Regio- and Stereoselective Hydride Addition at μ-Vinyliminium Ligands in Cationic Diiron Complexes

Abstract

The vinyliminium complexes [Fe2{μ-η1:η3-Cγ(R‘)CβHCαNMe2}(μ-CO)(CO)(Cp)2][SO3CF3] (R‘ = Tol, 2a; SiMe3, 2b; Me, 2c; CH2OH, 2d) undergo hydride addition at the iminium carbon (Cα), upon treatment with NaBH4, affording the corresponding μ-vinylalkylidene complexes [Fe2{μ-η1:η3-C(R‘)CHCHNMe2}(μ-CO)(CO)(Cp)2] (R‘ = Tol, 5a; SiMe3, 5b; Me, 5c; CH2OH, 5d). Similarly, the complexes [Fe2{μ-η1:η3-Cγ(R‘)CβHCαN(Me)(CH2Ph)}(μ-CO)(CO)(Cp)2][SO3CF3] (R‘ = Tol, 4a; SiMe3, 4b; COOMe, 4c) react with NaBH4 at the Cα, yielding [Fe2{μ-η1:η3-Cγ(R‘)CβHCα(H)N(Me)(CH2Ph)}(μ-CO)(CO)(Cp)2] (R‘ = Tol, 7a; SiMe3, 7b; COOMe, 7c). By contrast, the reactions of NaBH4 with [Fe2{μ-η1:η3-Cγ(R‘)CβHCαN(Me)(Xyl)}(μ-CO)(CO)(Cp)2] (R‘ = Tol, 3a; SiMe3, 3b; Me, 3c; CH2OH, 3d; Ph, 3e; COOMe, 3f; Bun, 3g; H, 3h), in which the substituent at the iminium nitrogen is the more sterically hindered Xyl group (Xyl = 2,6-Me2C6H3), lead to the formation of the bis-alkylidene complexes [Fe2{μ-η1:η2-C(R‘)CH2CN(Me)(Xyl)}(μ-CO)(CO)(Cp)2] (R‘ = Tol, 6a; SiMe3, 6b; Me, 6c; CH2OH, 6d; Ph, 6e; COOMe, 6f; Bun, 6g; H, 6h). Compounds 6a−h result from regioselective hydride addition at the Cβ, presumably because of the steric protection exerted by the Xyl group on the Cα carbon. All the new compounds have been investigated by IR and NMR spectroscopy, and the molecular structures of complexes 5a and 6f have been elucidated by X-ray diffraction studies. LiHBEt3 selectively attacks the Cα carbon, despite the presence of the Xyl substituent; therefore [Fe2{μ-η1:η3-Cγ(R‘)CβHCαN(Me)(Xyl)}(μ-CO)(CO)(Cp)2][SO3CF3] (R‘ = Me, 3c; COOMe, 3f) are converted into the corresponding μ-vinylalkylidene complexes [Fe2{μ-η1:η3-C(R‘)CHCHN(Me)(Xyl)}(μ-CO)(CO)(Cp)2] (R‘ = Me, 8a; COOMe, 8b).