With respect to AlCp* and GaCp*, the sterically less demanding compound GaCp (Cp = C₅H₅) is still a Sleeping Beauty since its discovery nearly twenty years ago. Up to now it was exclusively available by the reaction of metastable GaX solutions with, for example, LiCp.

A team around Hansgeorg Schnöckel, Karlsruher Institut für Technologie (KIT), and Andreas Schnepf, University Duisburg-Essen, Essen, Germany, presented an easy synthesis of GaCp that can be carried out with standard laboratory equipment. They treated solid “GaI” with NaCp in toluene at low temperatures to obtain a colorless solution of GaCp after filtration.

CaCp is less sterically demanding than the related Cp* compound and might therefore open the possibility of higher coordination numbers in coordination chemistry. Additionally Cp is in general a lot easier to obtain and a much more cost-efficient ligand than Cp*.

• A Convenient Synthesis of Cyclopentadienylgallium – The Awakening of a Sleeping Beauty in Organometallic Chemistry,
  Christian Schenk, Ralf Köppe, Hansgeorg Schnöckel, Andreas Schnepf,
  Europ. J. Inorg. Chem. 2011, 25, 3681–3685.
  DOI: 10.1002/ejic.201100672