Modification of silica-supported tungsten neosilyl oxo precatalysts: impact of substituted phenol on activity and stability in olefin metathesis†
A novel strategy to access a large variety of tungsten oxo pre-catalysts for olefin metathesis involving post-treatment of [(SiO)W(O)(CH2SiMe3)3], 1b, with the desired spectator ligands is presented. This method allowed establishing structure–reactivity relationships in propylene metathesis as a function of the spectator ligands of tungsten oxo species. Thus, the novel pre-catalysts [(SiO)W(O)R2X], 2a–c (X = 2,6-dimethylphenoxide, 2-trifluoromethylphenoxide, pentafluorophenoxide), are obtained by modification of well-defined monopodal species 1b by substituted phenols along with TMS release. These were demonstrated by mass balance analysis, elemental analysis, IR, advanced solid-state NMR (1D and 2D 1H, 13C and 19F) and EXAFS. The modified materials were proved to lead to stable and efficient supported tungsten oxo catalysts for propene metathesis under dynamic conditions at 80 °C.