Olefin metathesis 1859894 221622301 2008-06-25T09:47:43Z 217.169.182.38 '''Olefin metathesis''' or '''transalkylidenation''' (in some literature, a [[disproportionation]]) is an [[organic reaction]] which involves redistribution of [[olefin]]ic ([[alkene]]) [[chemical bond|bonds]].<ref>{{cite journal | author = Astruc D. | title = "The metathesis reactions: from a historical perspective to recent developments" | journal = New J. Chem. | volume = 29 | issue = 1 | year = 2005 | pages = 42–56 | url=http://www.rsc.org/Publishing/Journals/NJ/article.asp?doi=b412198h | format=abstract | doi = 10.1039/b412198h }}</ref> Since its discovery, olefin metathesis has gained widespread use in [[research]] and [[industry]] for making products ranging from [[medicine]]s and [[polymer]]s to enhanced [[fuel]]s. Its advantages include the creation of fewer [[sideproduct]]s and [[hazardous waste]]s. [[Yves Chauvin]], [[Robert H. Grubbs]], and [[Richard R. Schrock]] shared the [[2005]] [[Nobel Prize in Chemistry]] for "the development of the metathesis method in [[organic synthesis]]".<ref>{{cite press release | title = The Nobel Prize in Chemistry 2005 | publisher = [[Nobelprize.org]] | date = 5 Oct 2005 | url = http://nobelprize.org/nobel_prizes/chemistry/laureates/2005/press.html}}</ref> The reaction is [[catalysis|catalyzed]] by [[metals]] such as [[nickel]], [[tungsten]], [[ruthenium]] and [[molybdenum]]. The reaction consists of an [[alkene]] [[double bond]] [[bond cleavage|cleavage]], followed by a statistical redistribution of [[alkylidene]] fragments. The general scope is outlined by the following scheme: [[Image:Metathesis.PNG|250px|center|Olefin metathesis]] ==Overview== Olefin metathesis was first used in [[petroleum]] reformation for the synthesis of higher olefins from the products (α-olefins) from the [[Shell higher olefin process]] (SHOP) under high pressure and high temperatures. Many traditional catalysts are derived from a reaction of the metal halides with alkylation agents for example WCl<sub>6</sub>-EtOH-EtAlCl<sub>2</sub>. A metathesis reaction is a chain reaction that begins when a metallocarbene and an olefin react to form a '''metallacyclobutane'''. This intermediate then reacts further, decomposing into a new olefin (the product) and a new metallocarbene, which can then be recycled through the reaction pathway. [[Image:Metathesis mechanism.png|600px|center|Olefin metathesis mechanism]] The [[Grubbs' catalyst]] is a ruthenium carbenoid,<ref>{{cite paper | author = Ileana Dragutan*, Valerian Dragutan*, Petru Filip | title = Recent developments in design and synthesis of well-defined ruthenium metathesis catalysts – a highly successful opening for intricate organic synthesis | date = 2005 | url = http://arkat-usa.org/ark/journal/2005/I10_Balaban/1334/1334.asp }}. 105. From [[Arkivoc]].</ref> while molybdenum or tungsten catalysts are known as [[Schrock carbene]]s <ref>{{cite paper | author = R.R. Schrock | title = High-oxidation-state molybdenum and tungsten alkylidene complexes | date = 1986}} Acc. Chem Res.</ref>. These catalysts can also perform [[alkyne metathesis]] and related polymerizations. ==Reaction mechanism== Hérison and Chauvin first proposed the widely accepted mechanism of transition metal alkene metathesis.<ref>Hérisson, J.-L.; Chauvin, Y. ''Macromol. Chem.'' '''1970''', ''141'', 161.</ref> The direct [2+2] cycloaddition of two alkenes is formally [[Woodward-Hoffmann rules | symmetry forbidden]] and thus has a very high [[activation energy]]. The Chauvin mechanism involves the [2+2] cycloaddition of an alkene double bond to a transition metal alkylidene to form a metallocyclobutane intermediate. The metallocyclobutane produced can then cyclorevert 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:MetathesisMechanismGeneral.svg|center|Chauvin Mechanism for Olefin Metathesis]] ==Metathesis chemistry== Some important classes of [[metathesis (chemistry)|metathesis]] chemistry: *[[Cross-metathesis]] (CM) *[[Ring-closing metathesis]] (RCM) *[[Enyne metathesis]] (EM) *[[Ring opening metathesis]] (ROM) *[[Ring opening metathesis polymerisation]] (ROMP) *[[Acyclic diene metathesis]] (ADMET) *[[Alkyne metathesis]] (AM) *[[Alkane metathesis]] *Alkene metathesis Like most organometallic reactions, the metathesis pathway is usually driven by a thermodynamic imperative; that is, the final products are determined by the energetics of the possible products, with a distribution of products proportional to the exponential of their respective energy values. Alkene metathesis is generally driven by the evolution of gaseous [[ethylene]]; and alkyne metathesis is driven by the evolution of [[acetylene]]. These are both dominated by the entropy gained by the net release of gas. Enyne metathesis cannot evolve a simple gas, and for that reason is usually disfavored unless there are accompanying ring-opening or ring-closing advantages. [[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 highly energetically favorable; although these reactions tend to also evolve [[ethylene]]. RCM has been used to close larger macrocycles, in which case the reaction may be kinetically controlled by running the reaction at extreme dilutions. The [[Thorpe-Ingold effect]] may be exploited to improve both reaction rates and selectivity. Alkene 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]]. ==Scope== One study reported a ring-opening cross-olefin metathesis based on a [[Hoveyda-Grubbs Catalyst]]:<ref> ''A Recyclable Chiral Ru Catalyst for Enantioselective Olefin Metathesis. Efficient Catalytic Asymmetric Ring-Opening/Cross Metathesis in Air'' Joshua J. Van Veldhuizen, Steven B. Garber, Jason S. Kingsbury, and [[Amir H. Hoveyda]] [[J. Am. Chem. Soc.]]; '''2002'''; 124(18) pp 4954 - 4955; (Communication) {{DOI|10.1021/ja020259c}} </ref> [[Image:RO-metathesis.png|center|500px|Ring opening / cross metathesis]] The metathesis reaction of [[1-hexene]] with the WCl<sub>4</sub>(OAr)<sub>2</sub> catalyst yields 5-decene<ref>{{cite journal | author = Ione M. Baibich, Carla Kern | title = "Reactivity of Tungsten-aryloxides with Hydrosilane Cocatalysts in Olefin Metathesis" | journal = Journal of the Brazilian Chemical Society | volume = 13 | issue=1 | year = 2002 | pages = 43–46 | url=http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532002000100006 }}</ref> plus many byproducts from secondary metathesis reactions. ==Historical overview== Known chemistry prior to the advent of olefin metathesis was introduced by [[Karl Ziegler]] in the 1950's who as part of ongoing work in what would later become known as [[Ziegler-Natta catalysis]] studied [[ethylene]] [[polymerization]] which on addition of certain metals resulted in [[1-butene]] instead of a saturated long-chain hydrocarbon (see [[nickel effect]]) <ref>''Polymerisation von Äthylen und anderen Olefinen'' Karl Ziegler, E. Holzkamp, H. Breil, H. Martin [[Angewandte Chemie]] Volume 67, Issue 16 , Pages 426 - 426 '''1955''' {{DOI|10.1002/ange.19550671610}}</ref>. In 1960 a [[Du Pont]] research group polymerized [[norbornene]] to [[polynorbornene]] using ''lithium aluminum tetraheptyl'' and [[titanium tetrachloride]] <ref>A. W. Anderson and N. G. Merckling, U. S. {{US Patent|2721189}} (October 18, 1955)</ref> (a patent by this company on this topic dates back to 1955 <ref>''Polynorbornene by Coordination Polymerization'' W. L. Truett, D. R. Johnson, I. M. Robinson, B. A. Montague [[J. Am. Chem. Soc.]] '''1960'''; 82(9); 2337-2340. {{DOI|10.1021/ja01494a057}}</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]]. [[Giulio Natta]] in 1964 also observed the formation of an unsaturated polymer when polymerizing [[cyclopentene]] with tungsten and molybdenum halides <ref>''Stereospecific Homopolymerization of Cyclopentene'' [[Angewandte Chemie International Edition in English]] Volume 3, Issue 11, Date: November '''1964''', Pages: 723-729 G. Natta, G. Dall'Asta, G. Mazzanti {{DOI|10.1002/anie.196407231}}</ref>. In a third development leading up to olefin metathesis researchers at [[Phillips Petroleum Company]] in 1964 <ref>''Olefin Disproportionation. A New Catalytic Process'' R. L. Banks and G. C. Bailey Ind. Eng. Chem. Prod. Res. Dev.; '''1964'''; 3(3) pp 170 - 173; {{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 another reason why it was quickly abandoned. Then in 1967 researchers at the [[Goodyear Tire and Rubber Company]] described a novel catalyst system for the [[metathesis]] of [[2-pentene]] based on [[tungsten hexachloride]], [[ethanol]] the [[organoaluminum]] compound EtAlMe<sub>2</sub> and also proposed a name for this reaction type: olefin metathesis <ref>''Olefin metathesis - A novel reaction for skeletal transformations of unsaturated hydrocarbons'' [[Tetrahedron Letters]], Volume 8, Issue 34, '''1967''', Pages 3327-3329 Nissim Calderon, Hung Yu Chen and Kenneth W. Scott {{DOI|10.1016/S0040-4039(01)89881-6}}</ref>. :[[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 wel and the reaction can be stopped by addition of [[methanol]]. The Goodyear group elegantly 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>''Olefin metathesis. I. Acyclic vinylenic hydrocarbons'' Nissim Calderon, Eilert A. Ofstead, John P. Ward, W. Allen Judy, and Kenneth W. Scott [[J. Am. Chem. Soc.]] '''1968'''; 90(15); 4133-4140. {{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 4-membered [[metallocycle]] intermediate to explain the statistical distribution of products found in certain metathesis reactions <ref>''Catalyse de transformation des oléfines par les complexes du tungstène. II. Télomérisation des oléfines cycliques en présence d'oléfines acycliques'' Die Makromolekulare Chemie Volume 141, Issue 1, Date: 9 February '''1971''', Pages: 161-176 Par Jean-Louis Hérisson, Yves Chauvin {{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]] The active catalyst, a [[metallocarbene]] .<ref>{{cite journal | author = E. O. Fischer, A. Maasböl | title = On the Existence of a Tungsten Carbonyl Carbene Complex | journal = Angewandte Chemie International Edition in English | year = 1964 | volume = 3 | issue = 8 | pages = 580–581 | doi = 10.1002/anie.196405801}}</ref>, was discovered by in 1964 by [[E. O. Fischer]]. Chauvins 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>''A proposed mechanism for the metal-catalysed disproportionation reaction of olefins'' [[Tetrahedron Letters]], Volume 12, Issue 11, '''1971''', Pages 789-793 Glenn S. Lewandos and R. Pettit {{DOI|10.1016/S0040-4039(01)96558-X}}</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>''Mechanism of the metal-catalyzed disproportionation of olefins'' Glenn S. Lewandos, R. Pettit [[J. Am. Chem. Soc.]] '''1971'''; 93(25); 7087-7088. {{DOI|10.1021/ja00754a067}} </ref> [[Robert H. Grubbs]] got involved in metathesis in 1972 and also proposed a metallacycle intermediate but one with 4 carbon atoms in the ring <ref>''Possible intermediate in the tungsten-catalyzed olefin metathesis reaction'' Robert H. Grubbs, Terence K. Brunck [[J. Am. Chem. Soc.]]; '''1972'''; 94(7); 2538-2540. {{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 metallocycle|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>''Crystal structure of bis(triphenylphosphine)tetramethyleneplatinum(II)'' Carol G. Biefeld, Harry A. Eick, Robert H. Grubbs Inorg. Chem.; '''1973'''; 12(9); 2166-2170. {{DOI|10.1021/ic50127a046}}</ref> In 1975 Katz also arrived at a metallacyclobutane intermediate consistent with the one proposed by Chauvin <ref>''Mechanism of the olefin metathesis reaction'' Thomas J. Katz, James McGinnis [[J. Am. Chem. Soc.]]; '''1975'''; 97(6); 1592-1594. {{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 wel 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>''Reactions of (diphenylcarbene)pentacarbonyltungsten(0) with alkenes. Role of metal-carbene complexes in cyclopropanation and olefin metathesis reactions'' Charles P. Casey, Terry J. Burkhardt [[J. Am. Chem. Soc.]]; '''1974'''; 96(25); 7808-7809. {{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>''Mechanism of the olefin metathesis reaction'' Robert H. Grubbs, Patrick L. Burk, Dale D. Carr [[J. Am. Chem. Soc.]] '''1975'''; 97(11); 3265-3267. {{DOI|10.1021/ja00844a082}}</ref> <ref>''Consideration of the mechanism of the metal catalyzed olefin metathesis reaction'' Robert H. Grubbs, D. D. Carr, C. Hoppin, P. L. Burk [[J. Am. Chem. Soc.]] '''1976'''; 98(12); 3478-3483. {{DOI|10.1021/ja00428a015}}</ref> :[[Image:Metathesisgrubbs1976.svg|600px|Metathesis Grubbs 1976]] In this reaction the [[ethylene]] product distribution (d4,d2,d0) at low conversion was found to be consistent with the carbene mechanism. On the other hand Grubbs did not rule out that the tetramethythene intermediate was a precursor to the carbene. The first practical metathesis system was introduced in 1978 by Tebbe based on the (what later became known as the) [[Tebbe reagent]] <ref>''Olefin homologation with titanium methylene compounds'' F. N. Tebbe, G. W. Parshall, G. S. Reddy [[J. Am. Chem. Soc.]] '''1978'''; 100(11); 3611-3613. {{DOI|10.1021/ja00479a061}}</ref>. In a model reaction isoptopically labeled carbon atoms in [[isobutene]] and [[methylenecyclohexane]] switched places: :[[Image:MetathesisTebbe.svg|500px|Metathesis Tebbe reagent]] The Grubbs group then isolated the first metallacyclobutane in 1980 also with this reagent together with 3-methyl-1-butene <ref>''Titanium metallacarbene-metallacyclobutane reactions: stepwise metathesis'' T. R. Howard, J. B. Lee, R. H. Grubbs [[J. Am. Chem. Soc.]] '''1980'''; 102(22); 6876-6878. {{DOI|10.1021/ja00542a050}}</ref> :[[Image:MetathesisGrubbs1980.svg|400px|Metathesis Grubbs 1980]] and isolated a similar compound in a [[total synthesis]] in 1986 <ref>''Synthesis of (+-)Δ<sup>9,12</sup>-capnellene using titanium reagents'' John R. Stille, Robert H. Grubbs [[J. Am. Chem. Soc.]] '''1986'''; 108(4); 855-856. {{DOI|10.1021/ja00264a058}}</ref> :[[Image:MetathesisGrubbs1986.svg|600px|Metathesis Grubbs 1986]] In that same year the Grubbs group was able to prove that metathesis polymerization of norbornene based on tebbe's reagent is a [[living polymerization]] system <ref>''Titanacyclobutanes derived from strained, cyclic olefins: the living polymerization of norbornene'' Laura R. Gilliom, Robert H. Grubbs [[J. Am. Chem. Soc.]] '''1986'''; 108(4); 733-742. {{DOI|10.1021/ja00264a027}}</ref> and a year later Grubbs and Schrock copublished an article describing living polymerization with a [[tungsten]] carbene complex <ref>Ring-opening polymerization of norbornene by a living tungsten alkylidene complex R. R. Schrock, J. Feldman, L. F. Cannizzo, R. H. Grubbs [[Macromolecules]]; 1987; 20(5); 1169-1172. {{DOI|10.1021/ma00171a053}}</ref> While Schrock focussed his research on tungsten and molybdenum catalysts for olefin metathesis, Grubbs started the development of catalysts based on ruthenium which he hoped would be less oxygen-sensitive and therefore more [[functional group]] tolerant. ===Grubbs catalysts=== Drawing on earlier work by Michelotti and Keaveney on norbornene polymerization with hydrated trichlorides of ruthenium, osmium, and iridium in alcoholic solvents <ref>''Coordinated polymerization of the bicyclo-[2.2.1]-heptene-2 ring system (norbornene) in polar media'' Journal of Polymer Science Part A: General Papers Volume 3, Issue 3, Date: March '''1965''', Pages: 895-905 Francis W. Michelotti, William P. Keaveney {{DOI|10.1002/pol.1965.100030305}}</ref> the Grubbs group successfully polymerized the 7-oxo norbornene derivative using [[ruthenium trichloride]], [[osmium trichloride]] or tungsten alkylidenes <ref>''The ring opening metathesis polymerization of 7-oxabicyclo[2.2.1]hept-5-ene derivatives: a new acyclic polymeric ionophore'' Bruce M. Novak, Robert H. Grubbs [[J. Am. Chem. Soc.]] '''1988'''; 110(3); 960-961. {{DOI|10.1021/ja00211a043}}</ref>. More research identified a Ru(II) carbene as an effective metal center such as (PPh<sub>3</sub>)<sub>2</sub>Cl<sub>2</sub>Ru=CHCH=CPh<sub>2</sub> <ref>''Ring-opening metathesis polymerization (ROMP) of norbornene by a Group VIII carbene complex in protic media '' SonBinh T. Nguyen, Lynda K. Johnson, Robert H. Grubbs, Joseph W. Ziller [[J. Am. Chem. Soc.]] '''1992'''; 114(10); 3974-3975. {{DOI|10.1021/ja00036a053}}</ref>: :[[Image:MetathesisGrubbs1992.svg|400px|Metathesis Grubbs 1992]] or (PCy<sub>3</sub>)<sub>2</sub>Cl<sub>2</sub>Ru=CHCH=CPh<sub>2</sub> (with [[tricyclohexylphosphine]] replacing [[triphenylphosphine]] ligands) <ref>''Syntheses and activities of new single-component, ruthenium-based olefin metathesis catalysts'' SonBinh T. Nguyen, Robert H. Grubbs, Joseph W. Ziller [[J. Am. Chem. Soc.]] '''1993'''; 115(21); 9858-9859. {{DOI|10.1021/ja00074a086}}</ref> culminating in the now commercially available [[Grubbs catalyst]] <ref>''A Series of Well-Defined Metathesis Catalysts-Synthesis of [RuCl2(CHR)(PR3)2] and Its Reactions'' [[Angewandte Chemie International Edition in English]] Volume 34, Issue 18, Date: October 2, '''1995''', Pages: 2039-2041 Peter Schwab, Marcia B. France, Joseph W. Ziller, Robert H. Grubbs {{DOI|10.1002/anie.199520391}}</ref> <ref>''Synthesis and Applications of RuCl2(=CHR')(PR3)2: The Influence of the Alkylidene Moiety on Metathesis Activity'' Peter Schwab, Robert H. Grubbs, and Joseph W. Ziller [[J. Am. Chem. Soc.]] pp 100 - 110; '''1996''' (Article) {{DOI|10.1021/ja952676d}}</ref> ===Schrock catalysts=== Schrock entered the olefin metathesis field in 1979 when he wondered how he could implement his [[tantalum]] carbenes he had been working on ever since 1974 <ref>''Pentamethyl complexes of niobium and tantalum'' R. R. Schrock, P. Meakin [[J. Am. Chem. Soc.]]; '''1974'''; 96(16); 5288-5290. {{DOI|10.1021/ja00823a064}} </ref>. The initial result was disappointing as reaction of CpTa(CHt-bu)Cl<sub>2</sub> with [[ethylene]] yielded only a metallacyclopentane but no metathesis products <ref>''Preparation and characterization of tantalum(III) olefin complexes and tantalum(V) metallacyclopentane complexes made from acyclic .alpha. olefins'' S. J. McLain, C. D. Wood, R. R. Schrock [[J. Am. Chem. Soc.]] '''1979'''; 101(16); 4558-4570. {{DOI|10.1021/ja00510a022}}</ref>: :[[Image:MetathesisSchrock1979.svg|300px|Metathesis Schrock 1979]] But by tweaking this structure to a PR<sub>3</sub>Ta(CHt-bu)(Ot-bu)<sub>2</sub>Cl (replacing [[chlorine]] by a [[t-butoxide]] group and a [[cyclopentadienyl]] group by a [[organophosphine]]) metathesis eventually did take place with cis-2-pentene a year later <ref>''Preparation and characterization of active niobium, tantalum and tungsten metathesis catalysts'' [[Journal of Molecular Catalysis]], Volume 8, Issues 1-3, May '''1980''', Pages 73-83 Richard Schrock, Scott Rocklage, Jeffrey Wengrovius, Gregory Rupprecht and Jere Fellmann {{DOI|10.1016/0304-5102(80)87006-4}}</ref> and in another development certain tungsten oxo complexes of the type W(O)(CHt-Bu)(Cl)<sub>2</sub>(PEt)<sub>3</sub> were also found to be effective <ref>''Multiple metal-carbon bonds. 16. Tungsten-oxo alkylidene complexes as olefins metathesis catalysts and the crystal structure of W(O)(CHCMe3(PEt3)Cl2'' Jeffrey H. Wengrovius, Richard R. Schrock, Melvyn Rowen Churchill, Joseph R. Missert, Wiley J. Youngs [[J. Am. Chem. Soc.]] '''1980'''; 102(13); 4515-4516. {{DOI|10.1021/ja00533a035}}</ref> [[Schrock carbene]]s for olefin metathesis of the type Mo(NAr)(CHMe<sub>2</sub>R)(OC(CH<sub>3</sub>)(CF<sub>3</sub>)<sub>2</sub>) were commercialized starting in 1990 <ref>''Synthesis of molybdenum imido alkylidene complexes and some reactions involving acyclic olefins'' Richard R. Schrock, John S. Murdzek, Gui C. Bazan, Jennifer Robbins, Marcello DiMare, Marie O'Regan [[J. Am. Chem. Soc.]] '''1990'''; 112(10); 3875-3886. {{DOI|10.1021/ja00166a023}}</ref> <ref>''Living ring-opening metathesis polymerization of 2,3-difunctionalized 7-oxanorbornenes and 7-oxanorbornadienes by Mo(CHCMe2R)(NC6H3-iso-Pr2-2,6)(O-tert-Bu)2 and Mo(CHCMe2R)(NC6H3-iso-Pr2-2,6)(OCMe2CF3)2'' Guillermo C. Bazan, John H. Oskam, Hyun Nam Cho, Lee Y. Park, Richard R. Schrock [[J. Am. Chem. Soc.]] '''1991'''; 113(18); 6899-6907. {{DOI|10.1021/ja00018a028}}</ref>. :[[Image:SchrockCatalyst.svg|205px|Commercial Schrock catalyst]] The first asymmetric catalyst followed in 1993 <ref>''Synthesis of chiral molybdenum ROMP initiators and all-cis highly tactic poly(2,3-(R)2norbornadiene) (R = CF3 or CO2Me)'' David H. McConville, Jennifer R. Wolf, Richard R. Schrock [[J. Am. Chem. Soc.]] '''1993'''; 115(10); 4413-4414. {{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. ==References== {{Reflist}} ==Further reading== #{{cite journal | title = Olefin Metathesis: Big-Deal Reaction | journal = [[Chemical & Engineering News]] | 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 | journal = [[Chemical & Engineering News]] | year = 2002 | volume = 80 | issue = 51 | pages = 34–38 | url = http://pubs.acs.org/cen/coverstory/8051/8051olefin2.html}} #{{cite journal |last=Schrock |first=R. R. |authorlink=Richard R. Schrock |year=1990 |title=Living ring-opening metathesis polymerization catalyzed by well-characterized transition-metal alkylidene complexes |journal=[[Accounts of Chemical Research|Acc. Chem. Res.]] |volume=23 |issue=5 |pages=158–165 |doi=10.1021/ar00173a007 }} #{{cite journal |last=Schrock |first=R. R. |authorlink=Richard R. Schrock |coauthors=Hoveyda, A. H. |year=2003 |title=Molybdenum and Tungsten Imido Alkylidene Complexes as Efficient Olefin-Metathesis Catalysts |journal=[[Angewandte Chemie|Angew. Chem. Int. Ed.]] |volume=42 |issue=38 |pages=4592–4633 |doi=10.1002/anie.200300576 }} #{{cite journal |last=Trnka |first=T. M. |coauthors=[[Robert H. Grubbs|Grubbs, R. H.]] |year=2001 |title=The Development of L2X2Ru=CHR Olefin Metathesis Catalysts: An Organometallic Success Story |journal=[[Accounts of Chemical Research|Acc. Chem. Res.]] |volume=34 |issue=1 |pages=18–29 |doi=10.1021/ar000114f }} #{{cite journal |last=Grubbs |first=R. H. |authorlink=Robert H. Grubbs |coauthors=Chang, S. |year=1998 |title=Recent advances in olefin metathesis and its application in organic synthesis |journal=[[Tetrahedron (journal)|Tetrahedron]] |volume=54 |issue=18 |pages=4413–4450 |doi=10.1016/S0040-4020(97)10427-6 }} #{{cite journal |last=Grubbs |first=R. H. |authorlink=Robert H. Grubbs |year=2004 |title=Olefin metathesis |journal=[[Tetrahedron (journal)|Tetrahedron]] |volume=60 |issue=34 |pages=7117–7140 |doi= 10.1016/j.tet.2004.05.124 }} ==See also== * [[Metathesis reaction (chemistry)]] {{Organometallics}} [[Category:Carbon-carbon bond forming reactions]] [[Category:Organometallic chemistry]] [[Category:Homogeneous catalysis]] [[Category:Industrial processes]] [[cs:Metatéze]] [[de:Alkenmetathese]] [[id:Metatesis olefin]] [[ja:メタセシス反応]] [[zh:烯烴複分解反應]]