Iron Pentacarbonyl - Fe(CO)₅

Introduction

The title compound [1] [and its higher order congeners Fe₂(CO)₉ and Fe₃(CO)₁₂] exhibits several features which have made it particularly attractive as a reagent in organic synthesis. These features include: (i) the nucleophilic attack at one of the CO ligands to generate iron carbonylates; [2] (ii) carbonyl insertion reactions; and (iii) its ability to undergo under thermal or photochemical conditions an in situ dissociative loss of one or more CO ligand and subsequent complexation of the coordinatively unsaturated iron to an organic substrate. Pattern (i) has proven useful mainly due to the reducing properties of iron carbonylates (Abstract A). Pattern (ii) now allows the efficient preparation of cyclohexenones (Abstract B), β-, γ- or δ-lactones and lactams (Abstract C) and also cyclopentadienones (Abstract D), compounds which have all proven useful in total synthesis. Finally and most importantly, reactions of type (iii) include the isomerisation of olefins with either a stoichiometric or catalytic amount of Fe(CO)₅, [3] the use of tricarbonyl iron group for the stabilization of highly labile molecules, the use of tricarbonyl(η⁴-1,3-diene)iron complexes [4] to protect, under a number of reaction conditions, (e.g. hydrogenation, acylation, hydroboration, cycloaddition, epoxydation, osmylation and Michael addition) a 1,3-diene unit (Abstract E), the use of the tricarbonyl iron moiety to control the stereoselectivity of reactions on a neighboring functional group (Abstract E), and mainly, the well known reactivity of the corresponding η⁵-dienyl salt (Abstract F). It should be noted here that, though the tricarbonyliron complexes are easy to prepare on a large scale, are stable and easily handled in classical laboratory conditions, the title reagent Fe(CO)₅ is highly toxic and volatile, and therefore great care must be taken in its handling and storage conditions.

References

• For previous reports on Fe(CO)₅, see:
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