Strongly σ Donating Thiophenoxide in Silica-Supported Tungsten Oxo Catalysts for Improved 1‑Alkene Metathesis Efficiency

We report the synthesis of tungsten
oxo alkylidene complexes bearing
bulky thiophenoxide ligands [W­(O)­(CHtBu)­(SHMT)2(PMe2Ph)] and [W­(O)­(CHtBu)­(SHMT)2] (SHMT = 2,6-dimesitylthiophenoxide) and their grafting on
partially dehydroxylated silica, affording the supported complexes
[(SiO)­W­(O)­(CHtBu)­(SHMT)­(PMe2Ph)]
and [(SiO)­W­(O)­(CHtBu)­(SHMT)]. While the molecular
precursors are not significantly active in the metathesis of alkenes,
the grafted analogue without bound phosphine ligands displays activity
comparable to that of its aryloxide analogue [(SiO)­W­(O)­(CHtBu)­(OHMT)]
(OHMT = 2,6-dimesitylphenoxide). It is worth noting that [(SiO)­W­(O)­(CHtBu)­(SHMT)]
showed unprecedented activity in the metathesis of 1-alkenes, probably
because of the lower stability of metallacyclobutane intermediates.