9-VERTEX AND 8-VERTEX POLYHEDRAL DICARBABORANE CHEMISTRY - NEW ARACHNO AND HYPHO-DICARBABORANES FROM ARACHNO-4,5-C2B7H13 - ISOLATION AND CHARACTERIZATION OF THE [ARACHNO-4,5-C2B7H12]- AND [HYPHO-7,8-C2B6H13]- ANIONS, AND OF THE NEUTRAL LIGAND DERIVATIVES EXO-6-(MENC)-ARACHNO-4,5-C2B7H11 AND EXO-5-L-HYPHO-4,9-C2B7H13 (L=NME3 AND NET3)

Deprotonation of neutral arachno-4,5-C2B7H13 (1) either with 1, 8-(NMe 2)2C10H6 (proton sponge, PS) or with a mixture of aqueous K2CO3 and [N Me4]Cl leads to the isolation in high yield of the [arachno-4,5-C2B7H1 2]- anion (2). Isostructural with this anion is the ligand derivative exo-6-(MeNC)-arachno-4,5-C2B7H11 (3), which is prepared in 20% yield f rom the reaction between arachno-4,5-C2B7H13 and MeNC in dichlorometha ne. Under comparable conditions compound 1 with tertiary amines gives the first representatives of the nine-vertex hypho family of dicarbabo ranes, the ligand derivatives exo-5-(NR3)-hypho-4,9-C2B7H13 (4a and 4b , where R = Me and Et, respectively) in moderate yields (20 - 55%), wh ereas the reaction between 1 and aqueous NaCN results in the selective removal of one boron vertex to yield the eight-vertex [hypho-7,8-C2B6 H13]- anion (5) in 61% yield. All compounds isolated were characterize d by B-11 and H-1 NMR spectroscopy, with two-dimensional and selective decoupling techniques giving unambiguous assignments.