Alkyne−Isocyanide Coupling in [Fe₂(CNMe)(CO)₃(Cp)₂]: A New Route to Diiron μ-Vinyliminium Complexes^†

Alkynes (RC⋮CR‘) insert into the metal−isocyanide bond of [Fe2(CNMe)(CO)3(Cp)2] (1), under UV
irradiation, affording the complexes [Fe2{μ-η1:η3-C(R)C(R‘)CN(Me)}(μ-CO)(CO)(Cp)2] (R = R‘= Ph,
2a; R = R‘ = Me, 2b; R = R‘ = Et, 2c; R = Ph, R‘ = H, 2d; R = Tol, R‘ = H, 2e; R = SiMe3, R‘ =
H, 2f; R = Me, R‘ = H, 2g; R = CH2OH, R‘ = H, 2h; Tol = 4-MeC6H4), with displacement of one CO
ligand. Compounds 2b,c exist as a mixture of cis and trans isomers (with reference to the mutual Cp
position), whereas 2a,d−h exclusively have the cis geometry. The insertion of terminal alkynes is
regioselective, since C−C bond formation occurs selectively between the isocyanide and the nonsubstituted
carbon of HC⋮CR. Compound 1 reacts with 2 equiv of HC⋮CCO2Me under UV irradiation, affording
[Fe2{μ-η2:η4-C(OH)C(CO2Me)C(H)CN(Me)(CHCHCO2Me}(CO)(Cp)2] (4). Complexes 2a,c undergo
electrophilic addition at the N atom by treatment with HSO3CF3, allyl iodide (ICH2CHCH2), and methyl
chloroformate (ClCOOMe), affording the corresponding vinyliminium cations [Fe2{μ-η1:η3-C(R)C(R)CN(Me)(E)}(μ-CO)(CO)(Cp)2]+ (R = Ph, E = H, 5a; R = Et, E = H, 5b; R = Ph, E = CH2CHCH2,
6; R = Ph, E = CO2Me, 7). The reactions of 6 with NaBH4 and NBu4CN afford [Fe2{μ-η1:η3-C(Ph)C(Ph)C(H)N(Me)(CH2CHCH2)}(μ-CO)(CO)(Cp)2] (8) and [Fe2{μ-η1:η3-C(Ph)C(Ph)C(CN)N(Me)(CH2CHCH2)}(μ-CO)(CO)(Cp)2] (9), respectively. The molecular structures of cis-2c, [Fe2{μ-η1:η3-C(Et)C(Et)C=N(Me)(Xyl)}(μ-CO)(CO)(Cp)2][SO3CF3] (3), 4, and 5a have been established by X-ray
diffraction studies.