Solvent-Free Ring-Opening Metathesis Polymerization of Norbornene over Silica-Supported Tungsten-Oxo Perhydrocarbyl Catalysts

On the use of 17O NMR for understanding molecular and silica-grafted tungsten oxo siloxide complexes

¹⁷O-labelled tungsten siloxide complexes [WOCl₂(OSitBu₃)₂] (1-Cl) and [WOMe₂(OSitBu₃)₂] (1-Me) were prepared and characterized by ¹⁷O MAS NMR, with input from theoretical calculations of NMR parameters. Guidelines linking ¹⁷O NMR parameters and the coordination sphere of molecular and silica-grafted tungsten oxo species are proposed. The grafting of 1-Me on SiO_2-700 afforded material 2, with surface species [(SiO)WOMe₂(OSitBu₃)] as shown by elemental analysis, IR and ¹H and ¹³C MAS NMR. The DFT calculations of the grafting mechanism are in line with the observed reactivity. They indicate the occurrence of several isomeric species of close energy for the grafted W centers, precluding efficient ¹⁷O MAS NMR studies. The lack of catalytic activity in olefin metathesis and ring-opening olefin metathesis polymerization indicates that initiation by α-H elimination is not operative in 2, contrary to related tungsten surface species, which illustrates the crucial influence of the nature of the metal coordination sphere.

Meziane K, Kaddouri A, Nguyen HP, Taoufik M. Well-defined surface tungstenocarbyne complex through the reaction of [W(CtBu)(CH2tBu)3] with CeO2: a highly stable precatalyst for NOx reduction with NH3

A highly-efficient NH₃-SCR single site catalyst W(CtBu)(CH₂tBu)₃/CeO_2–200, was prepared by surface organometallic chemistry approach. This catalyst showed high catalytic activity and stability with a broad operational temperature window.

Well-defined silica supported bipodal molybdenum oxo alkyl complexes: a model of the active sites of industrial olefin metathesis catalysts

A novel well-defined supported bipodal molybdenum alkyl oxo species for “modelling MoO₃/SiO₂ industrial catalysts” that efficiently catalyzes olefin metathesis has been unveiled.