Aromatic hydrocarbons as ligands. Recent advances in the synthesis, the reactivity and the applications of bis(η6-arene) complexes

Synthetic procedures for bis(η6-arene) metal derivatives and aspects of their reactivity are reviewed. Attention is focused on early transition metals (Groups 4–6) but, when necessary, reference will be made to arene derivatives of Groups 7–10, lanthanides and actinides.After a short historical presentation of bis(η6-arene) derivatives, aimed at illustrating the relevance of this class of compounds to the origin and the evolution of organometallic chemistry, the synthetic procedures to bis(η6-arenes) will be discussed in the light of the most recent results. As far as the reactivity of bis(η6-arene) compounds is concerned, particular attention is given to the electron transfer reactions occurring with or without arene displacement; data are reported for the use of low-valent bis(η6-arene) compounds as a useful entry into the inorganic and coordination chemistry of the corresponding metal in non aqueous systems.The use of bis(η6-arene) derivatives of transition metals in low oxidation states (0, +1) as precursors to catalytic systems for the oligomerisation and polymerization of unsaturated monomers and as starting compounds for the preparation of molecule-based magnets, ordered crystals and new materials and supports is described.