Diiron μ-vinyliminium complexes from acetylene insertion into a metal-aminocarbyne bond

The complexes [Fe2{μ-CN(Me)(R)}(μ-CO)(CO)(NCMe)(Cp)2] [SO3CF3] (R = Xyl, 1a; R = Me, 1b; R = CH2Ph, 1c; Xyl = 2,6-Me2C6H3), containing a labile NCMe ligand, react under mild conditions with a variety of terminal alkynes HC≡CR′ (R′= SiMe3, Me, Bun, Tol, Ph, H; Tol = 4-MeC6H4) to give the bridging vinyliminium complexex [Fe2{μ-σ:η3-C(R′)=CHC=N(Me)- (R)}(μ-CO)(CO)(Cp)2][SO3CF3] (R = Xyl, R′ = SiMe3, 2a; R = Me, R′ = SiMe3, 2b; R = CH2Ph, R′ = SiMe3, 2c; R = Xyl, R′ = Me, 3a; R = R′ = Me, 3b; R = Xyl, R′ = Bun, 4; R = Xyl, R′ = Tol, 5a; R = Me, R′ = Tol, 5b; R = CH2Ph, R′ = Tol, 5c; R = Xyl, R′ = Ph, 6; R = Xyl, R′ = H, 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′C≡CR′ (R′ = Me, Et) affords the analogous compounds [Fe2{μ-σ:η3-C(R′)=C(R′) C=N(Me)(R)}(μ-CO)(CO)(Cp)2][SO3CF3] (R = Xyl, R′ = Me, 8a; R = R′ = Me, 8b; R = CH2Ph, R′ = Me, 8c; R = Xyl, R′ = Et, 9a; R = Me, R′ = Et, 9b). The molecular structure of complex 2a has been elucidated by an X-ray diffraction study.