Construction of Two-Faced (Hetero)hydrocarbyl Diiron Complexes Mediated by the Interplay of Ligands

The functionalized allylidene complex [Fe2Cp2(CO)(mu-CO){mu-eta 1:eta 3-C gamma(Fc)-C beta HC alpha(CN)NMe2}], 1 [Cp = eta 5-C5H5; Fc = CpFe(eta 5-C5H4)], reacted with isocyanides (CNR), in isopropanol solution at ca. 100 degrees C, to give the CO-substitution products [Fe2Cp2(CO)(mu- CNR){mu-eta 1:eta 3-C gamma(Fc)C beta HC alpha(CN)NMe2}] [R = CH2P(O)(OEt)2, 2a; R = 2-naphthyl, 2b; R = CH2C(O)(OEt), 2c], which were isolated in 61-84% yields. The bridging coordination of CNR in 2a-c is forced by a stabilizing electrostatic interaction between the nitrogen lone pair belonging to the {NMe2} group and the terminal CO ligand. Isocyanide methylation with methyl triflate proceeded with the inversion of stereochemistry at the C alpha carbon and led to [Fe2Cp2(CO){mu- CN(Me)R}{mu-eta 1:eta 3-C gamma(Fc)C beta HC alpha(CN)NMe2}]CF3SO3 (R = CH2P(O)(OEt)2), ([3a]CF3SO3; R = 2-naphthyl, [3b]CF3SO3), containing bridging allylidene and aminocarbyne ligands (68-74% yields). All products were fully characterized by IR and multinuclear NMR spectroscopy, and the structures of 2a and [3a]CF3SO3 were elucidated by X-ray diffraction studies. Density functional theory (DFT) calculations were extensively carried out to shed light on structural, mechanistic, and thermodynamic features.