Reactions of alkynes with molybdenum and tungsten bis(alkyne) complexes [M(SR)(CF3C CCF3)(2)(eta(5)-C5H5)] (M = Mo, R = C6F5; M = W, R = C6H4Me-4): crystal and molecular structure of [Mo{eta(4)-C(CF3)=C(CF3)C(CO2Me)C(CO2Me)(SC6F5)}(CF3C CCF3)-(eta(5)-C5H5)]

The reaction of [Mo(SC6F5)(CF3C=CCF3)(2)(eta(5)-C5H5)] 1a with MeO2CC=CCO2M e at -30 degrees C gave a butadienyl complex [Mo{eta(4)-C(CF3)=C(CF3)C(CO2M e)C(CO2Me)(SC6F5)}(CF3C=CCF3)(eta(5)-C5H5)] which has been shown by X-ray a nalysis to contain an (eta(5)-C5H5)Mo(eta(2)-CF3C=CCF3) unit attached to th e C(CF3)=C(CF3)C(CO2Me)=C(CO2Me)SC6F5 butadienyl ligand through a CO2Me car bonyl 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 degree s 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-ordi nated 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(C F3)=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 instea d 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 sev en-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)- b utadienyl complexes [W{eta(3)-C(CF3)C(CF3)C(R)=C(R')SC6H4Me-4}(CF3C=CCF3)(e ta(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 le ad to different alkyne oligomerisation patterns are discussed.