1-ALKYL-1-AZA-CLOSO-DODECABORANE - A NOVEL ACCESS TO THE ICOSAHEDRAL NB11 SKELETON

arachno-B9H13(SMe2) was transformed into arachno-B9H13(NRH2) (1a-d; R = nBu, tBu, tBuCH2, PhCH2) by reaction with primary amines. The therma l dehydrogenation of 1a-d gave nido-RNB9H11 (2a-d). The addition of C= NtBu to the azaboranes 2b,d gave arachno-RNB9H11(CNtBu)(3b,d). The aza boranes 2c,d were heated with an excess of Me2S.BH3 at 170-degrees-C i n decalin, yielding closo-RNB11H11(4c,d). Aza-closo-dodecaboranes of t he same type (4e-g; R = Et, iPr, iBu) were also obtained by alkylating the azadodecaborate [Et3HN][NB11H11] with [Et3O]BF4 Or with the trifl ates RO3SCF3 (R = iPr, iBu), respectively. All of the products were ch aracterized by H-1 and B-11 NMR, using 2-D B-11/B-11 techniques in the case of 1c,2b, and 4e. The structure of the closo cluster 4d was show n to represent a distorted icosahedron. The N atom is distinctly close r to the polyhedral center M (M-N = 1.535 angstrom) than the atom B12 (M-B12 = 1.651 angstrom). The neighboring B-H bonds are shifted from t he radial direction toward the N atom. Crystal data for 4d: space grou p P2(1)/n, Z = 4, a = 9.041(4) angstrom, b = 14.651(7) angstrom, c = 1 1.224(4) angstrom, beta = 96.14(3)degrees, R = 0.053.