Building block for synthesis. Frequently used as precursors to di-tert-butylcyclopentadienyl (Cpt) ligand in many sandwich and half sandwich complexes. Di-tert-butylcyclopentadiene reacts with excess potassium tert-butoxide in the presence of elemental selenium to yield cyclopentadienes bridged by two or three selenium atoms through one or two diselenoketal functionalities. It reacts with excess potassium tert-butoxide in the presence of elemental sulfur to yield cyclopentadienes bridged by sulfur atoms via one or two dithioketal functionalities.