SYNTHESIS, REACTIONS, AND X-RAY STRUCTURES OF THE FUNCTIONALIZED ISOCYANIDE COMPLEXES [FE2(MU-CNC(O)SR)(MU-CO)(CO)2(CP)2](CP =ETA-C5H5, R = ME OR ET) AND OF THEIR CARBYNE AND CARBENE DERIVATIVES

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.