Hydride addition at μ-vinyliminium ligand obtained from disubstituted alkynes

New μ-vinylalkylidene complexes cis-[Fe2{μ-η1:η3-Cγ(R′)Cβ(R″)double bond; length as m-dashCαHN(Me)(R)}(μ-CO)(CO)(Cp)2] (R = Me, R′ = R″ = Me, 3a; R = Me, R′ = R″ = Et, 3b; R = Me, R′ = R″ = Ph, 3c; R = CH2Ph, R′ = R″ = Me, 3d; R = CH2Ph, R′ = R″ = COOMe, 3e; R = CH2 Ph, R′ = SiMe3, R″ = Me, 3f) have been obtained b yreacting the corresponding vinyliminium complexes [Fe2{μ-η1:η3-Cγ(R′)double bond; length as m-dashCβ(R″)Cαdouble bond; length as m-dashN(Me)(R)}(μ-CO)(CO)(Cp)2][SO3CF3] (2a–f) with NaBH4. The formation of 3a–f occurs via selective hydride addition at the iminium carbon (Cα) of the precursors 2a–f. By contrast, the vinyliminium cis-[Fe2{μ-η1:η3-Cγ (R′) = Cβ(R″)Cα = N(Me)(Xyl)}(μ-CO)(CO)(Cp)2][SO3CF3] (R′ = R″ = COOMe, 4a; R′ = R″ = Me, 4b; R′ = Prn, R″ = Me, 4c; Prn = CH2CH2CH3, Xyl = 2,6-Me2C6H3) undergo H− addition at the adjacent Cβ, affording the bis-alkylidene complexes cis-[Fe2{μ-η1:η2-C(R′)C(H)(R″)CN(Me)(Xyl)}(μ-CO)(CO)(Cp)2], (5a–c). The cis and trans isomers of [Fe2{μ-η1:η3-Cγ(Et)double bond; length as m-dashCβ(Et)Cαdouble bond; length as m-dashN(Me)(Xyl)}(μ-CO)(CO)(Cp)2][SO3CF3] (4d) react differently with NaBH4: the former reacts at Cα yielding cis-[Fe2{μ-η1:η3-Cγ(Et)Cβ(Et)double bond; length as m-dashCαHN(Me)(Xyl)}(μ-CO)(CO)(Cp)2], 6a, whereas the hydride attack occurs at Cβ of the latter, leading to the formation of the bis alkylidene trans-[Fe2{μ-η1:η2-C(Et)C(H)(Et)CN(Me)(Xyl)}(μ-CO)(CO)(Cp)2] (5d). The structure of 5d has been determined by an X-ray diffraction study. Other μ-vinylalkylidene complexes cis-[Fe2{μ-η1:η3-Cγ(R′)Cβ(R″)double bond; length as m-dashCαHN(Me)(Xyl)}(μ-CO)(CO)(Cp)2], (R′ = R″ = Ph, 6b; R′ = R″ = Me, 6c) have been prepared, and the structure of 6c has been determined by X-ray diffraction. Compound 6b results from treatment of cis-[Fe2{μ-η1:η3-Cγ(Ph)double bond; length as m-dashCβ(Ph)Cαdouble bond; length as m-dashN(Me)(Xyl)}(μ-CO)(CO)(Cp)2][SO3CF3] (4e) with NaBH4, whereas 6c has been obtained by reacting 4b with LiHBEt3. Both cis-4d and trans-4d react with LiHBEt3 affording cis-6a.