The beginnings of organometallic chemistry can be traced back to the discovery of ZEISE´s salt in 1827, the zinc alkyl synthesis by FRANKLAND in 1849 and, in 1901, the first preparation of KC5H5 out of potassium and cyclopentadiene by THIELE, who thus laid the foundation of cyclopentadienyl chemistry. Usually counted as one of the most significant discoveries during the early days of organometallic chemistry is,
50 years later, the synthesis of ferrocene (as the first reaction of a cyclopentadienyl ring with a transition metal) by KEALY, PAUSON and MILLER and the deduced sandwich structure by WILKINSON, WOODWARD and FISCHER in 1952, proposing for the first time the involvement of orbitals of the ligand for the metal-ligand connectivity. Since then, the coordination chemistry of cyclopentadienyl (Cp) compounds has grown extensively. Undoubtly, the cyclopentadienyl group is one of the most important ligands in organometallic chemistry as it forms stable and easily accessible complexes with all transition metals. We distinguish between metallocenes and half-sandwich complexes…