Reaction of Me2Si(C5H5)Cl with 1 equiv of Li2C2B10H10 in toluene/ether at 0℃, after hydrolysis, gave Me2Si(C5H5)(C2B10H11) (1) in 79% isolated yield. 1 can be conveniently converted into the monoanion [Me2Si(C5H4)(C2B10H11)]Na (2), the dianion [Me2Si(C5H4)-(C2B10H10)]Li2 (3), and the trianion [Me2Si(C5H4)(C2B10H11)]K3 (4) by treatment with NaH, MeLi, and K metal in THF at room temperature, respectively. 2 reacted with 1 equiv of LnCl3 in THF to give [η5-Me2Si(C5H4)(C2B10H11)]LnCl2(THF)3 (Ln) Nd (5), Sm (6), Er (7), Yb (8)) in good yield. Treatment of LnCl3 with 2 equiv of 2 or reaction of [è5-Me2Si(C5H4)-(C2B10H11)]LnCl2(THF)3 with an equimolar amount of 2 in THF resulted in the isolation of [η5-Me2Si(C5H4)(C2B10H11)]2LnCl(THF)2 (Ln) Nd (9), Sm (10), Y (11), Gd (12), Yb (13)) in good yield. Interaction of 3 with LnCl3 in THF in a molar ratio of 1∶1 or 2∶1 or reaction of [η5-Me2Si(C5H4)(C2B10H11)]2LnCl(THF)2 with 2 equiv of MeLi in THF gave the same compounds [{η5:σ-Me2Si(C5H4)(C2B10H10)}2Ln][Li(THF)4] (Ln) Nd (14), Y (15), Er (16), Yb (17)). Treatment of NdCl3 with an equimolar amount of 4 in THF or reaction of [η5-Me2Si-(C5H4)(C2B10H11)]NdCl2(THF)3 with excess K metal in THF produced [η5:η6-Me2Si(C5H4)-(C2B10H11)]Nd(THF)2 (18). Under similar reaction conditions, however, interaction of LnCl3 (Ln) Sm, Yb) with 4 in THF afforded the organolanthanide(Ⅱ) compounds {[η5:η6-Me2Si-(C5H4)(C2B10H11)]LnII(THF)2}{K(THF)2} (Ln) Sm (20), Yb (21)). The Sm analogue of 18, [η5:η6-Me2Si(C5H4)(C2B10H11)]Sm(THF)2 (19), was prepared from an unprecedented redox reaction of SmI2 with 2 equiv of 2 in THF. Reaction of 19 with excess K metal in THF gave 20. Unlike the SmI2 case, interaction of YbI2 with 2 equiv of 2 in THF gave [η5-Me2Si(C5H4)-(C2B10H11)]2YbII(THF)2 (22). All of these compounds were characterized by various spectroscopic and elemental analyses. The solid-state structures of compounds 5, 8, 9, 10, 14, 15, 16, 17, 19, and 22 were confirmed by single-crystal X-ray analyses. The reaction mechanism of the formation of 19 is also proposed.