A coupling reaction in organic chemistry is a catch-all for a range of reactions in Organometallic chemistry where two hydrocarbon radicals are coupled with the aid of a metal containing catalyst. Jump to: navigation, search Organic chemistry is the scientific study of the structure, properties, composition, reactions, and synthesis of organic compounds that by definition contain carbon. ... Organometallic chemistry is the study of chemical compounds containing bonds between carbon and a metal. ... Jump to: navigation, search // Definition In chemistry, a hydrocarbon is any chemical compound that consists only of the elements carbon (C) and hydrogen (H). ... In chemistry free radicals are uncharged atomic or molecular species with unpaired electrons or an otherwise open shell configuration. ... Jump to: navigation, search A catalyst (Greek: καταλύτης, catalytēs) is a substance that accelerates the rate (speed) of a chemical reaction without itself being transformed or consumed by the reaction (see also catalysis). ...

Coupling reactions include (not exhaustive), the Hiyama coupling, the Sonogashira coupling, the Wurtz reaction, the Ullmann reaction, the Stille cross coupling and coupling reactions based on grignard reagents. In organic chemistry, a Hiyama coupling is a palladium-catalyzed cross-coupling reaction of organosilanes with organic halides or triflates. ... In organic chemistry, a Sonogashira coupling is a coupling reaction of terminal alkynes with aryl or vinyl halides. ... The Wurzt reaction after Charles Adolphe Wurtz is a coupling reaction in organic chemistry and organometallic chemistry where by two alkyl halides are reacted with sodium: 2 R-X + Na → R-R + 2NaX This reaction involves the radical species R.. References A. Wurtz, Ann. ... Jump to: navigation, search The Ullmann reaction or Ullmann coupling is a coupling reaction between aryl halides with copper 1. ... A Stille cross coupling is a cross coupling reaction of an aryl halide with an aryl or alkenyl tin compound using a zero-valent palladium complex such as tetrakis(triphenylphosphine)palladium(0) as a catalyst. ... A Grignard Reagent is an alkyl- or aryl- magnesium halide. ...

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 catylised reaction of an aryl magnesium halide with an aryl halide to form a biaryl.

An example of a the other type of coupling 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 oftein requires very high tempertures, and has partly been replaced in synthetic chemistry by palladium based reactions. General Name, Symbol, Number copper, Cu, 29 Chemical series transition metals Group, Period, Block 11, 4, d Appearance metallic brown Atomic mass 63. ...

A common metal in this type of chemistry is palladium oftein added in the form of tetrakis triphenylphosphine palladium. This is an air sensitive compound which very good for coupling unsaturated halogen compounds with organometallics such as PhSnBu3 General Name, Symbol, Number palladium, Pd, 46 Chemical series transition metals Group, Period, Block 10, 5, d Appearance silvery white metallic Atomic mass 106. ... Tetrakis triphenylphosphine palladium is a brown crystalline solid which is used as a catalyst in many cross coupling reactions. ...

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 becuase 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 vaccent 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. Triphenyl phosphine is a cheap and air stable phosphine which has three phenyl groups attached to a phosphorus atom in the centre of the molecule. ...

In 2005 however a coupling reaction was presented ^[1] in which an organomolybdenum compound General Name, Symbol, Number molybdenum, Mo, 42 Chemical series transition metals Group, Period, Block 6, 5, d Appearance gray metallic Atomic mass 95. ...

not only sat on a shelf for 30 years without any sign of degradation but also decomposed in water to generate 2-butyne which is the coupling adduct of its two ethylidyne ligands. This according to the researchers opens another way for aqueous organometallic chemistry. chemical decomposition is the gradual fragmentation of a chemical compound into smaller molecules. ... Jump to: navigation, search In chemistry, a ligand is an atom, ion or functional group that is bonded to one or more central atoms or ions, usually metals generally through coordinate covalent bond. ...

References

• ^[1] Formation of a Carbon-Carbon Triple Bond by Coupling Reactions In Aqueous Solution Avi Bino, Michael Ardon, Elijah Shirman Science, Vol 308, Issue 5719, 234-235 , 8 April 2005