Pure and Applied Chemistry

Abstract: 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.