Acetylide addition to bridging vinyliminium ligands in dinuclear complexes

The (vinyliminium)diiron complexes [Fe2{μ-η1:η3-Cγ(R′)=Cβ(R′)Cα=N(Me)(R)}(μ-CO)(CO)(Cp)2][SO3CF3] [R = Xyl, R′ = Me (1a); R = Xyl, R′ = Et (1b); R = R′ = Me (1c); R = Me, R′ = Et (1d); R = CH2Ph, R′ = Me (1e); Xyl = 2,6-Me2C6H3] undergo regio- and stereoselective addition by lithium acetylides. Addition of LiC≡CR″ (R″ = Tol, Ph, SiMe3; Tol = 4-MeC6H4) to trans-1a occurs at the Cβ atom of the vinyliminium ligand and results in the formation of the bis(alkylidene) complexes cis-[Fe2{μ-η1:η2-C(Me)C(Me)(C≡CR″)CN(Me)(Xyl)}(μ-CO)(CO)(Cp)2] [R″ = Tol (2a), Ph (2b), SiMe3 (2c)]. The molecular structure of 2a has been determined by X-ray diffraction. Similarly, the diruthenium complex [Ru2{μ-η1:η3-C(Me)=C(Me)C=N(Me)(Xyl)}(μ-CO)(CO)(Cp)2][SO3CF3] (3) reacts with LiC≡CTol to give the bis(alkylidene) compound[Ru2{μ-η1:η2-C(Me)C(Me)(C≡CTol)CN(Me)(Xyl)}(μ-CO)(CO)(Cp)2] (4). Conversely, 1c and 1d undergo acetylide attack at the Cα atom of the vinyliminium ligand to yield the allylidenecomplexes [Fe2{μ-η1:η3-C(R′)C(R′)C(C≡CR″)N(Me)2}(μ-CO)(CO)(Cp)2] [R′ = Me, R″ = Tol (5a); R′ = Me, R″ = Ph (5b); R′ = Me, R″ = SiMe3 (5c); R′ = Me, R″ = nBu (5d); R′ = Me, R″ = C(Me)=CH2 (5e); R′ = Me, R″ = H (5f); R′ = Et, R″ = Tol (5g); R′ = Et, R″ = Ph (5h); R′ = Et, R″ = SiMe3 (5i); R′ = Et, R″ = C(Me)=CH2 (5j)]. Analogously, the reaction of 1e with LiC≡CPh affords [Fe2{μ-η1:η3-C(Me)C(Me)C(C≡CPh)N(Me)(CH2Ph)}(μ-CO)(CO)(Cp)2] (6). The molecular structure of 5h has been determined by X-ray diffraction. Finally, 1b, in both its cis and trans forms, undergoes acetylide attack at the Cα atom of the vinyliminium ligand to give the complexes[Fe2{μ-η1:η3-C(Et)C(Et)C(C≡CR″)N(Me)(Xyl)}(μ-CO)(CO)(Cp)2] [R″ = SiMe3 (7a), H (7b)].