Reactions of alkynes with molybdenum and tungsten bis(alkyne) complexes [M(SR)(CF3CCCF3)2(η5-C5H5)] (M = Mo, R = C6F5; M = W, R = C6H4Me-4): crystal and molecular structure of [Mo{η4-C(CF3)C(CF3)C(CO2Me)C(CO2Me)(SC6F5)}(CF3CCCF3)(η5-C5H5)]†

Abstract

The reaction of [Mo(SC₆F₅)(CF₃CCCF₃)₂(η⁵-C₅H₅)] 1a with MeO₂CCCCO₂Me at –30 °C gave a butadienyl complex [Mo{η⁴-C(CF₃)C(CF₃)C(CO₂Me)C(CO₂Me)(SC₆F₅)}(CF₃CCCF₃)(η⁵-C₅H₅)] which has been shown by X-ray analysis to contain an (η⁵-C₅H₅)Mo(η²-CF₃CCCF₃) unit attached to the C(CF₃)C(CF₃)C(CO₂Me)C(CO₂Me)SC₆F₅ butadienyl ligand through a CO₂Me carbonyl oxygen atom and C_α, C_γ, and C_δ of the butadiene chain. The structure and bonding in this complex and in related butadienyl and co-ordinated ester complexes are compared. It rearranges above ca. –20 °C to give isomeric complexes [Mo{η⁵-C(CF₃)C(CF₃)C(CF₃)C(CF₃)C(CO₂Me)C(CO₂Me)SC₆F₅}(η⁵-C₅H₅)] in which linkage of the butadienyl and co-ordinated alkynes has occurred to give η⁵ or η⁶ tris- (alkyne) ligands. The complex [W(SC₆H₄Me-4)(CF₃CCCF₃)₂(η⁵-C₅H₅)] 1b and MeO₂CCCCO₂Me reacted at –20 to –15 °C to give a butadienyl complex [W{η⁵-C(CF₃)C(CF₃)C(CO₂Me)C(CO₂Me)(SC₆H₄Me-4)}(CF₃CCCF₃)(η⁵-C₅H₅)] similar to the molybdenum complex but containing a co-ordinated thiolate sulfur instead of a carbomethoxy oxygen bonded to the metal. It isomerises above ca. –10 °C to give the sixteen electron complex [W(SC₆H₄Me-4){η⁴-C(CF₃)C(CF₃)C(CO₂Me)C(CO₂Me)C(CF₃)C(CF₃)}(η⁵-C₅H₅)] containing a novel seven-membered metallacyclic ring. In contrast 1b and non-activated alkynes RCCR′ (R = R′ = Me; R = Me or Ph, R′ = Ph) reacted to give the η³- and η⁴- butadienyl complexes [W{η³-C(CF₃)C(CF₃)C(R)C(R′)SC₆H₄Me-4}(CF₃CCCF₃)(η⁵-C₅H₅)] and [W{η⁴-C(CF₃)C(CF₃)C(Me)C(Me)SC₆H₄Me-4}(CF₃CCCF₃)(η⁵-C₅H₅)] with no evidence for alkyne trimerisation. The pathways which lead to different alkyne oligomerisation patterns are discussed.