Coupling reaction

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Coupling reaction

A coupling reaction in organic chemistry

Organic chemistry

Organic chemistry is a discipline within chemistry which involves the science study of the structure, properties, composition, chemical reaction, and preparation of chemical compounds that contain carbon....
is a catch-all for a range of reactions in organometallic chemistry

Organometallic chemistry

Organometallic chemistry is the study of chemical compounds containing chemical bonding 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....
where two hydrocarbon

Hydrocarbon

In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. With relation to chemical terminology, aromatic hydrocarbons or arenes, alkanes, alkenes and alkyne-based compounds composed entirely of carbon or hydrogen are referred to as "pure" hydrocarbons, whereas other hydrocarbons with bonded com...
radicals are coupled with the aid of a metal containing catalyst.

Coupling reactions should be divided into two main classes, there are the cross couplings in which two different molecules react to form one new molecule. For example the nickel chloride catalyzed reaction of an aryl magnesium halide with an aryl halide to form a biaryl.

An example of the other type of coupling (homocoupling) would be a Ullmann reaction

Ullmann reaction

The Ullmann reaction or Ullmann coupling is a coupling reaction between aryl halides with copper. The reaction is named after Fritz Ullmann....
, this is the reaction of copper

Copper

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A coupling reaction in organic chemistry

Organic chemistry

Organometallic chemistry

Hydrocarbon

Ullmann reaction

The Ullmann reaction or Ullmann coupling is a coupling reaction between aryl halides with copper. The reaction is named after Fritz Ullmann....
, this is the reaction of copper

Copper

Copper is a chemical element with the symbol Cu and atomic number 29.It is a ductile metal with very high thermal and electrical conductivity....
metal with two molecules of an aryl halide to form a biaryl. The Ullmann reaction often requires very high temperatures, and has partly been replaced in synthetic chemistry by palladium based reactions.

Many coupling reactions involve phenol

Phenol

Phenol, also known as carbolic acid, is a toxic, white crystalline solid with a sweet tarry odor, commonly referred to as a "hospital smell"....
s. BINOL

1,1'-Bi-2-naphthol

1,1'-Bi-2-naphthol is an organic compound that is often used as a ligand for transition-metal catalysed asymmetric synthesis. BINOL has axial chirality and the two enantiomers can be readily separated and are stable toward racemisation....
is the C-C coupling reaction product of 2-naphthol with copper(II) chloride

Copper(II) chloride

Copper chloride is the chemical compound with the chemical formula CuCl2. This a yellow-brown solid which slowly absorbs moisture to form a blue-green hydrate....
and 2,6-xylenol dimerises as well with iodosobenzene diacetate.

A common metal in this type of chemistry is palladium

Palladium

Tetrakis(triphenylphosphine)palladium(0)

Tetrakispalladium is the chemical compound Pd[P3]4, often abbreviated Pd4, or even PdP4. It is a bright yellow crystalline solid that becomes brown upon decomposition in air....
. This is an air sensitive compound which is very good for coupling unsaturated halogen compounds with organometallics such as tributyltin hydride

Tributyltin hydride

Tributyltin hydride is an organotin compound. It is a useful reagent in organic synthesis. Combined with azobisisobutylonitrile, tributyltin generates radicals by removing a hydrogen atom from the molecule of interest....
.

While many coupling reactions involve reagents that are extremely susceptible to presence of water or oxygen, it is unreasonable to assume that all coupling reactions need to be performed with strict exclusion of water. It is possible to perform palladium based coupling reactions in aqueous solutions using the water soluble sulfonated phosphines made by the reaction of triphenyl phosphine with sulfuric acid

Sulfuric acid

Sulfuric acid, hydrogen2sulfuroxygen4, is a strong mineral acid. It is soluble in water at all concentrations. Sulfuric acid has many applications, and is one of the top products of the chemical industry....
. In general the oxygen

Oxygen

Oxygen no O2 produced; 2) O2 produced, but absorbed in oceans & seabed rock; 3) O2 starts to gas out of the oceans, but is absorbed by land surfaces and formation of ozone layer; 4-5) O2 sinks filled and the gas accumulates]]...
in the air is more able to disrupt coupling reactions, this is because many of these reactions occur via unsaturated metal complexes which do not have 18 valence electrons. For example in nickel

Nickel

Nickel is a chemical element, with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge....
and palladium

Palladium

Palladium is a rare and lustrous silvery-white metal that was discovered in 1803 by William Hyde Wollaston, who named it palladium after the 2 Pallas, which in turn, was named after the epithet of the Greek mythology goddess Athena, acquired by her when she slew Athena#Pallas_Athena....
cross couplings a zerovalent complex with two vacant sites (or labile ligands) reacts with the carbon halogen bond to form a metal halogen and a metal carbon bond. Such a zerovalent complex with labile ligands or empty coordination sites is normally very reactive towards oxygen.

Coupling types

Coupling reactions include (not exhaustive):

Reaction	year	Reactant A		Reactant B		homo/cross	catalyst	remark
Wurtz reaction Wurtz reaction The Wurtz reaction, named after Charles-Adolphe Wurtz, is a coupling reaction in organic chemistry, organometallic chemistry and recently inorganic main group polymers, whereby two alkyl halides are reacted with sodium to form a new carbon-carbon bond:...	1855			R-X	sp³	homo	Na
Glaser coupling	1869			R-X	sp	homo	Cu
Ullmann reaction Ullmann reaction The Ullmann reaction or Ullmann coupling is a coupling reaction between aryl halides with copper. The reaction is named after Fritz Ullmann....	1901			R-X	sp²	homo	Cu
Gomberg-Bachmann reaction Gomberg-Bachmann reaction The Gomberg-Bachmann reaction, named for the Ukrainian-American chemist Moses Gomberg and the American chemist Werner Emmanuel Bachmann, is an aryl - aryl coupling reaction via a diazonium salt....	1924			R-N₂X	sp²	homo		requires base
Cadiot-Chodkiewicz coupling 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 ....	1957	alkyne	sp	R-X	sp	cross	Cu	requires base
Castro-Stephens coupling Castro-Stephens coupling The Castro-Stephens Coupling is a cross coupling reaction between a Copper acetylide and an aryl halide forming a disubstituted alkyne and a copper halide....	1963	R-Cu	sp	R-X	sp²	cross
Kumada coupling Kumada coupling A Kumada coupling or Kumada-Corriu coupling is a cross coupling reaction in organic chemistry between an alkyl or aryl Grignard reagent and an aryl or vinyl halocarbon catalysed by nickel or palladium....	1972	R-MgBr	sp², sp³	R-X	sp²	cross	Pd or Ni
Heck reaction Heck reaction The Heck reaction is the chemical reaction of an unsaturated halide with an alkene and a strong base and palladium catalyst to form a substituted alkene....	1972	alkene	sp²	R-X	sp²	cross	Pd	requires base
Sonogashira coupling Sonogashira coupling In organic chemistry, a Sonogashira coupling is a coupling reaction of terminal alkynes with aryl or vinyl halides. This reaction was first reported by Kenkichi Sonogashira and Nobue Hagihara in 1975....	1973	alkyne	sp	R-X	sp³ sp²	cross	Pd and Cu	requires base
Negishi coupling Negishi coupling The Negishi coupling is a cross coupling reaction in organic chemistry involving an organozinc compound, an organic halide and a nickel or palladium catalyst creating a new carbon-carbon covalent bond :...	1977	R-Zn-X	sp²	R-X	sp³ sp²	cross	Pd or Ni
Stille cross coupling	1977	R-SnR₃	sp³, sp², sp	R-X	sp³ sp²	cross	Pd
Suzuki reaction Suzuki reaction The Suzuki reaction is the organic reaction of an aryl- or vinyl-boronic acid with an aryl- or vinyl-halide catalyzed by a palladium. It is widely used to organic synthesis poly-olefins, styrenes, and substituted biphenyls, and has been extended to incorporate alkyl bromides ....	1979	R-B(OR)₂	sp²	R-X	sp³ sp²	cross	Pd	requires base
Hiyama coupling Hiyama coupling In organic chemistry, a Hiyama coupling is a palladium or nickel-catalyzed cross coupling reaction of organosilicons with Organic compound halides or triflates....	1988	R-SiR₃	sp²	R-X	sp³ sp²	cross	Pd	requires base
Buchwald-Hartwig reaction Buchwald-Hartwig reaction The Buchwald-Hartwig reaction in its original scope is an organic reaction describing a coupling reaction between an aryl halide and an amine in presence of base and a palladium catalyst forming a new carbon-nitrogen bond....	1994	R₂N-R SnR₃	sp	R-X	sp²	cross	Pd	N-C coupling, second generation free amine
Fukuyama coupling Fukuyama coupling The Fukuyama coupling is a coupling reaction taking place between a thioester and an organozinc halide in the presence of a palladium catalyst. The reaction product is a ketone....	1998	RCO(SEt)	sp²	R-Zn-I	sp³	cross	Pd
Coupling reaction overview. For references consult satellite pages

Miscellaneous reactions

In one study an unusual coupling reaction was described in which an organomolybdenum compound, [Mo₃(CCH₃)₂(OAc)₆(H₂O)₃](CF₃SO₃)₂ not only sat on a shelf for 30 years without any sign of degradation but also decomposed

Chemical decomposition

Chemical decomposition or analysis is the separation of a chemical compound into chemical element or smaller compounds. It is sometimes defined as the opposite of a chemical synthesis....
in water to generate 2-butyne which is the coupling adduct of its two ethylidyne ligand

Ligand

In chemistry, a ligand is either an atom, ion, or molecule that bonds to a central metal, generally involving formal donation of one or more of its electrons....
s. This according to the researchers opens another way for aqueous organometallic chemistry.

One method for palladium-catalyzed cross coupling reactions of aryl halides

Halogenoarene

In organic chemistry, a halogenoarene, haloarene, or aryl halide, is an organic compound in which a halogen atom is bonded to a carbon atom which is part of an aromatic ring....
with fluorinated arenes, involves DMA

Dimethylacetamide

Dimethylacetamide is the organic compound with the chemical formula CH3CN2. This colorless, water miscible, high boiling liquid is commonly used as a polar solvent in organic chemistry....
. It is unusual in that it involves C-H functionalisation at an electron deficient

Electron deficiency

Electron deficiency occurs when a compound has too few valence electrons for the connections between atoms to be described as covalent bonds. Electron deficient bonds are often better described as 3-center-2-electron bonds....
arene.