When THIELE prepared KC5H5 from potassium and cyclopentadiene in 1901, he laid the foundation for the discipline of cyclopentadieny chemistry. The synthesis of ferrocene – the first cyclopentadieny transition metal complex – by PAUSON and MILLER, is usually counted as the most outstanding discovery in this area. Subsequent to the synthesis, WILKINSON, WOODWARD and FISCHER concluded that the complex had a sandwich structure.
They proposed the orbitals of the ligand to be involved in the metal-ligand bonding. Nowadays the cyclopentadienyl group (Cp) is one of the most important ligands in organometallic chemistry, forming stable and easy accessible complexes with nearly every transition metal. Beside the metallocenes – which contain two cyclopentadieny ligands – the halfsandwich complexes are of huge scientific interest…
