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 complexes [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.