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

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.