13-Vertex Carbacobaltaboranes: Synthesis and Molecular Structures of the 4,1,6-, 4,1,8- and 4,1,12-Isomers of Cp*CoC2B10H12

Abstract

Attempted crystallographic studies of the known compounds 4-Cp-4,1,8-closo-CoC2B10H12 and 4-Cp-4,1,12-closo-CoC2B10H12 were frustrated because of disorder which was impossible satisfactorily to model. Thus the family of Cp* compounds 4-Cp*-4,1,6-closo-CoC2B10H12, 4-Cp*-4,1,8-closo-CoC2B10H12 and 4-Cp*-4,1,12-closo-CoC2B10H12 were prepared. The 11B NMR spectroscopic properties of these compounds are closely similar to those of their Cp analogues. All three compounds were studied crystallographically. The 4,1,8- and 4,1,12-species are isomorphous and partially disordered, however the disorder was successfully modelled and structural analyses of 4,1,8- and 4,1,12-MC2B10 compounds are reported for the first time. A new technique for distinguishing between cage C and B atoms in crystallographic study of (hetero)carboranes is reported. The 12-vertex compound 3-Cp*-3,1,2-closo-CoC2B9H11 is formed as a minor co-product along with 4-Cp*-4,1,6-closo-CoC2B10H12 and is believed to result from partial degradation of the latter. The 12-vertex species has also been subjected to crystallographic analysis.