Metallacarboranes as an anion and a cation in a single species: a unique example for ion pairs

The reaction of closo-exo-5,6-Na(THF)2-1-Na(THF)2-2,4-(SiMe3)2-2,4-C2B4H4 (1) with anhydrous NdCl3, in a molar ratio of 2:1, produced the full-sandwiched neodymacarborane, 2,2′,4,4′-(SiMe3)4-5,6-[(μ-H)2Na(THF)2]-1,1′-commo-Nd(η5-2,4-C2B4H4)2 (2), as a yellow-green crystalline solid in 80% yield. Compound 2 was further reacted with NdCl3, in 3:1 molar ratio, in a solvent mixture of dry benzene and THF to produce, in 75% yield, the novel dimeric ion-pair, {[closo-1-Nd(μ-H)6-2,4-(SiMe3)2-2,4-C2B4H4]+[1,1′-(THF)2-2,2′,4,4′-(SiMe3)4-5,5′,6,6′-(μ-H)4-1,1′-commo-Nd(η5-2,4-C2B4H4)]−(C4H8O)(C6H6)2}2 (3), consisting of a half-sandwich cationic neodymacarborane that is coordinated to anionic full-sandwiched neodymacarborane. Thus, a dual role of metallacarboranes as both the cation and the anion in a single species has been exemplified.