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

The functionalized allylidene complex [Fe2Cp2(CO)(μ-CO){μ-η1:η3-Cγ(Fc)CβHCα(CN)NMe2}], 1 [Cp = η5-C5H5; Fc = CpFe(η5-C5H4)], reacted with isocyanides (CNR), in isopropanol solution
at ca.
100 °C, to give the CO-substitution products [Fe2Cp2(CO)(μ-CNR){μ-η1:η3-Cγ(Fc)CβHCα(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 Cα carbon and led to [Fe2Cp2(CO){μ-CN(Me)R}{μ-η1:η3-Cγ(Fc)CβHCα(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.