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)-[PtII(RS)(RSCSO)(PPh3)2]. An X-ray crystal and molecular structure analysis of cis-(E)-[PtII(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)-[PtII(p-MeC6H4S)(p-MeC6H4SCSO)(PPh3)2] in CDCl3 as in cis-(E)-[PtII(PhS)(PhSCSO)(PPh3)2]. C6H6 in the solid state and (Z)-(2,4,6-Me3C6H2)(PhS) CSO in CDCl3, while in cis-(Z)-[PtII(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)-[PtII(RS)-(R′SCSO)(PPh3)2] and cis-(E)- and cis-(Z)-[PtII(R′S)(RSCSO)(PPh3)2]. These complexes have the same conformations as cis-(E)- and cis-(Z)-[PtII(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)-[PtIICl(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.