Mechanistic Aspects of Olefin Metathesis

Calderon, Nissim; Ofstead, E. A.; Judy, W. A.

doi:10.1002/anie.197604011

Cited by 87 publications

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“…n olefin metathesis reactions, olefinic bonds are rearranged with the help of a transition-metal catalyst 1,2 . In the early days following the discovery of this reaction, ill-defined catalysts 3 were used to carry out this transformation.…”

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Catalytic living ring-opening metathesis polymerization

Nagarkar

Kilbinger

2015

Nature Chem

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In living ring-opening metathesis polymerization (ROMP), a transition-metal-carbene complex polymerizes ring-strained olefins with very good control of the molecular weight of the resulting polymers. Because one molecule of the initiator is required for each polymer chain, however, this type of polymerization is expensive for widespread use. We have now designed a chain-transfer agent (CTA) capable of reducing the required amount of metal complex while still maintaining full control over the living polymerization process. This new method introduces a degenerative transfer process to ROMP. We demonstrate that substituted cyclohexene rings are good CTAs, and thereby preserve the 'living' character of the polymerization using catalytic quantities of the metal complex. The resulting polymers show characteristics of a living polymerization, namely narrow molecular-weight distribution, controlled molecular weights and block copolymer formation. This new technique provides access to well-defined polymers for industrial, biomedical and academic use at a fraction of the current costs and significantly reduced levels of residual ruthenium catalyst. In olefin metathesis reactions, olefinic bonds are rearranged with the help of a transition-metal catalyst 1,2 . In the early days following the discovery of this reaction, ill-defined catalysts 3 were used to carry out this transformation. After Herisson and Chauvin 4 had proposed a reaction mechanism, the olefin metathesis reaction was better understood and soon gained much popularity. Typical catalysts used for olefin metathesis reactions include those based on ruthenium (developed mainly by the Grubbs group 5 ), tungsten and molybdenum (developed mainly by the Schrock group 6 ). Owing to the low oxophilicity of ruthenium compared to those of molybdenum and tungsten, the ruthenium metathesis catalysts (commonly known as Grubbs' catalysts) are more tolerant towards many polar functional groups and residual impurities, as well as to water 7 . Therefore, these catalysts are the catalysts of choice in highly functional organic chemistry transformations as well as for the majority of metathesis polymerizations carried out today. Catalysts G1 (first generation) and G3 (third generation) are the most widely used ruthenium initiators for ring-opening metathesis polymerization (ROMP). In comparison to the G1 initiator, the third-generation catalyst G3 exhibits very fast initiation and propagation rates, and thereby gives polymers with very narrow dispersities and an excellent control over their molecular weights. Owing to its superior stability as well as the favourable polymerization kinetics, the third-generation Grubbs' catalyst G3 was used for this work. ROMP is a polymerization technique that uses the metathesis of cyclic olefins to synthesize linear polymers. Depending on the structure of the monomer, such polymerizations can be controlled perfectly to give polymers with a narrow molecular weight distribution and a controlled average molecular weight. Ring-strained monomers, li...

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Catalytic living ring-opening metathesis polymerization

Nagarkar

Kilbinger

2015

Nature Chem

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Das Tebbe-Reagens [Cp 2 Ti{(m-CH 2 )(m-Cl)Al(CH 3 ) 2 }] (A; Cp = Cyclopentadienyl) gehört zu den schillerndsten metallorganischen Verbindungen.[ [3] und Wolfram-Methylen-Verbindungen (vorgeschlagen als Olefinmetathese-Katalysatoren) [4] röntgenographisch charakterisiert.[3] Obgleich katalytisch aktiv in der Olefinmetathese, [5] wird das Tebbe-Reagens derzeit als effizientes Carbonyl-Methylenierungsreagens eingesetzt. [9, 10] Vorangegangene Untersuchungen unserer Arbeitsgruppe befassten sich mit Seltenerdmetall(III)-TetramethylaluminatKomplexen [L x Ln{Al(CH 3 ) 4 } y ] (y = 1, 2, 3; x + y = 3, L = einzähniger Hilfsligand, Ln = Seltenerdmetall und Sc, Y, La) als Polymerisationskatalysatoren [11,12] und führten zur Isolation von Ln III -Clustern mit Methylen-, [13,14] Methin- [15] und Carbidfunktionalitäten.

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“…[6] Im Rahmen seiner einleitenden Studien erwähnte Tebbe außerdem die Synthese des strukturell verwandten Methylderivats [Cp 2 Ti-{(m-CH 2 )(m-CH 3 )Al(CH 3 ) 2 2 ] (R = Cl, CH 3 ). [9,10] Vorangegangene Untersuchungen unserer Arbeitsgruppe befassten sich mit Seltenerdmetall(III)-TetramethylaluminatKomplexen [L x Ln{Al(CH 3 ) 4 } y ] (y = 1, 2, 3; x + y = 3, L = einzähniger Hilfsligand, Ln = Seltenerdmetall und Sc, Y, La) als Polymerisationskatalysatoren [11,12] und führten zur Isolation von Ln III -Clustern mit Methylen-, [13,14] Methin- [15] und Carbidfunktionalitäten. [16] [14] Die Röntgenstrukturanalyse, die an den farblosen Kristallen (das Rohprodukt wurde aus einer Toluol/Hexan-Mischung kristallisiert) [21] durchgeführt wurde, bestätigte die Molekül-struktur, die auf der Grundlage VT-1 H-NMR-spektroskopischer Studien (VT = variable Temperatur) vorgeschlagen worden war (Abbildung 1).…”

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“…Die Al(CH 3 ) 4 -Einheit zeigt die ungewöhnliche h 1 -Koordination, die bereits in der Festkörperstruktur von [(NNN)La{(m-CH 3 )Al(CH 3 ) 3 }(thf)] mit NNN = 2,6-[(2,6-iPr 2 -C 6 H 3 )NC(CH 3 ) 2 ] 2 C 5 H 3 N beobachtet worden ist. [22] Diese h 1 -Koordination des Al(CH 3 ) 4 -Liganden, in Kombination mit der terminalen CH 3 -Gruppe, illustriert die sterische Absätti-gung des Yttriumzentrums durch den hohen Raumanspruch des Tp tBu,CH 3 -Liganden sowie dessen Fähigkeit zur Stabilisierung von Metallkomplexen mit niedrigen Koordinationszahlen. [23] Die Y-C-Bindungslängen unterscheiden sich deutlich voneinander: [24] bzw.…”

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“…[25] Interessanterweise konnte bei der Anwendung der gleichen Salzmetatheseprozedur auf das größere Seltenerdmetall Lanthan (Radien: La 3+ 1.032 , Y 3+ 0.900 bei Sechsfachkoordination) [26] der neue Komplex [(Tp [27] und K(Tp tBu,CH 3 ) gewonnen werden (Schema 1). Nach der Abtrennung vom Nebenprodukt KAl(CH 3 ) 4 , dem Abdampfen des Lösungsmittels und dem Waschen mit geringen Mengen an kaltem Hexan wurde 3 als weißes Pulver in über 50 % Ausbeute erhalten. [19] Die molekulare Zusammensetzung von 3 wurde VT-NMR-spektroskopisch und röntgenographisch bestätigt.…”

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Eine Seltenerdmetallvariante des Tebbe‐Reagens

et al. 2008

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Synthesis and Catalyst Issues Associated with ADMET Polymerization

Schwendeman

Church

Wagener

2002

Advanced Synthesis & Catalysis

102

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Acyclic diene metathesis (ADMET) is a flexible approach for the production of diverse polymeric materials. The advent of well‐defined catalysts and the simplification of laboratory techniques has made the ADMET reaction useful for many applications, such as polyolefin model studies and the synthesis of organic/inorganic hybrid polymers, telechelics, copolymers, conjugated polymers, liquid crystalline polymers, and amino acid‐based chiral polymers. Many of the polymer architectures that have been produced using ADMET cannot be made by other means.

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Mechanistic Aspects of Olefin Metathesis

Cited by 87 publications

References 32 publications

Catalytic living ring-opening metathesis polymerization

Catalytic living ring-opening metathesis polymerization

Eine Seltenerdmetallvariante des Tebbe‐Reagens

Synthesis and Catalyst Issues Associated with ADMET Polymerization

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