SELECTIVE DISMANTLING OF CLOSO-1,2-C2B10H12 TO LOWER-CAGE DICARBABORANE SYSTEMS

A modified, high-yield synthesis of the two isomeric nido twelve-vertex [C2B10H13]- anions, "reactive" [nido-7,9-C2B10H13]- and "unreactive" [nido-7,12-C2B10H13]-, has been developed. A solution structure for the "reactive" [nido-7,9-C2B10H13]- isomer is proposed on the basis of the results of two-dimensional B-11 and H-1 correlation NMR spectroscopy. It is concluded that there is a marked similarity between this species and the eleven-vertex congener [nido-7,8--C2B9H12]-. In accord with this parallel, the "reactive" twelve-vertex species is found to undergo selective boron-vertex elimination reactions in the presence of oxidizing agents. These reactions give excellent yields of smaller-cage nido dicarbaborane compounds, namely [nido-7,8--C2B9H12]-, [9-(SMe2)-nido-7,8-C2B9H11], and nido-5,6-C2B8H12. NMR spectroscopy assigns cluster B-11 and H-1 resonances for all the compounds isolated, and thence permits comparison with the equivalent shielding patterns of structurally related analogues such as [nido-7-CB10H13]- and [nido-7,9-C2B9H12]-.