Co-ordination chemistry of sulphines. Part 5. σ-S and η3-SCS co-ordination of sulphines to rhodium(I). Fluxional behaviour of [RhICl(PR3)(XYCSO)](R = alkyl; X, Y = aryl, S-aryl, S-alkyl, or Cl) complexes and influence of sulphine geometry on the formation of [RhICl(PR3)2(XYCSO)]

Abstract

Sulphines react with [{Rh^ICl(cyclo-C₈H₁₄)₂}₂] and PR₃(R = C₆H₁₁ or Prⁱ) to afford complexes of the type [Rh^ICl(PR₃)_n(sulphine)](n= 1 or 2), in which the number of phosphines depends on the nature of the sulphine side bonds. If no reactive (C–S,C–Cl) side bonds are present, the sulphine co-ordinates viaσ-S to Rh^I with two phosphines in trans positions. If one or two C–S side bonds are present the sulphine co-ordinates η³-SCS to a rhodium(I) centre, which is bonded to only one phosphine. None of these complexes undergoes a C–S oxidative addition reaction. For the η³-SCS co-ordinated complexes [Rh^ICl(PR₃){(E)-(MeS)(p-MeC₆H₄)CSO}] and [Rh^ICl(PR₃){(E)-(R′S)₂CSO}](R = C₆H₁₁ or Prⁱ, R′= C₆H₄Me-p or Ph) a fluxional process is found (³¹P and ¹H n.m.r.), which can be described either as an (E)–(Z) isomerization of the MeS, p-MeC₆H₄S, or PhS group of the co-ordinated side bonds or as an intramolecular PR₃–Cl interchange. For the corresponding (Z) stereoisomers this process could not be detected. The complex [Rh^ICl{P(C₆H₁₁)₃}{(E)-(MeS)(p-MeC₆H₄)CSO}],(E)–(2b), and P(C₆H₁₁)₃ form an equilibrium mixture with trans-[Rh^ICl{P(C₆H₁₁)₃}₂{(E)-(MeS)(p-MeC₆H₄)CSO}],(E)-(4b), in which the sulphine is σ-S co-ordinated. On the other hand, the corresponding (Z) stereoisomer. (Z)-(2b), is in equilibrium with P(C₆H₁₁)₃ and cis-[Rh^ICl{P(C₆H₁₁)₃}₂{(Z)-(MeS)(p-MeC₆H₄)CSO}], (Z)-(6b), a five-co-ordinate rhodium(I) complex with an η³-SCS co-ordinated sulphine. This difference between the (E) and (Z) stereoisomers can be understood in terms of the geometric arrangement of the pseudo-allylic co-ordination.