Some Chemistry of Pentakis(methoxycarbonyl)cyclopentadiene, HC₅(CO₂Me)₅, and Related Molecules

Abstract

This article summarizes the results of investigations into the chemistry of HC₅(CO₂Me)₅ and, in particular, of metal complexes containing the C₅(CO₂Me)₅ ligand . As an anion, the ligand is very stable, forming air-stable, water-soluble salts with many cations with coordination to the metal atom in the solid state generally occurring through the ester carbonyl groups. Second- and third-row transition metals form complexes which retain the covalent ligand-metal bond in solution, 'harder' metals coordinating by the ester carbonyl groups, while 'softer' metals are bound to the ring carbons; a variety of behaviour is shown by the Group 11 metals. Even when the ligand is η⁵-bonded to the metal, ready displacement by other ligands may occur, as found with Ru (η-C₅H₅){η⁵-C₅(CO₂Me)₅}, for example. In the rhodium system, formal replacement of CO₂Me groups by hydrogen is found, as with the formation of [ Rh {η⁵-C₅H₂(CO₂Me)₃}₂][C₅(CO₂Me)₅]. Brief mention is made of other polysubstituted cyclopentadienyls with electron-withdrawing ligands and some related compounds, and their metal derivatives where known.