Given an outstanding variety of possible cyclopentadienyl (Cp) complexes reported so far, cyclopentadienyl ligands with dimethylsilyl (DMS) or trimethylsilyl (TMS) groups have found widespread synthetic applications. As they are superior in steric demand to the corresponding carbon containing analogues, iso-propyl and tert-butyl, they allow the isolation of reactive f-block and main group complexes and improve hydrocarbon solubility. Moreover, the introduction of silyl groups allows the generation of sensitive (redox)species due to hyperconjugation effects, allowing the isolation of highly reduced organic compounds or low-valent actinide and lanthanide compounds, like {[C5H5-n(SiMe3)n]3M} 1-(n = 1, 2) containing metal centers with a formal oxidation state of +II as demonstrated by the Evans group. Although higher degrees of silylation are expected to result in an increased kinetic stability of low-valent species due to steric demand and changed electronic properties of the Cp ligand, the demanded steric overload and the further changed electronic properties of the Cp ligands pose a formidable synthetic challenge.