Synthesis, reactions, and dynamic nuclear magnetic resonance studies of η2-vinyl complexes of tungsten, [W{η3-C(CF3)C(CF3)(SR)}(CF3cCCF3)(η5-C5H5)](R = Me, Et, Prn, Pri, or But)

Abstract

Reactions of the hexafluorobut-2-yne complex [WCl(CF3CCCF3)2(η5-C5H5)] with thallium(I) thiolates TI(SR) give the bis-alkyne derivative [W(SR)(CF3CCCF3)2(η5-C5H5)] when R = C6H4Me-4 whereas an isomeric η2-vinyl form [W{η3-C(CF3)C(CF3)(SR)(CF3CCCF3)(η5C5H5)], 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 But. When R = Pri or But one isomeric form is observed which undergoes fluxional behaviour involving total CF3 group scrambling, indicating reversible fission of the C–S bond of the η2-vinyl ligand. With R = Me, Et, or Prn two isomeric η2-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 η2-vinyl complexes (R = Pri or But) with tertiary phosphines and phosphites (L) give η2-vinyl complexes [W(SR){η2-C(CF3)C(CF3)(L)}(CF3CCCF3)(η5-C5H5)] 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.