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 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, 1-Np; E = Si, 1-Ns) onto silica dehydroxylated at 200 °C was performed. While 1-Np affords the monopodal species [(≡SiO)WO(CH2CMe3)3] (2-Np), the neosilyl derivative 1-Ns reacts to yield the well-defined bipodal species [(≡SiO)2WO(CH2SiMe3)2] (2-Ns), 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 2-Ns proved to lead to the most stable and efficient supported tungsten oxo catalyst for propene metathesis under dynamic conditions at 80 °C.