CHEMISTRY OF C-TRIMETHYLSILYL-SUBSTITUTED HETEROCARBORANES .11. SYNTHETIC, SPECTROSCOPIC, STRUCTURAL, AND BONDING STUDIES ON THE SODIUM, SODIUM-LITHIUM, AND DILITHIUM COMPLEXED CARBONS ADJACENT NIDO-CARBORANE ANIONS [2-(SIME3)-3-(R)-2,3-C2B4H6-N]N- (R = SIME3, ME, H, N = 1, 2) - HIGH-YIELD CONVERSION TO 1,2-DICARBA-CLOSO-HEXABORANE(6) DERIVATIVES - PRECURSORS TO CARBONS APART DIANIONIC CARBORANE LIGANDS

The reaction of nido-2-(SiMe3)-3-(R)-2,3-C2B4H6, with excess NaH in THF or TMEDA produces only the corresponding solvated monosodium nido species, 1-Na(THF or TMEDA)-2-(SiMe3)-3-(R)-2,3-C2B4H5 [R = SiMe3 (I or X), Me (II), H (III)] in almost quantitative yields. Further treatment of this compound in THF or TMEDA with 1 equiv of t-BuLi results in the second deprotonation to produce, in 86-94% yields, the corresponding mixed-metal derivative, closo-exo-Li(THF or TMEDA)-1-Na(THF or TMEDA)-2-(SiMe3)-3-(R)-2,3-C2B4H4 [R = SiMe3 (IV or XI), Me (V), H (VI)]. However, the corresponding dilithium derivatives, both the solvated closo-exo-4,5-[(mu-H)2Li(Me2NCH2)2]-1-Li[(Me2NCH2)2]-2,3-(SiMe3)2-2,3-C2B4H4 (XII) and unsolvated closo-exo-Li-1-Li-2-(SiMe3)-3-(R)-2,3-C2B4H4 [R = SiMe3 (VII), Me (VIII), H (IX)] species, were prepared from the reaction of the nido-carborane with 2 equiv of t-BuLi in TMEDA, THF, and. n-hexane, respectively. The H-1, Li-7, B-11, and C-13 NMR spectra and IR spectra of I-XII are all consistent with their molecular formulas. Molecular weight determinations of I and VII in benzene solution indicated that the compounds exist as monomers in solution. However, the solid state structures of both I and X, found by single crystal X-ray analysis, show the complexes to be dimeric in nature. On the other hand, the crystal structure of XII supports its monomeric structure in solution. While compound I crystallizes in the tricnlinic space group P1BAR, both X and XII crystallized in monoclinic space groups P2(1)/n and P2(1)/c with a = 6.326(17), 11.411(4), and 17.080(4) angstrom, b = 11.82(4),12.271(4), and 16.294(4) angstrom, c = 14.16(5), 17.769(7) and 11.775(4) angstrom, alpha = 75.47(25)-degrees, beta = 80.58(23), 104.43(3), and 97.73-degrees, gamma = 80.50(22)-degrees, V = 1003(5), 2410(l), and 3248(2) angstrom3, and Z = 1, 2, and 4, respectively. The final refinements of I, X, and XII converged at R = 0.086, 0.047, and 0.051 and R(w) = 0.112, 0.059, and 0.060, respectively. The reactions of NiCl2 with the unsolvated closo-dilithiacarboranes (VII-IX) produced the corresponding closo-1-(SiMe3)-2-(R)-1,2-C2B4H4 (XIII-XV) as colorless liquids, thus providing an alternative and inexpensive route for the formation of the 'carbons adjacent'' 1,2-dicarba-closo-hexaborane(6) derivatives.