Retro-Vinylidene Rearrangements of P- and S‑Substituted Ruthenium Vinylidene Complexes

P- and S-substituted vinylidene complexes, [Ru{CC(R)(E)}(dppe)Cp]BArF4 [E = PO(OMe)2, PO(OEt)2, POPh2, SPh,
and SO2Ph], were found to be active for retro-vinylidene
rearrangements to add new entries of reversible systems of vinylidene/alkyne
isomerization. Isotope labeling experiments revealed that PO(OMe)2- and POPh2-substituted complexes underwent the
retro-vinylidene rearrangement via selective 1,2-migration of the
P-substituents. In contrast, in the case of a SPh-substituted complex,
both the SPh and the R groups served as migrating groups during the
reversible alkyne/vinylidene isomerization, though the migration of
the SPh group was still the major reaction path. These findings would
deepen the mechanistic understanding of alkyne/vinylidene rearrangements
of heteroatom-substituted internal alkynes.