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.