Amination of Bridging Vinyliminium Ligands in Diiron Complexes: C-N Bond Forming Reactions for Amidine-Alkylidene Species

The vinyliminium complexes [Fe2μ-η1:η3-C(CO2Me)C(H)CN(Me)(R)(μ-CO)(CO)(Cp)2][SO3CF3] [R = Me, 1a; R = 4-C6H4OMe, 1b; R = CH2Ph, 1c] react with primary amines (NH2R′ R′= Me, Et, Bun, (CH2)2NH2, CH2Ph) and ammonia to give the corresponding bridging amidine-alkylidene complexes [Fe2μ-κ1(N): η1(C): η1(C)-C(CO2Me)CH2CN(Me)(R)(NR′)(μ-CO)(CO)(Cp)2] (4a-j) in 70-90% yields. Likewise, the vinyliminium complex [Fe2μ- η1:η3-C(CO2Me)C(CO2Me)CN(Me)2(μ-CO)(CO)(Cp)2][SO3CF3] (1d) reacts with NH2R′ (R′= Me, Et) to form the corresponding amidine-alkylidene [Fe2μ-κ1(N): η1(C): η1(C)-C(CO2Me)CH(CO2Me)C(NMe2)(NR′)(μ-CO)(CO)(Cp)2] [R′= Me, 8a; R′ = Et, 8b], generating selectively one of the two diastereoisomers associated with the presence of the methylidene unit CH(COO2Me)- within the bridging ligand. Amination of the vinyliminium complexes 1a-c takes place also with hydrazine, resulting in the formation of [Fe2μ-κ1(N): η1(C): η1(C)-C(CO2Me)CH2CN(Me)(R)(NNH2)(μ-CO)(CO)(Cp)2] [R = Me, 5a; R = 4-C6H4OMe, 5b; R = CH2Ph, 5c]. Complexes 1b and 1d react with NHMe2, affording the en-(1,1)diamino-alkylidene complexes [Fe2μ- η1:η3-C(CO2Me)C(R′)C(NMe2)N(Me)(R)(μ-CO)(CO)(Cp)2] [R = 4-C6H4OMe, R′ = H, 9b; R = Me, R′ = CO2Me, 9d]. The reaction of 1c with piperidine results in formation of the amidine-alkylidene [Fe2μ-κ1(N): η1(C): η1(C)-C(CO2Me)CH2CN(Me)(CH2Ph)(CH2CH2CH2CH=CH2)(μ-CO)(CO)(Cp)2] (10), which implies piperidine ring-opening. All the products have been purified by alumina chromatography and characterized by analytical and spectroscopic methods; in addition, the molecular structures of 4f, 5b, and 8a have been ascertained by X-ray diffraction studies.