Synthesis, reactions, and X-ray structures of the functionalized isocyanide complexes [Fe2{µ-CNC(O)SR}(µ-CO)(CO)2(cp)2](cp =η-C5H5, R = Me or Et) and of their carbyne and carbene derivatives

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Abstract
The cyanate ion NCO– inserts into the C–S bond of [Fe2(µ-CSR)(µ-CO)(CO)2(cp)2]+(cp =η-C5H5, R = Me or Et), to give the isocyanide-bridged complexes [Fe2{µ-CNC(O)SR}(µ-CO)(CO)2-(cp)2](1). These derivatives exist in solution as a mixture of cis and trans isomers with the strong electron-withdrawing CNC(O)SR group bridging in both forms. The X-ray crystal structure of complex (1b; R = Et)[monoclinic, a= 9.418(3), b= 14.827(3), c= 12.793(4)Å, β= 97.28(3)°, Z= 4, space group P21/n] reveals the CO groups in cis position relative to the Fe–Fe bond. The nitrogen atom in (1) is alkylated or protonated to generate the cationic aminocarbyne complexes [Fe2{µ-CN(R′)C(O)SR}(µ-CO)(CO)2(cp)2]+(2; R′= Me, Et, or H) which do not display cis–trans isomerization at room temperature. In accord with their carbyne nature, the µ-C atom in complexes (2) adds H– or CN–(X) to form the carbene derivatives [Fe2{µ-C(X)N(R′)C(O)SR}(µ-CO)-(CO)2(cp)2](3) which are not fluxional. The X-ray structure of (3a; X = CN, R′= R = Me)[orthorhombic, a= 9.238(3), b= 8.142(1), c= 24.712(2)Å, Z= 4, space group P212121] shows that the molecule retains the cis geometry of the parent species (1) and (2), with the bulkier µ-carbon substituent N(Me)C(O)SMe on the less-hindered carbonyl face of the complex.