Syntheses and reactions of η 2 -vinyl complexes of molybdenum and tungsten [M(SC 6 F 5 ){η 2 -C(CF 3 )C(CF 3 )(PR 3 )}-(CF 3 CCCF 3 )(cp)] and [Mo{η 3 -C(CF 3 )C(CF 3 )(SPr i )}-(CF 3 CCCF 3 )(cp)](cp =η-C 5 H 5 )

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.