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)}(CF3C CCF3)-(η5-C5H5)]

The reaction of [Mo(SC6F5)(CF3C=CCF3)(2)(eta(5)-C5H5)] 1a with MeO2CC=CCO2Me at -30 degrees C gave a butadienyl complex [Mo{eta(4)-C(CF3)=C(CF3)C(CO2Me)C(CO2Me)(SC6F5)}(CF3C=CCF3)(eta(5)-C5H5)] which has been shown by X-ray analysis to contain an (eta(5)-C5H5)Mo(eta(2)-CF3C=CCF3) unit attached to the C(CF3)=C(CF3)C(CO2Me)=C(CO2Me)SC6F5 butadienyl ligand through a CO2Me carbonyl oxygen atom and C-alpha, C-gamma, and C-delta 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 degrees C to give isomeric complexes [Mo{eta(5)-C(CF3)C(CF3)C(CF3)C(CF3)C(CO2Me)=C(CO2Me)SC6F5}(eta(5)-C5H5)] in which linkage of the butadienyl and co-ordinated alkynes has occurred to give eta(5) or eta(6) tris- (alkyne) ligands. The complex [W(SC6H4Me-4)(CF3C=CCF3)(2)(eta(5)-C5H5)] 1b and MeO2CC=CCO2Me reacted at -20 to -15 degrees C to give a butadienyl complex [W{eta(5)-C(CF3)=C(CF3)C(CO2Me)C(CO2Me)(SC6H4Me-4)}(CF3C=CCF3)(eta(5)-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 degrees C to give the sixteen electron complex [W(SC6H4Me-4){eta(4)-C(CF3)=C(CF3)C(CO2Me)=C(CO2Me)C(CF3)=C(CF3)}(eta(5)-C5H5)] containing a novel seven-membered metallacyclic ring. In contrast 1b and non-activated alkynes RC=CR' (R=R'=Me; R=Me or Ph, R'=Ph) reacted to give the eta(3)- and eta(4)- butadienyl complexes [W{eta(3)-C(CF3)C(CF3)C(R)=C(R')SC6H4Me-4}(CF3C=CCF3)(eta(5)-C5H5)] and [W{eta(4)-C(CF3)C(CF3)=C(Me)C(Me)SC6H4Me-4}(CF3C=CCF3)(eta(5)-C5H5)] with no evidence for alkyne trimerisation. The pathways which lead to different alkyne oligomerisation patterns are discussed.