Synthesis of a New Class of Compounds Containing a Ln−O−Al Arrangement and Their Reactions and Catalytic Properties

Synthesis of a new class of compounds containing a Ln−O−Al moiety has been accomplished by the reaction of LAlOH(Me) (L = HC(CMeNAr)₂, Ar = 2,6-iPr₂C₆H₃) with a series of Cp₃Ln compounds. The terminal Al−OH group shows selective reactivity, and the complexes Cp₂Ln(THF)−O−AlL(Me) (Ln = Yb, 1; Er, 2; Dy, 3), Cp₂Yb−O−AlL(Me) (4), and Cp₃Ln(μ-OH)AlL(Me) (Ln = Er, 5; Dy, 6; Sm, 7) were obtained. This allows further insight into the proton exchange process, and two different mechanisms, intermolecular and intramolecular elimination of CpH, are proposed under different conditions. Complexes 1−4, 6, and 7 have been characterized by X-ray structural analyses which reveals a Ln−O−Al or Ln(μ-OH)Al core in these complexes. The obtuse Ln−O−Al angles fall in the range 151.9−169.8°. The reaction of 1 or 4 with Me₃SnF in toluene under refluxing conditions unexpectedly yielded the compounds [Cp₂Yb(μ-OSnMe₃)]₂ (8) and LAl(Me)F (9). Reactions of LAlOH(Me) with the mono- and dicyclopentadienyl complexes LYbCp(Cl) (10) and LYbCp₂ (11) supported by the bulky β-diketiminate ligand were unsuccessful. However, the reaction of LAl(OH)Me with LYbN(SiMe₃)₂Cl (12) containing a labile Yb−N bond leads to the formation of LYbCl−O−AlL(Me) (13) under elimination of HN(SiMe₃)₂. Furthermore, complexes 1, 3, 4, and 6 exhibit good catalytic activity for the polymerization of ε-caprolactone.