Cyclopentadienyl and Phospholyl Complexes of the Group 4 Metals

Organometallic complexes containing the 5-membered rings cyclopentadienyl or phospholyl as π-ligands (so-called metallocene complexes) with group 4 metals have been investigated for several decades with a sustained effort in the scientific community. Titanium, zirconium and hafnium compounds containing one, or two Cp rings (“half-sandwich” or “sandwich” complexes, respectively) and their phospholyl analogues have witnessed a widespread use in many application areas including organic synthesis, homogeneous catalysis and material science. The last two decades have seen a significant development of this research field, with new classes of sandwich and half-sandwich complex emerging, and particular applications in small molecule activation, dehydrocoupling reactions and polymerization catalysis. This article gives a detailed account of the research into cyclopentadienyl and phospholyl complexes with group 4 metals (Ti, Zr and Hf) over the period 2000–2020.