Syntheses and reactions of η2-vinyl complexes of molybdenum and tungsten [M(SC6F5){η2-C(CF3)C(CF3)(PR3)}-(CF3CCCF3)(cp)] and [Mo{η3-C(CF3)C(CF3)(SPri)}-(CF3CCCF3)(cp)](cp =η-C5H5)

Abstract

Reactions of bis(hexafluorobut-2-yne) complexes [M(SC₆F₅)(CF₃CCCF₃)₂(cp)](M = Mo, 1a; or W, 1b with tertiary phosphines and phosphites (L) give η²-vinyl complexes [M(SC₆F₅){η²-C(CF₃)C(CF₃)L}-(CF₃CCCF₃)(cp)]3[(M = Mo or W; L = PEt₃, PMe₂Ph or PMePh₂; M = W, L = P(OMe)₃] as a result of attack at an alkyne carbon. Several isomeric forms of complexes 3 have been detected by NMR spectroscopy. Reactions of phosphines with the η²-C,C vinyl complex [Mo{η³-C(CF₃)C(CF₃)SPrⁱ}(CF₃CCCF₃)(cp)]2 in contrast give η⁴-butadienyl derivatives [Mo{C(CF₃)=C(CF₃)C(CF₃)=C(CF₃)-(SPrⁱ)}L(cp)]4(L = PEt₃, PMe₂Ph, or MeCCPPH₂) apparently as a result of insertion of the alkyne into the MC bond of the η²-C,C vinyl. A similar complex 4 is obtained when 3(M = Mo, L = PMe₂Ph) is allowed to isomerise in diethyl ether at room temperature. In contrast 3(M = Mo, L = PMe₂Ph) isomerises in refluxing hexane to the tetrakis(trifluoromethyl)cyclobutadiene complex [Mo(SC₆F₅)-(PMe₂Ph){η⁴-C₄(CF₃)₄}(cp)]9. An alternative isomerisation process is observed in diethyl ether at 18°C where the product [MoF{η³-C(CF₂)C(CF₃)=C(CF₃)C(CF₃)(SC₆F₅)}L(cp)]8(L = PEt₃ or PMe₂Ph) results from linking of two CF₃CCCF₃ ligands and a C₆F₅S group and fluorine transfer from a CF₃ to the metal. Fluxional behaviour in complexes 3,8 and 9 has been studied by ¹⁹F NMR spectroscopy.