Alkylidene and alkylidyne surface complexes: Precursors and intermediates in alkane conversion processes on supported single-site catalysts

Rascón, Fernando; Copéret, Christophe

doi:10.1016/j.jorganchem.2011.07.015

Cited by 24 publications

(18 citation statements)

References 125 publications

(84 reference statements)

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“…113 In light of these results, the activities of supported tungsten species for alkanes metathesis have been investigated. 85,114 Tungsten carbyne species supported on silica (I), silica-alumina (III) and alumina (IV) have been tested for propane metathesis in a batch reactor at 150 1C. 64,65 III and IV are active catalyst precursors for the metathesis of propane (Table 2).…”

Section: Bifunctional Systemsmentioning

confidence: 99%

Expanding the scope of metathesis: a survey of polyfunctional, single-site supported tungsten systems for hydrocarbon valorization

et al. 2013

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Olefin metathesis is increasingly incorporated in polyfunctional industrial processes. The classical WO3/SiO2 olefin metathesis catalyst is combined to other catalysts in order to afford higher added-value chemicals. However, the combination of several reactions, not only in a single reactor, but also stemming from a single, multifunctional surface species is a desirable improvement regarding process issues. Well-defined surface organometallic tungsten species can be designed to implement targeted functionalities (carbene, hydride, alkyl, …). By tuning the metal's coordination sphere, it is possible to combine metathesis with several reactions, such as (de)hydrogenation, dimerization or isomerization. Novel, unconventional reactions for the production and upgrading of alkanes and alkenes have thus been uncovered. The reactivity of this library of supported catalysts is discussed based on the type of mediated transformations: monofunctional (alkene and alkyne metathesis), bifunctional (1-butene or 2-butenes to propylene), trifunctional (ethylene to propylene, alkane metathesis, …). Mechanistic considerations will be discussed to put these results in a wider perspective for future developments.

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Section: Bifunctional Systemsmentioning

confidence: 99%

Expanding the scope of metathesis: a survey of polyfunctional, single-site supported tungsten systems for hydrocarbon valorization

et al. 2013

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“…The stabilization of alkylidynes in such low‐coordinated compounds hence requires the presence of ancillary ligands, such as phosphines or, in the case of silica‐supported species, siloxane‐bridges. Similarly, ligand fields that can stabilize alkylidynes are also present in typical alkyl‐alkylidene catalysts, which are known to catalyze the alkane metathesis reaction . This also holds true for Ti‐species in certain ligand fields, such as these involving PNP (PNP=N[ 2 ‐P(CHMe 2 ) 2 ‐4‐methylphenyl] 2 ) pincer‐type ligands.…”

Section: Resultsmentioning

confidence: 91%

Metal Alkyls with Alkylidynic Metal‐Carbon Bond Character: Key Electronic Structures in Alkane Metathesis Precatalysts

Gordon

Copéret

2020

Angewandte Chemie

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The homologation of alkanes via alkane metathesis is catalyzed at low temperatures (150 °C) by the silica‐supported species (≡SiO)WMe5 and (≡SiO)TaMe4, while (≡SiO)TaMe3Cp* is inactive. The contrasting reactivity is paralleled by differences in the 13C NMR signature; the former display significantly more deshielded isotropic chemical shifts (δiso) and almost axially symmetric chemical shift tensors, similar to what is observed in their molecular precursors TaMe5 and WMe6. Analysis of the chemical shift tensors reveals the presence of a triple‐bond character in their metal‐carbon (formally single) bond. This electronic structure is reflected in their propensity to generate alkylidynes and to participate in alkane metathesis, further supporting the role of alkylidynes as key reaction intermediates. This study establishes chemical shift as a descriptor to identify potential alkane metathesis catalysts.

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“…In compounds like TaMe 5 such aligand field is not available,as(X)MeTaCH is acoordinatively unsaturated species.T he stabilization of alkylidynes in such low-coordinated compounds hence requires the presence of ancillary ligands,such as phosphines or, in the case of silica-supported species,s iloxane-bridges.S imilarly,l igand fields that can stabilize alkylidynes are also present in typical alkyl-alkylidene catalysts,w hich are known to catalyze the alkane metathesis reaction. [11,12,23,40] This also holds true for Ti-species in certain ligand fields,such as these involving PNP (PNP = N[ 2 -P(CHMe 2 ) 2 -4-methylphenyl] 2 )p incer-type ligands.I nf act, also in these systems the C À Ha ctivation that yields alkyl-alkylidene structures occurs via alkylidyne intermediates. [41][42][43][44] Thelarger deshielding of the studied W VI alkyl species compared to their Ta V analogues suggests that the W VI center develops stronger p(MÀC) interactions,l eading to am ore strongly developed triple-bond-character in the Wbased compounds.T his is reflected in the propensity of compounds such as WMe 6 and [Cp*WMe 4 ] + to generate alkylidynes.H owever, all of these compounds (both W-and Ta-based) with alkylidynic character of the MÀCbond feature al igand field that is,i np rinciple,a ble to stabilize alkylidyne species.…”

Section: Methodsmentioning

confidence: 89%

Metal Alkyls with Alkylidynic Metal‐Carbon Bond Character: Key Electronic Structures in Alkane Metathesis Precatalysts

Gordon

Copéret

2020

Angew Chem Int Ed

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The homologation of alkanes via alkane metathesis is catalyzeda tl ow temperatures (150 8 8C) by the silicasupported species (SiO)WMe 5 and (SiO)TaMe 4 ,w hile ( SiO)TaMe 3 Cp* is inactive.T he contrasting reactivity is paralleled by differences in the 13 CNMR signature;t he former displays ignificantly more deshielded isotropic chemical shifts (d iso )a nd almost axially symmetric chemical shift tensors, similar to what is observed in their molecular precursors TaMe 5 and WMe 6 .A nalysis of the chemical shift tensors reveals the presence of at riple-bond character in their metal-carbon (formally single) bond. This electronic structure is reflected in their propensity to generate alkylidynes and to participate in alkane metathesis,further supporting the role of alkylidynes as key reaction intermediates.T his study establishes chemical shift as ad escriptor to identify potential alkane metathesis catalysts.

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Alkylidene and alkylidyne surface complexes: Precursors and intermediates in alkane conversion processes on supported single-site catalysts

Cited by 24 publications

References 125 publications

Expanding the scope of metathesis: a survey of polyfunctional, single-site supported tungsten systems for hydrocarbon valorization

Expanding the scope of metathesis: a survey of polyfunctional, single-site supported tungsten systems for hydrocarbon valorization

Metal Alkyls with Alkylidynic Metal‐Carbon Bond Character: Key Electronic Structures in Alkane Metathesis Precatalysts

Metal Alkyls with Alkylidynic Metal‐Carbon Bond Character: Key Electronic Structures in Alkane Metathesis Precatalysts

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