Reactions of the molybdenum bis(alkyne) complex [Mo(SC6F5)(F3CCCCF3)2(η5-C5H5)] with alkynes leading to isomeric and fluxional η4-butadienyl complexes

Abstract

Reactions of the bis(hexafluorobut-2-yne) complex [Mo(SC₆F₅)(F₃CCCCF₃)₂(η⁵-C₅H₅)]1 with alkynes RCCR′ give the novel η⁴-butadienyl complex prone-[Mo{η⁴-C(CF₃)C(CF₃)CRCR(SC₆F₅)}(F₃CCCCF₃)(η⁵-C₅H₅)]2(R = R′= Me; R = H, R′= Me or Ph; R = Me, R′= CO₂Me) which undergoes isomerisation via an η²-C,C vinyl intermediate [Mo{η³-C(CF₃)C(CF₃)CRCR′(SC₆F₅)}(F₃CCCCF₃)(η⁵-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-[Mo{η⁴-CR′CRC(CF₃)C(CF₃)(SC₆F₅)}(F₃CCCCF₃)(η⁵-C₅H₅)]5(R = R′= Ph; R = Me, R′= Ph). Fluorine-19 NMR studies established that with PhCCPh 3 and 5 exist in solution as an equilibrium mixture. With PhCCMe exchange between 3, 4 and 5 is faster which allowed study by dynamic ¹⁹F NMR and spin-saturation-transfer experiments.