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

A new carbon-bridged versatile ligand Me 2 C(C 9 H 7 )(C 2 B 10 H 11 ) ( 1 ) has been designed and successfully prepared by treatment of Li 2 C 2 B 10 H 10 with 1 equiv of 6,6-dimethylbenzofulvene followed by hydrolysis with a saturated NH 4 Cl aqueous solution. 1 can be conveniently converted into the monoanion [Me 2 C(C 9 H 6 )(C 2 B 10 H 11 )]Li ( 2 ) and the dianion [Me 2 C(C 9 H 6 )(C 2 B 10 H 10 )]Li 2 ( 3 ) by treatment with 1 or 2 equiv of n -BuLi, respectively. Both NaNH 2 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, Me 2 Si(C 9 H 7 )(C 2 B 10 H 11 ). Treatment of SmI 2 with 1 equiv of 3, followed by reaction with 1 equiv of 2, gave the redox product rac -[Li(DME) 2 ][{η 5:σ-Me 2 C(C 9 H 6 )(C 2 B 10 H 10 )} 2 Sm] ( 4 ). 4 can also be prepared by reaction of SmI 2 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 CS 2 or PhC⋮CPh, which led to the isolation of rac -[Li(THF) 4 ][{η 5:σ-Me 2 C(C 9 H 6 )(C 2 B 10 H 10 )} 2 Sm] ( 5 ). Unlike the SmI 2 case, an equimolar reaction between 3 and YbI 2 afforded the Yb(II) compound [η 5:σ-Me 2 C(C 9 H 6 )(C 2 B 10 H 10 )]Yb(DME) 2 ( 6 ). 6 can react with 1 equiv of 2 to generate a C−H bond reduction product, rac -[Li(DME) 3 ][{η 5:σ-Me 2 C(C 9 H 6 )(C 2 B 10 H 10 )} 2 Yb]·C 6 H 5 CH 3 ( 7 ). Reaction of LnCl 3 with 1 or 2 equiv of 2 yielded organolanthanide dichloride and monochloride compounds, respectively, [η 5 -Me 2 C(C 9 H 6 )(C 2 B 10 H 11 )]GdCl 2 (THF) 2 ( 15 ) and [η 5 -Me 2 C(C 9 H 6 )(C 2 B 10 H 11 )] 2 LnCl(THF)(OEt 2 ) (Ln = Y ( 8 ), Yb ( 9 )). Treatment of 9 with 1 or 2 equiv of MeLi gave deprotonation products rac- [{η 5:σ-Me 2 C(C 9 H 6 )(C 2 B 10 H 10 )}{η 5 -Me 2 C(C 9 H 6 )(C 2 B 10 H 11 )}]Yb( μ -Cl)Li(DME) 2 ( 10 ) and rac -[Li(DME) 2 ][{η 5:σ-Me 2 C(C 9 H 6 )(C 2 B 10 H 10 )} 2 Yb] ( 11 ), respectively. Reaction of LnCl 3 with 2 equiv of 3 also afforded ionic compounds rac -[Li(DME) 2 ][{η 5:σ-Me 2 C(C 9 H 6 )(C 2 B 10 H 10 )} 2 Ln] (Ln = Yb ( 11 ), Nd ( 12 ), Er ( 13 )). Recrystallization of 7 from a mixed solvent of toluene/DME (10:1) gave meso -[Li(DME) 3 ][{η 5:σ-Me 2 C(C 9 H 6 )(C 2 B 10 H 10 )} 2 Yb]·2C 6 H 5 CH 3 ( 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.