Reactions of the metallacycle [(OC)(cp)FeC(SMe)SC(FeLn)S]+ with nucleophiles. X-Ray crystal structures of the complexes [(OC)(cp)FeC(NC5H10)SC(FeLn)S]SO3CF3 and [(OC)(cp)FeC{(CN)(SMe)}SC(FeLn)S][FeLn= Fe(cp)(CO)2, cp =η-C5H5]

Abstract

Reactions of the metallacyclic cation [(OC)(cp)[graphic omitted]]⁺[FeL_n= Fe(cp)(CO)₂, cp =η-C₅H₅] with nucleophilic agents have been investigated. The results indicate that the carbene carbon atom bonded to the endocyclic iron is the site of addition of all the nucleophiles examined. Primary amines NH₂R (R = Me, C₆H₁₁, or Buⁿ) form neutral isocyanide derivatives [(OC)(RNC)(cp)FeSC(S)FeL_n] with opening of the FeC₂S₂ ring, whereas secondary amines such as NHR₂(R = Me or Et) or H[graphic omitted]H₂(n= 3 or 4) produce stable cationic cyclic aminothiocarbenes. The structure of one of these, [(OC)(cp)[graphic omitted]]SO₃CF₃, has been determined by X-ray diffraction [triclinic, a= 11.570(2), b= 12.242(2), c= 10.552(2)Å, α= 104.60(2), β= 87.51(1), γ= 117.24(2)°, Z= 2, and space group P]. The cation contains the five-membered planar ring [graphic omitted] with the Fe(cp)(CO)₂ and NC₅H₁₀ groups bonded to the carbon atoms. The C(carbene)–N interaction exhibits strong double-bond character [1.32(1)Å], typical for an iminium cation. Methanethiol, Li(BHEt₃), and KCN yield neutral [(OC)(cp)[graphic omitted]](X = SMe, H, or CN). In the hydride addition an isomeric mixture has been ascertained by i.r. and n.m.r. spectra, whereas the cyanide ion adds stereoselectively at the prochiral carbene centre to form only one diastereoisomer whose steric nature has been determined by X-ray diffraction [triclinic, a= 6.894(2), b= 10.057(1), c= 14.520(2)Å, α= 96.00(2), β= 96.17(1), γ= 106.31(1)°, Z= 2, and space group P]. In this derivative the [graphic omitted] ring undergoes substantial changes because the iron-bonded carbon atom becomes four-co-ordinate with loss of its carbenic character and significant out-of-plane displacement. A comparative analysis of the relevant geometric features of all the members of this family is reported. Propane-1,3-dithiol produces the neutral spirocyclic [(OC)(cp)[graphic omitted]] which shows equivalence of the two diastereotopic SCH₂ carbons in the high-temperature ¹³C n.m.r. spectrum and splitting of v(CO) in the i.r. spectrum. These spectroscopic features are discussed and interpreted.