CHEMISTRY OF C-TRIMETHYLSILYL-SUBSTITUTED HETEROCARBORANES .14. SYNTHESES OF CLOSO-INDACARBORANES AND THEIR REACTIVITY TOWARD A BIS(BIDENTATE) LEWIS BASE, 2,2'-BIPYRIMIDINE - CRYSTAL-STRUCTURES OF CLOSO-1-(ME2CH)-1-IN-2,3-(SIME3)2-2,3-C2B4H4 AND 1-(2,2'-C8H6N4)-1-(ME2CH)-1-IN-2,3-(SIME3)2-2,3-C2B4H4

The reaction of (i-Pr)Inl2 with the THF-solvated sodium lithium compounds closo-exo-4,5-Li(THF)-l-Na(THF)-2-(SiMe3)-3-R-2,3-C2B4H4 (R = SiMe3, Me, H) in a molar ratio of 1:1 in THF produced closo-l-(Me2CH)-l-In-2,3-(SiMe3)2-2,3-C2B4H4 (1), ClOso-l-(Me2CH)-l-In-2-(SiMe3)-3-Me-2,3-C2B4H4 (II), and closo-l-(Me2CH)-1-In-2-(SiMe3)-2,3-C2B4H5 (III) as air-sensitive colorless oily liquids, in 39, 36, and 27% yields, respectively. The closo-indacarboranes I-III were characterized on the basis of H-1, B-11, and C-13 pulse Fourier transform NMR and IR spectra. Compound I was further characterized by mass spectrometry and X-ray diffraction. The low-temperature, single-crystal X-ray analysis of I shows that the indacarborane is a dimeric cluster having a distorted closo geometry in which the indium atom occupies an apical vertex of a pentagonal bipyramid and is slipped significantly toward the unique boron above the C2B3 face. The indium-bound isopropyl moiety is tilted, with the angle between the In-(i-Pr) bond and the normal from the C2B3 plane through the In atom being equal to 30.3 +/- 1.3-degrees. The closo-indacarborane I crystallized in the triclinic space group P1BAR with a = 11.018(3) angstrom, b = 12.394(3) angstrom, c = 14.485(4) angstrom, alpha = 73.01(2)-degrees, beta = 87.67(2)-degrees, gamma = 89.90(2)-degrees, V = 1890.0(9) angstrom3, and Z = 2. Full-matrix least-squares refinement of I converged at R = 0.027 and R(w) = 0.037. The instantaneous reactions between the closo-indacarboranes and 2,2'-bipyrimidine produced the donor-acceptor complexes 1-(2,2'-C8H6N4)-l-(Me2CH)-1-In-2,3-(SiMe3)2-2,3-C2B4H4 (IV), 1-(2,2'-C8H6N4)-l-(Me2CH)-l-In-2-(SiMe3)-3-Me-2,3-C2B4H4 (V), and 1-(2,2'-C8H6N4)-l-(Me2CH)-l-In-2-(SiMe3)-2,3-C2B4H5 (VI) in 68-91% yields. The complexes IV-VI were all characterized by H-1, B-11, and C-13 NMR and IR spectra. Compound V was also characterized by mass spectrometry and IV by single-crystal X-ray analysis. It crystallized in the monoclinic space group P2(1) with a = 11.428(3) angstrom, b = 9.802(3) angstrom, c = 11.972(3) angstrom, beta = 96.28(2)-degrees, V = 1333.0(6) angstrom3, and Z = 2. Full-matrix least-squares refinement of IV converged at R = 0.026 and R(w) = 0.034. The bonding in these complexes was discussed using molecular orbital theory.