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)SBut}(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.