morpholine-functionalized β-diketiminato ligand and their catalytic activities towards C–O and C–N bond formation

Abstract

Unusual tridentate β-diketiminato rare-earth metal chlorides LRECl(μ-Cl)₂Li(THF)₂ (RE = Y (1a), Yb (1b), and Lu (1c); L = MeC(NDipp)CHC(Me)N(CH₂)₂NC₄H₈O; Dipp = 2,6-ⁱPr₂C₆H₃) and the corresponding dialkyl complexes LRE(CH₂SiMe₃)₂ (RE = Y (2a), Yb (2b), and Lu (2c)) were prepared by reaction of a morpholine-functionalized β-diketiminato proligand HL with anhydrous RECl₃ and rare-earth metal trialkyl complexes RE(CH₂SiMe₃)₃(THF)₂, respectively. In 1 and 2, the morpholine moiety displayed a stable chair conformation and the resulting ligand coordinated to the rare-earth metal ion in a [NNN]-tridentate chelating fashion. Further studies demonstrated that these dialkyl complexes showed high activity towards the catalytic formation of C–O and C–N bonds in the alcoholysis of isothiocyanates and aminolysis of epoxides. A series of O-thiocarbamate derivatives were achieved in good to excellent yields by reaction of various alcohols with aromatic and aliphatic-substituted isothiocyanates at room temperature. In addition, under solvent-free conditions, the ring-opening reaction of terminal and internal epoxides with arylamines yielded the corresponding β-amino alcohols with excellent regioselectivity. More importantly, a novel β-diketiminato/anilido yttrium alkyl complex LY(NHDipp)(CH₂SiMe₃) (5a) was isolated and characterized by the stoichiometric reaction of 2a with diisopropylaniline.