Co-ordination chemistry of sulphines. Part 3. Oxidative addition of the carbon–chlorine bond of (E)-chloro(arylthio)-sulphine, (E)-(RS)CICSO, to tetrakis(triphenylphosphine) platinum(0) and of a carbon–sulphur bond in [Pt0(PPh3)2{(RS)2CSO}] by an intramolecular process. X-Ray crystal and molecular structure of cis-(E)-[PtII(PhS)(PhSCSO)(PPh3)2]·C6H6

Abstract

The platinum–sulphine complexes [Pt⁰(PPh₃)₂{(RS)₂CSO}](R = Ph or C₆H₄Me-p), in which the sulphines are η²-CS co-ordinated, undergo in solution (CDCl₃) complete and intramolecular oxidative addition of a C–S bond to Pt⁰ yielding and equilibrium mixture of the stereoisomers cis-(E)- and cis-(Z)-[Pt^II(RS)(RSCSO)(PPh₃)₂]. An X-ray crystal and molecular structure analysis of cis-(E)-[Pt^II(PhS)(PhSCSO)(PPh₃)₂]·C₆H₆ revealed that in this stereoisomer the Pt and O atoms are situated anti, the (PPt)(S)CSO fragment is coplanar and perpendicular to the P₂Pt plane, and that the phenyl ring of the PhS–CSO fragment is folded under the Pt atom resulting in an s-cis conformation. Hydrogen-1 n.m.r. studies revealed that the p-MeC₆H₄S–CSO fragment has the same s-cis conformation in cis-(E)-[Pt^II(p-MeC₆H₄S)(p-MeC₆H₄SCSO)(PPh₃)₂] in CDCl₃ as in cis-(E)-[Pt^II(PhS)(PhSCSO)(PPh₃)₂]. C₆H₆ in the solid state and (Z)-(2,4,6-Me₃C₆H₂)(PhS) CSO in CDCl₃, while in cis-(Z)-[Pt^II(p-MeC₆H₄S)(p-MeC₆H₄SCSO)(PPh₃)₂] it has a gauche conformation, the same as in (E)-(2,4,6-Me₃C₆H₂)(PhS)CSO. An equimolar mixture of the two stereoisomers of [Pt⁰(PPh₃)₂{(RS)(R′S)CSO}](R′= C₆H₄OMe-p; R = C₆H₄Me-p) in CDCl₃ is completely converted into an equimolar mixture of cis-(E)- and cis-(Z)-[Pt^II(RS)-(R′SCSO)(PPh₃)₂] and cis-(E)- and cis-(Z)-[Pt^II(R′S)(RSCSO)(PPh₃)₂]. These complexes have the same conformations as cis-(E)- and cis-(Z)-[Pt^II(RS)(RSCSO)(PPh₃)₂]. The mechanism of the intramolecular oxidative addition taking as example [Pt⁰(PPh₃)₂{(RS)₂CSO}] could be gliding movements of the Pt⁰(PPh₃)₂ unit along two different S–CS frames via two stereoisomeric intermediates [Pt⁰(PPh₃)₂{(E)-RSC(SR)SO}] and [Pt⁰(PPh₃)₂{(Z)-RSC(SR)SO}], in which the sulphines are η³-SCS co-ordinated in a pseudo-allylic fashion. Sulphines containing a C–Cl and a C–S side bond, e.g.(E)-(RS) CICSO (R = Ph, C₆H₄Me-p) gave a fast oxidative addition of the C–Cl bond to Pt⁰ yielding the stereoisomers, cis-(E)-, cis-(Z)-, trans-(E)-, and trans-(Z)-[Pt^IICl(RSCSO)(PPh₃)₂]. In the case where R = C₆H₄Me-p, ¹H n.m.r. evidence has revealed that the RS–CSO fragments in the cis-(E) and trans-(E) stereoisomers have a s-cis conformation, while in cis-(Z) and trans-(Z) a gauche conformation exists.