Olefin metathesis

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Olefin metathesis
Reaction typeCarbon-carbon bond forming reaction
Identifiers
Organic Chemistry Portal olefin-metathesis
RSC ontology ID RXNO:0000280
Reaction scheme of the olefin metathesis - changing groups are colored Reaction scheme of the olefin metathesis.svg
Reaction scheme of the olefin metathesis – changing groups are colored

In organic chemistry, olefin metathesis is an organic reaction that entails the redistribution of fragments of alkenes (olefins) by the scission and regeneration of carbon-carbon double bonds. [1] [2] Because of the relative simplicity of olefin metathesis, it often creates fewer undesired by-products and hazardous wastes than alternative organic reactions. For their elucidation of the reaction mechanism and their discovery of a variety of highly active catalysts, Yves Chauvin, Robert H. Grubbs, and Richard R. Schrock were collectively awarded the 2005 Nobel Prize in Chemistry. [3]

Contents

Catalysts

The reaction requires metal catalysts. Most commercially important processes employ heterogeneous catalysts. The heterogeneous catalysts are often prepared by in-situ activation of a metal halide (MClx) using organoaluminium or organotin compounds, e.g. combining MClx–EtAlCl2. A typical catalyst support is alumina. Commercial catalysts are often based on molybdenum and ruthenium. Well-defined organometallic compounds have mainly been investigated for small-scale reactions or in academic research. The homogeneous catalysts are often classified as Schrock catalysts and Grubbs catalysts. Schrock catalysts feature molybdenum(VI)- and tungsten(VI)-based centers supported by alkoxide and imido ligands. [4]

Commercially available schrock catalysts SchrockMetathesisCatalysts.png
Commercially available schrock catalysts

Grubbs catalysts, on the other hand, are ruthenium(II) carbenoid complexes. [5] Many variations of Grubbs catalysts are known. Some have been modified with a chelating isopropoxybenzylidene ligand to form the related Hoveyda–Grubbs catalyst.

Common Grubbs catalysts GrubbsMetathesisCatalysts.png
Common Grubbs catalysts

Applications

Olefin metathesis has several industrial applications. Almost all commercial applications employ heterogeneous catalysts using catalysts developed well before the Nobel-Prize winning work on homogeneous complexes. [6] Representative processes include: [1]

Homogeneous catalyst potential

Molecular catalysts have been explored for the preparation of a variety of potential applications. [9] the manufacturing of high-strength materials, the preparation of cancer-targeting nanoparticles, [10] and the conversion of renewable plant-based feedstocks into hair and skin care products. [11]

Types

Some classes of olefin metathesis include:

Mechanism

Hérisson and Chauvin first proposed the widely accepted mechanism of transition metal alkene metathesis. [12] The direct [2+2] cycloaddition of two alkenes is formally symmetry forbidden and thus has a high activation energy. The Chauvin mechanism involves the [2+2] cycloaddition of an alkene double bond to a transition metal alkylidene to form a metallacyclobutane intermediate. The metallacyclobutane produced can then cycloeliminate to give either the original species or a new alkene and alkylidene. Interaction with the d-orbitals on the metal catalyst lowers the activation energy enough that the reaction can proceed rapidly at modest temperatures.

Olefin metathesis mechanism Metathesis mechanism jypx3.png
Olefin metathesis mechanism

Olefin metathesis involves little change in enthalpy for unstrained alkenes. Product distributions are determined instead by le Chatelier's Principle, i.e. entropy.

Classification of Olefin metathesis reactions Wikipedia-OlefinMetathesisCategories.png
Classification of Olefin metathesis reactions

Cross metathesis and ring-closing metathesis are driven by the entropically favored evolution of ethylene or propylene, which can be removed from the system because they are gases. Because of this CM and RCM reactions often use alpha-olefins. The reverse reaction of CM of two alpha-olefins, ethenolysis, can be favored but requires high pressures of ethylene to increase ethylene concentration in solution. The reverse reaction of RCM, ring-opening metathesis, can likewise be favored by a large excess of an alpha-olefin, often styrene. Ring-opening metathesis usually involves a strained alkene (often a norbornene) and the release of ring strain drives the reaction. Ring-closing metathesis, conversely, usually involves the formation of a five- or six-membered ring, which is enthalpically favorable; although these reactions tend to also evolve ethylene, as previously discussed. RCM has been used to close larger macrocycles, in which case the reaction may be kinetically controlled by running the reaction at high dilutions. [13] The same substrates that undergo RCM can undergo acyclic diene metathesis, with ADMET favored at high concentrations. The Thorpe–Ingold effect may also be exploited to improve both reaction rates and product selectivity.

Cross-metathesis is synthetically equivalent to (and has replaced) a procedure of ozonolysis of an alkene to two ketone fragments followed by the reaction of one of them with a Wittig reagent.

Historical overview

"Olefin metathesis is a child of industry and, as with many catalytic processes, it was discovered by accident." [1] As part of ongoing work in what would later become known as Ziegler–Natta catalysis Karl Ziegler discovered the conversion of ethylene into 1-butene instead of a saturated long-chain hydrocarbon (see nickel effect). [14]

In 1960 a Du Pont research group polymerized norbornene to polynorbornene using lithium aluminum tetraheptyl and titanium tetrachloride [15] (a patent by this company on this topic dates back to 1955 [16] ),

MetathesisDupont.svg

a reaction then classified as a so-called coordination polymerization. According to the then proposed reaction mechanism a RTiX titanium intermediate first coordinates to the double bond in a pi complex. The second step then is a concerted SNi reaction breaking a CC bond and forming a new alkylidene-titanium bond; the process then repeats itself with a second monomer:

MetathesisDuPontMechanism.svg

Only much later the polynorbornene was going to be produced through ring opening metathesis polymerisation. The DuPont work was led by Herbert S. Eleuterio. Giulio Natta in 1964 also observed the formation of an unsaturated polymer when polymerizing cyclopentene with tungsten and molybdenum halides. [17]

In a third development leading up to olefin metathesis, researchers at Phillips Petroleum Company in 1964 [18] described olefin disproportionation with catalysts molybdenum hexacarbonyl, tungsten hexacarbonyl, and molybdenum oxide supported on alumina for example converting propylene to an equal mixture of ethylene and 2-butene for which they proposed a reaction mechanism involving a cyclobutane (they called it a quasicyclobutane) – metal complex:

MetathesisCyclobutaneMech.svg

This particular mechanism is symmetry forbidden based on the Woodward–Hoffmann rules first formulated two years earlier. Cyclobutanes have also never been identified in metathesis reactions, which is another reason why it was quickly abandoned.

Then in 1967 researchers led by Nissim Calderon at the Goodyear Tire and Rubber Company described a novel catalyst system for the metathesis of 2-pentene based on tungsten hexachloride, ethanol, and the organoaluminum compound EtAlMe2. The researchers proposed a name for this reaction type: olefin metathesis. [19] Formerly the reaction had been called "olefin disproportionation."

MetathesisCalderon1967.svg

In this reaction 2-pentene forms a rapid (a matter of seconds) chemical equilibrium with 2-butene and 3-hexene. No double bond migrations are observed; the reaction can be started with the butene and hexene as well and the reaction can be stopped by addition of methanol.

The Goodyear group demonstrated that the reaction of regular 2-butene with its all-deuterated isotopologue yielded C4H4D4 with deuterium evenly distributed. [20] In this way they were able to differentiate between a transalkylidenation mechanism and a transalkylation mechanism (ruled out):

MetathesisCalderon1976Mechanism.svg

In 1971 Chauvin proposed a four-membered metallacycle intermediate to explain the statistical distribution of products found in certain metathesis reactions. [21] This mechanism is today considered the actual mechanism taking place in olefin metathesis.

MetathesisMetallacyclemechanism.svg

Chauvin's experimental evidence was based on the reaction of cyclopentene and 2-pentene with the homogeneous catalyst tungsten(VI) oxytetrachloride and tetrabutyltin:

MetathesisChauvin1971.svg

The three principal products C9, C10 and C11 are found in a 1:2:1 regardless of conversion. The same ratio is found with the higher oligomers. Chauvin also explained how the carbene forms in the first place: by alpha-hydride elimination from a carbon metal single bond. For example, propylene (C3) forms in a reaction of 2-butene (C4) with tungsten hexachloride and tetramethyltin (C1).

In the same year Pettit who synthesised cyclobutadiene a few years earlier independently came up with a competing mechanism. [22] It consisted of a tetramethylene intermediate with sp3 hybridized carbon atoms linked to a central metal atom with multiple three-center two-electron bonds.

MetathesisPettitmechanism.svg

Experimental support offered by Pettit for this mechanism was based on an observed reaction inhibition by carbon monoxide in certain metathesis reactions of 4-nonene with a tungsten metal carbonyl [23]

Robert H. Grubbs got involved in metathesis in 1972 and also proposed a metallacycle intermediate but one with four carbon atoms in the ring. [24] The group he worked in reacted 1,4-dilithiobutane with tungsten hexachloride in an attempt to directly produce a cyclomethylenemetallacycle producing an intermediate, which yielded products identical with those produced by the intermediate in the olefin metathesis reaction. This mechanism is pairwise:

MetathesisGrubbs1972tetramethylenemetallocycle.svg

In 1973 Grubbs found further evidence for this mechanism by isolating one such metallacycle not with tungsten but with platinum by reaction of the dilithiobutane with cis-bis(triphenylphosphine)dichloroplatinum(II) [25]

In 1975 Katz also arrived at a metallacyclobutane intermediate consistent with the one proposed by Chauvin [26] He reacted a mixture of cyclooctene, 2-butene and 4-octene with a molybdenum catalyst and observed that the unsymmetrical C14 hydrocarbon reaction product is present right from the start at low conversion.

MetathesisKatz.svg

In any of the pairwise mechanisms with olefin pairing as rate-determining step this compound, a secondary reaction product of C12 with C6, would form well after formation of the two primary reaction products C12 and C16.

In 1974 Casey was the first to implement carbenes into the metathesis reaction mechanism: [27]

MetathesisCasey1974.svg

Grubbs in 1976 provided evidence against his own updated pairwise mechanism:

MetathesisPairWiseMechanism.svg

with a 5-membered cycle in another round of isotope labeling studies in favor of the 4-membered cycle Chauvin mechanism: [28] [29]

Metathesisgrubbs1976.svg

In this reaction the ethylene product distribution at low conversion was found to be consistent with the carbene mechanism. On the other hand, Grubbs did not rule out the possibility of a tetramethylene intermediate.

The first practical metathesis system was introduced in 1978 by Tebbe based on the (what later became known as the) Tebbe reagent. [30] In a model reaction isotopically labeled carbon atoms in isobutene and methylenecyclohexane switched places:

MetathesisTebbe.svg

The Grubbs group then isolated the proposed metallacyclobutane intermediate in 1980 also with this reagent together with 3-methyl-1-butene: [31]

MetathesisGrubbs1980.svg

They isolated a similar compound in the total synthesis of capnellene in 1986: [32]

MetathesisGrubbs1986.svg

In that same year the Grubbs group proved that metathesis polymerization of norbornene by Tebbe's reagent is a living polymerization system [33] and a year later Grubbs and Schrock co-published an article describing living polymerization with a tungsten carbene complex [34] While Schrock focussed his research on tungsten and molybdenum catalysts for olefin metathesis, Grubbs started the development of catalysts based on ruthenium, which proved to be less sensitive to oxygen and water and therefore more functional group tolerant.

Grubbs catalysts

In the 1960s and 1970s various groups reported the ring-opening polymerization of norbornene catalyzed by hydrated trichlorides of ruthenium and other late transition metals in polar, protic solvents. [35] [36] [37] This prompted Robert H. Grubbs and coworkers to search for well-defined, functional group tolerant catalysts based on ruthenium. The Grubbs group successfully polymerized the 7-oxo norbornene derivative using ruthenium trichloride, osmium trichloride as well as tungsten alkylidenes. [38] They identified a Ru(II) carbene as an effective metal center and in 1992 published the first well-defined, ruthenium-based olefin metathesis catalyst, (PPh3)2Cl2Ru=CHCH=CPh2: [39]

MetathesisGrubbs1992.svg

The corresponding tricyclohexylphosphine complex (PCy3)2Cl2Ru=CHCH=CPh2 was also shown to be active. [40] This work culminated in the now commercially available 1st generation Grubbs catalyst. [41] [42]

Schrock catalysts

Schrock entered the olefin metathesis field in 1979 as an extension of work on tantalum alkylidenes. [43] The initial result was disappointing as reaction of CpTa(=CH−t−Bu)Cl2 with ethylene yielded only a metallacyclopentane, not metathesis products: [44]

MetathesisSchrock1979.svg

But by tweaking this structure to a PR3Ta(CHt−bu)(Ot−bu)2Cl (replacing chloride by t-butoxide and a cyclopentadienyl by an organophosphine, metathesis was established with cis-2-pentene. [45] In another development, certain tungsten oxo complexes of the type W(O)(CHt−Bu)(Cl)2(PEt)3 were also found to be effective. [46]

Schrock alkylidenes for olefin metathesis of the type Mo(NAr)(CHC(CH3)2R){OC(CH3)(CF3)2}2 were commercialized starting in 1990. [47] [48]

SchrockCatalyst.svg

The first asymmetric catalyst followed in 1993 [49]

MetathesisROMPSchrock1993.svg

With a Schrock catalyst modified with a BINOL ligand in a norbornadiene ROMP leading to highly stereoregular cis, isotactic polymer.

See also

Related Research Articles

In polymer chemistry, living polymerization is a form of chain growth polymerization where the ability of a growing polymer chain to terminate has been removed. This can be accomplished in a variety of ways. Chain termination and chain transfer reactions are absent and the rate of chain initiation is also much larger than the rate of chain propagation. The result is that the polymer chains grow at a more constant rate than seen in traditional chain polymerization and their lengths remain very similar. Living polymerization is a popular method for synthesizing block copolymers since the polymer can be synthesized in stages, each stage containing a different monomer. Additional advantages are predetermined molar mass and control over end-groups.

Grubbs catalysts are a series of transition metal carbene complexes used as catalysts for olefin metathesis. They are named after Robert H. Grubbs, the chemist who supervised their synthesis. Several generations of the catalyst have also been developed. Grubbs catalysts tolerate many functional groups in the alkene substrates, are air-tolerant, and are compatible with a wide range of solvents. For these reasons, Grubbs catalysts have become popular in synthetic organic chemistry. Grubbs, together with Richard R. Schrock and Yves Chauvin, won the Nobel Prize in Chemistry in recognition of their contributions to the development of olefin metathesis.

A transition metal carbene complex is an organometallic compound featuring a divalent carbon ligand, itself also called a carbene. Carbene complexes have been synthesized from most transition metals and f-block metals, using many different synthetic routes such as nucleophilic addition and alpha-hydrogen abstraction. The term carbene ligand is a formalism since many are not directly derived from carbenes and most are much less reactive than lone carbenes. Described often as =CR2, carbene ligands are intermediate between alkyls (−CR3) and carbynes (≡CR). Many different carbene-based reagents such as Tebbe's reagent are used in synthesis. They also feature in catalytic reactions, especially alkene metathesis, and are of value in both industrial heterogeneous and in homogeneous catalysis for laboratory- and industrial-scale preparation of fine chemicals.

<span class="mw-page-title-main">Alkyne metathesis</span>

Alkyne metathesis is an organic reaction that entails the redistribution of alkyne chemical bonds. The reaction requires metal catalysts. Mechanistic studies show that the conversion proceeds via the intermediacy of metal alkylidyne complexes. The reaction is related to olefin metathesis.

<span class="mw-page-title-main">Robert H. Grubbs</span> American chemist and Nobel Laureate (1942–2021)

Robert Howard GrubbsForMemRS was an American chemist and the Victor and Elizabeth Atkins Professor of Chemistry at the California Institute of Technology in Pasadena, California. He was a co-recipient of the 2005 Nobel Prize in Chemistry for his work on olefin metathesis.

<span class="mw-page-title-main">Richard R. Schrock</span> American chemist and Nobel laureate (born 1945)

Richard Royce Schrock is an American chemist and Nobel laureate recognized for his contributions to the olefin metathesis reaction used in organic chemistry.

<span class="mw-page-title-main">Yves Chauvin</span> French chemist and Nobel Prize laureate

Yves Chauvin was a French chemist and Nobel Prize laureate. He was honorary research director at the Institut français du pétrole and a member of the French Academy of Science. He was known for his work for deciphering the process of olefin metathesis for which he was awarded the 2005 Nobel Prize in Chemistry along with Robert H. Grubbs and Richard R. Schrock.

Ring-closing metathesis (RCM) is a widely used variation of olefin metathesis in organic chemistry for the synthesis of various unsaturated rings via the intramolecular metathesis of two terminal alkenes, which forms the cycloalkene as the E- or Z- isomers and volatile ethylene.

Barrelene is a bicyclic organic compound with chemical formula C8H8 and systematic name bicyclo[2.2.2]octa-2,5,7-triene. First synthesized and described by Howard Zimmerman in 1960, the name derives from the resemblance to a barrel, with the staves being three ethylene units attached to two methine groups. It is the formal Diels–Alder adduct of benzene and acetylene. Due to its unusual molecular geometry, the compound is of considerable interest to theoretical chemists.

In polymer chemistry, ring-opening metathesis polymerization (ROMP) is a type of chain-growth polymerization involving olefin metathesis. The driving force of the reaction is relief of ring strain in cyclic olefins. A variety of heterogeneous and homogeneous catalysts have been developed. Most large-scale commercial processes rely on the former while some fine chemical syntheses rely on the homogeneous catalysts. Catalysts are based on transition metals such as tungsten, molybdenum, rhenium, rubidium, and titanium.

<span class="mw-page-title-main">Enyne metathesis</span> Organic reaction

An enyne metathesis is an organic reaction taking place between an alkyne and an alkene with a metal carbene catalyst forming a butadiene. This reaction is a variation of olefin metathesis.

<span class="mw-page-title-main">Metallacycle</span>

In organometallic chemistry, a metallacycle is a derivative of a carbocyclic compound wherein a metal has replaced at least one carbon center; this is to some extent similar to heterocycles. Metallacycles appear frequently as reactive intermediates in catalysis, e.g. olefin metathesis and alkyne trimerization. In organic synthesis, directed ortho metalation is widely used for the functionalization of arene rings via C-H activation. One main effect that metallic atom substitution on a cyclic carbon compound is distorting the geometry due to the large size of typical metals.

<span class="mw-page-title-main">Organomolybdenum chemistry</span> Chemistry of compounds with Mo-C bonds

Organomolybdenum chemistry is the chemistry of chemical compounds with Mo-C bonds. The heavier group 6 elements molybdenum and tungsten form organometallic compounds similar to those in organochromium chemistry but higher oxidation states tend to be more common.

In organic chemistry, ethenolysis is a chemical process in which internal olefins are degraded using ethylene as the reagent. The reaction is an example of cross metathesis. The utility of the reaction is driven by the low cost of ethylene as a reagent and its selectivity. It produces compounds with terminal alkene functional groups (α-olefins), which are more amenable to other reactions such as polymerization and hydroformylation.

<span class="mw-page-title-main">Herbert S. Eleuterio</span> American industrial chemist (1927–2022)

Herbert S. Eleuterio was an American industrial chemist noted for technical contributions to catalysis, polymerization, industrial research management, and science education. In particular, he discovered the olefin metathesis reaction and several novel fluoropolymers. Additionally, he explored techniques for research leadership, especially methods for fostering collaboration, globalization, and scientific creativity.

Functionalized polyolefins are olefin polymers with polar and nonpolar functionalities attached onto the polymer backbone. There has been an increased interest in functionalizing polyolefins due to their increased usage in everyday life. Polyolefins are virtually ubiquitous in everyday life, from consumer food packaging to biomedical applications; therefore, efforts must be made to study catalytic pathways towards the attachment of various functional groups onto polyolefins in order to affect the material's physical properties.

<span class="mw-page-title-main">Zhan catalyst</span> Chemical compound

A Zhan catalyst is a type of ruthenium-based organometallic complex used in olefin metathesis. This class of chemicals is named after the chemist who first synthesized them, Zheng-Yun J. Zhan.

<span class="mw-page-title-main">Metallacyclopentanes</span>

In organometallic chemistry, metallacyclopentanes are compounds with the formula LnM(CH2)4 (Ln = ligands, and M = metal). They are a type of metallacycle. Metallacyclopentanes are intermediates in some metal-catalysed reactions in homogeneous catalysis.

Olefin Conversion Technology, also called the Phillips Triolefin Process, is the industrial process that interconverts propylene with ethylene and 2-butenes. The process is also called the ethylene to propylene (ETP) process. In ETP, ethylene is dimerized to 1-butene, which is isomerized to 2-butenes. The 2-butenes are then subjected to metathesis with ethylene.

Carbonyl olefin metathesis is a type of metathesis reaction that entails, formally, the redistribution of fragments of an alkene and a carbonyl by the scission and regeneration of carbon-carbon and carbon-oxygen double bonds respectively. It is a powerful method in organic synthesis using simple carbonyls and olefins and converting them into less accessible products with higher structural complexity.

References

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  25. ↑ Biefeld, Carol G.; Eick, Harry A.; Grubbs, Robert H. (1973). "Crystal structure of bis(triphenylphosphine)tetramethyleneplatinum(II)". Inorganic Chemistry. 12 (9): 2166–2170. doi:10.1021/ic50127a046.
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  29. ↑ Grubbs, Robert H.; Carr, D. D.; Hoppin, C.; Burk, P. L. (1976). "Consideration of the mechanism of the metal catalyzed olefin metathesis reaction". Journal of the American Chemical Society. 98 (12): 3478–3483. doi:10.1021/ja00428a015.
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  31. ↑ Howard, T. R.; Lee, J. B.; Grubbs, R. H. (1980). "Titanium metallacarbene-metallacyclobutane reactions: stepwise metathesis". Journal of the American Chemical Society. 102 (22): 6876–6878. doi:10.1021/ja00542a050.
  32. ↑ Stille, John R.; Grubbs, Robert H. (1986). "Synthesis of (.+-.)-.DELTA.9,12-capnellene using titanium reagents". Journal of the American Chemical Society. 108 (4): 855–856. doi:10.1021/ja00264a058.
  33. ↑ Gilliom, Laura R.; Grubbs, Robert H. (1986). "Titanacyclobutanes derived from strained, cyclic olefins: the living polymerization of norbornene". Journal of the American Chemical Society. 108 (4): 733–742. doi:10.1021/ja00264a027.
  34. ↑ Schrock, R. R.; Feldman, J.; Cannizzo, L. F.; Grubbs, R. H. (1987). "Ring-opening polymerization of norbornene by a living tungsten alkylidene complex". Macromolecules. 20 (5): 1169–1172. Bibcode:1987MaMol..20.1169S. doi:10.1021/ma00171a053.
  35. ↑ Michelotti, Francis W.; Keaveney, William P. (1965). "Coordinated Polymerization of the Bicyclo-(2.2.1)-heptene-2 Ring System (Norbornene) in Polar Media". Journal of Polymer Science Part A: General Papers. 3 (3): 895–905. doi:10.1002/pol.1965.100030305.
  36. ↑ Rinehart, Robert E.; Smith, Homer P. (1965). "The Emulsion Polymerization of the Norbornene Ring System Catalyzed by Noble Metal Compounds". Journal of Polymer Science Part B: Polymer Letters. 3 (12): 1049–1052. Bibcode:1965JPoSL...3.1049R. doi:10.1002/pol.1965.110031215.
  37. ↑ Porri, Lido; Rossi, Renzo; Diversi, Pietro; Lucherini, Antonio (1974). "Ring-Opening Polymerization of Cycloolefins with Catalysts Derived from Ruthenium and Iridium". Die Makromolekulare Chemie. 175 (11): 3097–3115. doi:10.1002/macp.1974.021751106.
  38. ↑ Novak, Bruce M.; Grubbs, Robert H. (1988). "The ring opening metathesis polymerization of 7-oxabicyclo[2.2.1]hept-5-ene derivatives: a new acyclic polymeric ionophore". Journal of the American Chemical Society. 110 (3): 960–961. doi:10.1021/ja00211a043.
  39. ↑ Nguyen, Sonbinh T.; Johnson, Lynda K.; Grubbs, Robert H.; Ziller, Joseph W. (1992). "Ring-opening metathesis polymerization (ROMP) of norbornene by a Group VIII carbene complex in protic media" (PDF). Journal of the American Chemical Society. 114 (10): 3974–3975. doi:10.1021/ja00036a053.
  40. ↑ Nguyen, Sonbinh T.; Grubbs, Robert H.; Ziller, Joseph W. (1993). "Syntheses and activities of new single-component, ruthenium-based olefin metathesis catalysts". Journal of the American Chemical Society. 115 (21): 9858–9859. doi:10.1021/ja00074a086.
  41. ↑ Schwab, Peter; France, Marcia B.; Ziller, Joseph W.; Grubbs, Robert H. (1995). "A Series of Well-Defined Metathesis Catalysts–Synthesis of [RuCl2(CHR′)(PR3)2] and Its Reactions". Angewandte Chemie International Edition in English. 34 (18): 2039–2041. doi:10.1002/anie.199520391.
  42. ↑ Schwab, Peter; Grubbs, Robert H.; Ziller, Joseph W. (1996). "Synthesis and Applications of RuCl2(=CHR')(PR3)2: The Influence of the Alkylidene Moiety on Metathesis Activity". Journal of the American Chemical Society. 118: 100–110. doi:10.1021/ja952676d.
  43. ↑ Schrock, R. R.; Meakin, P. (1974). "Pentamethyl complexes of niobium and tantalum". Journal of the American Chemical Society. 96 (16): 5288–5290. doi:10.1021/ja00823a064.
  44. ↑ McLain, S. J.; Wood, C. D.; Schrock, R. R. (1979). "Preparation and characterization of tantalum(III) olefin complexes and tantalum(V) metallacyclopentane complexes made from acyclic α olefins". Journal of the American Chemical Society. 101 (16): 4558–4570. doi:10.1021/ja00510a022.
  45. ↑ Schrock, R; Rocklage, Scott; Wengrovius, Jeffrey; Rupprecht, Gregory; Fellmann, Jere (1980). "Preparation and characterization of active niobium, tantalum and tungsten metathesis catalysts". Journal of Molecular Catalysis. 8 (1–3): 73–83. doi:10.1016/0304-5102(80)87006-4.
  46. ↑ Wengrovius, Jeffrey H.; Schrock, Richard R.; Churchill, Melvyn Rowen; Missert, Joseph R.; Youngs, Wiley J. (1980). "Multiple metal-carbon bonds. 16. Tungsten-oxo alkylidene complexes as olefins metathesis catalysts and the crystal structure of W(O)(CHCMe3(PEt3)Cl2". Journal of the American Chemical Society. 102 (13): 4515–4CF6. doi:10.1021/ja00533a035.
  47. ↑ Schrock, Richard R.; Murdzek, John S.; Bazan, Gui C.; Robbins, Jennifer; Dimare, Marcello; O'Regan, Marie (1990). "Synthesis of molybdenum imido alkylidene complexes and some reactions involving acyclic olefins". Journal of the American Chemical Society. 112 (10): 3875–3886. doi:10.1021/ja00166a023.
  48. ↑ Bazan, Guillermo C.; Oskam, John H.; Cho, Hyun Nam; Park, Lee Y.; Schrock, Richard R. (1991). "Living Ring-Opening Metathesis Polymerization of 2,3-Difunctionalized 7-Oxanorbornenes and 7-Oxanorbornadienes by Mo(CHCMe2R)(N-2,6-C6H3-i-Pr2)(O-t-Bu)2 and Mo(CHCMe2R)(N-2,6-C6H3-i-Pr2)(OCMe2CF3)2". 113 (18): 6899–6907. doi:10.1021/ja00018a028.{{cite journal}}: Cite journal requires |journal= (help)
  49. ↑ McConville, David H.; Wolf, Jennifer R.; Schrock, Richard R. (1993). "Synthesis of chiral molybdenum ROMP initiators and all-cis highly tactic poly(2,3-(R)2norbornadiene) (R = CF3 or CO2Me)". Journal of the American Chemical Society. 115 (10): 4413–4414. doi:10.1021/ja00063a090.

Further reading

  1. "Olefin Metathesis: Big-Deal Reaction". 80 (51). 2002: 29–33. doi:10.1021/cen-v080n016.p029.{{cite journal}}: Cite journal requires |journal= (help)
  2. "Olefin Metathesis: The Early Days". 80 (51). 2002: 34–38. doi:10.1021/cen-v080n029.p034.{{cite journal}}: Cite journal requires |journal= (help)
  3. Schrock, R. R. (1990). "Living ring-opening metathesis polymerization catalyzed by well-characterized transition-metal alkylidene complexes". Accounts of Chemical Research. 23 (5): 158–165. doi:10.1021/ar00173a007.
  4. Schrock, R. R.; Hoveyda, A. H. (2003). "Molybdenum and Tungsten Imido Alkylidene Complexes as Efficient Olefin-Metathesis Catalysts". Angewandte Chemie International Edition. 42 (38): 4592–4633. doi:10.1002/anie.200300576. PMID   14533149. S2CID   35370749.
  5. Samojłowicz, C.; Grela, K. (2009). "Ruthenium-Based Olefin Metathesis Catalysts Bearing N-Heterocyclic Carbene Ligands". Chemical Reviews. 109 (8): 3708–3742. doi:10.1021/cr800524f. PMID   19534492.
  6. Vougioukalakis, G. C.; Grubbs, R. H. (2010). "Ruthenium-Based Heterocyclic Carbene-Coordinated Olefin Metathesis Catalysts". Chemical Reviews. 110 (3): 1746–1787. doi:10.1021/cr9002424. PMID   20000700. S2CID   4589661.
  7. Trnka, T. M.; Grubbs, R. H. (2001). "The Development of L2X2Ru=CHR Olefin Metathesis Catalysts: An Organometallic Success Story". Accounts of Chemical Research. 34 (1): 18–29. doi:10.1021/ar000114f. PMID   11170353. S2CID   22145255.
  8. Grubbs, R. H.; Chang, S. (1998). "Recent advances in olefin metathesis and its application in organic synthesis". Tetrahedron. 54 (18): 4413–4450. doi:10.1016/S0040-4020(97)10427-6.
  9. Grubbs, R. H. (2004). "Olefin metathesis". Tetrahedron. 60 (34): 7117–7140. doi:10.1016/j.tet.2004.05.124.
  10. Grela, K. (2010). Grela, K. (ed.). "Progress in metathesis chemistry (Editorial for Open Access Thematic Series)". Beilstein Journal of Organic Chemistry. 6: 1089–1090. doi:10.3762/bjoc.6.124. PMC   3002079 . PMID   21160917.
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