Co-ordination chemistry of sulphines. Part 4. Influence of the phosphine cone angle on both the oxidative addition of carbon–sulphur and carbon–chlorine side bonds in [Pt0(PR3)2(XYCSO)] complexes and the (E)–(Z) isomerization

Abstract

The co-ordination compounds [Pt⁰{P(C₆H₁₁)₃}₂(C₁₂H₈CSO)](5a)(C₁₂H₈CSO = fluorene-9-ylidenesulphine), [Pt⁰{P(C₆H₁₁)₃}₂{(E)-(MeS)R′CSO}](E)-(5b), [Pt⁰{P(C₆H₁₁)₃}₂{(Z)-(MeS)R′CSO}](Z)-(5b), [Pt⁰{P(C₆H₁₁)₃}₂{(R′S)₂CSO}](5c)(R′=p-MeC₆H₄), and [Pt⁰{P(C₆H₁₁)₃}₂{(E)-(PhS)CICSO}](E)-(5d′) may be synthesized with retention of configuration from [Pt⁰(cod)₂], P(C₆H₁₁)₃, and the corresponding sulphines (cod = cyclo-octa-1,5-diene). The complexes (5a) and (5c) remain unchanged in CDCl₃ solution, while (Z)-(5b) isomerizes to (E)-(5b) and vice versa, until a 4 : 1 (E) : (Z) equilibrium is reached. The complex (E)-(5d′) undergoes in CDCl₃ a fast oxidative addition of the C–Cl side bond, yielding the kinetically preferred cis-(E)-[Pt^IICl(PhSCSO){P(C₆H₁₁)₃}₂](E)-(6d′), which then isomerizes to the thermodynamically more stable trans-(E)- and -(Z)-[Pt^IICl(PhSCSO){P(C₆H₁₁)₃}₂](E)- and (Z)-(7d′). This shows that replacement of the PPh₃ ligands by the bulkier P(C₆H₁₁)₃ ligands increases the barrier to intramolecular C–S oxidative addition. An overall mechanism for the intramolecular C–S oxidative-addition and reductive-coupling reactions on Pt(PR₃)₂ centres (R = C₆H₁₁ or Ph) and the (E)–(Z) isomerization of co-ordinated sulphines and metal-substituted sulphines (oxidative-addition products) is put forward.