Reactions of bridging C3 ligands in diiron complexes: Unconventional routes to new functionalized organic frames

Diiron complexes containing C3 ligands, such as vinyliminium and vinylalkylidene bridging units, display unusual reaction patterns, not observed when the same organic fragments are bound to a single metal center, or not coordinated. Bridging vinyliminium complexes [Fe2{μ-η1:η3-C(NMe2)CH=CR}(μ-CO)(CO)(Cp)2][SO3CF3] undergo nucleophilic addition at the iminium C or at α-C position, which is uncommon since non-coordinated vinyliminium species generally undergo conjugated (Michael type) nucleophilic attack. Likewise, bridging vinyliminium ligands undergo new and unusual transformations consisting of the deprotonation and replacement of the α-CH by a variety of functional groups. These reactions, resulting in the formation of C–C and C–heteroatom single and double bonds, produce new bridging ligands of the type [μ-C(NMe2)C(X)CR) (X = S, O, Se, SPh, CNMe, NNCHCO2Me]. Removal of the vinylalkylidene ligands from the bridging coordination is achieved by a [3 + 2] cycloaddition with alkynes. The reaction leads to the formation of ferrocenes containing one polysubstituted Cp ring, which results from the cycloaddition of the bridging C3 ligand with alkynes. This result suggests a new possible route for the synthesis of polyfunctionalized ferrocenes.