Ferrabenzene formation and other outcomes in the base-driven reaction of diiron µ-vinyliminium complexes with ethyl diazoacetate

The reaction of a series of diiron μ-vinyliminium complexes, [Fe2Cp2(CO)(µ-CO){µ-η1-η2-C(R’)CHCN(Me)(R)}]CF3SO3 (2a-h), with N2CHCO2Et and tBuOK in THF solution led to different outcomes depending on R and R’, including formation of iron-coordinated six-membered ferracycles, hydrazone-vinyliminium ligands, alkyne de-insertion and fragmentation to monoiron products. A mixture of [FeCp2(CO)(µ-CO){µ-η1-η2-C(Cy)C{=NN=CH(CO2Et)}CN(Me)(Bn)}], 3c, and [FeCp{κFe,k5C-FeCp(CO)C(O)C(CO2Et)C(NMeBn)CHC(Cy)}], 5c, was obtained for R = benzyl (Bn) and R’ = cyclohexyl (Cy). Analogously, a mixture of [Fe2Cp2(CO)(µ-CO){µ-η1:η2-C(2-C6H4F)C(N(Me)N=CHCO2Et)C=NMe2}]CF3SO3, 4e, and [FeCp{κFe,κ5C-FeCp(CO)C(OMe)C(CO2Et)C(NMe2)CHC(2-C6H4F)}]CF3SO3, 6e, was recovered from R = Me, R’ = 2-C6H4F after a final methylation step. The hydrazone complex [Fe2Cp2(CO)(µ-CO){µ-η1-η2-C(Cy)C(=NN=CHCO2Et)CN(Me)(Cy)}], 3d, was isolated along with impurities from R = R’ = Cy. The μ-aminocarbyne complexes [Fe2Cp2{C(O)Me}(CO)(µ-CO){µ-CN(Me)(R)}] (R = Me, 7a; Bn, 7b) were isolated in 36–50 % yields from R = Me, Bn and R’ = SiMe3 after alumina chromatography. The monoiron complex [FeCp(CO){C(NMeXyl)CHC(Tol)C(=O)}], 9, was formed in 55 % yield from R = meta-xylyl (Xyl), R' = para-tolyl (Tol). All products were identified by IR and multinuclear NMR spectroscopy, and crystallographic characterization was performed on the ferrabenzene compound [FeCp{κFe,κ5C-FeCp(CO)C(OMe)C(CO2Et)C(NMe2)CHC(Cy)}]CF3SO3, 6a, and on 7a.