Olefin metathesis is an
organic reaction that entails the redistribution of fragments of
alkene
In organic chemistry, an alkene is a hydrocarbon containing a carbon–carbon double bond.
Alkene is often used as synonym of olefin, that is, any hydrocarbon containing one or more double bonds.H. Stephen Stoker (2015): General, Organic, an ...
s (olefins) by the scission and regeneration of carbon-carbon
double bonds
In chemistry, a double bond is a covalent bond between two atoms involving four bonding electrons as opposed to two in a single bond. Double bonds occur most commonly between two carbon atoms, for example in alkenes. Many double bonds exist betw ...
.
[ 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
Yves Chauvin (; 10 October 1930 – 27 January 2015) 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 ...
, Robert H. Grubbs
Robert Howard Grubbs ForMemRS (February 27, 1942 – December 19, 2021) 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 ...
, and Richard R. Schrock were collectively awarded the 2005 Nobel Prize in Chemistry
)
, image = Nobel Prize.png
, alt = A golden medallion with an embossed image of a bearded man facing left in profile. To the left of the man is the text "ALFR•" then "NOBEL", and on the right, the text (smaller) "NAT•" then "M ...
.
Catalysts
The reaction requires metal catalysts. Most commercially important processes employ heterogeneous catalysts
In chemistry, heterogeneous catalysis is catalysis where the phase of catalysts differs from that of the reactants or products. The process contrasts with homogeneous catalysis where the reactants, products and catalyst exist in the same phase. P ...
. The heterogeneous catalysts are often prepared by in-situ activation of a metal halides (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
Organometallic chemistry is the study of organometallic compounds, chemical compounds containing at least one chemical bond between a carbon atom of an organic molecule and a metal, including alkali, alkaline earth, and transition metals, and so ...
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
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 been develo ...
s. Schrock catalysts feature molybdenum(VI)- and tungsten(VI)-based centers supported by alkoxide and imido ligands.
Grubbs catalysts, on the other hand, are ruthenium(II) carbenoid complexes. Many variations of Grubbs catalysts are known. Some have been modified with a chelating
Chelation is a type of bonding of ions and molecules to metal ions. It involves the formation or presence of two or more separate coordinate bonds between a polydentate (multiple bonded) ligand and a single central metal atom. These ligands are ...
isopropoxybenzylidene ligand
In coordination chemistry, a ligand is an ion or molecule (functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's electr ...
to form the related Hoveyda–Grubbs catalyst
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 been develo ...
.
Applications
Olefin metathesis has several industrial applications. Almost all commercial applications employ heterogeneous catalyst
In chemistry, heterogeneous catalysis is catalysis where the phase of catalysts differs from that of the reactants or products. The process contrasts with homogeneous catalysis where the reactants, products and catalyst exist in the same phase. P ...
s using catalysts developed well before the Nobel-Prize winning work on homogeneous complexes. Representative processes include:[
*The Phillips Triolefin and the ]Olefin conversion technology 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 di ...
. 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.
*Shell higher olefin process
The Shell higher olefin process (SHOP) is a chemical process for the production of linear alpha olefins via ethylene oligomerization and olefin metathesis invented and exploited by Royal Dutch Shell.''Industrial Organic Chemistry'', Klaus Weisserm ...
(SHOP) produces (alpha-olefins
In organic chemistry, alpha-olefins (or α-olefins) are a family of organic compounds which are alkenes (also known as olefins) with a chemical formula , distinguished by having a double bond at the primary or alpha (α) position.''Petrochemical ...
) for conversion to detergents. The process recycles certain olefin fractions using metathesis.
*Neohexene
Neohexene is the hydrocarbon compound with the chemical formula . It is a colorless liquid, with properties similar to other hexenes. It is a precursor to commercial synthetic musk perfumes.
Preparation and reactions
Neohexene is prepared by ...
production, which involves ethenolysis of isobutene dimers. The catalyst is derived from tungsten trioxide
Tungsten(VI) oxide, also known as tungsten trioxide is a chemical compound of oxygen and the transition metal tungsten, with formula WO3. The compound is also called tungstic anhydride, reflecting its relation to tungstic acid . It is a light ...
supported on silica
Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is ...
and MgO.
* 1,5-Hexadiene and 1,9-decadiene, useful crosslinking agents and synthetic intermediates, are produced commercially by ethenolysis of 1,5-cyclooctadiene
Cycloocta-1,5-diene is a cyclic hydrocarbon with the chemical formula , specifically .
There are three configurational isomers with this structure, that differ by the arrangement of the four C–C single bonds adjacent to the double bonds. Each ...
and cyclooctene Cyclooctene is the cycloalkene with a formula . Its molecule has a ring of 8 carbon atoms, connected by seven single bonds and one double bond.
Cyclooctene is notable because it is the smallest cycloalkene that can exist stably as either the cisâ ...
. The catalyst is derived from Re2O7 on alumina.
*Synthesis of pharmaceutical drug
A medication (also called medicament, medicine, pharmaceutical drug, medicinal drug or simply drug) is a drug used to diagnose, cure, treat, or prevent disease. Drug therapy (pharmacotherapy) is an important part of the medical field and re ...
s,
Homogeneous catalyst potential
Molecular catalysts have been explored for the preparation of a variety of potential applications. the manufacturing of high-strength materials, the preparation of cancer-targeting nanoparticle
A nanoparticle or ultrafine particle is usually defined as a particle of matter that is between 1 and 100 nanometres (nm) in diameter. The term is sometimes used for larger particles, up to 500 nm, or fibers and tubes that are less than 1 ...
s, and the conversion of renewable plant-based feedstocks into hair and skin care products.
Types
Some important classes of olefin metathesis include:
* Cross metathesis (CM)
* Ring-opening metathesis (ROM)
*Ring-closing metathesis
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-' ...
(RCM)
* Ring-opening metathesis polymerization (ROMP)
*Acyclic diene metathesis Acyclic diene metathesis or ADMET (distinguish from ADME) is a special type of olefin metathesis used to polymerize terminal dienes to polyenes:
The new double bonds formed can be in cis- or trans-configurations. The exact ratio depends on th ...
(ADMET)
*Ethenolysis
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 ...
Mechanism
Hérisson and Chauvin first proposed the widely accepted mechanism of transition metal alkene metathesis. The direct +2cycloaddition of two alkenes is formally symmetry forbidden and thus has a high activation energy
In chemistry and physics, activation energy is the minimum amount of energy that must be provided for compounds to result in a chemical reaction. The activation energy (''E''a) of a reaction is measured in joules per mole (J/mol), kilojoules pe ...
. The Chauvin mechanism involves the +2cycloaddition 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 involves little change in enthalpy for unstrained alkenes. Product distributions are determined instead by le Chatelier's Principle
Le Chatelier's principle (pronounced or ), also called Chatelier's principle (or the Equilibrium Law), is a principle of chemistry used to predict the effect of a change in conditions on chemical equilibria. The principle is named after French c ...
, i.e. entropy
Entropy is a scientific concept, as well as a measurable physical property, that is most commonly associated with a state of disorder, randomness, or uncertainty. The term and the concept are used in diverse fields, from classical thermodynam ...
.
Cross metathesis and ring-closing metathesis are driven by the entropically favored evolution of ethylene
Ethylene (IUPAC name: ethene) is a hydrocarbon which has the formula or . It is a colourless, flammable gas with a faint "sweet and musky" odour when pure. It is the simplest alkene (a hydrocarbon with carbon-carbon double bonds).
Ethylene i ...
or propylene
Propylene, also known as propene, is an unsaturated organic compound with the chemical formula CH3CH=CH2. It has one double bond, and is the second simplest member of the alkene class of hydrocarbons. It is a colorless gas with a faint petro ...
, which can be removed from the system because they are gases. Because of this CM and RCM reactions often use alpha-olefins
In organic chemistry, alpha-olefins (or α-olefins) are a family of organic compounds which are alkenes (also known as olefins) with a chemical formula , distinguished by having a double bond at the primary or alpha (α) position.''Petrochemical ...
. The reverse reaction of CM of two alpha-olefins, ethenolysis
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 ...
, 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
Styrene () is an organic compound with the chemical formula C6H5CH=CH2. This derivative of benzene is a colorless oily liquid, although aged samples can appear yellowish. The compound evaporates easily and has a sweet smell, although high concen ...
. 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. The same substrates that undergo RCM can undergo acyclic diene metathesis, with ADMET favored at high concentrations. The Thorpe–Ingold effect The Thorpe–Ingold effect, gem-dimethyl effect, or angle compression is an effect observed in chemistry where increasing steric hindrance favours ring closure and intramolecular reactions. The effect was first reported by Beesley, Thorpe, and In ...
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
In organic chemistry, ozonolysis is an organic reaction where the unsaturated bonds of alkenes (), alkynes (), or azo compounds () are cleaved with ozone (). Alkenes and alkynes form organic compounds in which the multiple carbon–carbon b ...
of an alkene to two ketone fragments followed by the reaction of one of them with a Wittig reagent In organic chemistry, Wittig reagents are organophosphorus compounds of the formula R3P=CHR', where R is usually phenyl. They are used to convert ketones and aldehydes to alkenes:
:
Preparation
Because they typically hydrolyze and oxidize readily ...
.
Historical overview
"Olefin metathesis is a child of industry and, as with many catalytic processes, it was discovered by accident."
As part of ongoing work in what would later become known as Ziegler–Natta catalysis Karl Ziegler discovered the conversion of ethylene
Ethylene (IUPAC name: ethene) is a hydrocarbon which has the formula or . It is a colourless, flammable gas with a faint "sweet and musky" odour when pure. It is the simplest alkene (a hydrocarbon with carbon-carbon double bonds).
Ethylene i ...
into 1-butene instead of a saturated long-chain hydrocarbon (see nickel effect).
In 1960 a Du Pont research group polymerized norbornene to polynorbornene
Norbornene or norbornylene or norcamphene is a highly strained bridged cyclic hydrocarbon. It is a white solid with a pungent sour odor. The molecule consists of a cyclohexene ring with a methylene bridge between carbons 1 and 4. The molecule carr ...
using ''lithium aluminum tetraheptyl'' and titanium tetrachloride
Titanium tetrachloride is the inorganic compound with the formula . It is an important intermediate in the production of titanium metal and the pigment titanium dioxide. is a volatile liquid. Upon contact with humid air, it forms thick clouds ...
(a patent by this company on this topic dates back to 1955),
:
a reaction then classified as a so-called coordination polymerization Coordination polymerisation is a form of polymerization that is catalyzed by transition metal salts and complexes.
Types of coordination polymerization of alkenes Heterogeneous Ziegler–Natta polymerization
Coordination polymerization started in t ...
. According to the then proposed reaction mechanism a RTiX titanium intermediate first coordinates to the double bond in a pi complex
The number (; spelled out as "pi") is a mathematical constant that is the ratio of a circle's circumference to its diameter, approximately equal to 3.14159. The number appears in many formulas across mathematics and physics. It is an irratio ...
. The second step then is a concerted SNi reaction SNI may refer to:
Science and technology
* Substitution nucleophilic internal, a chemistry reaction mechanism
* Swedish Standard Industrial Classification, a Swedish economic classification system
* Server Name Indication, an extension to the TL ...
breaking a CC bond and forming a new alkylidene-titanium bond; the process then repeats itself with a second monomer:
:
Only much later the polynorbornene was going to be produced through ring opening metathesis polymerisation
Ring-opening metathesis polymerization (ROMP) is a type of olefin metathesis chain-growth polymerization. The driving force of the reaction is relief of ring strain in cyclic olefins (e.g. norbornene or cyclopentene). A variety of heterogeneo ...
. The DuPont work was led by Herbert S. Eleuterio. Giulio Natta
Giulio Natta (26 February 1903 – 2 May 1979) was an Italian chemical engineer and Nobel laureate. He won a Nobel Prize in Chemistry in 1963 with Karl Ziegler for work on high polymers. He also received a Lomonosov Gold Medal in 1969.
Biograph ...
in 1964 also observed the formation of an unsaturated polymer when polymerizing cyclopentene
Cyclopentene is a chemical compound with the formula . It is a colorless liquid with a petrol-like odor. It has few applications, and thus is mainly used as a minor component of gasoline, present in concentrations of less than 1%. It is one of t ...
with tungsten and molybdenum halides.
In a third development leading up to olefin metathesis, researchers at Phillips Petroleum Company
Phillips Petroleum Company was an American oil company incorporated in 1917 that expanded into petroleum refining, marketing and transportation, natural gas gathering and the chemicals sectors. It was Phillips Petroleum that first found oil in the ...
in 1964 described olefin disproportionation
In chemistry, disproportionation, sometimes called dismutation, is a redox reaction in which one compound of intermediate oxidation state converts to two compounds, one of higher and one of lower oxidation states. More generally, the term can ...
with catalyst
Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...
s molybdenum hexacarbonyl
Molybdenum hexacarbonyl (also called molybdenum carbonyl) is the chemical compound with the formula Mo(CO)6. This colorless solid, like its chromium and tungsten analogues, is noteworthy as a volatile, air-stable derivative of a metal in its zero ...
, tungsten hexacarbonyl
Tungsten hexacarbonyl (also called tungsten carbonyl) is the chemical compound with the formula W(CO)6. This complex gave rise to the first example of a dihydrogen complex.Kubas, G. J., Metal Dihydrogen and σ-Bond Complexes, Kluwer Academic/Plenu ...
, and molybdenum oxide Molybdenum oxide may refer to:
* Molybdenum(IV) oxide (molybdenum dioxide, )
* Molybdenum(VI) oxide
Molybdenum trioxide describes a family of inorganic compounds with the formula MoO3(H2O)n where n = 0, 1, 2. These compounds are produced on the ...
supported on alumina for example converting propylene
Propylene, also known as propene, is an unsaturated organic compound with the chemical formula CH3CH=CH2. It has one double bond, and is the second simplest member of the alkene class of hydrocarbons. It is a colorless gas with a faint petro ...
to an equal mixture of ethylene
Ethylene (IUPAC name: ethene) is a hydrocarbon which has the formula or . It is a colourless, flammable gas with a faint "sweet and musky" odour when pure. It is the simplest alkene (a hydrocarbon with carbon-carbon double bonds).
Ethylene i ...
and 2-butene for which they proposed a reaction mechanism involving a cyclobutane
Cyclobutane is a cycloalkane and organic compound with the formula (CH2)4. Cyclobutane is a colourless gas and commercially available as a liquefied gas. Derivatives of cyclobutane are called cyclobutanes. Cyclobutane itself is of no commercial ...
(they called it a quasicyclobutane) – metal complex:
:
This particular mechanism is symmetry forbidden based on the Woodward–Hoffmann rules The Woodward–Hoffmann rules (or the pericyclic selection rules), devised by Robert Burns Woodward and Roald Hoffmann, are a set of rules used to rationalize or predict certain aspects of the stereochemistry and activation energy of pericyclic rea ...
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
The Goodyear Tire & Rubber Company is an American multinational tire manufacturing company founded in 1898 by Frank Seiberling and based in Akron, Ohio. Goodyear manufactures tires for automobiles, commercial trucks, light trucks, motorcycles, S ...
described a novel catalyst system for the metathesis of 2-pentene based on tungsten hexachloride
Tungsten hexachloride is the chemical compound of tungsten and chlorine with the formula WCl6. This dark violet blue species exists as a volatile solid under standard conditions. It is an important starting reagent in the preparation of tungsten ...
, ethanol
Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an Alcohol (chemistry), alcohol with the chemical formula . Its formula can be also written as or (an ethyl ...
, and the organoaluminum
Organoaluminium chemistry is the study of compounds containing bonds between carbon and aluminium. It is one of the major themes within organometallic chemistry. Illustrative organoaluminium compounds are the dimer trimethylaluminium, the monome ...
compound EtAlMe2. The researchers proposed a name for this reaction type: olefin metathesis. Formerly the reaction had been called "olefin disproportionation."
:
In this reaction 2-pentene forms a rapid (a matter of seconds) chemical equilibrium
In a chemical reaction, chemical equilibrium is the state in which both the Reagent, reactants and Product (chemistry), products are present in concentrations which have no further tendency to change with time, so that there is no observable chan ...
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
Methanol (also called methyl alcohol and wood spirit, amongst other names) is an organic chemical and the simplest aliphatic alcohol, with the formula C H3 O H (a methyl group linked to a hydroxyl group, often abbreviated as MeOH). It is a ...
.
The Goodyear group demonstrated that the reaction of regular 2-butene with its all-deuterated
Isotopic labeling (or isotopic labelling) is a technique used to track the passage of an isotope (an atom with a detectable variation in neutron count) through a reaction, metabolic pathway, or cell. The reactant is 'labeled' by replacing specific ...
isotopologue
In chemistry, isotopologues are molecules that differ only in their isotopic composition. They have the same chemical formula and bonding arrangement of atoms, but at least one atom has a different number of neutrons than the parent.
An exampl ...
yielded C4H4D4 with deuterium evenly distributed. In this way they were able to differentiate between a transalkylidenation mechanism and a transalkylation
In organic chemistry, transalkylation is a chemical reaction involving the transfer of an alkyl group from one organic compound to another. The reaction is used for the transfer of methyl and ethyl groups between benzene rings. This is of particul ...
mechanism (ruled out):
:
In 1971 Chauvin proposed a four-membered metallacycle
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 ...
intermediate to explain the statistical distribution of products found in certain metathesis reactions. This mechanism is today considered the actual mechanism taking place in olefin metathesis.
:
Chauvin's experimental evidence was based on the reaction of cyclopentene
Cyclopentene is a chemical compound with the formula . It is a colorless liquid with a petrol-like odor. It has few applications, and thus is mainly used as a minor component of gasoline, present in concentrations of less than 1%. It is one of t ...
and 2-pentene with the homogeneous catalyst
In chemistry, homogeneous catalysis is catalysis by a soluble catalyst in a solution. Homogeneous catalysis refers to reactions where the catalyst is in the same phase as the reactants, principally in solution. In contrast, heterogeneous catalysis ...
tungsten(VI) oxytetrachloride
Tungsten(VI) oxytetrachloride is the inorganic compound with the formula W O Cl4. This diamagnetic solid is used to prepare other complexes of tungsten. The yellow-green compound is soluble in nonpolar solvents but it reacts with alcohols an ...
and tetrabutyltin:
:
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
Propylene, also known as propene, is an unsaturated organic compound with the chemical formula CH3CH=CH2. It has one double bond, and is the second simplest member of the alkene class of hydrocarbons. It is a colorless gas with a faint petro ...
(C3) forms in a reaction of 2-butene (C4) with tungsten hexachloride
Tungsten hexachloride is the chemical compound of tungsten and chlorine with the formula WCl6. This dark violet blue species exists as a volatile solid under standard conditions. It is an important starting reagent in the preparation of tungsten ...
and tetramethyltin (C1).
In the same year Pettit who synthesised cyclobutadiene
Cyclobutadiene is an organic compound with the formula . It is very reactive owing to its tendency to dimerize. Although the parent compound has not been isolated, some substituted derivatives are robust and a single molecule of cyclobutadiene is ...
a few years earlier independently came up with a competing mechanism. It consisted of a tetramethylene intermediate with sp3 hybridized carbon atoms linked to a central metal atom with multiple three-center two-electron bond
A three-center two-electron (3c–2e) bond is an electron-deficient chemical bond where three atoms share two electrons. The combination of three atomic orbitals form three molecular orbitals: one bonding, one ''non''-bonding, and one ''anti''-b ...
s.
:
Experimental support offered by Pettit for this mechanism was based on an observed reaction inhibition by carbon monoxide
Carbon monoxide (chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simple ...
in certain metathesis reactions of 4-nonene with a tungsten metal carbonyl
Metal carbonyls are coordination complexes of transition metals with carbon monoxide ligands. Metal carbonyls are useful in organic synthesis and as catalysts or catalyst precursors in homogeneous catalysis, such as hydroformylation and Reppe c ...
Robert H. Grubbs
Robert Howard Grubbs ForMemRS (February 27, 1942 – December 19, 2021) 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 ...
got involved in metathesis in 1972 and also proposed a metallacycle intermediate but one with four carbon atoms in the ring. 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:
:
In 1973 Grubbs found further evidence for this mechanism by isolating one such metallacycle not with tungsten but with platinum
Platinum is a chemical element with the symbol Pt and atomic number 78. It is a dense, malleable, ductile, highly unreactive, precious, silverish-white transition metal. Its name originates from Spanish , a diminutive of "silver".
Platinu ...
by reaction of the dilithiobutane with ''cis-bis(triphenylphosphine)dichloroplatinum(II)''
In 1975 Katz also arrived at a metallacyclobutane intermediate consistent with the one proposed by Chauvin He reacted a mixture of cyclooctene Cyclooctene is the cycloalkene with a formula . Its molecule has a ring of 8 carbon atoms, connected by seven single bonds and one double bond.
Cyclooctene is notable because it is the smallest cycloalkene that can exist stably as either the cisâ ...
, 2-butene and 4-octene with a molybdenum
Molybdenum is a chemical element with the symbol Mo and atomic number 42 which is located in period 5 and group 6. The name is from Neo-Latin ''molybdaenum'', which is based on Ancient Greek ', meaning lead, since its ores were confused with lea ...
catalyst and observed that the unsymmetrical C14 hydrocarbon reaction product is present right from the start at low conversion.
:
In any of the pairwise mechanisms with olefin pairing as rate-determining step
In chemical kinetics, the overall rate of a reaction is often approximately determined by the slowest step, known as the rate-determining step (RDS or RD-step or r/d step) or rate-limiting step. For a given reaction mechanism, the prediction of the ...
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:
:
Grubbs in 1976 provided evidence against his own updated pairwise mechanism:
:
with a 5-membered cycle in another round of isotope labeling studies in favor of the 4-membered cycle Chauvin mechanism:
:
In this reaction the ethylene
Ethylene (IUPAC name: ethene) is a hydrocarbon which has the formula or . It is a colourless, flammable gas with a faint "sweet and musky" odour when pure. It is the simplest alkene (a hydrocarbon with carbon-carbon double bonds).
Ethylene i ...
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
Tebbe's reagent is the organometallic compound with the formula (C5H5)2TiCH2ClAl(CH3)2. It is used in the methylenation of carbonyl compounds, that is it converts organic compounds containing the R2C=O group into the related R2C=CH2 derivative. It ...
. In a model reaction isotopically labeled carbon atoms in isobutene
Isobutylene (or 2-methylpropene) is a hydrocarbon with the chemical formula . It is a four-carbon branched alkene (olefin), one of the four isomers of butylene. It is a colorless flammable gas, and is of considerable industrial value.
Productio ...
and methylenecyclohexane
Methylenecyclohexane (IUPAC name: methylidenecyclohexane) is an organic compound with the molecular formula C7H12.
Synthesis
It can be produced by a Wittig reaction or a reaction with a Tebbe's reagent from cyclohexanone. It can also be synth ...
switched places:
:
The Grubbs group then isolated the proposed metallacyclobutane intermediate in 1980 also with this reagent together with 3-methyl-1-butene:
:
They isolated a similar compound in the total synthesis
Total synthesis is the complete chemical synthesis of a complex molecule, often a natural product, from simple, commercially-available precursors. It usually refers to a process not involving the aid of biological processes, which distinguishes ...
of capnellene in 1986:
:
In that same year the Grubbs group proved that metathesis polymerization of norbornene by Tebbe's reagent is a living polymerization
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 ...
system and a year later Grubbs and Schrock co-published an article describing living polymerization with a tungsten
Tungsten, or wolfram, is a chemical element with the symbol W and atomic number 74. Tungsten is a rare metal found naturally on Earth almost exclusively as compounds with other elements. It was identified as a new element in 1781 and first isol ...
carbene complex 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
In organic chemistry, a functional group is a substituent or moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions regardless of the rest ...
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. This prompted Robert H. Grubbs
Robert Howard Grubbs ForMemRS (February 27, 1942 – December 19, 2021) 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 ...
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
Ruthenium(III) chloride is the chemical compound with the formula RuCl3. "Ruthenium(III) chloride" more commonly refers to the hydrate RuCl3·''x''H2O. Both the anhydrous and hydrated species are dark brown or black solids. The hydrate, with a va ...
, osmium trichloride as well as tungsten alkylidenes. 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:
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The corresponding tricyclohexylphosphine
Tricyclohexylphosphine is the tertiary phosphine with the formula P( C6H11)3. Commonly used as a ligand in organometallic chemistry, it is often abbreviated to PCy3, where Cy stands for cyclohexyl. It is characterized by both high basicity (p''K'' ...
complex (PCy3)2Cl2Ru=CHCH=CPh2 was also shown to be active. This work culminated in the now commercially available 1st generation Grubbs catalyst
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 been develo ...
.
Schrock catalysts
Schrock entered the olefin metathesis field in 1979 as an extension of work on tantalum
Tantalum is a chemical element with the symbol Ta and atomic number 73. Previously known as ''tantalium'', it is named after Tantalus, a villain in Greek mythology. Tantalum is a very hard, ductile, lustrous, blue-gray transition metal that is ...
alkylidenes. The initial result was disappointing as reaction of with ethylene
Ethylene (IUPAC name: ethene) is a hydrocarbon which has the formula or . It is a colourless, flammable gas with a faint "sweet and musky" odour when pure. It is the simplest alkene (a hydrocarbon with carbon-carbon double bonds).
Ethylene i ...
yielded only a metallacyclopentane, not metathesis products:
:
But by tweaking this structure to a (replacing chloride
The chloride ion is the anion (negatively charged ion) Cl−. It is formed when the element chlorine (a halogen) gains an electron or when a compound such as hydrogen chloride is dissolved in water or other polar solvents. Chloride salts ...
by t-butoxide and a cyclopentadienyl by an organophosphine Organophosphines are organophosphorus compounds with the formula PR''n''H3−''n'', where R is an organic substituent. These compounds can be classified according to the value of ''n'': primary phosphines (''n'' = 1), secondary phosphine ...
, metathesis was established with cis-2-pentene. In another development, certain tungsten oxo complexes of the type were also found to be effective.
Schrock alkylidenes for olefin metathesis of the type were commercialized starting in 1990.
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The first asymmetric catalyst followed in 1993
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With a Schrock catalyst modified with a BINOL ligand in a norbornadiene
Norbornadiene is an organic compound and a bicyclic hydrocarbon. Norbornadiene is of interest as a metal-binding ligand, whose complexes are useful for homogeneous catalysis. It has been intensively studied owing to its high reactivity and distin ...
ROMP Romp or ROMP may refer to:
* IBM ROMP
The ROMP is a reduced instruction set computer (RISC) microprocessor designed by IBM in the late 1970s. It is also known as the Research OPD Miniprocessor (after the two IBM divisions that collaborated on i ...
leading to highly stereoregular cis, isotactic
Tacticity (from el, τακτικός, taktikos, "relating to arrangement or order") is the relative stereochemistry of adjacent chiral centers within a macromolecule. The practical significance of tacticity rests on the effects on the physical p ...
polymer.
See also
* Alkane metathesis
* Alkyne metathesis
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. T ...
* Enyne metathesis
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.
The general scheme is given by ''scheme 1'':
:
When the ...
* Salt metathesis reaction
A salt metathesis reaction, sometimes called a double displacement reaction, is a chemical process involving the exchange of bonds between two reacting chemical species which results in the creation of products with similar or identical bonding a ...
References
Further reading
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{{Organic reactions
Carbon-carbon bond forming reactions
Organometallic chemistry
Homogeneous catalysis
Industrial processes