Carbon–carbon bond formation in the reactions of diiron µ-carbyne complexes with 2-thienyllithium, synthesis and structural characterization

Abstract

The reactions of 2-thienyllithium (Lith) with a variety of carbyne complexes result in C–C bond formation at different sites of the molecules. The thiocarbyne cis-[Fe₂(µ-CSMe)(µ-CS)(CO)₂(Cp)₂]⁺1 (Cp = η-C₅H₅) underwent Cp addition forming [Fe₂(µ-CSMe)(µ-CS)(CO)₂(Cp)(η⁴-C₅H₅th)] 3 and trace amounts of [Fe₂(µ-CSMe)(µ-CS){C(O)th}(CO)(Cp)₂] 4. By contrast all the aminocarbynes [Fe₂(µ-CNRR′)(µ-CO)(CO)₂(Cp)₂]⁺ (R = R′ = Me 2a; R = Me, R′ = PhCH₂2b) and [Ru₂(µ-CNMe₂)(µ-CO)(CO)₂(Cp)₂]⁺6 gave the corresponding acyl derivatives [M₂(µ-CNRR′)(µ-CO)(CO){C(O)th}(Cp)₂] (M = Fe 5a and 5b; R = R′ = Me, M = Ru 7). When R ≠ R′, the NMR spectra of these neutral species show the presence of two isomers α and β arising from hindered rotation around the µ-CN bond. The relevance of these reactions is discussed in terms of selective C–C bond formation in comparison with analogous carbon nucleophile addition at [Fe₂(µ-CSMe)(µ-CO)(CO)₂(Cp)₂]⁺. The crystal structures of 3 and [Fe₂{µ-CN(Me)CH₂Ph}(µ-CO)(CO){C(O)th}(Cp)₂] 5b are reported and discussed. The conformation of the Fe₂C₂ diamond is shown to depend on the nature of the bridging ligands. Simple models of electronic structure are outlined on the basis of the geometric evidence.