How big is a Cp? Novel cycloheptatrienyl zirconium complexes with tri-, tetra- and pentasubstituted cyclopentadienyl ligands

The new bulky cyclopentadienyl anions 1,2,4-tri(cyclopentypcyclopentadienide and 2,3-diisopropyl-1,4-dimethyl-5-trimethylsityl-cyclopentadienide were prepared. These and the already known 1,2,4-tri(cyclohexyl)-, 1,2,4-triasopropylk 2,3-diisopropyl-1,4-dimethyl-, 1,3,4-triisopropyt-2,5-dimethyl-, pentaphenyt-, and p-butylphenyl-tetraphenyl-cyclopentadienide as well as tert-butytindenide were coordinated to the cyctoheptatrienylzirconium fragment RCHT)ZrCl(tmeda)1. The nine zirconium complexes of the RCHT)Zr(Cp)] type were characterized by elemental analysis and NMR spectroscopy. For five of the sandwich complexes X-ray crystal structure determination could be carried out; structures of the four others were obtained by DFT calculations. The data serve as a basis for cone angle measurements of cyclopentadienyt ligands to evaluate the steric demand of these tigands.