Preparation and reactivity of η-cyclopentadienyl(thiocarbonyl)(triphenylphosphine)-rhodium(I) and -iridium(I): formation of methyl(methylthio)methylene complexes

Abstract

The complexes [M(η-C₅H₅)(CS)(PPh₃)][M = Rh (1) or Ir (2)] have been synthesized from [MCl(CS)(PPh₃)₂] and sodium cyclopentadienide. The behaviour of the new thiocarbonyl complexes in their reactions with halogens or dry hydrogen chloride is similar to that observed for analogous carbonyl derivatives. The complexes [Rh(η-C₅H₅)X(CS)(PPh₃)]X (X = Cl, Br, or I) have been obtained by treating (1) with halogens at liquid-nitrogen temperature; on increasing the temperature these rearrange to [Rh(η-C₅H₅)X₂(PPh₃)]. The analogous cationic iridium(III) complexes are more stable and can be obtained at room temperature. Complex (1) reacts with dry HCl giving probably [{RhCl(CS)(PPh₃)}₂]; in the same reaction (2) gives the cationic hydride [Ir(η-C₅H₅)H(CS)(PPh₃)]Cl. The reactions of (1) and (2) with Mel afford the thiocarbene species [M(η-C₅H₅){CMe(SMe)}I(PPh₃)]I which has been isolated analytically pure only for the iridium derivative. The reactions of the complexes [MCl(CS)(PPh₃)₂](M = Rh or Ir) with Mel have also been investigated. A possible mechanism of formation of the carbene species is proposed, and the influence of the metal–methyl σ-bond strength in the oxidative-addition product formed in the first step of this reaction is discussed. Complexes (1) and (2) react with HgCl₂ giving the adducts [M(η-C₅H₅)(CS)(HgCl₂)(PPh₃)]. The i.r. and ¹H n.m.r. spectra of the complexes prepared are discussed.