Polysubstituted ferrocenes from [3 + 2] cycloaddition of alkynes with diiron bridging C3 ligands: Vinyliminium, bis-alkylidene and enimine

• [3 + 2] cycloaddition of bridging C3 ligands and alkynes.
• Straightforward synthesis of functionalized Ferrocenes.
• Activation of bridging ligands in diiron complexes.
• Iron promoted cycloaddition reactions.

The vinyliminium complexes [Fe2{μ-η1:η3-C(R′)C(R)CNMe2}(μ-CO)(CO)(Cp)2][SO3CF3] (R = H, R′ = Tol, 6a; R = H, R′ = Me, 6b; R = R′ = Me, 6c; R = H, R′ = CO2Me, 6d; R = R′ = Et, 6e; R = H, R′ = nBu 6f; Tol = p-MeC6H4) react with HCCCPh2OH affording the corresponding polysubstituted ferrocenes [1-NMe2-2-CPh2OH-4-R′-5-R-Fc] (7a–f). The polysubstituted Cp ring results from [3 + 2] cycloaddition of the bridging ligand with the alkyne, and formation of ferrocenyl products implies fragmentation of the diiron parent complexes. The reaction of 6a yields also the oxo-η5-cyclohexadienyl complex [Fe{η5–C6H2O(NMe2)(Tol)(CPh2OH)}(Cp)] (8), which results from a [3 + 2 + 1] cycloaddition involving the bridging vinyliminium, the alkynol and CO.The bis-alkylidene complex [Fe2{μ-η1:η2-C(R′)CH2C = N(Me)(Xyl)}(μ-CO)(CO)(Cp)2] (9) (Xyl = 2,6-Me2C6H3) reacts similarly with alkynes (HC≡CR, R = Ph, CPh2OH, CO2Me) affording polysubstituted ferrocenes as a mixture of the two isomeric forms: [1-N(Me)(Xyl)-3-R-4-Tol-Fc] (R = Ph, 10a; R = CPh2OH, 11a, R = CO2Me 12a) and [1-N(Me)(Xyl)-2-R-4-Tol-Fc] (10b, 11b, 12b), respectively. Likewise, the μ-enimine complex [Fe2{μ-η1:η3-C(Et) = C(Et)C=NMe}(μ-CO)(CO)(Cp)2] (13) undergoes [3 + 2] cycloaddition with alkynes (HCCR, R = Tol, CH2OH) leading to the formation of the corresponding polysubstituted ferrocenes [1-NH(Me)-2-R-4-Et-5-Et-Fc] (R = Tol, 14; R = CH2OH, 15). The X-ray molecular structure of 7c has been determined.

Diiron bridging C3 ligands (vinyliminium, bis-alkylidene and enimine) undergo [3 + 2] cycloaddition with alkynes affording polysubstituted ferrocenes, which are otherwise difficult to obtain.Figure optionsDownload as PowerPoint slide