View source for Olefin metathesis

{{short description|Organic reaction involving the breakup and reassembly of alkene double bonds}}
{{Use dmy dates|date=January 2024}}

{{Reactionbox
| Name = Olefin metathesis
| Type = Carbon-carbon bond forming reaction
| Section3 = {{Reactionbox Identifiers
   | OrganicChemistryNamed = olefin-metathesis
   | RSC_ontology_id = 0000280
 }}
}}
[[Image:Reaction scheme of the olefin metathesis.svg|thumb|upright=1.4|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 [[alkene]]s (olefins) by the [[Bond cleavage|scission]] and regeneration of carbon-carbon [[double bonds]].<ref name=KO/><ref>{{cite journal | author = Astruc D. | title = The metathesis reactions: from a historical perspective to recent developments | journal = New Journal of Chemistry| volume = 29 | issue = 1 | year = 2005 | pages = 42–56 | doi = 10.1039/b412198h | s2cid = 98046245 }}</ref> Because of the relative simplicity of olefin metathesis, it often creates fewer undesired [[by-product]]s and [[hazardous waste]]s than alternative organic reactions. For their elucidation of the reaction mechanism and their discovery of a variety of highly active [[Catalysis|catalysts]], [[Yves Chauvin]], [[Robert H. Grubbs]], and [[Richard R. Schrock]] were collectively awarded the 2005 [[Nobel Prize in Chemistry]].<ref>{{cite press release | title = The Nobel Prize in Chemistry 2005 | publisher = [[Nobelprize.org]] | date = 5 October 2005 | url = http://nobelprize.org/nobel_prizes/chemistry/laureates/2005/press.html}}</ref>

==Catalysts==
The reaction requires [[catalysis|metal catalysts]].  Most commercially important processes employ [[heterogeneous catalysis|heterogeneous catalysts]].  The heterogeneous catalysts are often prepared by in-situ activation of a metal halide (MCl<sub>x</sub>) using [[organoaluminium]] or [[organotin compound]]s, e.g. combining MCl<sub>x</sub>–EtAlCl<sub>2</sub>. 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 catalyst]]s. Schrock catalysts feature molybdenum(VI)- and tungsten(VI)-based centers supported by [[alkoxide]] and [[Transition metal imido complex|imido]] ligands.<ref>{{cite journal | author = R.R. Schrock | title = High-oxidation-state molybdenum and tungsten alkylidene complexes | year = 1986 | journal = Accounts of Chemical Research| doi = 10.1021/ar00131a003 | volume = 19 | issue = 11 | pages = 342–348}}</ref>

[[File:SchrockMetathesisCatalysts.png|500px|center|Commercially available schrock catalysts]]

Grubbs catalysts, on the other hand, are ruthenium(II) carbenoid complexes.<ref>{{cite journal | author1 = Ileana Dragutan | author2 = Valerian Dragutan | author3 = Petru Filip | title = Recent developments in design and synthesis of well-defined ruthenium metathesis catalysts – a highly successful opening for intricate organic synthesis | year = 2005 | url = http://arkat-usa.org/ark/journal/2005/I10_Balaban/1334/1334.asp | pages = 105–129 | journal = Arkivoc | access-date = 6 October 2005 | archive-url = https://web.archive.org/web/20060512173852/http://arkat-usa.org/ark/journal/2005/I10_Balaban/1334/1334.asp | archive-date = 12 May 2006  }}</ref> Many variations of Grubbs catalysts are known.  Some have been modified with a [[Chelation|chelating]] isopropoxybenzylidene [[ligand]] to form the related [[Grubbs' catalyst#Hoveyda–Grubbs catalysts|Hoveyda–Grubbs catalyst]].

[[File:GrubbsMetathesisCatalysts.png|500px|center|Common Grubbs catalysts]]

==Applications==
Olefin metathesis has several industrial applications. Almost all commercial applications employ [[heterogeneous catalyst]]s using catalysts developed well before the Nobel-Prize winning work on homogeneous complexes.<ref name="MG">{{cite journal|last1=Ghashghaee|first1=Mohammad|title=Heterogeneous catalysts for gas-phase conversion of ethylene to higher olefins|journal=Reviews in Chemical Engineering|volume=34|issue=5|pages=595–655|doi=10.1515/revce-2017-0003|year=2018|s2cid=103664623 }}</ref> Representative processes include:<ref name=KO/>
*The Phillips Triolefin and the [[Olefin conversion technology]].  This process interconverts propylene with ethylene and 2-butenes. Rhenium and molybdenum catalysts are used. Nowadays, only the reverse reaction, i.e., the conversion of ethylene and 2-butene to propylene is industrially practiced, however.<ref name="MG" />
*[[Shell higher olefin process]] (SHOP) produces ([[alpha-olefins]]) for conversion to detergents.  The process recycles certain olefin fractions using metathesis.<ref name=Weissermel>{{cite book|title=Industrial Organic Chemistry|author=Klaus Weissermel, Hans-Jurgen Arpe|publisher=John Wiley & Sons|edition=3rd|year=1997|isbn=3-527-28838-4}}</ref> 
*[[Neohexene]] production, which involves [[ethenolysis]] of [[Diisobutene|isobutene dimers]].  The catalyst is derived from [[tungsten trioxide]] supported on [[silica]] and [[Magnesium oxide|MgO]].
*[[1,5-Hexadiene]] and [[1,9-decadiene]], useful crosslinking agents and synthetic intermediates, are produced commercially by ethenolysis of [[1,5-Cyclooctadiene|1,5-cyclooctadiene]] and [[cyclooctene]].  The catalyst is derived from [[Rhenium(VII) oxide|Re<sub>2</sub>O<sub>7</sub>]] on alumina.

===Homogeneous catalyst potential===

Molecular catalysts have been explored for the preparation of a variety of potential applications,<ref>{{cite journal|last=Kotha|first=S|author2=Waghule GT|title=Diversity Oriented Approach to Crownophanes by Enyne Metathesis and Diels–Alder Reaction as Key Steps|journal=The Journal of Organic Chemistry|date=June 2012|volume=77|issue=14|pages=6314–6318|doi=10.1021/jo300766f|pmid=22731677}}</ref> such as the synthesis of [[pharmaceutical drug]]s,<ref>{{cite journal |vauthors=McCauley JA, McIntyre CJ, Rudd MT, Nguyen KT, Romano JJ, Butcher JW, Gilbert KF, Bush KJ, Holloway MK, Swestock J, Wan BL, Carroll SS, DiMuzio JM, Graham DJ, Ludmerer SW, Mao SS, Stahlhut MW, Fandozzi CM, Trainor N, Olsen DB, Vacca JP, Liverton NJ | title = Discovery of vaniprevir (MK-7009), a macrocyclic hepatitis C virus NS3/4a protease inhibitor | journal = Journal of Medicinal Chemistry| volume = 53 | issue = 6 | pages = 2443–63 |date=March 2010 | pmid = 20163176 | doi = 10.1021/jm9015526 }}</ref> the manufacturing of high-strength materials, the preparation of cancer-targeting [[nanoparticle]]s,<ref>{{cite journal |vauthors=Matson JB, Grubbs RH | title = Synthesis of Fluorine-18 Functionalized Nanoparticles for use as in vivo Molecular Imaging Agents | journal = Journal of the American Chemical Society| volume = 130 | issue = 21 | year = 2008 | pages = 6731–6733 | doi = 10.1021/ja802010d | pmid = 18452296 | url = https://authors.library.caltech.edu/77503/2/ja802010d-file002.pdf }}</ref> and the conversion of renewable plant-based feedstocks into hair and skin care products.<ref>{{cite press release | title = Dow Corning and Elevance Announce Partnership to Market Naturally Derived Ingredients in Personal Care Applications | publisher = Elevance Renewable Sciences | date = 9 September 2008 | url = http://www.elevance.com/media/news-releases/dow-corning-and-elevance-announce-partnership-to-market-naturally-derived-ingredients-in-personal-care-applications/ | access-date = 19 January 2012 | archive-date = 9 December 2011 | archive-url = https://web.archive.org/web/20111209204012/http://www.elevance.com/media/news-releases/dow-corning-and-elevance-announce-partnership-to-market-naturally-derived-ingredients-in-personal-care-applications/ | url-status = dead }}</ref>

==Types==
Some classes of olefin metathesis include:
* Cross metathesis (CM)
* Ring-opening metathesis (ROM)
*[[Ring-closing metathesis]] (RCM)
*[[Ring-opening metathesis polymerization]] (ROMP)
*[[Acyclic diene metathesis]] (ADMET)
*[[Ethenolysis]]

==Mechanism==
Hérisson and Chauvin first proposed the widely accepted mechanism of transition metal alkene metathesis.<ref>{{cite journal | last1 = Jean-Louis Hérisson | first1 = Par | last2 = Chauvin | first2 = Yves | journal = Die Makromolekulare Chemie| title=Catalyse de transformation des oléfines par les complexes du tungstène. II. Télomérisation des oléfines cycliques en présence d'oléfines acycliques | language=fr | volume = 141| issue=1 | pages = 161–176 | year = 1971 | doi = 10.1002/macp.1971.021410112 }}</ref> The direct [2+2] cycloaddition of two alkenes is formally [[Woodward–Hoffmann rules|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 [[Electron configuration|d-orbitals]] on the metal catalyst lowers the activation energy enough that the reaction can proceed rapidly at modest temperatures.
[[Image:Metathesis mechanism jypx3.png|400px|center|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]].

[[File:Wikipedia-OlefinMetathesisCategories.png|400px|center|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.<ref>{{cite journal | doi = 10.1002/ejoc.200700744 |author1=Sambasivarao Kotha |author2=Kuldeep Singh | title = Cross-enyne and ring-closing metathesis cascade: A building-block approach suitable for diversity-oriented synthesis of densely functionalized macroheterocycles with amino acid scaffolds| year = 2007 | pages = 5909–5916 | issue = 35 | volume = 2007 | journal = European Journal of Organic Chemistry}}</ref> 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."<ref name=KO>{{cite encyclopedia|encyclopedia=Kirk-Othmer Encyclopedia of Chemical Technology|author=Lionel Delaude |author2=Alfred F. Noels |year=2005| doi=10.1002/0471238961.metanoel.a01|place=Weinheim|publisher=Wiley-VCH|isbn = 978-0-471-23896-6|chapter = Metathesis}}</ref>
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]]).<ref>{{cite journal | last1 = Ziegler | first1 = Karl | last2 = Holzkamp | first2 = E. | last3 = Breil | first3 = H. | last4 = Martin | first4 = H. | title = Polymerisation von Äthylen und anderen Olefinen | journal = Angewandte Chemie| volume = 67 | issue=16 | page = 426 | year = 1955 | doi = 10.1002/ange.19550671610| bibcode = 1955AngCh..67..426Z }}</ref>

In 1960 a [[DuPont (1802–2017)|Du Pont]] research group polymerized [[norbornene]] to [[polynorbornene]] using ''lithium aluminum tetraheptyl'' and [[titanium tetrachloride]]<ref>{{cite journal | last1 = Truett | first1 = W. L. | last2 = Johnson | first2 = D. R. | last3 = Robinson | first3 = I. M. | last4 = Montague | first4 = B. A. |title= Polynorbornene by Coördination Polymerization| journal = Journal of the American Chemical Society| volume = 82 |issue=9 | pages = 2337–2340 | year = 1960 | doi = 10.1021/ja01494a057}}</ref> (a patent by this company on this topic dates back to 1955<ref>A. W. Anderson and N. G. Merckling, U. S. {{US Patent|2721189}}
(18 October 1955)</ref>),

:[[Image:MetathesisDupont.svg|metathesis Duport 1960|300px]]

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:

:[[Image:MetathesisDuPontMechanism.svg|Metathesis DuPont mechanism|500px]]

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.<ref>{{cite journal | last1 = Natta | first1 = G. | last2 = Dall'asta | first2 = G. | last3 = Mazzanti | first3 = G. | title = Stereospecific Homopolymerization of Cyclopentene | journal = Angewandte Chemie International Edition in English| volume = 3 | issue=11 | pages = 723–729 | year = 1964 | doi = 10.1002/anie.196407231}}</ref>
 
In a third development leading up to olefin metathesis, researchers at [[Phillips Petroleum Company]] in 1964<ref>{{cite journal | last1 = Banks | first1 = R. L. | last2 = Bailey | first2 = G. C. | title = Olefin Disproportionation. A New Catalytic Process | journal = Industrial & Engineering Chemistry Product Research and Development| volume = 3 |issue=3| pages = 170–173 | year = 1964 | doi = 10.1021/i360011a002}}</ref> described olefin [[disproportionation]] with [[catalyst]]s [[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:

:[[Image:MetathesisCyclobutaneMech.svg|500px|Metathesis cyclobutane mechanism]]

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 (scientist)|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 EtAlMe<sub>2</sub>. The researchers proposed a name for this reaction type: olefin metathesis.<ref>{{cite journal | last1 = Calderon | first1 = N | title = Olefin metathesis – A novel reaction for skeletal transformations of unsaturated hydrocarbons | journal = Tetrahedron Letters| volume = 8 |issue = 34 | pages = 3327–3329 | year = 1967 | doi = 10.1016/S0040-4039(01)89881-6 | last2 = Chen | first2 = Hung Yu | last3 = Scott | first3 = Kenneth W.}}</ref> Formerly the reaction had been called "olefin disproportionation."

:[[Image:MetathesisCalderon1967.svg|500px|Metathesis Calderon 1967]]

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 C<sub>4</sub>H<sub>4</sub>D<sub>4</sub> with deuterium evenly distributed.<ref>{{cite journal | last1 = Calderon | first1 = Nissim. | last2 = Ofstead | first2 = Eilert A. | last3 = Ward | first3 = John P. | last4 = Judy | first4 = W. Allen. | last5 = Scott | first5 = Kenneth W. | title = Olefin metathesis. I. Acyclic vinylenic hydrocarbons | journal = Journal of the American Chemical Society| volume = 90 | issue=15 | pages = 4133–4140 | year = 1968 | doi = 10.1021/ja01017a039}}</ref> In this way they were able to differentiate between a '''transalkylidenation''' mechanism and a '''[[transalkylation]] mechanism''' (ruled out):

:[[Image:MetathesisCalderon1976Mechanism.svg|600px|Metathesis Calderon 1976 Mechanism]]

In 1971 Chauvin proposed a four-membered [[metallacycle]] intermediate to explain the statistical distribution of products found in certain metathesis reactions.<ref>{{cite journal | last1 = Jean-Louis Hérisson | first1 = Par | last2 = Chauvin | first2 = Yves | title=Catalyse de transformation des oléfines par les complexes du tungstène. II. Télomérisation des oléfines cycliques en présence d'oléfines acycliques | journal = Die Makromolekulare Chemie| volume = 141 | issue=1 | pages = 161–176 | year = 1971 | doi = 10.1002/macp.1971.021410112}}</ref> This mechanism is today considered the actual mechanism taking place in olefin metathesis.

:[[Image:MetathesisMetallacyclemechanism.svg|500px|Metathesis metallacycle mechanism]]

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

:[[Image:MetathesisChauvin1971.svg|700px|Metathesis Chauvin 1971]]

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.<ref>{{cite journal | last1 = S. Lewandos | first1 = G | title = A proposed mechanism for the metal-catalysed disproportionation reaction of olefins | journal = Tetrahedron Letters| volume = 12 | issue=11 | pages = 789–793 | year = 1971 | doi = 10.1016/S0040-4039(01)96558-X | last2 = Pettit | first2 = R.}}</ref> It consisted of a tetramethylene intermediate with sp<sup>3</sup> [[orbital hybridization|hybridized]] carbon atoms linked to a central metal atom with multiple [[three-center two-electron bond]]s.

:[[Image:MetathesisPettitmechanism.svg|Metathesis Pettit mechanism|400px]]

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]]<ref>{{cite journal | last1 = Lewandos | first1 = Glenn S. | last2 = Pettit | first2 = R. | title = Mechanism of the metal-catalyzed disproportionation of olefins | journal = Journal of the American Chemical Society| volume = 93 | issue=25 | pages = 7087–7088 | year = 1971 | doi = 10.1021/ja00754a067}}</ref>

[[Robert H. Grubbs]] got involved in metathesis in 1972 and also proposed a metallacycle intermediate but one with four carbon atoms in the ring.<ref>{{cite journal | last1 = Grubbs | first1 = Robert H. | last2 = Brunck | first2 = Terence K. | title = Possible intermediate in the tungsten-catalyzed olefin metathesis reaction | journal = Journal of the American Chemical Society| volume = 94 | issue=7 | pages = 2538–2540 | year = 1972 | doi = 10.1021/ja00762a073}}</ref> 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:

:[[Image:MetathesisGrubbs1972tetramethylenemetallocycle.svg|Metathesis Grubbs 1972 tetramethylene metallacycle|600px]]

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)''<ref>{{cite journal | last1 = Biefeld | first1 = Carol G. | last2 = Eick | first2 = Harry A. | last3 = Grubbs | first3 = Robert H. | title = Crystal structure of bis(triphenylphosphine)tetramethyleneplatinum(II) | journal = Inorganic Chemistry| volume = 12 | issue=9 | pages = 2166–2170 | year = 1973 | doi = 10.1021/ic50127a046}}</ref>

In 1975 Katz also arrived at a metallacyclobutane intermediate consistent with the one proposed by Chauvin<ref>{{cite journal | last1 = Katz | first1 = Thomas J. | last2 = McGinnis | first2 = James | title = Mechanism of the olefin metathesis reaction | journal = Journal of the American Chemical Society| volume = 97 | issue=6 | pages = 1592–1594 | year = 1975 | doi = 10.1021/ja00839a063}}</ref> 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.

:[[Image:MetathesisKatz.svg|Metathesis Katz 1975|600px]]

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:<ref>{{cite journal | last1 = Casey | first1 = Charles P. | last2 = Burkhardt | first2 = Terry J. | title = Reactions of (diphenylcarbene)pentacarbonyltungsten(0) with alkenes. Role of metal-carbene complexes in cyclopropanation and olefin metathesis reactions | journal = Journal of the American Chemical Society| volume = 96 |issue=25| pages = 7808–7809 | year = 1974 | doi = 10.1021/ja00832a032}}</ref>

:[[Image:MetathesisCasey1974.svg|MetathesisCasey1974|600px]]

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

:[[Image:MetathesisPairWiseMechanism.svg|600px|Metathesis pairwise mechanism]]

with a 5-membered cycle in another round of isotope labeling studies in favor of the 4-membered cycle Chauvin mechanism:<ref>{{cite journal |last1=Grubbs |first1=Robert H. |last2=Burk |first2=Patrick L. |last3=Carr |first3=Dale D. |title=Mechanism of the olefin metathesis reaction |year=1975 |journal=Journal of the American Chemical Society|volume= 97|issue= 11 |pages= 3265–3267 |doi=10.1021/ja00844a082}}</ref><ref>{{cite journal | last1 = Grubbs | first1 = Robert H. | last2 = Carr | first2 = D. D. | last3 = Hoppin | first3 = C. | last4 = Burk | first4 = P. L. | title = Consideration of the mechanism of the metal catalyzed olefin metathesis reaction | journal = Journal of the American Chemical Society| volume = 98 |issue=12| pages = 3478–3483 | year = 1976 | doi = 10.1021/ja00428a015}}</ref>

:[[Image:Metathesisgrubbs1976.svg|600px|Metathesis Grubbs 1976]]

In this reaction the [[ethylene]] product distribution <math>(d_4,d_2,d_0)</math> 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]].<ref>{{cite journal | last1 = Tebbe | first1 = F. N. | last2 = Parshall | first2 = G. W. | last3 = Reddy | first3 = G. S. | title = Olefin homologation with titanium methylene compounds | journal = Journal of the American Chemical Society| volume = 100 |issue=11| pages = 3611–3613 | year = 1978 | doi = 10.1021/ja00479a061}}</ref> In a model reaction isotopically labeled carbon atoms in [[isobutene]] and [[methylenecyclohexane]] switched places:
:[[Image:MetathesisTebbe.svg|500px|Metathesis Tebbe reagent]]

The Grubbs group then isolated the proposed metallacyclobutane intermediate in 1980 also with this reagent together with 3-methyl-1-butene:<ref>{{cite journal | last1 = Howard | first1 = T. R. | last2 = Lee | first2 = J. B. | last3 = Grubbs | first3 = R. H. | title = Titanium metallacarbene-metallacyclobutane reactions: stepwise metathesis | journal = Journal of the American Chemical Society| volume = 102 | issue=22 | pages = 6876–6878 | year = 1980 | doi = 10.1021/ja00542a050}}</ref>
:[[Image:MetathesisGrubbs1980.svg|400px|Metathesis Grubbs 1980]]

They isolated a similar compound in the [[total synthesis]] of [[capnellene]] in 1986:<ref>{{cite journal | last1 = Stille | first1 = John R. | last2 = Grubbs | first2 = Robert H. | title = Synthesis of (.+-.)-.DELTA.9,12-capnellene using titanium reagents | journal = Journal of the American Chemical Society| volume = 108 | pages = 855–856 | year = 1986 | doi = 10.1021/ja00264a058 | issue = 4}}</ref>

:[[Image:MetathesisGrubbs1986.svg|600px|Metathesis Grubbs 1986]]

In that same year the Grubbs group proved that metathesis polymerization of norbornene by Tebbe's reagent is a [[living polymerization]] system<ref>{{cite journal | last1 = Gilliom | first1 = Laura R. | last2 = Grubbs | first2 = Robert H. | title = Titanacyclobutanes derived from strained, cyclic olefins: the living polymerization of norbornene | journal = Journal of the American Chemical Society| volume = 108 |issue=4| pages = 733–742 | year = 1986 | doi = 10.1021/ja00264a027}}</ref> and a year later Grubbs and Schrock co-published an article describing living polymerization with a [[tungsten]] carbene complex<ref>{{cite journal | last1 = Schrock | first1 = R. R. | last2 = Feldman | first2 = J. | last3 = Cannizzo | first3 = L. F. | last4 = Grubbs | first4 = R. H. | title = Ring-opening polymerization of norbornene by a living tungsten alkylidene complex | journal = Macromolecules| volume = 20 |issue=5| pages = 1169–1172 | year = 1987 | doi = 10.1021/ma00171a053|bibcode = 1987MaMol..20.1169S }}</ref> 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===
{{Main|Grubbs catalyst}}
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.<ref>{{cite journal | first1 = Francis W. | last1 = Michelotti | first2 = William P. | last2 = Keaveney | journal = Journal of Polymer Science Part A: General Papers| volume = 3 | issue = 3 | pages = 895–905 | year = 1965 | title = Coordinated Polymerization of the Bicyclo-(2.2.1)-heptene-2 Ring System (Norbornene) in Polar Media | doi=10.1002/pol.1965.100030305}}</ref><ref>{{cite journal | first1 = Robert E. | last1 = Rinehart | first2 = Homer P. | last2 = Smith | title = The Emulsion Polymerization of the Norbornene Ring System Catalyzed by Noble Metal Compounds | journal = Journal of Polymer Science Part B: Polymer Letters| volume = 3 | issue = 12 | pages = 1049–1052 | year = 1965 | doi=10.1002/pol.1965.110031215|bibcode = 1965JPoSL...3.1049R }}</ref><ref>{{cite journal | first1 = Lido | last1 = Porri | first2 = Renzo | last2 = Rossi | first3 = Pietro | last3 = Diversi | first4 = Antonio | last4 = Lucherini | title = Ring-Opening Polymerization of Cycloolefins with Catalysts Derived from Ruthenium and Iridium | journal = Die Makromolekulare Chemie| volume = 175 | pages = 3097–3115 | year = 1974 | doi=10.1002/macp.1974.021751106 | issue = 11}}</ref> 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.<ref>{{cite journal | last1 = Novak | first1 = Bruce M. | last2 = Grubbs | first2 = Robert H. | title = The ring opening metathesis polymerization of 7-oxabicyclo[2.2.1]hept-5-ene derivatives: a new acyclic polymeric ionophore | journal = Journal of the American Chemical Society| volume = 110| issue=3 | pages = 960–961 | year = 1988 | doi = 10.1021/ja00211a043}}
</ref> They identified a Ru(II) carbene as an effective metal center and in 1992 published the first well-defined, ruthenium-based olefin metathesis catalyst, (PPh<sub>3</sub>)<sub>2</sub>Cl<sub>2</sub>Ru=CHCH=CPh<sub>2</sub>:<ref>{{cite journal | last1 = Nguyen | first1 = Sonbinh T. | last2 = Johnson | first2 = Lynda K. | last3 = Grubbs | first3 = Robert H. | last4 = Ziller | first4 = Joseph W. | title = Ring-opening metathesis polymerization (ROMP) of norbornene by a Group VIII carbene complex in protic media | journal = Journal of the American Chemical Society| volume = 114 | issue=10 | pages = 3974–3975 | year = 1992 | doi = 10.1021/ja00036a053| url = https://authors.library.caltech.edu/88217/2/ja00036a053_si_001.pdf }}</ref>

:[[Image:MetathesisGrubbs1992.svg|400px|Metathesis Grubbs 1992]]

The corresponding [[tricyclohexylphosphine]] complex (PCy<sub>3</sub>)<sub>2</sub>Cl<sub>2</sub>Ru=CHCH=CPh<sub>2</sub> was also shown to be active.<ref>{{cite journal | last1 = Nguyen | first1 = Sonbinh T. | last2 = Grubbs | first2 = Robert H. | last3 = Ziller | first3 = Joseph W. | title = Syntheses and activities of new single-component, ruthenium-based olefin metathesis catalysts | journal = Journal of the American Chemical Society| volume = 115 |issue=21| pages = 9858–9859 | year = 1993 | doi = 10.1021/ja00074a086}}
</ref> This work culminated in the now commercially available 1st generation [[Grubbs catalyst]].<ref>{{cite journal | last1 = Schwab | first1 = Peter | last2 = France | first2 = Marcia B. | last3 = Ziller | first3 = Joseph W. | last4 = Grubbs | first4 = Robert H. | title = A Series of Well-Defined Metathesis Catalysts–Synthesis of [RuCl<sub>2</sub>(CHR′)(PR<sub>3</sub>)<sub>2</sub>] and Its Reactions | journal = Angewandte Chemie International Edition in English| volume = 34 | pages = 2039–2041 | year = 1995 | doi = 10.1002/anie.199520391 | issue = 18}}</ref><ref>{{cite journal | last1 = Schwab | first1 = Peter | last2 = Grubbs | first2 = Robert H. | last3 = Ziller | first3 = Joseph W. | title = Synthesis and Applications of RuCl<sub>2</sub>(=CHR')(PR<sub>3</sub>)<sub>2</sub>: The Influence of the Alkylidene Moiety on Metathesis Activity | journal = Journal of the American Chemical Society| volume = 118 | pages = 100–110 | year = 1996 | doi = 10.1021/ja952676d}}</ref>

===Schrock catalysts===
Schrock entered the olefin metathesis field in 1979 as an extension of work on [[tantalum]] alkylidenes.<ref>{{cite journal | last1 = Schrock | first1 = R. R. | last2 = Meakin | first2 = P. | title = Pentamethyl complexes of niobium and tantalum | journal = Journal of the American Chemical Society| volume = 96 | issue=16 | pages = 5288–5290 | year = 1974 | doi = 10.1021/ja00823a064}}</ref> The initial result was disappointing as reaction of {{chem2|CpTa(\dCH\st\sBu)Cl2}} with [[ethylene]] yielded only a metallacyclopentane, not metathesis products:<ref>{{cite journal | last1 = McLain | first1 = S. J. | last2 = Wood | first2 = C. D. | last3 = Schrock | first3 = R. R. | title = Preparation and characterization of tantalum(III) olefin complexes and tantalum(V) metallacyclopentane complexes made from acyclic α olefins | journal = Journal of the American Chemical Society| volume = 101 | issue=16 | pages = 4558–4570 | year = 1979 | doi = 10.1021/ja00510a022}}</ref>

:[[Image:MetathesisSchrock1979.svg|300px|Metathesis Schrock 1979]]

But by tweaking this structure to a {{chem2|PR3Ta(CHt\sbu)(Ot\sbu)2Cl}} (replacing [[chloride]] by [[t-butoxide]] and a [[cyclopentadienyl]] by an [[organophosphine]], metathesis was established with cis-2-pentene.<ref>{{cite journal | last1 = Schrock | first1 = R | title = Preparation and characterization of active niobium, tantalum and tungsten metathesis catalysts | journal = Journal of Molecular Catalysis| volume = 8 |issue=1–3| pages = 73–83 | year = 1980 | doi = 10.1016/0304-5102(80)87006-4 | last2 = Rocklage | first2 = Scott | last3 = Wengrovius | first3 = Jeffrey | last4 = Rupprecht | first4 = Gregory | last5 = Fellmann | first5 = Jere}}</ref> In another development, certain tungsten oxo complexes of the type {{chem2|W(O)(CHt\sBu)(Cl)2(PEt)3}} were also found to be effective.<ref>{{cite journal | last1 = Wengrovius | first1 = Jeffrey H. | last2 = Schrock | first2 = Richard R. | last3 = Churchill | first3 = Melvyn Rowen | last4 = Missert | first4 = Joseph R. | last5 = Youngs | first5 = Wiley J. | title =  Multiple metal-carbon bonds. 16. Tungsten-oxo alkylidene complexes as olefins metathesis catalysts and the crystal structure of W(O)(CHCMe<sub>3</sub>(PEt<sub>3</sub>)Cl<sub>2</sub>| journal = Journal of the American Chemical Society| volume = 102|issue=13 | pages = 4515–4CF6 | year = 1980 | doi = 10.1021/ja00533a035}}</ref>

[[Schrock alkylidene]]s for olefin metathesis of the type {{chem2|Mo(NAr)(CHC(CH3)2R){OC(CH3)(CF3)2}2}} were commercialized starting in 1990.<ref>{{cite journal | last1 = Schrock | first1 = Richard R. | last2 = Murdzek | first2 = John S. | last3 = Bazan | first3 = Gui C. | last4 = Robbins | first4 = Jennifer | last5 = Dimare | first5 = Marcello | last6 = O'Regan | first6 = Marie | title = Synthesis of molybdenum imido alkylidene complexes and some reactions involving acyclic olefins | journal = Journal of the American Chemical Society| volume = 112 | issue=10 | pages = 3875–3886 | year = 1990 | doi = 10.1021/ja00166a023}}</ref><ref>{{cite journal | last1 = Bazan | first1 = Guillermo C. | last2 = Oskam | first2 = John H. | last3 = Cho | first3 = Hyun Nam | last4 = Park | first4 = Lee Y. | last5 = Schrock | first5 = Richard R. | title = Living Ring-Opening Metathesis Polymerization of 2,3-Difunctionalized 7-Oxanorbornenes and 7-Oxanorbornadienes by Mo(CHCMe<sub>2</sub>R)(N-2,6-C<sub>6</sub>H<sub>3</sub>-''i''-Pr<sub>2</sub>)(O-''t''-Bu)<sub>2</sub> and Mo(CHCMe<sub>2</sub>R)(N-2,6-C<sub>6</sub>H<sub>3</sub>-''i''-Pr<sub>2</sub>)(OCMe<sub>2</sub>CF<sub>3</sub>)<sub>2</sub> | volume = 113 | issue=18 | pages = 6899–6907 | year = 1991 | doi = 10.1021/ja00018a028}}</ref>

:[[Image:SchrockCatalyst.svg|205px|Commercial Schrock catalyst]]

The first asymmetric catalyst followed in 1993<ref>{{cite journal | last1 = McConville | first1 = David H. | last2 = Wolf | first2 = Jennifer R. | last3 = Schrock | first3 = Richard R. | title = Synthesis of chiral molybdenum ROMP initiators and all-cis highly tactic poly(2,3-(R)2norbornadiene) (R = CF<sub>3</sub> or CO<sub>2</sub>Me) | journal = Journal of the American Chemical Society| volume = 115 | issue=10 | pages = 4413–4414 | year = 1993 | doi = 10.1021/ja00063a090}}</ref>

:[[Image:MetathesisROMPSchrock1993.svg|500px|Metathesis ROMP Schrock 1993]]

With a Schrock catalyst modified with a [[BINOL]] ligand in a [[norbornadiene]] [[Ring opening metathesis polymerisation|ROMP]] leading to highly stereoregular cis, [[isotactic]] polymer.

==See also==
* [[Alkane metathesis]]
* [[Alkyne metathesis]]
* [[Enyne metathesis]]
* [[Salt metathesis reaction]]

==References==
{{Reflist}}

==Further reading==
#{{cite journal | doi = 10.1021/cen-v080n016.p029 | title = Olefin Metathesis: Big-Deal Reaction | year = 2002 | volume = 80 | issue = 51 | pages = 29–33 | url = http://pubs.acs.org/cen/coverstory/8051/8051olefin.html}}
#{{cite journal | title = Olefin Metathesis: The Early Days | year = 2002 | volume = 80 | issue = 51 | pages = 34–38 | url = http://pubs.acs.org/cen/coverstory/8051/8051olefin2.html | doi = 10.1021/cen-v080n029.p034}}
#{{cite journal |last=Schrock |first=R. R. |author-link=Richard R. Schrock |year=1990 |title=Living ring-opening metathesis polymerization catalyzed by well-characterized transition-metal alkylidene complexes |journal= Accounts of Chemical Research|volume=23 |issue=5 |pages=158–165 |doi=10.1021/ar00173a007 }}
#{{cite journal |last=Schrock |first=R. R. |author-link=Richard R. Schrock |author2=Hoveyda, A. H. |year=2003 |title=Molybdenum and Tungsten Imido Alkylidene Complexes as Efficient Olefin-Metathesis Catalysts |journal= Angewandte Chemie International Edition|volume=42 |issue=38 |pages=4592–4633 |doi=10.1002/anie.200300576 |pmid=14533149 |s2cid=35370749 }}
#{{cite journal |last=Samojłowicz |first=C. |author2=Grela, K. |year=2009 |title=Ruthenium-Based Olefin Metathesis Catalysts Bearing N-Heterocyclic Carbene Ligands |journal= Chemical Reviews|pmid=19534492 |volume=109 |issue=8 |pages=3708–3742 |doi=10.1021/cr800524f }}
#{{cite journal |last=Vougioukalakis |first=G. C. |author2=Grubbs, R. H. |author-link2=Robert H. Grubbs  |year=2010 |title=Ruthenium-Based Heterocyclic Carbene-Coordinated Olefin Metathesis Catalysts |journal= Chemical Reviews|pmid=20000700 |volume=110 |issue=3 |pages=1746–1787 |doi=10.1021/cr9002424 |s2cid=4589661 }}
#{{cite journal |last=Trnka |first=T. M. |author2=Grubbs, R. H. |author-link2=Robert H. Grubbs  |year=2001 |title=The Development of L2X2Ru=CHR Olefin Metathesis Catalysts: An Organometallic Success Story |journal= Accounts of Chemical Research|volume=34 |issue=1 |pages=18–29 |doi=10.1021/ar000114f |pmid=11170353|s2cid=22145255 }}
#{{cite journal |last=Grubbs |first=R. H. |author-link=Robert H. Grubbs |author2=Chang, S. |year=1998 |title=Recent advances in olefin metathesis and its application in organic synthesis |journal= Tetrahedron|volume=54 |issue=18 |pages=4413–4450 |doi=10.1016/S0040-4020(97)10427-6 }}
#{{cite journal |last=Grubbs |first=R. H. |author-link=Robert H. Grubbs |year=2004 |title=Olefin metathesis |journal= Tetrahedron|volume=60 |issue=34 |pages=7117–7140 |doi= 10.1016/j.tet.2004.05.124 }}
#{{cite journal |editor-last=Grela |editor-first=K.  |year=2010 |title=Progress in metathesis chemistry (Editorial for Open Access Thematic Series)|journal= Beilstein Journal of Organic Chemistry|volume=6 |pages=1089–1090 |doi=10.3762/bjoc.6.124 |pmid=21160917 |pmc=3002079 |last1=Grela |first1=K. }}

{{Alkenes}}
{{Organometallics}}
{{Organic reactions}}

[[Category:Carbon-carbon bond forming reactions]]
[[Category:Organometallic chemistry]]
[[Category:Homogeneous catalysis]]
[[Category:Industrial processes]]