Carbon versus Silicon Bridges. Synthesis of a New Versatile Ligand and Its Applications in Organolanthanide Chemistry

A new carbon-bridged versatile ligand Me2C(C9H7)(C2B10H11) (1) has been designed and
successfully prepared by treatment of Li2C2B10H10 with 1 equiv of 6,6-dimethylbenzofulvene
followed by hydrolysis with a saturated NH4Cl aqueous solution. 1 can be conveniently
converted into the monoanion [Me2C(C9H6)(C2B10H11)]Li (2) and the dianion [Me2C(C9H6)(C2B10H10)]Li2 (3) by treatment with 1 or 2 equiv of n-BuLi, respectively. Both NaNH2 and
NaH can only convert 1 into the monoanion, but cannot deprotonate the CH proton of the
carborane cage in 1. These results differ significantly from those of a closely related analogue,
Me2Si(C9H7)(C2B10H11). Treatment of SmI2 with 1 equiv of 3, followed by reaction with 1
equiv of 2, gave the redox product rac-[Li(DME)2][{η5:σ-Me2C(C9H6)(C2B10H10)}2Sm] (4). 4
can also be prepared by reaction of SmI2 with 1 equiv of 3 in a relatively lower yield. These
two reactions may undergo different pathways, an intramolecular electron-transfer pathway
for the former and an intermolecular electron-transfer pathway for the latter. The latter
reaction can be accelerated by addition of CS2 or PhC⋮CPh, which led to the isolation of
rac-[Li(THF)4][{η5:σ-Me2C(C9H6)(C2B10H10)}2Sm] (5). Unlike the SmI2 case, an equimolar
reaction between 3 and YbI2 afforded the Yb(II) compound [η5:σ-Me2C(C9H6)(C2B10H10)]Yb(DME)2 (6). 6 can react with 1 equiv of 2 to generate a C−H bond reduction product, rac-[Li(DME)3][{η5:σ-Me2C(C9H6)(C2B10H10)}2Yb]·C6H5CH3 (7). Reaction of LnCl3 with 1 or 2 equiv
of 2 yielded organolanthanide dichloride and monochloride compounds, respectively, [η5-Me2C(C9H6)(C2B10H11)]GdCl2(THF)2 (15) and [η5-Me2C(C9H6)(C2B10H11)]2LnCl(THF)(OEt2) (Ln
= Y (8), Yb (9)). Treatment of 9 with 1 or 2 equiv of MeLi gave deprotonation products
rac-[{η5:σ-Me2C(C9H6)(C2B10H10)}{η5-Me2C(C9H6)(C2B10H11)}]Yb(μ-Cl)Li(DME)2 (10) and rac-[Li(DME)2][{η5:σ-Me2C(C9H6)(C2B10H10)}2Yb] (11), respectively. Reaction of LnCl3 with 2 equiv
of 3 also afforded ionic compounds rac-[Li(DME)2][{η5:σ-Me2C(C9H6)(C2B10H10)}2Ln] (Ln =
Yb (11), Nd (12), Er (13)). Recrystallization of 7 from a mixed solvent of toluene/DME (10:1)
gave meso-[Li(DME)3][{η5:σ-Me2C(C9H6)(C2B10H10)}2Yb]·2C6H5CH3 (14). All of these compounds were fully characterized by various spectroscopic and elemental analyses. The
molecular structures of 4−7, 11, 12, and 14 have been confirmed by single-crystal X-ray
analyses. The structural analyses reveal that the anions in 7 (or 11) and 14 are one pair of
diastereomers.