The enhanced structural carborane effect

Comparison of the structure of 3-Cp-1,2-μ-(C4H4)-1,2-closo-CoC2B9H9 with that of 3-Cp-1,2-μ-(C4H6)-1,2-closo-CoC2B9H9 supports the idea of an enhanced structural carborane effect in the former arising from partial involvement of the cage carbon pπ orbitals in the exopolyhedral C6 ring, affording this a degree of aromaticity.156