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.

The complexes [Fe 2 {µ-CN(Me)(R)}(µ-CO)(CO)(NCMe)(Cp) 2 ][SO 3 CF 3 ] (R ) Xyl, 1a; R ) Me, 1b; R ) CH 2 Ph, 1c; Xyl ) 2,6-Me 2 C 6 H 3 ), containing a labile NCMe ligand, react under mild conditions with a variety of terminal alkynes HCtCR′ (R′) SiMe 3 , Me, Bu n , Tol, Ph, H; Tol ) 4-MeC 6 H 4 ) to give the bridging vinyliminium complexes [Fe 2 {µ-σ: 7). Insertion of the alkyne into the metal-carbyne carbon bond is regiospecific, resulting only in the product containing the R′ group on the carbon bound to Fe. Similarly, insertion of the disubstituted alkynes R′CtCR′ (R′ ) Me, Et) affords the analogous compounds [Fe 2 {µ-σ:). The molecular structure of complex 2a has been elucidated by an X-ray diffraction study.

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The C β -H hydrogen in the diiron vinyliminium complexes [Fe 2 {µ-η 1 :η) is easily removed by sodium hydride; different products are consequently formed, depending on the nature of the substituents R and R′. Thus, deprotonation of [Fe 2 {µ-R′ ) COOMe, 3e; R ) Xyl, R′ ) CMe 2 OH, 3f) with NaH afford the 1-metalla-2-aminocyclopenta-1,3-dien-5-one species [Fe(Cp)(CO){CN(Me)(R)CHC(R′)C(O)}] (R ) Me, R′ ) Bu n , 7a; R ) Xyl, R′ ) Me, 7b; R ) Xyl, R′ ) COOMe, 7c; R ) Xyl, R′ ) CMe 2 OH, 7d). The molecular structures of 4a‚CH 2 Cl 2 , 4b, 5e, and 7b have been determined by X-ray diffraction studies.