On the Track to Silica-Supported Tungsten Oxo Metathesis Catalysts: Input from ¹⁷O Solid-State NMR

Abstract

The grafting of an oxo chloro trisalkyl tungsten derivative on silica dehydroxylated at 700 °C was studied by several techniques that showed reaction via W-Cl cleavage, to afford a well-defined precatalyst for alkene metathesis. This was further confirmed by DFT calculations on the grafting process. (17)O labeling of the oxo moiety of a series of related molecular and supported tungsten oxo derivatives was achieved, and the corresponding (17)O MAS NMR spectra were recorded. Combined experimental and theoretical NMR studies yielded information on the local structure of the surface species. Assessment of the (17)O NMR parameters also confirmed the nature of the grafting pathway by ruling out other possible grafting schemes, thanks to highly characteristic anisotropic features arising from the quadrupolar and chemical shift interactions.

Silica-Supported Tungsten Neosilyl Oxo Precatalysts: Impact of the Podality on Activity and Stability in Olefin Metathesis

“…The 29 Si CP MAS NMR spectrum exhibits two signals at 1.2 and −100 ppm, accounting for the neosilyl fragment and the silica support, 24 respectively ( Figure 3). From these combined spectroscopic and analytical elements, it can be concluded that the reaction of The solid-state NMR data ( 1 H, 13 C, 29 Si) of 2a feature the expected signals of an anchored tungsten oxo neosilyl species. The relative peak intensity between 2a and 2b may indicate the number of neosilyl ligands and the nature of the grafted species.…”

“…In all experiments, the rotation frequency was set to 10 kHz unless otherwise specified. Chemical shifts were given with respect to TMS as external reference for 1 H and 13 Quantification of HCl Released during Grafting. The gas phase released during grafting was condensed into an IR cell equipped with CaF windows.…”

“…62 The value of the scale factor, S 0 2 = 0.94, was determined from the k 2 and k 3 χ(k) spectra of a reference compound, a sample of [WO(CH 2 tBu) 3 Cl] complex diluted in BN and carefully mixed and pressed as a pellet (one oxo at 1.70(1) Å, three carbon atoms at 2.10(1) Å, and one chlorine at 2.43(1) Å in the first coordination sphere, with three carbon atoms at 3.28(3) Å). 13 The refinements were performed by fitting the structural parameters N i , R i , σ i , and the energy shift, ΔE 0 (the same for all shells). The fit residue, ρ(%), was calculated by the following formula: As recommended by the Standards and Criteria Committee of the International XAFS Society, the quality factor, (Δχ) 2 /ν, where ν is the number of degrees of freedom in the signal, was calculated, and its minimization considered in order to control the number of variable parameters in the fits.…”

“…NMR characterization: 1 H MAS NMR spectra of 2a (a) and 2b (c) and13 C CPMAS NMR spectra of 2a (b) and 2b (d) (11.75 T, spinning rate 10 kHz).…”

Supported Single-Site Organometallic Catalysts for the Synthesis of High-Performance Polyolefins

“…For example, it has been shown that well-defined zirconium hydrides supported on alumina are highly active catalysts for alkane hydrogenolysis (Fig. 6a) [74] and silica-supported tungsten [75][76][77][78] and molybdenum complexes (Fig. 6b) [79][80][81][82] are effective catalysts for alkane metathesis [69,71,77,[83][84][85].…”