ELECTRON-ACCEPTOR BEHAVIOR OF 2,4,7,9-TETRACARBA-NIDO-DODECABORANE(12) WITH GROUP 1 AND GROUP 2 METALS : SYNTHESES AND CRYSTAL STRUCTURES OF (THF)4LI( SIME3)4C4B8H9 AND (THF)2MG(SIME3)4C4B8H8

The room-temperature reaction between a THF solution of 2,4,7,9-tetracarba-nido-dodecaborane(12) (SiMe3)4C4B8H8 and finely cut excess lithium or magnesium metal, in the absence of naphthalene and aromatic solvents, produced either {[(THF)4Li][(SiMe3)4C4B8H9]} (1) as an EPR-silent transparent crystalline solid in 41% yield or [(THF)2Mg(SiMe3)4C4B8H8] (2) as an off-white crystalline solid in 88% yield. While the solid-state structure of 1 showed a single anionic [(SiMe3)4C4B8H9]- unit that was well-separated from a discrete [Li(THF)4]+ cation, the structure of 2 is that of a novel magnesacarborane in which the carborane cage incorporates both electron-precise and electron-deficient carbon and boron atoms.