Propene metathesis over silica-supported tungsten oxide catalyst?Catalyst induction mechanism

Basrur, A. G.; Patwardhan, S. R.; Vyas, S.N.

doi:10.1016/0021-9517(91)90211-l

Cited by 57 publications

(41 citation statements)

References 9 publications

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“…allows the process to be operated at lower temperatures, thus indicating that the high temperature conditions are mostly needed for generating the active sites. [15][16][17][18][19] Similar pre-treatment effect has also been reported for supported Mo based catalysts. [20][21][22] Recently, our group has reported a low temperature activation method based on organosilicon reductants, which allow MO 3 /SiO 2 (M = Mo or W) and the related well-defined silica-supported metal-oxo species to catalyze alkene metathesis at 70 °C.…”

Section: Introductionsupporting

confidence: 76%

C–H Activation and Proton Transfer Initiate Alkene Metathesis Activity of the Tungsten(IV)–Oxo Complex

et al. 2018

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In alkene metathesis, while group 6 (Mo or W) high-oxidation state alkylidenes are accepted to be key reaction intermediates for both homogeneous and heterogeneous catalysts, it has been proposed that low valent species in their +4 oxidation state can serve as precatalysts. However, the activation mechanism for these latter species-generating alkylidenes-is still an open question. Here, we report the syntheses of tungsten(IV)-oxo bisalkoxide molecular complexes stabilized by pyridine ligands, WO(OR)py (R = CMe(CF) (2a), R = Si(O tBu) (2b), and R = C(CF) (2c); py = pyridine), and show that upon activation with B(CF) they display alkene metathesis activities comparable to W(VI)-oxo alkylidenes. The initiation mechanism is examined by kinetic, isotope labeling and computational studies. Experimental evidence reveals that the presence of an allylic CH group in the alkene reactant is crucial for initiating alkene metathesis. Deuterium labeling of the allylic C-H group shows a primary kinetic isotope effect on the rate of initiation. DFT calculations support the formation of an allyl hydride intermediate via activation of the allylic C-H bond and show that formation of the metallacyclobutane from the allyl "hydride" involves a proton transfer facilitated by the coordination of a Lewis acid (B(CF)) and assisted by a Lewis base (pyridine). This proton transfer step is rate determining and yields the metathesis active species.

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Section: Introductionsupporting

confidence: 76%

C–H Activation and Proton Transfer Initiate Alkene Metathesis Activity of the Tungsten(IV)–Oxo Complex

et al. 2018

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“…10 wt%, is required to reach high catalytic activities, despite only a low fraction of metal sites is active. 25 Based on studies that unravelled the structure of the active species, [26][27][28] surface organometallic chemistry has led to the development of well-defined highly active catalysts that contain only a low amount of metal. [29][30][31][32][33] On the other hand, surface organometallic chemistry on oxidizing support and for deNOx applications is rare.…”

Section: Introductionmentioning

confidence: 99%

Well-defined surface tungstenocarbyne complex through the reaction of [W(CtBu)(CH₂tBu)₃] with CeO₂: a highly stable precatalyst for NOx reduction with NH₃

et al. 2021

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“…4 Typically, WO 3 /SiO 2 operates at high temperature (> 400 °C), 14 but various pre-treatment methods, such as thermal treatment under reducing conditions, have been shown to increase the activity at low temperatures. [14][15][16][17][18][19][20][21][22] However, despite years of studies, the molecular-level understanding of the activation process remains very limited and the nature of active species is still under debate. 14,21 Several studies have reported the formation of oxygenates (e.g.…”

Section: Introductionmentioning

confidence: 99%

Well-Defined Silica-Supported Tungsten(IV)–Oxo Complex: Olefin Metathesis Activity, Initiation, and Role of Brønsted Acid Sites

et al. 2019

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Despite the importance of the heterogeneous tungsten-oxo based olefin metathesis catalyst (WO 3 /SiO 2) in industry, understanding of its initiation mechanism is still very limited. It has been proposed that reduced W(IV)-oxo surface species act as precatalysts. In order to understand the reactivity and initiation mechanism of surface W(IV)-oxo species, we synthesized a well-defined silica-supported W(IV)-oxo species (≡SiO)WO(OtBuF 6)(py) 3 (OtBuF 6 = OC(CH 3)(CF 3) 2 ; py = pyridine) (F6@SiO 2-700) via Surface Organometallic Chemistry (SOMC). F6@SiO 2-700 was shown to be highly active in olefin metathesis upon removal of pyridine ligands through the addition of tris(pentafluorophenyl)borane (B(C 6 F 5) 3) or thermal treatment under high vacuum. The metathesis activity towards olefins with and without allylic C−H groups, namely β-methylstyrene and styrene, respectively, was investigated. In the case of styrene, we demonstrate the role of surface OH groups in initiating metathesis activity. In particular, the presence of strong Brønsted acidic surface OH sites, revealed by 15 N-labeled pyridine, likely arises from the presence of adjacent W sites in the catalyst and assist styrene metathesis, an olefin having no allylic C-H bond. In contrast, initiation of olefins containing allylic C−H group (e.g. β-methylstyrene) is independent of surface OH group concentration and likely involves allylic C−H activation mechanism like the molecular W(IV)-oxo species. This study indicates that initiation mechanisms depend on the olefinic substrates and reveals the synergistic effect of Brønsted acidic surface sites and reduced W(IV) sites in the initiation of olefin metathesis.

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Propene metathesis over silica-supported tungsten oxide catalyst?Catalyst induction mechanism

Cited by 57 publications

References 9 publications

C–H Activation and Proton Transfer Initiate Alkene Metathesis Activity of the Tungsten(IV)–Oxo Complex

C–H Activation and Proton Transfer Initiate Alkene Metathesis Activity of the Tungsten(IV)–Oxo Complex

Well-defined surface tungstenocarbyne complex through the reaction of [W(CtBu)(CH₂tBu)₃] with CeO₂: a highly stable precatalyst for NOx reduction with NH₃

Well-Defined Silica-Supported Tungsten(IV)–Oxo Complex: Olefin Metathesis Activity, Initiation, and Role of Brønsted Acid Sites

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Propene metathesis over silica-supported tungsten oxide catalyst?Catalyst induction mechanism

Cited by 57 publications

References 9 publications

C–H Activation and Proton Transfer Initiate Alkene Metathesis Activity of the Tungsten(IV)–Oxo Complex

C–H Activation and Proton Transfer Initiate Alkene Metathesis Activity of the Tungsten(IV)–Oxo Complex

Well-defined surface tungstenocarbyne complex through the reaction of [W(CtBu)(CH2tBu)3] with CeO2: a highly stable precatalyst for NOx reduction with NH3

Well-Defined Silica-Supported Tungsten(IV)–Oxo Complex: Olefin Metathesis Activity, Initiation, and Role of Brønsted Acid Sites

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Well-defined surface tungstenocarbyne complex through the reaction of [W(CtBu)(CH₂tBu)₃] with CeO₂: a highly stable precatalyst for NOx reduction with NH₃