Dicarbaheteroborane Chemistry. Representatives of Two Eleven-Vertex Dicarbaazaundecaborane Families: nido-10,7,8-NC(2)B(8)H(11), Its N-Substituted Derivatives, and arachno-1,8,11-NC(2)B(8)H(13).

Treatment of an acidified solution of the [nido-7,8-C(2)B(9)H(12)](-) anion (1(-)) with NaNO(2) at 0 degrees C in the presence of benzene resulted in the formation of two eleven-vertex azadicarbaboranes, nido-10,7,8-NC(2)B(8)H(11) (2) and arachno-1,8,11-NC(2)B(8)H(13)( )()(3), isolated in yields of 15 and 35%, respectively, together with a small amount (0.9%) of 5-Ph-nido-7,8,10-C(2)NB(8)H(10) (5-Ph-2). Compound 3 was converted in 68% yield into 2 by reaction with PS (PS = "proton sponge"; 1,8-(dimethylamino)naphthalene and acetone. Deprotonation of 2 at the N(10)H vertex gave the [nido-10,7,8-NC(2)B(8)H(10)](-) anion (2(-)), which was easily alkylated with Me(2)SO(4) or PhCH(2)Br to produce the N-alkylated derivatives of 2, 10-R-nido-10,7,8-NC(2)B(8)H(10), where R = Me (10-Me-2, 86%) and PhCH(2) (10-PhCH(2)-2, 69%). The geometries of the parent dicarbazaboranes 2 and 3 were optimized at the MP2(fc)/6-31G level, and the structures of all compounds were thence confirmed by the excellent agreement between experimental data and IGLO/NMR calculations of the (11)B chemical shifts for the parent compounds at the DZ//6-31G, DZ//MP2/6-31G, and II'//MP2/6-31G levels.