Chemistry of metallacyclic complexes containing the FeCSCS ring obtained by metal-promoted CS2–CS coupling. X-Ray crystal structures of [(CO)(cp)FeC{SW(CO)5}SC(FeLn)S] and [(CO)(cp)FeC(SEt)SC(FeLn)S]SO3CF3[FeLn= Fe(cp)(CO)2, cp =η-C5H5]

Abstract

Nucleophilic addition of the thione sulphur atom in the complexes [FeL_nC(S)SML_n][FeL_n= Fe(cp)(CO)₂, ML_n= FeL_n or Re(CO)₅, cp =η-C₅H₅] at the thiocarbonyl carbon atom in the complex [FeL_n(CS)] SO₃CF₃ promotes CS₂–CS coupling to yield five-membered ring metallacycles [(CO)(cp)[graphic omitted]]SO₃CF₃, through an unstable open-chain intermediate followed by ring closure at the Fe atom of the dithioester precursor. These derivatives react with nucleophiles to give [(CO)(cp)[graphic omitted]]via S–ML_n bond cleavage. The thioanhydride-like C₂S₃ grouping disproportionates under u.v. irradiation to restore the CS₂ and CS fragments co-ordinated to the same metal centre in [(CS)(cp)[graphic omitted]]. The co-ordinating ability of [(CO)(cp)[graphic omitted]] is proved by reactions with [M′(CO)₅(thf)](M′= Cr, Mo, or W; thf = tetrahydrofuran), HgX₂(X = Cl, Br, or I) and AgBF₄ which afford derivatives with a metallacycle: metal ratio of 1 : 1 in the first two cases and 2 : 1 in the latter. Other electrophiles (E) such as H⁺, R⁺(R = Me or Et), or BF₃ also give addition at the thionic end of the molecule, forming [(CO)(cp)[graphic omitted]]. Hydrogen-1 and ¹³C n.m.r. and i.r. spectra of the complexes are presented and discussed. The i.r. analyses reveal the presence of conformers arising from restricted rotation around C(sp²)–Fe(exo). The crystal structures of the complexes [(CO)(cp)[graphic omitted]][monoclinic, a= 13.162(2), b= 13.156(1), c= 14.029(3)Å, β= 93.66(1)°, Z= 4, space group P2₁/a] and of [(CO)(cp)[graphic omitted]]SO₃CF₃[monoclinic, a= 14.565(4), b= 10.369(2), c= 16.176(2)Å, β= 101.73(1)°, Z= 4, space group P2₁/n] have been determined. Both species contain a planar, five-membered metallacyclic ring. Corresponding bond distances in the two species do not show great differences and reveal the carbenic character of both the endocyclic carbon atoms. Extensive delocalization of electrons promotes charge equalization on all the atoms and minimizes the differences between the neutral and cationic species.