The imidazolin-2-imino-functionalized tetramethylcyclopentadiene, 3-H, has been prepared by the reaction of two equivalents of 1,3-diisopropyl-4,5- dimethylimidazolin-2-imine (1) with 5-(chlorodimethylsilyl)-1,2,3,4-tetramethyl- 1,3-cyclopentadiene (2). The reactions of 3-H with the trimethylsilylmethyl (neosilyl) [Ln(CH2SiMe3)3(THF)2] (Ln = Sc, Y, Lu) complexes afford tetramethylsilane and the constrained-geometry [(η5:η1-3)Ln(CH2SiMe3) 2] (Ln = Sc, 4a; Ln = Y, 4b; Ln = Lu, 4c) complexes, whereas the analogous bis(trimethylsilyl)amido (HMDS) calcium complex, [(η5: η1-3)-Ca(HMDS)(THF)] (5), can be obtained from 3-H and [Ca(HMDS)2(THF)2] with loss of hexamethyldisilazane, (Me3Si)2NH. The molecular structures of 4a-4c and 5 have been established by X-ray diffraction analyses, which confirm in all cases the formation of complexes with a chelating Me2Si-bridged cyclopentadienyl- imidazolin-2-imine ligand. The presence of short Ln-N and Ca-N bonds is indicative of the strong electron-donating capacity of the imidazolin-2-imino nitrogen atom, which is based on the ability of the imidazolium ring to effectively stabilize a positive charge. The rare earth metal complexes 4a-4c can be used as efficient catalysts for the hydroamination/cyclization reaction of terminal aminoalkenes and aminoalkynes. © 2008 Wiley-VCH Verlag GmbH & Co. KGaA.