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

Abstract

In order to access realistic models to the industrial olefin metathesis catalyst WO 3 /SiO 2, which is the bigrafted tungsten oxo alkylidene species [(≡SiO) 2 WO(═CHR)], we targeted the parent bis-alkyl oxo derivative [(≡SiO) 2 WOR 2 ] prone to carbene formation. Thus, grafting of [WO(CH 2 EMe 3 ) 3 Cl] (E = C, 1-Np; E = Si, 1-Ns ) onto silica dehydroxylated at 200 °C was performed. While 1-Np affords the monopodal species [(≡SiO)WO(CH 2 CMe 3 ) 3 ] ( 2-Np ), the neosilyl derivative 1-Ns reacts to yield the well-defined bipodal species [(≡SiO) 2 WO(CH 2 SiMe 3 ) 2 ] ( 2-Ns ), via consecutive HCl and SiMe 4 release. This was demonstrated by mass balance analysis, elemental analysis, IR, advanced solid-state NMR (1D and 2D 1 H, 13 C, 29 Si, and 17 O), and EXAFS. Furthermore, DFT calculations allowed understanding and rationalizing the experimental results regarding grafting selectivity. The material 2-Ns proved to lead to the most stable and efficient supported tungsten oxo catalyst for propene metathesis under dynamic conditions at 80 °C.