REACTIONS OF THE MOLYBDENUM BIS(ALKYNE) COMPLEX [MO(SC6F5)(F3CCCCF3)2(ETA-5-C5H5)] WITH ALKYNES LEADING TO ISOMERIC AND FLUXIONAL ETA-4-BUTADIENYL COMPLEXES

Reactions of the bis(hexafluorobut-2-yne) complex [Mo(SC6F6)(FCC=CCF3)2(eta5-C5H5)] 1 with alkynes RC=CR' give the novel eta4-butadienyl complex prone-[Mo{eta4-C(CF3)C(CF3)=CRCR(SC6F5)}(F3CC= CCF3)(eta5-C5H5)] 2 (R = R'= Me; R = H, R'= Me or Ph; R = Me, R'= CO2Me) which undergoes isomerisation via an eta2-C,C vinyl intermediate [Mo{eta3-C(CF3)C(CF3)CR=CR'(SC6F5)}(F3CC=CCF3)(eta5-C5H5)] 3 (R = R' = Me, Et or Ph; R = Me, R'= CO2Me or Ph; R = H, R' = Ph) to the supine isomer 4 (R = R' = Me or Et; R = Me, R' = CO2Me or Ph; R = H, R' = Me or Ph) followed by a novel 1,4 thiolate migration to give supine-[M{eta4-CR'CR=C(CF3)C(CF3)(SC6F5)}(F3CC=CCF3)(eta5-C5H5)] 5 (R = R' = Ph; R = Me, R' = Ph). Fluorine-19 NMR studies established that with PhC=CPh 3 and 5 exist in solution as an equilibrium mixture. With PhC=CMe exchange between 3, 4 and 5 is faster which allowed study by dynamic F-19 NMR and spin-saturation-transfer experiments.