The synthesis, X-ray and DFT structures of the free ansa–cyclopentadiene ligand C5H5CMe2CMe2C5H5

The title compound 2,3-dicyclopentadiene-2,3-dimethylbutane (C5H5CMe2CMe2C5H5) 1 shows the typical staggered conformation of a highly substituted ethane derivative with the two largest substituents (C5H5) adopting a trans position. The molecule shows C2 symmetry about the central C–C bond. Due to the high substitution, the central bond of the ethane is elongated to 160.0 pm (X-ray structure analysis) while the DFT calculation finds a value of 159.2 pm.