Synthesis of a new class of compounds containing a Ln-O-Al moiety has been accomplished by the reaction of LAIOH(Me) (L = HC(CMeNAr)(2), Ar = 2,6-iPr(2)C(6)H(3)) with a series of CP(3)Ln compounds. The terminal Al-OH group shows selective reactivity, and the complexes CP(2)Ln(THF)-O-AlL(Me) (Ln = Yb, 1; Er, 2; Dy, 3), CP2Yb-O-AlL(Me) (4), and CP(3)Ln(mu-OH)AIL(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(mu-OH)AI core in these complexes. The obtuse Ln-O-Al angles fall in the range 151.9-169.8 degrees. The reaction of 1 or 4 with Me3SnF in toluene under refluxing conditions unexpectedly yielded the compounds [CP2Yb(mu-OSnMe3)](2) (8) and LAI(Me)F (9). Reactions of LAIOH(Me) with the mono- and dicyclopentaclienyl complexes LYbCp(CI) (10) and LYbCp2 (11) Supported by the bulky beta-diketiminate ligand were unsuccessful. However, the reaction of LAI(OH)Me with LYbN(SiMe3)(2)Cl (12) containing a labile Yb-N bond leads to the formation of LYbCl-O-AIL(Me) (13) under elimination of HN(SiMe3)(2). Furthermore, complexes 1, 3, 4, and 6 exhibit good catalytic activity for the polymerization of c-caprolactone.