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-dimethylbenzafulvene followed by hydrolysis with a saturated NH4Cl aqueous solution. I can be conveniently converted into the monoanion [Me2C(C9H6)(C2B10H11)]Li (2) and the dianion [Me2C(C9H6)(C2B10H10)]Li-2 (3) by treatment with 1 or 2 equiv of n-BuLi, respectively Both NaNH2 and Nail can only convert 1 into the monoanion, but cannot deprotonate the CH proton of the carborane cage in I. 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)][{eta(5):sigma-Me2C(C9H6)(C2B10H10)}(2)Sm] (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)][{eta(5):sigma-Me2C(C9H6)(C2B10H10)}(2)Sm](5). Unlike the SmI2 case, an equimolar reaction between 3 and YbI2 afforded the Yb(II) compound [eta(5):sigma-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)][(eta(5):sigma-M(e)2C(C9H6)(C2B10H10)}(2)Yb]. C6H5CH3 (7) Reaction of LnCl(3) with 1 or 2 equiv of 2 yielded organolanthanide dichloride and monochloride compounds, respectively, [eta(5)-Me2C(C9H6)(C2B10H11)]GdCl2(THF)(2) (15) and [eta(5)-Me2C(C9H6)(C2B10H11)](2)LnCl(THF)(OEt2) (Ln = Y (8), Yb (9)). Treatment of 9 with 1 or 2 equiv of MeLi gave deprotonation products rac- [(eta(5):sigma-Me2C(C9H6)(C2B10H10)}(eta(5)-Me2C(C9H6)(C2B10H11)}]Yb(mu-Cl)Li(DME)(2) (10) and rac-[Li(DME)(2)][{eta(5):sigma-Me2C(C9H6)(C2B10H10)}(2)Yb] (11), respectively. Reaction of LnCl(3) with 2 equiv of 3 also afforded ionic compounds rac-[Li(DME)(2)][(eta(5):sigma-Me2C(C9H6)(C2B10H10)}(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)][(eta(5):sigma-Me2C(C9H6)(C2B10H10)}(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.