exo-nido- versus closo-lanthanacarboranes.: Synthesis and structure of exo-nido-[(C6H5CH2)2C2B10H10]Ln(DME)3, [exo-nido-{(C6H5CH2)2C2B9H9}Ln(THF)3]2 (Ln = Sm, Yb), and closo-exo-[(C6H5CH2)2C2B10H10]4Sm2Na3

Treatment of LnI(2) with 1 equiv of K-2[(C6H5CH2)(2)C2B10H10] in THF at room temperature gave, after recrystallization from DME, the monomeric exo-nido-[(C6H5CH2)(2)C2B10H10]Ln(DME)(3) (Ln = Sm (1), Yb (2)). They can react with another equivalent of Na-2[(C6H5CH2)(2)C2B10H10] to afford closo-exo-[(C6H5CH2)(2)C2B10H10](4)Ln(2)Na(4)(THF)(2) (Ln = Sm (4), Yb (5)). Reaction of YbCl3 with 2 equiv of K-2[(C6H5CH2)(2)C2B10H10] in THF/DME yielded 2, while treatment of SmCl3 with 2 equiv of K-2[(C6H5CH2)(2)C2B10H10] in THF generated a novel cluster closo-exo-[(C6H5CH2)(2)C2B10H10](4)Sm2Na3 (3). LnI(2) reacted with 2 equiv of Na-2[(C6H5CH2)(2)C2B9H9] in THF to produce the dimeric [exo-nido-{(C6H5CH2)(2)C2B9H9}Ln(THF)(3)](2) (Ln = Sm (6), Yb (7)). These new compounds were fully characterized by spectroscopy and elemental analyses. The solid-state structures of 1-3, 6, and a have been further confirmed by single-crystal X-ray analyses. This study indicates that;steric factors dominate the formation of exo-nido-lanthanacarboranes. In case the substituents are benzyl groups, closo- and exo-nido-lanthanacarboranes of C2B10 systems are exchangeable by changing the ratio of metal to carborane.