Coupling reaction 1711465 221111042 2008-06-23T02:36:50Z DOI bot 6652755 Citation maintenance. Initiated by [[User:Fconaway|Fconaway]]. You can [[WP:DOI|use this bot]] yourself! Please [[User:DOI_bot/bugs|report any bugs]]. A '''coupling reaction''' or '''oxidative coupling''' in [[organic chemistry]] is a catch-all for a range of reactions in [[Organometallic chemistry]] where two [[hydrocarbon]] [[free radical|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]], this is the reaction of [[copper]] 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]]s. [[1,1'-bi-2-naphthol|BINOL]] is the C-C coupling reaction product of [[2-naphthol]] with [[copper(II) chloride]] and [[2,6-xylenol]] dimerises as well with [[iodosobenzene diacetate]]. A common metal in this type of chemistry is [[palladium]] often added in the form of [[tetrakis(triphenylphosphine)palladium(0)]]. This is an air sensitive compound which is very good for coupling unsaturated halogen compounds with organometallics such as [[tributyltin hydride]]. 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]]. In general the [[oxygen]] 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]] and [[palladium]] 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): {|align="center" class="wikitable" width=90% |'''Reaction'''||'''year''' | colspan="2" align=left |'''Reactant A''' | colspan="2" align=left |'''Reactant B'''||'''homo/cross'''||'''catalyst'''||'''remark''' |- |[[Wurtz reaction]]||1855||||||R-X||sp³||homo||Na|| |- |[[Glaser coupling]]||1869||||||R-X||sp<sup></sup>||homo||Cu|| |- |[[Ullmann reaction]]||1901||||||R-X||sp²||homo||Cu|| |- |[[Gomberg-Bachmann reaction]]||1924||||||R-N<sub>2</sub>X||sp²||homo||||requires base |- |[[Cadiot-Chodkiewicz coupling]]||1957||alkyne||sp<sup></sup>||R-X||sp||cross||Cu||requires base |- |[[Castro-Stephens coupling]]||1963||R-Cu||sp<sup></sup>||R-X || sp²||cross|||| |- |[[Kumada coupling]]||1972||R-MgBr||sp², sp³||R-X || sp²||cross||Pd or Ni|| |- |[[Heck reaction]]||1972||alkene||sp²||R-X || sp²||cross||Pd||requires base |- |[[Sonogashira coupling]]||1973||alkyne||sp<sup></sup>||R-X ||sp³ sp²||cross||Pd and Cu||requires base |- |[[Negishi coupling]]||1977||R-Zn-X||sp²||R-X ||sp³ sp²||cross||Pd or Ni|| |- |[[Stille cross coupling]]||1977||R-SnR<sub>3</sub>||sp²||R-X ||sp³ sp²||cross||Pd|| |- |[[Suzuki reaction]]||1979||R-B(OR)<sub>2</sub>||sp²||R-X ||sp³ sp²||cross||Pd||requires base |- |[[Hiyama coupling]]||1988||R-SiR<sub>3</sub>||sp²||R-X ||sp³ sp²||cross||Pd||requires base |- |[[Buchwald-Hartwig reaction]]||1994||R<sub>2</sub>N-R SnR<sub>3</sub>||sp<sup></sup>||R-X||sp²||cross||Pd|| N-C coupling, second generation free amine |- |[[Fukuyama coupling]]||1998||R<sub></sub>CO(SEt)||sp<sup>2</sup>||R-Zn-I||sp<sup>3</sup>||cross||Pd|| |- | colspan=9 align=left style="background: #ccccff;"| '''Coupling reaction overview'''. ''For references consult satellite pages'' |} ==Miscellaneous reactions== In one study an unusual coupling reaction was described in which an [[organomolybdenum]] compound, [Mo<sub>3</sub>(CCH<sub>3</sub>)<sub>2</sub>(OAc)<sub>6</sub>(H<sub>2</sub>O)<sub>3</sub>](CF<sub>3</sub>SO<sub>3</sub>)<sub>2</sub> not only sat on a shelf for 30 years without any sign of degradation but also [[chemical decomposition|decomposed]] in water to generate [[2-butyne]] which is the coupling adduct of its two [[ethylidyne]] [[ligand]]s. This according to the researchers opens another way for aqueous organometallic chemistry.<ref>{{cite journal | author = A. Bino, M. Ardon and E. Shirman | title = Formation of a Carbon-Carbon Triple Bond by Coupling Reactions In Aqueous Solution | year = 2005 | journal = [[Science]] | volume = 308 | issue = 5719 | pages = 234–235 | doi = 10.1126/science.1109965 | pmid = 15821086}}</ref> One method for palladium-catalyzed cross coupling reactions of [[Halogenoarene|aryl halides]] with fluorinated arenes, involves [[dimethylacetamide|DMA]]. It is unusual in that it involves [[Carbon-hydrogen bond activation|C-H functionalisation]] at an [[electron deficiency|electron deficient]] arene.<ref>{{cite journal | author = M. Lafrance, C. N. Rowley, T. K. Woo and K. Fagnou | title = Catalytic Intermolecular Direct Arylation of Perfluorobenzenes | year = 2006 | journal = [[J. Am. Chem. Soc.]] | volume = 128 | issue = 27 | pages = 8754–8756 | doi = 10.1021/ja062509l}}</ref> [[Image:Fagnou fluoroarene coupling.png|center|500px|Fluoroarene coupling]] == References== {{reflist}} [[Category:Organometallic chemistry]] [[Category:Carbon-carbon bond forming reactions]] [[de:Kupplungsreaktion]] [[fr:Réaction de couplage]] [[it:Accoppiamento ossidativo]] [[he:ריאקציות מצומדות]] [[ja:カップリング反応]]