Synthesis, structure, and reactivity of 13-vertex carboranes and 14-vertex metallacarboranes

Syntheses, properties, and synthetic applications of 13-vertex closo- and nido-carboranes are reported. Reactions of the nido-carborane salt [(CH2)3C2B10H10]Na2 with dihaloborane reagents afforded 13-vertex closo-carboranes 1,2-(CH2)3-3-R-1,2-C2B11H10 (R = H (2), Ph (3), Z-EtCH=C(Et) (4), E-(t)BuCH=CH (5)). Treatment of the arachno-carborane salt [(CH2)3C2B10H10]Li4 with HBBr2.SMe2 gave both the 13-vertex carborane 2 and a 14-vertex closo-carborane (CH2)3C2B12H12 (8). On the other hand, the reaction of [C6H4(CH2)2C2B10H10]Li4 with HBBr2.SMe2 generated only a 13-vertex closo-carborane 1,2-C6H4(CH2)2-1,2-C2B11H11 (9). Electrophilic substitution reactions of 2 with excess MeI, Br2, or I2 in the presence of a catalytic amount of AlCl3 produced the hexa-substituted 13-vertex carboranes 8,9,10,11,12,13-X6-1,2-(CH2)3-1,2-C2B11H5 (X = Me (10), Br (11), I (12)). The halogenated products 11 and 12 displayed unexpected instability toward moisture. The 13-vertex closo-carboranes were readily reduced by groups 1 and 2 metals. Accordingly, several 13-vertex nido-carborane dianionic salts [nido-1,2-(CH2)3-1,2-C2B11H11][Li2(DME)2(THF)2] (13), [[nido-1,2-(CH2)3-1,2-C2B11H11][Na2(THF)4]]n (13a), [[nido-1,2-(CH2)3-3-Ph-1,2-C2B11H10][Na2(THF)4]]n (14), [[nido-1,2-C6H4(CH2)2-1,2-C2B11H11][Na2(THF)4]]n (15), and [nido-1,2-(CH2)3-1,2-C2B11H11][M(THF)5] (M = Mg (16), Ca (17)) were prepared in good yields. These carbon-atom-adjacent nido-carboranes were not further reduced to the corresponding arachno species by lithium metal. On the other hand, like other nido-carborane dianions, they were useful synthons for the production of super-carboranes and supra-icosahedral metallacarboranes. Interactions of 13a with HBBr2.SMe2, (dppe)NiCl2, and (dppen)NiCl2 gave the 14-vertex carborane 8 and nickelacarboranes [eta5-(CH2)3C2B11H11]Ni(dppe) (18) and [eta5-(CH2)3C2B11H11]Ni(dppen) (19), respectively. All complexes were fully characterized by various spectroscopic techniques and elemental analyses. Some were further confirmed by single-crystal X-ray diffraction studies.