Synthesis, structures, and reactions of ethenethiolato complexes of molybdenum and tungsten [M{η3–SC(CF3)C(CF3)H}(CF3CCCF3)(η5-C5H5)](M = Mo or W). Their relevance to the mechanism of metal-promoted isomerisation of carbon–carbon double bonds

Abstract

Thermolysis of the η²-C,C-vinyl complexes [M{η³-C(CF₃)C(CF₃)SBu^t}(CF₃CCCF₃)(η⁵-C₅H₅)](1)(M = Mo or W) gives η³-ethenethiolato complexes Z-endo-[M{η³-SC(CF₃)C(CF₃)H}(CF₃CCCF₃)(η⁵-C₅H₅)](2). With M = W an intermediato E-exo-[W{η³-SC(CF₃)C(CF₃)H}(CF₃CCCF₃)(η⁵-C₅H₅)](3) was isolated and structurally characterised, illustrating that exo→endo and E→Z isomerisations are concomitant processes. The relevance of this observation for mechanism(s) of metal-pormoted alkyne isomerisations is discussed. Reactions of (2) and (3) with tertiary phosphines and dioxygen give σ-ethenethiolato complexes [M{SC(CF₃)C(CF₃)H}L(CF₃CCCF₃)(η⁵-C₅H₅)](M = Mo, L = O or PPh₃; M = W, L = O, PPh₃,PMe₂Ph, or PPh₂CCPh) with retention of stereochemistry about the CC bond. Dynamic ¹⁹F n.m.r. studies reveal fluxional behaviour in some complexes due to alkyne propeller rotation.