Tsüklopentadienyl

Tsüklopentadienyl, often abbreviated as Cp, is a chemical species with the formula C5H5. It is an aromatic cyclic anion derived from cyclopentadiene by the removal of a proton. In its neutral form, cyclopentadiene is a diene that readily dimerizes. However, when deprotonated, the resulting cyclopentadienyl anion is highly resonance-stabilized due to its aromatic character, possessing 6 pi electrons that fulfill Hückel's rule. This stability makes the anion a common ligand in organometallic chemistry.

The tsüklopentadienyl ligand typically binds to metal atoms in a η5 (eta-five) fashion, meaning all five carbon atoms of the ring are coordinated to the metal center. This forms a class of compounds known as metallocenes, which are characterized by a metal atom sandwiched between two tsüklopentadienyl rings, such as ferrocene. Alternatively, it can coordinate in a η1 or η2 fashion, though these are less common. Tsüklopentadienyl complexes are widely used as catalysts in various organic reactions, including polymerization and hydrogenation. They also play significant roles in materials science and medicinal chemistry. The synthesis of tsüklopentadienyl compounds often involves reacting a metal halide with a tsüklopentadienyl salt, like sodium tsüklopentadienide.