This document discusses metal cyclopentadiene complexes, including their preparation, properties, and bonding. It introduces cyclopentadiene, noting that it dimerizes at room temperature and is used as a precursor for metallocenes. Metal cyclopentadiene complexes can be prepared by reacting sodium cyclopentadienide with metal halides like nickel chloride. Cyclopentadiene is used as a precursor for catalysis and copolymers, and can be semi-hydrogenated to form cyclopentene. It is also a precursor in the synthesis of compounds like dodecahedrane.