Reaction of coupling

A reaction of coupling or oxydative coupling in Organic chemistry is a generic name for a category of reactions in organometallic Chimie in which two radical Hydrocarbure S are coupled with the assistance of a Catalyseur containing a métal.
The reactions of coupling must be divided into two principal types: the cross couplings and the homocouplages .

The cross couplings relate to two different molecules reacting to form a new molecule. One can quote for example a reaction catalyzed by nickel chloride of a aryl-magnesium halide with an aryl halide to form a diaryle.
The Réaction of Ullmann is of an example of homocouplage: it is about the reaction catalyzed by metal copper of two molecules of an aryl halide in order to form a biaryle. The reaction of Ullmann requires sometimes very high temperatures, and can be sometimes replaced in chemistry of synthesis by reactions catalyzed by palladium.

Many reactions of coupling relate to the phenol S. BINOL is the product of reaction DC of the 2-naphthol with Cuprous chloride (II) and the 2,6-xylenol dimérise with the Diacétate of iodosobenzene.

One of the base metals in this type of chemistry is the palladium, sometimes added in the form of the Tétrakis (triphénylphosphine) palladium (0). It is a compound sensitive to the particularly powerful air in the coupling of halogenous compounds not-saturated like tributyle-tin the Hydrure.

Whereas many reactions of coupling imply reagents extremely sensitive to the presence of water or oxygen, it is reasonable to affirm that all the reactions of couplings must be realized in strict absence of water. It is possible to carry out reactions of coupling with palladium in aqueous solutions by using water soluble sulfonic phosphines synthesized by the reaction of the Triphénylphosphine with sulphuric Acid . In general, the Oxygène of the air is even able to make fall through the reactions of couplings: indeed, many these reactions occur thanks to unsaturated metal complexes not having 18 electrons of valence. Thus, the couplings crossed by Nickel or palladium a complex with null valence with two vacant sites (or ligands unstable) reacts with the connection carbon-halogen in order to form a connection metal-halogen and a connection metal-carbon. Such a complex with valence zero with unstable ligands or empty sites of coordination is normally very reactive with oxygen.

Types of couplings

The reactions of couplings include (nonexhaustive list):

Various reactions

In a study, an unusual reaction of coupling was described in which a compound Organomolybdénien:

$\backslash \; mathrm\; \{(Mo\_3\; (CCH\_3)\; \_2\; (OAc)\; \_6\; (H\_2O)\; \_3)\; ^\; \{2+\}\; (CF\_3SO\_3)\; \_2^-\}$

remained not only on a rack during 30 years without any sign of degradation but is also broken up in water to generate 2-butyne which is the adduit of coupling from its two Ligand S éthylidyne. That opens, according to the researchers, another way for the aqueous organometallic chemistry .

A method for the reactions of cross couplings of aryl the halides with arenas fluorinated catalyzed by palladium use DMA. It is unusual owing to the fact that it includes/understands a fonctionnalisation on an overdrawn arena in electrons.

References and notes

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