Coupling of allenes with m-alkylidyne ligands in diiron complexes: synthesis of novel bridging thio- and aminobutadienylidene complexes

The diiron aminocarbyne complexes [Fe2{μ-CN(Me)(R)}(μ-CO)(CO)2(Cp)2][SO3CF3] (R = Xyl, 1a; R = 4-C6H4OMe, 1b; R = Me, 1c; Xyl = 2,6-Me2C6H3) react with allenes of the type CH2=C=CR′R″, in the presence of Me3NO/Et3N, to give the novel butadienylidene complexes [Fe2{μ-η1:η3-CαN(R)(Me)Cβ(H)CγCδ(R′)(R″)}(μ-CO)(CO)(Cp)2] (R = Xyl, R′ = R″ = Me, 3a; R = Xyl, R′ = Me, R″ = H, 3b; R = Xyl, R′ = CO2Et, R″ = H, 3c; R = 4-C6H4OMe, R′ = CO2Et, R″ = H, 3d; R = R′ = R″ = Me, 3e; R = Me, R′ = CO2Et, R″ = H, 3f) in high yields. Analogously, the diiron thiocarbyne complex [Fe2(μ-CSMe)(μ-CO)(CO)2(Cp)2][SO3CF3] (2) reacts with CH2=C=CR′R″, in the presence of Me3NO/Et3N, to afford the compounds[Fe2{μ-η1:η3-CαS(Me)Cβ(H)CγCδ(R′)(R″)}(μ-CO)(CO)(Cp)2](R′ = R″ = Me, 4a; R′ = CO2Et, R″ = H, 4b; R′ = SiMe3, R″ = Me, 4c). Complexes 3–4 exist in solution as mixtures of cis and trans isomers. Compounds 3a and 3e, upon treatment with HSO3CF3, are transformed into the corresponding vinyliminium complexes [Fe2{μ-η1:η3-Cγ(CδHMe2)CβHCαN(R)(Me)}(μ-CO)(CO)(Cp)2][SO3CF3] (R = Xyl, 5a; R = Me, 5b), in nearly quantitative yields. Conversely, compounds 4a,b undergo methylation (by CH3SO3CF3) at the sulfur to give the cationic complexes [Fe2{μ-η1:η3-Cα(SMe2)Cβ(H)CγCδ(R′)(R″)}(μ-CO)(CO)(Cp)2][SO3CF3] (R′ = R″ = Me, 7a; R′ = CO2Et, R″ = H, 7b). Protonation of 3a is not reversible: treating 5a with sodium hydride results in the formation of the 1-metalla-2-amino-cyclopenta-1,3-dien-5-one species [Fe(Cp)(CO){CN(Me)(Xyl)CHC(CHMe2)C(O)}] (6). The molecular structures of cis-3a, cis-4b, 5a[CF3SO3]·CH2Cl2 and 7a[CF3SO3]·0.5CH2Cl2 have been determined by X-ray diffraction studies.