Zwitterionic diiron vinyliminium complexes: alkylation, metalation and oxidative coupling at the S and Se functionalities

The zwitterionic vinyliminium complex [Fe2{μ-η1:η3-C(R′)C(S)CN(Me)(Xyl)}(μ-CO)(CO)(Cp)2] (2a) (R′ = p-Me-C6H4 (Tol), Xyl = 2,6-Me2C6H3) undergoes electrophilic addition at the S atom by HSO3CF3, MeSO3CF3, SiMe3Cl, BrCH2Ph, ICH2CHdouble bond; length as m-dashCH2 affording the complexes [Fe2{μ-η1:η3-C(Tol)C(SX)CN(Me)(Xyl)}(μ-CO)(CO)(Cp)2][Y] (X = H, Y = SO3CF3, 4a; X = Me, Y = SO3CF3, 4b; X = SiMe3, Y = Cl, 4c; X = CH2Ph, Y = Br, 4d; X = CH2CH; CH2, Y = I, 4e). Compound 2a and the corresponding vinyliminium complexes 2b and 2c (R′ = CH2OH, 2b; R′ = Me, 2c) react also with etherated BF3 leading to the formation of the corresponding S-adducts [Fe2{μ-η1:η3-C(R′)C(SBF3)CN(Me)(Xyl)}(μ-CO)(CO)(Cp)2] (R′ = Tol, 5a; R′ = CH2OH, 5b; R′ = Me, 5c). In analogous reactions, the zwitterionic vinyliminium complexes undergo S-metalation upon treatment with in situ generated [Fp]+[SO3CF3]− [Fp = Fe(CO)2(Cp)], leading to the formation of [Fe2{μ-η1:η3-C(R′)C(S–Fp)CN(Me)(Xyl)}(μ-CO)(CO)(Cp)2][SO3CF3](R′ = CH2OH, 6a; R′ = Me, 6b; R′ = Bun, 6c). Similarly, zwitterionic vinyliminium containing Se in the place of S also undergo Se-electrophilic addition. Thus, the complexes [Fe2{μ-η1:η3-C(R′)C(SeX)CN(Me)(R)}(μ-CO)(CO)(Cp)2][SO3CF3] (R = X = Me, R′ = Tol, 7a; R = Xyl, R′ = Me, X = Fp+, 7b) are obtained upon treatment of the neutral zwitterionic precursors with MeSO3CF3 and [Fp][SO3CF3], respectively. Alkylation at the S or Se atom of the bridging ligand is also accomplished by CH2Cl2, used as solvent, although the reaction is slower compared to more efficient alkylating reagents. The complexes formed by this route are [Fe2{μ-η1:η3-C(R′)C(E-CH2Cl)CN(Me)(R)}(μ-CO)(CO)(Cp)2][X] [E = S, R = Xyl, R′ = Tol, X = Cl, 8a; E = S, R = Xyl, R′ = Me, X = Cl, 8b; E = Se, R = R′ = Me, X = BPh4, 8c]. Finally, treatment of the zwitterionic vinyliminium complexes with I2 results in the oxidative coupling with formation of S–S (disulfide) or Se–Se (diselenide) bond. The reactions, performed in the presence of NaBPh4 afford the tetranuclear complexes [Fe2{μ-η1:η3-C(R′)C(E)CN(Me)(R)}(μ-CO)(CO)(Cp)2]2[BPh4]2 [R = Xyl, R′ = CH2OH, E = S, 9a; R = Xyl, R′ = Me, E = S, 9b; R = Xyl, R′ = Bun, E = S, 9c; R = Xyl, R′ = Me, E = Se, 9d; R = Me, R′ = Bun, E = Se, 9e].