Synthesis and Characterization of Silica-Stabilized Chromium(IV) Alkylidene Complexes

Ajjou, Jamila Amor Nait; Scott, Susannah L.; Paquet, Valérie E.

doi:10.1021/ja973177a

Cited by 90 publications

(44 citation statements)

References 29 publications

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“…In the presence of ethylene,t he reduced Cr II site is proposed to form Cr IV -alkyl complexes that could coordinate and insert ethylene (Scheme 17). [259,[273][274][275][276][277][278][279][280] Another possibility is the oxidative coupling of ethylene on aC r II site to form aC r IV -metallacyclopentane (Scheme 17) [262,281] that can grow into ap olymer by ring expansion [282] or by b-H elimination to form aC r IV -allyl hydride (SiO) 2 Cr(H)(h 3 -allyl) that is able to insert ethylene and start polymer growth. Insertion of ethylene in either the Cr-vinyl or the Cr À Hb ond of this species can initiate the polymerization.…”

Section: Chain Growth In the Phillips Catalystmentioning

confidence: 99%

“…[278,279,[298][299][300][301] Thep utative (SiO) 2 Cr(=CHEMe 3 )s pecies is proposed to react with ethylene to form oligomers and polymers (Scheme 19). Heating ( SiO) 2 Cr(CH 2 EMe 3 ) 2 to 70 8 8Co r150 8 8C results in the elimination of 1equiv of the corresponding alkane per Cr, which suggests the formation of ( SiO) 2 Cr-(=CHEMe 3 )t hrough a-H abstraction.…”

Section: Chain Growth In the Phillips Catalystmentioning

confidence: 99%

“…Insertion of ethylene in either the Cr‐vinyl or the Cr−H bond of this species can initiate the polymerization . It could also isomerize to Cr IV ‐alkylidene (≡SiO) 2 Cr(=CHMe), which could propagate polymer growth through a Green–Rooney mechanism . Another possibility is the oxidative coupling of ethylene on a Cr II site to form a Cr IV ‐metallacyclopentane (Scheme ) that can grow into a polymer by ring expansion or by β‐H elimination to form a Cr IV ‐allyl hydride (≡SiO) 2 Cr(H)(η 3 ‐allyl) that is able to insert ethylene and start polymer growth .…”

Section: Alkene Polymerizationmentioning

confidence: 99%

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Bridging the Gap between Industrial and Well‐Defined Supported Catalysts

et al. 2018

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Many industrial catalysts contain isolated metal sites on the surface of oxide supports. Although such catalysts have been used in a broad range of processes for more than 40 years, there is often a very limited understanding about the structure of the catalytically active sites. This Review discusses how surface organometallic chemistry (SOMC) engineers surface sites with well-defined structures and provides insight into the nature of the active sites of industrial catalysts; the Review focuses in particular on olefin production and conversion processes.

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Section: Chain Growth In the Phillips Catalystmentioning

confidence: 99%

Section: Chain Growth In the Phillips Catalystmentioning

confidence: 99%

Section: Alkene Polymerizationmentioning

confidence: 99%

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Bridging the Gap between Industrial and Well‐Defined Supported Catalysts

et al. 2018

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“…Durch Ethyleninsertion in die Cr‐Vinyl‐ oder die Cr‐H‐Bindung kann diese Spezies die Polymerisation einleiten . Sie könnte auch zu dem Cr IV ‐Alkyliden (≡SiO) 2 Cr(=CHMe) isomerisieren, das durch einen Green‐Rooney‐Mechanismus zu Polymerwachstum führen könnte . Eine weitere Möglichkeit ist die oxidative Kupplung von Ethylen an ein Cr II ‐Zentrum zu einem Cr IV ‐Metallacyclopentan (Schema ), von dem aus durch Ringerweiterung oder nach β‐H‐Eliminierung zu einem Cr IV ‐Allyl‐Hydrid (≡SiO) 2 Cr(H)(η 3 ‐Allyl) unter Ethyleninsertion ein Polymer wachsen kann .…”

Section: Alkenpolymerisationunclassified

“…Cr(CH 2 EMe 3 ) 4 (E=C oder Si) reagiert mit teildehydroxyliertem Siliciumdioxid zu (≡SiO) 2 Cr(CH 2 EMe 3 ) 2 (Schema b). Erhitzen von (≡SiO) 2 Cr(CH 2 EMe 3 ) 2 auf 70 °C oder 150 °C führt zur Eliminierung von 1 Äquiv des entsprechenden Alkans pro Cr, ein Hinweis auf die Entstehung von (≡SiO) 2 Cr(=CHEMe 3 ) durch α‐H‐Abstraktion . Es wird vermutet, dass die Spezies (≡SiO) 2 Cr(=CHEMe 3 ) mit Ethylen reagiert, um Oligomere und Polymere zu bilden (Schema ).…”

Section: Alkenpolymerisationunclassified

Eine Brücke zwischen industriellen und wohldefinierten Trägerkatalysatoren

et al. 2018

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Viele industrielle Katalysatoren enthalten isolierte Metallzentren an der Oberfläche von Oxidträgern. Derartige Katalysatoren werden seit über 40 Jahren bei verschiedensten Verfahren verwendet – die Struktur ihrer katalytischen Zentren bleibt aber bis heute nur ungenügend verstanden. Dieser Aufsatz zeigt, wie mit metallorganischer Oberflächenchemie (SOMC) Oberflächenzentren mit gut definierten Strukturen erzeugt werden können, und beschreibt die Beschaffenheit aktiver Zentren in industriellen Katalysatoren, insbesondere für die Herstellung und Umwandlung von Olefinen.

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Polyethylene, High Density

Benham

McDaniel

2005

Kirk-Othmer Encyclopedia of Chemical Technology

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Polyethylene (PE) is the most widely used plastic throughout the world, and high density polyethylene (HDPE) is the most widely used type of polyethylene. It was invented independently in the early 1950s in three different laboratories across the world. Commercial catalytic processes were quickly developed based on three different transition metals: Cr, Mo, and Ti. Today, hundreds of different grades of HDPE are manufactured by dozens of different commercial processes worldwide to meet the demands of applications too numerous to describe completely. The properties of HDPE can be made to vary widely for these specialized applications by varying its molecular structure, such as the molecular weight (MW); the MW distribution; the amount; type, and placement of short‐chain branching; the end group composition; and the degree of long‐chain branching. These affect the stiffness of the polymer; the gloss or clarity; the impact, puncture, and tear resistance; chemical resistance; electrical insulation properties; molding characteristics; and tensile properties. Common uses for HDPE include food packaging, bottles, bags, medical applications, drums, fuel tanks and other automotive parts, pipe, film, geomembranes, toys, film, and filament.

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Synthesis and Characterization of Silica-Stabilized Chromium(IV) Alkylidene Complexes

Cited by 90 publications

References 29 publications

Bridging the Gap between Industrial and Well‐Defined Supported Catalysts

Bridging the Gap between Industrial and Well‐Defined Supported Catalysts

Eine Brücke zwischen industriellen und wohldefinierten Trägerkatalysatoren

Polyethylene, High Density

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