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

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-[Fe-2(mu-CSMe)(mu-CS)(CO)(2)(Cp)(2)](+) 1 (Cp=eta-C5H5) underwent Cp addition forming [Fe-2(mu-CSMe)(mu-CS)(CO)(2)(Cp)(eta(4)-C(5)H(5)th)] 3 and trace amounts of [Fe-2(mu-CSMe)(mu-CS)-{C(O)th}(CO)(Cp)(2)] 4. By contrast all the aminocarbynes [Fe-2(mu-CNRR')(mu-CO)(CO)(2)(Cp)(2)](+) (R=R'=Me 2a; R=Me, R'=PhCH2 2b) and [Ru-2(mu-CNMe2)(mu-CO)(CO)(2)(Cp)(2)](+) 6 gave the corresponding acyl derivatives [M-2(mu-CNRR')(mu-CO)(CO){C(O)th}(Cp)(2)] (M=Fe 5a and 5b; R=R'=Me, M=Ru 7). When R not equal R', the NMR spectra of these neutral species show the presence of two isomers alpha and beta arising from hindered rotation around the mu-C=N bond. The relevance of these reactions is discussed in terms of selective C-C bond formation in comparison with analogous carbon nucleophile addition at [Fe-2(mu-CSMe)(mu-CO)(CO)(2)(Cp)(2)](+). The crystal structures of 3 and [Fe-2{mu-CN(ME)CH2Ph}(mu-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.