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

Abstract

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‘)CN(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)(CHCHCO2Me}(CO)(Cp)2] (4). Complexes 2a,c undergo electrophilic addition at the N atom by treatment with HSO3CF3, allyl iodide (ICH2CHCH2), and methyl chloroformate (ClCOOMe), affording the corresponding vin...