REVERSIBLE INSERTION OF ALKYNES INTO MOLYBDENUM SULFUR AND TUNGSTEN SULFUR BONDS

Reactions of the bis-hexafluorobut-2-yne complex [MoCl(CF3CCCF3)2(η5-C5H5)] with thallium salts T1SR give η2-C,C vinyl complexes [M{η3-C(CF3)C(CF3)SR}(CF3CCCF3)(η5-C5H5)] (1), fully characterised in the cases M = Mo, R = Pri, But, but only partially so in the case M = Mo, R = 4-MeC6H4. Air oxidation of η2-C,C vinyls 1 (M = Mo, R = 4-MeC6H4; = W, R = Pri) and the isomeric bis-alkyne derivatives [MSR(CF3CCCF3)2(η5-C5H5)] (2) (M = Mo, R = C6F5; M = W, R = 4-MeC6H4) gives cis σ-alkenyl-oxo derivatives [M{C(CF3)C(CF3)SR}(O)(CF3CCCF3)(η5-C5H5)] (3). With 1 (M = Mo, R = Pri) a cis-cis η2-butadienyl complex [Mo{η2-C(CF3)C(CF3)C(CF3)C(CF3)SPri}(O)(η5-C5H5)] 4 is obtained instead, whereas air oxidation of [WSC6F5(CF3CCCF3)2(η5-C5H5)] gives a dimeric alkyne derivative [W2(CF3CCCF3)4(O)n(η5-C5H5)2] (n = 1 or 2) (5) resulting from loss of the thiolate ligand. Reactions of σ-alkenyl-oxo complexes 3 (M = Mo, R = C6F5; M = W, R = 4-MeC6H4) with tertiary phosphines L give η2-vinyl complexes [MSR{η2-C(CF3)C(CF3)L}(CF3CCCF3)(η5-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 MIV → MII and thiolate migration to the metal. © 1990.