C–C bond formation through olefin–thiocarbyne coupling in diiron complexes

The bridging diiron thiocarbyne complex [Fe2{μ-CS(Me)}(μ-CO)(CO)2(Cp)2][SO3CF3] (1) reacts with activated olefins (methyl acrylate, acrylonitrile, styrene, diethyl maleate), in the presence of Me3NO and NaH, to give the corresponding μ-allylidene complexes [Fe2{μ-η1:η3-Cα(SMe)Cβ(R′)Cγ(H)(R″)} (μ-CO)(CO)(Cp)2] (R″ = CO2Me, R′ = H, 3a; R″ = CN, R′ = H, 3b; R″ = C6H5, R′ = H, 3c; R″ = R′ = CO2Et, 3d). The coupling reaction of olefin with thiocarbyne is regio- and stereospecific, leading to the formation of only one isomer. C–C bond formation occurs between the less substituted alkene carbon and the thiocarbyne. Moreover, olefinic hydrogens of the bridging ligands are mutually trans. The reactions of 3a–b with MeSO3CF3 result, selectively, in the formation of the cationic μ-sulphonium allylidene complexes [Fe2{μ-η1:η3-Cα(SMe2)Cβ (H)Cγ(H)(R)}(μ-CO)(CO)(Cp)2][SO3CF3] (R = CO2Me, 4a; R = CN, 4b). Compound 4a undergoes displacement of the SMe2 group by nucleophiles such as NaBH4, NBu4CN and NaOMe, affording the complexes [Fe2{μ-η1:η3-Cα(R)Cβ (H)Cγ(H)(CO2Me)}(μ-CO)(CO)(Cp)2] (R = H, 5a; R = CN, 5b; R = OMe, 5c), respectively. The molecular structures of 3a and 5a have been determined by X-ray diffraction studies.