Abstract The action of cyclopentadienide anions on (Cp) 2− n (RCp) n NbCl 2 complexes (n= 2, 1 or 0; R= C (CH 3) 3) is reported. In all cases, the formation of tricyclopentadienyl complexes, identified by ESR spectroscopy, is observed. Some tricyclopentadienyl species are able to be transformed by η 1–η 5 fluctuation. An example of a tricyclopentadienyl complex involving a stereochemical blocking is presented. By use of this intermediate a ...