13-vertex carbacobaltaboranes: Synthesis and molecular structures of the 4,1,6-, 4,1,8- and 4,1,12-isomers of Cp*CoC₂B₁₀H₁₂

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.