Organocopper compounds in
organometallic chemistryOrganometallic chemistry is the study of chemical compounds containing bonds between carbon and a metal. Since many compounds without such bonds are chemically similar, an alternative may be compounds containing metal-element bonds of a largely covalent character...
contain
carbonCarbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
to
copperCopper is a chemical element with the symbol Cu and atomic number 29.It is a ductile metal with very high thermal and electrical conductivity. Pure copper is rather soft and malleable and a freshly-exposed surface has a pinkish or peachy color...
chemical bondA chemical bond is an interaction between atoms or molecules and allows the formation of polyatomic chemical compounds. A chemical bond is the attraction caused by the electromagnetic force between opposing charges, either between electrons and nuclei, or as the result of a dipole attraction...
s.
Organocopper chemistry is the science of organocopper compounds describing their physical properties, synthesis and reactions. They are reagents in
organic chemistryOrganic chemistry is a discipline within chemistry which involves the scientific study of the structure, properties, composition, reactions, and preparation of chemical compounds that contain carbon...
.
The first organocopper compound, the explosive
copper(I) acetylideCopper acetylide, or cuprous acetylide, is an inorganic chemical compound with the formula Cu
2C
2. It is a heat and shock sensitive high explosive, more sensitive than silver acetylide. It is a metal acetylide...
Cu
2C
2 was synthesized by Bottger in 1859.
Henry GilmanHenry Gilman was an American organic chemist known as the father of organometallic chemistry, the field within which his most notable work was done. He discovered the Gilman reagent, which bears his name....
prepared methylcopper in 1936. In 1941 Kharash discovered that reaction of a Grignard reagent with cyclohexenone in presence of Cu(I) resulted in 1,4-addition instead of 1,2-addition.
Organocopper compounds in
organometallic chemistryOrganometallic chemistry is the study of chemical compounds containing bonds between carbon and a metal. Since many compounds without such bonds are chemically similar, an alternative may be compounds containing metal-element bonds of a largely covalent character...
contain
carbonCarbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
to
copperCopper is a chemical element with the symbol Cu and atomic number 29.It is a ductile metal with very high thermal and electrical conductivity. Pure copper is rather soft and malleable and a freshly-exposed surface has a pinkish or peachy color...
chemical bondA chemical bond is an interaction between atoms or molecules and allows the formation of polyatomic chemical compounds. A chemical bond is the attraction caused by the electromagnetic force between opposing charges, either between electrons and nuclei, or as the result of a dipole attraction...
s.
Organocopper chemistry is the science of organocopper compounds describing their physical properties, synthesis and reactions. They are reagents in
organic chemistryOrganic chemistry is a discipline within chemistry which involves the scientific study of the structure, properties, composition, reactions, and preparation of chemical compounds that contain carbon...
.
Brief history
The first organocopper compound, the explosive
copper(I) acetylideCopper acetylide, or cuprous acetylide, is an inorganic chemical compound with the formula Cu
2C
2. It is a heat and shock sensitive high explosive, more sensitive than silver acetylide. It is a metal acetylide...
Cu
2C
2 was synthesized by Bottger in 1859.
Henry GilmanHenry Gilman was an American organic chemist known as the father of organometallic chemistry, the field within which his most notable work was done. He discovered the Gilman reagent, which bears his name....
prepared methylcopper in 1936. In 1941 Kharash discovered that reaction of a Grignard reagent with cyclohexenone in presence of Cu(I) resulted in 1,4-addition instead of 1,2-addition. In 1952 Gilman investigated for the first time dialkylcuprates.
Properties
Organocopper compounds are very reactive towards oxygen and water forming
copper(I) oxideCopper oxide or cuprous oxide is an oxide of copper. It is insoluble in water and organic solvents. Copper oxide dissolves in concentrated ammonia solution to form the colorless complex [Cu2]+, which easily oxidizes in air to the blue [Cu42]2+...
, tend to be thermally unstable and are generally insoluble in inert solvents. They are therefore difficult to handle and of little practical value. On the other hand organocopper reagents are used very frequently in
organic chemistryOrganic chemistry is a discipline within chemistry which involves the scientific study of the structure, properties, composition, reactions, and preparation of chemical compounds that contain carbon...
as alkylating reagents prepared
in situIn situ is a Latin phrase meaning in the place. It is used in many different contexts.-Aerospace:In the aerospace industry, equipment on board aircraft must be tested in situ, or in place, to confirm everything functions properly as a system. Individually, each piece may work but interference from...
in an inert environment with in general more
functional groupIn organic chemistry, functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. The same functional group will undergo the same or similar chemical reaction regardless of the size of the molecule it is a part...
tolerance than corresponding Grignards or organolithium reagents. The
electronegativityElectronegativity, symbol χ, is a chemical property that describes the ability of an atom to attract electrons towards itself in a covalent bond. An atom's electronegativity is affected by both its atomic weight and the distance that its valence electrons reside from the charged nucleus...
of copper is much higher than its next-door neighbour in the
group 12 elementA group 12 element is one of the elements in group 12 in the periodic table, consisting of zinc , cadmium and mercury . The inclusion of ununbium in group 12 is conjectural as sufficient quantity of that element has not been prepared to allow its chemistry to be evaluated.All elements in this...
s,
zincZinc , also known as spelter, is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...
, suggesting less nucleophilicity for carbon.
Copper belongs to the group of coinage metals together with silver and gold and their chemistries have many similarities. The
oxidation stateIn chemistry, the oxidation state is an indicator of the degree of oxidation of an atom in a chemical compound. The formal oxidation state is the hypothetical charge that an atom would have if all bonds to atoms of different elements were 100% ionic. Oxidation states are typically represented by...
can be +1 or +2 and intermediates can have oxidation state +3. Monovalent alkylcopper compounds (R-Cu) form divalent
cuprateCuprates are chemical compounds containing copper oxide. From 1986 to 2008 almost all known high temperature superconductors were cuprate superconductors....
s R
2CuLi with organolithium compounds (R-Li) now known as
Gilman reagentA Gilman reagent is a lithium and copper reagent compound, R2CuLi, where R is an organic radical. These are useful because they react with chlorides, bromides, and iodides to replace the halide group with an R group. This is extremely useful in creating larger molecules from smaller...
s. Organocopper compounds can be stabilized with organophosphanes (R
3P).
The cuprates have complex aggregation states in crystalline form and in solution. Lithium dimethylcuprate is a dimer in
diethyl etherDiethyl ether, also known as ether, ethyl ether and ethoxyethane, is a clear, colorless, and highly flammable liquid with a low boiling point and a characteristic odor. It is the most common member of a class of chemical compounds known generically as ethers. It is an isomer of butanol...
forming an 8-membered ring with two lithium atoms coordinating between two methyl groups. Similarly, lithium diphenylcuprate forms a dimeric etherate, [{Li(OEt
2)}(CuPh
2)]
2, in the solid state.
The first ever crystal structure was determined in 1972 by Lappert for CuCH
2SiMe
3. This compound is relatively stable because the bulky
trimethylsilylA trimethylsilyl group is a functional group in organic chemistry. This group consists of three methyl groups bonded to a silicon atom [−Si
3], which is in turn bonded to the rest of a molecule...
groups provide steric protection. It is a tetramer forming an 8-membered ring with alternating Cu-C bonds. In addition the four copper atoms form a planar Cu
4 ring based on
three-center two-electron bondA three-center two-electron 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-bonding. The two electrons go into the bonding orbital, resulting in a...
s. The copper to copper
bond lengthIn molecular geometry, bond length or bond distance is the average distance between nuclei of two bonded atoms in a molecule.- Explanation :...
is 242 pm compared to 256 pm in bulk copper. In
pentamesitylpentacopper a 5-membered copper ring is formed and
pentafluorophenylcopper is a tetramer.
With
carbon monoxideCarbon monoxide is a colorless, odorless and tasteless gas, yet very toxic to humans. It consists of one carbon atom and one oxygen atom, connected by a covalent double bond and a dative covalent bond...
copper forms a non-classical metal carbonyl.
Cu(III) intermediates
In many organometallic reactions involving copper, the
reaction mechanismIn chemistry, a reaction mechanism is the step by step sequence of elementary reactions by which overall chemical change occurs .Although only the net chemical change is directly observable for most chemical reactions, experiments can often be designed that suggest the possible sequence of steps in...
invokes a copper intermediate with
oxidation stateIn chemistry, the oxidation state is an indicator of the degree of oxidation of an atom in a chemical compound. The formal oxidation state is the hypothetical charge that an atom would have if all bonds to atoms of different elements were 100% ionic. Oxidation states are typically represented by...
+3. For instance, in reductive elimination processes, Cu(III) is reduced to Cu(I). However Cu(III) compounds are rare in chemistry in general and until recently organocopper(III) species have been elusive. In 2007 the first spectroscopic evidence was obtained for the involvement of Cu(III) in the conjugate addition of the
Gilman reagentA Gilman reagent is a lithium and copper reagent compound, R2CuLi, where R is an organic radical. These are useful because they react with chlorides, bromides, and iodides to replace the halide group with an R group. This is extremely useful in creating larger molecules from smaller...
to an
enoneAn enone is an unsaturated chemical compound or functional group consisting of a conjugated system of an alkene and a ketone. The simplest enone is methyl vinyl ketone or CH2=CHCOCH3....
:
In a so-called rapid-injection
NMRNuclear magnetic resonance spectroscopy, most commonly known as NMR spectroscopy, is the name given to a technique which exploits the magnetic properties of certain nuclei. This phenomenon and its origins are detailed in a separate section on nuclear magnetic resonance. The most important...
experiment at -100°C, the Gilman reagent Me
2CuLi (stabilized by
lithium iodideLithium iodide, or LiI, is a compound of lithium and iodine. When exposed to air, it becomes yellow in color, due to the oxidation of iodide to iodine.-Applications:...
) was introduced to
cyclohexenoneCyclohexenone is an organic compound which is a versatile intermediate used in the synthesis of a variety of chemical products such as pharmaceuticals and fragrances...
(
1) enabling the detection of the copper — alkene pi complex
2. On subsequent addition of
trimethylsilyl cyanideTrimethylsilyl cyanide is the chemical compound with the formula 3SiCN. This volatile liquid consists of a cyanide group, that is CN, attached to a trimethylsilyl group. The molecule is used in organic synthesis as the equivalent of hydrogen cyanide...
the Cu(III) species
3 is formed (indefinitely stable at that temperature) and on increasing the temperature to -80°C the conjugate addition product
4. According to an accompanying
in silicoIn silico is an expression used to mean "performed on computer or via computer simulation." The phrase is coined in analogy to the Latin phrases in vivo and in vitro which are commonly used in biology and refer to experiments done in living organisms and outside of living organisms, respectively...
experiments the Cu(III) intermediate has a square planar molecular geometry with the cyano group in cis orientation with respect to the cyclohexenyl
methineIn chemistry, methine is a tri-valent functional group CH, derived formally from methane. The methine group consists of a carbon atom bound by two single bonds and one double bond, where one of the single bonds is to a hydrogen...
group and anti-parallel to the methine proton. With other ligands than the cyano group this study predicts
room temperatureRoom temperature is a common term to denote a certain temperature within enclosed space at which humans are accustomed. Room temperature is thus often indicated by general human comfort, with the common range of 68°F to 77°F , though climate may acclimatize people to higher or lower...
stable Cu(III) compounds.
Synthesis
- Copper halides react with organolithium reagent
An organolithium reagent is an organometallic compound with a direct bond between a carbon and a lithium atom. As the electropositive nature of lithium puts most of the charge density of the bond on the carbon atom, effectively creating a carbanion, organolithium compounds are extremely powerful...
s to form the organocopper compound. Phenyl copper is prepared by reaction of phenyllithium with copper(I) bromideCopper bromide is the chemical compound with the formula CuBr. This diamagnetic solid adopts a polymeric structure akin to that for zinc sulfide. The compound is widely used in the synthesis of organic compounds....
in diethyl etherDiethyl ether, also known as ether, ethyl ether and ethoxyethane, is a clear, colorless, and highly flammable liquid with a low boiling point and a characteristic odor. It is the most common member of a class of chemical compounds known generically as ethers. It is an isomer of butanol...
.
- Reaction with a second equivalent of R-Li to R-Cu gives the lithium diorganocopper compound.
- Copper halides also react with Grignard reagents. The compound pentamesitylpentacopper is prepared from mesityl magnesium bromide and copper(I) chloride
Copper chloride, commonly called cuprous chloride, is the lower chloride of copper, with the formula CuCl.This colorless solid is a versatile precursor to other copper compounds, including some of commercial significance. It occurs naturally as the rare mineral nantokite. Unlike other first-row...
.
- Copper salts add to terminal alkyne
Alkynes are hydrocarbons that have a triple bond between two carbon atoms, with the formula CnH2n-2. Alkynes are traditionally known as acetylenes, although the name acetylene also refers specifically to C2H2, known formally as ethyne using IUPAC...
s to form copper acetylides
- The copper metallocene
A metallocene is a compound with the general formula 2M consisting of two cyclopentadienyl anions bound to a metal center in the oxidation state II. Closely related to the metallocenes are the metallocene derivatives, e.g. titanocene dichloride...
(η-cyclopentadienyl triethylphosphine) copper can be prepared by reaction of copper(II) oxideCopper oxide or cupric oxide is the higher oxide of copper. As a mineral, it is known as tenorite.- Chemistry :It is a black solid with an ionic structure which melts above 1200 °C with some loss of oxygen...
with cyclopentadieneCyclopentadiene is a chemical compound with the formula C5H6. This colorless liquid organic chemical has a strong and unpleasant odor. At room temperature, this cyclic diene dimerizes over the course of hours to give dicyclopentadiene via a Diels-Alder reaction...
and triethylphosphine in pentanePentane is any or one of the organic compounds with the formula C
5H
12. This alkane is a component of some fuels and is employed as a specialty solvent in the laboratory. Its properties are very similar to those of butane and hexane...
at refluxReflux is a technique involving the condensation of vapors and the return of this condensate to the system from which it originated. It is used in industrial and laboratory distillations...
.
Reactions
Organocopper reactions are classified in a number of reaction types:
- Substitution reaction
In a substitution reaction, a functional group in a particular chemical compound is replaced by another group . In organic chemistry, the electrophilic and nucleophilic substitution reactions are of prime importance...
s of cuprates R2CuLi to alkyl halides R'-X gives the alkylcopper compound R'-Cu, the coupling product R-R and the lithium halide. The reaction mechanismIn chemistry, a reaction mechanism is the step by step sequence of elementary reactions by which overall chemical change occurs .Although only the net chemical change is directly observable for most chemical reactions, experiments can often be designed that suggest the possible sequence of steps in...
is based on nucleophilic attack, namely oxidative additionOxidative addition and reductive elimination are two important classes of reactions in organometallic chemistry . Their relationship is shown below where y represents the number of ligands on the metal and n is the oxidation state of the metal....
of the alkyl halide to Cu(I) elevating it to a planarIn chemistry, trigonal planar is a molecular geometry with one atom at the center and three atoms at the corners of a triangle all in one plane. In an ideal trigonal planar species, all three ligands are identical and all bond angles are 120°. Such species belong to the point group D3h...
Cu(III) intermediate followed by reductive elimination. The nucleophilic attack is the rate-determining step. In the case for substitution of iodide, single electron transfer mechanism is proposed.
- Many electrophiles will work. The approximate order of reactivity, beginning with the most reactive, is as follows: acid chlorides > aldehyde
An aldehyde is an organic compound containing a terminal carbonyl group. This functional group, which consists of a carbon atom bonded to a hydrogen atom and double-bonded to an oxygen atom , is called the aldehyde group...
s > tosylates ~ epoxideAn epoxide is a cyclic ether with three ring atoms. This ring approximately defines an equilateral triangle, which makes it highly strained. The strained ring makes epoxides more reactive than other ethers. Simple epoxides are named from the parent compound ethylene oxide or oxirane, such as in...
s > iodides > bromides > chlorides > ketoneIn organic chemistry, a ketone is a type of compound that features a carbonyl group bonded to two other carbon atoms, i.e., R3CCO-CR3 where R can be a variety of atoms and groups of atoms...
s > esterEsters are chemical compounds derived by reacting an oxoacid with a hydroxyl compound such as an alcohol or phenol. Esters are usually derived from an inorganic acid or organic acid in which at least one -OH group is replaced by an -O-alkyl group, and most commonly from carboxylic acids and...
s > nitrileA nitrile is any organic compound which has a -C≡N functional group. The -C≡N functional group is called a nitrile group. In the -CN group, the carbon atom and the nitrogen atom are triple bonded together. The prefix cyano is used in chemical nomenclature to indicate the presence of a nitrile...
s >> alkeneIn organic chemistry, an alkene, olefin, or olefine is an unsaturated chemical compound containing at least one carbon-to-carbon double bond...
s
- Oxidative coupling: coupling of copper acetylides
A metal acetylide is an alkyne for which the terminal proton has been replaced by a metal such as sodium or an organolithium. So, for example, the alkyne CH3C≡CH could be deprotonated to form the acetylide ion CH3C≡C−. Once it has been deprotonated it...
to conjugated alkynes in the Glaser coupling (for example in the synthesis of cyclooctadecanonaene[18]annulene is an annulene with chemical formula C18H18. This hydrocarbon obeys Hückel's rule and is therefore an aromatic compound. The compound was first synthesised by F. Sondheimer...
) or to aryl halides in the Castro-Stephens CouplingThe Castro-Stephens Coupling is a cross coupling reaction between a Copper acetylide and an aryl halide forming a disubstituted alkyne and a copper halide....
- Reductive coupling: coupling reaction
A coupling reaction in organic chemistry is a catch-all for a range of reactions in organometallic chemistry where two hydrocarbon fragments are coupled with the aid of a metal containing catalyst....
of aryl halides with a stoichiometric equivalent of copper metal occurs in the Ullmann reactionThe Ullmann reaction or Ullmann coupling is a coupling reaction between aryl halides with copper. The reaction is named after Fritz Ullmann....
. In an example of a present-day cross-coupling reaction called decarboxylative coupling, a catalytic amount of Cu(I) displaces a carboxyl group forming the arylcopper (ArCu) intermediate. Simultaneously, a palladium catalyst converts an aryl bromide to the organopalladium intermediate (Ar'PdBr), and on transmetallation the biaryl is formed from ArPdAr'.
- Redox neutral coupling: the coupling of terminal alkynes with halo-alkynes with a copper(I) salt in the Cadiot-Chodkiewicz coupling
The Cadiot-Chodkiewicz coupling in organic chemistry is a coupling reaction between a terminal alkyne and a haloalkyne catalyzed by a copper salt such as copper bromide and an amine base. The reaction product is a di-acetylene or di-alkyne....
- Thermal coupling of organocopper compounds
- Conjugate additions to enone
An enone is an unsaturated chemical compound or functional group consisting of a conjugated system of an alkene and a ketone. The simplest enone is methyl vinyl ketone or CH2=CHCOCH3....
s are done with organocuprates. Note that if a Grignard reagent (such as RMgBr) is used, the reaction with an enone would instead proceed through a 1,2-addition. The 1,4-addition mechanism of cuprates to enones goes through the nucleophilic addition of the Cu(I) species at the beta-carbon of the alkene to form a Cu(III) intermediate, followed by reductive elimination of Cu(I). In the original paper describing this reaction, methylmagnesium bromide is reacted with isophorone Isophorone is an α,β-Unsaturated cyclic ketone, a colorless to yellowish liquid with characteristic smell, that is used as a solvent and as an intermediate in organic synthesis...
with and without 1 mole percent of added copper chlorideCopper forms two stable chlorides:*Copper chloride , CuCl, mineral name nantokite.*Copper chloride , CuCl2, mineral name eriochalcite....
:
- Without added salt the main products are alcohol
In chemistry, an alcohol is any organic compound in which a hydroxyl group is bound to a carbon atom of an alkyl or substituted alkyl group. An important group of acohols is formed by the simple acyclic alcohols, the general formula for which is C
nH
2n+1OH...
B (42%) from nucleophilic additionIn organic chemistry, a nucleophilic addition reaction is an addition reaction where in a chemical compound a π bond is removed by the creation of two new covalent bonds by the addition of a nucleophile....
to the carbonyl group and dieneDienes or diolefins are hydrocarbons which contain two double bonds. Dienes are intermediate between alkenes and polyenes.-Classes:Dienes can be divided into three classes:...
C (48%) as its dehydration reactionIn chemistry, a dehydration reaction is usually defined as a chemical reaction that involves the loss of water from the reacting molecule. Dehydration reactions are a subset of elimination reactions...
product. With added salt the main product is 1,4-adduct A (82%) with some C (7%).
- Carbocupration is a nucleophilic addition
In organic chemistry, a nucleophilic addition reaction is an addition reaction where in a chemical compound a π bond is removed by the creation of two new covalent bonds by the addition of a nucleophile....
of organocopper reagents (R-Cu) to acetyleneAcetylene is the chemical compound with the formula HC
2H. It is a hydrocarbon and the simplest alkyne. This colourless gas is widely used as a fuel and a chemical building block...
or terminal alkynes resulting in an alkenylcopper compound (RC=C-Cu).. It is a special case of carbometalationCarbometalation is an organometallic reaction involving the nucleophilic addition to alkenes and alkynes of a diverse range of organometallic reagents such as organolithium compounds, organocopper compounds and Grignard reagents according to the following general alkyne scheme:The addition can...
and also called the Normant reaction .
See also
- Chemistries of carbon with other elements of the periodic table: