Synthesis, reactions, and dynamic nuclear magnetic resonance studies of η²-vinyl complexes of tungsten, [W{η³-C(CF ₃)C(CF₃)(SR)}(CF₃C≡CCF ₃)(η⁵-C₅H₅)] (R = Me, Et, Prⁿ, Prⁱ, or Bu^t)

Reactions of the hexafluorobut-2-yne complex [WCl(CF₃C= CCF₃)₂(?⁵-C₅H₅)] with thallium(I) thiolates TI(SR) give the bis-alkyne derivative [W(SR)(CF ₃C=CCF₃)₂(?⁵-C ₅H₅)] when R = C₆H₄Me-4 whereas an isomeric ?²-vinyl form [W{?³-C(CF ₃)C(CF₃)(SR)(CF₃C=CCF₃) (?⁵C₅H₅)], resulting from migration of the SR ligand to a bridging mode between the metal and a fluorocarbon ligand, is obtained when R = Me, Et, Prⁿ, Prⁱ, or Bu^t. When R = Prⁱ or Bu^t one isomeric form is observed which undergoes fluxional behaviour involving total CF₃ group scrambling, indicating reversible fission of the C-S bond of the ?²-vinyl ligand. With R = Me, Et, or Prⁿ two isomeric ?²-vinyl forms are observed, both of which undergo CF₃ group exchange in addition to isomer exchange, according to ¹⁹F n.m.r. studies. Reactions of both bis-alkyne (R = C₆H₄Me-4) and ?²-vinyl complexes (R = Prⁱ or Bu^t) with tertiary phosphines and phosphites (L) give ?²-vinyl complexes [W(SR){?²-C(CF₃)C(CF₃)(L)}(CF ₃C=CCF₃)(?⁵-C₅H ₅)] the stability of which increases with the nucleophilic character of the phosphorus ligand. ¹⁹F N.m.r. studies have established that in some cases the reactions proceed via two unstable kinetic isomers which undergo thermal rearrangement to a thermodynamically more stable form.