Unprecedented Zwitterionic Iminium−Chalcogenide Bridging Ligands in Diiron Complexes

The diiron vinyliminium complexes [Fe2{μ-η1:η3-C(R‘)CHCN(Me)(R)}(μ-CO)(CO)(Cp)2][SO3CF3] [R = Xyl, R‘ = Me, 1a; R = Xyl, R‘ = Tol, 1b; R = Xyl, R‘ = CO2Me, 1c; R = Xyl, R‘ =
CH2OH, 1d; R = Xyl, R‘ = Bun, 1e; R = Me, R‘ = Me, 1f; R = Me, R‘ = Tol, 1g; R = Me, R‘ =
CO2Me, 1h; R = Me, R‘ = Bun, 1i; R = Me, R‘ = CH2OH, 1l; R = p-C6H4-CN, R‘ = Tol, 1m; R =
p-C6H4-OMe, R‘ = Me, 1n; Tol = 4-C6H4-Me; Xyl = 2,6-Me2C6H3] react with elemental sulfur or
selenium, in the presence of NaH, to give the zwitterionic vinyliminium compounds [Fe2{μ-η1:η3-C(R‘)C(E)CN(Me)(R)}(μ-CO)(CO)(Cp)2] [R = Xyl, R‘ = Me, E = S, 2a; R = Xyl, R‘ = Tol, E = S, 2b;
R = Xyl, R‘ = CO2Me, E = S, 2c; R = Xyl, R‘ = CH2OH, E = S, 2d; R = Xyl, R‘ = Bun, E = S, 2e;
R = Xyl, R‘ = Me, E = Se, 3a; R = Xyl, R‘ = Tol, E = Se, 3b; R = Me, R‘ = Me, E = Se, 3c; R =
Me, R‘ = Tol, E = Se, 3d; R = Me, R‘ = CO2Me, E = Se, 3e; R = Me, R‘ = Bun, E = Se, 3f; R =
Me, R‘ = CH2OH, E = Se, 3g]. Similarly, the reaction of 1a with Me3NO/NaH results in the formation
of [Fe2{μ-C(Me)C(O)CN(Me)(Xyl)}(μ-CO)(CO)(Cp)2] (4), in which the bridging ligand is better described
as a bis-alkylidene. The reactions of 1a,c with S8/NaH afford also the five-membered metallacycles [Fe(Cp)(CO){Cα(NMe(Xyl))Cβ(H)Cγ(R‘)S}] [R‘ = Me, 6a; R‘ = CO2Me, 6b], as secondary products, in
about 15% yield. Conversely, complexes [Fe2{μ-η1:η3-C(R‘)CHCN(Me)(R)}(μ-CO)(CO)(Cp)2][SO3CF3], 1f−h,m,n, react with S8/NaH, giving selectively the five-membered metallacycles [Fe(Cp)(CO){C(R‘)C(H)C{N(Me)(R)}S}] [R = Me, R‘ = Me, 7a; R = Me, R‘ = Tol, 7b; R = Me, R‘ = CO2Me,
7c; R = p−C6H4−CN, R‘ = Tol, 7d; R = p-C6H4-OMe, R‘ = Me, 7e]. The molecular structures of
2b·CH2Cl2, 3a, 4, 6a, and 7b have been determined by X-ray diffraction studies.