Reversible insertion of alkynes into molybdenum- and tungsten-sulphur bonds

Reactions of the bis-hexafluorobut-2-yne complex [MoCl(CF₃CCCF₃)₂(?⁵-C₅H₅)] with thallium salts T1SR give ?²-C,C vinyl complexes [M{?³-C(CF₃)C(CF₃)SR}(CF₃CCCF₃)(?⁵-C₅H₅)] (1), fully characterised in the cases M = Mo, R = Prⁱ, Bu^t, but only partially so in the case M = Mo, R = 4-MeC₆H₄. Air oxidation of ?²-C,C vinyls 1 (M = Mo, R = 4-MeC₆H₄; = W, R = Prⁱ) and the isomeric bis-alkyne derivatives [MSR(CF₃CCCF₃)₂(?⁵-C₅H₅)] (2) (M = Mo, R = C₆F₅; M = W, R = 4-MeC₆H₄) gives cis s-alkenyl-oxo derivatives [M{C(CF₃)C(CF₃)SR}(O)(CF₃CCCF₃)(?⁵-C₅H₅)] (3). With 1 (M = Mo, R = Prⁱ) a cis-cis ?²-butadienyl complex [Mo{?²-C(CF₃)C(CF₃)C(CF₃)C(CF₃)SPrⁱ}(O)(?⁵-C₅H₅)] 4 is obtained instead, whereas air oxidation of [WSC₆F₅(CF₃CCCF₃)₂(?⁵-C₅H₅)] gives a dimeric alkyne derivative [W₂(CF₃CCCF₃)₄(O)_n(?⁵-C₅H₅)₂] (n = 1 or 2) (5) resulting from loss of the thiolate ligand. Reactions of s-alkenyl-oxo complexes 3 (M = Mo, R = C₆F₅; M = W, R = 4-MeC₆H₄) with tertiary phosphines L give ?²-vinyl complexes [MSR{?²-C(CF₃)C(CF₃)L}(CF₃CCCF₃)(?⁵-C₅H₅)] (M = Mo, R = C₆F₅, L = PEt₃ or PMe₂Ph; M = W, R = 4-MeC₆H₄, L = PEt₃, PMe₂Ph or PMePh₂) (6) as a result of reduction of the metal M^IV ? M^II and thiolate migration to the metal. © 1990.