Reactions of alkynes with molybdenum and tungsten bis(alkyne) complexes [M(SR)(CF3CCCF3)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)}(CF3CCCF3)(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 Cα, Cγ, and Cδ 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.