Cationic (η⁶‐arene)‐ and Neutral (η⁵‐cyclohexadienyl)‐tricarbonylmanganese Complexes: Synthesis and Reactivity

Abstract

The tricarbonyl‐chromium and ‐manganese groups are known to easily coordinate arene rings to form η 6 ‐arene complexes. The electrophilic nature of the tricarbonyl metal fragments makes the arene electron‐deficient and renders it susceptible to nucleophilic attack. It is for these reasons that a new trend has emerged, the study of the chemistry of (η 5 ‐cyclohexadienyl)Mn(CO) 3 complexes which are easily obtained by addition of a nucleophile to the arene ring. In the last ten years, the discovery of new methods of functionalization involving Pd cross‐coupling and lithiation reactions has greatly expanded the scope of the (η 5 ‐cyclohexadienyl)Mn(CO) 3 complexes and consequently represents a key step in the development of the arene manganese chemistry since [(η 6 ‐arene)Mn(CO) 3 ] + complexes can be easily obtained by rearomatization of the corresponding (η 5 ‐cyclohexadienyl)Mn derivatives. The present review aims to describe the situation for the synthesis and the reactivity of η 6 ‐arene‐Mn complexes as well as that of η 5 ‐cyclohexadienyl‐Mn complexes to highlight the recent breakthrough in their chemistry. The main reactivities described for η 5 Mn complexes correspond to nucleophilic addition, lithiation/electrophilic quench, lithium/halogen exchange and Pd catalyzed reactions. These types of reactions can be efficiently compared with those well studied in η 6 arenetricarbonylchromium complexes. All these recent developments in the functionalization of η 5 ‐ and η 6 ‐Mn complexes described in this chapter clearly open a revival period for this type of complexes which are starting to emerge as a valuable and versatile class of compounds more environmentally friendly than their Cr analogs.