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

The vinyliminium complexes [Fe2{μ-η1:η3-Cγ(R‘)CβHCαNMe2}(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‘)CHCHNMe2}(μ-CO)(CO)(Cp)2] (R‘ = Tol, 5a; SiMe3, 5b; Me,
5c; CH2OH, 5d). Similarly, the complexes [Fe2{μ-η1:η3-Cγ(R‘)CβHCαN(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‘)CβHCα(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‘)CβHCαN(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‘)CβHCαN(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‘)CHCHN(Me)(Xyl)}(μ-CO)(CO)(Cp)2] (R‘ = Me, 8a; COOMe, 8b).