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

The diiron mu-vinyliminium compounds [Fe2Cp2(CO)(mu-CO){mu-eta(1):eta(3)-(CHCHCNMe)-H-3-H-2-N-1(R)}]CF3SO3(R = Me,2a; R = Xyl = 2,6-C6H3Me2,2b; Cp = eta(5)-C5H5) reacted with grey selenium, in the presence of sodium methoxide, to give the corresponding Se-functionalized derivatives [Fe2Cp2(CO)(mu-CO){mu-eta(1):eta(3)-(CHC2)-H-3(Se)(CNMe)-N-1(R)}],3a-b, in ca. 50 % yields. The monoiron zwitterionic complex [FeCp(CO){SeC1(NMe2)(CHCH)-H-2-H-3}],4, was obtained as a side-product (31 %) of the reaction leading to3a. The treatment of3bwith S-8/NaOMe afforded the 2-ferra-thiophene [FeCp(CO){(SCHCHCNMe)-H-3-H-2-N-1(Xyl)}],5, in 49 % yield. The straightforward reactions of3awith a two-fold excess of dialkylacetylenedicarboxylates led to functionalized 3-amino-selenophenes appended to the diiron frame through a bridging allylidene ligand, [Fe2Cp2(CO)(mu-CO){mu-eta(1):eta(3)-C-7(CO2R)C-6(CO2R)(CHCSeC5)-H-3-Se-2(CO2R)C-4(CO2R)C-1(NMe2)}] (R = Me,6a; R = Et,6b; R =tBu,6c), in approximately 50 % yields. The synthesis of6a-cis 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-mu-alkylidene. All the products were characterized by means of elemental analysis, IR and multinuclear NMR spectroscopy, and the molecular structure of6awas elucidated by a single-crystal X-ray diffraction study.