Disproportionation of alkynes

Pennella, Filippo; Banks, R. L.; Bailey, G. C.

doi:10.1039/c19680001548

Cited by 60 publications

(81 citation statements)

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“…Although several mechanisms were proposed, the correct one appeared first in a publication by Hérrison and Chauvin in 1971, 5 namely the reversible reaction between a metal complex that contains a metal-carbon double bond (M=CHR) and a C=C bond to yield an intermediate that contains a metallacyclobutane (MC 3 ) ring. A related reaction that involves alkynes was discovered to be catalyzed by a heterogeneous catalyst in 1968 6 and a homogeneous catalyst in 1972. 7 This "alkyne disproportionation" reaction was proposed to consist of a reversible reaction between a M≡CR bond (R≠H) and a C≡C bond to give all possible alkynes via a metallacyclobutadiene intermediate.…”

Section: Introductionmentioning

confidence: 99%

Metathesis by Molybdenum and Tungsten Catalysts

Schrock¹

2015

Chimia

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IntroductionIn the early 1970's organometallic, organic, and polymer chemists were attracted to a new type of catalytic reaction called Olefin Disproportionation by Banks and Bailey, who published results in the open literature in 1964; 1 the reaction also was reported by Natta in 1964 2 and had appeared in patents filed at duPont 3 and Standard Oil 4 several years earlier. The basic process, which was shown to be catalyzed by various molybdenum or tungsten, and later rhenium, compounds of unknown type, resulted in an "exchange" of alkylidene (usually CHR, where R = H or alkyl) units in alkenes with one another, e.g., propylene could be equilibrated with ethylene and cis and trans-2-butenes (equation 1) or norbornene could be polymerized through a "ringopening" of its double bonds (equation 2). Although several mechanisms were proposed, the correct one appeared first in a publication by Hérrison and Chauvin in 1971, 5 namely the reversible reaction between a metal complex that contains a metal-carbon double bond (M=CHR) and a C=C bond to yield an intermediate that contains a metallacyclobutane (MC 3 ) ring. A related reaction that involves alkynes was discovered to be catalyzed by a heterogeneous catalyst in 1968 6 and a homogeneous catalyst in 1972. 7 This "alkyne disproportionation" reaction was proposed to consist of a reversible reaction between a M≡CR bond (R≠H) and a C≡C bond to give all possible alkynes via a metallacyclobutadiene intermediate. 8 Neither process resulted in any positional isomerization of the C=C or C≡C bonds. Although Fischer-type "low oxidation state" carbene 9 complexes were known at the time, and the synthesis of carbyne complexes soon followed, 10 they did not promote what came to be known as alkene metathesis 11 and alkyne metathesis, respectively, in the rapid manner often observed for what are now known as "classical" alkene and alkyne metathesis catalysts. However, experiments first published in 1976 showed that polymerization of cyclic olefins, metathesis of linear olefins, enyne metathesis, and polymerization of acetylenes could be initiated by certain Fischer-type carbene complexes, although new alkylidenes of the same type as the initiator were not observed. 12 Classical metathesis catalysts often are formed from metal oxides on silica or alumina 13 or in solution from a variety of metal complexes. An alkylating agent is often required, but simply exposing the supported metal oxide to alkenes or alkynes at high temperatures will generate the catalyst through some unknown mechanism of mechanisms.

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Section: Introductionmentioning

confidence: 99%

Metathesis by Molybdenum and Tungsten Catalysts

Schrock¹

2015

Chimia

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“…Following this result, other trisalkoxy or phenoxy tungstacarbynes were synthesized: none of them were as reactive as the former t-butoxy one, but remarkably, the sterically hindered [2,6-(iPr) 2 [29] Other metallacyclobutadienes bearing fluorinated alkoxy ligands have also been prepared and behave similarly [30].…”

Section: Well Defined Carbyne Based Catalystsmentioning

confidence: 99%

“…Following their discovery related to the Triolefin Process using molybdenum carbonyl on alumina (eqn 1) [1], Banks and Bailey reported with Penella the first heterogeneous catalyst for alkyne metathesis in 1968, applying tungsten oxide on silica at 350°C for pent-2-yne metathesis with a 55% selectivity (eqn 2) [2]. + Mo(CO) 6 The same catalyst applied to a terminal alkyne such as pent-1-yne has been found to produce exclusively aromatic trimers [3], whereas a CoO-MoO 3 -SiO 2 catalyst has been claimed to be selective in metathesis of this substrate [4].…”

Section: Heterogeneous Catalystsmentioning

confidence: 99%

“…Rhenium(VII) monoimido alkylidyne R'C Re(NAr)(OR) 2 complexes have also been shown to be active alkyne metathesis catalysts, but only with disubstituted acetylenes containing bulky groups, and with complexes that contains OC(CF 3 ) 2 Me withdrawing ligands [32].…”

Section: Well Defined Carbyne Based Catalystsmentioning

confidence: 99%

“…4 cyclobutadiene metal complex mechanism [2] Cyclobutadiene molybdenum complexes have been isolated from a reaction between paratolylphenylacetylene and molybdenum hexacarbonyl, but were considered to be too stable to suggest that this type of intermediate would be those involved in catalysis, due to too high reaction time and temperature for their decomposition [6]. …”

Section: Mechanism Using Molybdenum/aroh Catalystsmentioning

confidence: 99%

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Alkyne Metathesis Catalysts: Scope and Future

Mortreux¹,

Coutelier²

2007

ChemInform

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This paper presents the evolution of alkyne metathesis since the early discoveries, essentially from the catalyst point of view. It is shown that although well defined carbynes may be useful for this reaction, further work has been made, aimed at the synthesis of new catalysts or catalytic systems, based on molybdenum precursors , associated or not with phenolic cocatalysts. The major objectives have been to obtain more functional groups tolerants catalysts, for their application in organic synthesis, including RCM for further stereoselective hydrogenation of the triple bond in the cycle, as well as for polymerization of aromatic diynes. Some insights into the possible mechanisms are given, and data relevant to the metathesis of terminal alkynes, a still challenging reaction where polymerization is occurring via the formation of deprotonated metallacyclobutadiene, are also presented and discussed.2

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Ring‐Closing Alkyne Metathesis in Natural Product Synthesis

Davies

2010

Metathesis in Natural Product Synthesis

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Disproportionation of alkynes

Cited by 60 publications

References 0 publications

Metathesis by Molybdenum and Tungsten Catalysts

Metathesis by Molybdenum and Tungsten Catalysts

Alkyne Metathesis Catalysts: Scope and Future

Ring‐Closing Alkyne Metathesis in Natural Product Synthesis

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