Construction of a Functionalized Selenophene-Allylidene Ligand via Alkyne Double Action at a Diiron Complex

The diiron µ-vinyliminium compounds [Fe2Cp2(CO)(µ-CO){µ-η1:η3-C3HC2HC1NMe(R)}]CF3SO3 (R = Me, 2a; R = Xyl = 2,6-C6H3Me2, 2b; Cp = η5-C5H5) reacted with grey selenium, in the presence of sodium methoxide, to give the corresponding Se-functionalized derivatives [Fe2Cp2(CO)(µ-CO){µ-η1:η3-C3HC2(Se)C1NMe(R)}], 3a–b, in ca. 50 % yields. The monoiron zwitterionic complex [FeCp(CO){SeC1(NMe2)C2HC3H}], 4, was obtained as a side-product (31 %) of the reaction leading to 3a. The treatment of 3b with S8/NaOMe afforded the 2-ferra-thiophene [FeCp(CO){SC3HC2HC1NMe(Xyl)}], 5, in 49 % yield. The straightforward reactions of 3a with a two-fold excess of dialkylacetylenedicarboxylates led to functionalized 3-amino-selenophenes appended to the diiron frame through a bridging allylidene ligand, [Fe2Cp2(CO)(µ-CO){µ-η1:η3-C7(CO2R)C6(CO2R)C3HC2SeC5(CO2R)C4(CO2R)C1(NMe2)}] (R = Me, 6a; R = Et, 6b; R = tBu, 6c), in approximately 50 % yields. The synthesis of 6a–c is the result of two distinct modes of reactivity exhibited by the alkyne reactant in one pot, i.e. 1,3-dipolar cycloaddition to C and Se atoms and insertion into Fe-µ-alkylidene. All the products were characterized by means of elemental analysis, IR and multinuclear NMR spectroscopy, and the molecular structure of 6a was elucidated by a single-crystal X-ray diffraction study.