Accessing Realistic Models for the WO₃–SiO₂ Industrial Catalyst through the Design of Organometallic Precursors

In order to access realistic models to the industrial olefin metathesis catalyst WO₃/SiO₂, which is the bigrafted tungsten oxo alkylidene species [(SiO)₂WO­(CHR)], we targeted the parent bis-alkyl oxo derivative [(SiO)₂WOR₂] prone to carbene formation. Thus, grafting of [WO­(CH₂EMe₃)₃Cl] (E = C, <b>1-Np</b>; E = Si, <b>1-Ns</b>) onto silica dehydroxylated at 200 °C was performed. While <b>1-Np</b> affords the monopodal species [(SiO)­WO­(CH₂CMe₃)₃] (<b>2-Np</b>), the neosilyl derivative <b>1-Ns</b> reacts to yield the well-defined bipodal species [(SiO)₂WO­(CH₂SiMe₃)₂] (<b>2-Ns</b>), via consecutive HCl and SiMe₄ release. This was demonstrated by mass balance analysis, elemental analysis, IR, advanced solid-state NMR (1D and 2D ¹H, ¹³C, ²⁹Si, and ¹⁷O), and EXAFS. Furthermore, DFT calculations allowed understanding and rationalizing the experimental results regarding grafting selectivity. The material <b>2-Ns</b> proved to lead to the most stable and efficient supported tungsten oxo catalyst for propene metathesis under dynamic conditions at 80 °C