Selective C–C bond formation at diiron µ-aminocarbyne complexes†

Abstract

The reactions of [Fe₂{µ-CN(Me)R}(µ-CO)(CO)₂(Cp)₂]SO₃CF₃ (Cp = η-C₅H₅, R = Me 2a or CH₂Ph 2b) with a variety of carbon nucleophiles result in C–C bond formation at different sites of the molecules depending on the nature of the carbanions: (i) R′Li (R′ = Me, Buⁿ or Ph) and R′MgCl (R′ = Me, CH₂Ph or Prⁱ) added at the Cp ligand giving η⁴-cyclopentadiene complexes [Fe₂{µ-CN(Me)R}(µ-CO)(CO)₂(η⁴-C₅H₅R′)(Cp)] 3; (ii) Li₂Cu(CN)R′₂ (R′ = Me or Buⁿ) and LiCCR′ (R′ = Ph or p-tolyl) afforded the stable acyl complexes [Fe₂{µ-CN(Me)R}(µ-CO)(CO){C(O)R′}(Cp)₂] 4 and [Fe₂{µ-CN(Me)R}(µ-CO)(CO){C(O)CCR′}(Cp)₂] 5, respectively. With R ≠ Me the NMR spectra of type 3–5 derivatives show the presence of two isomers arising from the double-bond character of the µ-CN group ascertained from the crystal structure of [Fe₂(µ-CNMe₂)(µ-CO)(CO){C(O)Buⁿ}(Cp)₂] 4b. The structural study reveals the presence of interligand interactions involving the acyl oxygen and the µ-CNMe₂ moiety which is also in accord with an extended-Hückel calculation of the charge distribution.